Preliminary Evidence for Universality in (V-K)(t) in Type Ia SNe, and Implications for Host Galaxy Extinction Determination

Details Preliminary Evidence for Universality in (V-K)(t) in Type Ia SNe, and Implications for Host Galaxy Extinction Determination Preliminary Evidence for Universality in (V-K)(t) in Type Ia SNe, and Implications for Host Galaxy Extinction Determination

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aas...195.3803k&link_type=abstract

American Astronomical Society, 195th AAS Meeting, #38.03; Bulletin of the American Astronomical Society, Vol. 31, p.1424

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We present optical photometry of seven Type Ia supernovae: SNe 1998es, 1999aa, 1999cc, 1999cl, 1999cp, 1999da, and 1999dk. We also obtained near infrared photometry of three of these. A more direct route to determining AV (and hence the correct distance to a host glaxy) is to use the V-K color excess rather than E(B-V). One often assumes that the unreddened B-V color of a Type Ia SN is 0.00 at the time of B-band maximum, so the observed B-V color at that time is taken as the color excess. This is not true for all Type Ia SNe, especially the rapidly declining ones. [The maximum brightness and rate of decline of Type Ia SNe can be characterized by the parameter Δ (Riess, Press, & Kirshner 1996; Riess et al. 1998, Appendix). More luminous (Δ < 0) SNe are slow decliners. Less luminous (Δ > 0) SNe are faster decliners.] The B-V color excess of Type Ia SNe can also be determined from the photometry between 30 and 90 days after light maximum (Phillips et al. 1999, astro-ph/9907052). We find that the V-K color near light maximum for Type Ia SNe unreddened in their host galaxies (SNe 1999cp, 1980N, 1981B, 1981D, and 1983R) implies a ``universal'' pair of linear relationships that intersect at 6 days after maximum. If we let t be the number of days since B-band maximum, for -10 <= t <= +6, V-K = -0.68 - 0.055 ; t, while for +6 <= t <= +25, V-K = -1.51 + 0.075 ; t. The RMS deviation of the fits is +/- 0.1 mag. This is based on SNe with -0.2 <= Δ <= 0.2 which have been corrected for small amounts of reddening in our Galaxy (Schlegel, Finkbeiner, & Davis 1998). Perhaps there are families of V-K curves as a function of Δ . Since AV 3.1 E(B-V) scales any error in E(B-V) by a factor of three, while AV 1.13 E(V-K), AV might be more easily determined from the V-band light curve of a Type Ia SN (which can be easily interpolated) and a small amount of K-band data obtained near maximum light.

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