96 research outputs found
Polarimetric survey of asteroids with the Asiago telescope
We present the first results of an asteroid photo--polarimetry program started at Asiago--Cima Ekar Observatory. The aim of our survey is to estimate diversity in polarimetric properties of asteroids belonging to different taxonomic and dynamical classes. The data were obtained with the polarization analyser placed inside the Faint Object Spectrographic Camera (AFOSC) of the 1.8m telescope. This instrument allows simultaneous measurements of the two first Stokes parameters without any lambda/2 retarding plate. Our survey began in 2002, and up to now we have obtained data on a sample of 36 asteroids; most of them are being investigated with the polarimetric technique for the first time. Combining our data with those already available in literature, we present an estimate of the inversion angle for 7 asteroids in this paper. Furthermore, we present the polarimetric measurements of the rare asteroid classes belonging to the A and D types and a detailed VRI observations at extremely small phase angles of the low albedo asteroid 1021 Flammari
The nature and evolution of Nova Cygni 2006
AIMS: Nova Cyg 2006 has been intensively observed throughout its full
outburst. We investigate the energetics and evolution of the central source and
of the expanding ejecta, their chemical abundances and ionization structure,
and the formation of dust. METHOD: We recorded low, medium, and/or
high-resolution spectra (calibrated into accurate absolute fluxes) on 39
nights, along with 2353 photometric UBVRcIc measures on 313 nights, and
complemented them with IR data from the literature. RESULTS: The nova displayed
initially the normal photometric and spectroscopic evolution of a fast nova of
the FeII-type. Pre-maximum, principal, diffuse-enhanced, and Orion absorption
systems developed in a normal way. After the initial outburst, the nova
progressively slowed its fading pace until the decline reversed and a second
maximum was reached (eight months later), accompanied by large spectroscopic
changes. Following the rapid decline from second maximum, the nova finally
entered the nebular phase and formed optically thin dust. We computed the
amount of formed dust and performed a photo-ionization analysis of the
emission-line spectrum during the nebular phase, which showed a strong
enrichment of the ejecta in nitrogen and oxygen, and none in neon, in agreement
with theoretical predictions for the estimated 1.0 Msun white dwarf in Nova Cyg
2006. The similarities with the poorly investigated V1493 Nova Aql 1999a are
discussed.Comment: in press in Astronomy and Astrophysic
Interacting supernovae and supernova impostors. SN 2007sv: the major eruption of a massive star in UGC 5979
We report the results of the photometric and spectroscopic monitoring
campaign of the transient SN 2007sv. The observables are similar to those of
type IIn supernovae, a well-known class of objects whose ejecta interact with
pre-existing circum-stellar material. The spectra show a blue continuum at
early phases and prominent Balmer lines in emission, however, the absolute
magnitude at the discovery of SN 2007sv (M_R = - 14.25 +/- 0.38) indicate it to
be most likely a supernova impostor. This classification is also supported by
the lack of evidence in the spectra of very high velocity material as expected
in supernova ejecta. In addition we find no unequivocal evidence of broad lines
of alpha - and/or Fe-peak elements. The comparison with the absolute light
curves of other interacting objects (including type IIn supernovae) highlights
the overall similarity with the prototypical impostor SN 1997bs. This supports
our claim that SN 2007sv was not a genuine supernova, and was instead a
supernova impostor, most likely similar to the major eruption of a luminous
blue variable.Comment: Accepted for publication in MNRAS. 15 pages, 11 figures, 5 table
ESC Supernova spectroscopy of non-ESC targets
We present the spectra of 36 Supernovae (SNe) of various types, obtained by
the European Supernova Collaboration. Because of the spectral classification
and the phase determination at their discovery the SNe did not warrant further
study, and the spectra we present are the only available for the respective
objects. In this paper we present and discuss this material using a new
software for the automated classification of SNe spectra.
As a validation of the software, we verify the classification and phase
estimate reported for these objects in their discovery / classification
circulars. For the comparison, the software uses the library of template
spectra of Padova-Asiago Supernova Archive (ASA).
