COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3392 Konkoly Observatory Budapest 30 October 1989 HU ISSN 0374 - 0676 NEW PHOTOELECTRIC OBSERVATIONS AND THE PERIOD BEHAVIOR OF BX PEGASI Recently, I reported on photoelectric observations obtained in the fall of 1986 of the very short period system, BX Peg (Samec and Bookmyer 1987). The observing history for this system was summarized in that report. The present observations were made on 20, 21 June and 11, 12, 15, and 16 October 1988. The 0.6-m Morgan F/13.5 reflector at Lowell Observatory in Flagstaff, Arizona was used with standard U, B, V filters and a thermoelectrically cooled EMI 6256 photomultiplier tube. The comparison and check stars were BD +25d4584 and BD +25d4582, respectively. The observations were transformed to the standard system from observations of eight stars in standard cluster Pleiades (Johnson and Morgan 1953, and Johnson and Mitchell 1958). More than 500 observations were obtained in both B and V Three epochs of minimum light were determined from observations made during one primary and two secondary eclipses. All minima were determined by an iterative technique based on the Hertzsprung method (1928). These are the last three epochs given in Table I. Table I JD Hel 2440000+ Minimum Cycles O-C Source 3790.17075 I -6637.0 +0.0008 Zhai and Zhang 1979 5651.3219 I 0.0 +0.0001 BAV #38 1984 6701.7787 I 3746.0 +0.0011 Samec and Bookmyer 1987 6703.7409 I 3753.0 +0.0003 Samec and Bookmyer 1987 6703.8797 II 3753.5 -0.0010 Samec and Bookmyer 1987 6704.7227 II 3756.5 0.0007 Samec and Bookmyer 1987 7333.8400 I 6000.0 -0.0057 Present Observations 7450.6339 II 6416.5 -0.0070 Present Observations 7451.7556 II 6420.5 -0.0070 Present Observations [FIGURE 1] Fig. 1 - Standard Light Curves of BX Peg defined by the individual observations All the published epochs of minimum light determined from photoelectric observations excluding the early determination by Chou (1966) and our present observations were introduced into a least squares solution to obtain the following improved ephemeris: JD Hel Min. I=2445651.3218 + 0.28042066 * E +-0.0002 +-0.00000004 (p.e.) This was used in calculating the O-C's of the timings of minimum light included in Table I. Apparently, the period of BX Peg has remained constant for over 10400 cycles previous to our 1986 observations. Earlier timings including the one by Chou indicate that a rather major period decrease took place about the time Zhai and Zhang (1979) made their observations. Indeed, our newly determined minima may indicate that yet another period decrease has taken place! Additional timings of minimum light are needed to confirm this preliminary result. Several combinations of timings of minimum light were introduced into least squares fits to obtain periods for possible use in phasing our observations. The period, 0.28042024(11)d was found to produce the best fit. This was calculated by combining all the photoelectric epochs of minimum light subsequent to the one determined by Chou. The B and V light curves of V728 Her defined by the individual observations are shown in Figure 1 as Delta m versus phase. The analysis of the observations is underway. RONALD G. SAMEC J.I. Holcomb Observatory and Physics Department Butler University Indianapolis, IN 46208 USA References: Chou, K.C. 1966, Rocznik Astron. Krakow, 37, Hertzsprung, E. 1928, Bull. Astron. Inst. Neth. 4, 179. [BIBCODE 1928BAN.....4..178H ] Johnson, H.L., and Mitchell, R.I. 1958, Ap. J. 128, 31. [BIBCODE 1958ApJ...128...31J ] Johnson, H.L., and Morgan, W.W. 1953, Ap. J. 117, 313. [BIBCODE 1953ApJ...117..313J ] Samec, R.G., and Bookmyer, B.B. 1987, I.B.V.S. No. 2999. Zhai, D.S., and Zhang, Y.X. 1979, Kexue Tongbao 21, 895.