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Exoplanets in the Antarctic Sky. II. 116 Transiting Exoplanet Candidates Found by AST3-II (CHESPA) within the Southern CVZ of TESS

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Published 2019 January 22 © 2019. The American Astronomical Society. All rights reserved.
, , Citation Hui Zhang et al 2019 ApJS 240 17 DOI 10.3847/1538-4365/aaf583

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Abstract

We report first results from the CHinese Exoplanet Searching Program from Antarctica (CHESPA)—a wide-field high-resolution photometric survey for transiting exoplanets carried out using telescopes of the AST3 (Antarctic Survey Telescopes times 3) project. There are now three telescopes (AST3-I, AST3-II, and CSTAR-II) operating at Dome A—the highest point on the Antarctic Plateau—in a fully automatic and remote mode to exploit the superb observing conditions of the site, and its long and uninterrupted polar nights. The search for transiting exoplanets is one of the key projects for AST3. During the austral winters of 2016 and 2017 we used the AST3-II telescope to survey a set of target fields near the southern ecliptic pole, falling within the continuous viewing zone of the TESS mission. The first data release of the 2016 data, including images, catalogs, and light curves of 26,578 bright stars ($7.5\leqslant {{\boldsymbol{m}}}_{i}\leqslant 15$), was presented in Zhang et al. The best precision, as measured by the rms of the light curves at the optimum magnitude of the survey (${{\boldsymbol{m}}}_{i}=10$), is around 2 mmag. We detect 222 objects with plausible transit signals from these data, 116 of which are plausible transiting exoplanet candidates according to their stellar properties as given by the TESS Input Catalog, Gaia DR2, and TESS-HERMES spectroscopy. With the first data release from TESS expected in late 2018, this candidate list will be timely for improving the rejection of potential false-positives.

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1. Introduction

The rapidly expanding sample size of exoplanets discovered over the last two decades has allowed entirely new classes of study of planetary demographics, and has dramatically expanded our understanding of the distribution of planetary orbital parameters. To further increase this understanding, more exoplanet detections covering a wider parameter space are required—and in particular more detections of planets orbiting host stars bright enough for ground-based follow-up to measure dynamical masses. The TESS mission's satellite (Ricker et al. 2010) was launched successfully in 2018 April, and is expected to produce a substantial crop of exactly this class of exoplanets (Stassun et al. 2017), allowing it to have a potentially even larger impact than the Kepler (Borucki et al. 2010) and CoRoT (Auvergne et al. 2009) missions.

In advance of these substantial detections of exoplanets by space telescopes, the first transiting exoplanets were discovered by ground-based, small-aperture telescopes, and these facilities have continued to operate in parallel over the last decade, delivering hundreds of exoplanets from projects including HATNET (Bakos et al. 2004), WASP/SuperWASP (Pollacco et al. 2006), HATSouth (Bakos et al. 2013), and KELT (Pepper et al. 2007). The common features of these ground-based searching programs have been the use of Small-apertures, Wide-fields, and Arrays of Telescopes (SWAT). SWATs have been proved to be one of the most efficient and economical ways to search for new transiting exoplanets from the ground.

However, photometric surveys using ground-based SWATs suffer from two major drawbacks compared to space-based surveys: lower photometric precision and lower duty-cycle coverage. As present and future space-based wide-field surveys continue to progress, from Kepler and CoRoT to TESS to PLATO2.0 (Rauer et al. 2014), these drawbacks have called the value of the ground-based SWAT facilities into question. Ground-based SWAT surveys have to improve their capabilities and work in partnership with present and future space-based wide-field surveys to achieve the greatest impact. On one hand, as experience has been gained and new technologies adopted, new-generation wide-field transit searching programs such as NGTS (Wheatley et al. 2018) and Pan-Planets (Obermeier et al. 2016) have been pushing photometric precision to levels precision (i.e., a few millimagnitudes). Their experience has shown that instruments that are stable over the long-term, combined with optimized operations (e.g., precision auto-guiding) are critical for improving long-term photometric precision. On the other hand, choosing a good site with superb observing conditions (e.g., a steady atmosphere and a clear dark sky) is also essential to guaranteeing an efficient observation by a ground-based SWAT facility.

Because of its extremely cold, dry, and clear atmosphere, the Antarctic Plateau provides favorable conditions for optical, infrared, and THz astronomical observations. Lawrence et al. (2004) reported a median seeing of 0farcs23 (average of 0farcs27) above a 30 m boundary layer at Dome C, drawing worldwide attention. Subsequently, many studies have focused on the astronomical conditions at a variety of Antarctic sites, and have shown low sky brightness and extinction (Kenyon & Storey 2006; Zou et al. 2010; Yang et al. 2017), low water vapor (Shi et al. 2016), very low wind speeds, and exceptional seeing above a thin boundary layer (Aristidi et al. 2009; Bonner et al. 2010; Fossat et al. 2010; Giordano et al. 2012; Okita et al. 2013; Hu et al. 2014). Furthermore, the decreased high-altitude turbulence above the plateau results in reduced scintillation noise, further improving photometric precision (Kenyon & Storey 2006). Saunders et al. (2009) studied eight major factors, such as the boundary layer thickness, cloud coverage, auroral emission, airglow, atmospheric thermal backgrounds, precipitable water vapor, telescope thermal backgrounds, and the free-atmosphere seeing, at Domes A, B, C and F, and also Ridge A and B. After a systematic comparison, they concluded that Dome A, the highest point of the Antarctic Plateau, would be the best site overall.

In addition to the excellent photometric conditions at Dome A, the small variation in the elevation of targets as they track around the sky at Dome A will reduce the systematics. And most importantly, the uninterrupted polar nights offer an opportunity to obtain nearly continuous photometric monitoring for periods of more than a month. As shown by a series of previous studies (Crouzet et al. 2010; Daban et al. 2010; Law et al. 2013), this greatly increases the detectability of transiting exoplanets with orbital periods longer than a few days. The outstanding photometric advantages of the Antarctic Plateau have been shown by observing facilities at different sites, such as SPOT (Taylor et al. 1988) at the South Pole, the small-IRAIT (Tosti et al. 2006), ASTEP-South (Crouzet et al. 2010) and ASTEP-400 (Daban et al. 2010; Mékarnia et al. 2016) at Dome C, and CSTAR (Wang et al. 2011, 2014; Yang et al. 2015; Zong et al. 2015; Liang et al. 2016; Oelkers et al. 2016) and AST3-I (Wang et al. 2017; Ma et al. 2018) at Dome A.

To utilize the superb observing conditions, the construction of a remote observatory at Dome A commenced in 2008, with the installation of a first-generation telescope CSTAR (the Chinese Small Telescope ARray; Yuan et al. 2008; Zhou et al. 2010). Based on a successful experience with CSTAR (and the lessons learned from it), a second generation of survey telescopes—the AST3 telescopes (Antarctic Survey Telescopes times 3, Cui et al. 2008; Yuan et al. 2014)—were conceived to implement wide-field high-resolution photometric surveys at Dome A. The first and second AST3 telescopes—AST3-I and AST3-II—were installed at Dome A in 2012 and 2015 by the 28th and 29th CHINARE (CHInese National Antarctic Research Expeditions), respectively. Using the CSTAR and AST3 telescopes, we have been running an exoplanet survey program called CHESPA (the CHinese Exoplanet Searching Program from Antarctica). The primary science goal of CHESPA is finding super Earth-sized or Neptune-sized transiting exoplanets around a variety of host-star stellar types that are sufficiently bright for radial velocity confirmation and dynamical mass measurement. The combination of dynamical masses and planetary sizes will allow us to determine the true masses, orbital eccentricities, and most critically their bulk densities. With accurate physical and dynamic properties determined, these exoplanets will be good targets for a wide range of characterization techniques, e.g., studies of their atmospheric structure and composition (see, e.g., Seager et al. 2007; Baraffe et al. 2008). The first six exoplanet candidates around the South Celestial Pole were reported by Wang et al. (2014), and (although not yet confirmed) they demonstrate the potential power of CHESPA for the discovery of new exoplanets.

Although the basic design of CHESPA is much the same as most other ground-based SWAT facilities, we do have a few additional advantages over other, similar surveys: a large FoV combined with a relatively high angular resolution of 1'' pixel−1, multi-band filters, and superb observing conditions from Antarctica. To maximize our linkage with upcoming space-based surveys like TESS, we have scheduled our ongoing survey to make observations that scan TESS' high-value target zones, but with a higher angular resolution and in a different filter (Sloan i band). During the austral winters of 2016 and 2017, we have surveyed two sets of fields selected within the Southern Continuous Viewing Zone (CVZ) of TESS (Ricker et al. 2010) using AST3-II. The remaining target fields will be scanned in 2019. The reason we chose these fields is that the stars in the CVZ will be over a 13 times longer observing period than most of objects of the TESS survey (i.e., continuously over a full year). Hence, light curves for objects in the CVZ will be much more sensitive to small planets in short-period-orbits (Stassun et al. 2017), as well as sensitive to larger planets with orbits with much longer periods. In addition, the TESS CVZ and the JWST CVZ are both over the same area of sky (i.e., the south ecliptic pole), so planets detected in these overlapping regions will have enormous potential for further detailed follow-up to characterize in detail their atmosphere and internal structure.

Zhang et al. (2018) presented the first release of 2016 data from AST3-II, as well as a catalog of 221 newly discovered variables. In this paper, we present the detection of 116 transiting exoplanet candidates from the same data. As more data are returned from Antarctica, new results will be presented in forthcoming papers. In this work, we introduce the AST3-II facility in Section 2 and describe the observations of CHESPA briefly in Section 3; in Section 4 we detail the data reduction pipeline, including lightcurve detrending, transit signal searching, and the transit signal validation software modules; finally, we present the survey results in Section 5 and summarize the paper in Section 6.

2. Instruments

Detailed descriptions of the AST3 telescopes were presented by Cui et al. (2008), Yuan et al. (2014, 2015), and Wang et al. (2017). Here, we only focus on the key properties of the AST3-II telescope. The AST3-II telescope (which acquired all the data presented in this paper) has an effective aperture of 50 cm. It is designed to obtain wide-field (1.5 × 2.9 deg2 in R.A. × decl.) and high-resolution (≈1'' pixel−1) imaging in the Sloan i band. It employs a modified Schmidt optical design (Yuan & Su 2012) and a 10K × 10K pixel frame transfer STA1600FT CCD camera. To withstand the extremely harsh environment at Dome A, careful design work has been done to implement multiple innovations in the telescope's snow-proofing and defrosting systems. As a result, AST3-II worked well during the extremely cold austral winters of 2016 and 2017, and acquired over 30 TB of high-quality images. During the observational seasons in austral winter, AST3-II is operated remotely and the scheduled observations are executed in a fully automatic mode. The hardware and software for the facility—including the hardware operation monitor, telescope control computer, and data storage array—were developed by the National Astronomical Observatories, Chinese Academy of Sciences (NAOC; Shang et al. 2012; Hu et al. 2016). The electrical power supply and internet communication were provided by a similarly reliable on-site observatory platform, PLATO-A, which is an improved version of the PLATO system developed by UNSW Sydney as an automated observatory platform for CSTAR and other earlier instruments. PLATO-A was designed to provide a continuous 1 kW power source, a warm environment for equipment, and internet communications to the AST3 telescopes for a year without servicing (Lawrence et al. 2009; Ashley et al. 2010).

3. Observations

The scientific background and observational strategy of CHESPA are described in Zhang et al. (2018). We summarize the key points here. The CHESPA program is dedicated to searching for transiting exoplanets in the southern polar sky at highly negative declinations. It has been running since 2012 using the CSTAR and AST3 telescopes, with a first batch of six exoplanet candidates published by Wang et al. (2014). To maximize collaboration with TESS and enhance the scientific importance of our searching program, we selected 48 target fields close to the South Ecliptic Pole (${\rm{R}}.{\rm{A}}.\,={06}^{{\rm{h}}}{00}^{{\rm{m}}}{00}^{{\rm{s}}},\mathrm{decl}.\,=\,-66^\circ {33}^{{\prime} }00^{\prime\prime} $) and within the TESS' Southern CVZ (see Figure 1 and Table 1 for details). All target fields are suitable for low-airmass observation from Antarctica. Target stars located in these fields will also be monitored by TESS for a continuous 12 month period. Thus, any candidate of interest found within these fields may be followed up and studied thoroughly in the future.

Figure 1.

Figure 1. Scheduled survey of 48 target fields in 2016, 2017, and 2018. Each field has a sky coverage of ∼4.3 deg2. Fields close to the LMC are excluded to avoid crowded fields of giant stars. Group 1 (10 fields) and group 2 (22 fields) were scanned in 2016 and 2017, respectively.

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Table 1.  Center Coordinates of the 48 AST3-II Target Fields Surveyed/Scheduled in 2016–2019

Field Name Field Center Observation Date Valid Images
  R.A.(J2000) Decl.(J2000)    
AST3II001 93.000 −76.000 2018–2019
AST3II002 99.000 −76.000 2018–2019
AST3II003 105.000 −76.000 2018–2019
AST3II004 93.000 −73.000 2016 May 15–2016 Jun 22 3179
AST3II005 98.500 −73.000 2016 May 15–2016 Jun 22 3080
AST3II006 104.000 −73.000 2016 May 15–2016 Jun 22 3049
AST3II007 109.500 −73.000 2016 May 15–2016 Jun 22 3103
AST3II008 115.000 −73.000 2016 May 15–2016 Jun 22 3248
AST3II009 93.000 −70.000 2016 May 15–2016 Jun 22 3090
AST3II010 97.750 −70.000 2016 May 15–2016 Jun 22 3000
AST3II011 102.500 −70.000 2016 May 15–2016 Jun 22 2991
AST3II012 107.250 −70.000 2016 May 15–2016 Jun 22 3021
AST3II013 112.000 −70.000 2016 May 15–2016 Jun 22 3128
AST3II014 116.750 −70.000 2017 Apr 6–2017 May 12 ≥3000
AST3II015 93.000 −67.000 2018–2019
AST3II016 97.000 −67.000 2018–2019
AST3II017 101.000 −67.000 2017 Apr 6–2017 May 12 ≥3000
AST3II018 105.000 −67.000 2017 Apr 6–2017 May 12 ≥3000
AST3II019 109.000 −67.000 2017 Apr 6–2017 May 12 ≥3000
AST3II020 113.000 −67.000 2017 Apr 6–2017 May 12 ≥3000
AST3II021 117.000 −67.000 2017 Apr 6–2017 May 12 ≥3000
AST3II022 82.500 −64.000 2018–2019
AST3II023 86.000 −64.000 2018–2019
AST3II024 89.500 −64.000 2018–2019
AST3II025 93.000 −64.000 2018–2019
AST3II026 96.500 −64.000 2018–2019
AST3II027 100.000 −64.000 2017 Apr 6–2017 May 12 ≥3000
AST3II028 103.500 −64.000 2017 Apr 6–2017 May 12 ≥3000
AST3II029 107.000 −64.000 2017 Apr 6–2017 May 12 ≥3000
AST3II030 110.500 −64.000 2017 Apr 6–2017 May 12 ≥3000
AST3II031 114.000 −64.000 2017 Apr 6–2017 May 12 ≥3000
AST3II032 83.250 −61.000 2018–2019
AST3II033 86.500 −61.000 2018–2019
AST3II034 89.750 −61.000 2018–2019
AST3II035 93.000 −61.000 2017 May 14–2017 Jun 11 ≥4100
AST3II036 96.250 −61.000 2017 May 14–2017 Jun 11 ≥4100
AST3II037 99.500 −61.000 2017 May 14–2017 Jun 11 ≥4100
AST3II038 102.750 −61.000 2017 May 14–2017 Jun 11 ≥4100
AST3II039 106.000 −61.000 2017 May 14–2017 Jun 11 ≥4100
AST3II040 109.250 −61.000 2017 May 14–2017 Jun 11 ≥4100
AST3II041 84.000 −58.000 2018–2019
AST3II042 87.000 −58.000 2018–2019
AST3II043 90.000 −58.000 2018–2019
AST3II044 93.000 −58.000 2017 May 14–2017 Jun 11 ≥4100
AST3II045 96.000 −58.000 2017 May 14–2017 Jun 11 ≥4100
AST3II046 99.000 −58.000 2017 May 14–2017 Jun 11 ≥4100
AST3II047 102.000 −58.000 2017 May 14–2017 Jun 11 ≥4100
AST3II048 105.000 −58.000 2017 May 14–2017 Jun 11 ≥4100

