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  • 1
    Online Resource
    Online Resource
    Final Targeting Strategy for the SDSS-IV APOGEE-2S Survey
    American Astronomical Society ; 2021
    In:  The Astronomical Journal Vol. 162, No. 6 ( 2021-12-01), p. 303-
    Details
    In: The Astronomical Journal, American Astronomical Society, Vol. 162, No. 6 ( 2021-12-01), p. 303-
    Abstract: APOGEE is a high-resolution ( R ∼ 22,000), near-infrared, multi-epoch, spectroscopic survey of the Milky Way. The second generation of the APOGEE project, APOGEE-2, includes an expansion of the survey to the Southern Hemisphere called APOGEE-2S. This expansion enabled APOGEE to perform a fully panoramic mapping of all of the main regions of the Milky Way; in particular, by operating in the H band, APOGEE is uniquely able to probe the dust-hidden inner regions of the Milky Way that are best accessed from the Southern Hemisphere. In this paper we present the targeting strategy of APOGEE-2S, with special attention to documenting modifications to the original, previously published plan. The motivation for these changes is explained as well as an assessment of their effectiveness in achieving their intended scientific objective. In anticipation of this being the last paper detailing APOGEE targeting, we present an accounting of all such information complete through the end of the APOGEE-2S project; this includes several main survey programs dedicated to exploration of major stellar populations and regions of the Milky Way, as well as a full list of programs contributing to the APOGEE database through allocations of observing time by the Chilean National Time Allocation Committee and the Carnegie Institution for Science. This work was presented along with a companion article, Beaton et al. (2021), presenting the final target selection strategy adopted for APOGEE-2 in the Northern Hemisphere.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    URL: Article
    DOI: 10.3847/1538-3881/ac2cbc
    RVK:
    US 1090
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
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    SSG: 16,12
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  • 2
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    Late-time Hubble Space Telescope Observations of AT 2018cow. I. Further Constraints on the Fading Prompt Emission and Thermal Properties 50–60 days Post-discovery
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 955, No. 1 ( 2023-09-01), p. 42-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 955, No. 1 ( 2023-09-01), p. 42-
    Abstract: The exact nature of the luminous fast blue optical transient AT 2018cow is still debated. In this first of a two-paper series, we present a detailed analysis of three Hubble Space Telescope (HST) observations of AT 2018cow covering ∼50–60 days post-discovery in combination with other observations throughout the first two months and derive significantly improved constraints of the late thermal properties. By modeling the spectral energy distributions (SEDs), we confirm that the UV–optical emission over 50–60 days was still a smooth blackbody (i.e., optically thick) with a high temperature ( T BB ∼ 15,000 K) and small radius ( R BB ≲ 1000 R ⊙ ). Additionally, we report for the first time a break in the bolometric light curve: the thermal luminosity initially declined at a rate of L BB ∝ t −2.40 but faded much faster at t −3.06 after day 13. Reexamining possible late-time power sources, we disfavor significant contributions from radioactive decay based on the required 56 Ni mass and lack of UV line blanketing in the HST SEDs. We argue that the commonly proposed interaction with circumstellar material may face significant challenges in explaining the late thermal properties, particularly the effects of the optical depth. Alternatively, we find that continuous outflow/wind driven by a central engine can still reasonably explain the combination of a receding photosphere, optically thick and rapidly fading emission, and intermediate-width lines. However, the rapid fading may have further implications on the power output and structure of the system. Our findings may support the hypothesis that AT 2018cow and other “Cow-like transients” are powered mainly by accretion onto a central engine.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ace965
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 3
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    An Early-time Optical and Ultraviolet Excess in the Type-Ic SN 2020oi
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 924, No. 2 ( 2022-01-01), p. 55-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 924, No. 2 ( 2022-01-01), p. 55-
