915 research outputs found
Dynamical analysis on cosmology
We use a dynamical system approach to study the cosmological viability of
gravity theories. The method consists of formulating the
evolution equations as an autonomous system of ODEs, using suitable variables.
The formalism is applied to a class of models in which and its solutions and corresponding stability are
analysed in detail. New accelerating solutions that can be attractors in the
phase space are found. We also find that this class of models does not exhibit
a matter-dominated epoch, a solution which is inconsistent with current
cosmological observations.Comment: 12 pages, 4 figures. Accepted for publication in Classical and
Quantum Gravit
Long Gamma-Ray Bursts and Type Ic Core Collapse Supernovae Have Similar Locations in Hosts
When the afterglow fades at the site of a long-duration gamma-ray burst
(LGRB), Type Ic supernovae (SN Ic) are the only type of core collapse supernova
observed. Recent work found that a sample of LGRB in high-redshift galaxies had
different environments from a collection of core-collapse environments, which
were identified from their colors and light curves. LGRB were in the brightest
regions of their hosts, but the core-collapse sample followed the overall
distribution of the galaxy light. Here we examine 504 supernovae with types
assigned based on their spectra that are located in nearby (z < 0.06) galaxies
for which we have constructed surface photometry from the Sloan Digital Sky
Survey (SDSS). The distributions of the thermonuclear supernovae (SN Ia) and
some varieties of core-collapse supernovae (SN II and SN Ib) follow the galaxy
light, but the SN Ic (like LGRB) are much more likely to erupt in the brightest
regions of their hosts. The high-redshift hosts of LGRB are overwhelmingly
irregulars, without bulges, while many low redshift SN Ic hosts are spirals
with small bulges. When we remove the bulge light from our low-redshift sample,
the SN Ic and LGRB distributions agree extremely well. If both LGRB and SN Ic
stem from very massive stars, then it seems plausible that the conditions
necessary for forming SN Ic are also required for LGRB. Additional factors,
including metallicity, may determine whether the stellar evolution of a massive
star leads to a LGRB with an underlying broad-lined SN Ic, or simply a SN Ic
without a gamma-ray burst.Comment: Accepted by the Astrophysical Journal, 12 pages, 3 tables, 4 figures,
SN sample size increases from 263 to 504 in v2, varying host magnitude and
distance shown not to introduce systematic error in measurement
Observed and Physical Properties of Core-Collapse Supernovae
I use photometry and spectroscopy data for 24 Type II plateau supernovae to
examine their observed and physical properties. This dataset shows that these
objects encompass a wide range of ~5 mag in their plateau luminosities, their
expansion velocities vary by x5, and the nickel masses produced in these
explosions go from 0.0016 to 0.26 Mo. From a subset of 16 objects I find that
the explosion energies vary between 0.6x and 5.5x10^51 ergs, the ejected masses
encompass the range 14-56 Mo, and the progenitors' radii go from 80 to 600 Ro.
Despite this great diversity several regularities emerge, which reveal that
there is a continuum in the properties of these objects from the faint,
low-energy, nickel-poor SNe 1997D and 1999br, to the bright, high-energy,
nickel-rich SN 1992am. This study provides evidence that more massive
progenitors produce more energetic explosions, thus suggesting that the outcome
of the core collapse is somewhat determined by the envelope mass. I find also
that supernovae with greater energies produce more nickel. Similar
relationships appear to hold for Type Ib/c supernovae, which suggests that both
Type II and Type Ib/c supernovae share the same core physics. When the whole
sample of core collapse objects is considered, there is a continous
distribution of energies below 8x10^51 ergs. Far above in energy scale and
nickel production lies the extreme hypernova 1998bw, the only supernova firmly
associated to a GRB.Comment: 25 pages, 7 figures, accepted for Part 1 of Astrophysical Journa
Robust and Biocompatible Functionalization of ZnS Nanoparticles by Catechol-Bearing Poly(2-Methyl-2-Oxazoline)s.
