COMMISSIONS 27 AND 42 OF THE IAU INFORMATION BULLETIN ON VARIABLE STARS Number 4028 Konkoly Observatory Budapest 19 May 1994 HU ISSN 0374 - 0676 FURTHER PHOTOMETRY OF alpha Ori AND gamma Ori We present photometry of alpha Ori and gamma Ori, obtained differentially with respect to phi^2 Ori (V=4.09, B-V=0.95). These data were obtained from November 1992 to April 1994, primarily with a 15-cm reflector at the 2800-m elevation of Mauna Kea in Hawaii. The data of 8/9 January 1994 were obtained with the Lowell 0.6-m telescope at Cerro Tololo, stopped down to about 0.36-m, and using a 3.7 magnitude neutral density filter. Transformation coefficients for conversion of the data to the UBV system were obtained from observations of red-blue pairs (Hall 1983). Typically, each data point on alpha Ori in Table 1 and Figure 1 represents three bracketed differential measures. For previous data see Krisciunas and Fisher (1988), Krisciunas (1990), and Krisciunas (1992). Guinan et al. (1993) noted the relatively rapid decrease in brightness of alpha Ori by nearly 0.5 magnitude from October 1992 to February 1993 (approx. JD 2448900 to 9000). A previous such dimming, by 0.7 mag, occurred from April 1988 to February 1989 (approx. JD 2447300 to 7600). Krisciunas and Fisher (1988) noted that the check star, gamma Ori, was variable. Since this star is one of the secondary standards of the UBV system (Johnson, 1963) one might say that its V magnitude is, by definition, 1.64. But when we have carried out all-sky photometry, multiple measures of gamma Ori have been noted to be inconsistent with each other, and their mean value can indicate that gamma Ori does not always fit with other standards. We believe that phi^2 Ori is constant and that gamma Ori is a low amplitude (irregular?) variable. Table 1. Photometry of alpha Orionis Date Julian Date V B-V 25/26 Nov 1992 0834 2448952.8569 0.581 +/- 0.015 24/25 Jan 1993 0803 9012.8354 0.838 0.008 18/19 Feb 1993 0648 9037.7833 0.858 0.002 14/15 Mar 1993 0601 9061.7507 0.881 0.002 23/24 Mar 1993 0559 9070.7493 0.891 0.009 28/29 Mar 1993 0636 9075.7750 0.835 0.016 13/14 Apr 1993 0632 9091.7722 0.864 0.012 22/23 Apr 1993 0602 9100.7514 0.823 0.019 8/9 Sep 1993 1450 9240.1180 0.818 0.013 10/11 Nov 1993 0914 9302.8851 0.588 0.018 19/20 Dec 1993 0753 9341.8313 0.607 0.003 20/21 Dec 1993 0924 9342.8917 0.589 0.006 8/9 Jan 1994 0406 9361.6706 0.693 0.001 1.871 6/7 Mar 1994 0645 9418.7813 0.666 0.015 7/8 Apr 1994 0607 9450.7552 0.651 0.012 [FIGURE 1] Figure 1 - Photometry of alpha Ori (open circles) and gamma Ori (dots), derived with respect to phi2 Ori. [FIGURE 2] Figure 2 - Photometry of gamma Ori, derived with respect to phi2 Ori. Pluses: data of David Fisher. Open circles: Krisciunas data, based on two or more differential measures. Dots: Krisciunas data based on a single differential measure. [FIGURE 3] Figure 3 - Histogram of data in Figure 2. In Figure 2 we give the gamma Ori data of the last eight observing seasons. The mean V magnitude is 1.626 +/-0.004, and the standard deviation of the distribution is +/-0.027 mag, based on 61 nightly means. In Figure 3 note the evidence for a bimodal distribution of values. K. KRISCIUNAS Joint Astronomy Centre 660 N. A'ohoku Place University Park Hilo, Hawaii 96720 USA kevin@jach.hawaii.edu (Internet) References: Guinan, E., Deeney, B., and Miller, K., 1993, I.A.U. Circ., No. 5708 [BIBCODE 1993IAUC.5708....1G ] Hall, D. S., 1983, I.A.P.P.P. Communic., No. 11, 3 [BIBCODE 1983IAPPP..11....3H ] Johnson, H. L., 1963, in Basic Astronomical Data, Univ. of Chicago Press, p. 204 [BIBCODE 1963bad..book..204J ] Krisciunas, K. and Fisher, D., 1988, IBVS, No. 3227 Krisciunas, K., 1990, IBVS, No. 3477 Krisciunas, K., 1992, IBVS, No. 3728