COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 3728 Konkoly Observatory Budapest 14 May 1992 HU ISSN 0374 - 0676 Photometry of alpha Orionis (Nov 1990 to Apr 1992) We present new photometry of Betelgeuse derived from differential measurements with respect to Phi^2 Ori (= HR 1907, for which V = 4.09, B-V = 0.95). The color of Betelgeuse was taken to be B-V = 1.84, as given by the 4th edition of the Bright Star Catalogue (1982). Transformation to the UBV system was accomplished by means of transformation coefficients derived from differential measures of the red-blue pair 27 and 28 LMi (Hall 1983). From observations obtained over several years our system has epsilon_V = -0.054, mu = 0.940. The data were obtained at the 2800-m level of Mauna Kea, Hawaii, using a 15-cm Newtonian reflector, a DC photometer, and a strip chart recorder. The data are given in Table I. Previous data are given in Krisciunas and Fisher (1988) and Krisciunas (1990). Table I Photometry of alpha Orionis Date Julian Date V B-V 13/14 Nov 1990 1032 2448209.94 0.475+/-0.015 27/28 Dec 1990 0623 8253.77 0.548 0.013 3/4 Jan 1991 0700 8260.79 0.459 0.016 20/21 Jan 1991 0643 8277.78 0.488 0.006 6/7 Mar 1991 0656 8322.79 0.524 0.013 3/4 Apr 1991 0659 8350.79 0.555 0.011 12/13 Oct 1991 1144 8542.99 0.292 0.006 9/10 Nov 1991 0920 8570.89 0.365 0.006 26/27 Dec 1991 0750 8617.83 0.345 0.019 1.844 29/30 Dec 1991 0710 8620.80 0.352 0.004 26/27 Jan 1992 0656 8648.79 0.352 0.012 2/3 Feb 1992 1105 8655.96 0.320 0.023 22/23 Mar 1992 0641 8704.78 0.394 0.018 16/17 Apr 1992 0604 8729.75 0.423 0.008 [FIGURE 1] Fig. 1 - Data from Table I and from IBVS Numbers 3227 and 3477. Squares: alpha Ori data by Krisciunas reduced with respect to gamma Ori. Dots: alpha Ori data by David Fisher, using Phi^2 Ori as comparison star. Open circles: alpha Ori data by Krisciunas reduced with respect to Phi^2 Ori. Filled triangles: gamma Ori data reduced with respect to Phi^2 Ori. The check star was gamma Ori (V = 1.64, B-V = -0.22), which in the 1987/88 season exhibited some evidence of variability on the order of 0.1 magnitude. Since then it has not shown any evidence of variability. The redder color of Phi^2 Ori makes it a much better comparison star for Betelgeuse than gamma Ori. Because the light curve of Betelgeuse did not show great changes in the past two seasons, in Figure 1 we give the light curve over the past 6 1/2 years. This is greater than the principal period of variation, traditionally quoted as 5.781 years (Sanford 1933). The approx.420 day period of smaller amplitude, also observed photometrically by Dupree et al. (1987), and in radial velocity data by Smith, Patten, and Goldberg (1989) and by Dupree et al. (1990), seems to have diminished greatly in amplitude or to have died out. KEVIN KRISCIUNAS Joint Astronomy Centre 665 Komohana Street Hilo, Hawaii 96720 USA References : Dupree, A. K., Baliunas, S. L., Guinan, E. G., Hartmann, L., Nassiopoulos, G. E., and Sonneborn, G. 1987, Ap. J. Lett. 317, L85. [BIBCODE 1987ApJ...317L..85D ] Dupree, A. K., Baliunas, S. L., Guinan, E. F., Hartmann, L., and Sonneborn, G. 1990, in Confrontation between Stellar Pulsation and Evolution, C. Cacciari and G. Clementini, eds. (San Francisco: Astronomical Society of the Pacific), ASP Conference Series 11, 468. [BIBCODE 1990ASPC...11..468D ] Hall, D. S. 1983, IAPPP Communic. No. 11, 3. [BIBCODE 1983IAPPP..11....3H ] Krisciunas, K., and Fisher, D. 1988, IBVS No. 3227. Krisciunas, K. 1990, IBVS No. 3477. Sanford, R. F. 1933, Ap. J. 77, 110. [BIBCODE 1933ApJ....77..110S ] Smith, M. A., Patten, B. M., and Goldberg, L. 1989, Astron. J. 98, 2233. [BIBCODE 1989AJ.....98.2233S ]