COMMISSIONS 27 AND 42 OF THE IAU
              INFORMATION BULLETIN ON VARIABLE STARS
                           Number 4023

                                                     Konkoly Observatory
                                                     Budapest
                                                     11 May 1994

                                                     HU ISSN 0374 - 0676


              THE OBSERVATION OF SUPERHUMPS IN T LEONIS


  T Leo, a SU UMa type dwarf nova experienced a superoutburst in March 30 - April 9,
1994. Figure 1 shows the long term light curve around the superoutburst, characterized
by a sudden increase, subsequent gradual decrease and steep decline at the end of the
superoutburst. The abscissa is day count from the first day of the superoutburst (March
30,1994 0.00 UT). The big arrow indicates the epoch of our observation which was in the
midst of the superoutburst. The six smaller arrows indicate upper limits.
  We observed this star on April 4, 1994 using 576 x 384 pixels Thomson CCD camera
(TH7882CDA) attached to the Cassegrain focus of 60 cm reflector at Ouda Station, Kyoto
University (Ohtani et al., 1992). The mode of 2 x 2 on-chip summation, the V-band
filter designed to reproduce the Johnson V-band, and exposure time between 55 and 70
seconds were chosen to get a better time resolution but with sufficiently high counts. The
observation was done for four hours, covering almost three superhump periods within one
night, therefore no one-day alias problem arises in the period analysis.
  The reduction was done using the personal-computer-based aperture photometry package 
developed by one of the authors (T.K.). This package enables us to de-bias, apply flat
fielding and estimate the instrumental magnitudes automatically. The aperture size was
8" in radius and the sky level was determined from the pixels whose distance from the
individual objects are between 16" and 30". Table 1 gives the coordinates and magnitudes
of the comparison and check stars from Guide Star Catalog (GSC).
  The short term light curve of differential magnitude between the object and comparison
is shown in Figure 2. The constancy of comparison star was confirmed using nearby check
stars. No systematic variation larger than its corresponding photon statistic error (0.03m
for check star in a single frame) was found during the observation. The expected error
for one measurement of the differential magnitude between the object and comparison is
about 0.01m. One can clearly see the steep brightening and more gradual fading which are
characteristics of superhumps.
  The light curve was analyzed using PDM program within IRAF package (IRAF is
distributed by National Optical Astronomy Observatories, U.S.A.). Figure 3 shows the
Theta diagram, the abscissa is frequency per day. The lowest minimum point corresponds to
86.4 minutes period, the second lowest minimum corresponds to twice this period. For
the estimation of error, another period analysis was made. We smoothed the curve and
took the maxima, minima and the middle of rising and fading stages. From the distances
between two adjacent points with the same phase we get the periods. The average of the
periods was precisely the same with the PDM result, that is, 86.4 minutes, with the r.m.s.
error of 0.4 minutes.


			Table 1

		alpha_2000 	 delta_2000	m_V
		h  m s           d  '   "
Comparison 	11 38 16.71      +03 27 12.4    11.9
Check 1 	11 38 13.37      +03 27 31.8    13.1
Check 2 	11 38 30.56      +03 25 53.7    14.0


                               [FIGURE 1]
                               [FIGURE 2]
                               [FIGURE 3]


  This observation gives us a chance to discriminate the true period between two 
published values. Kato and Fujino (1987) found the period of 92.3 minutes, whereas the
observations by Lemm et al. (1993) gave 86.8 minutes. One of these is probably the true
period and the other is its one-day alias. The difference is small but crucial in judging
whether this star is normal or peculiar from the view-point of fractional superhump period
excess epsilon = (P_superhump - P_orb)/P_orb, (c.f. figure 1 of Molnar and Kobulnicky,1992).
  The period we found is clearly in good agreement with that of Lemm et al. (1993)
This implies that T Leo is a normal SU UMa type dwarf nova in superhump period excess
  The authors are grateful to the members of Variable Stars Observer League in Japan.
(VSOLJ), for the superoutburst notification and supplying the authors with the 
magnitude estimation. Thanks also to J. Pietz, P. Schmeer, G. Poyner, L. Szentasko, B.H
Granslo, H. Dahle, T. Vanmunster, A. Diepvens and P. van Cauteren, for supplying the
magnitude estimation.
  Part of this work is supported by Research Fellowships of the Japan Society for 
Promotion of Science for Young Scientists.


   Chatief KUNJAYA ^1,2
   Taichi KATO ^1
   Ryuko HIRATA ^1
   1 Department of Astronomy,
   Faculty of Science, Kyoto University
   Sakyo-ku, Kyoto 606-01, Japan
   e-mail address : kunjaya@kusastro.kyoto-u.ac.jp
   tkato @ kusastro.kyoto-u.ac.jp
   hirata @ kusastro.kyoto-u.ac.jp

   2 Department of Astronomy, Faculty of Science;
   Institute of Technology Bandung
   Ganesha 10, Bandung 40132, Indonesia



References

Kato, T., and Fujino, S., 1987, Var. Star Bull., No. 3, 10
Lemm, K., Patterson, J., and Thomas, G., 1993, PASP, 105, 1120 [BIBCODE 1993PASP..105.1120L ]
Molnar, L.A., and Kobulnicky, H.A., 1992, ApJ, 392, 678 [BIBCODE 1992ApJ...392..678M ]
Ohtani, H., Uesugi, A., Tomita, Y., Yoshida, M., Kosugi, G., Noumaru, J., Araya, S.,
   Ohta, K. and Mikayama, Y., 1992, Mem. Fac. of Sci., Kyoto Univ., Series A of
   Physics, Astrophysics, Geophysics and Chemistry, 38, 167