Download table as:  ASCIITypeset image

These chosen fields are divided into three groups, each of which was originally scheduled for observation over an austral winter in 2016, 2017, and 2018. From 2016 May 16 to June 22, we observed the first group consisting of 10 fields (AST3II004–AST3II013). The second group comprises 22 fields observed from 2017 April 6 to June 11 (see Table 1 for details). The ten 2016 fields were monitored by the AST3-II telescope for over 350 hr, spanning 37 available or half-available nights. (The remaining time was allocated to instrument maintenance and used for other key projects, including a supernova search.) To avoid saturating bright stars, and to maximize the survey's dynamic range, we adopted a short-exposure-stacking strategy. The 10 target fields were scanned one by one in a loop with three consecutive 10 s exposures being taken in each field, before moving on to the next field. The resulting sampling cadence is about 12 minutes for each field, including the dead time caused by slewing (∼24 s) and CCD readout (∼48 s). Twilight sky frames were taken at each dawn and dusk during the periods when the Sun was still rising and setting from Dome A. These frames were then median-combined to produce a master flat-field image. To reduce the systematic errors caused by the imperfection of the flat-field correction, we adjusted the focus of the optics to sample stars with point-spread function (PSF) sizes between FWHM = 3 pixels to FWHM = 5 pixels, while the pixel-scale of AST3-II is 1'' pixel−1, which is designed to match the average seeing at Dome A within the boundary layer. We made template images for each target field, and determined accurate astrometric solutions. Every time the telescope points to a new field, any small offsets in R.A. and decl. are corrected by cross-matching the first image with the template, and correcting pointing for the second and third images. Then the last two frames are resampled and matched to the first one to guarantee pixel alignments. At last, all three pixel-aligned images are median-combined by the Swarp code (Bertin et al. 2002) to produce a new image.

During 2016, over 35,000 science images in our 10 target fields were acquired by AST3-II and brought back on hard disks by the 33rd CHINARE team. The first data release, including 18,729 coadded images/catalogs and 26,578 light curves of stars brighter than 15th magnitude in the Sloan i band, were presented in Zhang et al. (2018). In 2017, more than 80,000 images were taken and we await the return of this data from the next polar servicing expedition. In 2018, however, due to some technical problems, no expedition was sent to the Kunlun station. And the scheduled CHESPA 2018 survey was canceled after the on-site fuel storage was exhausted.

3.1. Detection Probability versus Orbital Period

To demonstrate the advantages of Antarctica for finding transiting exoplanets within the Southern CVZ of TESS, we simulated the relation between the orbital period of a transiting exoplanet and its probability of being found at two sites: Dome A and La Silla (i.e., a representative temperate-latitude observing site with good weather and seeing). The simulated observation campaign lasts from the beginning of April to the end of September, which covers the entire austral winter from Dome A. We assume the fraction of bad weather to be 20% at both sites. Two sampling cadences are adopted—12 and 36 minutes—consistent with our Dome A observing strategies. In addition, we performed simulations implementing the actual real-time epochs of observation from our 2016 data. Due to some technical failures caused by the harsh environment at Dome A, the observation in 2016 ended in the end of June and the overall operation coverage is around ∼40%, which is much less than the coverage we expected: ∼75%. As a result, the detection probability in 2016 is not quite improved and it is even worse at the long-period end. The results are shown in Figure 2. The detection probability of a transiting planet is calculated following the method of Beatty & Gaudi (2008). These figures highlight three key features. First, the limited amount of actual data obtained in 2016 does not have significantly different sensitivity from a temperature latitude site. But, that more extended continuous observations with no diurnal gaps (i.e., from Dome A) massively improves the efficiency of the detection of planets at periods of longer than ∼10 days. Finally, when observing at Dome A, the choice of a 12 minute or 36 minute cadence makes little difference to the detectability of planets out to orbital periods of ∼40 days. Figure 3 shows the total available hours as a function of position on the sky as visible from Dome A and La Silla. The dashed circle shows the position of the Southern CVZ of TESS, which can clearly be monitored for a much longer period from Dome A, making the detection of planets at periods of 30–40 days feasible from Dome A.

Figure 2.

Figure 2. Panel a: simulated detection probabilities of transiting exoplanets observed from Dome A and La Silla, assuming the observations last from April to September Panel b: simulated detection probabilities of transiting exoplanets observed from Dome A and La Silla, using the real time-series obtained in 2016.

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Figure 3.

Figure 3. Panel a: total usable hours from Dome A, assuming the observations last from April to September. Panel b: total usable hours from La Silla, assuming the observations last from April to September. The dashed circle denotes the Southern CVZ of TESS in each panel.

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Figure 4.

Figure 4. Flow chart of our "Lightcurve Detrending Module."

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4. Transit Signal Searching Pipeline

A detailed description of the "Image Reduction Module" is provided in Zhang et al. (2018), including the standard image processing steps (e.g., the 2D over-scan subtraction, flat-field correction, zero-point magnitude correction), plus some treatments unique to our data (e.g., cross-talk correction and electromagnetic interference noise fringe correction). In this paper we focus on the light-curve production process, which comprises "Lightcurve Detrending," "Transit Signal Searching," and "Transit Signal Validation" modules.

4.1. Lightcurve Detrending Module

Wide-field photometry surveys usually suffer from serious systematic errors, e.g., scattered light, imperfect flat-fields, and tracking errors. To identify all sources of such systematics and remove them is not an easy task and sometimes is not even feasible (Mékarnia et al. 2016). The widely used simple ensemble photometry (e.g., Honeycutt 1992) assumes that all stars in the field are affected by the same systematics (e.g., transparency changes), and can be modeled by averaging out all incoming fluxes from the ensemble (or selected reference stars). However, even when color and spatial terms due to differential extinction are applied, systematic errors remain. To reveal tiny transit signals (e.g., ≲1%) it is essential to reach photometric precisions of a few mmag (rms). This task is approaching the fundamental limits for ground-based photometry surveys and requires further treatments of systematics.

Modern algorithms for systematic filtering assume that while systematic errors are specific to each star, they can be modeled by a linear combination of the systematics of selected reference stars and auxiliary measurable quantities such as the centroid position and width of the PSF (Bakos et al. 2007). The determination of coefficients for this linear combination is usually performed by standard least-squares techniques. Two kinds of methods have been extensively used in the data reduction of wide-field photometric surveys: SYSREM (SYStematic effects REMove, Tamuz et al. 2005) and Trend Filtering Algorithm (TFA, Kovács et al. 2005). These approaches have been proved to be effective against systematic errors from unknown sources and are also known as "blind-detrending" algorithms. However, sometimes they are too effective: to reach a high precision (i.e., low rms) light curves are often "flattened out" to the extent that there may be substantial suppression of the signals we are searching for. The success of these kinds of methods is quite dependent on the selection of the reference stars. TFA (for example) uses a "brute force" fit of many selected template stars from the target field; if the number of template stars is too small, the detrending procedure may be ineffective, while if the number of template stars is too large, the procedure is very time-consuming and the target light curve may be "over-fitted" with all real physical variations removed (Kovács et al. 2016).

On one hand, we need to remove all unwanted signals (systematics). On the other hand, we have to retain the strength of all wanted (transit) signals. Many efforts have been made to achieve a balance between these conflicting requirements. One approach is to run the filtering methods in the "signal-reconstructive" mode, once the signal frequency (in the case of TFA) or basis of trends (in the case of SysRem) is determined (Kovács & Bakos 2007). Another approach is based on a careful selection of the template time-series. Kim et al. (2009) used a hierarchical clustering method to select an optimum number of co-trending light curves. A Primary Component Analysis (PCA)-based criterion is used in the algorithm proposed by Petigura & Marcy (2012) for the analysis of the Kepler light curves. The more involved PDC-MAP pipeline (Stumpe et al. 2012; Smith et al. 2012) of the Kepler mission also utilizes PCA for selecting the basis vectors for the correction of systematics. In a similar manner, Roberts et al. (2013) discussed the advantage of using Bayesian linear regression for robust filtering, and employing an entropy criterion for selecting the most relevant corrections.

We implement a TFA-based algorithm with both a signal-reconstructive mode and an optimal-template selection. The detailed process is composed of the following steps (a flow chart is shown in Figure 4):

Step I. Filter out non-physical outliers: these outliers, caused mainly by mismatches of stars or bad weather, will cause serious problems in the following detrending processes. Occasionally they may also crash the BLS (Box-function Least Square Fitting algorithm Kovács et al. 2002) procedure when searching for transit signals. To eliminate these outliers while retaining the time-dependent astrophysical variations, the mean magnitude is subtracted from each light curve and a Gaussian Process Regression (GPR) model is fitted to the mean-subtracted measurements. GPR is a nonparametric kernel-based probabilistic method that can be used to predict responses of a function with multiple variables when a kernel function is given. A description of GPR models and their application in removing multi-variate systematics and intrinsic variations from light curves can be found in Aigrain et al. (2016). In our case, we simply set the observation time, ti, as the only variate, and consider the following model of the magnitude response mi:

Equation (1)

where Nobs is the number of observations and ${f}_{i}(t)\sim \mathrm{GP}(0,{\boldsymbol{K}})$, that is ${f}_{i}(t)$ are from a zero mean Gaussian Process with covariance matrix ${{\boldsymbol{K}}}_{{ij}}={k}_{t}({t}_{i},{t}_{j})$. To model the time-dependent variation, a squared exponential kernel function is adopted:

Equation (2)

The amplitude At and coefficients β and α are estimated directly from the time-series by a build-in function "fitrgp" of MATLAB. All measurements that are 3σ away from this GPR fitted model are clipped. Note that the fitted model is not subtracted from the observations at this step.

Step II. Build a target list and a reference star library: the target list contains all light curves with magnitude ${{\boldsymbol{m}}}_{i,\mathrm{apass}}\,\leqslant 15.0;$ the reference library contains all the stars with light curves having a completeness of observations greater than 90% and magnitudes ranging from ${{\boldsymbol{m}}}_{i,\mathrm{apass}}=10$ to ${{\boldsymbol{m}}}_{i,\mathrm{apass}}=14$.

Step III. Build a template for each light curve about to be detrended: reference stars in the individual template are selected from the reference library according to several criteria. (i) The rms of a reference light curve should be less than the median value of all light curves. (ii) The angular distance between a reference star and the target should be less than 1fdg0 to ensure they have been affected by similar kinds of systematics. (iii) Reference stars that are too close to the target ($\leqslant 30\buildrel{\prime\prime}\over{.} 0$) are removed to avoid self-detrending. (iv) The brightness variation of a reference star should be highly correlated with that of the target. In practice we calculate the Pearson correlation coefficient (PCC) between the target light curve and each valid reference light curve, with the top ${N}_{\mathrm{ref}}$ reference light curves with $\mathrm{PCC}\gt 0.2$ being selected. (v) A reference star located within the same readout channel with the target star has a higher priority to be selected. If the number of valid stars within the same readout channel is less than the required number, ${N}_{\mathrm{ref}}$, we supplement the reference stars with those in nearby readout channels.

Step IV. Build individual trend matrices for each target light curve: each trend matrix contains two kind of measurements: the first ${N}_{\mathrm{ref}}$ columns are the magnitudes of the ${N}_{\mathrm{ref}}$ reference stars and remaining columns are external parameters of the target star, e.g., its pixel coordinates, variances of the centroid, airmass, distance to the Moon, distance to the Sun, local background variation, and FWHM and elongation of the photometric aperture. All the measurements are interpolated to the same time-series as the target light curve.

Step V. Multiple linear regression fit: for each target light curve, we perform a multi-variable linear regression on the trend matrix with each column marked as an "independent variable" (similarly to Roberts et al. 2013). The resulting model is then subtracted from the target light curve.

Step VI. Update reference stars: when all light curves have been processed, the rms of each light curve is recalculated. Those reference stars with large rms are removed from the individual reference templates and other stars with low variability are appended into the templates as reference stars.

With the updated reference stars, we then repeat Steps I–VI until the target list is empty. Light curves in the target list are removed if any one of the following criteria are met. (i) If the rms of a target light curve is almost unchanged after the last run, ${\rm{\Delta }}\mathrm{rms}\leqslant 0.001$, this target light curve is removed from the target list since no further detrending is required on it. (ii) If there is no valid reference star left in the individual template of the target star, for example, no reference light curve is highly correlated with the target light curve with $\mathrm{PCC}\gt 0.2$, or no reference star is located within the valid distance range, then this target is removed from the target list. Note that the loop (from step I to step VI) will be done at least once for all target light curves. In our experience, two loops is sufficient in most cases.

As with any other "blind-detrending" algorithm, the quality of our detrending procedure depends on the number of stars in the template. Although a larger number of template stars results in a lower rms for the light curve, real transit signals may be suppressed to a strength below the detection threshold of our pipeline. Furthermore, large dips caused by eclipsing binaries may be reduced in amplitude to a level where they mimic planetary transits, thereby increasing the false-positive rate. To find the optimal number of template stars, we ran a series of tests on a number of light curves with injected transit signals. We selected 1000 raw light curves from our original data set and injected modeled transit signals into each of them. The radius of the host star was fixed to $1{R}_{\odot }$, while the radius and period of the transiting planet were randomly selected in the ranges 0.25–2.0 ${R}_{{\rm{J}}}$ and 0.1–7.0 days, respectively. Raw light curves with injected transits were then detrended and processed by our pipeline to find transit signals. Periods of all revealed signals were compared with the injected periods to remove any false detections. Figure 5 shows the distribution of the revealed number of transits versus the signal suppression ratio, ${\mathrm{Depth}}_{\mathrm{reveal}}/{\mathrm{Depth}}_{\mathrm{inject}}$. Five numbers of reference stars in the template were tested: ${N}_{\mathrm{ref}}=50$, 100, 200, 300, 400. When the number of template stars was small, systematic errors were not removed effectively. Injected transit signals may be distorted by the remaining systematics and lead to a suppression ratio $\geqslant 1$. When we increase the number of template stars, the suppression ratio decreases and its median goes well below unity. The total number of revealed signals also decreases with increasing ${N}_{\mathrm{ref}}$ and the optimum value is around ${N}_{\mathrm{ref}}=100$. By adopting this ${N}_{\mathrm{ref}}$, we have achieved a photometric precision of ∼2.0 mmag around ${m}_{i}=10.0$ and $\leqslant $ 10.0 mmag for stars brighter than ${m}_{i}=12.5$ (see Figure 6). It is marginally enough to reveal a Jupiter-sized exoplanet around a solar-type star or an exo-Neptune around an M-dwarf. To go down below 1.0 mmag precision is quite difficult for us. The major drawbacks are the uncertainties within the flat-field correction and the intra/inter-pixel variations raised by the unperfect tracking operation that is caused by the frosting problem at Dome A. They are basically the same issue—if we could either fix the same stars on the same pixels all the time, or make a perfect flat-field, then the photometric precision will be improved significantly and allow us to detect smaller exoplanet. Unfortunately, none of them are an easy task at the Dome A, Antarctica. The good news is, as the number of sky images we acquired grows, we will be able to make better flat-fields in future data releases.

