Ouda highlight (IP Peg) OUDA HIGHLIGHT -- a step to mapping the accretion disk during a dwarf nova outburst

   The only SS Cyg-type dwarf nova which show eclipses of the white dwarf,
   IP Peg, was quite fortunately caught during its rise to an outburst
   by a VSOLJ visual observer.  Thanks to his alert, we (T. Kato and
   C. Kunjaya) were able to get excellent coverage of an eclipse which
   occurred only 30 minutes(!) after the alert.  The light curve showed
   a totality of three minutes, indicating the accretion disk was not
   fully grown at the time of the observation.  During subsequent nights,
   the development of the accretion disk has been followed with high
   precision.  The preliminary results may be summaried as below:

               start         center    prediction       end
                                        (Yamada)
             JST   mag     JST    mag      JST        JST    mag
                                                                    duration
 ----------------------------------------------------------------------------
  Jan.11   19h34m  13.1   19h53m  15.3    19h54m    20h18m   13.1
             -19m   2.2                               +25m    2.2     44m

  Jan.12   18h20m- 13.0   18h41m  14.7    18h41m    19h05m   12.7
             -21m-  1.7                               +24m    2.0     45m+

  Jan.14   19h35m: 12.3   20h01m  13.9    20h02m    20h36m   12.2
             -26m:  1.6                               +35m    1.7     61m:

  Jan.15   18h29m  12.5   18h49m  14.1    18h50m    19h17m   12.4
             -20m   1.6                               +28m    1.7     48m

  Jan.16   -- --    ---   -- --    ---    17h37m    18h02m   12.4
                                                      +25m    ---     ---
 ----------------------------------------------------------------------------

   The observations indicate that the accretion disk expanded between Jan. 12
   and 14, then followed by a rapid shrinkage.  Comparison of the eclipse
   duration (disk size) and the system magnitude roughly indicate that the
   temperture or the energy distribution on the disk dramatically changed
   before and after the peak luminosiy.  This observation may serve a unique
   opportunity for verification of the theory of the dwarf nova outbursts. //