COMMISSION 27 OF THE I. A. U.
        INFORMATION BULLETIN ON VARIABLE STARS
                    Number 2899


                                   Konkoly Observatory
                                   Budapest
                                   30 May 1986

                                   HU ISSN 0374 - 0676


    A SECONDARY PHOTOMETRIC PERIOD OF TT ARIETIS



 The resemblance of TT Ari to intermediate polars, particularly
to TV Col, prompted us to search for a secondary photometric
period analogous to the 32 minutes X-ray and optical period of
TV Col (Schrijver et al., 1984; Bonnet-Bidaut, Motch, and
Mouchet, 1985). For this purpose we have collected 22
photometric runs of TT Ari obtained by various observers in
various observatories, including 7 already published (Smak and
Stepien, 1969). The observations were made during six seasons
spanning the time interval from 1966 till 1985. The length of
runs varied from one to more than 6 hours, most were at least 3
hours long.
 These data were subject to the power spectrum analysis. In
most runs the 3 hour period (Smak and Stepien, 1975) appeared
with a high amplitude. However, we found in our power spectra
another persistent feature corresponding to a secondary
photometric period of about 20 minutes. This conclusion is based
on the following facts:

 i) A peak at the consistent position appeared on all nights,
albeit its amplitude varied from night to night.

 ii) In 13 of 22 nights the corresponding peak was the
strongest feature in the relevant frequency band.

 iii) We have used two techniques, the Fourier analysis and
the maximum entropy method, which gave mutually consistent
results.




 iv) Same conclusions could be drawn from ours and Smak and
Stepien's data separately.


                        [FIGURE 1]


  Although on different nights of a season the peak appeared at
 the same frequency, the period varied smoothly from season to
 season. In the time interval 1966 - 1985 the secondary
 photometric period decreased from the value of 24 minutes to the
 value of 17 minutes. The season mean values of the period
 versus time are plotted in Fig. 1.

  We cannot say yet whether this periodicity is coherent or not.
 Williams (1966) and Smak and Stepien (1969) searched for
 periodic oscillations in data taken during a single night and
 could only conclude that quasiperiodic and transient fluctuations
 with the periods 14 - 20 minutes are present in their data. Our
 conclusion about persistence of this phenomenon is founded on
 more nights and two independent methods.




   The fast rate of period decrease restrains us from identifying
 it with the rotation period of the compact star as it was done for
 the 32 minutes period of TV Col. We have analysed additionally
 the X-ray observations of TT Ari by Jensen et al. (1982)
 obtained on two consecutive days. In the power spectra for each
 day there were peak at frequencies around 1 mHz although
 inconsistent with each other and with our optical data. Full
 details of our analysis will be given elsewhere.


   We would like to thank Prof. J. Smak and Prof. K. Stepien
 for providing us with their observations and to Prof.
 A. Kruszewski for helpful discussions and encouragement.



I. SEMENIUK, A. SCHWARZENBERG-CZERNY,      H. DUERBECK, M. HOFFMANN,
     Warsaw University                      Astronomical Institute
       Observatory                          University of Munster
     Warsaw, Poland                         Munster, F.R.G,


                 J. TREMKO
             Astronomical Institute
             Slovak Academy of Science
             Tatranska Lomnica
             Czechoslovakia


  References:

  Bonnet-Bidaut, J. M., Motch, C., and Mouchet, M., 1985,
     Astron. Astrophys., 143, 313. [BIBCODE 1985A&A...143..313B ]

  Schrijver, J., Brinkman, A. C. , van der Woerd, J.,
     Watson, M. G., King, A. R., van Paradijs, J., and
     van der Klis, M., 1984, 18th ESLAB Symp. ed. A. Peacock,
     Reidel, in press. [BIBCODE 1985SSRv...40..121S ]

  Smak, J. and Stepien, K., 1969, Nonperiodic Phenomena in
     Variable Stars, ed. L. Detre (Budapest: Academic Press),
     p. 335. [BIBCODE 1969CoKon..65..355S ]
			[CoKon No. 65]

  Smak, J. and Stepien, K., 1975, Acta Astron., 25, 379. [BIBCODE 1975AcA....25..379S ]

  Williams, J. O., 1966, P.A.S.P. 78, 279. [BIBCODE 1966PASP...78..279W ]