Figure 5.

Figure 5. Number of revealed transit signals vs. signal distortion of the injected transits. We inject a model transit signal with a random transit depth and period into each of 1000 raw light curves. The total number of injected transits revealed by our pipeline is affected by Nref, the number of reference stars within the templates. When Nref is too large or too small, distortion or suppression of the injected signals can be observed. The larger Nref is, the more serious is the suppression, so the total revealed number of transit signals decreases with increasing Nref. An optimum value of Nref for our case is around 100.

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Figure 6.

Figure 6. Light-curve rms vs. magnitude of 26,578 stars. Each point represents the overall rms of a detrended light curve with time spanning the whole observation campaign of ∼31 24 hr periods. The black points are light curves with a cadence of ∼12 minutes and the red ones are light curves binned to 36 minutes. Stars brighter than ${{\boldsymbol{m}}}_{i}=10$ mag are likely to be saturated and thus suffer large variations. However, due to large extinction variations, some parts of the light curves of some bright stars are still unsaturated and we have found some obvious variables (Zhang et al. 2018) and transit candidates within this magnitude range (see Section 5).

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4.2. Transit Signal Searching Module

The transit signals within a light curve can be modeled as a series of box-shape dips that show up periodically. One of the most effective ways to reveal this kind of signal is the BLS (Box-function Least Square Fitting) algorithm (Kovács et al. 2002). Our transit signal searching module is based on this well-tested method with some adjustments. The whole module can be divided into the following steps:

  • 1.  
    Pre-search by BLS fitting: the purpose of the first BLS run is to generate the frequency spectrum for each light curve. The range of periods P and the fractional transit length q are set to be wide enough to enclose as many potential transit signals as possible: $0.2\leqslant P\leqslant 10.0$ and $0.025\leqslant q\leqslant 0.25$. The period resolution is set to be four times smaller than the sampling interval, which results in ∼2000 steps in period. At each period step, the light curve is folded and binned to 200 phase bins before a box-function is fitted to it. The resulting Signal Residue (SR Kovács et al. 2002) periodogram is then subtracted using a moving median filter to remove the background trend caused by low-frequency systematic errors present in the light curve (Bakos et al. 2004; Wang et al. 2014). Figure 7 shows an example of the candidate "AST3II105.3950−70.3906" whose signal is revealed after the periodogram detrending. We further calculate the Signal Detection Efficiency (SDE, Alcock et al. 2000; Kovács et al. 2002) for each peak identified from this detrended spectrum. Finally, we reject all peaks with $\mathrm{SDE}\lt 1.5$ and those peaks with periods very close to integer days (e.g., ∼1.0 ± 0.01 days).
  • 2.  
    BLS fitting over a refined period range: the first BLS run results in numerous candidate signals for each light curve. The second BLS run is to refine the parameters of signals found by the first run and filter out invalid ones. For each signal passing the first step, we perform a second BLS search in a narrow range of the earlier found period: $0.95P\mbox{--}1.05P$. The period sampling number is fixed at 2000. Only the strongest signal within this period range is selected and delivered to the next step, provided the following criteria are matched: $\&{N}_{\mathrm{tr}}\geqslant 3$,${{\rm{\Delta }}}_{\mathrm{mag}}\leqslant 0.05$ and $\mathrm{SPN}\geqslant 6.0$, where ${N}_{\mathrm{tr}}$ is the number of transit dips, ${{\rm{\Delta }}}_{\mathrm{mag}}$ is the transit depth, and SPN is the Signal-to-Pink Noise ratio of the signal in the frequency spectrum. From the known statistics of exoplanets, the transit depths of confirmed planets are rarely greater than 5%, so it is safe to restrict the range of depths to below 0.05; larger depths are likely to be eclipsing binaries.
  • 3.  
    Further detrending by TFA with signal-reconstruction: as mentioned above, our lightcurve detrending module may cause some signal suppression due to over-fitting. So when an interesting signal is revealed by the previous steps, we perform an additional detrending process to the target light curve with the signal-reconstructive mode. This is done using the "-TFA_SR" command in the VARTOOLS environment with the signals found by the last BLS refinement. Note that some light curves may contain multiple strong signals and they will be copied and detrended multiple times with the corresponding signals. This process will further reduce the rms of the target light curve and enhance the strength of the target signal.
  • 4.  
    Parameter filtering: the last step is to run BLS on each newly detrended light curve with a fixed period found in step 2, since the parameters of the transit signal may be changed after the TFA process with signal-reconstructive mode. The final transit signal is then filtered according to the following criteria: ${\rm{S}}/{\rm{N}}\gt 3$,  $0.001\lt {{\rm{\Delta }}}_{\mathrm{mag}}\lt 0.05$ and $0.5\lt {T}_{\mathrm{dur}}\lt 12$, where S/N is the signal-to-noise ratio of the transit signal, and ${T}_{\mathrm{dur}}$ is the transit duration in hours, which are fitted by the BLS method.

Figure 7.

Figure 7. Panel a: phase-folded light curve of candidate "AST3II105.3950−70.3906." Panel b: the SR periodogram from the BLS algorithm. Panel c: the background-subtracted SR periodogram. The arrow denotes the signal caused by "AST3II105.3950−70.3906."

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After running all our data through the above steps (Figure 8), 1120 transit candidates (TCs) were found. This number of potential candidates is too high for easy visual inspection, so we designed a "Transit Signal Validation Module," described in the next section, to assist.

Figure 8.

Figure 8. Flow chart of the "Transit Signal Searching Module."

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4.3. Transit Signal Validation Module

Wide-field transiting exoplanet surveys tend to suffer from a high false-positive rate, especially when the photometric precision is marginally adequate to detect transit signals. Besides systematic errors, some true astrophysical variabilities, e.g., low-mass eclipsing binaries, grazing binaries, and blended background binaries, may also mimic true transit signals. Therefore, effective validation procedures must be performed before further follow-up observations. A series of validation methods have been adopted in previous successful ground-based wide-field surveys such as WASP/SuperWASP (Pollacco et al. 2006), HATNET (Bakos et al. 2004), HATSouth (Bakos et al. 2013), KELT (Pepper et al. 2007), OGLE (Udalski et al. 2002), and TrES (Alonso et al. 2004). Some key methods have been integrated into our validation module and proved to be effective in our previous work (Wang et al. 2014). In this section we present a similar version with some adjustments for the characteristics of the AST3-II data.

Our validation module (Figure 8) includes quantitative analysis and visual inspections as follows:

  • 1.  
    Primary and secondary eclipses check: detached eclipsing binaries are one of the major sources of false alarms in many transiting exoplanet surveys. The reason is that an eclipsing low-mass star and a transiting planet will produce similar Box-shape signals, which are almost indistinguishable using the BLS method. The transit depth tells us about the secondary-to-primary radius ratio, ${R}_{{\rm{p}}}/{R}_{* }$. According to the statistics of confirmed exoplanets, transiting exoplanets with transit depths ${{\rm{\Delta }}}_{\mathrm{mag}}\,\gt 0.05$ are very rare. So we may safely filter out some eclipsing binaries with very large transit depths in the previous filtering module. However, low transit depths may also be caused by a dwarf star transiting a giant or supergiant host. Detecting such objects requires using other features of the light curve. Other than the transit depth, one major difference between an eclipsing binary and a transiting exoplanet is the secondary eclipse that occurs when the secondary star or the planet is blocked by the host star. Since a planet does not self-illuminate, the depth of its secondary eclipse will be much shallower than that of an eclipsing binary. So our first step is to check the existence of any secondary eclipse within a candidate light curve. We phase-fold the light curve and fix the primary eclipse at phase 0.5, according to the detected period. Then we subtract the fitted model given from the BLS fitting and calculate the rms of the residuals at phases around 0.0 and 0.5. Since the model will only fit the primary eclipse, if a secondary eclipse exists, the rms at phase 0.0 will be significantly greater than the rms at phase 0.5. Any candidate with ${\mathrm{rms}}_{\mathrm{phase}=0.0}/{\mathrm{rms}}_{\mathrm{phase}=0.5}\gt 2.0$ is labeled as suspect and requires visual inspection. For each candidate that passes the above procedure, we further estimate the statistical difference between the odd and even transits, and use the significance level of the consistency in transit depth, PΔ, to determine whether the odd and even transits are drawn from the same population (Wu et al. 2010). The smaller this statistic is, the more inconsistent the odd and even transits are, and the more likely the event is a false-positive. The acceptance boundary is set to be 0.05 and we rejected 355 candidates with ${P}_{{\rm{\Delta }}}\lt 0.05$.
  • 2.  
    Aperture blending check: a blended eclipsing binary is another major source of mimics for genuine transiting planet signals in wide-field surveys. The pixel-scale of AST3-II is ∼1'' pixel−1, so it is unlikely that more than one bright star will fall into a single pixel. However, to avoid saturating bright stars, we defocus the optics slightly to have a FWHM ∼ 5 pixels and employ three photometric apertures: 8, 10, and 12 pixels (Zhang et al. 2018). When the target field is too crowded with stars, it is likely that there will be background stellar objects within the photometric apertures of the target star. And the target star could also be contaminated by scattered light from nearby bright stars. If the contaminating star or the target star itself is in fact an eclipsing binary, its eclipsing depth will be diluted, making it look like a planetary transit. In this case, the secondary eclipse will also be made shallower, to a level that may be undetectable by our precision. So we perform a further blending check on those candidates that passed the first step. To do this we cut a stamp from the image with a size of 150 × 150 pixels for each candidate and check for blending or contaminating objects by human inspections. Since the angular resolution of AST3-II is reasonably high, this procedure is quite accurate and efficient, and 180 candidates with suspicious blending events were rejected.
  • 3.  
    Sinusoidal variation check: besides low-depth eclipses caused by binaries, some brightness variations can be caused by systematic errors or intrinsic stellar variability with a timescale similar to the planetary transit—the dimming part of the variation is easily mistaken as a dip caused by a planetary transit when we fit the phase-folded light curve with a box-shape function. However, measurements caused by systematics or the intrinsic stellar variability are often strongly correlated. And in such a light curve, the dimming and brightening parts should show up periodically, typically with a sinusoidal variation. A phase-folded light curve with a genuine transit event will result in only one obvious transit (dimming) detection without any strong anti-transit (brightening) detection. In this step, we calculate the ratio of improvements for the best-fit transit (dimming), ${\rm{\Delta }}{\chi }_{-}^{2}$, to the improvements for the best-fit anti-transit (brightening), ${\rm{\Delta }}{\chi }_{+}^{2}$, for each light curve. This measurement provides an estimate of whether a detection has the expected properties of a credible transit signal, rather than the properties of the systematic error or intrinsic stellar sinusoidal variability (Burke et al. 2006). At the end of this step, 320 candidates with ${\rm{\Delta }}{\chi }_{-}^{2}/{\rm{\Delta }}{\chi }_{+}^{2}\lt 1.5$ were rejected.
  • 4.  
    Transit shape check: a plausible transit shape is one of the most important criteria to validate a good TC. Since the checks above have reduced the number of potential candidates to a level where visual inspection by human eyes is feasible, we checked each candidate independently by two authors (Dr. Zhouyi Yu and Dr. Ming Yang) with the same criteria: (I) a complete transit dip with both the ingress and egress parts present; (II) two flat "shoulders" before and after the transit; (III) a smooth phase coverage without too many gaps. Candidates were labeled as "bad target" if they showed clear evidence of variability out of transit, including a secondary eclipse, an ellipsoidal variation, or a realistic variability of other forms. If both human inspectors labeled the same candidate as "bad target," this candidate was removed. At the end of this stage, the number of remaining candidates was reduced to 243.
  • 5.  
    Transit model fit: during this stage we perform theoretical model fits to each remaining candidate. The aim is to determine some key parameters of the transit event and filter out inconsistent systems. Before the transit model fit, we calculate the SRN (the signal-to-red-noise ratio) of each light curve. Besides the uncorrelated white noise, the errors of bright stars in ground-based wide-field photometric surveys are usually dominated by correlated red noise (Pont et al. 2006). Therefore, SRN is a simple and robust parameter to assess the significance of the detected transit event:
    Equation (3)
    where d is the best-fitting transit depth, ${\sigma }_{{\rm{r}}}$ is the uncertainty of the transit depth in the presence of red noise and ${N}_{\mathrm{tr}}$ is the number of observed transit dips. The simplest way of assessing the level of red noise (${\sigma }_{{\rm{r}}}$) present in the data is to compute a sliding average of the out-of-transit data over the n data points contained in a transit length interval. This method was proposed by Pont et al. (2006) and has been successfully applied to the SuperWASP candidates (Christian et al. 2006; Clarkson et al. 2007; Lister et al. 2007; Street et al. 2007; Kane et al. 2008). Pont et al. (2006) suggested a typical threshold range of $\mathrm{SRN}\sim 7$–9 based on a red noise level of ${\sigma }_{r}\sim 3.0$ mmag. The typical value of ${\sigma }_{{\rm{r}}}$ present in the AST3-II light curves of bright stars is 2.3 mmag and we find that some candidates with $\mathrm{SRN}\sim 5$ look plausible. To avoid missing some interesting systems, we saved all candidates with $\mathrm{SRN}\geqslant 5$. This threshold filters out 21 candidates and passes 222 candidates. The remaining 222 light curves are then modeled using the Mandel–Agol algorithm (Mandel & Agol 2002) integrated in VARTOOLS (Hartman & Bakos 2016). The fitted parameters of these candidates, such as period(P), epoch, planet-to-star radius ratio (${R}_{{\rm{p}}}/{R}_{* }$), semimajor axis (${a}_{{\rm{p}}}/{R}_{* }$), and inclination (i) of the planet's orbit are listed in Table 2. We also calculate the ratio of the observed duration to the theoretical duration (η). This is another quantitative parameter that can be used as a filter, based on the theoretical model of the transit method. If a transit event is caused by a real planet, its transit duration, ${T}_{\mathrm{dur}}$ measured directly from the phase-folded light curve should be close to the theoretical duration, ${T}_{\mathrm{theory}}$, calculated from the fitted parameters. This means that if $\eta \equiv {T}_{\mathrm{dur}}/{T}_{\mathrm{theory}}\approx 1$, the exoplanet candidate is expected to have a high probability of being a real planet. Here we employ an approximation to ${T}_{\mathrm{theory}}$:
    Equation (4)
    where P is the measured period of the transit signal, ${R}_{{\rm{p}}}$ is the fitted planet radius, a is the fitted orbital semimajor axis, i is the fitted inclination of planet's orbit, and R* is the fitted radius of the central star. This criterion was first introduced by Tingley & Sackett (2005) in checking for candidates found by OGLE, and has been successfully applied to many WASP candidates. For each candidate, we provide η in the 11th column of Table 2 and most of our candidates have a value close to unity.
  • 6.  
    Stellar properties check: the last step is to check the stellar radius to eliminate giant stars. For each candidate, we calculate three radii, ${R}_{{\rm{p}}}^{\mathrm{tic}}$, ${R}_{{\rm{p}}}^{\mathrm{gaia}}$, and ${R}_{{\rm{p}}}^{\mathrm{hem}}$, according to the transit depth and the stellar radii from the TIC (TESS Input Catalog, Stassun et al. 2017), Gaia DR2 (Gaia Collaboration 2018), and TESS-HERMES (Sharma et al. 2018) catalogs. We set a critical radius, ${R}_{\mathrm{crit}}=2{R}_{{\rm{J}}}$, to distinguish giant planets from stellar objects. If ${R}_{{\rm{p}}}^{\mathrm{tic}}\leqslant {R}_{\mathrm{crit}}$ and ${R}_{{\rm{p}}}^{\mathrm{gaia}}\,\leqslant {R}_{\mathrm{crit}}$, this candidate is labeled as a "TC." If both ${R}_{{\rm{p}}}^{\mathrm{tic}}$ and ${R}_{{\rm{p}}}^{\mathrm{gaia}}$ are greater than ${R}_{\mathrm{crit}}$, this candidate is removed and labeled as a "LB" (low-depth eclipsing binary). We notice that many stellar radii from TIC and Gaia are not consistent, especially for dwarf stars in the TIC catalog—they are often labeled as giants in the Gaia DR2 catalog (see Figure 9). When ${R}_{{\rm{p}}}^{\mathrm{tic}}$ and ${R}_{{\rm{p}}}^{\mathrm{gaia}}$ are not consistent, e.g., ${R}_{{\rm{p}}}^{\mathrm{tic}}\leqslant {R}_{\mathrm{crit}}$ and ${R}_{{\rm{p}}}^{\mathrm{gaia}}\gt {R}_{\mathrm{crit}}$, this candidate is labeled by a tag of "TC?" which means further inspection of the stellar properties is required. If both ${R}_{{\rm{p}}}^{\mathrm{tic}}$ and ${R}_{{\rm{p}}}^{\mathrm{gaia}}$ are not available, we use ${R}_{{\rm{p}}}^{\mathrm{hem}}$ as a reference. Finally, if no stellar radius is available, these candidates are also labeled "TC?." For easy retrieval, these transit tags are listed in both Tables 2 and 3.

