J/ApJ/757/164 Oxygen abundances of dwarf stars (Ramirez+, 2012)
Oxygen abundances in low- and high-α field halo stars and the discovery
of two field stars born in globular clusters.
Ramirez I., Melendez J., Chaname J.
<Astrophys. J., 757, 164 (2012)>
=2012ApJ...757..164R 2012ApJ...757..164R
ADC_Keywords: Abundances ; Stars, dwarfs ; Stars, halo ; Effective temperatures
Keywords: Galaxy: disk; Galaxy: evolution; Galaxy: formation; Galaxy: halo;
stars: abundances; stars: Population II
Abstract:
Oxygen abundances of 67 dwarf stars in the metallicity range
-1.6<[Fe/H]←0.4 are derived from a non-LTE analysis of the 777nm OI
triplet lines. These stars have precise atmospheric parameters
measured by Nissen and Schuster (Cat. J/A+A/511/L10), who find that
they separate into three groups based on their kinematics and
α-element (Mg, Si, Ca, Ti) abundances: thick disk, high-α
halo, and low-α halo. We find the oxygen abundance trends of
thick-disk and high-α halo stars very similar. The low-α
stars show a larger star-to-star scatter in [O/Fe] at a given [Fe/H]
and have systematically lower oxygen abundances compared to the other
two groups. Thus, we find the behavior of oxygen abundances in these
groups of stars similar to that of the α elements. We use
previously published oxygen abundance data of disk and very metal-poor
halo stars to present an overall view (-2.3<[Fe/H]<+0.3) of oxygen
abundance trends of stars in the solar neighborhood. Two field halo
dwarf stars stand out in their O and Na abundances. Both G53-41 and
G150-40 have very low oxygen and very high sodium abundances, which
are key signatures of the abundance anomalies observed in globular
cluster (GC) stars. Therefore, they are likely field halo stars born
in GCs. If true, we estimate that at least 3%±2% of the local field
metal-poor star population was born in GCs.
Description:
Non-LTE oxygen abundances from the 777nm OI triplet lines have been
derived for as many as possible of the stars in the work by Nissen+,
Cat. J/A+A/511/L10. First, we used data from the Ramirez+, 2007,
Cat. J/A+A/465/271, work on oxygen abundances in nearby stars. Nearly
all of these spectra were acquired with the R. G. Tull coude
spectrograph on the 2.7m Telescope at McDonald Observatory (R∼60000).
Then, we searched for spectra taken with the HIRES spectrograph at the
Keck I Telescope.
We performed spectroscopic observations of 24 additional stars using
the MIKE spectrograph on the 6.5m Magellan/Clay Telescope at Las
Campanas Observatory. We acquired the data for these stars in four
observing runs in July, September, and November of 2011, as well as in
February of 2012 (R∼65000).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 67 Stellar parameters and oxygen abundances of stars
from the sample of Nissen and Schuster
(2010, Cat. J/A+A/511/L10)
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See also:
J/ApJ/764/78 : Oxygen abundances in nearby FGK stars (Ramirez+, 2013)
J/ApJ/735/41 : Carbon and oxygen abundances in FGK stars (Petigura+, 2011)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/A+A/465/271 : Oxygen abundances in nearby stars (Ramirez+, 2007)
J/A+A/402/343 : IR OI triplet, [O I] lines in F-K dwarfs/giants (Takeda, 2003)
J/ApJ/595/1154 : Oxygen abundances in metal-poor stars (Fulbright+, 2003)
J/A+A/390/235 : OI & FeII equivalent widths in metal-poor stars (Nissen+ 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Name Star name
11 A1 --- m_Name Multiplicity index on Name
13- 16 I4 K Teff Effective temperature (1)
18- 21 F4.2 [cm/s2] log(g) Log of the surface gravity (1)
23- 27 F5.2 [Sun] [Fe/H] Metallicity (1)
29- 33 F5.2 [Sun] [O/H] LTE derived log O/H abundance
35- 38 F4.2 [Sun] e_[O/H] Uncertainty in [O/H]
40- 43 F4.2 [Sun] [O/Fe] LTE derived log O/Fe abundance
45- 48 F4.2 [Sun] e_[O/Fe] Uncertainty in [O/Fe]
50- 54 F5.2 [Sun] [O/H]N NLTE derived log O/H abundance
56- 59 F4.2 [Sun] e_[O/H]N Uncertainty in [O/H]N
61- 64 F4.2 [Sun] [O/Fe]N NLTE derived log O/Fe abundance
66- 69 F4.2 [Sun] e_[O/Fe]N Uncertainty in [O/Fe]N
71- 74 A4 --- a/Fe The α/Fe abundance description
(high, low, or tdk=thick disk star) (1)
76- 89 A14 --- Source Source of the data (reference and/or
instrument) (2)
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Note (1): From Nissen & Schuster (2010, Cat. J/A+A/511/L10).
Note (2): References abbreviations:
R07 = Ramirez et al., 2007, Cat. J/A+A/465/271
Nissen02 = Nissen et al., 2002, Cat. J/A+A/390/235
Akerman04 = Akerman et al., 2004A&A...414..931A 2004A&A...414..931A
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 25-Jun-2014