    Abstract: We present photometric and spectroscopic observations of Supernova 2020oi (SN 2020oi), a nearby (∼17 Mpc) type-Ic supernova (SN Ic) within the grand-design spiral M100. We undertake a comprehensive analysis to characterize the evolution of SN 2020oi and constrain its progenitor system. We detect flux in excess of the fireball rise model δ t ≈ 2.5 days from the date of explosion in multiband optical and UV photometry from the Las Cumbres Observatory and the Neil Gehrels Swift Observatory, respectively. The derived SN bolometric luminosity is consistent with an explosion with M ej = 0.81 ± 0.03 M ⊙ , E k = 0.79 ± 0.09 × 10 51 erg s −1 , and M Ni56 = 0.08 ± 0.02 M ⊙ . Inspection of the event’s decline reveals the highest Δ m 15,bol reported for a stripped-envelope event to date. Modeling of optical spectra near event peak indicates a partially mixed ejecta comparable in composition to the ejecta observed in SN 1994I, while the earliest spectrum shows signatures of a possible interaction with material of a distinct composition surrounding the SN progenitor. Further, Hubble Space Telescope pre-explosion imaging reveals a stellar cluster coincident with the event. From the cluster photometry, we derive the mass and age of the SN progenitor using stellar evolution models implemented in the BPASS library. Our results indicate that SN 2020oi occurred in a binary system from a progenitor of mass M ZAMS ≈ 9.5 ± 1.0 M ⊙ , corresponding to an age of 27 ± 7 Myr. SN 2020oi is the dimmest SN Ic event to date for which an early-time flux excess has been observed, and the first in which an early excess is unlikely to be associated with shock cooling.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ac35ec
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 4
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    Variability of Massive Stars in M31 from the Palomar Transient Factory
    American Astronomical Society ; 2020
    In:  The Astrophysical Journal Vol. 893, No. 1 ( 2020-04-08), p. 11-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 893, No. 1 ( 2020-04-08), p. 11-
    Type of Medium: Online Resource
    ISSN: 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ab7b7b
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2020
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
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  • 5
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    Online Resource
    Spectroscopic r-Process Abundance Retrieval for Kilonovae. I. The Inferred Abundance Pattern of Early Emission from GW170817
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 944, No. 2 ( 2023-02-01), p. 123-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 944, No. 2 ( 2023-02-01), p. 123-
    Abstract: Freshly synthesized r -process elements in kilonovae ejecta imprint absorption features on optical spectra, as observed in the GW170817 binary neutron star merger. These spectral features encode insights into the physical conditions of the r -process and the origins of the ejected material, but associating features with particular elements and inferring the resultant abundance pattern is computationally challenging. We introduce Spectroscopic r -Process Abundance Retrieval for Kilonovae ( SPARK ), a modular framework to perform Bayesian inference on kilonova spectra with the goals of inferring elemental abundance patterns and identifying absorption features at early times. SPARK inputs an atomic line list and abundance patterns from reaction network calculations into the TARDIS radiative transfer code. It then performs fast Bayesian inference on observed kilonova spectra by training a Gaussian process surrogate for the approximate posteriors of kilonova ejecta parameters, via active learning. We use the spectrum of GW170817 at 1.4 days to perform the first inference on a kilonova spectrum, and recover a complete abundance pattern. Our inference shows that this ejecta was generated by an r -process with either (1) high electron fraction Y e ∼ 0.35 and high entropy s / k B ∼ 25, or, (2) a more moderate Y e ∼ 0.30 and s / k B ∼ 14. These parameters are consistent with a shocked, polar dynamical component, and a viscously driven outflow from a remnant accretion disk, respectively. We also recover previous identifications of strontium absorption at ∼8000 Å, and tentatively identify yttrium and/or zirconium at ≲4500 Å. Our approach will enable computationally tractable inference on the spectra of future kilonovae discovered through multimessenger observations.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/acae72
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 6
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    Online Resource
