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Astron. Astrophys. 337, 349-355 (1998)


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The stellar population of the decoupled nucleus in M 31

O.K. Sil'chenko 1, 2, A.N. Burenkov 3, 4 and V.V. Vlasyuk 3

1 Sternberg Astronomical Institute, University av. 13, 119899 Moscow, Russia
2 Isaac Newton Institute, Chile, Moscow Branch
3 Special Astrophysical Observatory, 357147 Nizhnij Arkhyz, Russia
4 RGO Astronomy Data Centre, Guest Investigator

Received 10 February 1998 / Accepted 21 April 1998

Abstract

The results of a spectroscopic and photometric investigation of the central region of M 31 are presented. An analysis of absorption-index radial profiles involving magnesium, calcium, and iron lines has shown that the unresolved nucleus of M 31 is distinct by its increased metallicity; unexpectedly, among two nuclei of M 31, it is the faintest one located exactly in the dynamical center of the galaxy (and dynamically decoupled) which is chemically distinct. The Balmer absorption line [FORMULA] has been included into the analysis to disentangle metallicity and age effects; an age difference by a factor 3 is detected between stellar populations of the nucleus and of the bulge, the nucleus being younger. The morphological analysis of CCD images has revealed the presence of a nuclear stellar-gaseous disk with a radius of some 100 pc, the gas component of which looks non-stationary, well inside the bulge of M 31.

Key words: galaxies: individual: M 31 – galaxies: nuclei – galaxies: structure – galaxies: stellar content – galaxies: abundances

Send offprint requests to: O. K. Sil'chenko

© European Southern Observatory (ESO) 1998

Online publication: August 17, 1998

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