For each spectrum of our sample we present a brief, individual discussion,
highlighting the main characteristics and possible peculiarities. The
comparison with ASA spectra confirms the previous classification of all objects
and refines the age estimates. For our software we determine numerical limits
of "safe" spectral classification and the uncertainties of the phase
determination.Comment: 22 pages, accepted for publication in A&
Supernovae in isolated galaxies, in pairs and in groups of galaxies
In order to investigate the influence of the environment on the supernova
(SN) production we have performed a statistical investigation of the SNe
discovered in isolated galaxies, in pairs and in groups of galaxies. 22 SNe in
18 isolated galaxies, 48 SNe in 40 galaxies members of 37 pairs and 211 SNe in
170 galaxies members of 116 groups have been selected and studied. We found
that the radial distributions of core-collapse SNe in galaxies located in
different environments are similar, and consistent with that reported by
Bartunov, Makarova & Tsvetkov (1992). SNe discovered in pairs do not privilege
a particular direction with respect to the companion galaxy. Also the azimuthal
distributions inside the hosts members of galaxy groups are consistent with
being isotropics. The fact that SNe are more frequent in the brighter
components of the pairs and groups is expected from the dependence of the SN
rates on the galaxy luminosity. There is an indication that the SN rate is
higher in galaxy pairs compared with that in groups. This can be related to the
enhanced star formation rate in strongly interacting systems. It is concluded
that, with the possible exception of strongly interacting system, the parent
galaxy environment has no direct influence on the SN productionComment: 10 pages, accepted for publication to MNRA
SN 2006gy: was it really extra-ordinary?
We present an optical photometric and spectroscopic study of the very
luminous type IIn SN 2006gy for a time period spanning more than one year. In
photometry, a broad, bright (M_R~-21.7) peak characterizes all BVRI light
curves. Afterwards, a rapid luminosity fading is followed by a phase of slow
luminosity decline between day ~170 and ~237. At late phases (>237 days),
because of the large luminosity drop (>3 mag), only upper visibility limits are
obtained in the B, R and I bands. In the near-infrared, two K-band detections
on days 411 and 510 open new issues about dust formation or IR echoes
scenarios. At all epochs the spectra are characterized by the absence of broad
P-Cygni profiles and a multicomponent Halpha profile, which are the typical
signatures of type IIn SNe. After maximum, spectroscopic and photometric
similarities are found between SN 2006gy and bright, interaction-dominated SNe
(e.g. SN 1997cy, SN 1999E and SN 2002ic). This suggests that ejecta-CSM
interaction plays a key role in SN 2006gy about 6 to 8 months after maximum,
sustaining the late-time-light curve. Alternatively, the late luminosity may be
related to the radioactive decay of ~3M_sun of 56Ni. Models of the light curve
in the first 170 days suggest that the progenitor was a compact star (R~6-8
10^(12)cm, M_ej~5-14M_sun), and that the SN ejecta collided with massive
(6-10M_sun), opaque clumps of previously ejected material. These clumps do not
completely obscure the SN photosphere, so that at its peak the luminosity is
due both to the decay of 56Ni and to interaction with CSM. A supermassive star
is not required to explain the observational data, nor is an extra-ordinarily
large explosion energy.Comment: 33 pages, 8 figures. Accepted by ApJ. Paper with high-resolution
figures available at
http://web.oapd.inaf.it/supern/sn2006gy_astroph/agnoletto_2006gy.pd
SN 2009E: a faint clone of SN 1987A
In this paper we investigate the properties of SN 2009E, which exploded in a
relatively nearby spiral galaxy (NGC 4141) and that is probably the faintest
1987A-like supernova discovered so far. Spectroscopic observations which
started about 2 months after the supernova explosion, highlight significant
differences between SN 2009E and the prototypical SN 1987A. Modelling the data
of SN 2009E allows us to constrain the explosion parameters and the properties
of the progenitor star, and compare the inferred estimates with those available
for the similar SNe 1987A and 1998A. The light curve of SN 2009E is less
luminous than that of SN 1987A and the other members of this class, and the
maximum light curve peak is reached at a slightly later epoch than in SN 1987A.
Late-time photometric observations suggest that SN 2009E ejected about 0.04
solar masses of 56Ni, which is the smallest 56Ni mass in our sample of
1987A-like events. Modelling the observations with a radiation hydrodynamics
code, we infer for SN 2009E a kinetic plus thermal energy of about 0.6 foe, an
initial radius of ~7 x 10^12 cm and an ejected mass of ~19 solar masses. The
photospheric spectra show a number of narrow (v~1800 km/s) metal lines, with
unusually strong Ba II lines. The nebular spectrum displays narrow emission
lines of H, Na I, [Ca II] and [O I], with the [O I] feature being relatively
strong compared to the [Ca II] doublet. The overall spectroscopic evolution is
reminiscent of that of the faint 56Ni-poor type II-plateau supernovae. This
suggests that SN 2009E belongs to the low-luminosity, low 56Ni mass, low-energy
tail in the distribution of the 1987A-like objects in the same manner as SN
1997D and similar events represent the faint tail in the distribution of
physical properties for normal type II-plateau supernovae.Comment: 19 pages, 9 figures (+7 in appendix); accepted for publication in A&A
on 3 November 201
- …