COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3616 Konkoly Observatory Budapest 5 June 1991 HU ISSN 0374 - 0676 SEMI-REGULAR BEHAVIOR FOR THE SUPERGIANT RHO CAS The F8 yellow supergiant Ia-0 star Rho Cas undergoes mass-loss episodes with accompanying changes in brightness, spectrum and radial velocity. Sheffer & Lambert (1986) have suggested that the star undergoes semi-regular pulsation of the atmosphere with a dominant radial pulsation mode of about 500 days. Boyarchuk et al. (1988) noted that at the beginning of 1986, the spectrum of the star changed dramatically: TiO bands and other characteristics of late stars appeared. This change was accompanied by a light minimum. Photometrically, Rho Cas is well observed. Recent magnitudes have been published by Leiker & Hoff (1987), Leiker et al. (1988), Leiker et al. (1989a), Leiker & Hoff (1990) and Halbedel (1988). This paper reports on more recent unpublished magnitudes obtained by Halbedel at the Corralitos Observatory, and combines all recent observations into a light curve for the previous 6 years. All observations were made with the 0.6-m. telescope of the Corralitos Observatory and its single channel uncooled photon-counting photometer equipped with an EMI 9924A tube. The comparison stars utilized were HD 223173 (V=5.510; B- V=+1.650) and Tau Cas (V=4.867; B-V=+1.116). These stars were stable to within 0.016 in V and 0.018 in B-V. It has been suggested by Leiker & Hoff (1988) and Leiker et al. (1989b) that Tau Cas is itself a variable star: indeed it appears in the New Catalogue of Suspected Variable Stars. However, as previously observed by the author (Halbedel, 1989), no such variation can be confirmed. On the basis of 59 measures over the JD range 2446994-8244, this conclusion is reaffirmed: the average standard errors about the mean for Tau Cas were 0.012 in V magnitude and 0.015 in B-V. If variability exists, it is below the level that can be detected with this system. Therefore, it was continued in usage as a comparison star for Rho Cas. [FIGURE 1] FIGURE 1: MAGNITUDES AND COLORS FOR RHO CAS. THE TOP DIAGRAM SHOWS V MAGNITUDE. THE BOTTOM B-V. TABLE 1: MAGNITUDES FOR RHO CAS JD JD (2440000+) V B-V (2440000+) V B-V 7411.90069 4.485 +1.266 7810.74583 4.669 +1.387 7412.78588 4.456 1.301 7818.75139 4.678 1.396 7435.87916 4.533 1.263 7827.74971 4.673 1.405 7436.75069 4.539 1.239 7835.70139 4.692 1.382 7437.72083 4.553 1.244 7861.60486 4.662 1.342 7440.76458 4.574 1.286 7878.64374 4.669 1.317 7441.72569 4.540 1.302 7896.61250 4.640 1.313 7470.69930 4.599 1.292 7915.59513 4.617 1.298 7472.69305 4.558 1.324 7917.59236 4.591 1.297 7475.66041 4.588 1.307 8122.81875 4.508 1.191 7501.68611 4.618 1.297 8133.83541 4.500 1.219 7516.61874 4.591 1.329 8159.78611 4.481 1.215 7525.61944 4.586 1.306 8176.69028 4.517 1.225 7526.60763 4.586 1.310 8178.72639 4.479 1.244 7540.59027 4.528 1.282 8201.68263 4.568 1.227 7703.91458 4.515 1.286 8204.61111 4.474 1.245 7790.76528 4.643 1.400 8225.62917 4.498 1.286 7793.82639 4.666 1.381 8228.64097 4.538 1.222 7806.79444 4.642 1.412 8244.63819 4.544 1.262 The newly obtained, thusfar unpublished values for Rho Cas are detailed in Table 1. Figure 1 represents all the magnitudes published in the papers previously cited as well as the new values from Table 1. There is surprisingly little scatter when one considers the multiplicity of sources. The behavior of the star is characterised by an initial brightening, followed by semi-regular cycles with possibly gradually decreasing maxima. The color changes are in phase with the V mag behavior. The star blues as it brightens and reddens as it fades. At any rate, of late Rho Cas appears to be following semi-regular behavior with an approximate cycle time of 400-420 days. Since the star has bean known to undergo outbursts in the past, it will be of interest to follow its behavior in the future. It will continue to be observed at the Corralitos Observatory indefinitely. E.M. HALBEDEL Corralitos Observatory P.O. Box 16314 Las Cruces, NM 88004-6314 U.S.A. REFERENCES Boyarchuk, A.A., Boyarchuk, M.E., & Petrov, P.P. 1988, in Proc. Soviet-Finnish Astro. Meeting, eds. U. Hanni & I. Tuominen (Tartu) Halbedel, E.M. 1988, IBVS No. 3171 Halbedel, E.M. 1989, IBVS No. 3394 Leiker, P.S. & Hoff, D.B. 1987, IBVS No. 3020 Leiker, P.S. & Hoff, D.B. 1988, IBVS No. 3176 Leiker, P.S. & Hoff, D.B. 1990, IBVS No. 3490 Leiker, P.S., Hoff, D.B., Nesbella, J., Gainer, M., Milton, R., & Pray, D. 1988, IBVS No. 3172 Leiker, P.S., Hoff, D.B., & Milton, R. 1989a, IBVS No. 3345 Leiker, P.S., Hoff, D.B., & Tuttle, M.M. 1989b, IBVS No. 3341 Sheffer, Y. & Lambert, D.L. 1986, PASP, 98, 914 [BIBCODE 1986PASP...98..914S ]