290 research outputs found
On the Rates of Type Ia Supernovae in Dwarf and Giant Hosts with ROTSE-IIIb
We present a sample of 23 spectroscopically confirmed Type Ia supernovae that
were discovered in the background of galaxy clusters targeted by ROTSE-IIIb and
use up to 18 of these to determine the local (z = 0.05) volumetric rate. Since
our survey is flux limited and thus biased against fainter objects, the
pseudo-absolute magnitude distribution (pAMD) of SNeIa in a given volume is an
important concern, especially the relative frequency of high to low-luminosity
SNeIa. We find that the pAMD derived from the volume limited Lick Observatory
Supernova Search (LOSS) sample is incompatible with the distribution of SNeIa
in a volume limited (z<0.12) sub sample of the SDSS-II. The LOSS sample
requires far more low-luminosity SNeIa than the SDSS-II can accommodate. Even
though LOSS and SDSS-II have sampled different SNeIa populations, their
volumetric rates are surprisingly similar. Using the same model pAMD adopted in
the SDSS-II SNeIa rate calculation and excluding two high-luminosity SNeIa from
our sample, we derive a rate that is marginally higher than previous
low-redshift determinations. With our full sample and the LOSS pAMD our rate is
more than double the canonical value. We also find that 5 of our 18 SNeIa are
hosted by very low-luminosity (M_B > -16) galaxies, whereas only 1 out 79
nearby SDSS-II SNeIa have such faint hosts. It is possible that previous works
have under-counted either low luminosity SNeIa, SNeIa in low luminosity hosts,
or peculiar SNeIa (sometimes explicitly), and the total SNeIa rate may be
higher than the canonical value.Comment: 18 pages; accepted for publication in The Astronomical Journa
SN 2006bp: Probing the Shock Breakout of a Type II-P Supernova
HET optical spectroscopy and unfiltered ROTSE-III photometry spanning the
first 11 months since explosion of the Type II-P SN 2006bp are presented. Flux
limits from the days before discovery combined with the initial rapid
brightening suggest the supernova was first detected just hours after shock
breakout. Optical spectra obtained about 2 days after breakout exhibit narrow
emission lines corresponding to HeII 4200, HeII 4686, and CIV 5805 in the rest
frame, and these features persist in a second observation obtained 5 hours
later; however, these emission lines are not detected the following night nor
in subsequent observations. We suggest that these lines emanate from material
close to the explosion site, possibly in the outer layers of the progenitor
that have been ionized by the high energy photons released at shock breakout. A
P-Cygni profile is observed around 4450 A in the +2 and +3 day spectra.
Previous studies have attributed this feature to high velocity H-beta, but we
discuss the possibility that this profile is instead due to HeII 4687. Further
HET observations (14 nights in total) covering the spectral evolution across
the photometric plateau up to 73 days after breakout and during the nebular
phase around day +340 are presented, and expansion velocities are derived for
key features. The measured decay slope for the unfiltered light curve is 0.0073
+/- 0.0004 mag/day between days +121 and +335, which is significantly slower
than the decay of rate 56Co. We combine our HET measurements with published
X-ray, UV, and optical data to obtain a quasi-bolometric light curve through
day +60. We see a slow cooling over the first 25 days, but no sign of an early
sharp peak; any such feature from the shock breakout must have lasted less than
~1 day.[ABRIDGED]Comment: ApJ accepted, 43 page
A New Cationic Liposome DNA Complex Enhances the Efficiency of Arterial Gene Transfer In Vivo
Overview summary GAP-DLRIE/DOPE, a new cationic liposome preparation, is an efficient liposomal vector that increases gene expression in arteries compared to naked DNA or previously described cationic DNA–liposome complexes by more than 15-fold. Although less efficient than adenoviral gene transfer, these levels of gene expression represent a significant improvement in liposome transfection in vivo and approach levels observed with clinically acceptable doses of adenoviral vectors. The improvement in gene expression, together with the relative safety associated with liposomal gene transfer, suggests that such nonviral vectors may be appropriate for human gene therapy protocols which utilize catheter-based gene delivery.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63105/1/hum.1996.7.15-1803.pd
SN 2008in—Bridging the Gap between Normal and Faint Supernovae of Type IIP
We present optical photometric and low-resolution spectroscopic observations of the Type II plateau supernova (SN) 2008in, which occurred in the outskirts of the nearly face-on spiral galaxy M61. Photometric data in the X-ray, ultraviolet, and near-infrared bands have been used to characterize this event. The SN field was imaged with the ROTSE-IIIb optical telescope about seven days before the explosion. This allowed us to constrain the epoch of the shock breakout to JD = 2454825.6. The duration of the plateau phase, as derived from the photometric monitoring, was ~98 days. The spectra of SN 2008in show a striking resemblance to those of the archetypal low-luminosity IIP SNe 1997D and 1999br. A comparison of ejecta kinematics of SN 2008in with the hydrodynamical simulations of Type IIP SNe by Dessart et al. indicates that it is a less energetic event (~5 × 10^(50) erg). However, the light curve indicates that the production of radioactive ^(56)Ni is significantly higher than that in the low-luminosity SNe. Adopting an interstellar absorption along the SN direction of AV ~ 0.3 mag and a distance of 13.2 Mpc, we estimated a synthesized ^(56)Ni mass of ~0.015 M_☉. Employing semi-analytical formulae derived by Litvinova and Nadezhin, we derived a pre-SN radius of ~126 R_☉, an explosion energy of ~5.4 × 10^(50) erg, and a total ejected mass of ~16.7 M_☉. The latter indicates that the zero-age main-sequence mass of the progenitor did not exceed 20 M_☉. Considering the above properties of SN 2008in and its occurrence in a region of sub-solar metallicity ([O/H] ~ 8.44 dex), it is unlikely that fall-back of the ejecta onto a newly formed black hole occurred in SN 2008in. We therefore favor a low-energy explosion scenario of a relatively compact, moderate-mass progenitor star that generates a neutron star
