742 research outputs found
Spectroscopically Peculiar Type Ia Supernovae and Implications for Progenitors
In a recent paper Li et al. (2000) reported that 36 percent of 45 Type Ia
supernovae (SNe Ia) discovered since 1997 in two volume-limited supernova
searches were spectroscopically peculiar, and they suggested that because this
peculiarity rate is higher than that reported for an earlier observational
sample by Branch et al. (1993), it is now more likely that SNe Ia are produced
by more than one kind of progenitor. In this paper I discuss and clarify the
differences between the results of Li et al. and Branch et al. and I suggest
that multiple progenitor systems are now less likely than they were before.Comment: 11 pages; accepted by PASP; several minor changes, 2 references
added, main conclusions unchange
Early-time Spitzer observations of the type II-Plateau supernova, 2004dj
We present mid-infrared observations with the Spitzer Space Telescope of the
nearby type II-P supernova, SN 2004dj, at epochs of 89 to 129 days. We have
obtained the first mid-IR spectra of any supernova apart from SN 1987A. A
prominent [NiII] 6.64 micron line is observed, from which we deduce that the
mass of stable nickel must be at least 2.2e10(-4) Msun. We also observe the red
wing of the CO-fundamental band. We relate our findings to possible progenitors
and favour an evolved star, most likely a red supergiant, with a probable
initial mass between ~10 and 15 Msun.Comment: ApJ Letters (accepted
A Spitzer Space Telescope study of SN 2002hh: an infrared echo from a Type IIP supernova
We present late-time (590-994 d) mid-IR photometry of the normal, but
highly-reddened Type IIP supernova SN 2002hh. Bright, cool, slowly-fading
emission is detected from the direction of the supernova. Most of this flux
appears not to be driven by the supernova event but instead probably originates
in a cool, obscured star-formation region or molecular cloud along the
line-of-sight. We also show, however, that the declining component of the flux
is consistent with an SN-powered IR echo from a dusty progenitor CSM. Mid-IR
emission could also be coming from newly-condensed dust and/or an ejecta/CSM
impact but their contributions are likely to be small. For the case of a CSM-IR
echo, we infer a dust mass of as little as 0.036 M(solar) with a corresponding
CSM mass of 3.6(0.01/r(dg))M(solar) where r(dg) is the dust-to-gas mass ratio.
Such a CSM would have resulted from episodic mass loss whose rate declined
significantly about 28,000 years ago. Alternatively, an IR echo from a
surrounding, dense, dusty molecular cloud might also have been responsible for
the fading component. Either way, this is the first time that an IR echo has
been clearly identified in a Type IIP supernova. We find no evidence for or
against the proposal that Type IIP supernovae produce large amounts of dust via
grain condensation in the ejecta. However, within the CSM-IR echo scenario, the
mass of dust derived implies that the progenitors of the most common of
core-collapse supernovae may make an important contribution to the universal
dust content.Comment: 41 pages, 11 figures, 4 tables, accepted for publication in
Astrophysical Journal (References corrected
On the High--Velocity Ejecta of the Type Ia Supernova 1994D
Synthetic spectra generated with the parameterized supernova
synthetic-spectrum code SYNOW are compared to spectra of the Type Ia SN 1994D
that were obtained before the time of maximum brightness. Evidence is found for
the presence of two-component Fe II and Ca II features, forming in high
velocity ( \kms) and lower velocity ( \kms) matter.
Possible interpretations of these spectral splits, and implications for using
early--time spectra of SNe Ia to probe the metallicity of the progenitor white
dwarf and the nature of the nuclear burning front in the outer layers of the
explosion, are discussed.Comment: 15 pages, 3 figures, 3 tables, Astrophysical Journal, in pres
The Rise Times of High and Low Redshift Type Ia Supernovae are Consistent
We present a self-consistent comparison of the rise times for low- and
high-redshift Type Ia supernovae. Following previous studies, the early light
curve is modeled using a t-squared law, which is then mated with a modified
Leibundgut template light curve. The best-fit t-squared law is determined for
ensemble samples of low- and high-redshift supernovae by fitting simultaneously
for all light curve parameters for all supernovae in each sample. Our method
fully accounts for the non-negligible covariance amongst the light curve
fitting parameters, which previous analyses have neglected. Contrary to Riess
et al. (1999), we find fair to good agreement between the rise times of the
low- and high-redshift Type Ia supernovae. The uncertainty in the rise time of
the high-redshift Type Ia supernovae is presently quite large (roughly +/- 1.2
days statistical), making any search for evidence of evolution based on a
comparison of rise times premature. Furthermore, systematic effects on rise
time determinations from the high-redshift observations, due to the form of the
late-time light curve and the manner in which the light curves of these
supernovae were sampled, can bias the high-redshift rise time determinations by
up to +3.6/-1.9 days under extreme situations. The peak brightnesses - used for
cosmology - do not suffer any significant bias, nor any significant increase in
uncertainty.Comment: 18 pages, 4 figures, Accepted for publication in the Astronomical
Journal. Also available at http://www.lbl.gov/~nugent/papers.html Typos were
corrected and a few sentences were added for improved clarit
A Spitzer Space Telescope Study of SN 2003gd: Still No Direct Evidence that Core-Collapse Supernovae are Major Dust Factories
We present a new, detailed analysis of late-time mid-infrared (IR)
observations of the Type II-P supernova (SN) 2003gd. At about 16 months after
the explosion, the mid-IR flux is consistent with emission from 4 x 10^(-5)
M(solar) of newly condensed dust in the ejecta. At 22 months emission from
point-like sources close to the SN position was detected at 8 microns and 24
microns. By 42 months the 24 micron flux had faded. Considerations of
luminosity and source size rule out the ejecta of SN 2003gd as the main origin
of the emission at 22 months. A possible alternative explanation for the
emission at this later epoch is an IR echo from pre-existing circumstellar or
interstellar dust. We conclude that, contrary to the claim of Sugerman et al.
