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1

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Metal-poor Stars Observed with the Automated Planet Finder Telescope. II. Chemodynamical Analysis of Six Low-metallicity Stars in the Halo System of the Milky Way

Mardini, Mohammad K. ; Placco, Vinicius M. ; Taani, Ali ; [et al.]

American Astronomical Society ; 2019

In: The Astrophysical Journal Vol. 882, No. 1 ( 2019-08-28), p. 27-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 882, No. 1 ( 2019-08-28), p. 27-

Type of Medium: Online Resource

ISSN: 1538-4357

URL: Article

DOI: 10.3847/1538-4357/ab3047

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2019

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 1473835-1

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2

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The R -process Alliance: The Peculiar Chemical Abundance Pattern of RAVE J183013.5−455510

Placco, Vinicius M. ; Santucci, Rafael M. ; Yuan, Zhen ; [et al.]

American Astronomical Society ; 2020

In: The Astrophysical Journal Vol. 897, No. 1 ( 2020-07-06), p. 78-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 897, No. 1 ( 2020-07-06), p. 78-

Type of Medium: Online Resource

ISSN: 1538-4357

URL: Article

DOI: 10.3847/1538-4357/ab99c6

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

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Detailed Chemical Abundances of Stars in the Outskirts of the Tucana II Ultrafaint Dwarf Galaxy*

Chiti, Anirudh ; Frebel, Anna ; Ji, Alexander P. ; [et al.]

American Astronomical Society ; 2023

In: The Astronomical Journal Vol. 165, No. 2 ( 2023-02-01), p. 55-

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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

URL: Article

DOI: 10.3847/1538-3881/aca416

RVK:

US 1090

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

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The Atari Disk, a Metal-poor Stellar Population in the Disk System of the Milky Way

Mardini, Mohammad K. ; Frebel, Anna ; Chiti, Anirudh ; [et al.]

American Astronomical Society ; 2022

In: The Astrophysical Journal Vol. 936, No. 1 ( 2022-09-01), p. 78-

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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

URL: Article

DOI: 10.3847/1538-4357/ac8102

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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5

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Stellar Metallicities from SkyMapper Photometry. II. Precise Photometric Metallicities of ∼280,000 Giant Stars with [Fe/H] 〈 −0.75 in the Milky Way

Chiti, Anirudh ; Frebel, Anna ; Mardini, Mohammad K. ; [et al.]

American Astronomical Society ; 2021

In: The Astrophysical Journal Supplement Series Vol. 254, No. 2 ( 2021-06-01), p. 31-

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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

URL: Article

DOI: 10.3847/1538-4365/abf73d

RVK:

UA 1000

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

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The Nucleosynthesis and Reaction Rates of Fluorine 19 ( 19 F) in the Sun

Mardini, Mohammad K. ; Ershiadat, Nidal ; Al-Wardat, Mashhoor A. ; [et al.]

IOP Publishing ; 2019

In: Journal of Physics: Conference Series Vol. 1258, No. 1 ( 2019-10-01), p. 012024-

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In: Journal of Physics: Conference Series, IOP Publishing, Vol. 1258, No. 1 ( 2019-10-01), p. 012024-

Abstract: We investigate the abundance of 19 F in the Sun through the nucleosynthesis scenario. In addition, we calculate the rate equations and reaction rates of the nucleosynthesis of 19 F at different temperature scale. Other important functions of this nucleosynthesis (nuclear partition function and statistical equilibrium conditions) are also obtained. The resulting stability of 19 F occurs at nucleus with A = 19 and Mass Excess = -1.4874 MeV. As a result, this will tend to a series of neutron captures and beta-decay until 19 F is produced. The reaction rate of 15 N ( α, γ ) 19 F was dominated by the contribution of three low-energy resonances, which enhanced the final 19 F abundance in the envelope.

Type of Medium: Online Resource

ISSN: 1742-6588 , 1742-6596

URL: Article

DOI: 10.1088/1742-6596/1258/1/012024

Language: Unknown

Publisher: IOP Publishing

Publication Date: 2019

detail.hit.zdb_id: 2166409-2

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7

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Metal-poor Stars Observed with the Automated Planet Finder Telescope. I. Discovery of Five Carbon-enhanced Metal-poor Stars from LAMOST

Mardini, Mohammad K. ; Li, Haining ; Placco, Vinicius M. ; [et al.]

American Astronomical Society ; 2019

In: The Astrophysical Journal Vol. 875, No. 2 ( 2019-04-19), p. 89-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 875, No. 2 ( 2019-04-19), p. 89-

Type of Medium: Online Resource

ISSN: 1538-4357

URL: Article

DOI: 10.3847/1538-4357/ab0fa2

Language: Unknown

Publisher: American Astronomical Society

Publication Date: 2019

detail.hit.zdb_id: 2207648-7

detail.hit.zdb_id: 1473835-1

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8

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Cosmological Insights into the Early Accretion of r -process-enhanced Stars. I. A Comprehensive Chemodynamical Analysis of LAMOST J1109+0754

Mardini, Mohammad K. ; Placco, Vinicius M. ; Meiron, Yohai ; [et al.]

American Astronomical Society ; 2020

In: The Astrophysical Journal Vol. 903, No. 2 ( 2020-11-06), p. 88-

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In: The Astrophysical Journal, American Astronomical Society, Vol. 903, No. 2 ( 2020-11-06), p. 88-

Type of Medium: Online Resource

ISSN: 1538-4357

URL: Article

DOI: 10.3847/1538-4357/abbc13

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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9

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The regular dynamics through the finite‐time Lyapunov exponent distributions in 3D Hamiltonian systems

Taani, Ali ; Abushattal, Ahmad ; Mardini, Mohammad K.

Wiley ; 2019

In: Astronomische Nachrichten Vol. 340, No. 9-10 ( 2019-11), p. 847-851

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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

URL: Article

DOI: 10.1002/asna.v340.9-10

DOI: 10.1002/asna.201913713

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

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Metal‐poor stars observed with the automated planet finder telescope. III . CEMP ‐no stars are the descendant of population III stars

Almusleh, Nour Aldein ; Taani, Ali ; Özdemir, Sergen ; [et al.]

Wiley ; 2021

In: Astronomische Nachrichten Vol. 342, No. 4 ( 2021-05), p. 625-632

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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

URL: Article

DOI: 10.1002/asna.v342.4

DOI: 10.1002/asna.202113867

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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