Figure 9.

Figure 9. Stellar radii of our candidates obtained from Gaia DR2 vs. those obtained from TIC. Most stellar radii of our candidates are consistent between Gaia and TIC. However, many dwarf stars in the TIC catalog are labeled as giants in the Gaia DR2 database. For targets with inconsistent stellar radii from the two databases, we label them as "TC?" which means that further inspection of the stellar properties are needed.

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Table 2.  Fitted Parameters of Exoplanet Candidates from AST3-II Observations in 2016

Target IDa iapassb Epoch Pc ${{\rm{\Delta }}}_{\mathrm{mag}}$ d ${T}_{\mathrm{dur}}$ e SRNf ${R}_{{\rm{p}}}/{R}_{* }$ g $a/{R}_{* }$ h ii ηj tagk
AST3II+ (mag) JD2456000+ (day) (mag) (hr) (degree)
AST3II111.6612−69.5763 7.57 1524.843179 4.4290 0.008 5.549 8.5 0.083 6.342 89.61 0.96 ${TC}?$
AST3II111.9600−68.7566 7.70 1526.252284 4.6350 0.014 4.161 7.0 0.116 8.878 89.84 0.93 LB
AST3II093.6747−73.6265 7.81 1513.297757 1.4756 0.008 1.934 5.9 0.086 6.088 89.66 0.96 ${TC}?$
AST3II097.8006−70.5159 7.81 1513.325399 4.9037 0.024 3.606 10.2 0.144 10.860 89.77 0.91 LB
AST3II091.4863−72.6481 8.12 1513.100016 3.9331 0.005 4.391 6.2 0.070 7.194 89.85 0.98 LB
AST3II096.5573−73.5055 8.14 1514.770168 4.8477 0.011 3.998 5.9 0.104 9.538 89.77 0.93 ${TC}?$
AST3II092.2981−73.5978 8.18 1513.507046 3.8446 0.008 3.585 7.6 0.090 8.556 89.78 0.96 ${TC}?$
AST3II115.7163−72.6862 8.20 1512.691684 4.5790 0.006 5.952 7.6 0.077 6.127 89.78 0.96 LB
AST3II092.6774−73.0130 8.21 1515.241308 3.2899 0.008 2.118 7.1 0.086 12.274 89.85 0.95 TC
AST3II098.2585−73.7513 8.36 1512.679419 3.6759 0.003 4.232 5.7 0.057 6.873 89.75 0.98 TC
AST3II096.4206−73.8669 8.37 1512.646819 0.9628 0.004 1.753 6.3 0.067 4.293 89.66 0.95 ${TC}?$
AST3II097.9925−71.2737 8.39 1512.951248 3.4102 0.009 3.838 5.9 0.095 7.050 89.87 0.94 ${TC}?$
AST3II093.8005−73.4527 8.42 1513.553541 3.8440 0.005 5.105 7.0 0.070 6.032 89.65 0.98 LB
AST3II110.2039−69.4500 8.44 1525.343785 3.8020 0.007 3.877 6.9 0.067 8.187 89.45 1.02 LB
AST3II105.2594−74.0175 8.56 1516.017356 4.4220 0.016 5.482 7.2 0.124 6.475 89.79 0.93 TC
AST3II092.1469−74.3934 8.70 1513.291485 3.7178 0.012 4.045 8.9 0.110 7.045 89.05 0.91 ${TC}?$
AST3II109.5863−72.9851 8.70 1515.191356 3.2973 0.008 2.517 6.3 0.090 10.403 89.90 0.95 LB
AST3II102.8569−69.0175 8.72 1513.699849 3.7841 0.004 5.411 7.7 0.062 5.192 89.60 0.91 LB
AST3II108.6480−71.7319 8.79 1512.941901 1.4973 0.010 1.612 9.4 0.101 7.309 89.82 0.93 LB
AST3II105.5428−73.2557 8.83 1513.283077 2.6707 0.015 4.084 9.9 0.119 5.192 89.66 0.92 LB
AST3II108.1477−73.7258 8.84 1512.412260 1.1862 0.003 2.069 5.7 0.052 4.418 89.05 0.95 LB
AST3II093.0883−72.8076 8.91 1513.826244 1.9404 0.003 2.315 6.9 0.052 6.634 89.76 0.98 TC
AST3II103.2566−69.1107 8.91 1517.612826 5.9529 0.009 4.640 9.4 0.090 10.175 89.76 0.95 LB
AST3II107.6807−70.5830 8.94 1513.486838 3.0622 0.022 4.082 13.3 0.148 5.974 89.72 0.90 LB
AST3II093.1733−71.0405 8.97 1515.213181 3.0711 0.012 1.645 8.0 0.108 14.868 89.87 0.94 LB
AST3II091.2351−70.1065 9.05 1513.830133 3.8446 0.007 2.402 7.8 0.086 12.561 89.83 0.95 LB
AST3II103.7047−68.7485 9.05 1514.495588 4.6829 0.006 3.177 7.7 0.075 11.720 89.89 0.97 ${TC}?$
AST3II104.0645−73.8668 9.16 1514.773768 2.5527 0.005 3.748 6.3 0.068 5.380 89.60 0.96 LB
AST3II096.2622−70.9976 9.16 1513.910238 4.9465 0.008 3.947 7.0 0.085 9.984 89.72 0.96 TC
AST3II104.0051−69.0223 9.17 1512.776310 3.4045 0.011 2.204 9.0 0.103 12.251 89.89 0.94 TC
AST3II093.7421−69.1334 9.22 1516.106964 4.7067 0.007 3.527 8.6 0.065 11.054 89.61 1.02 LB
AST3II113.1241−72.7767 9.23 1514.502942 2.3129 0.004 4.547 5.2 0.062 4.066 89.59 0.97 ${TC}?$
AST3II108.0571−74.0719 9.24 1512.918276 1.8958 0.005 1.996 6.2 0.078 7.142 89.75 0.91 LB
AST3II100.8620−73.4833 9.29 1529.721051 3.2475 0.025 4.687 7.8 0.159 5.325 89.05 0.86 LB
AST3II112.6104−68.9966 9.31 1526.262433 1.9122 0.005 2.504 5.9 0.067 6.016 89.68 0.96 TC
AST3II100.5198−69.7065 9.36 1526.023254 1.0599 0.004 1.439 8.0 0.054 6.165 89.63 1.04 TC
AST3II094.4082−73.2087 9.36 1514.321763 2.8210 0.004 2.362 5.2 0.060 9.437 89.84 0.97 LB
AST3II094.7107−73.7936 9.37 1513.455812 3.3341 0.003 2.103 5.7 0.056 12.413 89.81 0.97 TC
AST3II103.8009−71.3423 9.38 1515.218426 4.5544 0.007 4.997 8.4 0.082 7.239 89.86 0.96 LB
AST3II094.2446−72.6618 9.41 1512.530151 1.5264 0.003 2.242 8.6 0.054 5.366 89.83 0.97 LB
AST3II107.8426−70.7727 9.45 1512.304499 0.7411 0.002 0.808 6.8 0.045 7.210 89.69 0.98 TC
AST3II091.4449−73.7009 9.46 1515.049569 2.9698 0.004 2.903 6.9 0.045 9.537 89.42 1.17 TC
AST3II108.3339−71.6719 9.50 1515.499350 3.3878 0.004 2.174 6.4 0.066 12.232 89.84 0.96 LB
AST3II110.3016−70.7089 9.58 1525.988448 2.3173 0.007 2.706 6.7 0.085 6.861 89.80 0.96 ${TC}?$
AST3II097.9410−71.8464 9.59 1513.311537 1.7795 0.002 1.997 8.2 0.044 7.104 89.80 1.00 TC
AST3II093.2211−73.9730 9.65 1512.895397 3.4161 0.003 3.489 8.3 0.053 7.852 89.66 0.99 LB
AST3II100.5421−69.9876 9.65 1514.764083 4.1279 0.022 3.074 9.3 0.144 10.591 89.84 0.90 LB
AST3II093.5220−74.2702 9.66 1513.237956 2.2585 0.003 2.400 5.4 0.048 4.000 89.39 0.53 ${TC}?$
AST3II096.8038−73.4548 9.68 1513.805829 2.1984 0.004 1.269 6.5 0.064 13.851 89.88 0.98 ${TC}?$
AST3II103.4152−69.1200 9.69 1513.627225 5.5573 0.008 3.812 6.7 0.088 11.507 89.86 0.95 ${TC}?$
AST3II103.0897−72.7837 9.74 1514.178510 2.8484 0.003 2.301 8.5 0.053 9.920 89.71 1.00 LB
AST3II093.1651−73.1078 9.78 1516.196945 4.6660 0.006 3.399 6.8 0.073 10.939 89.75 0.97 LB
AST3II098.0104−69.1538 9.81 1515.451792 3.5820 0.007 3.410 7.7 0.064 11.806 86.93 1.72 LB
AST3II094.2606−73.4253 9.82 1513.359890 5.4696 0.003 3.480 6.7 0.052 12.530 89.85 0.99 TC
AST3II095.4729−74.2954 9.85 1526.661107 4.4580 0.043 2.262 6.4 0.187 16.660 89.81 0.93 LB
AST3II099.4576−73.2028 9.86 1514.516180 3.8505 0.010 1.929 8.3 0.076 16.905 89.70 1.03 TC
AST3II099.4420−72.7620 9.88 1513.044493 1.4857 0.003 1.102 7.1 0.057 10.655 89.85 0.98 ${TC}?$
AST3II104.1878−69.3581 9.89 1512.768775 4.5079 0.006 2.795 10.5 0.075 12.761 89.94 0.96 TC
AST3II093.5835−73.5518 9.90 1512.350884 1.7837 0.002 1.858 5.3 0.047 7.600 89.90 0.99 LB
AST3II100.4993−72.0335 9.95 1513.352165 2.9310 0.006 2.168 7.1 0.077 10.721 89.81 0.96 TC
AST3II094.3030−73.9828 9.96 1513.463628 2.4323 0.003 2.105 7.2 0.055 9.125 89.83 0.98 TC
AST3II097.9286−74.0363 9.97 1514.467896 3.4030 0.004 1.892 5.9 0.064 14.240 89.86 0.97 ${TC}?$
AST3II103.8453−70.1019 9.97 1514.046779 3.5735 0.003 2.229 5.9 0.051 12.759 89.76 0.99 ${TC}?$
AST3II102.6105−69.1826 10.00 1514.688664 2.8143 0.004 1.461 6.3 0.064 15.280 89.87 0.98 TC
AST3II093.4203−74.2969 10.01 1515.190043 3.5258 0.004 3.008 6.9 0.063 9.325 89.88 0.98 TC
AST3II094.0410−73.4832 10.01 1514.577476 2.8862 0.004 2.068 6.2 0.062 11.016 89.84 0.97 TC
AST3II099.0930−73.2224 10.04 1513.393179 1.9004 0.003 2.160 6.3 0.051 6.960 89.75 0.98 TC
AST3II093.6172−72.0786 10.05 1513.016108 4.1671 0.004 4.211 9.3 0.065 7.826 89.79 0.97 TC
AST3II107.7565−73.9416 10.05 1515.568594 4.7153 0.017 2.485 12.3 0.090 15.715 89.69 1.00 TC
AST3II095.2512−73.4038 10.06 1526.508897 5.8881 0.004 6.215 8.4 0.049 7.540 89.68 0.99 LB
AST3II091.2047−69.6554 10.06 1513.129378 2.6594 0.013 2.695 8.2 0.115 7.824 89.87 0.93 ${TC}?$
AST3II095.0409−73.9450 10.08 1513.532447 1.6494 0.004 2.596 8.7 0.065 5.057 89.73 0.97 TC
AST3II092.2555−73.9632 10.20 1512.331058 0.5982 0.004 0.707 6.9 0.066 6.596 90.12 0.95 ${TC}?$
AST3II112.0963−70.3691 10.21 1526.599354 3.5401 0.006 1.693 6.6 0.074 16.484 89.90 0.96 LB
AST3II098.3127−71.8679 10.24 1518.039934 5.8142 0.004 4.598 6.9 0.065 10.103 89.79 0.98 LB
AST3II091.6853−70.8273 10.25 1514.319649 3.4247 0.017 3.243 10.3 0.092 9.496 88.66 1.10 TC
AST3II100.6281−73.3872 10.26 1512.764507 4.7983 0.008 1.381 5.0 0.087 27.533 89.97 0.95 LB
AST3II111.1846−71.0505 10.26 1527.050189 2.8922 0.004 2.706 6.0 0.065 11.645 92.30 1.49 TC
AST3II097.6969−68.6766 10.27 1515.183550 4.1239 0.009 2.299 6.3 0.087 14.282 89.83 0.96 LB
AST3II093.4638−72.7059 10.32 1513.370074 3.0455 0.004 4.481 5.7 0.063 5.357 89.83 0.96 LB
AST3II105.5325−70.4656 10.32 1514.134618 2.1402 0.041 1.288 11.1 0.194 13.108 89.86 0.86 LB
AST3II091.9232−74.2267 10.35 1513.012472 1.8958 0.004 2.961 7.9 0.060 4.925 89.05 0.95 ${TC}?$
AST3II110.2309−73.2423 10.36 1514.416826 2.6403 0.004 4.043 6.7 0.061 5.250 89.68 0.99 TC
AST3II098.1755−73.8864 10.37 1512.707813 3.6047 0.005 2.338 6.1 0.068 12.203 89.85 0.97 LB
AST3II092.0368−70.4582 10.38 1512.868591 1.0745 0.003 1.670 5.5 0.050 4.949 89.05 0.95 LB
AST3II094.7844−72.4654 10.40 1514.306401 3.7312 0.013 3.603 14.2 0.107 8.256 89.72 0.94 TC
AST3II092.8597−74.2383 10.41 1514.952010 3.1911 0.006 3.178 7.0 0.080 7.963 89.87 0.96 TC
AST3II114.4984−71.8869 10.44 1528.006598 2.4923 0.004 1.775 11.6 0.055 11.219 89.81 0.99 TC
AST3II108.4261−73.2631 10.44 1512.847941 4.2029 0.006 2.666 6.2 0.075 12.433 89.86 0.96 TC
AST3II094.3738−70.2934 10.45 1513.063920 2.9525 0.018 2.002 11.0 0.097 13.242 89.56 1.07 ${TC}?$
AST3II106.1317−71.6480 10.47 1526.835186 2.5769 0.012 2.025 10.2 0.097 10.230 89.70 0.96 LB
AST3II111.7619−73.8759 10.48 1477.654944 1.4197 0.015 2.499 10.2 0.120 4.564 89.66 0.93 LB
AST3II110.2798−68.5784 10.49 1526.660685 1.9642 0.004 2.227 10.3 0.043 7.238 89.38 1.03 TC
AST3II095.0393−74.4243 10.49 1528.177284 3.0619 0.021 3.265 7.8 0.122 8.367 89.30 1.04 LB
AST3II096.5435−72.2488 10.59 1514.823584 4.1225 0.012 6.019 9.7 0.109 5.424 89.72 0.93 ${TC}?$
AST3II097.7213−72.0819 10.59 1515.329508 3.2558 0.005 1.157 6.4 0.070 22.375 89.90 0.97 TC
AST3II096.2924−72.5197 10.60 1513.837130 4.3481 0.012 2.733 6.9 0.089 13.148 89.77 0.99 ${TC}?$
AST3II091.0912−69.8567 10.60 1514.592610 4.1952 0.020 5.085 7.3 0.139 6.986 89.84 0.97 LB
AST3II109.7369−74.2405 10.61 1513.416264 4.4963 0.011 1.841 7.4 0.104 19.259 89.91 0.93 LB
AST3II107.3458−71.0765 10.67 1528.822469 4.6595 0.003 3.350 11.8 0.067 10.900 90.28 0.96 TC
AST3II097.9730−71.7985 10.68 1512.356322 1.6023 0.004 1.152 6.1 0.064 11.024 89.82 0.97 TC
AST3II094.7073−68.7874 10.72 1527.232573 3.3267 0.003 2.097 8.3 0.039 16.810 89.92 1.33 LB
AST3II115.6743−72.5314 10.75 1512.800553 1.5934 0.005 2.381 5.3 0.073 5.325 89.64 0.96 TC
AST3II111.3460−72.6509 10.79 1514.610807 4.1897 0.012 4.651 8.7 0.110 7.065 89.68 0.92 TC
AST3II097.3120−73.5895 10.81 1529.235157 3.9082 0.007 3.905 13.0 0.077 7.885 89.48 0.96 LB
AST3II110.2809−70.3141 10.81 1526.701498 4.4040 0.008 3.373 10.2 0.089 10.315 89.81 0.95 TC
AST3II107.0456−74.0770 10.86 1526.718780 0.7519 0.005 2.616 11.6 0.051 2.284 87.93 0.96 TC
