No abstract

We have compiled a sample of 45 Type Ia supernovae (SNe Ia) discovered by the Lick Observatory Supernova Search (LOSS) and the Beijing Astronomical Observatory Supernova Survey (BAOSS), and determined the rate of spectroscopically peculiar SNe Ia (i.e., SN 1986G-like, SN 1991bg-like, and SN 1991T-like objects) and the luminosity function of SNe Ia. Because of the nature of the two surveys (distance-limited with small baselines and deep limiting magnitudes), nearly all SNe Ia have been discovered in the sample galaxies of LOSS and BAOSS; thus, the observed peculiarity rate and luminosity function of SNe Ia are intrinsic. We find that 36±9% of nearby SNe Ia are peculiar; specifically, the luminosity function of SNe Ia consists of 20% SN 1991T-like, 64% normal, and 16% SN 1991bg-like objects. We have compared our results to those found by earlier studies, and to those found at high redshift. The apparent dearth of SN 1991T-like objects at high redshift may be due to extinction, and especially to the difficulty of recognizing them from spectra obtained past maximum brightness or from spectra with low signal-to-noise ratios. Implications of the high peculiarity rate for the progenitor systems of SNe Ia are also briefly discussed.

No abstract

We report on SN 1997bs in NGC 3627 (M66), the Ðrst supernova discovered by the Lick Observatory Supernova Search using the 0.75 m Katzman Automatic Imaging Telescope (KAIT). Based on its early-time optical spectrum, SN 1997bs was classiÐed as Type IIn. However, from the BV RI light curves obtained by KAIT early in the supernovaÏs evolution, and F555W and F814W light curves obtained from Hubble Space T elescope archival WFPC2 images at late times, we question the identiÐcation of SN 1997bs as a bona Ðde supernova. We believe that it is more likely a superoutburst of a very massive luminous blue variable star, analogous to

No abstract

We present 30 optical spectra and 49 photometric epochs sampling the first 517 days after discovery of supernova (SN) 1999em, and derive its distance through the expanding photosphere method (EPM). SN 1999em is shown to be a Type II-plateau (II-P) event, with a photometric plateau lasting until about 100 days after explosion. We identify the dominant ions responsible for most of the absorption features seen in the optical portion of the spectrum during the plateau phase. Using the weakest unblended absorption features to estimate photospheric velocity, we find the distance to SN 1999em to be D = 8.2 +0.6 −0.6 Mpc, with an explosion date of HJD 2, 451, 475.6 ± 1.4, or 5.3 ± 1.4 days before discovery. We show that this distance estimate is about 10% closer than the distance that results if the strong Fe II λλ4924, 5018, 5169 absorption features, -2which have often been used in previous EPM studies, are used to estimate photospheric velocity.We examine potential sources of systematic error in EPM-derived distances, and find the most significant to result from uncertainty in the theoretical modeling of the flux distribution emitted by the SN photosphere (i.e., the "flux dilution factor"). We compare previously derived EPM distances to 8 SNe II in galaxies (or members of the same group) for which a recently revised Cepheid distance exists from the HST Key Project and find D Cepheids /D EPM = 0.87 ± 0.06 (statistical); eliminating the 3 SNe II distances for which a Cepheid distance only exists to a group member, and not the host galaxy itself, yields D Cepheids /D EPM = 0.96 ± 0.09. Additional direct comparisons, especially to spectroscopically and photometrically normal SNe II-P, will certainly help to produce a more robust comparison.Finally, we investigate the possible use of SNe II-P as standard candles and find that for 8 photometrically confirmed SNe II-P with previously derived EPM distances and SN 1999em, the mean plateau absolute brightness is M V (plateau) = −16.4 ± 0.6 mag, implying that distances good to ∼ 30% (1σ) may be possible without the need for a complete EPM analysis. At M V (plateau) = −15.9 ± 0.2 mag, SN 1999em is somewhat fainter than the average SN II-P. The general consistency of absolute SNe II-P brightness during the plateau suggests that the standard candle assumption may allow SNe II-P to be viable cosmological beacons at z > 2.Subject headings: cosmology: observations -distance scale -galaxies: individual (NGC 1637) -supernovae: individual (SN 1999em) 13 "L" for their linearly declining light curves, lacking a plateau; these events are generally believed to result from progenitors that have lost a substantial fraction of their hydrogen envelope prior to exploding (e.g., Filippenko 1997).

We present extensive photometric and spectroscopic observations of the Type Ia supernova (SN Ia) 2000cx in the S0 galaxy NGC 524, which reveal it to be peculiar. Photometrically, SN 2000cx is different from all known SNe Ia, and its light curves cannot be fit well by the fitting techniques currently available. There is an apparent asymmetry in the $B$-band peak, in which the premaximum brightening is relatively fast (similar to that of the normal SN 1994D), but the postmaximum decline is relatively slow (similar to that of the overluminous SN 1991T). The color evolution of SN 2000cx is also peculiar: the $(B - V)_0$ color has a unique plateau phase and the $(V - R)_0$ and $(V - I)_0$ colors are very blue. Although the premaximum spectra of SN 2000cx are similar to those of SN 1991T-like objects (with weak Si II lines), its overall spectral evolution is quite different. The Si II lines that emerged near maximum $B$-band brightness stay strong in SN 2000cx until about three weeks past maximum. The change in the excitation stages of iron-peak elements is slow. Both the iron-peak and the intermediate-mass elements are found to be moving at very high expansion velocities in the ejecta of SN 2000cx. We discuss theoretical models for SN 2000cx. SN 2000cx may be an overluminous object like SN 1991T, but with a larger yield of $^{56}$Ni and a higher kinetic energy in the ejecta. We also briefly discuss the implications of our observations for the luminosity vs. light-curve width relation.Comment: Accepted to be published in the Oct issue of PAS

We present optical photometry for the type Ic SN 1994I in M51 (NGC 5194) from UT March 31 to Aug 6, 1994, starting eight days before B-band maximum and ending three months later. We estimate the extinction to SN 1994I was considerable and quite uncertain, A V = 1:4 0:5 mag, making a detailed comparison to other supernovae di cult. Using a distance modulus = 29:6 0:3 mag to M51, we calculate absolute magnitudes and a quasi-bolometric light curve for the supernova. It appears that SN 1994I was less luminous than \normal" type Ia SNe. There is strong evidence that the ejecta of SN 1994I were much less massive than those of other SNe.