2003/12/05 by Ricardo P. Schiavon, Nelson Caldwell, Schiavon, Ricardo P. +3 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics (astro-ph) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0312164
49 Pages, including 9 figures and 6 tables. To appear in the March/2004 issue of the Astronomical Journal
arxiv created 2003/12/05 · openalex publication_date 2003/12/05 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We construct an integrated spectrum of the intermediate age, solar\nmetallicity Galactic cluster M67, from individual spectra of cluster members.\nThe integrated spectrum is used as a template to test our stellar population\nsynthesis (SPS) models, in an age and [Fe/H] regime where such models remain\nlargely untested. We show that our models predict a spectroscopic age of 3.5\n+/- 0.5 Gyr for M67, in excellent agreement with the age we derive from the\ncolor-magnitude diagram of the cluster. The same age is obtained when using\nHbeta, Hgamma or Hdelta as the age indicator. Our models predict the abundances\nof Fe, Mg, C and N in agreement with detailed abundance analyses of cluster\nstars, to within 0.1 dex. Encouraged by the high degree of consistency of our\nmodels, we apply them to the study of the integrated spectrum of the central 3\narcsec of the compact elliptical galaxy M32. The resulting luminosity-weighted\nage of the galaxy ranges between 2 and 3.5 Gyr, depending on the Balmer line\nused. According to our models, the center of M32 seems to have a super-solar\nlight-weighted Fe abundance, ranging between [Fe/H] ~ +0.1 and +0.3, depending\non the Fe line adopted. Light-weighted abundance ratios found for the center of\nM32 are as follows: [Mg/Fe] ~ -0.1 -- -0.2, [C/Fe] and [N/Fe] ~ 0. We find that\nsingle SPS models with a solar-scaled abundance pattern cannot fit all the\nBalmer and metal lines in the integrated spectrum of M32. There is a systematic\ntrend in the sense that bluer absorption lines indicate a younger age and a\nhigher [Fe/H]. This slight inconsistency can be due either to (unaccounted for)\nabundance ratio effects on blue iron and Balmer line indices, or to a spread of\nthe ages of the stellar populations in M32. Current stellar population models\ncannot break this degeneracy at the level of accuracy required to address this\nproblem.\n