COMMISSION 27 OF THE I. A. U.
           INFORMATION BULLETIN ON VARIABLE STARS
                        NUMBER 850

                           	     Konkoly Observatory
                                     Budapest
                               	     1973 November 30



      HIGH SPEED PHOTOMETRY OF THE X-RAY BINARY HD 153919


   HD 153919, an O6F star (Thackeray and Walker, 1973), lies in
the error box of the variable X-ray source 2U 1700-37 (Giacconi
et al, 1972).
   Photometric observations in the UBV system (Penny, Olowin,
Penfold and Warren, 1973) made at the SAAO have confirmed that
the star is optically variable with a period of 3.4120 days equal
to that of the X-ray source. The variation has two minima of equal
depth, but of differing shape. One minimum is coincident with the
X-ray occultation, which occurs at phase 0.68 +/- 0.02. Both the X-ray
and V-band data from Penny et al are presented in Fig. 1.
   Due to the rapid fluctuations observed in similar objects such
as the black hole candidate Cyg X-1, a pilot attempt was made to
monitor the star with a high-speed photometric system. This was done
at the SAAO observing station at Sutherland using a 50cm telescope
and a computer supported photometer with an uncooled EMI phototomultiplier 
designed at the university of Cape Town.
   Integrations of one second duration in the V band were made for
1.14 hours on 11 May 1973 and integration of 100ms duration using
a clear aperture for 350 seconds were made on the night of 12 May
1973. The observations refer to phases 0.61 and 0.91 respectively
of the X-ray source according to the ephemeris calculated by Penny,
et al, and are indicated by arrows in fig. 1.
   The resulting observations were subject to spectral analysis by
performing a fast Fourier transform using the Cooley-Tukey algorithm
on a set of equally spaced data points. The input was normalized to
remove the instrumental sensitivity as well as smoothed to remove any
linear trends. This normalization allows the comparison of power
spectra taken with different instruments, sampling intervals and data
lengths. The procedure is similar to that used by Robinson and Warner,
1972.

   The power spectra of the observations of HD 153919 made on the
nights in question reveal no coherent periodicities for all 
frequencies investigated. The power level at frequencies higher than



                       [FIGURE 1]

   Optical and X-ray variations of HD 153919 from Penny, et al.

0.01 HZ represents the constitution to the signal from photon counting
noise and scintillation. There are no significant power peaks above
this general trend within the interval defined by the frequency
.02 <= HZ <= 5. For periods shorter than 100 second the lack of large
spikes in the power spectrum indicates that at the epoch of observations, 
the power spectrum is due entirely to stochastic processes.
      This lack of significant power during the period of observation 
demonstrates either the lack of intrinsic variability of the 
object, or that it was observed during a quiescent phase. Further 
observations are being made in order to resolve this question.




                                R.P. OLOWIN
                                SAAO Cape



References:
Giacconi, R., Murray, S., Gursky, H., Kellog, E., Schrier, E. and Tananbaum,
   H., 1972  Astrophys.J. 178, 281. [BIBCODE 1972ApJ...178..281G ]
Penny, A., Olowin, R., Penfold, J., Warren, P., 1973 MNRAS 162, 7p. [BIBCODE 1973MNRAS.163P...7P ]
Robinson, E.L and Warner, B., 1972 MNRAS, 157, 85. [BIBCODE 1972MNRAS.157...85R ]