56 Ni Mass in Type IIP SNe: Light Curves and Ha Luminosity Diagnostics A. Elmhamdi 1 , N.N. Chugai 2 , and I.J. Danziger 3 1 SISSA / ISAS , via Beirut 4, 34014 Trieste, Italy elmhamdi@sissa.it 2 Institute of Astronomy RAS, Pyatnitskaya 48, 109017 Moscow, Russia 3 Osservatorio Astronomico di Trieste, Via G.B.Tiepolo 11, 34131 Trieste, Italy Summary. We analyze late-time observations, available photometry and spectra, of a sample of type II plateau supernovae (SNe IIP). The possibility of using Ha luminosity at the nebular epoch as a tracer of 56 Ni mass in this class of objects is in- vestigated, yielding a consistency with the photometry-based estimates within 20%. Interesting correlations are found and their impacts on our present understanding of the physics of core collapse SNe are discussed. 1 Results and Discussion The study of SNe IIP (i.e., optical properties, asymmetry, clumping, nu- cleosynthesis and yields) provides constraints on the explosion models and pre-supernova parameters. In particular, the 56 Ni mass is one of the crucial parameters since it presumably depends on the presupernova structure and the explosion model [1]. We select a sample of type IIP SNe on the basis of available photometry and spectra, especially at latter epochs. In Fig. l(left) we display the absolute V—light curves of the SNe sample together with that of SN 1987A. We adopt unique distance determination methodology, namely using the recession ve- locity of the host galaxy corrected for Local Group in fall onto the Virgo Cluster and assuming a Hubble constant Ho=70 km s _1 Mpc _1 . Galactic ex- tinction is removed using the map of galactic dust extinction by Schlegel et al. [7], while the host galaxy reddening is estimated from the "B — V" and "V — i?" color excess compared to the intrinsic color curves of SN 1987A. This is based on the fact that at the late photospheric phase, through the end of the recombination phase, SNe IIP seem to follow color evolution similar to SN 1987A [8]. The computed late time decline slopes, in the 150 — 400 d time range, are consistent with the radioactive decay of 56 Co and consequent trapping of the gamma-rays. Indeed a mean value of about < 7 V > ~ 0.99 (±0.13) for the sample SNe is measured. Once we fix the points related to the extinction and distance, which are crucial when dealing with a SN-sample study, we proceed with computing the amounts of ejected 56 Ni using the absolute V—light curve of SN 1987A terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0252921100009337 Downloaded from https://www.cambridge.org/core. IP address: 54.162.69.248, on 23 May 2020 at 23:25:20, subject to the Cambridge Core