SN2012ab: A Peculiar Type IIn Supernova with Aspherical Circumstellar Material
We present photometry, spectra, and spectropolarimetry of supernova (SN)
2012ab, mostly obtained over the course of days after discovery. SN
2012ab was a Type IIn (SN IIn) event discovered near the nucleus of spiral
galaxy 2MASXJ12224762+0536247. While its light curve resembles that of SN
1998S, its spectral evolution does not. We see indications of CSM interaction
in the strong intermediate-width emission features, the high luminosity (peak
at absolute magnitude ), and the lack of broad absorption features in
the spectrum. The H emission undergoes a peculiar transition. At early
times it shows a broad blue emission wing out to km
and a truncated red wing. Then at late times (
100days) it shows a truncated blue wing and a very broad red emission wing
out to roughly km . This late-time broad red wing
probably arises in the reverse shock. Spectra also show an asymmetric
intermediate-width H component with stronger emission on the red side
at late times. The evolution of the asymmetric profiles requires a density
structure in the distant CSM that is highly aspherical. Our spectropolarimetric
data also suggest asphericity with a strong continuum polarization of % and depolarization in the H line, indicating asphericity in the
CSM at a level comparable to that in other SNe IIn. We estimate a mass-loss
rate of for km extending back at least 75yr prior to the
SN. The strong departure from axisymmetry in the CSM of SN 2012ab may suggest
that the progenitor was an eccentric binary system undergoing eruptive mass
loss.Comment: 18 pages, 12 figure
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Tropical Cyclone Prediction on Subseasonal Time-Scales
Here we discuss recent progress in understanding tropical cyclone (TC) subseasonal variability and its prediction. There has been a concerted effort to understand the sources of predictability at subseasonal time-scales, and this effort has continued to make progress in recent years. Besides the Madden-Julian Oscillation (MJO), other modes of variability affect TCs at these time-scales, in particular various equatorial waves. Additionally, TC activity is also modulated by extratropical processes via Rossby wave breaking.
There has also been progress in the ability of models to simulate the MJO and its modulation of TC activity. Community efforts have created multi-model ensemble datasets, which have made it possible to evaluate the forecast skill of the MJO and TCs on subseasonal time-scales in multiple forecasting systems. While there is positive skill in some cases, there is strong dependence on the ensemble system considered, the basin examined, and whether the storms have extratropical influences or not. Furthermore, the definition of skill differs among studies. Forecasting centers are currently issuing subseasonal TC forecasts using various techniques (statistical, statistical-dynamical and dynamical). There is also a strong interest in the private sector for forecasts with 3-4 weeks lead time
Safety and Short-Term Toxicity of a Novel Cationic Lipid Formulation for Human Gene Therapy
Overview summary Although several viral vectors have been widely applied to the treatment of human disease, the development of nonviral vectors is still in their infancy. In this report, a novel cationic lipid, DMRIE/DOPE, has been incorporated into the DNA–liposome formulation that improves transfection efficiencies and allows up to 1,000-fold higher concentrations of DNA to be administered in vivo. In this paper, the safety and toxicity of this formulation is described in two species, mice and pigs, suggesting that it may prove useful for human gene therapy.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/63224/1/hum.1993.4.6-781.pd
An early developmental vertebrate model for nanomaterial safety:Bridging cell-based and mammalian toxicity assessment
Background. With the rise in production of nanoparticles for an ever-increasing number of applications, there is an urgent need to efficiently assess their potential toxicity. We propose a nanoparticle hazard assessment protocol that combines mammalian cytotoxicity data with embryonic vertebrate abnormality scoring to determine an overall toxicity index. Results. We observed that, after exposure to a range of nanoparticles, Xenopus phenotypic scoring showed a strong correlation with cell based in vitro assays. Magnetite-cored nanoparticles, negative for toxicity in vitro and Xenopus, were further confirmed as non-toxic in mice. Conclusion. The results highlight the potential of Xenopus embryo analysis as a fast screening approach for toxicity assessment of nanoparticles, which could be introduced for the routine testing of nanomaterials
Cosmological Distance Measurement of 12 Nearby Supernovae IIP with ROTSE-IIIB
We present cosmological analysis of 12 nearby () Type IIP supernovae
(SNe IIP) observed with the ROTSE-IIIb telescope. To achieve precise
photometry, we present a new image differencing technique that is implemented
for the first time on the ROTSE SN photometry pipeline. With this method, we
find up to a 20\% increase in the detection efficiency and significant
reduction in residual RMS scatter of the SN lightcurves when compared to the
previous pipeline performance. We use the published optical spectra and
broadband photometry of well studied SNe IIP to establish temporal models for
ejecta velocity and photospheric temperature evolution for our SNe IIP
population. This study yields measurements that are competitive to other
methods even when the data are limited to a single epoch during the
photospheric phase of SNe IIP. Using the fully reduced ROTSE photometry and
optical spectra, we apply these models to the respective photometric epochs for
each SN in the ROTSE IIP sample. This facilitates the use of the Expanding
Photosphere Method (EPM) to obtain distance estimates to their respective host
galaxies. We then perform cosmological parameter fitting using these EPM
distances from which we measure the Hubble constant to be
, which is consistent with the
standard model values derived using other independent techniques.Comment: 19 pages, 13 figure
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