1,636 research outputs found
Spectral libraries and their uncertainties
Libraries of stellar spectra are fundamental tools in the study of stellar
populations and in automatic determination of atmospheric parameters for large
samples of observed stars. In the context of the present volume, here I give an
overview of the current status of stellar spectral libraries from the
perspective of stellar population modeling: what we have currently available,
how good they are, and where we need further improvement
The End of Amnesia: Measuring the Metallicities of Type Ia SN Progenitors with Manganese Lines in Supernova Remnants
The Mn to Cr mass ratio in supernova ejecta has recently been proposed as a
tracer of Type Ia SN progenitor metallicity. We review the advantages and
problems of this observable quantity, and discuss them in the framework of the
Tycho Supernova Remnant. The fluxes of the Mn and Cr Kalpha lines in the X-ray
spectra of Tycho observed by the Suzaku satellite suggests a progenitor of
supersolar metallicity.Comment: 4 pages, 1 figure, Proceedings of 'Probing Stellar Populations out to
the Distant Universe'. September 15-19 2008, Cefalu, Sicily, Ital
Surface Brightness Fluctuations as Stellar Population Indicators
Surface Brightness Fluctuations (SBF) can provide useful information about
the unresolved stellar content of early-type galaxies and spiral bulges. The
absolute SBF magnitude Mbar in a given passband depends on the properties of
the stellar population and can be predicted by population synthesis models. SBF
measurements in different bandpasses are sensitive to different evolutionary
stages within the galaxy stellar population. Near-IR SBF magnitudes are
sensitive to the evolution of stars within the AGB phase, especially the
thermally pulsing AGB, while SBF in the blue and UV are sensitive to the hot
horizontal branch and post-AGB stages. Thus, multi-band SBF studies can
constrain important evolutionary parameters. Empirically, SBF data at the red
end of the optical spectrum (i, z, and potentially y) remain excellent distance
indicators. I briefly review some recent work on stellar populations using SBF,
primarily from an observational point of view.Comment: 8 pages, Invited review presented at "Probing Stellar Populations out
to the Distant Universe," September 2008, Cefalu, Ital
The CHilean Automatic Supernova sEarch (CHASE)
The CHASE project started in 2007 with the aim of providing young southern
supernovae (SNe) to the Carnegie Supernova Project (CSP) and Millennium Center
for Supernova Studies (MCSS) follow-up programs. So far CHASE has discovered 33
SNe with an average of more than 2.5 SNe per month in 2008. In addition to the
search we are carrying out a follow-up program targeting bright SNe. Our fully
automated data reduction allows us to follow the evolution on the light curve
in real time, triggering further observations if something potentially
interesting is detectedComment: 4 pages, 2 figures, conference proceedin
Evolution and Nucleosynthesis of Zero Metal Intermediate Mass Stars
New stellar models with mass ranging between 4 and 8 Mo, Z=0 and Y=0.23 are
presented. The models have been evolved from the pre Main Sequence up to the
Asymptotic Giant Branch (AGB). At variance with previous claims, we find that
these updated stellar models do experience thermal pulses in the AGB phase. In
particular we show that: a) in models with mass larger than 6 Mo, the second
dredge up is able to raise the CNO abundance in the envelope enough to allow a
"normal" AGB evolution, in the sense that the thermal pulses and the third
dredge up settle on; b) in models of lower mass, the efficiency of the CNO
cycle in the H-burning shell is controlled by the carbon produced locally via
the 3alpha reactions. Nevertheless the He-burning shell becomes thermally
unstable after the early AGB. The expansion of the overlying layers induced by
these weak He-shell flashes is not sufficient by itself to allow a deep
penetration of the convective envelope. However, immediately after that, the
maximum luminosity of the He flash is attained and a convective shell
systematically forms at the base of the H-rich envelope. The innermost part of
this convective shell probably overlaps the underlying C-rich region left by
the inter-shell convection during the thermal pulse, so that fresh carbon is
dredged up in a "hot" H-rich environment and a H flash occurs. This flash
favours the expansion of the outermost layers already started by the weak
thermal pulse and a deeper penetration of the convective envelope takes place.
Then, the carbon abundance in the envelope rises to a level high enough that
the further evolution of these models closely resembles that of more metal rich
AGB stars. These stars provide an important source of primary carbon and
nitrogen.Comment: 28 pages, 5 tables and 17 figures. Accepted for publication in Ap
Galactic chemical evolution of heavy elements: from Barium to Europium
We follow the chemical evolution of the Galaxy for elements from Ba to Eu,
using an evolutionary model suitable to reproduce a large set of Galactic
(local and non local) and extragalactic constraints. Input stellar yields for
neutron-rich nuclei have been separated into their s-process and r-process
components. The production of s-process elements in thermally pulsing
asymptotic giant branch stars of low mass proceeds from the combined operation
of two neutron sources: the dominant reaction 13C(alpha,n)16O, which releases
neutrons in radiative conditions during the interpulse phase, and the reaction
22Ne(alpha,n)25Mg, marginally activated during thermal instabilities. The
resulting s-process distribution is strongly dependent on the stellar
metallicity. For the standard model discussed in this paper, it shows a sharp
production of the Ba-peak elements around Z = Z_sun/4. Concerning the r-process
yields, we assume that the production of r-nuclei is a primary process
occurring in stars near the lowest mass limit for Type II supernova
progenitors. The r-contribution to each nucleus is computed as the difference
between its solar abundance and its s-contribution given by the Galactic
chemical evolution model at the epoch of the solar system formation. We compare
our results with spectroscopic abundances of elements from Ba to Eu at various
metallicities (mainly from F and G stars) showing that the observed trends can
be understood in the light of the present knowledge of neutron capture
nucleosynthesis. Finally, we discuss a number of emerging features that deserve
further scrutiny.Comment: 34 pages, 13 figures. accepted by Ap
The Peculiar Type Ib Supernova 2006jc: A WCO Wolf-Rayet Star Explosion
We present a theoretical model for Type Ib supernova (SN) 2006jc. We
calculate the evolution of the progenitor star, hydrodynamics and
nucleosynthesis of the SN explosion, and the SN bolometric light curve (LC).
