COMMISSION 27 OF THE I. A. U.
     INFORMATION BULLETIN ON VARIABLE STARS
                 Number 2005

                             Konkoly Observatory
                             Budapest
                             1981 August 25

                             HU ISSN 0374-0676




      NOTE ON THE PERIOD OF THE W UMa STAR AH Vir




AH Vir belongs to Binnendijk's subclass "W" of the W UMa stars.
It is well known to have a variable lightcurve and a variable
period (Bakos, 1977). The most recent period of Bakos is

    t_MinI = 2442155.6164d + 0.40753126d*E.

The latest published photoelectric observations are given by
Hoffmann (1981) made in March 1977. He determined four minima
items which showed that the last period of Bakos was still
valid.
On April 14./15., 1980, we made 80 V and 77 B photoelectric 
measurements with the 75 cm telescope of the Wilhelm Foerster 
Observatory Berlin and an 1P21 photomultiplier with usual Schott 
filter combinations for the UBV system. With the Pogson method we
determined one primary minimum :

         V 2444 344.4535d +- 0.0009d (hel.)
         B      344.4510  +- 0.0010

Using the mean value from the both colours and Bakos' above given
elements, we derive an O-C value of O-C = - 0.0146d (E=5371). This
large O-C value indicates that the orbital period of AH Vir has
changed again between 1977 and 1980.
The only other source of published minima times since Hoffmann's
observations are the BBSAG-Bulletins No. 31-53, where one photoelectric 
and 22 visual minima determinations are given. From the minima 
items given by Bakos, Hoffmann, in the BBSAG-Bulletins and in
this notice, one can estimate that the period change took place
around May 1979. As a first approximation of the new period value,
based strongly on the lower accurate visual minima determinations,
we estimate P=0.40751314d. Notice that the trend of increasing 
periods found by Bakos has stopped and the period decreased.
Our observations cover about 40% of the lightcurve and show no
hints of lightcurve activities during Max.II and the primary
minimum. Delta m = m_MinI - m_MaxII is found to be:


            Delta m (V) = 0.58 +- 0.02
            Delta m (B) = 0.64 +- 0.02.




                     U. HOPP, S. WITZIGMANN


                     Wilhelm Foerster Observatory

                     D-1000 Berlin - 41, F.R.G.


References :


Bakos, G.A.: 1977, Bull.Astron.Inst.Czech. 28. 157 [BIBCODE 1977BAICz..28..157B ]
Hoffmann, M.: 1981, Inf. Bull.Var.Stars No. 1933