1,403 research outputs found
Reading the Spectra of the Most Peculiar Type Ia Supernova 2002cx
In spite of the apparent lack of Si II and S II features in its spectra, SN
2002cx was classified as a peculiar Type Ia supernova (SN Ia) on the basis of
its overall photometric and spectroscopic behavior. Spectra obtained near
maximum light contained Fe III features, as in SN 1991T-like events, but the
blueshifts of the Fe III absorptions were exceptionally low. The luminosity
also was low. We use the supernova synthetic--spectrum code SYNOW to study line
identifications in SN 2002cx. We find that the maximum-light spectra appear to
contain weak features of Si II, S II, Si III, and Ca II, which strengthens the
connection with SN 1991T-like events. We show that later spectra, obtained 12,
25, and 56 days after maximum, consist of P-Cygni resonance-scattering features
due to permitted Fe II and Co II lines. SN 2002cx had been thought to have made
the transition from a permitted-line to a forbidden-line spectrum between 25
and 56 days. Owing to the low expansion velocities the postmaximum spectral
features are narrower and easier to identify than they are in other SNe Ia. SN
2002cx will lead to improved line identifications in other SNe Ia and clarify
when the transition from a permitted-line to a forbidden-line spectrum occurs.
In the context of current SN Ia explosion models, we suggest that the
properties of SN 2002cx may be consistent with 3D deflagration models, which
are not favored for normal SNe Ia.Comment: 21 pages including 7 figures and 4 tables; accepted by PAS
The Progenitors of Recent Core-Collapse Supernovae
We present the results of our analysis of Hubble Space Telescope (HST) and deep ground-based images to isolate the massive progenitor stars of the two recent core-collapse supernovae 2008 bk and 2008 cn. The identification of the progenitors is facilitated in one of these two cases by high-precision astrometry based on our HST imaging of SNe at late times
Preliminary Spectral Analysis of SN 1994I
We present optical spectra of the Type Ic supernova 1994I in M51 and
preliminary non-LTE analysis of the spectra. Our models are not inconsistent
with the explosions of C+O cores of massive stars. While we find no direct
evidence for helium in the optical spectra, our models cannot rule out small
amounts of helium. More than 0.1~\msol\ of helium seems unlikely.Comment: LaTeX, MN style, psfig, and natbib substyles, 7 pages, 4 figures, to
appear in MNRAS. Postscript file available from
http://www.nhn.uoknor.edu/~baro
GRB 021004: A Possible Shell Nebula around a Wolf-Rayet Star Gamma-Ray Burst Progenitor
The rapid localization of GRB 021004 by the HETE-2 satellite allowed nearly
continuous monitoring of its early optical afterglow decay, as well as
high-quality optical spectra that determined a redshift of z=2.328 for its
host, an active starburst galaxy with strong Lyman-alpha emission and several
absorption lines. Spectral observations show multiple absorbers blueshifted by
up to 3,155 km/s relative to the host galaxy Lyman-alpha emission.We argue that
these correspond to a fragmented shell nebula, gradually enriched by a
Wolf-Rayet wind over the lifetime of a massive progenitor bubble. In this
scenario, the absorbers can be explained by circumstellar material that have
been radiatively accelerated by the GRB emission. Dynamical and photoionization
models are used to provide constraints on the radiative acceleration from the
early afterglow.Comment: 5 pages, 3 figures, to appear in the proceedings of the 2003 GRB
Conferenc
Supernova Environments in Hubble Space Telescope Images
The locations of supernovae in the local stellar and gaseous environment in galaxies contain important clues to their progenitor stars. Access to this information, however, has been hampered by the limited resolution achieved by ground-based observations. High spatial resolution Hubble Space Telescope (HST) images of galaxy fields in which supernovae had been observed can improve the situation considerably. We have examined the immediate environments of a few dozen supernovae using archival post-refurbishment HST images. Although our analysis is limited due to signal-to-noise ratio and filter bandpass considerations, the images allow us for the first time to resolve individual stars in, and to derive detailed color-magnitude diagrams for, several environments. We are able to place more rigorous constraints on the masses of these supernovae. A search was made for late-time emission from supernovae in the archival images, and for the progenitor stars in presupernova images of the host galaxies. In particular, we highlight the results for the Type II SN 1979C in M100. In addition, we have identified the progenitor of the Type IIn SN 1997bs in NGC 3627. We also add to the statistical inferences that can be made from studying the association of SNe with recent star-forming regions
On The Progenitor of the Type II-Plateau Supernova 2003gd in Messier 74
HST WFPC2 archival F606W and F300W images obtained within one year prior to
the explosion of the nearby Type II supernova (SN) 2003gd in Messier 74 (NGC
628) have been analyzed to isolate the progenitor star. The SN site was located
using precise astrometry applied to the HST images. Two plausible candidates
are identified within 0.6" of the SN position in the F606W image. Neither
candidate was detected in the F300W image. SN 2003gd appears to be of Type
II-plateau (II-P), with age ~87 d on June 17 UT and with low reddening [E(B-V)
= 0.13 mag]. The most likely of the two progenitor candidates has M_V_0 ~ -3.5
mag (for an extinction-corrected distance modulus of 29.3 mag) and, based on
additional color information derived from a high-quality, archival ground-based
I-band image, we estimate that this star was a red supergiant with initial mass
M_ZAMS ~ 8 -- 9 Msun. This mass estimate is somewhat lower than, but relatively
consistent with, recent limits placed on the progenitor masses of other SNe
II-P, using HST data. Future HST imaging with the Advanced Camera for Surveys,
when the SN has faded considerably, will be extremely useful in pinpointing the
exact SN location and securing identification of the progenitor. If our
proposed candidate is confirmed, it will be only the sixth SN progenitor ever
directly identified.Comment: 10 pages, 6 figures, to appear now in PASP, 2003 Nov. This update
includes more detailed light and color curves for the S
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