Revisiting the Lick Observatory Supernova Search Volume-limited Sample: Updated Classifications and Revised Stripped-envelope Supernova Fractions

Abstract

We re-examine the classifications of supernovae (SNe) presented in the Lick Observatory Supernova Search (LOSS) volume-limited sample with a focus on the stripped-envelope SNe. The LOSS volumelimited sample, presented by Leaman et al. (2011) andLi et al. (2011b), was calibrated to provide meaningful measurements of SN rates in the local universe; the results presented therein continue to be used for comparisons to theoretical and modeling efforts. Many of the objects from the LOSS sample were originally classified based upon only a small subset of the data now available, however, and recent studies have both updated some subtype distinctions and improved our ability to perform robust classifications, especially for stripped-envelope SNe. We re-examine the spectroscopic classifications of all events in the LOSS volume-limited sample (180 SNe and SN impostors) and update them if necessary. We discuss the populations of rare objects in our sample including broad-lined Type Ic SNe, Ca-rich SNe, SN 1987A-like events (we identify SN 2005io as SN 1987A-like here for the first time), and peculiar subtypes. The relative fractions of Type Ia SNe, Type II SNe, and stripped-envelope SNe in the local universe are not affected, but those of some subtypes are. Most significantly, after discussing the often unclear boundary between SNe Ib and Ic when only noisy spectra are available, we find a higher SN Ib fraction and a lower SN Ic fraction than calculated by Li et al. (2011b): spectroscopically normal SNe Ib occur in the local universe 1.7 ± 0.9 times more often than do normal SNe Ic.

Measuring the Properties of Dark Energy with Photometrically Classified Pan-STARRS Supernovae. I. Systematic Uncertainty from Core-collapse Supernova Contamination

“…This change could reduce the Hubble residual discrepancy by half or more. However, Shivvers et al (2017) determined these rates by reclassifying a number of LOSS SNe Ic as SNe Ib, which in turn means that the SN Ib LF should be made fainter. Making the SN Ib LF fainter will increase the discrepancy in Hubble residuals.…”

The Carnegie Supernova Project I

“…If Hα was prominent while He i was either weak or absent, a SN IIb classification was preferred, while weak Hα and conspicuous He i absorption yielded a SN Ib subtyping. However, these criteria can be misleading, as they are highly dependent on the temporal phase of the earliest spectrum used to make the classification (Stritzinger et al 2009;Chornock et al 2011;Milisavljevic et al 2013;Shivvers et al 2017). For example, it is possible that an object classified as a SN Ib based on a spectrum taken at maximum brightness or even two weeks earlier could have appeared as a SN IIb soon after explosion.…”

“…Contemporary estimates from a volume-limited sample obtained during the Lick Observatory Supernova Search (LOSS; Filippenko et al 2001;Filippenko 2005) with the Katzman Automatic Imaging Telescope suggest that SE SNe account for ∼26% of the overall SN rate in the local Universe . The presence of residual hydrogen and helium maintained by the progenitor at the time of explosion, and how it manifests itself in the optical spectrum of the SN, provides the basis for today's spectral classification scheme of SE SNe (see, e.g., Filippenko 1997;Gal-Yam 2016;Liu et al 2017;Modjaz et al 2016;Shivvers et al 2017;Prentice & Mazzali 2017). Based mostly on historical observations, the current classification system has become somewhat ambiguous with the advent of detailed spectroscopic follow-up campaigns of low-redshift objects.…”

The Evolution of the Type Ia Supernova Luminosity Function

“…The resulting sample is complete for SNeIa out to 80 Mpc. The SNe in this volume-limited sample were recently reclassified, based on additional data and an updated understanding of SN physics, but SNeIa were unaffected (Graur et al 2017a(Graur et al , 2017bShivvers et al 2017).…”