J/AJ/154/52 Metal-poor stars from SDSS/SEGUE. I Unevolved stars (Matsuno+, 2017)
High-resolution spectroscopy of extremely metal-poor stars from SDSS/SEGUE.
III. Unevolved stars with [Fe/H]≤-3.5.
Matsuno T., Aoki W., Beers T.C., Lee Y.S., Honda S.
<Astron. J., 154, 52-52 (2017)>
=2017AJ....154...52M 2017AJ....154...52M (SIMBAD/NED BibCode)
ADC_Keywords: Stars, metal-deficient ; Abundances ; Equivalent widths
Keywords: Galaxy: halo - stars: abundances - stars: atmospheres -
stars: Population II
Abstract:
We present elemental abundances for eight unevolved extremely
metal-poor (EMP) stars with Teff>5500K, among which seven have
[Fe/H]<-3.5. The sample is selected from the Sloan Digital Sky
Survey/Sloan Extension for Galactic Understanding and Exploration
(SDSS/SEGUE) and our previous high-resolution spectroscopic follow-up
with the Subaru Telescope. Several methods to derive stellar
parameters are compared, and no significant offset in the derived
parameters is found in most cases. From an abundance analysis relative
to the standard EMP star G64-12, an average Li abundance for stars
with [Fe/H]←3.5 is A(Li)=1.90, with a standard deviation of
σ=0.10dex. This result confirms that lower Li abundances are
found at lower metallicity, as suggested by previous studies, and
demonstrates that the star-to-star scatter is small. The small
observed scatter could be a strong constraint on Li-depletion
mechanisms proposed for explaining the low Li abundance at lower
metallicity. Our analysis for other elements obtained the following
results: (i) a statistically significant scatter in [X/Fe] for Na, Mg,
Cr, Ti, Sr, and Ba, and an apparent bimodality in [Na/Fe] with a
separation of ∼0.8dex, (ii) an absence of a sharp drop in the
metallicity distribution, and (iii) the existence of a CEMP-s star at
[Fe/H]≃-3.6 and possibly at [Fe/H]≃-4.0, which may provide
a constraint on the mixing efficiency of unevolved stars during their
main-sequence phase.
Description:
The targets in our present study are selected from Aoki et al. 2013
(Cat. J/AJ/145/13; Paper I).
We have obtained new, higher-quality spectra for eight targets with
the High Dispersion Spectrograph on the Subaru Telescope. The spectral
resolution is R=60000 with 2*2 CCD binning; the wavelength coverage is
4000-6000Å.
We also analyze the spectra of two bright EMP main-sequence turnoff
stars, G64-12 ([Fe/H]=-3.38) and LP815-43 ([Fe/H]=-2.96). The spectrum
of G64-12 was taken on 2002 December 22 with R∼90000 and S/N∼650 at
6708Å (S/N∼454 at 4880Å) (Aoki et al. 2009ApJ...698.1803A 2009ApJ...698.1803A). The
spectrum of LP815-43, which was taken from the
Subaru-Mitaka-Okayama-Kiso Archive (SMOKA; Baba et al.
