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Abundances of Red Giants in the Andromeda II Dwarf Spheroidal Galaxy

Côté, Patrick and Oke, J. B. and Cohen, Judith G. (1999) Abundances of Red Giants in the Andromeda II Dwarf Spheroidal Galaxy. Astronomical Journal, 118 (4). pp. 1645-1656. ISSN 0004-6256. doi:10.1086/301054.

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We have obtained spectra for 50 candidate red giants in Andromeda II, a dwarf spheroidal companion of M31, using the Low Resolution Imaging Spectrometer on the Keck II Telescope. After eliminating background galaxies and Galactic foreground stars, we are left with a sample of 42 red giants for which membership in Andromeda II can be established unambiguously from radial velocities. Line indexes measured on the Lick/IDS system are combined with VI photometry obtained with the Keck II and Palomar 5 m telescopes to investigate the age and metallicity distribution of these stars. Based on a comparison of the measured line indexes with those of Lick/IDS standard stars in globular and open clusters, we derive a mean metallicity of 〈[Fe/H]〉 = -1.47 ± 0.19 dex. This confirms the earlier conclusion, based on Thuan-Gunn gr photometry, that Andromeda II obeys the familiar relation between mean stellar metallicity and galaxy luminosity. There is also evidence for a dispersion in metallicity of σ([Fe/H]) = 0.35 ± 0.10 dex, based on the scatter in the measured Mg b line indexes and the observed width of the galaxy's giant branch. We note that, while existing observations of Local Group dwarf galaxies indicate that their mean metallicity depends rather sensitively on total luminosity, the internal spread in metallicity appears to be relatively independent of galaxy luminosity. Our spectroscopic sample contains one carbon star. We measure MI ≃-3.8 for this star, which places it below the tip of the red giant branch and suggests a common origin with the CH stars found in the Galactic halo. Although this carbon star alone does not provide evidence of an intermediate-age component in Andromeda II, two other stars in our spectroscopic sample have MI ≃-4.7 and -4.5. Membership in Andromeda II is unambiguous in both cases, indicating that these stars fall along an extended asymptotic giant branch and pointing to the presence of a modest intermediate-age population in this galaxy.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Côté, Patrick0000-0003-1184-8114
Cohen, Judith G.0000-0002-8039-4673
Additional Information:© 1999 The American Astronomical Society. Received 1999 May 11; accepted 1999 June 17. The authors thank Christian König for sending us his Thuan-Gunn photometry and Ed Olszewski for providing coordinates of the four stars observed by Aaronson et al. (1985). P. C. acknowledges support provided by the Sherman M. Fairchild Foundation. The research of J. G. C. is supported, in part, by NSF grant 96-16729. The W. M. Keck Observatory is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Funding AgencyGrant Number
Sherman Fairchild FoundationUNSPECIFIED
NSFAST 96-16729
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies : abundances - galaxies : evolution - galaxies : individual (Andromeda II) - galaxies : structure - stars : abundances
Issue or Number:4
Record Number:CaltechAUTHORS:20190524-144115768
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Official Citation:Patrick Côté et al 1999 AJ 118 1645
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:95798
Deposited By: Tony Diaz
Deposited On:25 May 2019 15:47
Last Modified:16 Nov 2021 17:15

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