    Type II-P supernova progenitor star initial masses and SN 2020jfo: direct detection, light-curve properties, nebular spectroscopy, and local environment
    Oxford University Press (OUP) ; 2023
    In:  Monthly Notices of the Royal Astronomical Society Vol. 524, No. 2 ( 2023-07-12), p. 2161-2185
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 524, No. 2 ( 2023-07-12), p. 2161-2185
    Abstract: We present optical, ultraviolet, and infrared data of the type II supernova (SN II) 2020jfo at 14.5 Mpc. This wealth of multiwavelength data allows us to compare different metrics commonly used to estimate progenitor masses of SN II for the same object. Using its early light curve, we infer SN 2020jfo had a progenitor radius of ≈700 R⊙, consistent with red supergiants of initial mass MZAMS =11–13 M⊙. The decline in its late-time light curve is best fit by a 56Ni mass of 0.018 ± 0.007 M⊙ consistent with that ejected from SN II-P with ≈13 M⊙ initial mass stars. Early spectra and photometry do not exhibit signs of interaction with circumstellar matter, implying that SN 2020jfo experienced weak mass-loss within the final years prior to explosion. Our spectra at & gt;250 d are best fit by models from 12 M⊙ initial mass stars. We analysed integral field unit spectroscopy of the stellar population near SN 2020jfo, finding its massive star population had a zero age main sequence mass of 9.7$\substack{+2.5\\ -1.3}~{\rm M}_{\odot }$. We identify a single counterpart in pre-explosion imaging and find it has an initial mass of at most $7.2\substack{+1.2\\ -0.6}~{\rm M}_{\odot }$. We conclude that the inconsistency between this mass and indirect mass indicators from SN 2020jfo itself is most likely caused by extinction with AV = 2–3 mag due to matter around the progenitor star, which lowered its observed optical luminosity. As SN 2020jfo did not exhibit extinction at this level or evidence for interaction with circumstellar matter between 1.6 and 450 d from explosion, we conclude that this material was likely confined within ≈3000 R⊙ from the progenitor star.
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/stad1954
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2023
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 7
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    Online Resource
    Late-time Hubble Space Telescope Observations of AT 2018cow. II. Evolution of a UV-bright Underlying Source 2–4 Yr Post-discovery
    American Astronomical Society ; 2023
    In:  The Astrophysical Journal Vol. 955, No. 1 ( 2023-09-01), p. 43-
    Details
    In: The Astrophysical Journal, American Astronomical Society, Vol. 955, No. 1 ( 2023-09-01), p. 43-
    Abstract: In this second of a two-paper series, we present a detailed analysis of three Hubble Space Telescope observations taken ∼2–4 yr post-discovery, examining the evolution of a UV-bright underlying source at the precise position of AT 2018cow. While observations at ∼2–3 yr post-discovery revealed an exceptionally blue ( L ν ∝ ν 1.99 ) underlying source with relatively stable optical brightness, fading in the near-UV was observed at year 4, indicating flattening in the spectrum (to L ν ∝ ν 1.64 ). The resulting spectral energy distributions can be described by an extremely hot but small blackbody, and the fading may be intrinsic (cooling) or extrinsic (increased absorption). Considering possible scenarios and explanations, we disfavor significant contributions from stellar sources and dust formation, based on the observed color and brightness. By comparing the expected power and the observed luminosity, we rule out interaction with known radio-producing circumstellar material (CSM) as well as magnetar spin down with B ∼ 10 15 G as possible power sources, though we cannot rule out the possible existence of a denser CSM component (e.g., a previously ejected hydrogen envelope) or a magnetar with B ≲ 10 14 G. Finally, we find that a highly inclined precessing accretion disk can reasonably explain the color, brightness, and evolution of the underlying source. However, a major uncertainty in this scenario is the mass of the central black hole (BH), as both stellar-mass and intermediate-mass BHs face notable challenges that cannot be explained by our simple disk model, and further observations and theoretical works are needed to fully constrain the nature of this underlying source.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    URL: Article
    DOI: 10.3847/1538-4357/ace964
    RVK:
    UA 1000
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 8
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    Erratum: Inferring the parallax of Westerlund 1 from Gaia DR2
    Oxford University Press (OUP) ; 2020