AST3II100.5878−69.8255 10.88 1514.761707 4.1262 0.030 3.181 9.0 0.153 10.507 89.67 0.92 LB
AST3II098.5026−68.7022 10.93 1512.513779 3.6308 0.005 3.981 5.9 0.066 7.216 89.76 0.97 LB
AST3II107.6553−70.8608 10.96 1527.739673 2.3331 0.002 3.408 11.9 0.044 5.475 89.71 1.00 TC
AST3II097.0788−70.2585 10.98 1527.041460 1.6136 0.003 2.047 9.3 0.049 6.298 89.74 0.99 LB
AST3II117.1209−74.0344 10.99 1527.103575 2.2638 0.008 2.172 7.0 0.087 8.231 89.91 0.95 ${TC}?$
AST3II107.4180−73.4569 11.01 1515.229431 4.1200 0.032 2.693 9.9 0.170 12.165 89.83 0.89 TC
AST3II101.1153−68.6059 11.09 1526.708229 0.5982 0.003 1.024 13.2 0.049 4.734 89.62 1.00 LB
AST3II114.0495−70.8671 11.09 1526.659314 4.2828 0.026 2.893 6.3 0.152 11.796 89.78 0.90 LB
AST3II101.0898−70.6950 11.10 1514.887994 3.1795 0.012 2.073 6.8 0.102 12.252 89.80 0.95 ${TC}?$
AST3II103.2109−70.3661 11.11 1525.459395 2.4356 0.043 1.692 9.4 0.205 11.449 89.90 0.86 ${TC}?$
AST3II100.7601−68.5820 11.12 1529.149877 3.7922 0.015 3.001 6.0 0.122 10.102 89.84 0.93 ${TC}?$
AST3II107.2081−68.7009 11.15 1516.861254 5.2786 0.011 4.423 8.9 0.100 9.473 89.77 0.94 ${TC}?$
AST3II113.8507−68.6601 11.18 1526.821516 2.4980 0.033 1.450 7.7 0.175 15.071 89.15 0.99 ${TC}?$
AST3II102.6819−72.5412 11.28 1512.372246 1.5112 0.021 1.583 8.0 0.143 7.664 89.65 0.92 TC
AST3II095.8547−68.8100 11.30 1527.437464 2.7071 0.028 1.706 9.6 0.165 12.527 89.85 0.89 LB
AST3II102.1609−72.6500 11.40 1515.369163 4.5655 0.006 3.334 6.4 0.076 10.681 89.89 0.95 TC
AST3II096.4941−71.3646 11.45 1514.516290 4.9507 0.015 3.890 9.9 0.123 9.995 89.78 0.91 LB
AST3II113.4317−68.6947 11.45 1525.803009 3.5696 0.011 1.997 5.4 0.102 14.095 89.94 0.94 LB
AST3II093.8690−71.7830 11.59 1515.658580 3.4506 0.012 2.084 6.4 0.103 13.178 89.82 0.94 TC
AST3II096.5115−73.4489 11.61 1516.503767 4.6611 0.020 2.669 8.5 0.136 13.773 89.88 0.91 TC
AST3II099.7742−71.0987 11.65 1526.188352 1.4157 0.009 1.265 8.8 0.114 8.355 89.60 0.88 TC
AST3II101.6919−74.2132 11.67 1529.015944 4.5418 0.014 3.609 8.8 0.118 9.913 89.86 0.92 LB
AST3II113.9832−70.4051 11.68 1526.193173 3.5920 0.012 4.030 7.4 0.108 7.031 89.86 0.93 LB
AST3II113.5485−68.7457 11.70 1527.160264 2.8647 0.012 3.199 8.1 0.108 7.088 89.76 0.93 TC
AST3II101.4806−69.0980 11.72 1513.041283 3.8274 0.047 2.424 10.3 0.213 12.479 89.86 0.85 LB
AST3II098.6818−71.9115 11.74 1525.466992 1.2525 0.015 0.624 9.7 0.118 15.890 89.88 0.93 TC
AST3II091.4330−73.7113 11.75 1525.807294 1.1831 0.014 1.031 7.9 0.119 9.035 89.75 0.92 TC
AST3II104.4380−71.1547 11.77 1526.625579 3.6992 0.050 2.513 6.9 0.218 11.626 89.85 0.85 LB
AST3II092.6094−71.8139 11.83 1528.344692 5.1183 0.005 5.886 10.0 0.071 6.990 89.78 0.98 TC
AST3II096.7487−72.2717 11.84 1513.101979 2.9727 0.011 2.123 9.2 0.080 11.531 90.51 1.00 TC
AST3II108.6428−70.8729 11.89 1512.574885 1.3973 0.016 1.366 9.3 0.102 8.203 89.51 0.95 TC
AST3II105.5046−69.6519 11.90 1512.777181 4.3865 0.027 2.057 6.2 0.162 16.793 89.89 0.89 LB
AST3II096.0455−73.2071 11.91 1525.783505 1.0321 0.028 0.921 7.8 0.136 11.215 89.08 1.17 LB
AST3II114.4671−72.9671 11.93 1525.564191 2.6689 0.017 1.378 8.1 0.128 15.274 89.89 0.91 TC
AST3II106.9336−74.2982 11.93 1526.433032 5.3838 0.066 5.286 16.2 0.254 8.119 89.78 0.83 LB
AST3II091.5206−68.7046 11.95 1514.212333 3.7807 0.012 2.352 12.1 0.083 14.840 89.93 1.12 TC
AST3II105.3950−70.3906 11.96 1513.741152 2.5309 0.018 2.334 6.0 0.131 8.571 89.79 0.91 TC
AST3II109.8472−72.9997 11.99 1526.086003 1.3428 0.016 0.602 8.6 0.126 17.648 89.88 0.92 LB
AST3II105.3712−69.8769 12.00 1513.674972 2.5162 0.023 4.306 10.3 0.153 4.502 89.05 0.87 TC
AST3II105.7701−71.0600 12.01 1513.698354 2.3701 0.016 1.922 6.8 0.119 9.797 89.79 0.93 LB
AST3II091.0750−71.0982 12.04 1512.494973 2.3009 0.019 1.564 6.1 0.138 11.348 89.84 0.89 ${TC}?$
AST3II110.9429−69.2553 12.04 1526.427470 2.1764 0.013 1.832 7.0 0.113 9.334 89.79 0.92 TC
AST3II113.3396−69.2854 12.06 1526.438117 2.1531 0.012 1.802 7.2 0.108 9.522 89.86 0.94 TC
AST3II096.4722−70.7049 12.07 1515.528935 4.0638 0.034 2.028 9.7 0.155 16.334 89.74 0.92 LB
AST3II101.6774−74.3035 12.09 1525.870125 1.2716 0.020 0.616 8.3 0.138 16.476 89.95 0.92 TC
AST3II095.0182−74.3075 12.14 1515.357919 4.7427 0.036 4.399 8.7 0.188 8.543 89.92 0.87 LB
AST3II107.4879−69.6632 12.19 1513.932161 1.7979 0.034 1.342 15.0 0.133 10.879 88.87 0.95 LB
AST3II112.7966−72.4464 12.22 1526.038879 1.8444 0.029 1.382 8.4 0.170 10.541 89.90 0.88 LB
AST3II111.8932−71.2748 12.22 1527.618026 3.1226 0.022 2.805 8.0 0.146 8.836 89.90 0.90 LB
AST3II101.4784−73.5149 12.23 1525.955959 3.2573 0.041 2.441 7.7 0.175 11.360 90.17 0.95 LB
AST3II094.8679−69.9848 12.23 1528.534221 4.9015 0.031 2.327 5.3 0.172 16.612 89.90 0.88 LB
AST3II093.5582−71.6861 12.25 1512.305334 0.7059 0.027 1.184 10.4 0.163 4.729 89.77 0.88 LB
AST3II090.4994−73.5064 12.26 1525.926277 0.5721 0.018 1.971 10.7 0.103 3.206 93.04 1.30 TC
AST3II093.1294−71.8551 12.28 1512.531030 1.8068 0.011 2.153 8.6 0.103 6.437 89.05 0.91 LB
AST3II111.0100−70.4422 12.28 1526.601713 5.5524 0.020 5.336 6.8 0.141 8.302 89.81 0.91 LB
AST3II090.4044−73.4748 12.35 1526.162986 1.2855 0.039 3.219 8.4 0.215 3.045 88.69 0.80 LB
AST3II101.7141−72.6493 12.36 1527.722916 2.6897 0.022 1.969 7.5 0.173 10.629 90.00 0.87 ${TC}?$
AST3II091.4301−72.3018 12.41 1526.543046 2.8216 0.023 1.275 11.8 0.146 8.543 87.87 0.46 ${TC}?$
AST3II110.1235−69.9953 12.46 1526.401172 4.4201 0.038 1.908 7.6 0.192 18.453 89.89 0.87 TC
AST3II106.8317−68.9080 12.54 1513.547431 4.7868 0.034 2.135 10.5 0.181 17.768 89.92 0.88 LB
AST3II109.6675−72.3196 12.56 1528.308577 2.9518 0.005 3.515 11.2 0.072 6.652 89.77 0.96 LB
AST3II109.1636−72.2965 12.57 1525.608166 4.9757 0.013 1.747 11.6 0.110 21.980 89.92 0.91 ${TC}?$
AST3II090.6760−71.3071 12.61 1527.215585 0.4113 0.020 1.040 9.7 0.140 3.077 89.05 0.87 TC
AST3II098.1569−71.6552 12.61 1513.305459 4.3165 0.029 3.833 11.8 0.169 8.945 89.90 0.89 ${TC}?$
AST3II092.5233−71.6505 12.62 1516.662682 4.6227 0.046 3.726 12.0 0.156 12.255 89.77 1.12 TC
AST3II101.6525−74.3692 12.63 1525.542541 3.6999 0.021 2.298 7.2 0.145 12.313 89.05 0.89 LB
AST3II104.6126−72.1077 12.64 1512.454927 4.5511 0.045 2.827 6.4 0.205 12.766 89.84 0.86 LB
AST3II101.3389−70.3578 12.71 1525.393724 1.4969 0.023 1.338 6.6 0.219 4.480 90.16 0.42 ${TC}?$
AST3II100.6533−68.8372 12.72 1527.421160 1.9711 0.024 2.393 9.4 0.152 6.513 89.72 0.89 LB
AST3II112.8477−69.9828 12.72 1525.228573 2.0433 0.042 1.123 6.8 0.202 14.497 89.86 0.87 LB
AST3II104.4241−69.3418 12.73 1526.763449 1.9295 0.021 3.616 9.8 0.126 4.841 90.80 1.05 LB
AST3II101.0393−70.3290 12.73 1514.385476 2.3129 0.021 2.490 6.9 0.143 7.303 89.69 0.90 ${TC}?$
AST3II100.4278−71.1780 12.76 1526.883158 4.9618 0.045 3.444 8.7 0.210 11.398 89.82 0.85 LB
AST3II114.2997−74.1009 12.76 1527.471878 2.8581 0.014 1.488 10.0 0.115 15.190 89.92 0.93 LB
AST3II114.5691−72.2254 12.78 1527.551370 2.4145 0.009 1.988 12.0 0.092 9.665 89.87 0.95 LB
AST3II096.8010−70.3804 12.80 1528.830123 4.0887 0.020 3.993 10.1 0.139 8.126 89.90 0.91 LB
AST3II115.5833−73.1553 12.80 1527.612886 1.4962 0.014 0.919 15.3 0.075 11.118 90.34 0.83 TC
AST3II091.2613−72.4481 12.82 1515.492504 3.3849 0.026 2.420 7.5 0.161 11.064 89.81 0.89 ${TC}?$
AST3II103.9593−70.7781 12.89 1527.602807 1.4960 0.010 2.262 11.9 0.085 5.460 89.17 0.99 TC
AST3II111.0495−71.0954 12.90 1525.524635 3.0228 0.034 2.549 8.4 0.181 9.484 89.76 0.88 LB
AST3II099.4467−74.0920 12.91 1525.886008 1.5823 0.048 0.712 7.5 0.215 17.700 89.90 0.86 LB
AST3II099.7651−73.1979 13.03 1528.356696 2.9466 0.010 3.351 10.1 0.100 7.040 89.76 0.95 LB
AST3II090.8687−72.0344 13.04 1528.776114 4.5886 0.043 2.366 9.6 0.205 15.384 89.89 0.86 LB
AST3II097.3187−71.4284 13.06 1528.558285 3.4000 0.044 3.617 11.7 0.174 7.683 89.54 0.91 ${TC}?$
AST3II101.5695−71.2333 13.18 1526.933085 1.6951 0.040 1.621 10.6 0.196 8.267 89.78 0.86 LB
AST3II115.2119−73.2237 13.20 1526.648605 0.7478 0.009 0.343 11.3 0.071 18.292 89.87 1.03 LB
AST3II091.8193−72.8341 13.22 1526.854850 5.7351 0.026 2.468 13.5 0.159 18.416 89.89 0.89 ${TC}?$
AST3II102.5813−72.9723 13.23 1527.209422 2.8768 0.029 2.260 11.4 0.170 9.955 89.77 0.87 ${TC}?$
AST3II104.0054−72.2511 13.28 1527.370764 2.3683 0.013 2.100 8.1 0.112 8.909 89.81 0.93 LB
AST3II090.8859−68.6828 13.36 1526.276429 1.2838 0.037 1.362 8.3 0.190 7.532 89.76 0.88 ${TC}?$
AST3II104.9721−71.9019 13.37 1525.565317 4.9635 0.020 2.873 9.1 0.141 13.445 89.92 0.89 LB
AST3II104.2707−73.7498 13.39 1526.912818 3.6382 0.025 2.860 9.8 0.159 10.050 89.91 0.89 ${TC}?$
AST3II113.6785−70.8760 13.42 1525.243621 1.7631 0.039 1.657 8.8 0.145 9.865 88.35 1.09 TC
AST3II102.7801−70.3515 13.45 1529.072507 2.9399 0.029 1.679 11.2 0.167 17.369 89.79 1.11 LB
AST3II113.9304−71.2085 13.45 1526.591273 0.3560 0.011 1.260 10.1 0.102 2.238 89.05 0.90 TC
AST3II101.8975−69.6679 13.48 1526.367594 0.4303 0.011 2.014 9.4 0.107 1.739 89.05 0.89 TC
AST3II110.9256−73.3381 13.81 1527.501348 2.0935 0.040 1.182 9.8 0.193 13.961 89.87 0.86 LB
AST3II113.8611−73.9091 13.86 1526.394788 0.2494 0.023 1.433 22.1 0.148 1.529 88.24 0.89 LB
AST3II114.3035−72.4173 13.88 1526.712754 0.4274 0.014 0.644 16.1 0.128 4.781 89.02 0.83 LB
AST3II091.0575−69.7418 13.91 1526.708050 0.3688 0.014 2.060 9.4 0.111 1.564 88.43 0.93 TC
AST3II105.7490−70.3309 13.93 1527.214905 1.3538 0.035 1.446 12.0 0.186 7.477 89.78 0.88 LB
AST3II116.1664−71.8892 14.04 1526.838168 1.3109 0.023 1.927 8.9 0.144 5.419 89.60 0.91 ${TC}?$
AST3II117.3299−74.0815 14.09 1526.667761 0.7477 0.012 0.527 11.2 0.108 11.236 89.88 0.93 LB
AST3II092.5485−69.7147 14.09 1526.400856 3.9550 0.057 4.281 9.4 0.233 7.304 89.76 0.84 LB
AST3II116.2456−72.1629 14.10 1526.712713 1.7634 0.022 3.445 10.3 0.135 4.135 89.35 0.92 TC
AST3II105.2828−71.2933 14.12 1526.501337 0.2494 0.049 0.939 18.9 0.163 2.422 88.16 0.99 LB
AST3II094.1993−69.6044 14.19 1527.279194 5.6589 0.044 3.906 10.1 0.205 11.421 89.85 0.86 LB
AST3II092.8856−73.5796 14.20 1527.377963 1.5026 0.022 1.617 15.2 0.149 7.403 89.81 0.90 TC
AST3II111.1474−69.7597 14.21 1526.934616 1.4960 0.027 0.856 13.0 0.139 14.489 89.63 0.96 LB
AST3II090.7885−72.9819 14.29 1530.224499 4.8924 0.036 3.210 12.0 0.186 12.073 89.88 0.87 LB
AST3II108.4073−72.6110 14.39 1527.206343 3.2891 0.033 2.850 10.7 0.182 9.105 89.89 0.87 LB
AST3II115.5773−73.7034 14.67 1526.413729 0.7252 0.045 3.542 9.6 0.162 2.283 90.16 1.20 ${TC}?$
AST3II116.7258−71.8829 14.71 1527.176483 1.3241 0.036 1.166 9.1 0.173 9.196 89.67 0.90 ${TC}?$
AST3II094.1317−73.7114 14.75 1527.194067 1.1852 0.031 1.915 10.3 0.171 4.912 89.65 0.88 TC
AST3II116.2229−73.4764 15.33 1526.391170 0.2494 0.051 0.988 16.3 0.225 2.018 89.05 0.80 LB

