COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 2190

                                 Konkoly Observatory
                                 Budapest
                                 1982 August 23

                                 HU ISSN 0374-0676





        RECENT PHOTOMETRY OF HR 1099 (V711 Tau)



  The RS CVn binary HR 1099 was observed on 26 nights during
January-February 1982 with the 34-cm Cassegrain reflector of the
Kavalur Observatory through standard B and V filters. An 
unrefrigerated 1P21 together with the conventional d.c. set up was
used for the observations. The faint visual companion (ADS 2644B)
was included in all the observations. The measurements were made
differentially with respect to the comparison star 10 Tau. The
Julian days of observation were converted into orbital phases
with the following ephemeris (Landis et al. 1978):

           JD = 2442766.069 + 2.83782d E.

                    [FIGURE 1]

  The figure is a plot of the DeltaV magnitudes against the orbital
phases. Each point is a mean of three or four independent 
measurements. The typical uncertainty of a value including systematic
error is about 0.01 mag. The amplitude of the light variation
is about 0.10 mag and the light minimum occurs at ~ 0.40 phase.
  In the recent analysis of the photometric behaviour of HR 1099,
Mekkaden, Raveendran and Mohin (1982) have shown that during the
1976-82 period, the brightness at light curve minimum was 
essentially constant with a mean value around DeltaV = 1.60 mag and a
change in the amplitude of light variation was directly related
to an increase in the brightness at light curve maximum. But
the present observations indicate that the brightness at light
minimum is brighter by about 0.10 mag than that of the previous
years. The light curve obtained during the 1980-81 season had
two minima (at phases close to 0.15 and 0.45), contrary to the
observations of the earlier epochs which always showed only one
minimum. The recent photometry shows a nearly sinusoidal light
variation indicating that drastic changes have occurred in the
distribution of 'active regions' during the period between the
present and previous observing runs. It is difficult to decide
to which of the two minima of the previous observing season the
present minimum corresponds to and hence no definite conclusion
on the migration of the photometric wave can be made.
  It is interesting to note that the present observations agree
well with those obtained by Cousins (1963) in the brightness at
both light curve maximum and minimum and the phases at which
these occur. It would be worthwhile to monitor this system 
continuously for the next few years for a better understanding of
the nature of its activity.


        S. MOHIN, A.V. RAVEENDRAN, M.V. MEKKADEN,

               K. JAYAKUMAR, M.J. ROSARIO

            Indian Institute of Astrophysics
                Bangalore 560034, India


References:

Cousins, A.W.J.: 1963, Mon.Not. astr. Soc. Sth.Afr.  22, 58 [BIBCODE 1963MNSSA..22...58C ]
Landis, H.J., Lovell, L.P., Hall, D.S., Henry, G.W., Renner, T.R.:
   1978, Astr. J., 83, 176 [BIBCODE 1978AJ.....83..176L ]
Mekkaden, M.V., Raveendran, A.V., Mohin, S.: 1982, J. Astrophys.
   Astr. 3, 27 [BIBCODE 1982JApA....3...27M ]