COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1733

                                   Konkoly Observatory
                                   Budapest
                                   1980 January 24


   PHOTOELECTRIC PHOTOMETRY OF THE SPECTROSCOPIC BINARY HD 91948


The star HD 91948 (BD+60d1274) has been found to be a spectroscopic binary by
Gorga (1971) with an orbital period of 2.7700266d. No photoelectric work on
this star is available in the literature. The purpose of our photoelectric
measurements was to study the variable nature of this binary star.

The star was observed by us photoelectrically on the 38-cm reflector of the
Uttar Pradesh State Observatory on a total of 17 nights during the period May
1973 - May 1978. The conventional UBV filters of Johnson and Morgan and
standard d.c. techniques were employed. The observations collected during
1973 to 1975 were obtained with an unrefrigerated 1P21 photomultiplier tube,
while the remaining ones were obtained using a similar tube refrigerated to
-20 deg C. Two comparison stars BD+60d1270 and BD+60d1289 were used to begin
with. However, the latter was found to be a better comparison star than the
former, hence all the final reductions were done using that star. The standard
deviations of the comparison star on typical nights when an unrefrigerated
photomultiplier tube was used were 0.013m(B) and 0.012m(V), while when a
cooled photomultiplier was used were 0.011m(B) and 0.010m(V). Our
observations were planned on the basis of the following ephemeris

Primary minimum = JD 2440243.334+2.7700266d*E (Gorga, 1971).
Due to the large scatter in U filter, on most of the nights, the light curves
only on B and V filters are given in Figure 1. On the first observational
night of 22 May 1973 (JD 2441825) which was planned near primary minimum (at
phase 0.09d), we noticed light variations in U, B and V. The differential
magnitudes (instrumental) against JD are given in Figure 2. Below each light
curve, the instrumental magnitude of the comparison star used, is also given,
with its magnitude scale on the right hand side. This variation demanded
further observations of the system in the entire phase region. However, on an
other night of 21 March 1977 (JD 2443224) at phase 0.25d, a variation of
0.26m in U, 0.15m in B and 0.10m in V filter, in two hours of duration was
noticed and is given in Figure 3. The individual observations on the night of
JD 2441825 and JD 2443224 are shown by cross and solid triangles respectively
in Figure 1.

                               [FIGURE 1]

   Figure 1.  Light curves of HD 91948 on an assumed period of
   2.7700266d. The differential magnitudes are in the sense variable
   minus comparison. The +-2 sigma error bars for the comparison star
   are indicated along the side.

                               [FIGURE 2]

   Figure 2.  Individual observations on the night of JD 2441825.
   The differential magnitudes are in the sense variable minus
   comparison. The solid line indicates free hand curve. Points with 
   (triangle) are instrumental magnitudes for comparison star used.

                               [FIGURE 3]

   Figure 3. Individual observations on the night of JD 2443224.
   The differential magnitudes are in the sense variable minus
   comparison. The solid line indicates free hand curve. Points with 
   (triangle) are instrumental magnitudes for comparison star used.
 
Gradual variation of light (increasing or decreasing) has been noticed in case
of Be stars which are also spectroscopic binaries. For example, Landis et al.
(1977) V measurements of 4 Her on the night of JD 2442542 indicate gradual
brightening of the star for at least 0.05m during 3 hours (0.13 days). But it
is unusual in case of HD 91948 which has been reported tentatively as spectral
class F6V. HD 91948 has a companion star of 11m at 4.4" apart (Batten et al.
1978). This companion star, could not be separated out in the diaphragm of
38-cm reflector and hence was observed together with the main star.
Considering that the latter is of magnitude M_v=7.3; the companion does not
contribute effectively to the total light coming through.

Due to lack of U observations, no definite colour class could be assigned to
this star. However, B-V values, based on the mean values of B and V filters in
Figure 1, were determined and came out to be +0.016m, which corresponds to A0V
spectral class. Our light curves in Figure 1 show the absence of eclipses at
scheduled primary and secondary minima phases. Unfortunately we could not get
any night in the gap which occurs just after the aforesaid night of JD 2443224.
The variability of this star in the aforesaid two nights is quite significant
as compared to the error of our observations. Since there is no consistency in
the shape of the light curves obtained on those two individual nights, it is
difficult to assign the type of variability to this star. However, we conclude
that HD 91948 is a suspected variable. Also the light curve does not point
towards the star being an eclipsing binary.

The author is thankful to Dr. S.D. Sinvhal for helpful discussions and
suggestions.


T. D. PADALIA
Uttar Pradesh State Observatory
Manora Peak, Naini Tal-263129
India

References:

Batten, A.H., Fletcher, J.M., Mann, P.J., 1978, Seventh catalogue of the
   Orbital Elements of Spectroscopic Binary Systems, DAO Publ. Vol. XV, No. 5,
   p. 156 [BIBCODE 1978coes.book.....B ]
Gorza, W., 1971, J.R.A.S. Can., 65, 277 [BIBCODE 1971JRASC..65..277G ]
Landis, H.J., Lovell, H.P., Hall, D.S., Uckotter, D.G., 1977 Acta Astronomica,
   27, 265 [BIBCODE 1977AcA....27..265L ]