557 research outputs found
Observations of supernova 1979c in M 100
The IUE observations of supernova 1979c in M 100 are presented and discussed. The main results are: (1) the bulk of the energy is in the form of continuous emission which is radiated by the main SN envelope; (2) the absorption features originate mostly in both the disks and the haloes of our Galaxy and M 100; and (3) the emission lines are produced in a highly ionized shell which has a radius greater than twice the radius of the main envelope and consists of compressed circumstellar material in which the abundance ratio N/C is about 30 times higher than solar
Two populations of progenitors for type Ia SNe?
We use recent observations of type Ia Supernova (SN Ia) rates to derive, on
robust empirical grounds, the distribution of the delay time (DTD) between the
formation of the progenitor star and its explosion as a SN. Our analysis finds:
i) delay times as long as 3-4 Gyr, derived from observations of SNe Ia at high
redshift, cannot reproduce the dependence of the SN Ia rate on the colors and
on the radio-luminosity of the parent galaxies, as observed in the local
Universe; ii) the comparison between observed SN rates and a grid of
theoretical "single-population" DTDs shows that only a few of them are possibly
consistent with observations. The most successful models are all predicting a
peak of SN explosions soon after star formation and an extended tail in the
DTD, and can reproduce the data but only at a modest statistical confidence
level; iii) present data are best matched by a bimodal DTD, in which about 50%
of type Ia SNe (dubbed "prompt" SN Ia) explode soon after their stellar birth,
in a time of the order of 10^8 years, while the remaining 50% ("tardy" SN Ia)
have a much wider distribution, well described by an exponential function with
a decay time of about 3 Gyr. This fact, coupled with the well established
bimodal distribution of the decay rate, suggests the existence of two classes
of progenitors. We discuss the cosmological implications of this result and
make simple predictions. [Abridged]Comment: 11 pages, MNRAS, in press, modified after referee's comment
On the Evolution of the Cosmic Supernova Rates
Ongoing searches for supernovae (SNe) at cosmological distances have recently
started to provide a link between SN Ia statistics and galaxy evolution. We use
recent estimates of the global history of star formation to compute the
theoretical Type Ia and Type II SN rates as a function of cosmic time from the
present epoch to high redshifts. We show that accurate measurements of the
frequency of SN events in the range 0<z<1 will be valuable probes of the nature
of Type Ia progenitors and the evolution of the stellar birthrate in the
universe. The Next Generation Space Telescope should detect of order 20 Type II
SNe per 4'x 4' field per year in the interval 1<z<4.Comment: LaTeX, 19 pages, 3 figures, to be published in the MNRA
Direct evidence for an early reionization of the Universe?
We examine the possible reionization of the intergalactic medium (IGM) by the
source UDF033238.7-274839.8 (hereafter HUDF-JD2), which was discovered in deep
{\it HST}/VLT/{\it Spitzer} images obtained as part of the Great Observatory
Origins Deep Survey and {\it Hubble} Ultra-Deep Field projects. Mobasher et al
(2005) have identified HUDF-JD2 as a massive ()
post-starburst galaxy at redshift z. We find that HUDF-JD2 may be
capable of reionizing its surrounding region of the Universe, starting the
process at a redshift as high as z.Comment: 6 pages, 2 figures. Accepted for publication in ApJ Letter
Theory of the continuous spectrum of gaseous nebula of pure hydrogen
It has been studied the formation of the continuum of nebular hydrogen when ionization is due to radiation and to collisions. Two photon emission and continuous emissivity in the reaction of formation of H- have been included. The continuum results extremely sensitive to the relative amount of the two types of thermal excitation.Asociación Argentina de AstronomÃ
Mass Determination of Black Holes in LMC X-1 and Nova Muscae 1991 from their High-Energy Spectra
We offer a brief description of the bulk-motion Comptonization (BMC) model
for accretion onto black holes, illustrated by its application to observational
data for LMC X-1, and Nova Muscae 1991. We then extract some physical
parameters of these systems from observables (within the context of the BMC
model}, drawing from results on GRO J1655-40, for which we presented extensive
analysis previously. We derive estimates of the mass, (16 +/- 1) solar masses
and mass accretion rate in the disk in Eddington units around 2 for LMC X-1,
and (24 +/- 1)d_{5.5} and the disk mass acretion rate around 3 for Nova Muscae
1991 [where d_{5.5} stands for the distance in 5.5 kpc units]. Differences
between these estimates and previous estimates based on dynamical studies are
discussed. It is further shown that the disk inner radius increases with the
high-to-low state transition in Nova Muscae 1991. Specifically, our analysis
suggests that the inner-disk radius increases to 17 Scwarzschild radii as the
transition to the low-hard state occurs.Comment: 14 pages, 3 figures, The paper is accepted for publication in the
Astrophysical Journal Letter
Theory of the continuous spectrum of gaseous nebula of pure hydrogen
It has been studied the formation of the continuum of nebular hydrogen when ionization is due to radiation and to collisions. Two photon emission and continuous emissivity in the reaction of formation of H- have been included. The continuum results extremely sensitive to the relative amount of the two types of thermal excitation.Asociación Argentina de AstronomÃ
Detecting Primordial Stars
We discuss the expected properties of the first stellar generations in the
Universe. We find that it is possible to discern truly primordial populations
from the next generation of stars by measuring the metallicity of high-z star
forming objects. The very low background of the future James Webb Space
Telescope (JWST) will enable it to image and study first-light sources at very
high redshifts, whereas its relatively small collecting area limits its
capability in obtaining spectra of z~10-15 first-light sources to either the
bright end of their luminosity function or to strongly lensed sources. With a
suitable investment of observing time JWST will be able to detect individual
Population III supernovae, thus identifying the very first stars that formed in
the Universe.Comment: [8 pages, 5 figures] Invited Talk, to appear in IMF@50: The Stellar
Initial Mass Function Fifty Years Later, eds E. Corbelli, F. Palla, and H.
Zinnecker (Dordrecht: Kluwer
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