J/ApJ/791/107 Parameters of NGC 5139 SGBs stars (Villanova+, 2014)
The metallicity spread and the age-metallicity relation of ω Centauri.
Villanova S., Geisler D., Gratton R.G., Cassisi S.
<Astrophys. J., 791, 107 (2014)>
=2014ApJ...791..107V 2014ApJ...791..107V (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Stars, supergiant ; Photometry, HST ;
Effective temperatures ; Abundances, [Fe/H] ; Stars, ages
Keywords: globular clusters: general - globular clusters: individual: NGC 5139
Abstract:
ω Centauri is a peculiar globular cluster formed by a complex
stellar population. To investigate it, we studied 172 stars belonging
to the five SGBs that we can identify in our photometry, in order to
measure their [Fe/H] content as well as estimate their age dispersion
and the age-metallicity relation. The first important result is that
all of these SGBs have a distribution in metallicity with a spread
that exceeds the observational errors and typically displays several
peaks that indicate the presence of several subpopulations. We were
able to identify at least six of them based on their mean [Fe/H]
content. These metallicity-based subpopulations are seen to varying
extents in each of the five SGBs. Taking advantage of the age
sensitivity of the SGB, we showed that, first of all, at least half of
the subpopulations have an age spread of at least 2 Gyr. Then, we
obtained an age-metallicity relation that is the most complete to date
for this cluster. Interpretation of the age-metallicity relation is
not straightforward, but it is possible that the cluster (or what we
can call its progenitor) was initially composed of two populations
with different metallicities. Because of their age, it is very
unlikely that the most metal-rich derives from the most metal-poor by
some kind of chemical evolution process, so they can be assumed to be
two independent primordial objects, or perhaps two separate parts of a
single larger object, that merged in the past to form the present-day
cluster.
Description:
The spectroscopic data come from the ESO proposal 082.D-0424(A), and
were collected in 2009 January-March with FLAMES@VLT+GIRAFFE. The
sky was clear, and the typical seeing was ∼0.8 arcsec (FWHM). We used
the MEDUSA mode, which obtains 132 spectra simultaneously. To have a
high enough S/N and spectral resolution, we used the HR13 setup, which
gives R = 22500 in the 6120-6405 Å range. Our main target was
the SGB, where we pointed 450 stars, divided into 7 placements and
observed for 4 or 5 hr each. The remaining fibers were placed on HB
(∼270) and RGB (∼80) stars and on the sky (10 fibers for each plate).
Results for the RGB targets were already presented in Marino et al.
(2011, J/ApJ/731/64; 2012ApJ...746...14M 2012ApJ...746...14M). SGB target stars were
selected from the 3x3 mosaic of HST fields presented in
Villanova et al. (2007, J/ApJ/663/296) in order to cover the five SGBs
of the mF435W, mF625W CMD identified in that paper.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
13 26 47.28 -47 28 46.1 NGC 5139 = GCl 24
----------------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 81 172 Parameters of the observed stars
--------------------------------------------------------------------------------
See also:
J/A+A/445/503 : Radial velocities in Omega Cen (NGC5139) (Reijns+, 2006)
J/ApJ/647/1075 : Age-metallicity relation of ω Cen (Stanford+, 2006)
J/ApJ/663/296 : UBV(RI)c phot. of omega Cen (NGC5139) subgiants
(Villanova+, 2007)
J/ApJ/722/1373 : ω Centauri giants abundances (Johnson+, 2010)
J/MNRAS/427/1153 : Stellar parameters of giants in ω Cen (Simpson+, 2012)
J/MNRAS/433/1892 : Abundances of 848 giants of ω Cen (Simpson+, 2013)
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 9 A9 --- ID SGB identifier (SGB_A.NNN)
11- 22 F12.8 deg RAdeg Right Ascension in decimal degrees (J2000)
24- 35 F12.8 deg DEdeg Declination in decimal degrees (J2000)
37- 42 F6.3 mag F435Wmag HST/ACS F435W band magnitude
44- 49 F6.3 mag F625Wmag HST/ACS F625W band magnitude
51- 54 I4 K Teff Effective temperature
56- 59 F4.2 [cm/s2] log(g) Log surface gravity
61- 64 F4.2 km/s VTurb Turbulent velocity
66- 70 F5.2 [-] [Fe/H] Metallicity
72- 76 F5.1 km/s RVel Radial velocity
78- 81 F4.1 Gyr Age Age
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 30-Mar-2017