    In:  Monthly Notices of the Royal Astronomical Society Vol. 495, No. 1 ( 2020-06-11), p. 1372-1373
    Details
    In: Monthly Notices of the Royal Astronomical Society, Oxford University Press (OUP), Vol. 495, No. 1 ( 2020-06-11), p. 1372-1373
    Type of Medium: Online Resource
    ISSN: 0035-8711 , 1365-2966
    URL: Article
    DOI: 10.1093/mnras/staa1222
    Language: English
    Publisher: Oxford University Press (OUP)
    Publication Date: 2020
    detail.hit.zdb_id: 2016084-7
    SSG: 16,12
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  • 9
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    Online Resource
    The Red Supergiant Content of M31 and M33
    American Astronomical Society ; 2021
    In:  The Astronomical Journal Vol. 161, No. 2 ( 2021-02-01), p. 79-
    Details
    In: The Astronomical Journal, American Astronomical Society, Vol. 161, No. 2 ( 2021-02-01), p. 79-
    Abstract: We identify red supergiants (RSGs) in our spiral neighbors M31 and M33 using near-IR (NIR) photometry complete to a luminosity limit of . Our archival survey data cover 5 deg 2 of M31, and 3 deg 2 for M33, and are likely spatially complete for these massive stars. Gaia is used to remove foreground stars, after which the RSGs can be separated from asymptotic giant branch (AGB) stars in the color–magnitude diagram. The photometry is used to derive effective temperatures and bolometric luminosities via MARCS stellar atmosphere models. The resulting H-R diagrams show superb agreement with the evolutionary tracks of the Geneva evolutionary group. Our census includes 6400 RSGs in M31 and 2850 RSGs in M33 within their Holmberg radii; by contrast, only a few hundred RSGs are known so far in the Milky Way. Our catalog serves as the basis for a study of the RSG binary frequency being published separately, as well as future studies relating to the evolution of massive stars. Here we use the matches between the NIR-selected RSGs and their optical counterparts to show that the apparent similarity in the reddening of OB stars in M31 and M33 is the result of Malmquist bias; the average extinction in M31 is likely higher than that of M33. As expected, the distribution of RSGs follows that of the spiral arms, while the much older AGB population is more uniformly spread across each galaxy’s disk.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    URL: Article
    DOI: 10.3847/1538-3881/abd01f
    RVK:
    US 1090
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
    SSG: 16,12
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  • 10
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    Discovery of a Short-period and Unusually Helium-deficient Dwarf Nova KSP-OT-201701a by the KMTNet Supernova Program
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Letters Vol. 925, No. 2 ( 2022-02-01), p. L22-
    Details
    In: The Astrophysical Journal Letters, American Astronomical Society, Vol. 925, No. 2 ( 2022-02-01), p. L22-
    Abstract: We present the first ever discovery of a short-period and unusually helium-deficient dwarf nova KSP-OT-201701a by the Korea Microlensing Telescope Network Supernova Program. The source shows three superoutbursts, each led by a precursor outburst, and several normal outbursts in BVI during the span of ∼2.6 yr with supercycle and normal cycle lengths of about 360 and 76 days, respectively. Spectroscopic observations near the end of a superoutburst reveal the presence of strong double-peaked H i emission lines together with weak He i emission lines. The helium-to-hydrogen intensity ratios measured by He i λ 5876 and H α lines are 0.10 ± 0.01 at a quiescent phase and 0.26 ± 0.04 at an outburst phase, similar to the ratios found in long-period dwarf novae, while significantly lower than those in helium cataclysmic variables (He CVs). Its orbital period of 51.91 ± 2.50 minutes, which is estimated based on time-series spectroscopy, is a bit shorter than the superhump period of 56.52 ± 0.19 minutes, as expected from the gravitational interaction between the eccentric disk and the secondary star. We measure its mass ratio to be 0.37 − 0.21 + 0.32 using the superhump period excess of 0.089 ± 0.053. The short orbital period, which is under the period minimum, the unusual helium deficiency, and the large mass ratio suggest that KSP-OT-201701a is a transition object evolving to an He CV from a long-period dwarf nova with an evolved secondary star.
    Type of Medium: Online Resource
    ISSN: 2041-8205 , 2041-8213
    URL: Article
    DOI: 10.3847/2041-8213/ac4c41
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
    detail.hit.zdb_id: 2207648-7
    detail.hit.zdb_id: 2006858-X
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