7 research outputs found
The Berkeley Sample of Stripped-Envelope Supernovae
We present the complete sample of stripped-envelope supernova (SN) spectra
observed by the Lick Observatory Supernova Search (LOSS) collaboration over the
last three decades: 888 spectra of 302 SNe, 652 published here for the first
time, with 384 spectra (of 92 SNe) having photometrically-determined phases.
After correcting for redshift and Milky Way dust reddening and reevaluating the
spectroscopic classifications for each SN, we construct mean spectra of the
three major spectral subtypes (Types IIb, Ib, and Ic) binned by phase. We
compare measures of line strengths and widths made from this sample to the
results of previous efforts, confirming that O I {\lambda}7774 absorption is
stronger and found at higher velocity in Type Ic SNe than in Types Ib or IIb
SNe in the first 30 days after peak brightness, though the widths of nebular
emission lines are consistent across subtypes. We also highlight newly
available observations for a few rare subpopulations of interest.Comment: 13 pages; 14 figures; 3 tables. Accepted for publication in MNRA
Berkeley Supernova Ia Program I: Observations, Data Reduction, and Spectroscopic Sample of 582 Low-Redshift Type Ia Supernovae
In this first paper in a series we present 1298 low-redshift (z\leq0.2)
optical spectra of 582 Type Ia supernovae (SNe Ia) observed from 1989 through
2008 as part of the Berkeley SN Ia Program (BSNIP). 584 spectra of 199 SNe Ia
have well-calibrated light curves with measured distance moduli, and many of
the spectra have been corrected for host-galaxy contamination. Most of the data
were obtained using the Kast double spectrograph mounted on the Shane 3 m
telescope at Lick Observatory and have a typical wavelength range of
3300-10,400 Ang., roughly twice as wide as spectra from most previously
published datasets. We present our observing and reduction procedures, and we
describe the resulting SN Database (SNDB), which will be an online, public,
searchable database containing all of our fully reduced spectra and companion
photometry. In addition, we discuss our spectral classification scheme (using
the SuperNova IDentification code, SNID; Blondin & Tonry 2007), utilising our
newly constructed set of SNID spectral templates. These templates allow us to
accurately classify our entire dataset, and by doing so we are able to
reclassify a handful of objects as bona fide SNe Ia and a few other objects as
members of some of the peculiar SN Ia subtypes. In fact, our dataset includes
spectra of nearly 90 spectroscopically peculiar SNe Ia. We also present
spectroscopic host-galaxy redshifts of some SNe Ia where these values were
previously unknown. [Abridged]Comment: 34 pages, 11 figures, 11 tables, revised version, re-submitted to
MNRAS. Spectra will be released in January 2013. The SN Database homepage
(http://hercules.berkeley.edu/database/index_public.html) contains the full
tables, plots of all spectra, and our new SNID template
The Peculiar SN 2005hk: Do Some Type Ia Supernovae Explode as Deflagrations?
We present extensive u'g'r'i'BVRIYJHKs photometry and optical spectroscopy of
SN 2005hk. These data reveal that SN 2005hk was nearly identical in its
observed properties to SN 2002cx, which has been called ``the most peculiar
known type Ia supernova.'' Both supernovae exhibited high ionization SN
1991T-like pre-maximum spectra, yet low peak luminosities like SN 1991bg. The
spectra reveal that SN 2005hk, like SN 2002cx, exhibited expansion velocities
that were roughly half those of typical type Ia supernovae. The R and I light
curves of both supernovae were also peculiar in not displaying the secondary
maximum observed for normal type Ia supernovae. Our YJH photometry of SN 2005hk
reveals the same peculiarity in the near-infrared. By combining our optical and
near-infrared photometry of SN 2005hk with published ultraviolet light curves
obtained with the Swift satellite, we are able to construct a bolometric light
curve from ~10 days before to ~60 days after B maximum. The shape and unusually
low peak luminosity of this light curve, plus the low expansion velocities and
absence of a secondary maximum at red and near-infrared wavelengths, are all in
reasonable agreement with model calculations of a 3D deflagration which
produces ~0.25 M_sun of 56Ni.Comment: Accepted by PASP, to appear in April 2007 issue, 63 pages, 16
figures, 11 table
A non-spherical core in the explosion of supernova SN 2004dj
An important and perhaps critical clue to the mechanism driving the explosion
of massive stars as supernovae is provided by the accumulating evidence for
asymmetry in the explosion. Indirect evidence comes from high pulsar
velocities, associations of supernovae with long-soft gamma-ray bursts, and
asymmetries in late-time emission-line profiles. Spectropolarimetry provides a
direct probe of young supernova geometry, with higher polarization generally
indicating a greater departure from spherical symmetry. Large polarizations
have been measured for 'stripped-envelope' (that is, type Ic) supernovae, which
confirms their non-spherical morphology; but the explosions of massive stars
with intact hydrogen envelopes (type II-P supernovae) have shown only weak
polarizations at the early times observed. Here we report multi-epoch
spectropolarimetry of a classic type II-P supernova that reveals the abrupt
appearance of significant polarization when the inner core is first exposed in
the thinning ejecta (~90 days after explosion). We infer a departure from
spherical symmetry of at least 30 per cent for the inner ejecta. Combined with
earlier results, this suggests that a strongly non-spherical explosion may be a
generic feature of core-collapse supernovae of all types, where the asphericity
in type II-P supernovae is cloaked at early times by the massive, opaque,
hydrogen envelope.Comment: Accepted for publication by Nature (results embargoed until 23 March
2006); 14 pages, 2 figure
Berkeley sample of stripped-envelope supernovae
We present the complete sample of stripped-envelope supernova (SN) spectra observed by the Lick Observatory Supernova Search (LOSS) collaboration over the last three decades: 888 spectra of 302 SNe, 652 published here for the first time, with 384 spectra (of 92 SNe) having photometrically determined phases. After correcting for redshift and Milky Way dust reddening and reevaluating the spectroscopic classifications for each SN, we construct mean spectra of the three major spectral subtypes (Types IIb, Ib, and Ic) binned by phase. We compare measures of line strengths and widths made from this sample to the results of previous efforts, confirming that O I λ7774 absorption is stronger and found at higher velocity in Type Ic SNe than in Types Ib or IIb SNe in the first ∼30 days after peak brightness, though the widths of nebular emission lines are consistent across subtypes. We also highlight newly available observations for a few rare subpopulations of interest