2002ASPC..281..298B 2002ASPC..281..298B), was originally obtained on 2005 May 18 with
R∼90000 and S/N∼260 at 6708Å (S/N∼142 at 4880Å).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 86 9 Observation log for the SDSS sample
table5.dat 52 424 Measured equivalent widths
table6.dat 49 112 Results of the chemical abundance analysis
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See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
J/AJ/145/13 : Metal-poor stars from SDSS/SEGUE. I. Abundances (Aoki+, 2013)
J/ApJS/208/27 : Sun and HD 84937 TiII log(gf) and abundances (Wood+, 2013)
J/ApJ/667/1267 : CrI transition probabilities (Sobeck+, 2007)
J/ApJ/645/613 : Abundances of HD 221170 (Ivans+, 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 24 A24 --- Object Object name (1)
26- 36 A11 "Y:M:D" Date1 Starting date of the observing run
38- 48 A11 "Y:M:D" Date2 Second/ending date of the observing run
50- 60 A11 "Y:M:D" Date3 Ending date of the observing run
62- 66 F5.2 mag Vmag ? The V band magnitude
68- 73 A6 s Exp Exposure time
75- 76 I2 --- S/N1 ? Signal-to-Noise ratio at 4877Å
78- 79 I2 --- S/N2 ? Signal-to-Noise ratio at 6708Å
81- 86 F6.1 km/s RV ? Radial velocity (vr)
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Note (1): Objects identifiers given by SDSS can be found in Aoki et al. 2013
(Cat. J/AJ/145/13; Paper I). The object name is abbreviated throughout the
other tables, e.g., SDSS J0120-1001 for SDSS J012032.63-100106.5. In this
table, G64-12 was added at CDS.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
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1- 15 A15 --- Name Abbreviated object identifier
17- 21 A5 --- Species Species identifier
23- 30 F8.3 0.1nm lambda [4045.8/6495] Wavelength λ; in Å
32- 36 F5.3 eV EP [0/4.35] Excitation potential
38- 43 F6.3 [-] log(gf) [-3.36/0.57] Log oscillator strength
45- 49 F5.1 0.1pm EW [1/159.8] Equivalent width; in mÅ
51- 52 I2 --- Ref [1/23] Reference code (1)
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Note (1): The reference codes are defined as follows:
1 = Morton (1991ApJS...77..119M 1991ApJS...77..119M);
2 = Froese Fischer (1975CaJPh..53..184F 1975CaJPh..53..184F);
3 = Aldenius et al. (2007A&A...461..767A 2007A&A...461..767A);
4 = Wiese & Martin (1980wtpa.book.....W 1980wtpa.book.....W);
5 = Smith & Raggett (1981JPhB...14.4015S 1981JPhB...14.4015S);
6 = Ivans et al. 2006 (Cat. J/ApJ/645/613);
7 = Lawler & Dakin (1989JOSAB...6.1457L 1989JOSAB...6.1457L);
8 = Piskunov et al. (1995A&AS..112..525P 1995A&AS..112..525P);
9 = Lawler et al. (2013ApJS..205...11L 2013ApJS..205...11L);
10 = Grevesse et al. (1989A&A...208..157G 1989A&A...208..157G);
11 = Wood et al. 2013 (Cat. J/ApJS/208/27);
12 = Pickering et al. (2001ApJS..132..403P 2001ApJS..132..403P);
13 = Ryabchikova et al. (1994MNRAS.267..697R 1994MNRAS.267..697R);
14 = Martin et al. (1988atps.book.....M 1988atps.book.....M);
15 = Sobeck et al. 2007 (Cat. J/ApJ/667/1267);
16 = O'Brian et al. (1991JOSAB...8.1185O 1991JOSAB...8.1185O);
17 = Fuhr et al. (1988JPCRD..17S....F 1988JPCRD..17S....F);
18 = Bard et al. (1991A&A...248..315B 1991A&A...248..315B);
19 = Melendez & Barbuy (2009A&A...497..611M 2009A&A...497..611M);
20 = Moity (1983A&AS...52...37M 1983A&AS...52...37M);
21 = Pinnington et al. (1995JPhB...28.2095P 1995JPhB...28.2095P);
22 = Grevesse et al. (1981LIACo..23..211G 1981LIACo..23..211G);
23 = Grevesse et al. (2015A&A...573A..27G 2015A&A...573A..27G).
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 15 A15 --- Name Abbreviated object identifier
17- 22 A6 --- Species Species identifier
24- 25 I2 --- N [1/78]? Number of lines used
27 A1 --- l_log(e) [<] Upper limit flag on log(e)
28- 32 F5.2 --- log(e) [-2.07/7.34] Abundance logε(X) (1)
34- 37 F4.2 --- e_log(e) [0.02/0.29]? The 1σ error in log(e) (2)
39 A1 --- l_[X/Fe] [<] Upper limit flag on [X/Fe]
40- 44 F5.2 [Sun] [X/Fe] [-1/6] Log abundance relative to iron (3)
46- 49 F4.2 [Sun] e_[X/Fe] [0.01/0.31]? The 1σ error in [X/Fe] (2)
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Note (1): Abundances are determined differentially using G64-12 as a reference.
Note (2): The uncertainty represents internal precision only.
Note (3): [X/Fe] is calculated using the solar abundance from Asplund et al.
(2009ARA&A..47..481A 2009ARA&A..47..481A).
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History:
From electronic version of the journal
References:
Aoki et al., Paper I 2013AJ....145...13A 2013AJ....145...13A, Cat. J/AJ/145/13
Aoki et al., Paper II 2015AJ....149...39A 2015AJ....149...39A
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 25-Oct-2017