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Session 45 - Supernovae.
Display session, Tuesday, January 14
Metropolitan Ballroom,

[45.09] The Spectroscopically Peculiar Supernovae 1995ac and 1995bd: 91T and Beyond

P. M. Garnavich, A. G. Riess, R. P. Kirshner, P. Challis (CfA), R. M. Wagner (OSU)

The existence of a relation between light curve shape and absolute magnitude at maximum for Type Ia supernovae is well established. The vast majority of SNe Ia fall near the center of this relation and are spectroscopically homogeneous. SNe Ia with peculiar spectra are rare, but appear to define the extremes in the range of light curve shape. SN 1991T was observed to have the slowest decline rate after maximum. It displayed strong FeIII and unusually weak SiII 6355Å\ absorption lines in its early spectra.

We present spectra of supernovae 1995ac and 1995bd near maximum brightness obtained with the FLWO 1.5m Tillinghast telescope and the MMT. The redshifts of 1995ac and 1995bd are 0.050 and 0.016 respectively, as measured from the narrow emission lines from the host galaxies. Before maximum, the strongest absorption features are seen at 4200Å\ and 4900Åcorresponding primarily to blends of FeIII at rest wavelengths 4410Å\ and 5140ÅSiII 6355Å\ is extremely weak and broad with an equivalent width of 20 to 30Åwhile in normal SNe Ia the SiII EW exceeds 80ÅThe features are indistinguishable from those seen in 1991T, however the continuum slopes are less steep for 1995ac and 1995bd, probably due to dust absorption. SN 1995bd has a strong NaI interstellar absorption feature with an EW of 2Åimplying that it is heavily reddened.

The light curves of 1995ac and 1995bd were obtained using the FLWO 1.2m telescope and late-time observations taken with the WIYN 3.5m. The light curves are well sampled with over 20 epochs of observations in BVRI filters starting before maximum. As expected from its spectroscopic similarity to 1991T, 1995ac is a slow decliner. Our B light curve shows it falling only 0.9 mags in 15 days after maximum. In contrast, the B and V light curves of 1995bd around maximum are well fit by standard Leibundgut templates. Only after 20 days does the light curve deviate from the templates and show evidence for a slow decline. The differences in light curves between the members of this peculiar class of supernovae may have important implications for models of the Type-Ia explosion mechanism and for their use as distance indicators.

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