The synthetic bolometric LC is compared with the observed bolometric LC
constructed by integrating the UV, optical, near-infrared (NIR), and
mid-infrared (MIR) fluxes. The progenitor is assumed to be as massive as
on the zero-age main-sequence. The star undergoes extensive mass
loss to reduce its mass down to as small as , thus becoming a WCO
Wolf-Rayet star. The WCO star model has a thick carbon-rich layer, in which
amorphous carbon grains can be formed. This could explain the NIR brightening
and the dust feature seen in the MIR spectrum. We suggest that the progenitor
of SN 2006jc is a WCO Wolf-Rayet star having undergone strong mass loss and
such massive stars are the important sites of dust formation. We derive the
parameters of the explosion model in order to reproduce the bolometric LC of SN
2006jc by the radioactive decays: the ejecta mass , hypernova-like
explosion energy ergs, and ejected Ni mass . We
also calculate the circumstellar interaction and find that a CSM with a flat
density structure is required to reproduce the X-ray LC of SN 2006jc. This
suggests a drastic change of the mass-loss rate and/or the wind velocity that
is consistent with the past luminous blue variable (LBV)-like event.Comment: 12 pages, 11 figures. Accepted for publication in the Astrophysical
Journa
Solar analogues in open clusters: The case of M67
Solar analogues are fundamental targets for a better understanding of our Sun
and our Solar System. Usually, this research is limited to field stars, which
offer several advantages and limitations. In this work, we present the results
of a research of solar twins performed for the first time in a open cluster,
namely M67. Our analysis allowed us to find five solar twins and also to derive
a solar colour of (B-V)0=0.649+/-0.016 and a cluster distance modulus of
9.63+/-0.08. This study encourages us to apply the same method to other open
clusters, and to do further investigations for planet search in the solar twins
we find.Comment: 4 pages, 2 figures; Proceedings of the conference "Probing Stellar
Populations out to the Distant Universe", Cefalu' (Italy), September 7 - 19,
2008. To be published in the AIP Conf. Proc. Serie
Intermediate-mass star models with different helium and metal contents
We present a comprehensive theoretical investigation of the evolutionary
properties of intermediate-mass stars. The evolutionary sequences were computed
from the Zero Age Main Sequence up to the central He exhaustion and often up to
the phases which precede the carbon ignition or to the reignition of the
H-shell which marks the beginning of the thermal pulse phase. The evolutionary
tracks were constructed by adopting a wide range of stellar masses
(\msun) and chemical compositions. In order to account for
current uncertainties on the He to heavy elements enrichment ratio, the stellar
models were computed by adopting at Z=0.02 two different He contents (Y=0.27,
0.289) and at Z=0.04 three different He contents (Y=0.29, 0.34, and 0.37). To
supply a homogeneous evolutionary scenario which accounts for young Magellanic
stellar systems the calculations were also extended toward lower metallicities
(Z=0.004, Z=0.01), by adopting different initial He abundances. We evaluated
for both solar (Z=0.02) and super-metal-rich (SMR, Z=0.04) models the
transition mass between the stellar structures igniting carbon and
those which develop a full electron degeneracy inside the CO core. This
evolutionary scenario allows us to investigate in detail the properties of
classical Cepheids. In particular, we find that the range of stellar masses
which perform the blue loop during the central He-burning phase narrows when
moving toward metal-rich and SMR structures.Comment: 25 pages, 10 figures (4 postscript + 6 gif files), 7 postscript
tables. accepted for publication on ApJ (November 2000
Uncertainties and Systematic Effects on the estimate of stellar masses in high z galaxies
We discuss the uncertainties and the systematic effects that exist in the
estimates of the stellar masses of high redshift galaxies, using broad band
photometry, and how they affect the deduced galaxy stellar mass function. We
use at this purpose the latest version of the GOODS-MUSIC catalog. In
particular, we discuss the impact of different synthetic models, of the assumed
initial mass function and of the selection band. Using Charlot & Bruzual 2007
and Maraston 2005 models we find masses lower than those obtained from Bruzual
& Charlot 2003 models. In addition, we find a slight trend as a function of the
mass itself comparing these two mass determinations with that from Bruzual &
Charlot 2003 models. As consequence, the derived galaxy stellar mass functions
show diverse shapes, and their slope depends on the assumed models. Despite
these differences, the overall results and scenario remains unchanged. The
masses obtained with the assumption of the Chabrier initial mass function are
in average 0.24 dex lower than those from the Salpeter assumption, at all
redshifts, causing a shift of galaxy stellar mass function of the same amount.
Finally, using a 4.5 um-selected sample instead of a Ks-selected one, we add a
new population of highly absorbed, dusty galaxies at z\simeq 2-3 of relatively
low masses, yielding stronger constraints on the slope of the galaxy stellar
mass function at lower masses.Comment: 5 pages, 4 figures, proceedings of the conference "Probing Stellar
Populations out to the Distant Universe", Cefalu (Italy), September 7 - 19,
2008. To be published in the AIP Conf. Proc. Serie
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