196 research outputs found
Photometry of SN 2002ic and Implications for the Progenitor Mass-Loss History
We present new pre-maximum and late-time optical photometry of the Type
Ia/IIn supernova 2002ic. These observations are combined with the published
V-band magnitudes of Hamuy et al. (2003) and the VLT spectrophotometry of Wang
et al. (2004) to construct the most extensive light curve to date of this
unusual supernova. The observed flux at late time is significantly higher
relative to the flux at maximum than that of any other observed Type Ia
supernova and continues to fade very slowly a year after explosion. Our
analysis of the light curve suggests that a non-Type Ia supernova component
becomes prominent days after explosion. Modeling of the non-Type Ia
supernova component as heating from the shock interaction of the supernova
ejecta with pre-existing circumstellar material suggests the presence of a
cm gap or trough between the progenitor system and the
surrounding circumstellar material. This gap could be due to significantly
lower mass-loss years prior to explosion or
evacuation of the circumstellar material by a low-density fast wind. The latter
is consistent with observed properties of proto-planetary nebulae and with
models of white-dwarf + asymptotic giant branch star progenitor systems with
the asymptotic giant branch star in the proto-planetary nebula phase.Comment: accepted for publication in Ap
Late-Time Optical and UV Spectra of SN 1979C and SN 1980K
A low-dispersion Keck I spectrum of SN 1980K taken in August 1995 (t = 14.8
yr after explosion) and a November 1997 MDM spectrum (t = 17.0 yr) show broad
5500 km s^{-1} emission lines of H\alpha, [O I] 6300,6364 A, and [O II]
7319,7330 A. Weaker but similarly broad lines detected include [Fe II] 7155 A,
[S II] 4068,4072 A, and a blend of [Fe II] lines at 5050--5400 A. The presence
of strong [S II] 4068,4072 A emission but a lack of [S II] 6716,6731 A emission
suggests electron densities of 10^{5-6} cm^{-3}. From the 1997 spectra, we
estimate an H\alpha flux of 1.3 \pm 0.2 \times 10^{-15} erg cm^{-2} s^{-1}
indicating a 25% decline from 1987--1992 levels during the period 1994 to 1997,
possibly related to a reported decrease in its nonthermal radio emission.Comment: 21 pages, 8 figures, submitted to the Astronomical Journa
Helium Emission in the Type Ic SN 1999cq
We present the first unambiguous detection of helium emission lines in
spectra of Type Ic supernovae (SNe Ic). The presence of He I lines, with full
width at half maximum ~ 2000 km/s, and the distinct absence of any other
intermediate-width emission (e.g., Halpha), implies that the ejecta of SN Ic
1999cq are interacting with dense circumstellar material composed of almost
pure helium. This strengthens the argument that the progenitors of SNe Ic are
core-collapse events in stars that have lost both their hydrogen and helium
envelopes, either through a dense wind or mass-transfer to a companion. In this
way, SN 1999cq is similar to supernovae such as SN 1987K and SN 1993J that
helped firmly establish a physical connection between Type Ib and Type II
supernovae. The light curve of SN 1999cq is very fast, with an extremely rapid
rise followed by a quick decline. SN 1999cq is also found to exhibit a high
level of emission at blue wavelengths (< 5500 A), likely resulting from either
an unusually large amount of iron and iron-group element emission or
uncharacteristically low reddening compared with other SNe Ic.Comment: 17 pages (AASTeX V5.0), 4 figures, accepted for publication in the
Astronomical Journa
Evidence for Asphericity in the Type IIn Supernova 1998S
We present optical spectropolarimetry obtained at the Keck-II 10-m telescope
on 1998 March 7 UT along with total flux spectra spanning the first 494 days
after discovery (1998 March 2 UT) of the peculiar type IIn supernova (SN)
1998S. The SN is found to exhibit a high degree of linear polarization,
implying significant asphericity for its continuum-scattering environment.
Prior to removal of the interstellar polarization, the polarization spectrum is
characterized by a flat continuum (at p ~ 2%) with distinct changes in
polarization associated with both the broad (FWZI >= 20,000 km/s) and narrow
(unresolved, FWHM < 300 km/s) line emission seen in the total flux spectrum.
