J/AJ/157/154 Abundances of RGs in Galactic globular clusters (Gerber+, 2019)
Carbon abundance inhomogeneities and deep mixing rates in Galactic globular
clusters.
Gerber J.M., Briley M.M., Smith G.H.
<Astron. J., 157, 154 (2019)>
=2019AJ....157..154G 2019AJ....157..154G (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Stars, giant ; Abundances ;
Photometry ; Optical ; Effective temperatures
Keywords: globular clusters: general - stars: abundances
Abstract:
Among stars in Galactic globular clusters the carbon abundance tends
to decrease with increasing luminosity on the upper red giant branch,
particularly within the lowest metallicity clusters. While such a
phenomena is not predicted by canonical models of stellar interiors
and evolution, it is widely held to be the result of some extra mixing
operating during red giant branch ascent which transports material
exposed to the CN(O)-cycle across the radiative zone in the stellar
interior and into the base of the convective envelope, whereupon it is
brought rapidly to the stellar surface. Here we present measurements
of [C/Fe] abundances among 67 red giants in 19 globular clusters
within the Milky Way. Building on the work of Martell et al.
(2008AJ....136.2522M 2008AJ....136.2522M), we have concentrated on giants with absolute
magnitudes of MV~-1.5 within clusters encompassing a range of
metallicity (-2.4<[Fe/H]←0.3). The Kitt Peak National Observatory (KPNO)
4 m and Southern Astrophysical Research (SOAR) 4.1 m telescopes were
used to obtain spectra covering the λ4300 CH and λ3883 CN
bands. The CH absorption features in these spectra have been analyzed
via synthetic spectra in order to obtain [C/Fe] abundances. These
abundances and the luminosities of the observed stars were used to infer
the rate at which C abundances change with time during upper red giant
branch evolution (i.e., the mixing efficiency). By establishing rates
over a range of metallicity, the dependence of deep mixing on metallicity
is explored. We find that the inferred carbon depletion rate decreases
as a function of metallicity, although our results are dependent on
the initial [C/Fe] composition assumed for each star.
Description:
Spectra were obtained for 67 stars chosen on the basis of various
photometric surveys for 19 GCs. Observations of the majority of the
stars (60) were obtained at Kitt Peak National Observatory (KPNO) with
the Mayall 4 m telescope, while 11 additional stars were observed using
the Southern Astrophysical Research Telescope (SOAR).
The observations made at KPNO used the 4 m Mayall telescope with the
R-C Spectrograph under National Optical Astronomy Observatory (NOAO)
Program 2010A-0388. This system employs the UV Fast camera to transmit
light to a 2048x2048 Tektronix (T2KB) CCD detector with 24 µm pixels.
The dispersive element used was the KPC-007 grating (632 l/mm in first
order blazed at 5200 Å), which produces a nominal inverse dispersion
of 1.4 Å/pixel at the CCD detector for a resolution of 4 Å FWHM.
Wavelength coverage ranged from the violet cutoff to ∼5500 Å, and so
includes the λ4300 CH band and the λ3883 CN band. The
spectrograph was used in the long-slit mode, with a width of 2"
(300 µm). For each star, usually 1-2 exposures were taken for total
exposure times of 900-1800 s. The observations were made over a five-night
period from 2010 June 10 to 14.
Observations with the SOAR 4.1 m telescope were made under NOAO Program
2011A-0352 during the three-day period of 2011 July 27-29. The Goodman
High Throughput Spectrograph was utilized. The spectrograph was configured
with a 600 l/mm diffraction grating, such that the resulting spectra
have a resolution of 2.3 Å FWHM and cover a wavelength range from the
atmospheric violet cutoff to 6200 Å. A slit width of 3" was used.
For each star, two to three exposures were taken to provide 1800 s of
total exposure time.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
clusters.dat 32 19 List of globular clusters
table1.dat 120 67 Abundances for program stars
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See also:
VII/195 : Globular Clusters in the Milky Way (Harris, 1996)
III/221 : Catalogue of [Fe/H] of F, G, K stars (Cayrel de Strobel+, 2001)
J/AJ/113/26 : Photometry of young globular clusters (Sarajedini+ 1997)
J/AJ/116/1775 : BV photometry of M53 (Rey+, 1998)
J/ApJ/611/323 : BVI photometry of M5 giant branch stars (Sandquist+, 2004)
J/AJ/135/1117 : Spectroscopic study of red giants in M15 (Meszaros+, 2008)
