Stellar content of nearby galaxies. II - The Local Group dwarf elliptical galaxy M32

Abstract

view Abstract Citations (99) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Stellar Content of Nearby Galaxies. II. The Local Group Dwarf Elliptical Galaxy M32 Freedman, Wendy L. Abstract A field in the elliptical galaxy M32 has been resolved into stars using the prime-focus CCD camera on the Canada-France-Hawaii telescope. From these observations color-magnitude diagrams have been obtained for the brightest stars in this high-surface-brightness companion galaxy to M31. Both the I vs (V - I) and I vs (R - I) CCD color-magnitude diagrams reveal a red population of stars, the brightest of which resolve at I~19.5 mag. A lower limit to the mean metallicity of this stellar population is estimated from the apparent mean (V - I) and (R - I) colors at the giant branch tip. For the available data, this method indicates that the mean metallicity is greater than that of the most metal-rich Galactic globular clusters, that is (M/H) > -0.5 dex. The dispersion in the (V - I) and (R - I) colors exceeds that due to the estimated photometric errors, probably indicating an intrinsic range in the metallicity of the population amounting to 0.6 dex. The observed numbers of stars bracketing the tip of the first red giant branch can, in principle, provide a constraint on the age of the observed population. The histogram Iband luminosity function shows two discontinuities and allows two possible interpretations. If the bright discontinuity seen at I = 20.15 +/- 0.10 mag is interpreted as the tip of the first red giant branch, it suggests that M32 is approximately 100 kpc closer than M31, and that the age of most of the M32 stars is comparable to those in Galactic globular clusters. This result is consistent with other determinations of the relative distances of M31 and M32. Alternatively, if the fainter discontinuity at I = 20.45 +/- 0.10 mag is interpreted as being the first red giant branch tip, this suggests that M32 is at a distance comparable to M31. In this case, the relative numbers of stars above and below the adopted red giant branch tip suggests that a significant population of asymptotic giant branch stars may be present which could have formed as recently as 5 Gyr ago. This interpretation is consistent with spectroscopic studies and population synthesis models of the nucleus of M32. An independent distance modulus estimate for M32 is needed to provide a means of discriminating between these two very different alternatives. Publication: The Astronomical Journal Pub Date: October 1989 DOI: 10.1086/115216 Bibcode: 1989AJ.....98.1285F Keywords: Color-Magnitude Diagram; Dwarf Galaxies; Elliptical Galaxies; Local Group (Astronomy); Stellar Spectrophotometry; Astronomical Catalogs; Background Radiation; Charge Coupled Devices; Stellar Luminosity; Astrophysics; GALAXIES: INDIVIDUAL; GALAXIES: LOCAL GROUP; GALAXIES: STELLAR CONTENT full text sources ADS | data products SIMBAD (5) NED (1) Related Materials (2) Part 1: 1988AJ.....96.1248F Part 3: 1990AJ.....99..149W