497 research outputs found
Adeno-associated viral vector-mediated human vascular endothelial growth factor gene transfer stimulates angiogenesis and wound healing in the genetically diabetic mouse
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The early spectral evolution of SN 2004dt
Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN
Ia) 2004dt, focusing our attention on the early epochs.
Methods. Observation triggered soon after the SN 2004dt discovery allowed us
to obtain a spectrophotometric coverage from day -10 to almost one year (~353
days) after the B band maximum. Observations carried out on an almost daily
basis allowed us a good sampling of the fast spectroscopic evolution of SN
2004dt in the early stages. To obtain this result, low-resolution, long-slit
spectroscopy was obtained using a number of facilities.
Results. This supernova, which in some absorption lines of its early spectra
showed the highest degree of polarization ever measured in any SN Ia, has a
complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is
present, moving at velocities as high as ~16,700 km/s, with some
intermediate-mass elements (Mg, Si, Ca) moving equally fast. Modeling of the
spectra based on standard density profiles of the ejecta fails to reproduce the
observed features, whereas enhancing the density of outer layers significantly
improves the fit. Our analysis indicates the presence of clumps of
high-velocity, intermediate-mass elements in the outermost layers, which is
also suggested by the spectropolarimetric data.Comment: 13 pages, 15 figures, accepted for pubblication in Astronomy and
Astrophysic
High-Velocity Features: a ubiquitous property of Type Ia SNe
Evidence of high-velocity features such as those seen in the near-maximum
spectra of some Type Ia Supernovae (eg SN 2000cx) has been searched for in the
available SNIa spectra observed earlier than one week before B maximum. Recent
observational efforts have doubled the number of SNeIa with very early spectra.
Remarkably, all SNeIa with early data (7 in our RTN sample and 10 from other
programmes) show signs of such features, to a greater or lesser degree, in CaII
IR, and some also in SiII 6255A line. High-velocity features may be interpreted
as abundance or density enhancements. Abundance enhancements would imply an
outer region dominated by Si and Ca. Density enhancements may result from the
sweeping up of circumstellar material by the highest velocity SN ejecta. In
this scenario, the high incidence of HVFs suggests that a thick disc and/or a
high-density companion wind surrounds the exploding white dwarf, as may be the
case in Single Degenerate systems. Large-scale angular fluctuations in the
radial density and abundance distribution may also be responsible: this could
originate in the explosion, and would suggest a deflagration as the more likely
explosion mechanism. CSM-interaction and surface fluctuations may coexist,
possibly leaving different signatures on the spectrum. In some SNe the HVFs are
narrowly confined in velocity, suggesting the ejection of blobs of burned
material.Comment: 12 pages, 2 figures, ApJ Letters in pres
Lower limits on the Hubble Constant from models of Type Ia Supernovae
By coupling observations of type Ia supernovae with results obtained from the
best available numerical models we constrain the Hubble constant, independently
of any external calibrators. We find an absolute lower limit of Ho > 50
km/s/Mpc. In addition, we construct a Hubble diagram with UVOIR light curves of
12 type Ia supernovae located in the Hubble flow, and when adopting the most
likely values (obtained from 1-D and 3-D deflagration simulations) of the
amount of (56)Ni produced in a typical event, we find values of Ho
668 and 789 km/s/Mpc, respectively. Our result may be
difficult to reconcile with recent discussions in the literature as it seems
that an Einstein-de Sitter universe requires Ho 46 km/s/Mpc in order
to fit the temperature power spectrum of the cosmic microwave background and
maintain the age constraints of the oldest stars.Comment: 11 pages, 3 figures; Accepted for publication in A&
The luminosity of supernovae of type Ia from TRGB distances and the value of H_0
Distances from the tip of the red-giant branch (TRGB) in the halo Population
of galaxies - calibrated through RR Lyr stars as well as tied to Hipparcos
parallaxes and further supported by stellar models - are used to determine the
luminosity of six nearby type Ia supernovae (SN 2011fe, 2007sr, 1998bu, 1989B,
1972E, and 1937C). The result is M_V^corr = -19.41 +/- 0.05. If this value is
applied to 62 SNe Ia with 3000< v < 20,000 km/s a large-scale value of the
Hubble constant follows of H_0 = 64.0 +/- 1.6 +/- 2.0. The SN HST Project gave
H_0 = 62.3 +/- 1.3 +/- 5.0 from ten Cepheid-calibrated SNe Ia (Sandage et al.
