COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2769 Konkoly Observatory Budapest 5 August 1985 HU ISSN 0374 - 0676 A SMALL ELLIPTICITY EFFECT IN THE RS CVn BINARY 33 PISCIUM 33 Psc = HR 3 = HD 28 first came to our attention when Young and Koniges (1977) and Lloyd Evans (1977) noted this SB1 showed Ca II H and K emission, indicating it is an RS CVn binary. Therefore we suspected photometry might show the characteristic "wave". Because of the large orbital eccentricity, e = 0.272 +/- 0.017, found by Harper (1926) it was additionally interesting in connection with the question of synchronous rotation in eccentric orbits (Eaton et al. 1983). The spectral type appears in the literature most often as K1 III. The orbital period is 72.93d (Harper 1926, 1935). The H and K emission is not very strong, only 2 on Wilson's 0-to-5 scale (Glebocki and Stawikowski 1979). According to Eggen (1978) "numerous UBV observations indicate a range of about 0.05mag in V." Percy and Welch (1982), however, made differential photoelectric measures on 9 nights over a 118-day interval and found no indication of variability. The rms deviation of their 9 measures was only +/- 0.004mag. Between July 1979 and January 1985 (JD 2444069.6 through 2446077.6) 11 different observers observed 33 Psc differentially with respect to the comparison star HR 29 = HD 587. Altogether they obtained 201 values of DeltaV, each a mean of generally three intercomparisons between variable and comparison. A few observed in B and U also, but in this note we analyze only the more numerous DeltaV values. This is summarized in Table I. All photometry was, of course, corrected for differential atmospheric extinction and transformed differentially to V of the UBV system with known transformation coefficients. Because 33 Psc and HR 29 differ in B-V color index by only 0.06mag, the 5.5 years of photometry from 11 different observatories resulted in an unusually homogeneous set. Some earlier photometry of 33 Psc was obtained in 1978 by Robert E. Montle at the James C. Veen Observatory, but unfortunately his comparison star was 30 Psc, the known variable YY Psc. To search for possible variability, we generated a periodogram by fitting a sinusoid to the DeltaV values, with periods ranging between 1d and 150d. Nowhere in that range did the resulting full amplitude exceed 0.010mag. We considered it significant, however, that a 0.008mag amplitude (and Table I Tally of Observations Observer Observatory Location Telescope Means Barksdale Barksdale Florida 14-inch 8 Boyd Fairborn Arizona 10-inch 124 Eaton Kitt Peak Arizona 16-inch 10 Fried Braeside Arizona 16-inch 3 Henry Dyer Tennessee 24-inch 11 Henry Kitt Peak Arizona 16-inch 12 Hopkins Hopkins-Phoenix Arizona 8-inch 10 Pazzi Nigel South Africa 12-inch 6 Poe Dyer Tennessee 24-inch 5 Renner Scuppernong Wisconsin 10-inch 7 Rogers Southwestern Oklahoma Oklahoma 14-inch 4 Sabia Keystone Pennsylvania 9-inch 1 corresponding diminution in the sum of the squares of the residuals) occurred at 36.51d +/- 0.12d, which is (within the uncertainty) exactly half the 72.93d orbital period. This can be explained most simply as a detection of the cos 2theta variation produced by the ellipticity effect. The amplitude at 72.93d was only 0.001mag, indicating that the cos (theta) reflection effect was undetectable. A portion of the periodogram, between 31d and 41d, is shown in Figure 1. Noting that 365 days is almost exactly 10 times 36.51d, we anticipate that the unavoidable 365-day observing window would produce aliases at P = 365d/9 = 40.6d and P = 365d/11 = 33.2d. Indeed, as Figure 1 shows, prominent peaks do appear at 40.5d +/- 0.3d and 33.2d +/- 0.1d. Analysis of our residuals identified 5 values of DeltaV which were larger than would be expected in a Gaussian distribution, i.e., greater than 3sigma. To check whether these were influencing our results, we redid the analysis with these 5 values excluded. The results, however, were not significantly altered. Table II is a summary of parameters deduced from the two sets of data. Both estimates of the period, 36.51d +/- 0.12d and 36.38d +/- 0.10d, are consistent with 36.465d, which is half the orbital period. The full amplitude of the light variation, an average for the two estimates, is 0.007mag. Note that the rms derivation from the Fourier fit was reduced to +/- 0.009mag when we used the abbreviated data set. The time of minimum light, given for the middle of the 5.5-year interval, should be useful as a recent time of conjunction. [FIGURE 1] Figure 1 Periodogram for 5.5 years of V-band photometry of 33 Piscium. The abscissa is assumed period, in days. The lower part is the full amplitude of a sinusoidal fit. The upper part is the sum of the squares of the residuals from that fit. Note the 0.007 amplitude at 36.5 days which is half the known orbital period; it probably arises from the ellipticity effect. Two other peaks, at 33.2 and 40.5 days, are aliases produced by the 365-day observing window. Table II Parameters from Fourier analysis number of points 201 196 best period 36.51d +/- 0.12d 36.38d +/- 0.10d mean DeltaV -1.218mag +/- 0.001mag -1.219mag +/- 0.001mag full amplitude in V 0.008mag +/- 0.003mag 0.006mag +/- 0.002mag JD (minimum light) 2445072 +/- 2 2445069 +/- 2 rms deviation +/- 0.014mag +/- 0.009mag Other possible periods seen in the complete periodogram may be significant but, because the amplitudes are so small and because the periods are neither close to nor commensurate with the orbital period, we are reluctant to make additional conclusions. WILLIAM S. BARKSDALE JEFFREY L. HOPKINS 633 Balmoral Road Hopkins-Phoenix Observatory Winter Park, Florida 32789, U.S.A. 7812 West Clayton Drive Phoenix, Arizona 85033, U.S.A. LOUIS J. BOYD RUSSELL M. GENET LUCIANO PAZZI Fairborn Observatory Nigel Observatory 629 North 30th Street 39 Buxton Avenue Phoenix, Arizona 85008, U.S.A. Nigel 1490, South Africa JOEL A. EATON THOMAS R. RENNER DOUGLAS S. HALL Scuppernong Observatory GREGORY W. HENRY 4512 Deerpark Drive CLINT H. POE Dousman, Wisconsin 53118, U.S.A. W. TIMOTHY PERSINGER CHARLES W. ROGERS Dyer Observatory Department of Physics Vanderbilt University Southwestern Oklahoma State University Nashville, Tennessee 37235, U.S.A. Weatherford, Oklahoma 73096, U.S.A. ROBERT E. FRIED JOHN D. SABIA Braeside Observatory Keystone Observatory P.O. Box 906 Keystone Junior College Flagstaff, Arizona 86002, U.S.A. Scranton, Pennsylvania 18508, U.S.A. References: Eaton, J. A., Hall, D. S., Henry, G. W., