J/A+A/587/A124 Metal-poor stars towards the Galactic bulge (Koch+, 2016)
Metal-poor stars towards the Galactic bulge: A population potpourri.
Koch A., McWilliam A., Preston G.W., Thompson I.B.
<Astron. Astrophys. 587, A124 (2016)>
=2016A&A...587A.124K 2016A&A...587A.124K (SIMBAD/NED BibCode)
ADC_Keywords: Stars, nearby ; Stars, carbon ; Stars, metal-deficient ;
Stars, population II ; Equivalent widths
Keywords: stars: abundances - stars: carbon - stars: Population II -
Galaxy: abundances - Galaxy: bulge - Galaxy: halo
Abstract:
We present a comprehensive chemical abundance analysis of five red
giants and two horizontal branch (HB) stars towards the south- ern
edge of the Galactic bulge, at (l, b)~(0°, -11°). Based on
high-resolution spectroscopy obtained with the Magellan/MIKE
spectrograph, we derived up to 23 chemical element abundances and
identify a mixed bag of stars, representing various populations in the
central regions of the Galaxy. Although cosmological simulations
predict that the inner Galaxy was host to the first stars in the
Universe, we see no chemical evidence of the ensuing massive supernova
explosions: all of our targets exhibit halo-like, solar [Sc/Fe]
ratios, which is in contrast to the low values predicted from
Population III nucleosynthesis. One of the targets is a CEMP-s star at
[Fe/H]=-2.52dex, and another target is a moderately metal-poor
([Fe/H]=-1.53dex) CH star with strong enrichment in s-process
elements (e.g., [Ba/Fe]=1.35). These individuals provide the first
contenders of these classes of stars towards the bulge. Four of the
carbon-normal stars exhibit abundance patterns reminiscent of halo
star across a metallicity range spanning -2.0 to -2.6dex, i.e.,
enhanced α-elements and solar Fe-peak and neutron-capture
elements, and the remaining one is a regular metal-rich bulge giant.
The position, distance, and radial velocity of one of the metal-poor
HB stars coincides with simulations of the old trailing arm of the
disrupted Sagittarius dwarf galaxy. While their highly uncertain
proper motions prohibit a clear kinematic separation, the stars'
chemical abundances and distances suggest that these metal-poor
candidates, albeit located towards the bulge, are not of the bulge,
but rather inner halo stars on orbits that make them pass through the
central regions. Thus, we caution similar claims of detections of
metal-poor stars as true habitants of the bulge.
Description:
The stars studied here were identified in a search for EMP stars
in the Galactic bulge (Preston et al. unpublished), near b=-10°,
employing the 2.5-m du Pont and 1-m Swope telescopes at Las
Campanas Observatory.
Observations of seven EMP candidates presented here were taken spread
over six nights in July 2007 with a median seeing of 0.95", while
individual exposures reached as high as 2" and notably better
conditions (∼0.6") during several nights. Our chosen set-up included
a 0.5" slit, 2x1 binning in spectral and spatial dimensions and
resulted in a resolving power of R∼45000. An observing log is given in
Table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 7 Observing log
table2.dat 80 229 Line list for the metal-poor sample
table3.dat 40 321 Line list for the metal-rich giant 899-14135
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Star Star designation (NNN-NNNNN)
11- 29 A19 --- Name IAU name (JHHMMSS.ss+DDMMSS.s)
31- 32 I2 h RAh Right ascension (J2000)
34- 35 I2 min RAm Right ascension (J2000)
37- 41 F5.2 s RAs Right ascension (J2000)
43 A1 --- DE- Declination sign (J2000)
44- 45 I2 deg DEd Declination (J2000)
47- 48 I2 arcmin DEm Declination (J2000)
50- 54 F5.2 arcsec DEs Declination (J2000)
56- 70 A15 --- Obs.date Observation date
71- 75 I5 s ExpTime Exposure time
77- 84 A8 --- S/N Signal-to-noise ratios
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 2 A2 --- El Element
4- 5 A2 --- Ion Ionization stage
8- 14 F7.2 0.1nm lambda Wavelength
19- 22 F4.2 eV Exp Excitation potential
27- 32 F6.3 [-] loggf Oscillator strength
38- 40 I3 0.1pm EW13971 ? Equivalent Width in star 872-13971
46- 48 I3 0.1pm EW17221 ? Equivalent Width in star 873-17221
54- 56 I3 0.1pm EW24995 ? Equivalent Width in star 874-24995
62- 64 I3 0.1pm EW27993 ? Equivalent Width in star 941-27993
70- 72 I3 0.1pm EW10464 ? Equivalent Width in star 958-10464
78- 80 I3 0.1pm EW37860 ? Equivalent Width in star 896-37860
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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- 2 A2 --- El Element
4- 5 A2 --- Ion Ionization stage
8- 14 F7.2 0.1nm lambda Wavelength
19- 22 F4.2 eV Exp Excitation potential
27- 32 F6.3 [-] loggf Oscillator strength
38- 40 I3 0.1pm EW14135 Equivalent width
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Acknowledgements:
Andreas Koch, akoch(at)lsw.uni-heidelberg.de
(End) Patricia Vannier [CDS] 04-Nov-2015