(2006, Science, 313, 196), the mid-IR emission from SN 2003gd does not support
the presence of 0.02 M(solar) of newly formed dust in the ejecta. There is, as
yet, no direct evidence that core-collapse supernovae are major dust factories.Comment: 26 pages, 2 figures, 2 tables, accepted for publication in
Astrophysical Journa
On the Spectroscopic Diversity of Type Ia Supernovae
A comparison of the ratio of the depths of two absorption features in the
spectra of TypeIa supernovae (SNe Ia) near the time of maximum brightness with
the blueshift of the deep red Si II absorption feature 10 days after maximum
shows that the spectroscopic diversity of SNe Ia is multi-dimensional. There is
a substantial range of blueshifts at a given value of the depth ratio. We also
find that the spectra of a sample of SNe Ia obtained a week before maximum
brightness can be arranged in a ``blueshift sequence'' that mimics the time
evolution of the pre-maximum-light spectra of an individual SN Ia, the well
observed SN 1994D. Within the context of current SN Ia explosion models, we
suggest that some of the SNe Ia in our sample were delayed-detonations while
others were plain deflagrations.Comment: accepted for publication in ApJ
Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models
We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D
hydro models: the very highly parameterized deflagration model W7, and two
delayed detonation models. We find that overall both models do about equally
well at fitting well observed SNe Ia near to maximum light. However, the Si II
6150 feature of W7 is systematically too fast, whereas for the delayed
detonation models it is also somewhat too fast, but significantly better than
that of W7. We find that a parameterized mixed model does the best job of
reproducing the Si II 6150 line near maximum light and we study the differences
in the models that lead to better fits to normal SNe Ia. We discuss what is
required of a hydro model to fit the spectra of observed SNe Ia near maximum
light.Comment: 29 pages, 14 figures, ApJ, in pres
Constraining the physical properties of Type II-P supernovae using nebular phase spectra
We present a study of the nebular phase spectra of a sample of Type
II-Plateau supernovae with identified progenitors or restrictive limits. The
evolution of line fluxes, shapes, and velocities are compared within the
sample, and interpreted by the use of a spectral synthesis code. The small
diversity within the dataset can be explained by strong mixing occurring during
the explosion, and by recognising that most lines have significant
contributions from primordial metals in the H envelope, which dominates the
total ejecta mass in these type of objects. In particular, when using the [O I]
6300, 6364 Angstrom doublet for estimating the core mass of the star, care has
to be taken to account for emission from primordial O in the envelope. Finally,
a correlation between the H-alpha line width and the mass of 56Ni is presented,
suggesting that higher energy explosions are associated with higher 56Ni
production.Comment: 18 pages, 15 figures, accepted for publication in MNRA
SN 2002cv: A Heavily Obscured Type Ia Supernova
We present VRIJHK photometry, and optical and near-infrared spectroscopy, of
the heavily extinguished Type Ia supernova (SN) 2002cv, located in NGC 3190,
which is also the parent galaxy of the Type Ia SN 2002bo. SN 2002cv, not
visible in the blue, has a total visual extinction of 8.74 +- 0.21 mag. In
spite of this we were able to obtain the light curves between -10 and +207 days
from the maximum in the I band, and also to follow the spectral evolution,
deriving its key parameters. We found the peak I-band brightness to be Imax =
16.57 +- 0.10 mag, the maximum absolute I magnitude to be MmaxI = -18.79 +-
0.20, and the parameter dm15(B) specifying the width of the B-band light curve
to be 1.46 +- 0.17 mag. The latter was derived using the relations between this
parameter and dm40(I) and the time interval dtmax(I) between the two maxima in
the I-band light curve. As has been found for previously observed, highly
extinguished SNe Ia, a small value of 1.59 +- 0.07 was obtained here for the
ratio Rv of the total-to-selective extinction ratio for SN 2002cv, which
implies a small mean size for the grains along the line of sight toward us.
Since it was found for SN 2002bo a canonical value of 3.1, here we present a
clear evidence of different dust properties inside NGC 3190.Comment: 18 pages, 18 figures. Accepted for publication in MNRAS. Added
co-author
- …