J/AJ/147/25 Atmospheric parameters of M4 stars (Malavolta+, 2014)
Atmospheric parameters and metallicities for 2191 stars in the globular
cluster M4.
Malavolta L., Sneden C., Piotto G., Milone A.P., Bedin L.R., Nascimbeni V.
<Astron. J., 147, 25 (2014)>
=2014AJ....147...25M 2014AJ....147...25M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Spectroscopy ; Effective temperatures ;
Abundances, [Fe/H]
Keywords: globular clusters: individual: NGC 6121 -
stars: fundamental parameters - techniques: spectroscopic
Abstract:
We report new metallicities for stars of Galactic globular cluster M4
using the largest number of stars ever observed at high spectral
resolution in any cluster. We analyzed 7250 spectra for 2771 cluster
stars gathered with the Very Large Telescope (VLT) FLAMES+GIRAFFE
spectrograph at VLT. These medium-resolution spectra cover a small
wavelength range, and often have very low signal-to-noise ratios. We
approached this data set by reconsidering the whole method of
abundance analysis of large stellar samples from beginning to end. We
developed a new algorithm that automatically determines the
atmospheric parameters of a star. Nearly all of the data preparation
steps for spectroscopic analyses are processed on the syntheses, not
the observed spectra. For 322 red giant branch (RGB) stars with
V≤14.7, we obtain a nearly constant metallicity, <[Fe/H]≥-1.07
(σ=0.02). No difference in the metallicity at the level of 0.01
dex is observed between the two RGB sequences identified by Monelli et
al. (2013MNRAS.431.2126M 2013MNRAS.431.2126M). For 1869 subgiant and main-sequence stars
with V>14.7, we obtain <[Fe/H]≥-1.16 (σ=0.09) after fixing the
microturbulent velocity. These values are consistent with previous
studies that have performed detailed analyses of brighter RGB stars at
higher spectroscopic resolution and wavelength coverage. It is not
clear if the small mean metallicity difference between brighter and
fainter M4 members is real or is the result of the low signal-to-noise
characteristics of the fainter stars. The strength of our approach is
shown by recovering a metallicity close to a single value for more
than 2000 stars, using a data set that is non-optimal for atmospheric
analyses. This technique is particularly suitable for noisy data taken
in difficult observing conditions.
Description:
Table includes coordinates, photometry and atmospheric parameters of
M4 member stars, as described in the paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
params.dat 145 2239 Coordinates and atmospheric parameters
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See also:
J/PAZh/22/847 : Identification and coordinates in M4 (Shokin+, 1996)
J/ApJS/120/265 : HST photometry of M4 (Ibata+, 1999)
J/A+A/490/625 : Abundances of NGC 6121 red giants (Marino+, 2008)
J/MNRAS/442/2381 : Variable stars in M4 primary field (Nascimbeni+, 2014)
Byte-by-byte Description of file: params.dat
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Bytes Format Units Label Explanations
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4- 13 F10.6 deg RAdeg Right ascension (J2000)
17- 26 F10.6 deg DEdeg Declination (J2000)
30- 33 I4 --- ID Internal numbering
35- 39 I5 --- Stet Numbering in Stetson Photometric catalogue
43- 48 F6.3 mag Vmag V magnitude from Stetson (2005PASP..117..563S 2005PASP..117..563S)
catalog
53- 57 F5.3 mag B-V B-V colour index from Stetson
(2005PASP..117..563S 2005PASP..117..563S) catalog
61- 66 F6.3 mag V-I V-I colour index from Stetson
(2005PASP..117..563S 2005PASP..117..563S) catalog
70- 75 F6.3 mag Vmag0 V magnitude corrected for reddening
80- 84 F5.3 mag B-V0 B-V colour index corrected for reddening
88- 93 F6.3 mag V-I0 V-I colour index corrected for reddening
100-106 F7.2 K Teff Temperature of the star
111-115 F5.3 [cm/s2] logg Gravity of the star
120-124 F5.3 km/s vmic Velocity or microturbulence
128-133 F6.3 [-] [Fe/H] Metallicity of the star
138-139 I2 --- Niter Number of iterations before convergence
145 A1 --- Pop [012] Multiple population membership (1)
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Note (1): That flag refers to Figure 20 of the paper, where the stars of the
sample have been matched with the catalogue of Monelli et al.
(2013MNRAS.431.2126M 2013MNRAS.431.2126M) using the same code, as follows:
0 = no match
1 = RGBa, stars are Na-poor and O-rich (green)
2 = RGBb, intermediate properties between RGBa (Na-poor and O-rich) and
RGBc (Na-enhanced and O-depleted) (magenta)
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Acknowledgements:
Luca Malavolta, luca.malavolta(at)unipd.it
References:
D'Antona et al., 2009MNRAS.399L.151D 2009MNRAS.399L.151D
Milone et al., 2012A&A...540A..16M 2012A&A...540A..16M
Monelli et al., 2013MNRAS.431.2126M 2013MNRAS.431.2126M
(End) Patricia Vannier [CDS] 17-Apr-2016