COMMISSION 27 OF THE I. A. U.
            INFORMATION BULLETIN ON VARIABLE STARS
                         Number 3320

                                          Konkoly Observatory
                                          Budapest
                                          17 April 1989

                                          HU ISSN 0374 - 0676


        DECEMBER 1988 PHOTOMETRY ON AB DORADUS (HD 36705)


We present (see Fig. 1) complete light curves in UBV colours and some Rc and Ic
data for the fast rotating active chromosphere single star HD 36705 (AB Dor).
A cooled extended S-20 tube was used on the 0.6 m telescope at Siding Spring
Observatory. The comparison and check stars used were HD 35537 and HD 37927.
The phase was computed using epoch and period HJD 2444296.575 and 0.51479 in
accordance with Innis et al. (1988). A summary of the V photometry on this
star from 1978 is shown in Fig. 2.

The Dec. 1988 data were standardized from the instrumental values using a set
of calibration equations previously obtained in August 1988 on the same
instrument by Dr. D.W. Coates using the E region standards (Vogt et al. 1981).
Unfortunately there was no U band calibration so these data are left as
instrumental.

The scatter in the data particularly in u around phase 0.4 we believe is real
and represents a change over two days of the stars magnitude at maximum.


                              [FIGURE 1a]
                              [FIGURE 1b]
                              [FIGURE 1c]
                              [FIGURE 1d]
                              [FIGURE 1e]

 Fig. 1 (a)(b)(c)(d)(e): The light curve for AB Dor in December 1988 in 
 Delta u (instrumental), Delta B, Delta V, Delta Rc and Delta Ic. The 
 phases are according  to epoch 2444296.575 and period 0.51479 Innis et. 
 al. (1988).

                              [FIGURE 2]

 Fig. 2  The mean light level and variation of V for AB Dor from a wide 
 variety of sources. For references see Innis et al. (1988). It is yet to 
 be seen if this long term variation is part of a spot cycle on AB Dor.


There are two broadband flares, one at phase 0.09 on the 20 December and the
larger at phase 0.78 on the 12 December. This latter flare occurred just at
dawn was rising and only after a careful check on sky levels and sky
subtractions is it believed to be real.

The flat portion of the curve from phase 0.65 to 0.15 indicates a spotted
region rather than just two spots since they would be 0.5 phase apart. The
night of the 15th was extremely poor photometrically and no great weight can be
given to the odd data point which is noted on that night.

It is a pleasure to thank Dr. B. Carter for help on three of the observing
nights.


K. THOMPSON* and I. THOMPSON

* Department of Physics, Monash University, Clayton 3168, Australia.

References:

Innis, J.L., Thompson, K., Coates, D.W. and Lloyd Evans, T. (1988)
   Observations of active chromosphere stars - II. Photometry of AB Dor,
   1978-1987. Mon. Not. R. astr. Soc. 235, 1411-1422. [BIBCODE 1988MNRAS.235.1411I ]
Vogt, N., Geisse, H.S., and Rojas, S. (1981) Up to Date UBVRI values for the
   E-region standard star. Astron. Astrophys. Suppl Ser 46, 7-11. [BIBCODE 1981A&AS...46....7V ]