J/AJ/163/252 Chemical abundances for 15 extreme-velocity stars (Reggiani+, 2022)
The Chemical Composition of Extreme-velocity Stars.
Reggiani H., Ji A.P., Schlaufman K.C., Frebel A., Necib L., Nelson T.,
Hawkins K., Galarza J.Y.
<Astron. J., 163, 252 (2022)>
=2022AJ....163..252R 2022AJ....163..252R
ADC_Keywords: Stars, high-velocity; Stars, population II; Abundances;
Spectra, optical
Keywords: Hypervelocity stars ; Population II stars ; Stellar abundances ;
Stellar populations
Abstract:
Little is known about the origin of the fastest stars in the Galaxy.
Our understanding of the chemical evolution history of the Milky Way
and surrounding dwarf galaxies allows us to use the chemical
composition of a star to investigate its origin and to say whether it
was formed in situ or was accreted. However, the fastest stars, the
hypervelocity stars, are young and massive and their chemical
composition has not yet been analyzed. Though it is difficult to
analyze the chemical composition of a massive young star, we are well
versed in the analysis of late-type stars. We have used
high-resolution ARCES/3.5m Apache Point Observatory, MIKE/Magellan
spectra to study the chemical details of 15 late-type hypervelocity
star candidates. With Gaia EDR3 astrometry and spectroscopically
determined radial velocities we found total velocities with a range of
274-520km/s and mean value of 381km/s. Therefore, our sample stars are
not fast enough to be classified as hypervelocity stars, and are what
is known as extreme-velocity stars. Our sample has a wide iron
abundance range of -2.5≲[Fe/H]≲-0.9. Their chemistry indicates that
at least 50% of them are accreted extragalactic stars, with iron-peak
elements consistent with prior enrichment by sub- Chandrasekhar mass
Type Ia supernovae. Without indication of binary companions, their
chemical abundances and orbital parameters indicate that they are the
accelerated tidal debris of disrupted dwarf galaxies.
Description:
We observed the targets with two instruments: the Magellan Inamori
Kyocera Echelle (MIKE) spectrograph on the Magellan Clay Telescope at
Las Campanas Observatory and the ARC echelle spectrograph (ARCES) on
the 3.5m Apache Point Observatory telescope. For MIKE observations we
used either the 0.35" slit, the 0.5" slit, or the 0.7" slit with
standard blue and red grating azimuths, yielding spectra between 335nm
and 950nm with resolving power varying from R∼83000 to R∼40000 in the
blue arm and from R∼65000 to R∼31000 in the red arm. On ARCES, we used
the standard 1.6" slit, yielding effective spectra with continuous
coverage between 390nm and 900nm with resolving power of R∼31000.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 88 15 Log of observations
table2.dat 60 3646 Atomic data, equivalent widths and line abundances
table4.dat 53 390 Chemical abundances
--------------------------------------------------------------------------------
See also:
I/337 : Gaia DR1 (Gaia Collaboration, 2016)
III/279 : RAVE 5th data release (Kunder+, 2017)
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
II/358 : SkyMapper Southern Sky Survey. DR1.1 (Wolf+, 2018)
I/352 : Distances to 1.47 billion stars in Gaia EDR3 (Bailer-Jones+, 2021)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/A+A/416/1117 : Abundances in the early Galaxy (Cayrel+, 2004)
