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  • 1
    In: The Astrophysical Journal, American Astronomical Society, Vol. 882, No. 1 ( 2019-08-28), p. 27-
    Type of Medium: Online Resource
    ISSN: 1538-4357
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2019
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    detail.hit.zdb_id: 1473835-1
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  • 2
    In: The Astrophysical Journal, American Astronomical Society, Vol. 897, No. 1 ( 2020-07-06), p. 78-
    Type of Medium: Online Resource
    ISSN: 1538-4357
    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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  • 3
    In: The Astronomical Journal, American Astronomical Society, Vol. 165, No. 2 ( 2023-02-01), p. 55-
    Abstract: We present chemical abundances and velocities of five stars between 0.3 and 1.1 kpc from the center of the Tucana II ultrafaint dwarf galaxy (UFD) from high-resolution Magellan/MIKE spectroscopy. We find that every star is deficient in metals (−3.6 〈 [Fe/H] 〈 −1.9) and in neutron-capture elements as is characteristic of UFD stars, unambiguously confirming their association with Tucana II. Other chemical abundances (e.g., C, iron peak) largely follow UFD trends and suggest that faint core-collapse supernovae (SNe) dominated the early evolution of Tucana II. We see a downturn in [ α /Fe] at [Fe/H] ≈ −2.8, indicating the onset of Type Ia SN enrichment and somewhat extended chemical evolution. The most metal-rich star has strikingly low [Sc/Fe] = −1.29 ± 0.48 and [Mn/Fe] = −1.33 ± 0.33, implying significant enrichment by a sub-Chandrasekhar mass Type Ia SN. We do not detect a radial velocity gradient in Tucana II ( dv helio / d θ 1 = − 2.6 − 2.9 + 3.0 km s −1 kpc −1 ), reflecting a lack of evidence for tidal disruption, and derive a dynamical mass of M 1 / 2 ( r h ) = 1.6 − 0.7 + 1.1 × 10 6 M ⊙ . We revisit formation scenarios of the extended component of Tucana II in light of its stellar chemical abundances. We find no evidence that Tucana II had abnormally energetic SNe, suggesting that if SNe drove in situ stellar halo formation, then other UFDs should show similar such features. Although not a unique explanation, the decline in [ α /Fe] is consistent with an early galactic merger triggering later star formation. Future observations may disentangle such formation channels of UFD outskirts.
    Type of Medium: Online Resource
    ISSN: 0004-6256 , 1538-3881
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2023
    detail.hit.zdb_id: 2207625-6
    detail.hit.zdb_id: 2003104-X
    SSG: 16,12
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  • 4
    Online Resource
    Online Resource
    American Astronomical Society ; 2022
    In:  The Astrophysical Journal Vol. 936, No. 1 ( 2022-09-01), p. 78-
    In: The Astrophysical Journal, American Astronomical Society, Vol. 936, No. 1 ( 2022-09-01), p. 78-
    Abstract: We have developed a chemodynamical approach to assign 36,010 metal-poor SkyMapper stars to various Galactic stellar populations. Using two independent techniques (velocity and action space behavior), Gaia EDR3 astrometry, and photometric metallicities, we selected stars with the characteristics of the “metal-weak” thick-disk population by minimizing contamination by the canonical thick disk or other Galactic structures. This sample comprises 7127 stars, spans a metallicity range of −3.50 〈 [Fe/H] 〈 −0.8, and has a systematic rotational velocity of 〈 V ϕ 〉 = 154 km s −1 that lags that of the thick disk. Orbital eccentricities have intermediate values between typical thick-disk and halo values. The scale length is h R = 2.48 − 0.05 + 0.05 kpc, and the scale height is h Z = 1.68 − 0.15 + 0.19 kpc. The metallicity distribution function is well fit by an exponential with a slope of Δ log N / Δ [ Fe / H ] = 1.13 ± 0.06 . Overall, we find a significant metal-poor component consisting of 261 SkyMapper stars with [Fe/H] 〈 −2.0. While our sample contains only 11 stars with [Fe/H] ≲ −3.0, investigating the JINAbase compilation of metal-poor stars reveals another 18 such stars (five have [Fe/H] 〈 −4.0) that kinematically belong to our sample. These distinct spatial, kinematic, and chemical characteristics strongly suggest that this metal-poor, phase-mixed kinematic sample represents an independent disk component with an accretion origin in which a massive dwarf galaxy radially plunged into the early Galactic disk. Going forward, we propose to call the metal-weak thick-disk population the Atari disk, given its likely accretion origin, and in reference to it sharing space with the Galactic thin and thick disks.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2022
