3,067 research outputs found
8.4GHz VLBI observations of SN2004et in NGC6946
We report on 8.4GHz Very Long Baseline Interferometry (VLBI) observations of
the type II-P supernova SN2004et in the spiral galaxy NGC 6946, made on 20
February 2005 (151 days after explosion). The Very Large Array (VLA) flux
density was 1.230.07 mJy, corresponding to an isotropic luminosity at
8.4GHz of (4.450.3) erg s Hz and a brightness
temperature of (1.30.3) K. We also provide an improved
source position, accurate to about 0.5 mas in each coordinate. The VLBI image
shows a clear asymmetry. From model fitting of the size of the radio emission,
we estimate a minimum expansion velocity of 15,7002,000 km s. This
velocity is more than twice the expected mean expansion velocity estimated from
a synchrotron self-absorbed emission model, thus suggesting that synchrotron
self-absorption is not relevant for this supernova. With the benefit of an
optical spectrum obtained 12 days after explosion, we favor an emission model
which consists of two hot spots on an underlying expanding shell of width
comparable to that of SN 1993J.Comment: Accepted for publication in A&A (22/05/07
VLBI imaging of the gravitational lens MGJ0414+0534
We observed the quadruple gravitationally lensed image of MGJ0414+0534 on 23
November 1997 with a global VLBI array at 8.4 GHz. We report wide-field imaging
results of its four components at submilliarcsecond resolution, displaying
complex core-like and jet-like extended structures. A simple model combining a
singular isothermal ellipsoid to represent the main lens galaxy, external
shear, and a singular isothermal sphere to represent an additional, nearby
object accounts well for the core positions and flux densities of the VLBI
images. This model predicts delays between the different lensed images of
several weeks.Comment: 6 pages, 3 figures, accepted for publication in Astronomy &
Astrophysic
Physics of Eclipsing Binaries: Heartbeat Stars and Tidally Induced Pulsations
Heartbeat stars are a relatively new class of eccentric ellipsoidal variable first discovered by Kepler. An overview of the current field is given with details of some of the interesting objects identified in our current Kepler sample of 135 heartbeats stars. Three objects that have recently been or are undergoing detailed study are described along with suggestions for further avenues of research. We conclude by discussing why heartbeat stars are an interesting new tool to study tidally induced pulsations and orbital dynamics
IAA : InformaciĂłn y actualidad astronĂłmica (44)
Sumario : La importancia de los cometas.--
Gamow, Alpher y el ylem.--
DECONSTRUCCIĂN Y otros ENSAYOS. El universo molecular.--
EL âMOBY DICKâ DE... Alberto Molino (IAG).--
CIENCIA EN HISTORIAS...Tras la estela de Plateau.--
ACTUALIDAD.--
SALA LIMPIA.--
CIENCIA: PILARES E INCERTIDUMBRES. Explosiones de rayos gamma.N
High-resolution observations of SN 2001gd in NGC 5033
We report on 8.4 GHz VLBI observations of SN2001gd in the spiral galaxy
NGC5033 made on 26 June 2002 and 8 April 2003. Our data nominally suggests a
relatively strong deceleration for the expansion of SN2001gd, but we cannot
dismiss the possibility of a free supernova expansion. From our VLBI
observations on 8 April 2003, we inferred a minimum total energy in
relativistic particles and magnetic fields in the supernova shell of E_min
=(0.3-14) 10^{47} ergs, and a corresponding equipartition average magnetic
field of B_min = (50--350) mG. We also present multiwavelength VLA measurements
of SN2001gd, which are well fit by an optically thin, synchrotron spectrum,
partially absorbed by thermal plasma. We obtain a supernova flux density of
(1.02 +/- 0.05) mJy at the observing frequency of 8.4 GHz for the second epoch,
which results in an isotropic radio luminosity of (6.0 +/- 0.3) * 10^{36} ergs
between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we
report on an XMM-Newton X-ray detection of SN2001gd on 18 December 2002. The
supernova X-ray spectrum is consistent with optically thin emission from a soft
component (associated with emission from the reverse shock) at a temperature
around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of
L_X = 1.4 +/- 0.4 * 10^{39} ergs/s in the (0.3-5) keV band. We suggest that
both radio and X-ray observations of SN2001gd indicate that a circumstellar
interaction similar to that displayed by SN1993J in M81 is taking place.Comment: 9 pages, 6 figures, 2 tables, accepted for publication in MNRA
A Decade of SN1993J: Discovery of Wavelength Effects in the Expansion Rate
We have studied the growth of the shell-like radio structure of supernova
SN1993J in M81 from September 1993 through October 2003 with very-long-baseline
interferometry (VLBI) observations at the wavelengths of 3.6, 6, and 18cm. For
this purpose, we have developed a method to accurately determine the outer
radius (R) of any circularly symmetric compact radio structure like SN1993J.
