408 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
Stellar Populations in Bulges of Spiral Galaxies
We have conducted a spectroscopic analysis of the bulges of a sample of 31
spiral galaxies, spanning the Hubble sequence from S0 to Scd type, in order to
study the radial distribution of their stellar population properties.Comment: To be published in "The Evolution of Galaxies. II. Basic Building
Blocks", ed. M. Sauvage et al., Kluwe
Observations of Lick Standard Stars Using the SCORPIO Multi-Slit Unit at the SAO 6-m Telescope
We present Lick line-index measurements of standard stars from the list of
Worthey. The spectra were taken with the multi-slit unit of the SCORPIO
spectrograph at the 6-m Special Astrophysical observatory telescope. We
describe in detail our method of analysis and explain the importance of using
the Lick index system for studying extragalactic globular clusters. Our results
show that the calibration of our instrumental system to the standard Lick
system can be performed with high confidence.Comment: 12 pages, 3 figure
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
VLT spectroscopy of NGC 3115 globular clusters
We present results derived from VLT-FORS2 spectra of 24 different globular clusters associated with the lenticular galaxy NGC 3115. A subsample of 17 globular clusters have sufficiently high signal-to-noise to allow precision measurements of absorption line-strengths. Comparing these indices to new stellar population models by Thomas et al. we determine ages, metallicities and element abundance ratios. For the first time these stellar population models explicitly take abundance ratio biases in the Lick/IDS stellar library into account. Our data are also compared with the Lick/IDS observations of Milky Way and M 31 globular clusters. Unpublished higher order Balmer lines (HgammaA ,F and HdeltaA ,F) from the Lick/IDS observations are given in the Appendix. Our best age estimates show that the observed clusters which sample the bimodal colour distribution of NGC 3115 are coeval within our observational errors (2-3 Gyr). Our best calibrated age/metallicity diagnostic diagram (Hbeta / vs. [MgFe]) indicates an absolute age of 11-12 Gyr consistent with the luminosity weighted age for the central part of NGC 3115. We confirm with our accurate line-strength measurements that the (V-I) colour is a good metallicity indicator within the probed metallicity range (-1.5 < [Fe/H] < 0.0). The abundance ratios for globular clusters in NGC 3115 give an inhomogeneous picture. We find a range from solar to super-solar ratios for both blue and red clusters. This is similar to the data for M 31 while the Milky Way seems to harbour clusters which are mainly consistent with [alpha / Fe] =~ 0.3. From our accurate recession velocities we detect, independent of metallicity, clear rotation in the sample of globular clusters. In order to explain the metallicity and abundance ratio pattern, particularly the range in abundance ratios for the metal rich globular clusters in NGC 3115, we favour a formation picture with more than two distinct formation episodes. Based on observations collected at the European Southern Observatory, Cerro Paranal, Chile (ESO No. 66.B-0131)
Modeling the color evolution of luminous red galaxies - improvements with empirical stellar spectra
Predicting the colors of Luminous Red Galaxies (LRGs) in the Sloan Digital
Sky Survey (SDSS) has been a long-standing problem. The g,r,i colors of LRGs
are inconsistent with stellar population models over the redshift range
0.1<z<0.7. The g-r colors in the models are on average redder than the data
while the r-i colors in the models are bluer towards low redshift. Beyond
redshift 0.4, the predicted r-i color becomes instead too red, while the
predicted g-r agrees with the data. We provide a solution to this problem,
through a combination of new astrophysics and a fundamental change to the
stellar population modeling. We find that the use of the empirical library of
Pickles (1998) instead of theoretical spectra modifies the predicted colors
exactly in the way suggested by the data. The reason is a lower flux in the
empirical libraries, with respect to the theoretical ones, in the wavelength
range 5500-6500 AA. The discrepancy increases with decreasing effective
temperature independently of gravity. This result has general implications for
a variety of studies from globular clusters to high-redshift galaxies. The
astrophysical part of our solution regards the composition of the stellar
populations of these massive Luminous Red Galaxies. We find that on top of the
previous effect one needs to consider a model in which ~3% of the stellar mass
is in old metal-poor stars. Other solutions such as substantial blue Horizontal
Branch at high metallicity or young stellar populations can be ruled out by the
data. Our new model provides a better fit to the g-r and r-i colors of LRGs and
gives new insight into the formation histories of these most massive galaxies.
Our model will also improve the k- and evolutionary corrections for LRGs which
are critical for fully exploiting present and future galaxy surveys.Comment: Submitted to ApJ Letters. High resolution version available at
http://www.maraston.eu/Maraston_etal_2008.pd
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