2006). The agreement of young Population I (Cepheids) and old, metal-poor
Population II (TRGB) distance indicators is satisfactory. The combined weighted
result is H_0 = 63.7 +/- 2.3 (i.e. +/-3.6%). The result can also be reconciled
with WMAP5 data (Reid et al. 2010).Comment: 9 pages, 3 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
NTT and NOT spectroscopy of SDSS-II supernovae
Context. The SDSS-II Supernova Survey, conducted between 2005 and 2007, was
designed to detect a large number of Type Ia supernovae (SNe Ia) around z~0.2,
the redshift "gap" between low-z and high-z SN searches. The survey has
provided multi-band photometric lightcurves for variable targets, and SN
candidates were scheduled for spectroscopic observations, primarily to provide
SN classification and accurate redshifts. We present SN spectra obtained in
2006 and 2007 using the NTT and the NOT. Aims. We provide an atlas of SN
spectra in the range z =0.03-0.32 that complements the well-sampled lightcurves
from SDSS-II in the forthcoming three-year SDSS SN cosmology analysis. The
sample can, for example, be used for spectral studies of SNe Ia, which are
critical for understanding potential systematic effects when SNe are used to
determine cosmological distances. Methods. The spectra were reduced in a
uniform manner, and special care was taken in estimating the uncertainties for
the different processing steps. Host-galaxy light was subtracted when possible
and the SN type fitted using the SuperNova IDentification code (SNID). We also
present comparisons between spectral and photometric dating using SALT
lightcurve fits to the photometry from SDSS-II, as well as the global
distribution of our sample in terms of the lightcurve parameters: stretch and
colour. Results. We report new spectroscopic data from 141 SNe Ia, mainly
between -9 and +15 days from lightcurve maximum, including a few cases of
multi-epoch observations. This homogeneous, host-galaxy subtracted, SN Ia
spectroscopic sample is among the largest such data sets and unique in its
redshift interval. The sample includes two potential SN 1991T-like SNe (SN
2006on and SN 2007ni) and one potential SN 2002cx-like SN (SN 2007ie). In
addition, the new compilation includes spectra from 23 confirmed Type II and 8
Type Ib/c SNe.Comment: Accepted for publication in A&
Adeno-associated viral vector-mediated human vascular endothelial growth factor gene transfer stimulates angiogenesis and wound healing in the genetically diabetic mouse
On the Use of Field RR Lyrae as Galactic Probes. I. The Oosterhoff Dichotomy Based on Fundamental Variables
We collected a large data set of field RR Lyrae stars (RRLs) by using catalogs already available in the literature and Gaia DR2. We estimated the iron abundances for a subsample of 2382 fundamental RRLs (ΔS method: Ca ii K, Hβ, Hγ, and Hδ lines) for which there are publicly available medium-resolution SDSS-SEGUE spectra. We also included similar estimates available in the literature, ending up with the largest and most homogeneous spectroscopic data set ever collected for RRLs (2903). The metallicity scale was validated by using iron abundances based on high-resolution spectra for a fundamental field RRL (V Ind), for which we collected X-shooter spectra covering the entire pulsation cycle. The peak ([Fe/H] =-1.59 ± 0.01) and the standard deviation (σ = 0.43 dex) of the metallicity distribution agree quite well with similar estimates available in the literature. The current measurements disclose a well-defined metal-rich tail approaching solar iron abundance. The spectroscopic sample plotted in the Bailey diagram (period versus luminosity amplitude) shows a steady variation when moving from the metal-poor ([Fe/H] =-3.0/-2.5) to the metal-rich ([Fe/H] =-0.5/0.0) regime. The smooth transition in the peak of the period distribution as a function of the metallicity strongly indicates that the long-standing problem of the Oosterhoff dichotomy among Galactic globular clusters is the consequence of the lack of metal-intermediate clusters hosting RRLs. We also found that the luminosity amplitude, in contrast with period, does not show a solid correlation with metallicity. This suggests that period-amplitude-metallicity relations should be cautiously treated
The UV/optical spectra of the Type Ia supernova SN 2010jn: a bright supernova with outer layers rich in iron-group elements
Radiative transfer studies of Type Ia supernovae (SNe Ia) hold the promise of
constraining both the time-dependent density profile of the SN ejecta and its
stratification by element abundance which, in turn, may discriminate between
different explosion mechanisms and progenitor classes. Here we present a
detailed analysis of Hubble Space Telescope ultraviolet (UV) and ground-based
optical spectra and light curves of the SN Ia SN 2010jn (PTF10ygu). SN 2010jn
was discovered by the Palomar Transient Factory (PTF) 15 days before maximum
light, allowing us to secure a time-series of four UV spectra at epochs from
-11 to +5 days relative to B-band maximum. The photospheric UV spectra are
excellent diagnostics of the iron-group abundances in the outer layers of the
ejecta, particularly those at very early times. Using the method of 'Abundance
Tomography' we have derived iron-group abundances in SN 2010jn with a precision
better than in any previously studied SN Ia. Optimum fits to the data can be
obtained if burned material is present even at high velocities, including
significant mass fractions of iron-group elements. This is consistent with the
slow decline rate (or high 'stretch') of the light curve of SN 2010jn, and
consistent with the results of delayed-detonation models. Early-phase UV
spectra and detailed time-dependent series of further SNe Ia offer a promising
probe of the nature of the SN Ia mechanism.Comment: 17 pages, 9 figures (v3: several small updates to content including
models; v2: metadata fixed), MNRAS, in pres
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