Zinc sulfide (ZnS) nanoparticles (NPs) are particularly interesting materials for their electronic and luminescent properties. Unfortunately, their robust and stable functionalization and stabilization, especially in aqueous media, has represented a challenging and not yet completely accomplished task. In this work, we report the synthesis of colloidally stable, photoluminescent and biocompatible core\u2013polymer shell ZnS and ZnS:Tb NPs by employing a water-in-oil miniemulsion (ME) process combined with surface functionalization via catechol-bearing poly-2-methyl-2-oxazoline (PMOXA) of various molar masses. The strong binding of catechol anchors to the metal cations of the ZnS surface, coupled with the high stability of PMOXA against chemical degradation, enable the formation of suspensions presenting excellent colloidal stability. This feature, combined with the assessed photoluminescence and biocompatibility, make these hybrid NPs suitable for optical bioimaging
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
Evidence of Asymmetry in SN 2007rt, a Type IIn Supernova
An optical photometric and spectroscopic analysis of the slowly-evolving Type
IIn SN2007rt is presented, covering a duration of 481 days after discovery. Its
earliest spectrum, taken approximately 100 days after the explosion epoch,
indicates the presence of a dense circumstellar medium, with which the
supernova ejecta is interacting. This is supported by the slowly-evolving light
curve. A notable feature in the spectrum of SN 2007rt is the presence of a
broad He I 5875 line, not usually detected in Type IIn supernovae. This may
imply that the progenitor star has a high He/H ratio, having shed a significant
portion of its hydrogen shell via mass-loss. An intermediate resolution
spectrum reveals a narrow Halpha P-Cygni profile, the absorption component of
which has a width of 128 km/s. This slow velocity suggests that the progenitor
of SN 2007rt recently underwent mass-loss with wind speeds comparable to the
lower limits of those detected in luminous blue variables. Asymmetries in the
line profiles of H and He at early phases bears some resemblance to
double-peaked features observed in a number of Ib/c spectra. These asymmetries
may be indicative of an asymmetric or bipolar outflow or alternatively dust
formation in the fast expanding ejecta. In addition, the late time spectrum, at
over 240 days post-explosion, shows clear evidence for the presence of newly
formed dust.Comment: Submitted to A&A on 4/2/2009. Accepted by A&A on 17/5/2009.15 pages
plus 3 pages of online materia
The diversity of Type Ia Supernovae: evidence for systematics?
The photometric and spectroscopic properties of 26 well observed Type Ia
Supernovae (SNeIa) were analyzed with the aim to explore SNIa diversity. The
sample includes (Branch-)normal SNe as well as extreme events like SNe 1991T
and 1991bg, while the truly peculiar SNIa, SN2000cx and SN2002cx are not
included in our sample . A statistical treatment reveals the existence of three
different groups. The first group (FAINT) consists of faint SNeIa similar to
SN1991bg, with low expansion velocities and rapid evolution of SiII velocity. A
second group consists of ``normal'' SNeIa, also with high temporal velocity
gradient (HVG), but with brighter mean absolute magnitude =-19.3 and
higher expansion velocities than the FAINT SNe. The third group includes both
``normal'' and SN1991T-like SNeIa: these SNe populate a narrow strip in the
SiII velocity evolution plot, with a small velocity gradient (SVG), but have
absolute magnitudes similar to HVGs. While the FAINT and HVG SNeIa together
seem to define a relation between RSi(II) and Dm15(B), the SVG ones either do
not conform with that relation or define a new, looser one. The RSi(II)
pre-maximum evolution of HVGs is strikingly different from that of SVGs. The
impact of this evidence on the understanding of SNIa diversity, in terms of
explosion mechanisms, degree of ejecta mixing, and ejecta-CSM interaction, is
discussed.Comment: 9 pages, 3 figures, accepted for publication to ApJ; few referee's
comments adde
The supernova impostor PSN J09132750+7627410 and its progenitor
We report the results of our follow-up campaign of the supernova impostor PSN
J09132750+7627410, based on optical data covering . From the
beginning, the transient shows prominent narrow Balmer lines with P-Cygni
profiles, with a blue-shifted absorption component becoming more prominent with
time. Along the of the spectroscopic monitoring, broad
components are never detected in the hydrogen lines, suggesting that these
features are produced in slowly expanding material. The transient reaches an
absolute magnitude at maximum, a typical
luminosity for supernova impostors. Amateur astronomers provided
of archival observations of the host galaxy, NGC 2748. The
detection of the quiescent progenitor star in archival images obtained with the
Hubble Space Telescope suggests it to be an \msun white-yellow
supergiant.Comment: 7 pages, 4 figures, supplemental material available in the source
file. Accepted for publication on Astrophysical Journal Letter
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