NASA/IPAC EXTRAGALACTIC DATABASE
Date and Time of the Query: 2019-06-25 T16:43:04 PDT
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For refcode 1990A&A...228...23B:
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Copyright by European Southern Observatory (ESO). Reproduced by permission
1990A&A...228...23B Star formation history and chemical enrichment in the nuclear regions of M 31 and its dwarf companions M 32 and NGC 205 E. Bica, D. Alloin, and A. A. Schmidt Universidade Federal do Rio Grande do Sul, Departamento de Astronomia, Av. Bento Goncalves, 9500 BR-91500 Porto Alegre-RS, Brazil Observatoire de Paris, Section de Meudon, Departement d'Astrophysique Extragalactique et de Cosmologie, F-92195 Meudon Principal Cedex-France Universidade Federal de Santa Maria, Departamento de Matematica/NEPAE, Faixa de Camobi, Km 5, BR-97100 Santa Maria-RS, Brazil Received April 27, accepted July 3, 1989 Abstract. We present a comparative discussion about the stellar population and chemical enrichment in the nuclear regions of M 31 and of its dwarf companions M 32 and NGC 205, from a new set of long slit CCD spectra in the range 3500-10 000 A. We have performed the population syntheses using a grid of star cluster spectral features as a function of age and metallicity. The algorithm is a multiple minimization procedure, including a statistical treatment of the acceptable solutions and for which we discuss as well the question of the uniqueness of the solution. It provides a more significant result with respect to classical minimization methods relying on a single optimal solution. We find that the semistellar nucleus (SSN) and the bulge of M 31 are dominated by old metal-rich populations. The overall enrichment in heavy elements is however larger in the SSN ([Z/Z_sun_] ~0.6 at least) than in the inner bulge ([Z/Z_sun_] = 0.3). In the visible, flux fractions of 10 to 20% arise from an intermediate age component. The old age components span the entire metallicity range. With a predominant contribution from the highly metallic ones. The young age component remains inconspicuous in the visible range. In the nucleus of M 32, the metal enrichment comes out to be around solar and the light is dominated by old components in the range -0.5 < [Z/Z_sun_] < 0. As much as 30% of the flux at 5870 A arises from an intermediate age component corresponding to a 15% mass fraction. Both the old metal-poor and the young components in M32 contribute very little to the visible flux. Finally, our synthesis shows that the dominant population in the nucleus of NGC 205 is young, in the range 10^8^ to 5 10^8^ yr. The old component with metallicity - 1 < [Z/Z_sun_] the intermediate age components provide each around 20% of the visible light. The maximum metallicity attained in this object [Z/Z_sun_] = -0.5. Key words: galaxies: stellar content of - galaxies: nuclei of galaxies: evolution of - galaxies: M 31, M 32 and NGC 205
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