J/A+A/573/A13 Metal abundances in 6 globular cluster (Dias+, 2015)
FORS2/VLT survey of Milky Way globular clusters.
I. Description of the method for derivation of metal abundances in the optical
and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426, and Terzan 8.
Dias B., Barbuy B., Saviane I., Held E.V., Da Costa G.S., Ortolani S.,
Vasquez S., Gullieuszik M., Katz D.
<Astron. Astrophys., 573, A13-13 (2015)>
=2015A&A...573A..13D 2015A&A...573A..13D
ADC_Keywords: Clusters, globular ; Abundances ; Effective temperatures
Keywords: stars: abundances - stars: kinematics and dynamics -
stars: Population II - globular clusters: general -
Galaxy: stellar content
Abstract:
We have observed almost one third of the globular clusters in the
Milky Way, targeting distant and/or highly reddened objects, as well
as a few reference clusters. A large sample of red giant stars was
observed with FORS2 at VLT/ESO at R∼2000. The method for deriving
stellar parameters is presented with application to six reference
clusters.
We aim at deriving the stellar parameters effective temperature,
gravity, metallicity, and α-element enhancement as well as the
radial velocity to confirm the membership of individual stars in each
cluster. We analyse the spectra collected for the reference globular
clusters NGC 6528 ([Fe/H]~-0.1), NGC 6553 ([Fe/H]~-0.2), M 71
([Fe/H]~-0.8), NGC 6558 ([Fe/H]~-1.0), NGC 6426 ([Fe/H]~-2.1), and
Terzan 8 ([Fe/H]~-2.2). They cover the full range of globular cluster
metallicities, and are located in the bulge, disc, and halo.
Full spectrum-fitting techniques were applied by comparing each target
spectrum with a stellar library in the optical region at
4560-5860Å. We employed the library of observed spectra MILES, and
the Coelho synthetic library. We validated the method by recovering
the known atmospheric parameters for 49 well-studied stars that cover
a wide range in the parameter space. We adopted as final stellar
parameters (effective temperatures, gravities, metallicities) the
average of results using the observed and synthetic spectral
libraries.
Description:
We observed with FORS2 at VLT/ESO 17 red giant stars in the globular
cluster NGC 6528, 17 in NGC 6553, 12 in M 71, 17 in NGC 6558,
10 in NGC 6426, and 13 in Terzan 8, under projects 077.D-0775(A)
and 089.D-0493(B).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 80 86 Star-by-star coordinates, magnitude, colour,
heliocentric radial velocity, and membership
selection
table6.dat 127 86 Atmospheric parameters for all stars analysed in
the six clusters: Teff, log(g), [Fe/H],
[Mg/Fe], and [α/Fe]
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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- 11 A11 --- Star Star identification (1)
13- 29 F17.13 deg RAdeg Right ascension (J2000)
31- 47 F17.13 deg DEdeg Declination (J2000)
49- 54 F6.3 mag Vmag V magnitude
56- 60 F5.3 mag V-I V-I colour index
62- 68 F7.2 km/s HV [-317/200] Heliocentric velocity
70- 78 F9.4 km/s HVt [231/209]? Ca triplet heliocentric velocity (2)
80 A1 --- Mmb [M] Membership (M=member)
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Note (1): Star identification as NGC NNNN_NN, M71_NN, Terzan8_NN and NGC NNNN_NN
for NGC 6426, 6528, 6553 and 6558.
Note (2): The velocities from CaT were taken from from Saviane et al.
(2012A&A...540A..27S 2012A&A...540A..27S, Cat. J/A+A/540/A27) for NGC 6528, NGC 6553, M 71, and
NGC 6558, and from Vasquez et al. (in prep.) for NGC 6426 and Terzan 8.
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 11 A11 --- Star Star designation
13- 16 I4 K Teffa Effective temperature from MILES library
18- 20 I3 K e_Teffa rms uncertainty on Teffa
22- 25 I4 K Teffb Effective temperature from Coelho library
27- 29 I3 K e_Teffb rms uncertainty on Teffb
31- 34 I4 K Teff Average of MILES and Coelho effective
temperature
36- 38 I3 K e_Teff rms uncertainty on Teff
40- 43 F4.2 [cm/s2] logga Surface gravity from MILES library
45- 48 F4.2 [cm/s2] e_logga rms uncertainty on logga
50- 53 F4.2 [cm/s2] loggb Surface gravity from Coelho library
55- 58 F4.2 [cm/s2] e_loggb rms uncertainty on loggb
60- 63 F4.2 [cm/s2] logg Average of MILES and Coelho surface gravity
65- 68 F4.2 [cm/s2] e_logg rms uncertainty on logg
70- 75 F6.3 [Sun] [Fe/H]a Metallicity from MILES library
77- 81 F5.3 [Sun] e_[Fe/H]a rms uncertainty on [Fe/H]a
83- 87 F5.2 [Sun] [Fe/H]b Metallicity from Coelho library
89- 92 F4.2 [Sun] e_[Fe/H]b rms uncertainty on [Fe/H]b
94- 98 F5.2 [Sun] [Fe/H] Average of MILES and Coelho metallicity
100-103 F4.2 [Sun] e_[Fe/H] rms uncertainty on [Fe/H]
105-110 F6.3 [Sun] [Mg/Fe] Abundance [Mg/Fe] from MILES library
112-115 F4.2 [Sun] e_[Mg/Fe] rms uncertainty on [Mg/Fe]
117-120 F4.2 [Sun] [a/Fe] Abundance [α/Fe] from Coelho library
122-125 F4.2 [Sun] e_[a/Fe] rms uncertainty on [α/Fe]
127 A1 --- Mmb [M] Membership (as in table3.dat)
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 06-Feb-2015