J/ApJ/765/156 CH(G) index of SDSS evolved stars (Chen+, 2013)
The CH(G) index as a new criterion for selecting red giant stars.
Chen Y.Q., Zhao G., Carrell K., Zhao J.K., Tan K.F.
<Astrophys. J., 765, 156 (2013)>
=2013ApJ...765..156C 2013ApJ...765..156C
ADC_Keywords: Abundances, [Fe/H] ; Photometry, SDSS ; Stars, giant
Keywords: Galaxy: abundances; globular clusters: general;
globular clusters: individual (M3,M15,M92);
stars: distances; stars: evolution; stars: late-type
Abstract:
We have measured the CH G band (CH(G)) index for evolved stars in the
globular cluster M3 based on the Sloan Digital Sky Survey (SDSS)
spectroscopic survey. It is found that there is a useful way to select
red giant branch (RGB) stars from the contamination of other evolved
stars such as asymptotic giant branch (AGB) and red horizontal branch
(RHB) stars by using the CH(G) index versus (g-r)0 diagram if the
metallicity is known from the spectra. When this diagram is applied to
field giant stars with similar metallicity, we establish a calibration
of CH(G)=1.625(g-r)0-1.174(g-r)20-0.934. This method is
confirmed by stars with [Fe/H]~-2.3 where spectra of member stars in
globular clusters M15 and M92 are available in the SDSS database. We
thus extend this kind of calibration to every individual metallicity
bin ranging from [Fe/H]~-3.0 to [Fe/H]∼0.0 by using field red giant
stars with 0.4≤(g-r)0≤1.0. The metallicity-dependent calibrations
give CH(G)=1.625(g-r)0-1.174(g-r)20+0.060[Fe/H]-0.830 for
-3.0<[Fe/H]≤-1.2 and
CH(G)=0.953(g-r)0-0.655(g-r)20+0.060[Fe/H]-0.650 for
-1.2<[Fe/H]<0.0. The calibrations are valid for the SDSS spectroscopic
data set, and they cannot be applied blindly to other data sets. With
the two calibrations, a significant number of the contaminating stars
(AGB and RHB stars) were excluded and thus a clear sample of red giant
stars is obtained by selecting stars within ±0.05mag of the
calibration. The sample is published online and it is expected that
this large and clean sample of RGB stars will provide new information
on the formation and evolution of the Galaxy.
Description:
There are eight globular clusters (GCs) in the SDSS spectroscopic
survey that have enough spectra of member stars for statistical study,
and Smolinski et al. (2011, J/AJ/141/89) have presented these cluster
stars. For field stars, we select a sample of stars from the SDSS DR9
catalog with a (g-r)0 range of -0.2 to 1.0mag, [Fe/H] from ←2.8 to
0.0, and logg less than 3.5dex, where the main targets are giant
stars. The sample is limited to stars with spectra available in the
DR7 database, but the stellar parameters and (g-r)0 were taken from
the SDSS DR9 database.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 33 18450 Stars in the selected RGB sample
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
II/294 : The SDSS Photometric Catalog, Release 7 (Adelman-McCarthy+, 2009)
J/ApJ/762/27 : Most metal-poor stars. III. [Fe/H]≤-3.0 stars (Yong+, 2013)
J/AJ/145/13 : Metal-poor stars from SDSS/SEGUE. I. Abundances (Aoki+, 2013)
J/AJ/143/128 : SDSS high-metallicity M giant candidates (Palladino+, 2012)
J/A+A/534/A136 : Halo red giants from the SEGUE survey (Martell+, 2011)
J/AJ/142/126 : CN & CH in SDSS Galactic globular clusters (Smolinski+, 2011)
J/AJ/141/89 : SEGUE stellar parameter pipeline. IV. (Smolinski+, 2011)
J/AJ/137/4377 : List of SEGUE plate pairs (Yanny+, 2009)
J/AJ/136/2050 : SEGUE stellar parameter pipeline. II. (Lee+, 2008)
J/ApJ/655/492 : Equivalent widths of 26 metal-poor stars (Aoki+, 2007)
http://www.sdss.org/ : SDSS home page
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Plate Plate identifier
6- 10 I5 --- MJD Modified Julian Date identifier
12- 14 I3 --- Fiber Fiber identifier
16- 20 F5.2 [Sun] [Fe/H] [-3.9/-0] Metallicity
22- 26 F5.3 mag (g-r)0 [0.4/1] Dereddened (g-r) color index
28- 33 F6.3 mag CH(G) [-0.6/-0.2] The CH(G) index (1)
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Note (1): CH G band at λ4300Å as defined by Lee S.-G.
(1999AJ....118..920L 1999AJ....118..920L).
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 05-Nov-2014