Observed Type II supernova colours from the Carnegie Supernova Project-I

DESSART, L.; HSIAO, E.Y.; CONTRERAS, C.; HAMUY, M.; ANDERSON, J.P.; FILIPPENKO, A.V.; MORRELL, N.; SUNTZEFF, N.B.; FOLATELLI, G.; GUTIÉRREZ, C.P.; PHILLIPS, M.M.; STRITZINGER, M.D.; GALBANY, L.; GONZÁLEZ-GAITÁN, S.; DE JAEGER, T.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Año: 2018 vol. 476 p. 4592 - 4616

0035-8711

We present a study of observed Type II supernova (SN II) colours using optical/near-infrared photometric data from the Carnegie Supernovae Project-I. We analyse four colours (B - V, u - g, g - r, and g - Y) and find that SN II colour curves can be described by two linear regimes during the photospheric phase. The first (s, 1colour) is steeper and has a median duration of ~40 d. The second, shallower slope (s, 2colour) lasts until the end of the ´plateau´ (~80 d). The two slopes correlate in the sense that steeper initial colour curves also imply steeper colour curves at later phases. As suggested by recent studies, SNe II form a continuous population of objects from the colour point of view as well. We investigate correlations between the observed colours and a range of photometric and spectroscopic parameters including the absolute magnitude, the V-band light-curve slopes, and metal-line strengths. We find that less luminous SNe II appear redder, a trend that we argue is not driven by uncorrected hostgalaxy reddening. While there is significant dispersion, we find evidence that redder SNe II (mainly at early epochs) display stronger metal-line equivalent widths. Host-galaxy reddening does not appear to be a dominant parameter, neither driving observed trends nor dominating the dispersion in observed colours. Intrinsic SN II colours are most probably dominated by photospheric temperature differences, with progenitor metallicity possibly playing a minor role. Such temperature differences could be related to differences in progenitor radius, together with the presence or absence of circumstellar material close to the progenitor stars.