The Luminosity of SN 1999by in NGC 2841 and the Nature of `Peculiar' Type Ia Supernovae

Preprint
Publisher Website
Google Scholar
Abstract
We present UBVRI photometry and optical spectroscopy of the `peculiar' type Ia supernova 1999by in NGC 2841. The observations began six days before visual maximum light which is well-defined by daily observations. The light curves and spectra are similar to the prototypical subluminous event SN 1991bg. We find that maximum light in B occurred on 1999 May 10.3 UT (JD 24501308.8+/-0.3) with B=13.66+/-0.02 and a color of B_max-V_max=0.51+/-0.03. The late-time color implies minimal dust extinction from the host galaxy. Our photometry when combined with the recent Cepheid distance to NGC 2841 (Macri et al. 2001) gives a peak absolute magnitude of M_B=-17.15+/-0.23, making SN 1999by one of the least luminous type Ia events ever observed. We estimate a decline-rate parameter of dm15(B)=1.90, versus 1.93 for SN 1991bg where 1.10 is typical for 'normal' events. We compare SN 1999by with other subluminous events and find that B_max-V_max color correlates strongly with decline rate and may be a more sensitive indicator of luminosity than fading rate for these objects. We find a good correlation between luminosity and the depth of the spectral feature at 580 nm, which had been attributed to Si II. We show that in cooler photospheres the 580 nm feature is dominated by Ti II which provides a simple physical explanation for the correlation. Using only subluminous type Ia supernovae we derive a Hubble parameter of H_0=75 +12/-11 km/s/Mpc, consistent with values found from brighter events.

This publication has 0 references indexed in Scilit: