The colour-lightcurve shape relation of type Ia supernovae and the reddening law
Abstract
Aims: We present a study of the time sequence of optical colours of a large sample of nearby type Ia supernovae (SNe Ia). We study the dependence of the colour time-evolution on the lightcurve shape, parametrized by the stretch factor.
Methods: We determine the spectral template that minimizes the dispersion in the colours of SNe Ia, measured by UBVRI photometry of nearby supernovae.
Results: A clear colour dependence upon lightcurve shape is found, such that the narrower lightcurves are redder up to about one month past lightcurve maximum. After correcting for lightcurve-shape differences in intrinsic colour, we derive an average reddening law, that is well described by a Cardelli, Clayton & Mathis law with RV = 1.75 ± 0.27 for 80 type Ia supernovae with E(B-V) ≤ 0.7 mag. A subset of 69 SNe that have modest reddening, E(B-V) < 0.25 mag, gives a significantly smaller value, RV ~ 1, which suggests that the observed reddening of type Ia supernovae may have a more complex origin, perhaps associated with other processes besides extinction by interstellar dust inside the host galaxy.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- August 2008
- DOI:
- 10.1051/0004-6361:20079292
- arXiv:
- arXiv:0712.1155
- Bibcode:
- 2008A&A...487...19N
- Keywords:
-
- stars: supernovae: general;
- ISM: dust;
- extinction;
- methods: statistical;
- Astrophysics
- E-Print:
- Major revision of the text. Accepted for publication in A&