1,464 research outputs found
Spectral Indices of Stars at Super-solar Regime
We derived Lick narrow-band indices for 139 candidate super metal-rich stars
of different luminosity class previously studied in Malagnini et al. (2000).
Indices include Iron Fe50, Fe52, Fe53, and Magnesium Mgb and Mg2 features. By
comparing observations with Kurucz' synthetic model atmospheres, no evidence is
found for non-standard Mg vs. Fe relative abundance (i.e. [Mg/Fe]~ 0, on the
average, for our sample). A comparison with the Worthey et al.(1994) and
Buzzoni et al.(1992, 1994) fitting function predictions for [Fe/H] > 0 is
performed and briefly discussed.Comment: 4 pages, 3 figures; proceedings of "New Quests in Stellar
Astrophysics: The link between Stars and Cosmology", 26-30 March, 2001,
Puerto Vallarta, Mexico, eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya,
to be published by the Kluwer Academic Publisher
Population Synthesis and the Diagnostics of High-redshift Galaxies
The effect of redshift on the observation of distant galaxies is briefly
discussed emphasizing the possible sources of bias in the interpretation of
high-z data. A general energetic criterion to assess physical self-consistency
of evolutionary population synthesis models is also proposed, for a more
appropriate use of this important tool to investigate distinctive properties of
primeval galaxies.Comment: 8 pages and 6 color figures. Invited talk at the conference "New
Quests in Stellar Astrophysics: The link between Stars and Cosmology", 26-30
March, 2001, Puerto Vallarta, Mexico, eds. M. Chavez et al., to be published
by Kluwe
Stellar lifetime and ultraviolet properties of the old metal-rich Galactic open cluster NGC6791: a pathway to understand the UV upturn of elliptical galaxies
The evolutionary properties of the old metal-rich Galactic open cluster
NGC6791 are assessed, based on deep UB photometry and 2Mass JK data. For 4739
stars in the cluster, bolometric luminosity and effective temperature have been
derived from theoretical (U-B) and (J-K) color fitting. The derived H-R diagram
has been matched with the UVBLUE grid of synthetic stellar spectra to obtain
the integrated SED of the system, together with a full set UV (Fanelli) and
optical (Lick) narrow-band indices. The cluster appears to be a fairly good
proxy of standard elliptical galaxies, although with significantly bluer
infrared colors, a shallower 4000A Balmer break, and a lower Mg2 index. The
confirmed presence of a dozen hot stars, along their EHB evolution, leads the
cluster SED to consistently match the properties of the most active UV-upturn
galaxies, with 1.7+/-0.4% of the total bolometric luminosity emitted shortward
of 2500A.
The cluster Helium abundance results Y=0.30 +/-0.04, while the Post-MS
implied stellar lifetime from star number counts fairly agrees with the
theoretical expectations from both the Padova and BASTI stellar tracks. A
Post-MS fuel consumption of 0.43 +/- 0.01 M_sun is found for NGC6791 stars, in
close agreement with the estimated mass of cluster He-rich white dwarfs. Such a
tight figure may lead to suspect that a fraction of the cluster stellar
population does actually not reach the minimum mass required to effectively
ignite He in the stellar core.Comment: A total of 15 pages, with 9 figures and 3 tables. The paper is to
appear in the Astrophysical Journal. See
http://www.bo.astro.it/~eps/home.html for further data retrieval and future
track of the projec
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