Notes.

aIDs of AST3-II targets are in the format "AST3II+RA+Dec." biapass: i-band magnitudes from the APASS catalog. cP: the observed period of the transit signal. d ${{\rm{\Delta }}}_{\mathrm{mag}}$: the transit depth in Sloan i-band magnitude. e ${T}_{\mathrm{dur}}$: the observed transit duration. fSRN: the signal-to-red-noise ratio of the transit event. g ${R}_{{\rm{p}}}/{R}_{* }$: the planet's fitted radius as a fraction of the host star radius. The fit is based the model given by Mandel & Agol (2002). h $a/{R}_{* }$: the fitted semimajor axis of a planet's orbit in the unit of its host star radius. ii: the fitted orbital inclination relative to the line-of-sight of observer. jη: the ratio of the observed transit duration to the theoretical duration: η = Tdur/Ttheory. kLabels from AST3-II observation: "TC," transit candidate; "TC?," transit candidate but needs further inspection; "LB," low-depth binary.

A machine-readable version of the table is available.

Download table as:  DataTypeset images: 1 2 3 4

At the end of this validation module, we have 116 transiting exoplanet candidates remaining: 72 of them are strong candidates and further inspections are required for the other 44 candidates. Detailed information for all 116 candidates is listed in Table 3.

Table 3.  Stellar Properties of Exoplanet Candidates from AST3-II Observations in 2016

