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J/ApJ/838/90   Abundance analysis of 9 very metal-poor stars   (O'Malley+, 2017)

A differential abundance analysis of very metal-poor stars. O'Malley E.M., McWilliam A., Chaboyer B., Thompson I. <Astrophys. J., 838, 90-90 (2017)> =2017ApJ...838...90O (SIMBAD/NED BibCode)
ADC_Keywords: Stars, metal-deficient ; Abundances ; Equivalent widths ; Radial velocities ; Parallaxes, trigonometric ; Photometry, HST Keywords: stars: abundances; stars: atmospheres Abstract: We have performed a differential line-by-line chemical abundance analysis, ultimately relative to the Sun, of nine very metal-poor main-sequence (MS) halo stars, near [Fe/H]=-2dex. Our abundances range from -2.66≤[Fe/H]≤-1.40dex with conservative uncertainties of 0.07dex. We find an average [α/Fe]=0.34±0.09dex, typical of the Milky Way. While our spectroscopic atmosphere parameters provide good agreement with Hubble Space Telescope parallaxes, there is significant disagreement with temperature and gravity parameters indicated by observed colors and theoretical isochrones. Although a systematic underestimate of the stellar temperature by a few hundred degrees could explain this difference, it is not supported by current effective temperature studies and would create large uncertainties in the abundance determinations. Both 1D and <3D> hydrodynamical models combined with separate 1D non-LTE effects do not yet account for the atmospheres of real metal-poor MS stars, but a fully 3D non-LTE treatment may be able to explain the ionization imbalance found in this work. Description: We were awarded time on HST to obtain fine guidance sensor (FGS) parallaxes of nine very metal-poor stars with the goal of extending the range of metallicities below at least [Fe/H]=-2.3dex for stars with well-determined parallaxes. High-resolution spectroscopy of the nine target stars were obtained between 2008 and 2012 using the Magellan Inamori Kyocera Echelle (MIKE) double spectrograph on the 6.5m Magellan II Clay Telescope at Las Campanas Observatory, Chile (R=48000 for the red side and R=55000 for the blue side), and the High-Resolution Echelle Spectrometer (HiRES) on the twin telescopes at the W. M. Keck Observatory (R∼70500). A log of the spectroscopic observations along with the HST F606W magnitudes and parallaxes appears in Table 1. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 57 10 Target star observations table2.dat 76 100 Fe line list table3.dat 79 52 Alpha-element line list table4.dat 39 131 Solar and HIP 66815 line equivalent widths table11.dat 58 9 Stellar abundances approaching ionization equilibrium with 1σ uncertainties
See also: B/hst : HST Archived Exposures Catalog (STScI, 2007) I/259 : The Tycho-2 Catalogue (Hog+ 2000) J/ApJ/469/355 : Teff, B-V and BC relation (Flower, 1996) J/A+A/326/751 : Chemical composition of halo and disk stars (Nissen+, 1997) J/A+A/356/238 : Atmospheric param. in metal-poor stars. III. (Carretta+ 2000) J/AJ/120/1841 : Abundances & Kinematics of Halo & Disk Stars (Fulbright 2000) J/AJ/124/1144 : Orbits of 171 single-lined spectroscopic bin. (Latham, 2002) J/A+A/404/187 : Equivalent widths for metal-poor stars (Gratton+, 2003) J/A+A/433/185 : Detailed abundance analysis of F and G dwarfs (Bensby+, 2005) J/A+A/442/961 : Lithium content of the Galactic Halo stars (Charbonnel+, 2005) J/ApJS/159/141 : Spectroscopic properties of cool stars. I. (Valenti+, 2005) J/AJ/131/2949 : Mn abundances in cluster and field stars (Sobeck+, 2006) J/AJ/135/1551 : Abundances of stars in 47 Tuc (Koch+, 2008) J/A+A/512/A54 : Teff and Fbol from Infrared Flux Method (Casagrande+, 2010) J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010) J/ApJ/743/140 : Abundances (Be,α) in metal-poor stars (Boesgaard+, 2011) J/A+A/530/A138 : Geneva-Copenhagen survey re-analysis (Casagrande+, 2011) J/AJ/142/63 : Abundance of five stars in NGC 6397 (Koch+, 2011) J/ApJ/735/41 : Carbon and oxygen abundances in FGK stars (Petigura+, 