J/ApJ/852/50 Galactic halo with APOGEE. II. Abundances. (Fernandez-Alvar+, 2018)
Disentangling the Galactic halo with APOGEE.
II. Chemical and star formation histories for the two distinct populations.
Fernandez-Alvar E., Carigi L., Schuster W.J., Hayes C.R., Avila-Vergara N.,
Majewski S.R., Allende Prieto C., Beers T.C., Sanchez S.F., Zamora O.,
Garcia-Hernandez D.A., Tang B., Fernandez-Trincado J.G., Tissera P.,
Geisler D., Villanova S.
<Astrophys. J., 852, 50 (2018)>
=2018ApJ...852...50F 2018ApJ...852...50F
ADC_Keywords: Abundances; Spectra, infrared; Stars, halo; Radial velocities
Keywords: Galaxy: evolution ; Galaxy: halo ; stars: abundances
Abstract:
The formation processes that led to the current Galactic stellar halo
are still under debate. Previous studies have provided evidence for
different stellar populations in terms of elemental abundances and
kinematics, pointing to different chemical and star formation
histories (SFHs). In the present work, we explore, over a broader
range in metallicity (-2.2<[Fe/H]<+0.5), the two stellar populations
detected in the first paper of this series from metal-poor stars in
DR13 of the Apache Point Observatory Galactic Evolution Experiment
(APOGEE). We aim to infer signatures of the initial mass function
(IMF) and the SFH from the two α-to-iron versus iron abundance
chemical trends for the most APOGEE-reliable α-elements (O, Mg,
Si, and Ca). Using simple chemical-evolution models, we infer the
upper mass limit (Mup) for the IMF and the star formation rate, and
its duration for each population. Compared with the low-α
population, we obtain a more intense and longer-lived SFH, and a
top-heavier IMF for the high-α population.
Description:
The first APOGEE phase was in SDSS-III and collected data between 2011
and 2014 July, obtaining high-resolution (R∼22500) spectra with a
typical signal-to-noise ≥100 using a multiobject infrared
spectrograph coupled to the 2.5m SDSS telescope at the Apache Point
Observatory.
The APOGEE Stellar Parameters and Abundances pipeline (ASPCAP) was
developed to obtain stellar atmospheric parameters and chemical
abundances from the H-band (1.5-1.7um), the spectral range covered by
the APOGEE spectrograph. The thirteenth data release (DR13; Albareti+
2017ApJS..233...25A 2017ApJS..233...25A) provides the final products of a reanalysis,
after including several improvements to the pipeline. Chemical
abundances of up to 26 chemical species are available for some stars,
including the α-elements: O, Mg, S, Si, Ca, and Ti.
From this database, we have selected 175 Galactic halo stars (see
Section 2 for further explanations).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 77 175 Halo stars selected within the DR13 APOGEE database,
with the stellar atmospheric parameters and
chemical abundances determined by ASPCAP
(Garcia Perez+ 2016, J/AJ/151/144) and used
in this work
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See also:
V/147 : The SDSS Photometric Catalogue, Release 12 (Alam+, 2015)
J/A+A/326/751 : Chemical composition of halo and disk stars (Nissen+, 1997)
J/ApJ/703/2177 : Metal-poor MS turnoff stars summary (Schlaufman+, 2009)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/ApJ/714/663 : Stellar density map of the Milky Way (de Jong+, 2010)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/A+A/530/A15 : Abundances of 94 stars (Nissen+, 2011)
J/ApJ/757/164 : Oxygen abundances of dwarf stars (Ramirez+, 2012)
J/ApJ/749/77 : MW halo. III. Statistical abundances (Schlaufman+, 2012)
J/ApJ/771/67 : Abundances for 97 metal-poor stars. II. (Ishigaki+, 2013)
J/A+A/566/A118 : A comprehensive view of Virgo stellar stream (Duffau+, 2014)
J/A+A/577/A81 : Deep SDSS Optical Spectroscopy. II. (Fernandez-Alvar+, 2015)
J/AJ/149/153 : Red giant abundances in 10 GCs (Meszaros+, 2015)
J/AJ/151/144 : ASPCAP weights for APOGEE chemical elements (Garcia+, 2016)
J/A+A/593/A28 : Halo metal-poor stars chemical data (Fernandez-Alvar+, 2016)
J/ApJ/819/103 : Abundances of two very metal-poor stars (Afsar+, 2016)
J/MNRAS/456/3655 : Masses and ages of red giants (Martig+, 2016)
J/MNRAS/460/3179 : APOGEE stars distance and extinction (Wang+, 2016)
J/A+A/604/A108 : UniDAM results (Mints+, 2017)
J/MNRAS/476/2117 : Outliers and similarity in APOGEE (Reis+, 2018)
J/ApJ/852/49 : Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- --- [2M]
3- 18 A16 --- 2MASS 2MASS identifier (HHMMSSss+DDMMSSs; J2000)
20- 22 A3 --- Pop Population (1)
24- 27 I4 K Teff [4001/4494] Effective temperature
29- 31 F3.1 [cm/s2] log(g) [0.4/2.4] log surface gravity
33- 41 F9.4 km/s RV [-462.4/382.1] Radial velocity
43- 47 F5.2 [Sun] [Fe/H] [-2.4/0.3] Metallicity
49- 56 F8.2 [Sun] [O/Fe] [-0.4/0.8]?=-9999 The O/Fe abundance
58- 62 F5.2 [Sun] [Mg/Fe] [-0.06/0.5] The Mg/Fe abundance
64- 71 F8.2 [Sun] [Si/Fe] [-0.2/0.7]?=-9999 The Si/Fe abundance
73- 77 F5.2 [Sun] [Ca/Fe] [-0.3/0.7] The Ca/Fe abundance
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Note (1): Population following the same classification derived from the
statistical analysis presented in Paper I (Hayes+, 2018, J/ApJ/852/49):
HMg = High-[Mg/Fe] population (48 sources)
LMg = Low_[Mg/Fe] population (127 sources)
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History:
From electronic version of the journal
References:
Hayes et al. Paper I. 2018ApJ...852...49H 2018ApJ...852...49H Cat. J/ApJ/852/49
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 13-Sep-2018