The source structure of SN1993J remains circularly symmetric (with deviations
from circularity under 2%) over almost 4000 days. We characterize the
decelerated expansion of SN 1993J through approximately day 1500 after
explosion with an expansion parameter ().
However, from that day onwards the expansion is different when observed at 6
and 18cm. Indeed, at 18cm, the expansion can be well characterized by the same
as before day 1500, while at 6cm the expansion appears more decelerated,
and is characterized by another expansion parameter, .
Therefore, since about day 1500 on, the radio source size has been
progressively smaller at 6cm than at 18cm. These findings are in stark contrast
to previous reports by other authors on the details of the expansion. In our
interpretation the supernova expands with a single expansion parameter, , and the 6cm results beyond day 1500 are due to physical
effects, perhaps also coupled to instrumental limitations. Two physical effects
may be involved: (a) a changing opacity of the ejecta to the 6cm radiation, and
(b) a radial decrease of the magnetic field in the emitting region.
(Long abstract cut. Please, read full abstract in manuscript).Comment: 21 pages, 19 figures, accepted in A&
Galaxy classification: deep learning on the OTELO and COSMOS databases
Context. The accurate classification of hundreds of thousands of galaxies
observed in modern deep surveys is imperative if we want to understand the
universe and its evolution. Aims. Here, we report the use of machine learning
techniques to classify early- and late-type galaxies in the OTELO and COSMOS
databases using optical and infrared photometry and available shape parameters:
either the Sersic index or the concentration index. Methods. We used three
classification methods for the OTELO database: 1) u-r color separation , 2)
linear discriminant analysis using u-r and a shape parameter classification,
and 3) a deep neural network using the r magnitude, several colors, and a shape
parameter. We analyzed the performance of each method by sample bootstrapping
and tested the performance of our neural network architecture using COSMOS
data. Results. The accuracy achieved by the deep neural network is greater than
that of the other classification methods, and it can also operate with missing
data. Our neural network architecture is able to classify both OTELO and COSMOS
datasets regardless of small differences in the photometric bands used in each
catalog. Conclusions. In this study we show that the use of deep neural
networks is a robust method to mine the cataloged dataComment: 20 pages, 10 tables, 14 figures, Astronomy and Astrophysics (in
press
The OTELO survey. A case study of [O III]4959,5007 emitters at <z> = 0.83
The OTELO survey is a very deep, blind exploration of a selected region of
the Extended Groth Strip and is designed for finding emission-line sources
(ELSs). The survey design, observations, data reduction, astrometry, and
photometry, as well as the correlation with ancillary data used to obtain a
final catalogue, including photo-z estimates and a preliminary selection of
ELS, were described in a previous contribution. Here, we aim to determine the
main properties and luminosity function (LF) of the [O III] ELS sample of OTELO
as a scientific demonstration of its capabilities, advantages, and
complementarity with respect to other surveys. The selection and analysis
procedures of ELS candidates obtained using tunable filter (TF) pseudo-spectra
are described. We performed simulations in the parameter space of the survey to
obtain emission-line detection probabilities. Relevant characteristics of [O
III] emitters and the LF([O III]), including the main selection biases and
uncertainties, are presented. A total of 184 sources were confirmed as [O III]
emitters at a mean redshift z=0.83. The minimum detectable line flux and
equivalent width (EW) in this ELS sample are 5 10 erg
s cm and 6 \AA, respectively. We are able to constrain the
faint-end slope () of the observed LF([O III]) at
z=0.83. This LF reaches values that are approximately ten times lower than
those from other surveys. The vast majority (84\%) of the morphologically
classified [O III] ELSs are disc-like sources, and 87\% of this sample is
comprised of galaxies with stellar masses of M 10
M.Comment: v1: 16 pages, 6 figures. Accepted in Astronomy \& Astrophysics. v2:
Author added in metadat
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