COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                      Number 3352

                                        Konkoly Observatory
                                        Budapest
                                        10 July 1989

                                        HU ISSN 0374 - 0676


          DETECTION OF NEW SHORT PERIOD OSCILLATIONS
                  IN PG 1711+336 (V795 HER)

Long period light variations of the cataclysmic variable PG 1711+336 (V795 Her)
were first noticed by Mironov et al. (1983a,b) who reported a photometric
period of 0.115883 day for the system. Baidak et al., (1985) improved the
ephemeris and refined the period to 0.114488 day (2.75 hour). If this period is
interpreted as the orbital period, then the system is unique in that its
orbital period falls within the period gap in the distribution of cataclysmic
variables versus their orbital periods. The detection by Thorstensen (1986) of
a spectroscopic period of 14.8 hours in the radial velocity data using H_alpha
emission line of the system coupled with the lack of and evidence of the 2.75
hour period in the power spectrum of the radial velocity data has further
deepened the mystery surrounding this object. In an attempt to study the time
variabilities in the system, we carried out high speed photometric observations
of the object.

The observations were carried nut with the 1 meter telescope of the UP State
Observatory at Nainital, and our two star photometer (Venkata Rao et al., 1989)
on April 7 and April 10, 1989. PG 1711+336 was observed in white light in the
main channel using an uncooled RCA 8850 PMT.

On April 7, we could collect only about 3600s of data. The fast variability of
the star was evident during this run. On April 10, we collected about 9000s of
data with an integration time of 5s.


                          [FIGURE 1]
                          [FIGURE 2]


Fig. 1. shows the sky subtracted light curve of the star on April 10. The 2.75
hour photometric variation is evident in the data. The maximum of the light
curve occurs at about 21.23 hour UT. The phase of this maximum is 0.3 when
calculated using the ephemeris of Baidak et al. This agrees well with the phase
of the maximum of their folded light curve.

The short period, structured oscillations of the star shown in fig. 1. as well
as in our April 7, 1989 data (not shown here). Also we were surprised to see
similar short period variations of the star in one of our earlier runs on May
12, 1986 taken with a single star photometer under poor sky conditions.

Visual inspections of the raw light curve in fig. 1. while indicating the
presence of more than one period, seems to reveal a period around 1400s. We
have subjected the April 10, 1989 data to a DFT analysis after removing the
clear 2.75 hour variation in it. The resulting normalised power spectrum is
shown in fig. 2. It shows a maximum around a period of 1389s and also next
significant power around 2040s. The width of the peak can be attributed to the
limited resolution due to the finite data length. The power spectrum also
reveals other peaks around 1136s, 935s, 735s, 658s and 562s. Even though the power
around 562s is rather low, the power spectrum of our April 7, 1989 data had the
maximum peak centred around this value. At present with the existing stretch of
data are not in a position to confidently pinpoint which of these peaks
represent genuine periods.

As a check on the consistency of the 1389s period, we decided to split the data
into two sets. A demarkation that divides the total data into two sets is
provided by the relatively large dip in the data lasting about 10 minutes from
21.23 UT to 21.48 UT. This remarkable dip does not show the flickers present in
the rest of the data. The dip also demarkates the data into an ascending and
descending portion of the 2.75 hour variation. We therefore subjected the
portion of the data upto 21.33 UT and the rest of the data separately to a DFT
analysis. The excess power around 1389s was seen only in the first portion of
the data. Also our data of 7 April did not show any excess power at this
period on subjecting it to a DFT analysis thereby indicating that the 1389s
period may be quasi-periodic in nature.

In conclusion, apart from confirming the 2.75 hour photometric variability
(most probably due to orbital variations) our detection of very large amplitude
(~0.2 magnitude), short period (tens of minutes) oscillations of the
system makes PG 1711+336 an extremely interesting object for further
detailed investigations.


ASHOKA, B.N., SEETHA, S., MARAR, T.M.K.,
PADMINI, V.N., KASTURIRANGAN, K., and RAO, U.R.
ISRO Satellite Centre,
Airport road,
Vimanapura P.O.
BANGALORE-560 017
INDIA

and

PANDE, M.C., and MAHRA, H.S.
UP State observatory,
NAINITAL-263 129
INDIA

References:

Baidak, A. V. et al., 1985: I.B.V.S., No. 2676
Mironov, A. V., Moshkalev, V. G., Shugarov, S. Yu., 
   1983a: Astr. Tsirk. No. 1279, 6 [BIBCODE 1983ATsir1279....6M ]
   1983b: I.B.V.S., No. 2438 
Thorstensen, J. R., 1986, A.J., 91, No. 4, 940 [BIBCODE 1986AJ.....91..940T ]
Venkata Rao, G. et al., 1989: Paper for presentation at the ASI meeting,
   Srinagar, INDIA June 1989