Target IDa IDticb CTLc IDgaiad magie ${\mathrm{mag}}_{\mathrm{tic}}$ b ${\mathrm{mag}}_{\mathrm{rp}}$ d ${R}_{* \mathrm{tic}}$ b ${R}_{* \mathrm{gaia}}$ d ${R}_{* \mathrm{her}}$ f ${M}_{* \mathrm{tic}}$ b ${P}_{\mathrm{ast}3}$ g ${R}_{{\rm{p}}}/{R}_{* }$ g tagh
AST3II+ Flag (mag) (mag) (mag) $({R}_{\odot })$ $({R}_{\odot })$ $({R}_{\odot })$ $({M}_{\odot })$ (days)
111.6612−69.5763 300443794 1 5267843496684819456 7.57 7.27 7.25 3.70 2.07 1.4177 4.4290 0.083 ${TC}?$
111.9600−68.7566 300448730 0 5268034438043742592 7.70 7.33 7.37 15.10 9.32 0.7235 4.6350 0.116 LB
093.6747−73.6265 141828072 0 5265058025713258496 7.81 6.59 6.57 1.4756 0.086 ${TC}?$
097.8006−70.5159 167251167 0 5278796457859305984 7.81 6.83 6.81 4.69 4.85 1.2205 4.9037 0.144 LB
091.4863−72.6481 141758352 0 5266143930882620288 8.12 7.13 7.29 77.39 3.9331 0.070 LB
096.5573−73.5055 142014846 0 5264975424897920896 8.14 7.10 7.23 0.36 62.38 0.3458 4.8477 0.104 ${TC}?$
092.2981−73.5978 141805865 0 5265113413611253888 8.18 7.27 7.33 0.64 15.14 0.6220 3.8446 0.090 ${TC}?$
115.7163−72.6862 272127358 0 5263146559102777728 8.20 7.69 7.76 9.96 9.48 0.7059 4.5790 0.077 LB
092.6774−73.0130 141808675 1 5265894960220144896 8.21 7.53 7.52 1.77 2.0468 3.2899 0.086 TC
098.2585−73.7513 142083629 1 5265272499195317376 8.36 7.67 7.64 2.06 2.49 1.8375 3.6759 0.057 TC
096.4206−73.8669 141979205 0 5264906774140482944 8.37 7.57 7.67 0.64 22.50 0.6186 0.9628 0.067 ${TC}?$
097.9925−71.2737 167250651 0 5266692930780534400 8.39 7.37 7.59 0.18 60.60 0.1546 3.4102 0.095 ${TC}?$
093.8005−73.4527 141867920 0 5265107916053817088 8.42 7.61 7.69 23.09 20.15 0.6680 3.8440 0.070 LB
110.2039−69.4500 300289543 0 5267888129981462400 8.44 8.11 8.14 8.78 7.84 0.8402 3.8020 0.067 LB
105.2594−74.0175 370236000 1 5262073263955639168 8.56 8.22 8.18 1.23 1.56 2.1637 4.4220 0.124 TC
092.1469−74.3934 141805180 0 5264831182718051328 8.70 8.18 8.26 0.65 16.23 0.6277 3.7178 0.110 ${TC}?$
109.5863−72.9851 271695092 0 5263727444839723136 8.70 8.35 8.41 18.08 10.98 0.6760 3.2973 0.090 LB
102.8569−69.0175 177039555 0 5280494271311835648 8.72 8.31 8.39 20.14 22.30 0.6651 3.7841 0.062 LB
108.6480−71.7319 300137618 0 5264082754597102208 8.79 8.38 8.44 10.84 11.03 0.7857 1.4973 0.101 LB
105.5428−73.2557 388180971 0 5262173044635590144 8.83 8.36 8.39 7.98 8.53 0.8279 2.6707 0.119 LB
108.1477−73.7258 391946903 0 5262825261189573120 8.84 8.45 8.49 9.94 9.50 0.7654 1.1862 0.052 LB
093.0883−72.8076 141825369 1 5265952787659436160 8.91 8.65 8.62 1.56 1.61 1.6075 1.9404 0.052 TC
103.2566−69.1107 177078253 0 5280478710645440640 8.91 8.57 8.60 10.55 8.88 0.7684 5.9529 0.090 LB
107.6807−70.5830 300084948 0 5267390570906745344 8.94 8.56 8.60 16.22 11.26 0.7446 3.0622 0.148 LB
093.1733−71.0405 41480659 0 5278357718363892352 8.97 8.45 8.56 43.67 3.0711 0.108 LB
091.2351−70.1065 41173886 0 5279430120158117248 9.05 8.60 8.68 34.93 3.8446 0.086 LB
103.7047−68.7485 177082444 0 5280551965609808128 9.05 8.64 8.72 0.59 24.55 1.03 0.5851 4.6829 0.075 ${TC}?$
104.0645−73.8668 177351076 0 5262116213628518528 9.16 8.73 8.84 40.80 2.50 2.5527 0.068 LB
096.2622−70.9976 167163613 1 5278404756845930496 9.16 8.88 8.87 1.21 1.23 1.3333 4.9465 0.085 TC
104.0051−69.0223 177115893 1 5280483486651183104 9.17 8.87 8.83 1.39 1.48 1.6112 3.4045 0.103 TC
093.7421−69.1334 41530565 1 5279774817056241152 9.22 8.98 8.97 3.08 3.10 1.2025 4.7067 0.065 LB
113.1241−72.7767 271892738 0 5263323717913862784 9.23 8.80 8.89 0.69 26.56 2.42 0.6650 2.3129 0.062 ${TC}?$
108.0571−74.0719 391947082 0 5262766162439438848 9.24 8.88 8.94 13.01 10.43 0.7793 1.8958 0.078 LB
100.8620−73.4833 176873950 0 5262300965941388160 9.29 8.87 8.96 14.67 22.09 2.16 0.6180 3.2475 0.159 LB
112.6104−68.9966 300555859 1 5267969360699323904 9.31 8.97 8.96 1.63 1.52 1.8789 1.9122 0.067 TC
100.5198−69.7065 176936735 1 5278947331468328576 9.36 7.53 7.52 3.52 2.3923 1.0599 0.054 TC
094.4082−73.2087 141870673 0 5265218928065981056 9.36 8.99 9.05 9.71 9.82 0.7543 2.8210 0.060 LB
094.7107−73.7936 141912469 1 5264944501133057536 9.37 9.13 9.10 1.48 1.28 1.3907 3.3341 0.056 TC
103.8009−71.3423 177114508 0 5265809713703963648 9.38 9.04 9.08 12.12 11.60 100.47 0.6997 4.5544 0.082 LB
094.2446−72.6618 141870126 0 5266045696392070272 9.41 9.06 9.10 10.18 10.59 0.7946 1.5264 0.054 LB
107.8426−70.7727 300085050 1 5267197056860253568 9.45 9.19 9.16 2.01 2.18 1.6842 0.7411 0.045 TC
091.4449−73.7009 141757230 1 9.46 9.21 1.53 1.3836 2.9698 0.045 TC
108.3339−71.6719 300137360 0 5264097224343982592 9.50 9.11 9.20 18.68 0.81 3.3878 0.066 LB
110.3016−70.7089 300291848 0 5267165613403897088 9.58 9.15 9.24 0.71 30.75 11.11 0.6830 2.3173 0.085 ${TC}?$
097.9410−71.8464 167250269 1 5266469901718160384 9.59 9.30 9.32 3.70 3.68 0.9052 1.7795 0.044 TC
093.2211−73.9730 141824276 0 5265034661091140992 9.65 9.30 9.35 7.24 7.07 0.7097 3.4161 0.053 LB
100.5421−69.9876 176936927 0 5278925547394209920 9.65 9.24 9.32 30.27 1.41 4.1279 0.144 LB
093.5220−74.2702 141828600 0 5264824340829965824 9.66 9.30 9.35 0.78 9.35 0.7539 2.2585 0.048 ${TC}?$
096.8038−73.4548 142014809 1 5264976009013474176 9.68 9.40 9.40 2.84 3.68 1.6360 2.1984 0.064 ${TC}?$
103.4152−69.1200 177078248 0 5280478195251438720 9.69 9.29 9.35 0.74 18.80 1.67 0.7099 5.5573 0.088 ${TC}?$
103.0897−72.7837 177307119 0 5265423127991329024 9.74 9.37 9.41 7.54 8.15 1.02 0.7467 2.8484 0.053 LB
093.1651−73.1078 141825063 0 5265883587146783488 9.78 9.40 9.45 14.58 11.50 4.6660 0.073 LB
098.0104−69.1538 167303030 0 5279187540401264512 9.81 9.45 9.49 9.13 6.67 11.44 0.7483 3.5820 0.064 LB
094.2606−73.4253 141870831 1 5265201168380980224 9.82 9.55 9.53 2.70 2.85 1.4725 5.4696 0.052 TC
095.4729−74.2954 141944417 1 5264859117183505536 9.85 9.60 9.56 4.11 2.87 1.2544 4.4580 0.187 LB
099.4576−73.2028 142142718 1 5265305484543891200 9.86 9.86 9.84 1.09 1.14 1.2558 3.8505 0.076 TC
099.4420−72.7620 142142950 0 5265564041575715712 9.88 9.51 9.54 0.88 10.04 0.8489 1.4857 0.057 ${TC}?$
104.1878−69.3581 177161030 1 5268453351974074880 9.89 9.59 9.58 1.34 1.08 25.14 1.2667 4.5079 0.075 TC
093.5835−73.5518 141828007 0 5265106301145639552 9.90 9.54 9.59 13.10 10.75 0.7097 1.7837 0.047 LB
100.4993−72.0335 176872955 1 5265668873137132672 9.95 9.57 9.56 1.69 1.63 0.9988 2.9310 0.077 TC
094.3030−73.9828 141871258 1 5264937148149034880 9.96 9.72 9.69 2.13 1.82 1.3262 2.4323 0.055 TC
097.9286−74.0363 142054354 0 5261888133684938752 9.97 9.59 9.64 0.77 8.41 0.7404 3.4030 0.064 ${TC}?$
103.8453−70.1019 177115200 0 5268180638730445824 9.97 9.61 9.64 0.80 9.83 11.14 0.7783 3.5735 0.051 ${TC}?$
102.6105−69.1826 177035316 1 5278988185197107584 10.00 9.70 9.71 1.78 1.47 1.84 1.1043 2.8143 0.064 TC
093.4203−74.2969 141828614 1 5264824242051315328 10.01 9.75 9.72 2.57 2.67 1.4495 3.5258 0.063 TC
094.0410−73.4832 0 5265200549905681024 10.01 10.08 1.41 2.8862 0.062 TC
099.0930−73.2224 142106374 1 5265350598880337024 10.04 9.74 9.73 2.88 2.97 0.98 1.3191 1.9004 0.051 TC
093.6172−72.0786 141826495 1 5266184544094121344 10.05 9.72 9.69 1.46 1.52 1.61 1.4630 4.1671 0.065 TC
107.7565−73.9416 391926574 1 5262818457961211392 10.05 9.76 9.73 1.87 1.48 1.73 1.4989 4.7153 0.090 TC
095.2512−73.4038 141940268 0 5265157462789906176 10.06 9.68 9.73 8.35 5.8881 0.049 LB
091.2047−69.6554 41173380 0 5279654347507177216 10.06 9.65 9.72 0.75 11.58 0.7192 2.6594 0.115 ${TC}?$
095.0409−73.9450 141940701 1 5264926634069137408 10.08 9.81 9.80 2.01 2.32 1.5065 1.6494 0.065 TC
092.2555−73.9632 141805507 0 5265043491544120192 10.20 9.76 9.86 0.73 19.20 0.6976 0.5982 0.066 ${TC}?$
112.0963−70.3691 300510247 0 5267562747555988480 10.21 9.75 9.84 17.30 1.66 3.5401 0.074 LB
098.3127−71.8679 167309554 0 5266428017197150336 10.24 9.86 9.92 10.02 5.8142 0.065 LB
091.6853−70.8273 41226271 1 5278583771081910912 10.25 9.87 9.89 0.73 0.69 0.6574 3.4247 0.092 TC
100.6281−73.3872 176872208 0 5262305982463154304 10.26 9.78 9.90 28.03 1.11 4.7983 0.087 LB
111.1846−71.0505 300384626 1 5264503184652492288 10.26 9.95 9.95 1.06 0.84 0.9657 2.8922 0.065 TC
097.6969−68.6766 167247946 1 5279989732913189504 10.27 9.99 9.97 3.62 3.27 11.10 1.1165 4.1239 0.087 LB
093.4638−72.7059 141827157 0 5265955227200950016 10.32 9.88 9.97 24.32 0.98 3.0455 0.063 LB
105.5325−70.4656 284196430 1 5268121432604842368 10.32 10.07 10.02 1.21 1.0938 2.1402 0.194 LB
091.9232−74.2267 141768810 0 5265001366505117056 10.35 9.97 10.01 0.81 8.86 11.31 0.7820 1.8958 0.060 ${TC}?$
110.2309−73.2423 271723044 1 5262956511094060288 10.36 10.10 10.09 2.48 1.98 1.17 1.5880 2.6403 0.061 TC
098.1755−73.8864 142083711 0 5261893115847009664 10.37 10.01 10.05 4.37 3.6047 0.068 LB
092.0368−70.4582 41257419 0 5279380539054778496 10.38 10.02 10.04 6.97 8.27 0.8058 1.0745 0.050 LB
094.7844−72.4654 141913647 1 5266055248399448704 10.40 10.10 10.08 1.75 1.76 1.2034 3.7312 0.107 TC
092.8597−74.2383 141809729 1 5264833824117754624 10.41 10.13 10.11 1.30 1.28 1.0692 3.1911 0.080 TC
114.4984−71.8869 300655749 1 5263432088528446208 10.44 9.32 9.30 1.95 2.01 1.5317 2.4923 0.055 TC
108.4261−73.2631 271595489 1 5263624052090759040 10.44 10.15 10.13 1.11 1.12 1.0183 4.2029 0.075 TC
094.3738−70.2934 41596339 0 5278720381103155712 10.45 10.06 10.12 0.78 9.94 0.7559 2.9525 0.097 ${TC}?$
106.1317−71.6480 299901252 0 5267041888281445120 10.47 8.59 8.64 12.55 9.66 0.7408 2.5769 0.097 LB
111.7619−73.8759 271808830 0 5262681293885428864 10.48 10.07 10.13 10.06 61.45 1.4197 0.120 LB
110.2798−68.5784 300293197 1 5268755820751031296 10.49 9.45 9.44 1.09 1.54 0.9663 1.9642 0.043 TC
095.0393−74.4243 141941016 0 5264851794260985088 10.49 10.09 10.14 10.02 3.0619 0.122 LB
096.5435−72.2488 142013907 0 5266040920388245120 10.59 10.19 10.25 0.75 7.95 11.23 0.7216 4.1225 0.109 ${TC}?$
097.7213−72.0819 142082267 1 5266416197447283840 10.59 10.26 10.25 2.08 1.55 11.40 1.1627 3.2558 0.070 TC
096.2924−72.5197 141980141 0 5266016589391775872 10.60 10.17 10.24 0.70 15.08 1.80 0.6721 4.3481 0.089 ${TC}?$
091.0912−69.8567 41111279 1 5279636690896928640 10.60 10.35 10.27 1.77 1.6156 4.1952 0.139 LB
109.7369−74.2405 271694351 0 5262582166040149504 10.61 10.14 10.25 23.94 1.95 4.4963 0.104 LB
107.3458−71.0765 300033585 1 5267094836636502400 10.67 9.99 9.94 1.69 1.53 72.34 1.5126 4.6595 0.067 TC
097.9730−71.7985 167250311 1 5266471306169866752 10.68 10.35 10.36 2.96 2.58 1.6885 1.6023 0.064 TC
094.7073−68.7874 166972175 0 5279821030904845568 10.72 8.82 8.86 10.42 11.65 0.8149 3.3267 0.039 LB
115.6743−72.5314 272086869 1 5263344707417846400 10.75 10.44 10.44 1.67 2.37 1.8513 1.5934 0.073 TC
111.3460−72.6509 271796478 1 5263758952718298240 10.79 10.61 10.57 0.96 0.96 3.80 0.9877 4.1897 0.110 TC
097.3120−73.5895 142050046 0 5264963948745184128 10.81 8.09 8.17 21.47 20.94 0.6684 3.9082 0.077 LB
110.2809−70.3141 300292095 1 5267610812532952960 10.81 10.47 10.48 1.82 1.50 1.81 1.1494 4.4040 0.089 TC
107.0456−74.0770 391923176 0 5262810104248410752 10.86 9.77 9.80 1.60 0.7519 0.051 TC
100.5878−69.8255 176936806 1 5278931109374070272 10.88 10.60 10.57 2.99 2.74 1.1394 4.1262 0.153 LB
098.5026−68.7022 167339417 0 5279951494825148032 10.93 10.44 10.51 16.83 2.16 3.6308 0.066 LB
107.6553−70.8608 300085109 1 5267194681741018240 10.96 9.78 9.77 2.06 2.20 1.74 0.9853 2.3331 0.044 TC
097.0788−70.2585 167203674 0 5278870400015997568 10.98 8.75 8.79 12.39 8.91 0.7087 1.6136 0.049 LB
117.1209−74.0344 272191504 0 5214927820263975296 10.99 10.61 10.66 0.83 11.00 0.8015 2.2638 0.087 ${TC}?$
107.4180−73.4569 358180414 1 5263597083992119552 11.01 10.72 10.72 0.84 0.75 1.1161 4.1200 0.170 TC
101.1153−68.6059 176959368 0 5279310166008119424 11.09 9.22 9.28 8.78 8.88 0.6705 0.5982 0.049 LB
114.0495−70.8671 453097413 0 5264474425551765888 11.09 10.56 10.69 65.99 4.2828 0.152 LB
101.0898−70.6950 176960661 1 5266822226474821760 11.10 10.76 10.77 1.89 2.22 9.34 1.1228 3.1795 0.102 ${TC}?$
103.2109−70.3661 177077527 1 5266672211856681600 11.11 10.80 10.80 1.08 0.96 1.82 1.0084 2.4356 0.205 ${TC}?$
100.7601−68.5820 176955817 1 5279290443518294784 11.12 10.82 10.80 1.57 4.02 1.4194 3.7922 0.122 ${TC}?$
107.2081−68.7009 300014168 0 5268565536520392576 11.15 10.71 10.76 0.76 10.21 0.7327 5.2786 0.100 ${TC}?$
113.8507−68.6601 453080848 1 5268001620196605952 11.18 10.86 10.85 1.36 1.09 16.01 1.1728 2.4980 0.175 ${TC}?$
102.6819−72.5412 177282921 1 5265444229167295232 11.28 10.95 10.96 1.01 0.77 4.19 0.8895 1.5112 0.143 TC
095.8547−68.8100 167087532 1 5279625042956700928 11.30 10.63 10.61 1.96 1.80 11.29 1.3286 2.7071 0.165 LB
102.1609−72.6500 177281995 1 5265437494658779520 11.40 11.08 11.07 2.06 1.96 1.18 1.0320 4.5655 0.076 TC
096.4941−71.3646 167163909 1 5266371353692646400 11.45 11.14 11.13 2.60 1.75 1.72 1.4729 4.9507 0.123 LB
113.4317−68.6947 300604083 0 5268002586566404096 11.45 10.91 11.03 27.35 3.5696 0.102 LB
093.8690−71.7830 41533731 1 5266344591757642112 11.59 11.27 11.27 1.79 1.6402 3.4506 0.103 TC
096.5115−73.4489 142014807 1 5264978787854518912 11.61 11.26 11.29 1.10 1.37 1.0162 4.6611 0.136 TC
099.7742−71.0987 167416896 1 5266534390648813952 11.65 10.88 10.88 1.56 1.02 1.0952 1.4157 0.114 TC
101.6919−74.2132 177254247 1 5262013478010685952 11.67 10.62 10.65 2.98 3.54 2.44 1.4954 4.5418 0.118 LB
113.9832−70.4051 453097153 0 5264639386656198016 11.68 11.16 11.28 25.32 3.5920 0.108 LB
113.5485−68.7457 300604049 1 5267999631628910336 11.70 11.32 11.31 1.29 1.15 1.0461 2.8647 0.108 TC
101.4806−69.0980 176981871 0 5279048142940439808 11.72 11.33 11.39 9.76 3.8274 0.213 LB
098.6818−71.9115 142105539 1 5266425474576551424 11.74 10.97 10.98 1.27 1.25 1.3750 1.2525 0.118 TC
091.4330−73.7113 141757221 1 5265088262282675584 11.75 10.98 10.99 1.50 1.01 1.3239 1.1831 0.119 TC
104.4380−71.1547 177163097 1 5267312677379803008 11.77 11.48 11.49 1.40 2.97 1.43 1.2100 3.6992 0.218 LB
092.6094−71.8139 41361844 1 5278257078688778112 11.83 11.13 11.11 0.72 1.42 1.86 1.1433 5.1183 0.071 TC
096.7487−72.2717 142013922 1 5266037720630866176 11.84 11.53 11.53 1.20 1.11 1.1379 2.9727 0.080 TC
108.6428−70.8729 300138080 1 5267186366684720256 11.89 11.59 11.58 1.51 1.73 2.58 1.2191 1.3973 0.102 TC
105.5046−69.6519 177238699 0 5268222317093051264 11.90 11.52 11.57 4.83 1.71 4.3865 0.162 LB
096.0455−73.2071 141974762 1 5265184469548087040 11.91 10.75 10.76 2.24 1.50 0.9941 1.0321 0.136 LB
114.4671−72.9671 271976918 1 5263120514420956032 11.93 11.16 11.19 1.21 13.74 1.1520 2.6689 0.128 TC
106.9336−74.2982 391923287 1 5262759664152489856 11.93 11.61 11.63 3.80 2.41 3.74 2.0735 5.3838 0.254 LB
091.5206−68.7046 41228591 0 5282757444198482432 11.95 11.62 11.64 0.78 3.7807 0.083 TC
105.3950−70.3906 177239153 1 5268125796291612032 11.96 11.61 11.62 1.23 0.95 1.1085 2.5309 0.131 TC
109.8472−72.9997 271696495 1 5263723871426945024 11.99 10.74 10.77 3.17 2.31 2.96 0.9918 1.3428 0.126 LB
105.3712−69.8769 177238828 1 5268199154332473984 12.00 11.70 11.69 1.00 9.74 1.0001 2.5162 0.153 TC
105.7701−71.0600 284196767 0 5267294118824067200 12.01 11.64 11.70 9.74 1.47 2.3701 0.119 LB
091.0750−71.0982 41109957 1 5278531539976625280 12.04 11.67 11.70 1.03 3.16 0.9672 2.3009 0.138 ${TC}?$
110.9429−69.2553 300378214 1 5267914969233792768 12.04 11.71 11.71 1.21 1.55 1.0909 2.1764 0.113 TC
113.3396−69.2854 300603684 1 5267764778521737472 12.06 11.66 11.70 1.29 1.55 1.67 1.0168 2.1531 0.108 TC
096.4722−70.7049 167163352 0 5278427670487738368 12.07 11.64 11.71 9.07 4.0638 0.155 LB
101.6774−74.3035 177254302 1 5262012000541937024 12.09 11.01 11.02 0.97 0.85 1.94 0.9825 1.2716 0.138 TC
095.0182−74.3075 141940953 0 5264857021239545728 12.14 11.75 11.81 10.59 4.7427 0.188 LB
107.4879−69.6632 300034410 0 5268255336802100736 12.19 11.80 11.87 8.63 1.7979 0.133 LB
112.7966−72.4464 271891753 1 5263390165350482048 12.22 11.33 11.33 2.76 1.91 11.46 1.0645 1.8444 0.170 LB
111.8932−71.2748 300508862 0 5264447208341774848 12.22 11.81 11.92 36.81 3.1226 0.146 LB
101.4784−73.5149 177242567 1 5262291134759656576 12.23 11.37 11.37 1.23 1.26 1.42 1.1028 3.2573 0.175 LB
094.8679−69.9848 167005309 1 5278740687704279168 12.23 11.91 11.91 1.35 1.21 1.2121 4.9015 0.172 LB
093.5582−71.6861 41481769 0 5266255771833340672 12.25 11.78 11.88 34.80 0.7059 0.163 LB
090.4994−73.5064 141685493 1 5265853625455131008 12.26 11.31 11.31 1.31 0.92 2.00 1.0461 0.5721 0.103 TC
093.1294−71.8551 41481475 0 5266249445342979584 12.28 11.88 11.95 3.46 1.8068 0.103 LB
111.0100−70.4422 300329917 1 5267547766710224512 12.28 11.87 11.93 2.08 1.41 1.3478 5.5524 0.141 LB
090.4044−73.4748 141685465 1 5265856885329446400 12.35 11.31 11.32 0.98 1.49 0.9327 1.2855 0.215 LB
101.7141−72.6493 177253253 1 5265483669850321280 12.36 11.26 11.27 1.28 1.10 0.95 0.9529 2.6897 0.173 ${TC}?$
091.4301−72.3018 141766094 1 5266202479878537216 12.41 11.50 11.51 1.14 2.10 1.0374 2.8216 0.146 ${TC}?$
110.1235−69.9953 300289895 1 5267809175599623808 12.46 12.13 12.13 0.78 0.86 1.25 0.9114 4.4201 0.192 TC
106.8317−68.9080 300010309 0 5268536090224517120 12.54 12.20 12.17 1.26 1.63 21.63 1.1369 4.7868 0.181 LB
109.6675−72.3196 271695522 0 5263820662809510016 12.56 8.75 8.93 71.61 11.32 2.9518 0.072 LB
109.1636−72.2965 271640678 1 5263818807383618944 12.57 11.57 11.59 1.86 1.76 1.42 1.3228 4.9757 0.110 ${TC}?$
090.6760−71.3071 41108527 1 5278520652241199488 12.61 11.58 11.59 1.07 1.01 0.9928 0.4113 0.140 TC
098.1569−71.6552 167309413 0 5266481755827918208 12.61 12.28 12.29 1.10 1.25 1.11 1.0165 4.3165 0.169 ${TC}?$
092.5233−71.6505 41361676 0 5278274563494195968 12.62 12.31 12.30 1.11 1.04 1.0224 4.6227 0.156 TC
101.6525−74.3692 177254343 0 5262007907436530432 12.63 11.02 11.09 9.22 2.05 3.6999 0.145 LB
104.6126−72.1077 177386396 0 5265480684849640704 12.64 12.25 12.37 9.30 4.5511 0.205 LB
101.3389−70.3578 176981132 0 5266847579664222848 12.71 12.36 12.37 1.4969 0.219 ${TC}?$
100.6533−68.8372 176936220 0 5279237052782266112 12.72 11.29 11.33 9.37 1.9711 0.152 LB
112.8477−69.9828 300559015 0 5267587795805477376 12.72 12.23 12.33 14.97 2.0433 0.202 LB
104.4241−69.3418 177164215 0 5268474066599155456 12.73 11.36 11.41 3.42 1.12 1.9295 0.126 LB
101.0393−70.3290 176960451 0 5266851397892383488 12.73 12.41 12.40 1.25 1.92 15.22 1.1244 2.3129 0.143 ${TC}?$
100.4278−71.1780 176930982 0 5266518722608118784 12.76 11.12 11.18 8.58 11.46 4.9618 0.210 LB
114.2997−74.1009 271976118 0 5214598409154996352 12.76 10.69 10.79 13.60 2.8581 0.115 LB
114.5691−72.2254 271998736 0 5263408238574147328 12.78 11.12 11.20 8.06 23.57 2.4145 0.092 LB
096.8010−70.3804 167165569 0 5278857613894015488 12.80 11.52 11.57 2.47 24.72 4.0887 0.139 LB
115.5833−73.1553 272087345 1 5263076667098340736 12.80 11.68 11.71 0.93 0.84 2.30 0.8955 1.4962 0.075 TC
091.2613−72.4481 141713760 0 5266196260765884800 12.82 12.50 12.49 1.13 1.62 1.0358 3.3849 0.161 ${TC}?$
103.9593−70.7781 177114813 0 5268087279024913536 12.89 12.22 12.22 1.54 1.70 11.20 1.3947 1.4960 0.085 TC
111.0495−71.0954 300329524 0 5264502669256405888 12.90 12.57 12.57 1.13 2.35 1.0360 3.0228 0.181 LB
099.4467−74.0920 142142214 0 5262205789466201472 12.91 12.10 12.12 1.46 1.31 1.3139 1.5823 0.215 LB
099.7651−73.1979 142144281 0 5265304900428370560 13.03 9.36 9.54 104.92 1.43 2.9466 0.100 LB
090.8687−72.0344 141713000 0 5278227529309020800 13.04 11.24 1.90 4.5886 0.205 LB
097.3187−71.4284 167205301 0 5266684306486644736 13.06 12.72 12.73 1.13 1.41 1.0339 3.4000 0.174 ${TC}?$
101.5695−71.2333 176980662 0 5266564146182675200 13.18 12.06 12.06 1.03 1.34 0.9690 1.6951 0.196 LB
115.2119−73.2237 272085365 0 5263053405555467776 13.20 11.01 11.12 12.29 1.17 0.7478 0.071 LB
091.8193−72.8341 141767522 0 5265938253489849984 13.22 12.30 12.32 1.15 1.90 1.0475 5.7351 0.159 ${TC}?$
102.5813−72.9723 177283229 0 5262411879176869888 13.23 12.31 12.31 1.29 1.16 31.06 1.1575 2.8768 0.170 ${TC}?$
104.0054−72.2511 177350045 0 5265477901710769280 13.28 10.30 10.44 79.55 2.3683 0.112 LB
090.8859−68.6828 41087772 0 5282807235768358144 13.36 12.31 12.32 1.06 0.87 0.67 0.9860 1.2838 0.190 ${TC}?$
104.9721−71.9019 177174051 0 5267031168043141632 13.37 11.62 11.71 7.29 0.42 4.9635 0.141 LB
104.2707−73.7498 177350981 0 5262143976297349120 13.39 12.36 12.38 1.45 1.19 1.15 1.2034 3.6382 0.159 ${TC}?$
113.6785−70.8760 453079416 0 5264476654638078720 13.42 13.14 13.16 1.19 1.15 1.0776 1.7631 0.145 TC
102.7801−70.3515 177034551 0 5266675166794131968 13.45 11.96 12.02 7.27 11.11 2.9399 0.167 LB
113.9304−71.2085 453097610 0 5264277406811830784 13.45 12.52 12.55 1.27 1.82 1.1452 0.3560 0.102 TC
101.8975−69.6679 176986367 0 5278959975852112512 13.48 12.57 12.57 1.08 1.61 1.0008 0.4303 0.107 TC
110.9256−73.3381 271724897 0 5262909545627328896 13.81 12.67 12.70 1.26 2.66 1.1332 2.0935 0.193 LB
113.8611−73.9091 271971367 0 5262642879698072320 13.86 11.97 12.07 16.71 0.2494 0.148 LB
114.3035−72.4173 271977336 0 5263335709462494848 13.88 12.43 12.45 3.08 0.4274 0.128 LB
091.0575−69.7418 41111412 0 5279641329469569792 13.91 12.96 12.97 1.14 1.25 1.0407 0.3688 0.111 TC
105.7490−70.3309 284196352 0 5268124391838898688 13.93 12.91 12.91 1.16 1.64 1.0560 1.3538 0.186 LB
116.1664−71.8892 453098052 0 5263514070864853120 14.04 13.17 13.18 1.35 2.15 1.2135 1.3109 0.144 ${TC}?$
117.3299−74.0815 272234076 0 5214924109412243840 14.09 12.14 12.23 10.02 0.7477 0.108 LB
092.5485−69.7147 41359668 0 5279477845835235456 14.09 13.70 13.71 1.11 2.73 1.0217 3.9550 0.233 LB
116.2456−72.1629 272128157 0 5263447481691888256 14.10 13.16 13.16 1.24 1.39 1.1185 1.7634 0.135 TC
105.2828−71.2933 177239735 0 5267255056098752256 14.12 13.17 13.19 1.25 1.80 1.1232 0.2494 0.163 LB
094.1993−69.6044 41595634 0 5279517496973862784 14.19 13.43 13.44 1.33 1.22 1.1943 5.6589 0.205 LB
092.8856−73.5796 141809204 1 5265102452854831872 14.20 12.92 12.95 0.94 0.94 0.8998 1.5026 0.149 TC
111.1474−69.7597 300330339 0 5267816975260273024 14.21 12.61 12.68 4.50 1.4960 0.139 LB
090.7885−72.9819 141711931 0 5265930453829719808 14.29 12.57 12.63 7.39 4.8924 0.186 LB
108.4073−72.6110 271595090 0 5263716067468907392 14.39 12.87 12.93 2.21 3.2891 0.182 LB
115.5773−73.7034 272087776 0 5214988671360522624 14.67 13.24 13.28 1.07 1.75 0.9948 0.7252 0.162 ${TC}?$
116.7258−71.8829 300812074 0 5263469678082951168 14.71 13.43 13.47 1.3241 0.173 ${TC}?$
094.1317−73.7114 141871071 0 5265135713079397376 14.75 13.01 13.09 0.53 1.1852 0.171 TC
116.2229−73.4764 272129211 0 5215016159151480320 15.33 14.00 14.03 1.08 1.18 0.9983 0.2494 0.225 LB

