SYSTEMATIC Non-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. I. STELLAR ATMOSPHERE PARAMETERS

Sitnova, T.; Zhao, Gang; Mashonkina, L.; Chen, Y. H.; Liu, F.; Pakhomov, Yu. V.; Tan, Kefeng; Bolte, Michael; Alexeeva, Sofya; Grupp, F.; Shi, Jianrong; Zhang, H.-W.

doi:10.1088/0004-637x/808/2/148

Cited by 82 publications

(80 citation statements)

References 69 publications

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“…). However, our results and many works have confirmed that it is a very young star with rotation and strong activity (e.g., Barnes 2007;Schröder et al 2013;Sitnova et al 2015). Moreover, Carney et al (2001) regarded it as a single-lined spectroscopic binary, which means that it has a very dim or far away companion object.…”

Section: Age-chemistry ([O/fe] [C/fe] and [Fe/h])supporting

confidence: 63%

Ages of 70 Dwarfs of Three Populations in the Solar Neighborhood: Considering O and C Abundances in Stellar Models

Chen

et al. 2016

ApJ

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Oxygen and carbon are important elements in stellar populations. Their behavior refers to the formation history of the stellar populations. C and O abundances would also obviously influence stellar opacities and the overall metal abundance Z. With observed high-quality spectroscopic properties, we construct stellar models with C and O elements, to give more accurate ages for 70 metal-poor dwarfs, which have been determined to be high-α halo, low-α halo and thick-disk stars. Our results show that high-α halo stars are relatively older than low-α halo stars by around 2.0 Gyr. The thick-disk population has an age range between the two halo populations. The age distribution profiles indicate that high-α halo and low-α halo stars match the in situ accretion simulation by Zolotov et al., and the thick-disk stars might be formed in a relatively quiescent and long-lasting process. We also note that stellar ages are very sensitive to O abundance, since the ages clearly increase with increasing [O/Fe] values. Additionally, we obtain several stars with peculiar ages, including 2 young thick-disk stars and 12 stars older than the universe age.

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Section: Age-chemistry ([O/fe] [C/fe] and [Fe/h])supporting

confidence: 63%

Ages of 70 Dwarfs of Three Populations in the Solar Neighborhood: Considering O and C Abundances in Stellar Models

Chen

et al. 2016

ApJ

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“…For HD 122563 we adopted T eff = 4600 K from Mashonkina et al (2011), and it is consistent with the recent value based on the interferometric observations of Creevey et al (2012 Notes. References: (1) Mashonkina et al (2003); (2) Mashonkina et al (2011); (3) Sitnova et al (2015) recommended by Sitnova et al (2015) based on the data of Alonso et al (1996), González Hernández & Bonifacio (2009), Casagrande et al (2010, and Casagrande et al (2011). For HD 29907 its effective temperature was determined from the Balmer line wing fits (Mashonkina et al 2003).…”

Section: Stellar Sample Observations and Stellar Parametersmentioning

confidence: 99%

“…Surface gravities. For HD 29907, HD 84937, HD 122563, and HD 140283 we adopted the Hipparcos parallax-based surface gravities calculated by Mashonkina et al (2003), and Sitnova et al (2015. For the remaining five stars, log g were derived by Sitnova et al (2015) from the NLTE analysis of the Fe I and Fe II lines.…”

Section: Stellar Sample Observations and Stellar Parametersmentioning

confidence: 99%

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Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

Alexeeva

Mashonkina

2015

Mon. Not. R. Astron. Soc.

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A comprehensive model atom was constructed for C I using the most up-to-date atomic data. We evaluated non-local thermodynamical equilibrium (NLTE) line formation for neutral carbon in classical 1D models representing atmospheres of late-type stars, where carbon abundance varies from solar value down to [C/H] = −3. NLTE leads to stronger C I lines compared with their LTE strength and negative NLTE abundance corrections, ∆ NLTE . The deviations from LTE are large for the strong lines in the infrared (IR), with ∆ NLTE = −0.10 dex to −0.45 dex depending on stellar parameters, and they are minor for the weak lines in the visible spectral range, with |∆ NLTE | 0.03 dex. The NLTE abundance corrections were found to be dependent of the carbon abundance in the model. As the first application of the treated model atom, carbon NLTE abundances were determined for the Sun and eight late-type stars with well-determined stellar parameters that cover the −2.56 [Fe/H] −1.02 metallicity range. Consistent abundances from the visible and IR lines were found for the Sun and the most metal-rich star of our sample, when applying a scaling factor of S H = 0.3 to the Drawinian rates of C+H collisions. Carbon abundances were also derived from the molecular CH lines and, for each star, they agree with that from the atomic C I lines. We present the NLTE abundance corrections for lines of C I in the grid of model atmospheres applicable to the carbon-enhanced (CEMP) stars.

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“…Following Sitnova et al (2015), neglecting the NLTE effects in the determination of the gravity from the ionization equilibrium of iron would lead, for metal-poor turnoff stars, to a shift in log g up to 0.5 dex. The influence of this kind of shift on the abundance of the neutral elements and, in particular, on the lithium abundance (<0.01 dex for A(Li)) is negligible.…”

Section: Observations and Analysismentioning

confidence: 99%

Lithium abundance in a turnoff halo star on an extreme orbit

Spite

Caffau

et al. 2015

A&A

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Context. The lithium abundance in turnoff stars of the old population of our Galaxy is remarkably constant in the metallicity interval −2.8 < [Fe/H] < −2.0, defining a plateau. The Li abundance of these turnoff stars is clearly lower than the abundance predicted by the primordial nucleosynthesis in the frame of the standard Big Bang nucleosynthesis. Different scenarios have been proposed for explaining this discrepancy, along with the very low scatter of the lithium abundance around the plateau. Aims. The recently identified very high velocity star, WISE J0725-2351 appears to belong to the old Galactic population, and appears to be an extreme halo star on a bound, retrograde Galactic orbit. In this paper, we study the abundance ratios and, in particular the lithium abundance, in this star. Methods. The available spectra (ESO-Very Large Telescope) are analyzed and the abundances of Li, C, Na, Mg, Al, Si, Ca, Sc, Ti, Cr, Mn, Fe, Co, Ni, Sr and Ba are determined. Results. The abundance ratios in WISE J0725-2351 are those typical of old turnoff stars. The lithium abundance in this star is in close agreement with the lithium abundance found in the metal-poor turnoff stars located at moderate distance from the Sun. This high velocity star confirms, in an extreme case, that the very small scatter of the lithium plateau persists independent of the dynamic and kinematic properties of the stars.

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SYSTEMATIC Non-LTE STUDY OF THE −2.6 ≤ [Fe/H] ≤ 0.2 F AND G DWARFS IN THE SOLAR NEIGHBORHOOD. I. STELLAR ATMOSPHERE PARAMETERS

Cited by 82 publications

References 69 publications

Ages of 70 Dwarfs of Three Populations in the Solar Neighborhood: Considering O and C Abundances in Stellar Models

Ages of 70 Dwarfs of Three Populations in the Solar Neighborhood: Considering O and C Abundances in Stellar Models

Carbon abundances of reference late-type stars from 1D analysis of atomic C i and molecular CH lines

Lithium abundance in a turnoff halo star on an extreme orbit

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