COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3714 Konkoly Observatory Budapest 21 April 1992 HU ISSN 0374 - 0676 VARIABILITY IN THE MINIMA DEPTH OF THE DOUBLE SYSTEM HD 135421 BV Dra and BW Dra (ADS 9537, HD 135421) were detected as eclipsing binaries in 1965 by Batten and Hardie. Photometric observations by Wood (1970), 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) and Dapergolas et al., 1990 have also carried out BV photoelectric observations of BV Dra and BW Dra respectively. These two eclipsing binaries were observed from 19 May through 21 May 1991 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 0.02 mag. 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 BV Dra BW Dra Date Phase Date Phase 19 May 1991 .70 - .31 19 May 1991 .21 - .94 20 May 1991 .45 - .16 20 May 1991 .49 - .34 21 May 1991 .39 - .03 21 May 1991 .01 - .75 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 ephemerides: BV Dra T = 2442878.372 +0.3500663d E (Geyer et al., 1982). BW Dra T = 2442572.538 +0.2921671d E (Geyer et al., 1982). [FIGURE 1a] [FIGURE 1b] [FIGURE 2a] [FIGURE 2b] Table II a) BV Dra V colour B colour Type of Heliocentric (O-C) Heliocentric (O-C) minima Jul. Day Phase Jul. Day Phase Primary 2448396.4684 0.0038 2448396.4684 0.0039 +/-.0002 +/-.0005 +/-.0003 +/-.0009 Secondary 2448397.3447 0.5071 2448397.3439 0.5046 +/-.0002 +/-.0004 +/-.0003 +/-.0008 Primary 2448397.5187 0.0041 2448397.5187 0.0041 +/-.0002 +/-.0006 +/-.0002 +/-.0006 Secondary 2448398.3948 0.5038 2448398.3953 0.5083 +/-.0001 +/-.0002 +/-.0001 +/-.0003 a) BW Dra V colour B colour Type of Heliocentric (O-C) Heliocentric (O-C) minima Jul. Day Phase Jul. Day Phase Secondary 2448396.4541 0.518 2448396.4552 0.5215 +/-.0003 +/-.001 +/-.0002 +/-.0007 Primary 2448397.4781 0.0228 2448397.4782 0.0229 +/-.0002 +/-.0007 +/-.0002 +/-.0007 Secondary 2448398.5002 0.5211 2448398.4997 0.519 +/-.0002 +/-.0007 +/-.0003 +/-.001 Table III Differences between the amplitudes of Primary and Secondary minima for BW Dra in B, V colours Date DeltaB(mag) DeltaV(mag) 1991 0.13 0.13 1990 0.18 0.17 1989 0.11 0.10 1982 0.13 0.12 1981 0.07 0.07 1980 0.06 0.05 Figures 1a and b show the light curve of BV Dra for B, V colours respectively whereas Figure 2a and b is the same for BW Dra. From Fig. 1a,b and Fig. 2a,b it can be seen that BV Dra and BW Dra have nearly symmetric light curves. The difference between primary and secondary minima is approx 0.13 mag in B and V for BW Dra whereas for BV Dra we measure 0.07 mag for B and V. 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 the amplitudes of primary and secondary minima varies from year to year (see Table III) and does not change from colour to colour for BW Dra. This variation from year to year is not found for BV Dra. A. DAPERGOLAS, E. KONTIZAS M. KONTIZAS National Observatory of Athens Section of Astrophysics, Astronomy and Astronomical Institute Mechanics P.O. Box 20048 Department of Physics, Univ. of Athens GR Athens 118-10 Panepistimiopolis Greece GR-15783, Zografos Athens, Greece 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. Dapergolas, A., Kontizas, E. and Kontizas, M.: 1990, IBVS No. 3538. Geyer, E.H., Hoffmann, M. and Karimie, M.T.: 1982, Astron. Astrophys. Suppl. Ser., 48, 85. [BIBCODE 1982A&AS...48...85G ] Kwee, K.K., 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 ]