3 research outputs found
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
Using Quantitative Spectroscopic Analysis to Determine the Properties and Distances of Type II-Plateau Supernovae: SNe 2005cs and 2006bp
We analyze the Type II Plateau supernovae (SN II-P) 2005cs and 2006bp with
the non-LTE model atmosphere code CMFGEN. We fit 13 spectra in the first month
for SN 2005cs and 18 for SN 2006bp. {\sl Swift} ultraviolet photometry and
ground-based optical photometry calibrate each spectrum. Our analysis shows
both objects were discovered less than 3 days after they exploded, making these
the earliest SN II-P spectra ever studied. They reveal broad and very weak
lines from highly-ionized fast ejecta with an extremely steep density profile.
We identify He{\sc ii} 4686\AA emission in the SN 2006bp ejecta. Days later,
the spectra resemble the prototypical Type II-P SN 1999em, which had a
supergiant-like photospheric composition. Despite the association of SN 2005cs
with possible X-ray emission, the emergent UV and optical light comes from the
photosphere, not from circumstellar emission.
We surmise that the very steep density fall-off we infer at early times may
be a fossil of the combined actions of the shock wave passage and radiation
driving at shock breakout. Based on tailored CMFGEN models, the direct-fitting
technique and the Expanding Photosphere Method both yield distances and
explosion times that agree within a few percent. We derive a distance to NGC
5194, the host of SN 2005cs, of 8.90.5 Mpc and 17.50.8 Mpc for SN
2006bp in NGC 3953. The luminosity of SN 2006bp is 1.5 times that of SN 1999em,
and 6 times that of SN 2005cs. Reliable distances to Type II-P supernovae that
do not depend on a small range in luminosity provide an independent route to
the Hubble Constant and improved constraints on other cosmological parameters.Comment: 27 pages, 16 figures, 11 tables, accepted to ApJ, high-resolution of
the paper available at
http://hermes.as.arizona.edu/~luc/snIIP/sn05cs_06bp.ps.g
SN 2005cs in M51 II. Complete Evolution in the Optical and the Near-Infrared
We present the results of the one year long observational campaign of the
type II-plateau SN 2005cs, which exploded in the nearby spiral galaxy M51 (the
Whirlpool Galaxy). This extensive dataset makes SN 2005cs the best observed
low-luminosity, 56Ni-poor type II-plateau event so far and one of the best
core-collapse supernovae ever. The optical and near-infrared spectra show
narrow P-Cygni lines characteristic of this SN family, which are indicative of
a very low expansion velocity (about 1000 km/s) of the ejected material. The
optical light curves cover both the plateau phase and the late-time radioactive
tail, until about 380 days after core-collapse. Numerous unfiltered
observations obtained by amateur astronomers give us the rare opportunity to
monitor the fast rise to maximum light, lasting about 2 days. In addition to
optical observations, we also present near-infrared light curves that (together
with already published UV observations) allow us to construct for the first
time a reliable bolometric light curve for an object of this class. Finally,
comparing the observed data with those derived from a semi-analytic model, we
infer for SN 2005cs a 56Ni mass of about 0.003 solar masses, a total ejected
mass of 8-13 solar masses and an explosion energy of about 3 x 10^50 erg.Comment: 18 pages, 18 figures, accepted for publication in MNRA