J/A+A/534/A53 Equivalent widths of 18 subgiant of ω Cen (Pancino+, 2011)
The subgiant branch of omega Cen seen through high-resolution spectroscopy.
II. The most metal-rich population.
Pancino E., Mucciarelli A., Bonifacio P., Monaco L., Sbordone L.
<Astron. Astrophys. 534, A53 (2011)>
=2011A&A...534A..53P 2011A&A...534A..53P
ADC_Keywords: Clusters, globular ; Stars, giant ; Stars, population II ;
Equivalent widths
Keywords: stars: abundances - globular clusters: individual: omega Centauri
Abstract:
We analyze spectra of 18 stars belonging to the faintest subgiant
branch in omega Centauri (the SGB-a), obtained with GIRAFFE@VLT at a
resolution of R~=17000 and a S/N ratio between 25 and 50. We measure
abundances of Al, Ba, Ca, Fe, Ni, Si, and Ti and we find that these
stars have <[Fe/H]≥-0.73±0.14dex, similarly to the corresponding
red giant branch population (the RGB-a). We also measure
<[alpha/Fe]≥+0.40±0.16dex, and <[Ba/Fe]≥+0.87±0.23dex, in
general agreement with past studies. It is very interesting to note
that we found a uniform Al abundance, <[Al/Fe]≥+0.32±0.14dex, for
all the 18 SGB-a stars analysed here, thus supporting past evidence
that the usual (anti-)correlations are not present in this population,
and suggesting a non globular cluster-like origin of this particular
population. In the dwarf galaxy hypothesis for the formation of omega
Cen, this population might be the best candidate for the field
population of its putative parent galaxy, although some of its
properties appear contradictory. It has also been suggested that the
most metal-rich population in omega Cen is significantly enriched in
helium. If this is true, the traditional abundance analysis
techniques, based on model atmospheres with normal helium content,
might lead to errors. We have computed helium enhanced atmospheres for
three stars in our sample and verified that the abundance errors due
to the use of non-enhanced atmospheres are negligible. Additional,
indirect support to the enhanced helium content of the SGB-a
population comes from our Li upper limits.
Description:
Equivalent widths and atomic data for all elements studied with a
classical equivalent width analysis in the 18 omega Centauri
subgiants studied.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 70 18 Observing Logs and atmospheric parameters
table2.dat 52 589 Equivalent widths for 18 subgiants in
ω Centauri
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See also:
J/MNRAS/357/265 : BVI photometry of omega Cen red giants (Sollima+, 2005)
J/ApJ/661/L155 : Radial velocities Rgb stars in omega Cen (Pancino+, 2007)
J/A+A/527/A18 : EW of 6 subgiants of ω Cen (Pancino+, 2011)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- WFI WFI identification number,
<Cl* NGC 5139 WFI NNNNNN> in Simbad
8- 12 I5 --- FORS FORS identification number (Sollima et al.
2005, Cat. J/MNRAS/357/265),
<Cl* NGC 5139 SGP NNNNNN> in Simbad (1)
14- 24 F11.7 deg RAdeg Right ascension in decimal degrees (J2000)
26- 36 F11.7 deg DEdeg Declination in decimal degrees (J2000)
38- 42 F5.2 mag Vmag V magnitude (1)
44- 47 F4.2 mag (B-V)0 Deredenned B-V colour index (1)
49- 52 F4.2 mag (V-I)0 Deredenned V-IJ colour index (1)
54 I1 --- Nobs Number of observations
56- 57 I2 --- S/N Signal-to-noise ratio
59- 62 I4 K Teff Hα effective temperature
64- 66 F3.1 [cm/s2] logg Surface gravity
68- 70 F3.1 km/s vt Microturbulent velocity
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Note (1): From Sollima et al., 2005, Cat. J/MNRAS/357/265
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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- 6 I6 --- WFI WFI identification number of subgiant
9- 15 F7.2 0.1nm lambda Wavelength in Angstroms
17- 20 A4 --- Ion Element name and ionization stage
22- 25 F4.2 eV EP Excitation potential
28- 32 F5.2 [-] loggf Logarithm of the oscillator strength
35- 39 F5.1 0.1pm EW Equivalent width in mÅ
42- 45 F4.1 0.1pm e_EW Formal DAOSPEC error on EW (in mÅ)
48- 52 F5.3 --- q_EW DAOSPEC Q parameter on EW
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Acknowledgements:
Elena Pancino, elena.pancino(at)oabo.inaf.it
References:
Pancino et al., Paper I 2011A&A...527A..18P 2011A&A...527A..18P, Cat. J/A+A/527/A18
(End) E. Pancino [INAF, Bologna Obs., Italy], P. Vannier [CDS] 06-Sep-2011