When analyzed in terms of a polarized continuum with unpolarized broad-line
recombination emission, an intrinsic continuum polarization of p ~ 3% results
(the highest yet found for a SN), suggesting a global asphericity of >= 45%
from the oblate, electron-scattering dominated models of Hoflich (1991). The
smooth, blue continuum evident at early times is shown to be inconsistent with
a reddened, single-temperature blackbody, instead having a color temperature
that increases with decreasing wavelength. Broad emission-line profiles with
distinct blue and red peaks are seen in the total flux spectra at later times,
perhaps suggesting a disk-like or ring-like morphology for the dense (n_e ~
10^7 cm^{-3}) circumstellar medium. Implications of the circumstellar
scattering environment for the spectropolarimetry are discussed, as are the
effects of uncertain removal of interstellar polarization.Comment: 25 pages + 2 tables + 14 figures, Submitted to The Astrophysical
Journa
Identification of the Red Supergiant Progenitor of Supernova 2005cs: Do the Progenitors of Type II-P Supernovae Have Low Mass?
The stars that end their lives as supernovae (SNe) have been directly
observed in only a handful of cases, due mainly to the extreme difficulty in
identifying them in images obtained prior to the SN explosions. Here we report
the identification of the progenitor for the recent Type II-plateau
(core-collapse) SN 2005cs in pre-explosion archival images of the Whirlpool
Galaxy (M51) obtained with the Hubble Space Telescope (HST) Advanced Camera for
Surveys (ACS). From high-quality ground-based images of the SN from the
Canada-France-Hawaii Telescope, we precisely determine the position of the SN
and are able to isolate the SN progenitor to within 0".04 in the HST/ACS
optical images. We further pinpoint the SN location to within 0".005 from
HST/ACS ultraviolet images of the SN, confirming our progenitor identification.
From photometry of the SN progenitor obtained with the pre-SN ACS images, and
also limits to its brightness in pre-SN HST/NICMOS images, we infer that the
progenitor is a red supergiant star of spectral type K0--M3, with initial mass
7--9 Msun. We also discuss the implications of the SN 2005cs progenitor
identification and its mass estimate. There is an emerging trend that the most
common Type II-plateau SNe originate from low-mass supergiants 8--15 Msun.Comment: Submitted to ApJ. A high resolution version can be found at
http://astron.berkeley.edu/~weidong/sn05cs.p
A Comparative Study of the Absolute-Magnitude Distributions of Supernovae
The Asiago Supernova Catalog is used to carry out a comparative study of
supernova absolute-magnitude distributions. An overview of the absolute
magnitudes of the supernovae in the current observational sample is presented,
and the evidence for subluminous and overluminous events is examined. The
fraction of supernovae that are underluminous (M_B > -15) appears to be higher
(perhaps much higher) than one fifth but it remains very uncertain. The
fraction that are overluminous (M_B < -20) is lower (probably much lower) than
0.01. The absolute-magnitude distributions for each supernova type, restricted
to events within 1 Gpc, are compared. Although these distributions are affected
by observational bias in favor of the more luminous events, they are useful for
comparative studies. We find mean absolute blue magnitudes (for H_0=60) of
-19.46 for normal Type Ia supernovae (SNe Ia), -18.04 for SNe Ibc, -17.61 and
-20.26 for normal and bright SNe Ibc considered separately, -18.03 for SNe
II-L, -17.56 and -19.27 for normal and bright SNe II-L considered separately,
-17.00 for SNe II-P, and -19.15 for SNe IIn.Comment: 27 pages, accepted for publication by the Astronomical Journal (Feb.
2002
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 MACHO Project: Microlensing Results from 5.7 Years of LMC Observations
We report on our search for microlensing towards the Large Magellanic Cloud
(LMC). Analysis of 5.7 years of photometry on 11.9 million stars in the LMC
reveals 13 - 17 microlensing events. This is significantly more than the
2 to 4 events expected from lensing by known stellar populations. The
timescales (\that) of the events range from 34 to 230 days. We estimate the
microlensing optical depth towards the LMC from events with 2 < \that < 400
days to be 1.2 ^{+0.4}_ {-0.3} \ten{-7} 0.15 \msun 0.9 \msun$, depending on the halo model, and the total mass in MACHOs out
to 50 kpc is found to be 9+4-3 10^{10} msun, independent of the halo model.
These results are marginally consistent with our previous results, but are
lower by about a factor of two. Besides a larger data set, this work also
includes an improved efficiency determination, improved likelihood analysis,
and more thorough testing of systematic errors, especially with respect to the
treatment of potential backgrounds to microlensing, such as supernovae in
galaxies behind the LMC. [Abridged]Comment: 53 pages, Latex with 12 postscript figures, submitted to Ap
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