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Astron. Astrophys. 359, 876-886 (2000)

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4. Epochs of maxima

For all 22 SNe Ia whose light curves were well-sampled around the peak (SNe 1989B, 1991T, 1991bg, 1992A, 1992bc, 1992bo, 1994D, 1995D, see Table 1 ; SN 1990N, Lira et al. 1998; SNe 1990af, 1992P, 1992al, 1992bh, 1992bp, 1992bs, 1993H, 1993O, 1993ag, Hamuy et al. 1996b; SNe 1994S, 1994ae, 1995E, 1995ac, 1995al, 1995bd, 1996X, Riess 1996, Riess et al. 1999) we determined the epochs of individual filter maxima. A general trend can be observed in Fig. 4, which presents the time of the filter maxima relative to the epoch of the maximum in B . The U band appears to rise faster than the B band, although the limited number of objects (4 supernovae) precludes any definitive statements. The V light curve clearly peaks some time after the B maximum for all observed SNe Ia. This behavior is more or less expected from models of an expanding cooling atmosphere (Arnett 1982), as indicated by the lines in Fig. 4. However, the behavior of the R and I band maxima do not agree with this simple model; for these bands, the light curve maxima are reached earlier than in a thermal model. The I histogram is very broad but for most objects the rise in I is clearly faster than in B . This trend is further continued in the JHK light curves which all peak before B (Elias et al. 1985, Leibundgut 1988, Meikle 2000). The early appearance of the peak in the infrared rules out the idea of an expanding, cooling sphere.

[FIGURE] Fig. 4. Histograms showing the times of the filter maxima from U to I and of the bolometric luminosity relative to the B maximum. The vertical lines show the time differences as expected for an expanding, adiabatic cooling sphere according to Arnett (1982).

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© European Southern Observatory (ESO) 2000

Online publication: July 13, 2000