486 research outputs found
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
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
Radial distributions of Gamma Ray Bursts and Supernovæ: Clues to their progenitors
In this paper wecomparetheobse rved radial distributions of Gamma Ray Bursts and of Supernovæ with respect to the host galaxy center. We investigate the possibility that the observed Gamma Ray Burst offset distribution (in kpc) is in
fact the distribution of I-b/c supernovæ modified by the kick received by the binary system when the first supernova explosion occurs. Our analysis lends support to the scenario in which all long-duration GRBs are produced by type Ib/c SNe. We ruled out that a significant fraction of long-duration GRBs could be due to merging of compact remnants of stellar evaluation
Anomalous extinction towards NGC 1938
Intrigued by the extended red-giant clump (RC) stretching across the
colour-magnitude diagram of the stars in a 50x50 pc^2 region of the Large
Magellanic Cloud (LMC) containing the clusters NGC 1938 and NGC 1939, we have
studied the stellar populations to learn about the properties of the
interstellar medium (ISM) in this area. The extended RC is caused by a large
and uneven amount of extinction across the field. Its slope reveals anomalous
extinction properties, with Av/E(B-V)=4.3, indicating the presence of an
additional grey component in the optical contributing about 30% of the total
extinction in the field and requiring big grains to be about twice as abundant
as in the diffuse ISM. This appears to be consistent with the amount of big
grains injected into the surrounding ISM by the about 70 SNII explosions
estimated to have occurred during the lifetime of the ~120 Myr old NGC 1938.
Although this cluster appears today relatively small and would be hard to
detect beyond the distance of M 31, with an estimated initial mass of ~4800
Msun NGC 1938 appears to have seriously altered the extinction properties in a
wide area. This has important implications for the interpretation of
luminosities and masses of star-forming galaxies, both nearby and in the early
universe.Comment: 8 pages, 4 figures, accepted for publication in The Astrophysical
Journa
Chandra and ASCA X-ray Observations of the Radio Supernova SN1979C IN NGC 4321
We report on the X-ray observation of the radio selected supernova SN1979C
carried out with ASCA in 1997 December and serendipitously available from a
Chandra Guaranteed Time Observation in 1999 November. The supernova, of type SN
II-Linear (SN IIL), was first observed in the optical and occurred in the
weakly barred, almost face on spiral galaxy NGC 4321 (M100). The galaxy, a
member of the Virgo S cluster, is at a distance of 17.1 Mpc, and contains at
least three other supernovae discovered in this century. The useful exposure
time was ~25 ks for the Solid-State Imaging Spectrometer (SIS), ~28 ks for the
Gas Scintillation Imaging Spectrometer (GIS), and ~2.5 ks for Chandra's
Advanced CCD Imaging Spectrometer (ACIS). No point source was detected at the
radio position of SN1979C in a 3' diameter half power response circle in the
ASCA data. The background and galaxy subtracted SN signal had a 3sigma upper
limit to the flux of 6.3x10^-14 ergs/s/cm^-2 in the full ASCA SIS band
(0.4-10.0 keV) and a 3sigma upper limit of <3-4x10^-14 erg/s/cm^2 in the 2-10
keV band. In the Chandra data, a source at the position of SN1979C is
marginally detected at energies below 2 keV at a flux consistent with the ROSAT
HRI detection in 1995. At energies above 2 keV, no source is detected with an
upper limit of ~3x10^-14 erg/s/cm^-2. These measurements give the first ever
x-ray flux limit of a Type IIL SN above 2 keV which is an important diagnostic
of the outgoing shock wave ploughing through the circumstellar medium.Comment: 8 pages, 2 figures, accepted A
The Radio Evolution of SN 2001gd
We present the results of observations of the radio emission from Supernova
2001gd in NGC 5033 from 2002 February 8 through 2006 September 25. The data
were obtained using the Very Large Array at wavelengths of 1.3 cm (22.4 GHz), 2
cm (14.9 GHz), 3.6 cm (8.4 GHz), 6 cm (4.9 GHz), and 20 cm (1.5 GHz), with one
upper limit at 90 cm (0.3 GHz). In addition, one detection has been provided by
the Giant Metrewave Radio Telescope at 21 cm (1.4 GHz). SN 2001gd was
discovered in the optical well past maximum light, so that it was not possible
to obtain many of the early radio "turn-on" measurements which are important
for estimating the local circumstellar medium (CSM) properties. Only at 20 cm
were turn-on data available. However, our analysis and fitting of the radio
light curves, and the assumption that the Type IIb SN 2001gd resembles the much
better studied Type IIb SN 1993J, enables us to describe the radio evolution as
being very regular through day ~550 and consistent with a nonthermal-emitting
model with a thermal absorbing CSM. The presence of synchrotron-self absorption
(SSA) at early times is implied by the data, but determination of the exact
relationship between the SSA component from the emitting region and the
free-free absorption component from the CSM is not possible as there are
insufficient early measurements to distinguish between models. After day ~550,
the radio emission exhibits a dramatically steeper decline rate which, assuming
similarity to SN 1993J, can be described as an exponential decrease with an
e-folding time of 500 days. We interpret this abrupt change in the radio flux
density decline rate as implying a transition of the shock front into a more
tenuous region of circumstellar material. A similar change in radio evolution
has been seen earlier in other SNe such as SN 1988Z, SN 1980K, and SN 1993J.Comment: 3 tables, 2 figures, To appear in the Astrophysical Journa
Observations of the nucleus of M100
The galaxy M100 = NGC 4321 is a spiral galaxy in which a bright Type II Supernova was discovered on April 19, 1979. Its spectral evolution was followed with IUE for more than two months (refs. 1,2). At all epochs, the spectrum was dominated by continuous radiation on which emission and absorption features were superimposed. The equivalent width of most of the absorption features appeared not to vary with time suggesting that they originated in the interstellar media of M100 and our own galaxy
The Optical Gravitational Lensing Experiment. Short Distance Scale to the LMC
We present {\it UBVI} photometry of the eclipsing binary HV2274 - the system
which has been recently used for distance determination to the LMC by Guinan et
al. (1998). We determine the interstellar reddening to the star,
E(B-V)=0.149+/-0.015 mag, based on observed colors of the star. This value is
in excellent agreement with the mean reddening towards HV2274 obtained from
photometry of the red clump stars in the surrounding field. The reddening is
almost twice as large as determined by Guinan et al. (1998).
We discuss the consequences of reddening underestimate. Most likely HV2274 is
located much closer with the distance modulus to the star and the LMC: m-M =
18.22+/-0.13 mag supporting the short distance scale to the LMC. Such a
distance modulus is in excellent agreement with the recent distance
determinations with RR Lyr and red clump stars.Comment: 11 pages, Latex, 2 Figures. Accepted for publication in Astrophysical
Journal Letters. New version - trimmed to fit ApJL. Additional determination
of the reddening towards HV2274 with OB star
The Quest for Primordial Stellar Populations and the James Webb Space Telescope
The NASA/ESA/CSA James Webb Space Telescope (JWST) will be the successor to
the Hubble Space Telescope and may be launched as early as mid-2011. The key
scientific goals for JWST are discovering and understanding the formation of
the first stars and galaxies, the evolution of galaxies and the production of
elements by stars, and the process of star and planet formation. Within this
context, 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 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: 12 pages, 9 figures (uses a number of CJAA style files to compile).
Invited talk given at the Frascati Workshop 2003 "Multifrequency Behaviour of
High Energy Cosmic Sources", eds. F. Giovannelli and Lola Sabau-Graziati; to
appear in a special issue of the Chinese Journal of Astronomy & Astrophysic
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