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    detail.hit.zdb_id: 1473835-1
    SSG: 16,12
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  • 5
    In: The Astrophysical Journal Supplement Series, American Astronomical Society, Vol. 254, No. 2 ( 2021-06-01), p. 31-
    Abstract: The Milky Way’s metal-poor stars are nearby ancient objects that are used to study early chemical evolution and the assembly and structure of the Milky Way. Here we present reliable metallicities of ∼280,000 stars with −3.75 ≲ [Fe/H] ≲ −0.75 down to g = 17 derived using metallicity-sensitive photometry from the second data release of the SkyMapper Southern Survey. We use the dependency of the flux through the SkyMapper v filter on the strength of the Ca ii K absorption features, in tandem with SkyMapper u , g , i photometry, to derive photometric metallicities for these stars. We find that metallicities derived in this way compare well to metallicities derived in large-scale spectroscopic surveys, and we use such comparisons to calibrate and quantify systematics as a function of location, reddening, and color. We find good agreement with metallicities from the APOGEE, LAMOST, and GALAH surveys, based on a standard deviation of σ ∼ 0.25 dex of the residuals of our photometric metallicities with respect to metallicities from those surveys. We also compare our derived photometric metallicities to metallicities presented in a number of high-resolution spectroscopic studies to validate the low-metallicity end ([Fe/H] 〈 −2.5) of our photometric metallicity determinations. In such comparisons, we find the metallicities of stars with photometric [Fe/H] 〈 −2.5 in our catalog show no significant offset and a scatter of σ ∼ 0.31 dex level relative to those in high-resolution work when considering the cooler stars ( g − i 〉 0.65) in our sample. We also present an expanded catalog containing photometric metallicities of ∼720,000 stars as a data table for further exploration of the metal-poor Milky Way.
    Type of Medium: Online Resource
    ISSN: 0067-0049 , 1538-4365
    RVK:
    Language: Unknown
    Publisher: American Astronomical Society
    Publication Date: 2021
    detail.hit.zdb_id: 2006860-8
    detail.hit.zdb_id: 2207650-5
    SSG: 16,12
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  • 6
    In: Advances in Space Research, Elsevier BV, ( 2023-7)
    Type of Medium: Online Resource
    ISSN: 0273-1177
    Language: English
    Publisher: Elsevier BV
    Publication Date: 2023
    detail.hit.zdb_id: 2023311-5
    SSG: 16,12
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  • 7
    In: The Astrophysical Journal, American Astronomical Society, Vol. 937, No. 1 ( 2022-09-01), p. 14-
    Abstract: The Milky Way has accreted many ultra-faint dwarf galaxies (UFDs), and stars from these galaxies can be found throughout our Galaxy today. Studying these stars provides insight into galaxy formation and early chemical enrichment, but identifying them is difficult. Clustering stellar dynamics in 4D phase space ( E , L z , J r , J z ) is one method of identifying accreted structure that is currently being utilized in the search for accreted UFDs. We produce 32 simulated stellar halos using particle tagging with the Caterpillar simulation suite and thoroughly test the abilities of different clustering algorithms to recover tidally disrupted UFD remnants. We perform over 10,000 clustering runs, testing seven clustering algorithms, roughly twenty hyperparameter choices per algorithm, and six different types of data sets each with up to 32 simulated samples. Of the seven algorithms, HDBSCAN most consistently balances UFD recovery rates and cluster realness rates. We find that, even in highly idealized cases, the vast majority of clusters found by clustering algorithms do not correspond to real accreted UFD remnants and we can generally only recover 6% of UFDs remnants at best. These results focus exclusively on groups of stars from UFDs, which have weak dynamic signatures compared to the background of other stars. The recoverable UFD remnants are those that accreted recently, z accretion ≲ 0.5. Based on these results, we make recommendations to help guide the search for dynamically linked clusters of UFD stars in observational data. We find that real clusters generally have higher median energy and J r , providing a way to help identify real versus fake clusters. We also recommend incorporating chemical tagging as a way to improve clustering results.
