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Hubble Space Telescope Observations of M32: The Color-Magnitude Diagram | | Carl J. Grillmair
; Tod R. Lauer
; Guy Worthey
; S. M. Faber
; Wendy L. Freedman
; Barry F. Madore
; Edward A. Ajhar
; William A. Baum
; Jon A. Holtzman
; C. Roger Lynds
; Earl J. O’Neil
; Jr.
; Peter B. Stetson
; | | Date: |
18 Jul 1996 | | Subject: | astro-ph | | Affiliation: | Caltech), Tod R. Lauer (NOAO), Guy Worthey (University of Michigan), S. M. Faber (UCO/Lick Observatory), Wendy L. Freedman (OCIW), Barry F. Madore (IPAC), Edward A. Ajhar (NOAO), William A. Baum (University of Washington), Jon A. Holtzman (New Mexico S | | Abstract: | We present a V-I color-magnitude diagram for a region 1’-2’ from the center of M32 based on Hubble Space Telescope WFPC2 images. The broad color-luminosity distribution of red giants shows that the stellar population comprises stars with a wide range in metallicity. This distribution cannot be explained by a spread in age. The blue side of the giant branch rises to M_I ~ -4.0 and can be fitted with isochrones having [Fe/H] ~ -1.5. The red side consists of a heavily populated and dominant sequence that tops out at M_I ~ -3.2, and extends beyond V-I=4. This sequence can be fitted with isochrones with -0.2 < [Fe/H] < +0.1, for ages running from 15 Gyr to 5 Gyr respectively. We do not find the optically bright asymptotic giant branch stars seen in previous ground-based work and argue that the majority of them were artifacts of crowding. Our results are consistent with the presence of the infrared-luminous giants found in ground-based studies, though their existence cannot be directly confirmed by our data. There is little evidence for an extended or even a red horizontal branch, but we find a strong clump on the giant branch itself. If the age spread is not extreme, the distribution of metallicities in M32 is considerably narrower than that of the closed-box model of chemical evolution, and also appears somewhat narrower than that of the solar neighborhood. Overall, the M32 HST color-magnitude diagram is consistent with the average luminosity-weighted age of 8.5 Gyr and [Fe/H] = -0.25 inferred from integrated spectral indices. | | Source: | arXiv, astro-ph/9607094 | | Services: | Forum | Review | PDF | Favorites | |
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