It follows that SNe IIL might be the explosions of stars with less massive H envelopes that cannot support a plateau in their light curve. As the shocked envelope expands and cools, it recombines, releasing radiation at a roughly constant rate, thus producing a plateau in the light curve (e.g., Popov 1993 Kasen & Woosley 2009). Such stars have thick hydrogen envelopes that are ionized by the explosion shock wave. Red supergiants (RSGs) have been directly identified as the progenitors of Type IIP SNe for several events (see Smartt 2009 and Leonard 2011 for reviews on this topic and Fraser et al. Finally, Type IIn SNe display narrow lines in their spectra, indicative of interaction between the SN ejecta and a dense circum stellar medium. Two subclasses of SNe IIb have been proposed, related to the compact and extended nature of their progenitors (cIIb and eIIb Chevalier & Soderberg 2010). A third class of events, Type IIb, characterized by its spectral rather than its photometric properties, develops prominent He features at late times. Those showing a plateau in their light curve are known as Type IIP events, while those showing a linear decline from peak magnitude are classified as IIL (see Patat et al. Several subtypes of Type II SNe have been observed.

Type II supernovae (SNe) are widely recognized as the end stages of massive H-rich stars and represent the bulk of observed core-collapse SNe (see Filippenko 1997 for a review of SN classifications). As analysis of additional CCCP data goes on and larger samples are collected, demographic studies of core-collapse SNe will likely continue to provide new constraints on progenitor scenarios. We find a large plateau luminosity range for SNe IIP, while the plateau lengths seem rather uniform at approximately 100 days.

We do not find any intermediate light curves, implying that these subclasses are unlikely to reflect variance of continuous parameters, but rather might result from physically distinct progenitor systems, strengthening the suggestion of a binary origin for at least some stripped SNe. The last class is composed solely of Type IIb SNe which present similar light curve shapes to those of SNe Ib, suggesting, perhaps, similar progenitor channels. With the exception of interacting (Type IIn) SNe and rare events with long rise times, we find that most light curve shapes belong to one of three apparently distinct classes: plateau, slowly declining, and rapidly declining events. We present R-band light curves of Type II supernovae (SNe) from the Caltech Core-Collapse Project (CCCP). 1 Department of Particle Physics and Astrophysics, The Weizmann Institute of Science, Rehovot 76100, Israel Department of Astronomy, University of California, Berkeley, CA 94720-3411, USAģ Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802, USAĤ Department of Astronomy, San Diego State University, San Diego, CA 92182, USAĥ Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, CanadaĦ Las Cumbres Observatory Global Telescope Network, Santa Barbara, CA 93117, USAħ Department of Physics, University of California, Santa Barbara, CA 93106, USAĨ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USAĩ Department of Physics, University of Wisconsin, Madison, WI 53706, USAġ0 King's College, University of Cambridge, Cambridge CB2 1ST, UKġ1 12 Amos St, Ramat Chen, Ramat Gan 52233, Israelġ2 20 Chen St, Petach Tikvah 49520, Israelġ3 101 Dunster Street, Box 398, Cambridge, MA 02138, USA

Cccp project