Notes.

aIDs of AST3-II targets in the format of "AST3II+RA+Dec." bIDs, TESS magnitudes, stellar radii, and stellar masses from the TESS Input Catalog (Stassun et al. 2017). cCTL flags: 1 means this target is also present in the Candidate Target List of TESS (Stassun et al. 2017). dIDs, RP magnitudes, and stellar radii from Gaia DR2 (Gaia Collaboration 2018). ei-band magnitudes from the APASS catalog. fStellar radii from the TESS-HERMES survey (Sharma et al. 2018). gPeriods and planetary-stellar radius ratios from AST3-II observations. hLabels from AST3-II observation: "TC," transit candidate; "TC?," transit candidate but needs further inspection; "LB," low-depth binary.

A machine-readable version of the table is available.

Download table as:  DataTypeset images: 1 2 3 4 5

5. Results

Our transit signal searching and validation modules have revealed a total of 222 plausible transit events. The transit signals were fitted by a Mandel–Agol model, and all the fitted parameters, including the transit epoch, period, depth, and duration, are listed in Table 2. Light curves for all 222 targets are shown in Figure 10. Each light curve has been folded to the fitted period and binned to 200 bins. The red solid line denotes the best-fit model for each phase-folded transit. All targets are cross-matched with the newly released TIC (Stassun et al. 2017), Gaia DR2 (Gaia Collaboration 2018), and TESS-HERMES (Sharma et al. 2018) catalogs to obtain the stellar properties (such as radius) of their host stars. The planetary radius of each TC is then derived according to the fitted value of ${R}_{{\rm{p}}}/{R}_{* }$. The stellar properties of the host stars are listed in Table 3. A tag is assigned to each target: "TC," "LB" or "TC?," which mean strong "TC," "low-depth binary" and "TC but further inspections are required," respectively. Of the 116 transiting exoplanet candidates found, 72 are strong candidates ("TC") and 44 need further checks on their host radii ("TC?"). The smallest transit signal revealed in this work is around ${{\rm{\Delta }}}_{\mathrm{mag}}\sim 2$ mmag (e.g., target AST3II107.8426−70.7727, AST3II093.5835−73.5518 and AST3II107.6553−70.8608) and the longest period is around $P\leqslant 6.0$ days (e.g., AST3II103.2566−69.1107), which shows the promising capability of AST3 telescopes to find small-radius short-period transiting planets in the high-decl. Antarctic sky. Raw and detrended light curves of these targets and other stars are available to the community through the website of the School of Astronomy and Space Science, Nanjing University24 and the Chinese Astronomical Data Center.25

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Figure 10. Transiting exoplanet candidates found within the data obtained in 2016 by AST3-II. The label above each panel contains the target ID ("AST3II+Ra+Dec"), the i-band magnitude in APASS database, the period in days, the transit depth, and the transit duration. The x-axis and the y-axis of each panel are the orbital phases [0, 1] and the ${{\rm{\Delta }}}_{\mathrm{mag}}$, respectively.

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6. Summary and Conclusions

AST3-II is a 50 cm telescope located at Dome A (the highest point of Antarctica), enabling near-continuous observations in the i band during the Antarctic polar nights. It is designed to withstand the harsh climatic conditions at Dome A and has been used to perform a wide-field (FoV $\approx 1\buildrel{\circ}\over{.} 5\times 3^\circ $) and high-resolution (≈1farcs0 pixel−1) photometric survey with a photometric precision of several millimagnitudes. Using the AST3 telescopes, the CHESPA survey has been running since 2012, and 48 target fields within the Southern CVZ of TESS were scheduled to be surveyed between 2016 and 2019. During the austral winters of 2016 and 2017, the AST3-II telescope has successfully scanned 32 target fields.

Data from the first 10 target fields surveyed in 2016 have been fully reduced and released by Zhang et al. (2018). We have achieved a precision (rms of the entire light curve) of <2 mmag at ${{\boldsymbol{m}}}_{i,\mathrm{apass}}\approx 10$ mag and ∼50 mmag at ${{\boldsymbol{m}}}_{i,\mathrm{apass}}\,\approx 15$ mag with a cadence of 36 minutes (Figure 6). In this work, we describe our lightcurve detrending, transit signal searching, and validation modules in detail and present a catalog of 222 plausible transit signals. When combined with the stellar information given by the TIC, Gaia DR2, and TESS-HERMES catalogs, 116 targets are labeled as TCs, of which 72 targets are strong candidates, and 44 candidates require further inspections of the stellar parameters of their hosts. The other 106 targets are ruled out because their derived planetary radii are too large, i.e., ${R}_{p}\gt 2{R}_{\mathrm{Jupiter}}$. Almost all of our new exoplanet candidates are listed in the input catalog of the TESS project and some are on the high priority list (CTL). Therefore high precision photometric follow-up from TESS will be available soon after the TESS data release in late 2018. We are now working on obtaining radial velocity observations of our candidates to confirm them using the new Veloce facility on the 3.9 m Anglo-Australian Telescope (Gilbert et al. 2018), and MINERVA-Australis facility (Wittenmyer et al. 2018). The results of these follow-up observations will be presented in forthcoming papers.

TESS was launched successfully in 2018 April and will map most bright stars within the southern hemisphere. Thousands of small exoplanet candidates orbiting bright nearby stars are expected to be revealed in the coming couple of years and follow-up observations with high angular resolution or different wavelengths are required. AST3-II is the first wide-field survey telescope to have worked through the long polar nights at the top of the Antarctica plateau, without any human attendance on-site during the observation campaigns. Our results demonstrate the high potential of the AST3 telescopes at Dome A to perform accurate and continuous wide-field photometric surveys. With the advantages of the polar site, the AST3 telescopes could continuously monitor hundreds of thousands of target stars around the South Ecliptic Pole for months without substantial interruption. This is particularly important for performing cross-validations of the TCs found by TESS. We believe our catalog of new TCs within the Southern CVZ of TESS will be a helpful reference for the flood of new candidates soon to emerge from TESS.

This work was supported by the Natural Science Foundation of China (NSFC grants 11673011, 11333002, 11273019), National Basic Research Program (973 Program) of China (grants No. 2013CB834900, 2013CB834904). The authors deeply appreciate all the CHINAREs for their great effort in installing/maintaining CSTAR, CSTAR-II, AST3-I, AST3-II and PLATO-A. This study has also been supported by the Chinese Polar Environment Comprehensive Investigation & Assessment Program (grant No. CHINARE2016-02-03), the Australian Antarctic Division, and the Australian National Collaborative Research Infrastructure Strategy administered by Astronomy Australia Limited. Zhang is also grateful to the High Performance Computing Center (HPCC) of Nanjing University for reducing the data used in this paper.

Software: Swarp (Bertin et al. 2002), VARTOOLS (Hartman & Bakos 2016), MATLAB.

Footnotes

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10.3847/1538-4365/aaf583