COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1117 Konkoly Observatory Budapest 1976 March 22 BV PHOTOMETRY OF BM Cas The long period eclipsing binary BM Cas (P=197.28d) is of considerable interest, especially since Thiessen (1956) has suggested that one component of the system is a classical Cepheid (P=27d). The two-colour photoelectric observations were obtained with the Ege University Observatory 48 cm Cassegrain telescope and an unrefrigerated 1P21 photomultiplier. The observations were made from February 1972 to May 1973, on 49 nights. BD+63d101 was used as comparison star. The differential magnitudes were corrected for differential extinction. The phases were calculated with the light elements given by Beyer (1952-1964); Hel.Min.I = J.D. 2425772.9 + 197.28d E + 2.6d sin(7.11d E+104d). The results are given in the Table, where the columns list the heliocentric Julian date, V and (B-V), respectively. The light and colour curves are shown in the figure, where the instrumental magnitude differences between the variable and the comparison star have been plotted against the phases. This study is a part of research project No. 76 supported by the Scientific and Technical Research Council of Turkey. [FIGURE 1] Table Differential BV Magnitudes ( BM Cas minus BD + 63d101 ) J.D.(Hel.) DeltaV (B-V) J.D.(Hel.) DeltaV (B-V) 2441000+ 2441000+ 356.2249 0.882 0.836 573.2761 0.476 0.845 365.2370 .785 .880 575.2586 .435 .853 366.2347 .745 .878 .2648 .443 .852 .2429 .760 .870 .2694 .455 .838 384.3967 .385 .853 576.3255 .433 .859 394.2550 .364 .930 .3318 .430 .857 .2613 .368 .829 .3383 .428 .849 .2672 .373 .827 577.2488 .427 .838 .2738 .372 .816 .2555 .427 .843 397.2397 .415 .822 .2613 .422 .868 .2438 .400 .867 578.2743 .431 .838 .2505 .405 .853 .2806 .446 .828 .2592 .410 .813 .2882 .419 .860 .2660 .405 .848 .2944 .416 .853 400.2519 .407 .853 581.2958 .435 .851 407.2678 .335 .840 .3027 .425 .850 478.5521 .450 .872 .3092 .435 .844 .5468 .435 .887 .3168 .432 .846 .5568 .462 .880 582.2688 .432 .844 481.4039 .437 .833 .2770 .427 .844 .4116 .434 .863 .2820 .432 .839 .4172 .424 .839 .2877 .437 .834 489.5452 .430 .870 583.4129 .450 .835 493.5123 .418 .868 .4203 .440 .855 .5183 .411 .870 .4300 .445 .850 .5249 .411 .870 .4371 .445 .840 499.5386 .436 .882 .4441 .440 .845 .5441 .439 .882 584.4190 .440 .845 .5497 .446 .872 .4280 .440 .850 504.5509 .437 .875 .4342 .430 .867 .5575 .441 .876 588.2449 .467 .859 510.5257 .388 .854 .2505 .457 .864 .5330 .398 .854 .2567 .462 .854 .5407 .403 .849 .2626 .462 .869 519.5586 .415 .845 594.4931 .448 .866 .5670 .435 .830 .4993 .453 .856 524.5422 .440 .840 .5060 .438 .871 .5478 .435 .855 .5127 .443 .859 .5531 .435 .845 603.2470 .454 .846 547.3099 .779 .896 .2709 .471 .853 .3157 .774 .871 .2771 .476 .837 .3216 .774 .881 604.2466 .456 .859 548.2759 .794 .867 .2532 .450 .849 .2823 .789 .847 .2585 .455 .865 .2880 .779 .872 624.2283 .418 .846 .2935 .794 .882 .2326 .409 .840 572.2866 .491 .864 .2368 .387 .871 .2932 .486 .844 639.5686 .464 .850 573.2631 .461 .860 .5738 .481 .833 .2698 .471 .860 .5792 .497 .804 Table (continued) J.D.(Hel.) DeltaV (B-V) J.D.(Hel.) DeltaV (B-V) 2441000+ 2441000+ 649.2809 0.446 0.804 670.2644 0.530 0.871 .2879 .452 .852 672.2398 .560 .825 .2961 .444 .820 .2526 .550 .835 .3040 .455 .822 .2600 .525 .870 .3111 .445 .838 675.1744 .505 .870 651.2475 .470 .834 .1810 .510 .865 .2555 .452 .831 .1898 .515 .837 .2634 .452 .834 678.2610 .485 .855 .2680 .449 .832 .2690 .460 .848 655.5133 .435 .836 .2759 .462 .858 .5206 .452 .833 693.2451 .446 .846 .5265 .447 .836 .2518 .446 .856 660.5180 .493 .847 .2562 .453 .849 .5257 .484 .828 719.3979 .455 .820 .5317 .503 .822 .4045 .445 .830 663.3224 .518 .853 .4104 .450 .820 .3276 .516 .853 722.3278 .445 .818 667.3059 .535 .880 .3346 .432 .833 .3132 .530 .885 .3400 .440 .815 .3205 .535 .880 .3448 .405 .845 670.2378 .540 .856 826.5073 .460 .877 .2499 .535 .853 .5129 .476 .867 .2576 .525 .881 .5178 .484 .868 S. BOZKURT N. GUDUR O. GULMEN C. IBANOGLU Ege University Observatory P.K. 21 Bornova-Izmir-Turkey References: Beyer, M., 1952., Astron.Nachr. 280, 267 [BIBCODE 1952AN....280..267B ] Beyer, M., 1964, ibid. 288, 87 [BIBCODE 1964AN....288...87B ] Hall, D.S., 1971, Com.27 of the I.A.U. Inf.Bull.Var.Stars No. 560 Thiessen, G., 1956, Z.f.Astrophysik. 39, 65 [BIBCODE 1956ZA.....39...65T ] CORRECTION TO I.B.V.S. No. 1113 "10-inch (25 cm)" should be read "8-inch (20 cm)" D.S. HALL and H.J. LANDIS