5,863 research outputs found
Supernova search at intermediate z. I. Spectroscopic analysis
We study 8 supernovae discovered as part of the International Time Programme
(ITP) project ``Omega and Lambda from Supernovae and the Physics of Supernova
Explosions'' at the European Northern Observatory (ENO). The goal of the
project is to increase the sample of intermediate redshift (0.1<z<0.4) SNe Ia
for testing properties of SNe Ia along z and for enlarging the sample in the
Hubble diagram up to large z.Comment: 2 pages, 2 figures, 1 table, to appear in ``1604-2004: Supernovae as
Cosmological Lighthouses'', (extended text upon request
56Ni dredge-up in the type IIp Supernova 1995V
We present contemporary infrared and optical spectra of the plateau type II
SN 1995V in NGC 1087 covering four epochs, approximately 22 to 84 days after
shock breakout. The data show, for the first time, the infrared spectroscopic
evolution during the plateau phase of a typical type II event. In the optical
region P Cygni lines of the Balmer series and of metals lines were identified.
The infrared (IR) spectra were largely dominated by the continuum, but P Cygni
Paschen lines and Brackett gamma lines were also clearly seen. The other
prominent IR features are confined to wavelengths blueward of 11000 \AA and
include Sr II 10327, Fe II 10547, C I 10695 and He I 10830 \AA. We demonstrate
the presence of He I 10830 \AA on days 69 and 85. The presence of this line at
such late times implies re-ionisation. A likely re-ionising mechanism is
gamma-ray deposition following the radioactive decay of 56Ni. We examine this
mechanism by constructing a spectral model for the He I 10830 \AA line based on
explosion model s15s7b2f of Weaver & Woosley (1993). We find that this does not
generate the observed line owing to the confinement of the 56Ni to the central
zones of the ejecta. In order to reproduce the He I line, it was necessary to
introduce additional upward mixing of the 56Ni, with 10^{-5} of the total
nickel mass reaching above the helium photosphere. In addition, we argue that
the He I line-formation region is likely to have been in the form of pure
helium clumps in the hydrogen envelope.Comment: Accepted for publication in MNRAS, 32 pages including 11 figures
(uses psfig.sty - included
Discovery of optically faint obscured quasars with Virtual Observatory tools
We use Virtual Observatory (VO) tools to identify optically faint, obscured
(i.e., type 2) active galactic nuclei (AGN) in the two Great Observatories
Origins Deep Survey (GOODS) fields. By employing publicly available X-ray and
optical data and catalogues we discover 68 type 2 AGN candidates. The X-ray
powers of these sources are estimated by using a previously known correlation
between X-ray luminosity and X-ray-to-optical flux ratio. Thirty-one of our
candidates have high estimated powers (Lx > 10^44 erg/s) and therefore qualify
as optically obscured quasars, the so-called ``QSO 2''. Based on the derived
X-ray powers, our candidates are likely to be at relatively high redshifts, z ~
3, with the QSO 2 at z ~ 4. By going ~ 3 magnitudes fainter than previously
known type 2 AGN in the two GOODS fields we are sampling a region of redshift -
power space which was previously unreachable with classical methods. Our method
brings to 40 the number of QSO 2 in the GOODS fields, an improvement of a
factor ~ 4 when compared to the only 9 such sources previously known. We derive
a QSO 2 surface density down to 10^-15 erg/cm^2/s in the 0.5 - 8 keV band of >~
330/deg^2, ~ 30% of which is made up of previously known sources. This is
larger than current estimates and some predictions and suggests that the
surface density of QSO 2 at faint flux limits has been underestimated. This
work demonstrates that VO tools are mature enough to produce cutting-edge
science results by exploiting astronomical data beyond ``classical''
identification limits (R <~ 25) with interoperable tools for statistical
identification of sources using multiwavelength information.Comment: 16 pages, 6 figures, accepted for publication in Astronomy &
Astrophysics. PDF file with higher resolution figures available at
http://www.eso.org/~ppadovan/AVO-paper.pd
Berenstein-Zelevinsky triangles, elementary couplings and fusion rules
We present a general scheme for describing su(N)_k fusion rules in terms of
elementary couplings, using Berenstein-Zelevinsky triangles. A fusion coupling
is characterized by its corresponding tensor product coupling (i.e. its
Berenstein-Zelevinsky triangle) and the threshold level at which it first
appears. We show that a closed expression for this threshold level is encoded
in the Berenstein-Zelevinsky triangle and an explicit method to calculate it is
presented. In this way a complete solution of su(4)_k fusion rules is obtained.Comment: 14 page
Heavy X-ray obscuration in the most-luminous galaxies discovered by WISE
Hot Dust-Obscured Galaxies (Hot DOGs) are hyperluminous
() infrared galaxies with
extremely high (up to hundreds of K) dust temperatures. The sources powering
both their extremely high luminosities and dust temperatures are thought to be
deeply buried and rapidly accreting supermassive black holes (SMBHs). Hot DOGs
could therefore represent a key evolutionary phase in which the SMBH growth
peaks. X-ray observations can be used to study their obscuration levels and
luminosities. In this work, we present the X-ray properties of the 20
most-luminous () known Hot DOGs at
. Five of them are covered by long-exposure ( ks) Chandra and
XMM-Newton observations, with three being X-ray detected, and we study their
individual properties. One of these sources (W01160505) is a Compton-thick
candidate, with column density
derived from X-ray spectral fitting. The remaining 15 Hot DOGs have been
targeted by a Chandra snapshot (3.1 ks) survey. None of these 15 is
individually detected; therefore we applied a stacking analysis to investigate
their average emission. From hardness-ratio analysis, we constrained the
average obscuring column density and intrinsic luminosity to be
log and
, which are consistent with
results for individually detected sources. We also investigated the
and relations, finding hints that Hot
DOGs are typically X-ray weaker than expected, although larger samples of
luminous obscured QSOs are needed to derive solid conclusions.Comment: MNRAS, accepted 2017 November 29 . Received 2017 November 29 ; in
original form 2017 October 11. 15 pages, 6 figure
Phenotypic and functional characterization of adult brain neuropoiesis
The modern concept of neurogenesis in the adult brain is predicated on the premise that multipotent glial cells give rise to new neurons throughout life. Although extensive evidence exists indicating that this is the case, the transition from glial to neuronal phenotype remains poorly understood. A unique monolayer cell-culture system was developed to induce, expose, and recapitulate the entire developmental series of events of subventricular zone (SVZ) neurogenesis. We show here, using immunophentoypic, ultrastructural, electrophysiological, and time-lapse analyses, that SVZ-derived glial fibrillary acidic protein(low)/A2B5(+)/nestin(+) candidate founder cells undergo metamorphosis to eventually generate large numbers of fully differentiated interneuron phenotypes. A model of postnatal neurogenesis is considered in light of known embryonic events and reveals a limited developmental potential of SVZ stem/progenitor cells, whereby ancestral cells in both embryonic and postnatal/adult settings give rise to glia and GABAergic interneurons
One dimensional drift-diffusion between two absorbing boundaries: application to granular segregation
Motivated by a novel method for granular segregation, we analyze the one
dimensional drift-diffusion between two absorbing boundaries. The time
evolution of the probability distribution and the rate of absorption are given
by explicit formulae, the splitting probability and the mean first passage time
are also calculated. Applying the results we find optimal parameters for
segregating binary granular mixtures.Comment: RevTeX, 5 pages, 6 figure
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