J/ApJ/682/1217 : Abundances in red giants in 7 globular clusters
(Kirby+, 2008)
J/A+A/505/117 : Abundances of red giants in 15 globular clusters
(Carretta+, 2009)
J/A+A/505/139 : Abundances of red giants in 17 globular clusters
(Carretta+, 2009)
J/A+A/507/803 : VI photometry of new M53 variables (Dekany+, 2009)
J/AJ/137/4282 : Red giant stars in clusters. II. M13 and M92
(Meszaros+, 2009)
J/AJ/149/153 : Abundances of red giants in 10 globular clusters
(Meszaros+, 2015)
J/A+A/590/A9 : RGB stars in Galactic GC stellar parameters (Dias+, 2016)
Byte-by-byte Description of file: clusters.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- GC Globular cluster identifier
10- 11 I2 h RAh Simbad Hour of Right Ascension (J2000)
13- 14 I2 min RAm Simbad Minute of Right Ascension (J2000)
16- 20 F5.2 s RAs Simbad Second of Right Ascension (J2000)
22 A1 --- DE- Simbad Sign of the Declination (J2000)
23- 24 I2 deg DEd Simbad Degree of Declination (J2000)
26- 27 I2 arcmin DEm Simbad Arcminute of Declination (J2000)
29- 32 F4.1 arcsec DEs Simbad Arcsecond of Declination (J2000)
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 8 A8 --- GC Globular cluster identifier (1)
10- 13 A4 --- OName Other globular cluster identifier
15- 24 A10 --- ID Stellar identifier(s)
26- 42 A17 --- 2MASS 2MASS identifier (JHHMMSSss-DDMMSSs)
44- 48 F5.2 [Sun] [Fe/H] [-2.37/-0.32] Metallicity
50- 55 F6.3 mag Vmag [12.58/15.85] Apparent V band magnitude
57- 61 F5.2 mag VMag [-2.03/-1.11] Absolute V band magnitude
63- 66 I4 K Teff [3942/4748] Effective temperature
68- 71 F4.2 [cm/s2] log(g) [0.76/1.53] Log surface gravity
73- 78 F6.3 --- S(3839) [-0.15/0.483] The CN index S(3839)
80- 84 F5.3 --- I(CH) [0.142/0.476] The I(CH) absorption index
86- 90 F5.2 [Sun] [C/Fe] [-0.9/-0.14] Log C/Fe abundance ratio (2)
92- 95 F4.2 [Sun] e_[C/Fe] [0.16/0.37] Uncertainty in [C/Fe]
97-100 F4.2 [Sun] [N/Fe] [0.6/1.76] Log N/Fe abundance ratio (2)
102-105 F4.2 [Sun] e_[N/Fe] [0.09/0.35] Uncertainty in [N/Fe]
107-113 F7.3 [Sun] [O/Fe] [-0.11/0.61]?=-99 Log O/Fe abundance ratio (2)
115 A1 --- f_[O/Fe] Flag on [O/Fe] (3)
117-120 A4 --- Tel Telescope (4)
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Note (1): The following are the resources for the identifiers and photometry
for each cluster:
Terzan 7 = Sarajedini & Layden (1997, J/AJ/113/264);
NGC 6362 = Alcaino (1972A&A....16..220A 1972A&A....16..220A);
NGC 6171 = Sandage & Katem (1964ApJ...139.1088S 1964ApJ...139.1088S);
NGC 6723 = Menzies (1974MNRAS.168..177M 1974MNRAS.168..177M);
NGC 5904 = Arp (1955AJ.....60..317A 1955AJ.....60..317A), Sandquist & Bolte (2004, J/ApJ/611/323);
NGC 6218 = Carretta et al. (2009, J/A+A/505/139), Kustner
(1933VeBon..26....1K 1933VeBon..26....1K), Racine (1971AJ.....76..331R 1971AJ.....76..331R);
NGC 6981 = Dickens (1972MNRAS.157..299D 1972MNRAS.157..299D);
NGC 6934 = Harris & Racine (1973AJ.....78..242H 1973AJ.....78..242H);
NGC 5257 = Sandage (1953AJ.....58...61S 1953AJ.....58...61S);
NGC 6205 = Arp (1955AJ.....60..317A 1955AJ.....60..317A), Cudworth & Monet (1979AJ.....84..774C 1979AJ.....84..774C);
NGC 6254 = Arp (1955AJ.....60..317A 1955AJ.....60..317A), Carretta et al. (2009, J/A+A/505/117),
Cayrel de Strobel, Soubiran, & Ralite (2001, Cat. III/221),
Harris, Racine, & de Roux (1976ApJS...31...13H 1976ApJS...31...13H);
NGC 7492 = Cuffey (1961PGLO...45..364C 1961PGLO...45..364C);
NGC 4147 = Sandage & Walker (1955AJ.....60..230S 1955AJ.....60..230S);
NGC 6779 = Hatzidimitriou et al. (2004MNRAS.348.1157H 2004MNRAS.348.1157H);
NGC 5024 = Dekany & Kovacs (2009, J/A+A/507/803), Rey et al. (1998,
J/AJ/116/1775), Sawyer Hogg (1973PDDO....3F...1S 1973PDDO....3F...1S);
NGC 7099 = Alcaino (1978A&AS...33..185A 1978A&AS...33..185A), Dickens (1972MNRAS.157..299D 1972MNRAS.157..299D);
NGC 5053 = Sandage, Katem & Johnson (1977AJ.....82..389S 1977AJ.....82..389S);
NGC 6341 = Buonanno et al. (1983A&AS...53....1B 1983A&AS...53....1B), Meszaros, Dupree & Szalai
(2009, J/AJ/137/4282);
NGC 7078 = Carretta et al. (2009, J/A+A/505/117), Buonanno et al.
(1983A&AS...51...83B 1983A&AS...51...83B), Meszaros, Dupree & Szentgyorgyi (2008,
J/AJ/135/1117).
Note (2): Based on solar abundances from Asplund et al. (2009ARA&A..47..481A 2009ARA&A..47..481A).
Note (3): Flag as follows:
N = No measurement;
A = Cluster average;
M = Measured value.
Note (4): Telescope as follows:
SOAR = The 4.1-m Southern Astrophysical Research Telescope;
KPNO = Mayall 4-m telescope at Kitt Peak National Observatory.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 16-Jul-2019