COMMISSION 27 OF THE I. A. U.
         INFORMATION BULLETIN ON VARIABLE STARS
                     Number 1850

                                   Konkoly Observatory
                                   Budapest
                                   1980 October 2

                                   HU ISSN 0374-0676



     PHOTOELECTRIC y AND lambda6585 OBSERVATIONS OF VW CEPHEI



   The W UMa-type eclipsing binary, VW Cep (HD 197433), was observed for about
5 hours on 29 July 1977 U.T. using a photoelectric photometer mounted on the 51 cm
Cassegrain reflector of Biruni Observatory. The photoelectric photometer is equipped
with an unrefrigerated RCA 4549 multiplier photocell (similar to the commercially
available RCA 8645 photocell), and a Leeds and Northrup Speedomax was used to record
the amplified signal from the photomultiplier. The observations were made using a
Stromgren y filter and an intermediate bandpass interference filter with a maximum
transmission of lambda_max = 6585Angs. and a full width at half maximum transmission of
FWHM = 280Angst.. A 40 arc second diaphragm was used and the observing sequence was
the usual pattern of sky-comparison-variable-comparison-sky, with each observation
lasting about 30 seconds.
   BD + 76^o 809 (SAO 9836; m = 7.1) was used as the comparison star and the
effects of differential atmosphere extinction were removed using the extinction coefficients 
derived from the comparison star observations. The extinction corrections
were, however, very small because of the angular proximity of the comparison star to the
variable star. The differential magnitudes in the sense (variable minus comparison) are
plotted in Figure 1 where the phases were computed according to the ephemeris of
Cristescu (1978):

           MinI = HJD 2443448.2663 + 0.2783176 E

A determination of the time of secondary minimum was obtained from the data yielding:
MinII = HJD 2443354.3410 +- 0.0008d. This minimum occurs at 0.475 phase according to
Cristescu's ephemeris and represents an O-C = -0.007d when the secondary minimum
is assumed to occur at the half period point. This timing is in good agreement with
other minimum determinations made during the same observing season (Hopp et al.
1979).

                         [FIGURE 1]

FIGURE 1: The alpha6585 and Delta y light curves of VW Cep as a function of
orbital phase. The phases were computed according to the ephemeris of 
Cristescu (1978).


  Although the light curve is only partially covered, the maxima are both defined by
the observations and appear to have slightly different heights where the maxima near
0.25 phase are brighter than the corresponding maxima near 0.75 phase by about 0.015
mag in each bandpass. The light curve of VW Cep is intrinsically variable, at times
showing asymmetries between adjacent maxima of 0.07 mag (Kwee, 1966).




EDWARD F.GUINAN                SEYED-IRAJ NAJAFI
Department of Astronomy        FARID ZAMANI-NOOR
Villanova University           Biruni Observatory
Villanova,Pennsylvania 19085   Shiraz University
U.S.A.                         Shiraz,Iran




References:
1. Cristescu, C., Inf. Bull. Var. Stars No. 1383, 1978.
2. Hopp, U., Witzigmann, S., and Kiehl, M., Inf. Bull. Var. Stars No. 1599, 1979.
3. Kwee, K. K., Bull. Astron. Inst. Netherlands 18, 448, 1966. [BIBCODE 1966BAN....18..448K ]