J/ApJ/705/328 : Abundance measurements in Sculptor dSph (Kirby+, 2009)
J/ApJS/182/80 : Rare earth abundances (Sneden+, 2009)
J/A+A/512/A41 : Abundances of microlensed stars in the Bulge (Bensby+, 2010)
J/A+A/523/A17 : Individual stars in Fornax dSph center (Letarte+, 2010)
J/A+A/511/L10 : Abundances and space velocities of 94 stars (Nissen+, 2010)
J/ApJ/743/156 : NEOWISE obs. of NEOs; preliminary results (Mainzer+, 2011)
J/A+A/564/A125 : AGN Torus model comparison of AGN in the CDFS (Buchner+, 2014)
J/ApJ/807/171 : SkyMapper Survey metalpoor star spectroscopy (Jacobson+, 2015)
J/ApJ/808/16 : The Cannon; new approach to determine abundances (Ness+, 2015)
J/ApJ/823/114 : The Cannon; a new approach to determine masses (Ness+, 2016)
J/ApJ/833/225 : -2.6≤[Fe/H]≤0.2 F and G dwarfs. II. Abundances (Zhao+, 2016)
J/A+A/608/A46 : Constraining cosmic scatter (Reggiani+, 2017)
J/ApJ/852/49 : Properties of metal-poor stars in APOGEE DR13 (Hayes+, 2018)
J/ApJ/868/110 : R-Process Alliance; 1st release Galactic halo (Sakari+, 2018)
J/A+A/627/A177 : Non-LTE analysis of K I in late-type stars (Reggiani+, 2019)
J/ApJ/891/85 : Manganese abundances GC & dSph galaxies (de los Reyes+, 2020)
J/AJ/160/181 : Chemical abundances in red giants with Magellan (Ji+, 2020)
J/AJ/160/173 : Abundances metal-poor stars in Inner Bulge (Reggiani+, 2020)
J/AJ/162/229 : 13 Magellanic Clouds metal-poor stars (Reggiani+, 2021)
J/AJ/163/159 : Species abundances in WASP-77A (Reggiani+, 2022)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Gaia Gaia EDR3 designation
21- 22 I2 h RAh [0/23] Hour of right ascension (J2000)
24- 25 I2 min RAm Minute of right ascension (J2000)
27- 31 F5.2 s RAs Second of right ascension (J2000)
33 A1 --- DE- [±] Sign of declination (J2000)
34- 35 I2 deg DEd [02/78] Degree of declination (J2000)
37- 38 I2 arcmin DEm Arcminute of declination (J2000)
40- 44 F5.2 arcsec DEs Arcsecond of declination (J2000)
46- 49 I4 yr Obs.Y [2017/2018] UT year of observation
51- 53 A3 "month" Obs.M UT month of observation
55- 56 I2 d Obs.d UT day of observation
58 I1 h Obs.h Hour of observation start, hour
60- 61 I2 min Obs.m Hour of observation start, minute
63- 64 I2 s Obs.s Hour of observation start, second
66- 69 F4.2 --- Slit [0.35/1.6] Slit width
71- 74 I4 s Texp [300/4110] Exposure time
76- 78 I3 --- S/N4500 [35/296] Signal-to-Noise ratio at 4500Å
80- 82 I3 --- S/N6500 [55/342] Signal-to-Noise ratio at 6500Å
84- 88 A5 --- Inst Instrument used; ARCES or MIKE
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Gaia Gaia EDR3 Designation
21- 28 F8.3 0.1nm Wave [3729/7789] Wavelength; Angstroms
30- 33 A4 --- Species Species identifier
35- 39 F5.3 eV ExPot [0/5.09] Excitation potential
41- 46 F6.3 [-] logg [-5.97/0.54] log oscillator strength
48- 53 F6.2 10-13m EW [1.5/379]? Equivalent width; milli-Angstroms
55- 60 F6.3 [-] logx [-0.9/8.04] log number abundance
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 A19 --- Gaia Gaia EDR3 Designation
21- 30 A10 --- Species Species identifier
32- 33 I2 --- N [1/76]? Number of lines used
35- 40 F6.3 [-] logx [-1.48/6.82]? log number abundance
42- 47 F6.3 [-] [X/Fe] [-1.55/1.9]? log abundance relative to Fe
49- 53 F5.3 [-] e_[X/Fe] [0.002/0.5]? Uncertainty in [X/Fe]
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie Fix [CDS], 23-Sep-2022