513 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
Explosion of a massive, He-rich star at z=0.16
We present spectroscopic and photometric data of the peculiar SN 2001gh,
discovered by the 'Southern inTermediate Redshift ESO Supernova Search'
(STRESS) at a redshift z=0.16. SN 2001gh has relatively high luminosity at
maximum (M_B = -18.55 mag), while the light curve shows a broad peak. An
early-time spectrum shows an almost featureless, blue continuum with a few weak
and shallow P-Cygni lines that we attribute to HeI. HeI lines remain the only
spectral features visible in a subsequent spectrum, obtained one month later. A
remarkable property of SN 2001gh is the lack of significant spectral evolution
over the temporal window of nearly one month separating the two spectra. In
order to explain the properties of SN 2001gh, three powering mechanism are
explored, including radioactive decays of a moderately large amount of 56Ni,
magnetar spin-down, and interaction of SN ejecta with circumstellar medium. We
favour the latter scenario, with a SN Ib wrapped in a dense, circumstellar
shell. The fact that no models provide an excellent fit with observations,
confirms the troublesome interpretation of the nature of SN 2001gh. A rate
estimate for SN 2001gh-like event is also provided, confirming the intrinsic
rarity of these objects.Comment: 11 pages, 8 figures, 3 tables. Accepted by MNRA
Supernova search at intermediate z. II. Host galaxy morphology
We discuss the host galaxy morphology of the 8 SNe discovered as a part of
the International Time Programme (ITP) project ``Omega and Lambda from
Supernovae, and the Physics of Supernovae Explosions'' at the European Northern
Observatory (ENO). Identification of the SN host galaxy types was done
exploiting both imaging and spectroscopy. A peculiar SNIa at z= 0.033 is found
in a spiral galaxy, as most other SNeIa with z between 0.1 and 0.4. A complete
account of these studies will be given elsewhere.Comment: 2 pages, 2 figures, 1 table, to appear in ``1604-2004: Supernovae as
Cosmological Lighthouses'', (extended text upon request
Supernova search at intermediate z. III. Expansion velocities of the ejecta
We discuss the expansion velocities of different elements in the ejecta of
the intermediate-z SNe Ia discovered as a 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
expansion velocities measured for each normal SNIa are found to be within the
typical velocity dispersion for their epoch. Meanwhile, the subluminous SN
2002lk SiII expansion velocity is significantly higher than that of SN 1991bg
shortly after maximum. The observed phase was younger in SN2002lk than in the
local subluminous SNIa SN1991bg.Comment: 2 pages, 1 figure, 1 table, to appear in ``1604-2004: Supernovae as
Cosmological Lighthouses'', (extended text upon request
Beneficial Effects of Polydeoxyribonucleotide (PDRN) in an In Vitro Model of Fuchs Endothelial Corneal Dystrophy
Fuchs endothelial corneal dystrophy (FECD) is a bilateral, hereditary syndrome characterized by progressive irreversible injury in the corneal endothelium; it is the most frequent cause for corneal transplantation worldwide. Oxidative stress induces the apoptosis of corneal endothelial cells (CECs), and has a crucial function in FECD pathogenesis. The stimulation of the adenosine A2A receptor (A2Ar) inhibits oxidative stress, reduces inflammation and modulates apoptosis. Poly-deoxyribonucleotide (PDRN) is a registered drug that acts through adenosine A2Ar. Thus, the goal of this study was to assess the effect of PDRN in an in vitro FECD model. Human Corneal Endothelial Cells (IHCE) were challenged with H2O2 (200 µM) alone or in combination with PDRN (100 µg/mL), PDRN plus ZM241385 (1 µM) as an A2Ar antagonist, and CGS21680 (1 µM) as a well-known A2Ar agonist. H2O2 reduced the cells’ viability and increased the expression of the pro-inflammatory markers NF-κB, IL-6, IL-1β, and TNF-α; by contrast, it decreased the expression of the anti-inflammatory IL-10. Moreover, the pro-apoptotic genes Bax, Caspase-3 and Caspase-8 were concurrently upregulated with a decrease of Bcl-2 expression. PDRN and CGS21680 reverted the negative effects of H2O2. Co-incubation with ZM241385 abolished the effects of PDRN, indicating that A2Ar is involved in the mode of action of PDRN. These data suggest that PDRN defends IHCE cells against H2O2-induced damage, potentially as a result of its antioxidant, anti-inflammatory and antiapoptotic properties, suggesting that PDRN could be used as an FECD therapy
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
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
SALT: a Spectral Adaptive Light curve Template for Type Ia Supernovae
We present a new method to parameterize Type Ia Supernovae (SN Ia)
multi-color light curves. The method was developed in order to analyze the
large number of SN Ia multi-color light curves measured in current
high-redshift projects. The technique is based on empirically modeling SN Ia
luminosity variations as a function of phase, wavelength, a shape parameter,
and a color parameter. The model is trained with a sample of well measured
nearby SN Ia and then tested with an independent set of supernovae by building
an optimal luminosity distance estimator combining the supernova rest-frame
luminosity, shape parameter and color reconstructed with the model. The
distances we measure using B- and V-band data show a dispersion around the
Hubble line comparable or lower than obtained with other methods. With this
model, we are able to measure distances using U- and B-band data with a
dispersion around the Hubble line of 0.16 +- 0.05.Comment: Accepted in A&A, June 23, 2005 (printer friendly replacement version,
includes language corrections
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