[vsnet-chat 967] Recent SNe light curves

[Yamaoka Hitoshi <yamaoka@rc.kyushu-u.ac.jp>]

Dear SN observers and all,

  Happyly, we have already three bright SNe in this half year. 
I wish to try an exercise with your reported observations. 

a) There has been a research about the correlation between the 
maximum luminosity of SN Ia and its decline rate just after the 
maximum.  The faster decliner is the dimmer, and the slower one 
is the brighter.  Now I take the days from the maximum to become 
1.5 mag fainter as an indicater of the decline rate. Two bright 
SNe Ia are: (data was taken from Kato's daily average)

1998aq peak 04/28.567 12.105 
       +1.5 05/23.603 13.574 -- about 25 days

1998bu peak 05/20.461 11.716 
       +1.5 ??

1998aq seems to be a typical SN Ia at the Virgo distance.  
Besides, SN 1998bu seems to be rather dimmer one (m-M of the 
host galaxy is about 1.6 mag smaller than that of 1998aq, and 
even considering the absorption A_V ~ 0.6 mag).  The following 
magnitude estimate of SN 1998bu will clear up the correlation.


b) After the maximum, SNe will decline fast for the first, and 
later it will become rather slow decline (linear phase).  The 
decline rate of linear phase is the important indicator of the 
ejected mass, and the distribution of the energy source 
(nucleosynthesized 56Ni).  
  SN 1998S was classified as of type II-n, but its nature has 
not become clear.  If the ejected mass is about 1 solar mass, 
the decline in linear phase would be similar to that of SNeIb/c. 
Otherwise, if the light curve is similar to that of SNeIa, its 
nature is very uncertain.  Note that 1998S was very bright. The 
peak magnitude is acceptable if 1998S is of type Ia.
  The decline rate of SN 1998S derived from Kato's average,

             1998S(II-n)  1998aq(Ia) 
max - +10d    0.564        0.397
+10d- +20d    0.546        0.507
+20d- +30d    0.195        ---
+30d- +40e    0.375
+40d- +50d    0.642
+50d- +60d    0.519

There is no comparison (well observed visually) light curves, (sorry 
I am now in home, not office) but its appearance resembles to that of
1998aq.  Comparison in the linear phase expects to solve the nature of
this peculier SN.  

After all, the magnitude estimate after maximum is also important 
and useful data.  If you are interested, please keep your eyes 
also on the SNe.

Sincerely Yours,
Hitoshi Yamaoka, Kyushu Univ., Japan

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