COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3538 Konkoly Observatory Budapest 5 November 1990 HU ISSN 0374 - 0676 VARIABILITY OF THE DEPTH OF THE MINIMA OF THE DOUBLE SYSTEM HD 135421 BV Dra and BW Dra (ADS 9537, HD 135421) have been detected as eclipsing binaries by Batten and Hardie (1965). Photometric observations by Wood (19.70) Rucinski (1976) and Yamasaki (1979) have shown that they are normal W UMa systems. New photometric observations have been presented by Rovithis and Rovithis (1987) for the system. Dapergolas et al. (1989a, b) have also carried out BV photoelectric observations of BV Dra and BW Dra respectively. These two eclipsing binaries were also observed from 16 May through 23 May 1990 with the 1.2m Kryonerion telescope and a single channel photon counting photometer. The photometer employs a high gain 9789QB phototube and conventional BV filters. Its output is fed directly to a microcomputer enabling rapid data access. The data reduction is the standard one. The comparison star is for both cases BD +62d 1385 and the accuracy of observations is +- 0.02mag. Table I lists the dates of observations and phases covered whereas Figures 1 and 2 summarize the results for B and V colours. TABLE I a) BV Dra Date Phase 16 May 1990 .27 - .09 18 May 1990 .0 - .76 22 May 1990 .58 - .78 23 May 1990 .27 - .02 b) BW Dra Date Phase 16 May 1990 .42 - .38 18 May 1990 .27 - .20 22 May 1990 .15 - .40 23 May 1990 .38 - .23 In Table II the times of minima and the O-C values are listed for the V and B bands respectively. Times of minima are calculated using the method described by Kwee and van Woerden (1956) whereas the O-C values were determined from the following linear ephemeris. BV Dra T= 2442878.372 + 0.3500663E (Geyer et al. (1982)). BW Dra T= 2442572.538 + 0.2921671E (Geyer et al. (1982)). [FIGURE 1a] [FIGURE 1b] [FIGURE 2a] [FIGURE 2b] Fig 1a, b shows the light curve of BV Dra for B, V colours respectively whereas Fig 2a, b are the same for BW Dra. TABLE II a) BV Dra V colour B colour Type of Heliocentric (O-C) Heliocentric (O-C) minima Jul. Day Phase Jul. Day Phase Secondary 2448028.3745 0.4982 2448028.3743 0.4977 q.0001 q.0003 q.0001 q.0003 Primary 2448028.5489 0.9966 2448028.5491 0.9971 q.0003 q.0008 q.0002 q.0006 Secondary 2448030.4756 0.5002 2448030.4752 0.4992 q.0002 q.0007 q.0002 q.0006 Secondary 2448035.3758 0.4983 2448035.3759 0.4985 q.0002 q.0007 q.0002 q.0005 a) BW Dra V colour B colour Type of Heliocentric (O-C) Heliocentric (O-C) minima Jul. Day Phase Jul. Day Phase Secondary 2448028.3251 0.516 2448028.3249 0.516 q.0003 q.001 q.0003 q.001 Primary 2448028.4688 0.0083 2448028.4685 0.0072 q.0001 q.0003 q.0002 q.0006 Secondary 2448030.37 0.5152 2448030.3705 0.517 q.0002 q.0007 q.0005 q.001 Primary 2448030.5138 0.0075 2448030.5137 0.007 q.0002 q.0006 q.0003 q.001 Secondary 2448035.3384 0.52 2448035.339 0.523 q.0005 q.002 q.0005 q.002 Primary 2448035.481 0.0086 2448030.4812 0.0095 q.0003 q.0009 q.0003 q.0009 From the Fig. 1a, b and Fig. 2a, b presented here it can be seen that BV Dra and BW Dra have symmetric light curves. The differences between primary and secondary minima are ~0.18mag in B and ~0.17mag in V for BW Dra. From the observations presented previously by Dapergolas et al. (1989b), Rovithis and Rovithis (1987) and Geyer et al. (1982) it is found that the difference between primary and secondary minima is variable (see Table III) from year to year and doesn't change from colour to colour. TABLE III Differences between Primary and Secondary minima for BW Dra in B, V colours. Date B(mag) V(mag) 1990 0.18 0.17 1989 0.11 0.1 1982 0.13 0.12 1981 0.07 0.07 1980 0.06 0.05 These differences between primary and secondary minima do not seem to exist for BV Dra. A. DAPERGOLAS National Observatory of Athens Astronomical Institute P.O. Box 20048 GR Athens 118-10 Greece E. KONTIZAS and M. KONTIZAS Laboratory for Astronomy and Solar Physics NASA, Goddard Space Flight Center Greenbelt Maryland 20771 U.S.A. References: Batten, A.H. and Hardie, R.H.: 1965, Astron. J. 70, 666. [BIBCODE 1965AJ.....70..666B ] Dapergolas, A., Kontizas, E. and Kontizas, M.: 1989a, IBVS no 3377. Dapergolas, A., Kontizas, E. and Kontizas, M.: 1989b, IBVS no 3382. Geyer, E.H., Hoffmann, M. and Karimie, M.T.: 1982, Astron. Astrophys. Suppl. Ser., 48, 85. [BIBCODE 1982A&AS...48...85G ] Kwee, K.K. and van Woerden, H.: 1956, Bull. Astr. Inst. Netherlands 12, 327 [BIBCODE 1956BAN....12..327K ] Rovithis, P. and Rovithis - Livaniou, H.: 1987, Astron. Astrophys. Suppl. Ser. 70, 63. [BIBCODE 1987A&AS...70...63R ] Rucinski, S.M.: 1976, IAU Symp. 73, 349. [BIBCODE 1976IAUS...73..349R ] Wood, D.B.: 1970, Bull. American Astron. Soc., 2, 357. [BIBCODE 1970BAAS....2Q.357W ] Yamasaki, A.: 1979, Astrophys. Space Sci., 60, 173. [BIBCODE 1979Ap&SS..60..173Y ]