727 research outputs found
Luminescence properties of piezoelectric single crystals with langasite structure
ArticleJOURNAL OF LUMINESCENCE. 122: 205-207 (2007)journal articl
Ejecta and progenitor of the low-luminosity Type IIP supernova 2003Z
The origin of low-luminosity Type IIP supernovae is unclear: they have been
proposed to originate either from massive (about 25 Msun) or low-mass (about 9
Msun) stars. We wish to determine parameters of the low-luminosity Type IIP
supernova 2003Z, to estimate a mass-loss rate of the presupernova, and to
recover a progenitor mass. We compute the hydrodynamic models of the supernova
to describe the light curves and the observed expansion velocities. The wind
density of the presupernova is estimated using a thin shell model for the
interaction with circumstellar matter. We estimate an ejecta mass of 14 Msun,
an explosion energy of 2.45x10^50 erg, a presupernova radius of 229 Rsun, and a
radioactive Ni-56 amount of 0.0063 Msun. The upper limit of the wind density
parameter in the presupernova vicinity is 10^13 g/cm, and the mass lost at the
red/yellow supergiant stage is less than 0.6 Msun assuming the constant
mass-loss rate. The estimated progenitor mass is in the range of 14.4-17.4
Msun. The presupernova of SN 2003Z was probably a yellow supergiant at the time
of the explosion. The progenitor mass of SN 2003Z is lower than those of SN
1987A and SN 1999em, normal Type IIP supernovae, but higher than the lower
limit of stars undergoing a core collapse. We propose an observational test
based on the circumstellar interaction to discriminate between the massive
(about 25 Msun) and moderate-mass (about 16 Msun) scenarios.Comment: 8 pages, 9 figures, 3 tables, accepted for publication in Astronomy &
Astrophysics; one reference remove
On the Progenitors of Core-Collapse Supernovae
Theory holds that a star born with an initial mass between about 8 and 140
times the mass of the Sun will end its life through the catastrophic
gravitational collapse of its iron core to a neutron star or black hole. This
core collapse process is thought to usually be accompanied by the ejection of
the star's envelope as a supernova. This established theory is now being tested
observationally, with over three dozen core-collapse supernovae having had the
properties of their progenitor stars directly measured through the examination
of high-resolution images taken prior to the explosion. Here I review what has
been learned from these studies and briefly examine the potential impact on
stellar evolution theory, the existence of "failed supernovae", and our
understanding of the core-collapse explosion mechanism.Comment: 7 Pages, invited review accepted for publication by Astrophysics and
Space Science (special HEDLA 2010 issue
Interaction and Localization of One-electron Orbitals in an Organic Molecule: Fictitious Parameter Analysis for Multi-physics Simulations
We present a new methodology to analyze complicated multi-physics simulations
by introducing a fictitious parameter. Using the method, we study quantum
mechanical aspects of an organic molecule in water. The simulation is
variationally constructed from the ab initio molecular orbital method and the
classical statistical mechanics with the fictitious parameter representing the
coupling strength between solute and solvent. We obtain a number of
one-electron orbital energies of the solute molecule derived from the
Hartree-Fock approximation, and eigenvalue-statistical analysis developed in
the study of nonintegrable systems is applied to them. Based on the results, we
analyze localization properties of the electronic wavefunctions under the
influence of the solvent.Comment: 4 pages, 5 figures, the revised version will appear in J. Phys. Soc.
Jpn. Vol.76 (No.1
Searching for the earliest galaxies in the 21 cm forest
We use a model developed by Xu et al. (2010) to compute the 21 cm line
absorption signatures imprinted by star-forming dwarf galaxies (DGs) and
starless minihalos (MHs). The method, based on a statistical comparison of the
equivalent width (W_\nu) distribution and flux correlation function, allows us
to derive a simple selection criteria for candidate DGs at very high (z >= 8)
redshift. We find that ~ 18% of the total number of DGs along a line of sight
to a target radio source (GRB or quasar) can be identified by the condition
W_\nu < 0; these objects correspond to the high-mass tail of the DG
distribution at high redshift, and are embedded in large HII regions. The
criterion W_\nu > 0.37 kHz instead selects ~ 11% of MHs. Selected candidate DGs
could later be re-observed in the near-IR by the JWST with high efficiency,
thus providing a direct probe of the most likely reionization sources.Comment: 8 pages, 3 figures. Accepted for publication in Science in China
Series
Bayesian astrostatistics: a backward look to the future
This perspective chapter briefly surveys: (1) past growth in the use of
Bayesian methods in astrophysics; (2) current misconceptions about both
frequentist and Bayesian statistical inference that hinder wider adoption of
Bayesian methods by astronomers; and (3) multilevel (hierarchical) Bayesian
modeling as a major future direction for research in Bayesian astrostatistics,
exemplified in part by presentations at the first ISI invited session on
astrostatistics, commemorated in this volume. It closes with an intentionally
provocative recommendation for astronomical survey data reporting, motivated by
the multilevel Bayesian perspective on modeling cosmic populations: that
astronomers cease producing catalogs of estimated fluxes and other source
properties from surveys. Instead, summaries of likelihood functions (or
marginal likelihood functions) for source properties should be reported (not
posterior probability density functions), including nontrivial summaries (not
simply upper limits) for candidate objects that do not pass traditional
detection thresholds.Comment: 27 pp, 4 figures. A lightly revised version of a chapter in
"Astrostatistical Challenges for the New Astronomy" (Joseph M. Hilbe, ed.,
Springer, New York, forthcoming in 2012), the inaugural volume for the
Springer Series in Astrostatistics. Version 2 has minor clarifications and an
additional referenc
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