COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 3462 Konkoly Observatory Budapest 14 May 1990 HU ISSN 0374 - 0676 TIME OF ECLIPSE FOR THE BINARY SYSTEM PV Cas We observed an eclipse of the binary system PV Cassiopeiae (1950: RA=23h07m53s, dec = +58d08s) on 27 August 1989, UT. Our observations were made with the 24-inch (0.6 m) Cassegrain telescope at Jet Propulsion Lab's Table Mountain Observatory in the San Gabriel Mountains near Wrightwood, California, U.S.A. Measurements of brightness were made through wide-band U, B, and V filters. Untiltered brightness measurements were also obtained. We used a single-channel photometer containing a dry- ice cooled (-78degC) RCA 1P-21 photomultiplier tube. Each of our measurements of program star, comparison stars, and sky brightness was made with a five-second integration through a 20" aperture. Figure (1) is the light curve of PV Cas obtained on 27 August 1989. It shows the difference in magnitude between PV Cas and our first comparison star, SAO 035187, on the vertical axis. The scale on the horizontal axis in time, in seconds, after 04:31:29 UT. We note from Figure (1) that the light curves in each color are of approximately the same depth and shape. Figures (2a)-(2d) show plots of the difference in magnitude between our second comparison star, SAO 035190, and SAO 035187 versus tine, in seconds, after 04:31:29 UT. The noise-level fluctuations in the comparison stars are, for the most part, less than 0.05 magnitude. (Values of (P-C1) and (C2-C1) were calculated by subtracting a second order polynomial fitted to the TABLE 1 ("time" is in seconds after 04:31:29, 27 August 1989, UT) time U(P-C1) time B(P-C1) time V(P-C1) time Open(P-C1) 7705 2.687 7712 2.241 7719 2.184 7725 2.297 7732 2.687 7739 2.249 7746 2.186 7752 2.299 7766 2.676 7773 2.251 7780 2.197 7786 2.304 7793 2.699 7800 2.256 7807 2.197 7813 2.311 8284 2.651 8291 2.245 8298 2.189 8304 2.299 8311 2.685 8318 2.247 8325 2.196 8331 2.297 8339 2.680 8346 2.246 8353 2.191 8359 2.300 [FIGURE 1] data of sky-brightness-corrected C1 magnitudes versus time from the sky-brightness-corrected magnitudes measured for P and C2.) We are primarily interested in the time of minimum for PV Cas. Table (1) shows a section of our data around the point of minimum on 27 Aug 1989. From this data we get the time of minimum as 7800 seconds after our reference time, 04:31:29 UT. The uncertainty in this number is less than 60 seconds, but due to a clock drift of 1 millisecond per second in our computer, we will assign the uncertainty an upper limit of +/- 60 seconds. [FIGURE 2ab] [FIGURE 2cd] Thus, the eclipse we observed occurred on JD 2447765.7788 +/- 0.0007. Using the method described by Hall and Genet (1), we converted this time to the heliocentric Julian day, HJD 2447765.7808 +/- 0.0007. The ephemerides of Gimenez and Margrave (2) predict an eclipse for PV Cas on HJD 2447765.7840 +/- 0.0153. Our observed time of eclipse agrees, to within the uncertainty, of their predicted time. We also note that the difference in the two times is only 0.0032 days, or about 4.6 minutes! Considering that Gimenez and Margrave calculated their ephemerides from observations made prior to seven years ago, this is a remarkable degree of agreement with the presently observed behavior of PV Cas. We conclude that the ephemerides calculated by Gimenez and Margrave accurately predict the times of minimum of PV Cas, within a resaonable uncertainty, for present as well as past eclipses. This research was supported in part by a grant from the Pew Foundation. D.W. HOARD ELNA NAGASAKO Dr. WILLIAM SANDMANN Harvey Mudd College Pomona College Harvey Mudd College Claremont, CA 91711 Claremont, CA 91711 Claremont, CA 91711 U.S.A. U.S.A. U.S.A. REFERENCES: (1) Hall, Douglas S. and Genet, Russell M., Photoelectric Photometry of Variable Stars, 2nd ed., Willman-Bell, Inc., 1988. [BIBCODE 1988ppvs.book.....H ] (2) Gimenez, Alvaro and Margrave, Thomas E., "Apsidal Motion of PV Cassiopeiae", The Astronomical Journal, vol.87, no.8, August 1982, pp.1233-1236. [BIBCODE 1982AJ.....87.1233G ]