840 research outputs found
Lack of observational evidence for quantum structure of space-time at Plank scales
It has been noted (Lieu & Hillmann, 2002) that the cumulative affect of
Planck-scale phenomenology, or the structure of space-time at extremely small
scales, can be lead to the loss of phase of radiation emitted at large
distances from the observer. We elaborate on such an approach and demonstrate
that such an effect would lead to an apparent blurring of distant
point-sources. Evidence of the diffraction pattern from the HST observations of
SN 1994D and the unresolved appearance of a Hubble Deep Field galaxy at z=5.34
lead us to put stringent limits on the effects of Planck-scale phenomenology.Comment: 12 pages, 3 figures, accepter for ApJ
Supernova 1996L: evidence of a strong wind episode before the explosion
Observations of the type II SN 1996L reveal the presence of a slowly
expanding (V~700$ km/s) shell at ~ 10^(16) cm from the exploding star. Narrow
emission features are visible in the early spectra superposed on the normal SN
spectrum. Within about two months these features develop narrow symmetric
P-Cygni profiles. About 100 days after the explosion the light curve suddenly
flattens, the spectral lines broaden and the Halpha flux becomes larger than
what is expected from a purely radioactive model. These events are interpreted
as signatures of the onset of the interaction between the fast moving ejecta
and a slowly moving outer shell of matter ejected before the SN explosion. At
about 300 days the narrow lines disappear and the flux drops until the SN fades
away, suggesting that the interaction phase is over and that the shell has been
swept away. Simple calculations show that the superwind episode started 9 yr
before the SN explosion and lasted 6 yr, with an average dM/dt=10^(-3)
M_solar/yr. Even at very late epochs (up to day 335) the typical forbidden
lines of [OI], CaII], [FeII] remain undetected or very weak. Spectra after day
270 show relatively strong emission lines of HeI. These lines are narrower than
other emission lines coming from the SN ejecta, but broader than those from the
CSM. These high excitation lines are probably the result of non-thermal
excitation and ionization caused by the deposition of the gamma-rays emitted in
the decay of radioactive material mixed in the He layer.Comment: 8 pages, 6 figures, Latex, To appear in M.N.R.A.
The Asiago Supernova Catalogue- 10 years after
Ten years after the publication of the previous release, we present a new
edition of the Asiago Supernova Catalogue updated to December 31, 1998 and
containing data for 1447 supernovae and their parent galaxies\footnote{Tables 1
and 2 are only available in electronic form at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/Abstract.html}. In addition to list the data for a
large number of new SNe, we made an effort to search the literature for new
information on past SNe as well. We also tried to update and homogenize the
data for the parent galaxies. To allow a global view of the Catalogue, a few
descriptive figures and a summary table is reported. The present Catalogue is
intended as a large and modern database for statistical studies on the
supernova phenomenon.Comment: 6 pages. To be published in A&A supplement. Enclosed as postscript
files are the full lists in chronological (snean.ps) and R.A. (snear.ps)
order (to be published only in electronic form.
Supernova 2002ic: the collapse of a stripped-envelope, massive star in a dense medium ?
We revisit the case of SN2002ic that recently revived the debate about the
progenitors of SNeIa after the claim of the unprecedented presence of hydrogen
lines over a diluted SNIa spectrum. As an alternative to the previous
interpretation, we suggest that SN2002ic actually was a type Ic SN, the core
collapse of a massive star which lost its hydrogen and helium envelope. In this
scenario the observed interaction with a dense circumstellar material (CSM) is
the predictable consequence of the intense mass-loss of the progenitor and/or
of the presence of a gas rich environment. With this view we establish a link
between energetic SNeIc and highly interacting SNeIIn and add some credits to
the proposed association of some SNeIIn to GRBs.Comment: Accepted for publication on ApJ
The 3-D ionization structure and evolution of NGC 7009 (Saturn Nebula)
Tomographic and 3-D analyses for extended, emission-line objects are applied
to long-slit ESO NTT + EMMI high-resolution spectra of the intriguing planetary
nebula NGC 7009, covered at twelve position angles. We derive the gas expansion
law, the diagnostics and ionic radial profiles, the distance and the central
star parameters, the nebular photo-ionization model and the spatial recovery of
the plasma structure and evolution. The Saturn Nebula (distance~1.4 kpc,
age~6000 yr, ionized mass~0.18 Mo) consists of several interconnected
components, characterized by different morphology, physical conditions,
excitation and kinematics. The internal shell, the main shell, the streams and
the ansae expand at V(exp)~4.0xR" km/s, the outer shell, the caps and the
equatorial pseudo-ring at V(exp)~3.15xR" km/s, and the halo at V(exp)~10 km/s.
We compare the radial distribution of the physical conditions and the line
fluxes observed in the eight sub-systems with the theoretical profiles coming
from the photo-ionization code CLOUDY, inferring that all the spectral
characteristics of NGC 7009 are explainable in terms of photo-ionization by the
central star, a hot (logT*~4.95) and luminous (log L*/Lo~3.70) 0.60--0.61 Mo
post--AGB star in the hydrogen-shell nuclear burning phase. The 3--D shaping of
the Saturn Nebula is discussed within an evolutionary scenario dominated by
photo-ionization and supported by the fast stellar wind: it begins with the
superwind ejection, passes through the neutral, transition phase (lasting ~
3000 yr), the ionization start (occurred ~2000 yr ago), and the full ionization
of the main shell (~1000 yr ago), at last reaching the present days: the whole
nebula is optically thin to the UV stellar flux, except the caps and the ansae.Comment: accepted for pub. in A&A, 28 pages, 14 figures, full text with
figures available at http://web.pd.astro.it/supern/ps/h4665.ps, movies on the
3D structure available at http://web.pd.astro.it/sabbadin
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