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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 (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). 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
The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line

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