R. Kirshner and P. Challis, Harvard-Smithsonian Center for Astrophysics; P. Garnavich, University of Notre Dame; and the Supernova Intensive Study collaboration report that Hubble Space Telescope Wide Field/Planetary Camera-2 (WFPC2) images of the peculiar type-Ia SN 1999by were obtained Sept. 28 with the F555W filter and again on Dec. 10 in both the F555W and F439W filters: "The derived magnitude 580 days after maximum is V = 24.6 +/- 0.1, which when combined with earlier groundbased photometry indicates a decline rate in V of 0.0106 mag/day (250-600 days after maximum). This is significantly slower than the 0.0139 mag/day rate of SN 1992A (N. Suntzeff, private comm.) over the same interval after maximum light. The B-band decline rate of 0.0099 mag/day is also slow compared to that (0.0128 mag/day) for SN 1992A. The B-V color at day 580 is -0.4 +/- 0.2 and is extremely blue for a type-Ia event, which typically show B-V = 0 at late times (Milne et al. 1999, Ap.J. Suppl. 124, 503)."
International Astronomical Union Circular
- Pub Date:
- December 2000