J/AJ/160/173 Abundances of metal-poor stars in the Inner Bulge (Reggiani+, 2020)
The most metal-poor stars in the Inner Bulge.
Reggiani H., Schlaufman K.C., Casey A.R., Ji A.P.
<Astron. J., 160, 173 (2020)>
=2020AJ....160..173R 2020AJ....160..173R
ADC_Keywords: Milky Way; Stars, metal-deficient; Optical; Abundances
Keywords: Galactic bulge ; Milky Way dynamics ; Milky Way formation ;
Population II stars ; Stellar abundances ; Type Ia supernovae
Abstract:
The bulge is the oldest component of the Milky Way. Since numerous
simulations of Milky Way formation have predicted that the oldest
stars at a given metallicity are found on tightly bound orbits, the
Galaxy's oldest stars are likely metal-poor stars in the inner bulge
with small apocenters (i.e., Rapo ≲4kpc). In the past, stars with
these properties have been impossible to find due to extreme reddening
and extinction along the line of sight to the inner bulge. We have
used the mid-infrared metal-poor star selection of Schlaufman & Casey
(2014) on Spitzer/Galactic Legacy Infrared Mid-Plane Survey
Extraordinaire data to overcome these problems and target candidate
inner bulge metal-poor giants for moderate-resolution spectroscopy
with Anglo-Australian Telescope/AAOmega. We used those data to select
three confirmed metal-poor giants ([Fe/H]=-3.15, -2.56, -2.03) for
follow-up high-resolution Magellan/Magellan Inamori Kyocera Echelle
spectroscopy. A comprehensive orbit analysis using Gaia DR2 astrometry
and our measured radial velocities confirms that these stars are
tightly bound inner bulge stars. We determine the elemental abundances
of each star and find high titanium and iron-peak abundances relative
to iron in our most metal-poor star. We propose that the distinct
abundance signature we detect is a product of nucleosynthesis in the
Chandrasekhar-mass thermonuclear supernova of a CO white dwarf
accreting from a helium star with a delay time of about 10Myr. Even
though chemical evolution is expected to occur quickly in the bulge,
the intense star formation in the core of the nascent Milky Way was
apparently able to produce at least one Chandrasekhar-mass
thermonuclear supernova progenitor before chemical evolution advanced
beyond [Fe/H]~-3.
Description:
We observed candidate inner bulge metal-poor giants using the
Anglo-Australian Telescope's (AAT) AAOmega multiobject spectrograph
fed by the 2 Degree Field (2dF) robotic fiber positioner. We used the
580V and 1700D gratings in the blue and red arms of the spectrograph,
providing a spectral resolution of R∼1300 between 370 and 580nm in the
blue and R∼10000 between 845 and 900nm in the red.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 66 5 Log of Magellan/MIKE observations
table3.dat 60 562 Line list, equivalent-width measurements, and
abundances
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See also:
B/simbad : Simbad objects catalogue (M.Wenger 2000)
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
I/347 : Distances to 1.33 billion stars in Gaia DR2 (Bailer-Jones+, 2018)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/ApJ/608/405 : Explosive yields of massive star (Z=0-Zsun) (Chieffi+, 2004)
J/A+A/501/519 : Extremely metal-poor turnoff stars abund. (Bonifacio+, 2009)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/A+A/512/A54 : Teff and Fbol from Infrared Flux Method (Casagrande+, 2010)
J/ApJ/724/341 : Nucleosynthesis of massive metal-free stars (Heger+, 2010)
J/ApJ/743/156 : NEOWISE obs. of NEOs: preliminary results (Mainzer+, 2011)
J/ApJ/749/175 : Abundances for stars in Plaut's window (Johnson+, 2012)
J/ApJ/769/57 : Equivalent widths of metal-poor stars (Frebel+, 2013)
J/AJ/145/107 : Zr, Ba, La, and Eu abund. in open clusters (Jacobson+, 2013)
J/AJ/147/136 : Stars very low metal abundance VI. Abund. (Roederer+, 2014)
J/ApJ/797/13 : Abundances of bright metal-poor stars (Schlaufman+, 2014)
J/A+A/586/A49 : r- & s- process elements Milky Way disk (Battistini+, 2016)
J/MNRAS/460/884 : EMBLA survey. Galactic bulge metal-poor stars (Howes+, 2016)
J/A+A/605/A89 : Abund. of microlensed Bulge dwarf stars VI. (Bensby+, 2017)
J/ApJ/850/179 : 2MASSJ15111324-2130030 metal-poor star abund (Casey+, 2017)
J/A+A/608/A46 : Constraining cosmic scatter (Reggiani+, 2017)
J/AJ/156/18 : APOGEE DR14:Binary companions stars (Price-Whelan+, 2018)
J/A+A/631/A80 : Mn lines 3D NLTE formation late-type stars (Bergemann+,2019)
J/MNRAS/488/2283 : COMBS survey. Galactic Bulge metal-poor stars (Lucey+, 2019)
J/A+A/638/A76 : StarHorse data for 5 surveys (Queiroz+, 2020)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- 2MASS Stellar identifier
21- 24 I4 yr Obs.Y [2017] UT year of observation
26- 28 A3 "month" Obs.M UT month of observation
30- 31 I2 d Obs.D UT day of observation
33- 40 A8 "h:m:s" Obs.S Hour of observation start
42- 49 A8 "h:m:s" Obs.E Hour of observation end
51- 53 F3.1 arcsec Slit [0.7/1] Slit width
55- 58 I4 s Texp [660/4800] Exposure time
60- 66 F7.2 km/s RVel [-196.42/9.23] Radial velocity
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- ID Stellar identifier
21- 28 F8.3 0.1nm Wave [3813/7789] Wavelength; Angstroms
30- 33 A4 --- Ion Ion identifier
35- 39 F5.3 eV EP [0/5.082] Excitation potential
41- 46 F6.3 [-] loggf [-4.76/0.54] log oscillator strength
48- 53 F6.2 10-13m EW [1.8/344] Equivalent width; milli-Angstroms
55- 60 F6.3 --- Abund [-1.722/5.902] Abundance (εx)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 17-Nov-2020