2011) J/A+A/526/A99 : Metal-poor solar-type stars spectro. and masses (Sousa+, 2011) J/ApJ/753/64 : Detailed abundances for 97 metal-poor stars (Ishigaki+, 2012) J/A+A/557/A26 : STAGGER-grid of 3D stellar models. I. (Magic+, 2013) J/AJ/147/136 : Stars of very low metal abundance. VI. (Roederer+, 2014) J/MNRAS/454/2863 : Teff against colours calibrations (Huang+, 2015) J/ApJ/835/152 : HST FGS-1r parallaxes for 8 metal-poor stars (Chaboyer+, 2017) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 6 I6 --- HIP [46120/108200] HIP number 8 A1 --- f_HIP s= our standard star HIP 66815 10- 17 A8 --- Tel Telescope 19- 29 A11 "Y/M/D" Date UT date of observation 31- 36 F6.2 pix-1 S/N [76.5/254] Signal to noise ratio (1) 38- 43 F6.3 mag F606W [9.9/11.4]? HST F606W magnitude 45- 50 F6.3 mas Plx [3.4/15.1]? HST parallax π 52- 57 F6.1 km/s HRV [-309/85] Heliocentric radial velocity
Note (1): S/N measured from rms scatter at a blaze peak near 6740Å.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Ion Species being measured 6- 12 F7.2 0.1nm lambda [4447.7/6750.2] Wavelength of spectral line; in Angstrom units 14- 17 F4.2 eV EP [0.09/5] Excitation Potential of spectral line 19- 24 F6.2 10-13m HIP46120 ? Equivalent width for HIP 46120 (1) 26- 30 F5.2 10-13m HIP54639 ? Equivalent width for HIP 54639 (1) 32- 36 F5.2 10-13m HIP80679 ? Equivalent width for HIP 80679 (1) 38- 43 F6.2 10-13m HIP87062 ? Equivalent width for HIP 87062 (1) 45- 49 F5.2 10-13m HIP87788 ? Equivalent width for HIP 87788 (1) 51- 56 F6.2 10-13m HIP98492 ? Equivalent width for HIP 98492 (1) 58- 63 F6.2 10-13m HIP103269 ? Equivalent width for HIP 103269 (1) 65- 69 F5.2 10-13m HIP106924 ? Equivalent width for HIP 106924 (1) 71- 76 F6.2 10-13m HIP108200 ? Equivalent width for HIP 108200 (1)
Note (1): In units of milli-Angstroms.
Byte-by-byte Description of file: table3.dat
Bytes Format Units Label Explanations
1- 3 A3 --- Ion Species being measured 5- 11 F7.2 0.1nm lambda [4283/8718] Wavelength of spectral line 13- 16 F4.2 eV EP [0/9.2] Excitation Potential of spectral line 18- 23 F6.2 10-13m HIP46120 [1/142]? Equivalent width for HIP 46120 (1) 25- 30 F6.2 10-13m HIP54639 [0.6/217]? Equivalent width for HIP 54639 (1) 32- 37 F6.2 10-13m HIP80679 [0.2/186]? Equivalent width for HIP 80679 (1) 39- 44 F6.2 10-13m HIP87062 [0.3/144]? Equivalent width for HIP 87062 (1) 46- 51 F6.2 10-13m HIP87788 [0.2/151]? Equivalent width for HIP 87788 (1) 53- 58 F6.2 10-13m HIP98492 [1/221]? Equivalent width for HIP 98492 (1) 60- 65 F6.2 10-13m HIP103269 [3/212]? Equivalent width for HIP 103269 (1) 67- 72 F6.2 10-13m HIP106924 [0.4/107]? Equivalent width for HIP 106924 (1) 74- 79 F6.2 10-13m HIP108200 [1/280]? Equivalent width for HIP 108200 (1)
Note (1): In units of milli-Angstroms.
Byte-by-byte Description of file: table4.dat
Bytes Format Units Label Explanations
1- 4 A4 --- Ion Species to be measured 6- 18 F13.8 0.1nm lambda [4730/8773] Wavelength of spectral line; in Angstrom units 20- 25 F6.3 eV EP [0/68] Excitation Potential 27- 32 F6.2 10-13m HIP66815 [3/126] Equivalent width for HIP 66815 (1) 34- 39 F6.2 10-13m Sun [8/113]? Equivalent width for Sun (1)
Note (1): In units of milli-Angstroms.
Byte-by-byte Description of file: table11.dat
Bytes Format Units Label Explanations
1- 6 I6 --- HIP [46120/108200] HIP number 8- 12 F5.2 [-] [FeI/H] [-2.7/-1.4] [FeI/H] abundance 14- 17 F4.2 [-] e_[FeI/H] [0.07] [FeI/H] uncertainty 19- 23 F5.2 [-] [FeII/H] [-2.6/-1.3] [FeII/H] abundance 25- 28 F4.2 [-] e_[FeII/H] [0.1/0.3] [FeII/H] uncertainty 30- 33 F4.2 [-] [O/Fe] [0.1/0.8]? [O/Fe] abundance 35- 38 F4.2 [-] e_[O/Fe] [0.05/0.08]? [O/Fe] uncertainty 40- 43 F4.2 [-] [Mg/Fe] [0.05/0.5]? [Mg/Fe] abundance 45- 48 F4.2 [-] e_[Mg/Fe] [0.1/0.3]? [Mg/Fe] uncertainty 50- 53 F4.2 [-] [Ca/Fe] [0.1/0.8] [Ca/Fe] abundance 55- 58 F4.2 [-] e_[Ca/Fe] [0.03/0.08] [Ca/Fe] uncertainty
History: From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-Oct-2017
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