    Type of Medium: Online Resource
    ISSN: 0004-637X , 1538-4357
    RVK:
    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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  • 8
    In: Research in Astronomy and Astrophysics, IOP Publishing, Vol. 21, No. 7 ( 2021-08-01), p. 161-
    Abstract: Data release 2 (DR2) from the Gaia mission was of great help in precise determination of fundamental parameters of Close Visual Binary and Multiple Systems (CVBMSs), especially masses of their components, which are crucial parameters in understanding formation and evolution of stars and galaxies. This article presents the complete set of fundamental parameters for two nearby close visual binary systems (CVBSs), which are HIP 19206 and HIP 84425. We utilised a combination of two methods; the first one is Tokovinin’s dynamical method to solve the orbit of the system and to estimate orbital elements and the dynamical mass sum, and the second one is Al-Wardat’s method for analysing CVBMSs to estimate the physical parameters of the individual components. The latest method employs grids of Kurucz line-blanketed plane parallel model atmospheres to build synthetic Spectral Energy Distributions (SEDs) of the individual components. Trigonometric parallax measurements given by Gaia DR2 and Hipparcos catalogues are used to analyse the two systems. The difference in these measurements yielded slight discrepancies in the fundamental parameters of the individual components, especially masses. So, a new dynamical parallax is suggested in this work based on the most convenient mass sum as given by each of the two methods. The new dynamical parallax for the system HIP 19205 of 22.97 ± 0.95 mas coincides well with the trigonometric one reported recently (in December 2020) by Gaia EDR3 of 22.3689 ± 0.4056 mas. The positions of the components of the two systems on the evolutionary tracks and isochrones are plotted, which suggest that all components are solar-type main sequence stars. Their most probable formation and evolution scenarios are also discussed.
    Type of Medium: Online Resource
    ISSN: 1674-4527
    Language: Unknown
    Publisher: IOP Publishing
    Publication Date: 2021
    detail.hit.zdb_id: 2511247-8
    SSG: 6,25
    SSG: 16,12
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  • 9
    Online Resource
    Online Resource
    Wiley ; 2019
    In:  Astronomische Nachrichten Vol. 340, No. 9-10 ( 2019-11), p. 847-851
    In: Astronomische Nachrichten, Wiley, Vol. 340, No. 9-10 ( 2019-11), p. 847-851
    Abstract: We investigate the application as a technique of the so‐called finite‐time Lyapunov exponent , a scalar value that measures the average, or integrated, separation between trajectories in integrable dynamical systems to quantify the predictability limit of the asymptotic global behavior of old compact star systems (1–10 Gyr), for instance, neutron stars. For this purpose, the Hamiltonian systems with a three‐dimensional self‐gravitating axisymmetric potential are superimposed due to the influence of different birth and kick velocity distributions. We find the behavior of the density distributions P ( x ) for the finite‐time exponents, which follow a log‐normal distribution (transformed into a Gaussian distribution), with a given mean deviation centered around the global values, at larger Δ t . It is shown that simple models of distributions reflect the underlying dynamics. We also analyze the predictability and the deviation vector ω ( t ), obtained from the distributions, by randomly selecting the initial deviation directions, and consequently the stellar dynamic stability of the periodic orbits, in three‐dimensional (3D) Hamiltonian systems over time. The behavior of the orbits is strongly influenced by the regular nature of the motion.
    Type of Medium: Online Resource
    ISSN: 0004-6337 , 1521-3994
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2019
    detail.hit.zdb_id: 2025762-4
    detail.hit.zdb_id: 2171222-0
    SSG: 16,12
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  • 10
    In: Astronomische Nachrichten, Wiley, Vol. 342, No. 4 ( 2021-05), p. 625-632
    Abstract: This study reports a probabilistic insight into the stellar‐mass and supernovae (SNe) explosion energy of five CEMP‐no stars' possible progenitors. As such, a direct comparison between the abundance ratios [X/Fe] of the light‐elements and the predicted nucleosynthetic yields of SN of high‐mass metal‐free stars has been performed. This comparison suggests that the possible progenitors have a stellar‐mass range of 11 − 22 M ⊙ and explosion energies of 0.3 − 1.8 × 10 51  erg. In addition, we investigate the kinematic signatures, derived from Gaia DR2, to conclude that these five CEMP‐no stars have halo‐like kinematic and do not enter the outer‐halo region. In addition, we link the abundance patterns with kinematic signatures to investigate the Gaia ‐Sausage and Gaia ‐Sequoia memberships. This chemo‐dynamical analysis suggests that these CEMP‐no stars are neither Gaia ‐Sausage nor Gaia ‐Sequoia remnant stars, but another accretion event might be responsible for the contribution of these stars to the Galactic Halo.
    Type of Medium: Online Resource
    ISSN: 0004-6337 , 1521-3994
    URL: Issue
    Language: English
    Publisher: Wiley
    Publication Date: 2021
    detail.hit.zdb_id: 2025762-4
    detail.hit.zdb_id: 2171222-0
    SSG: 16,12
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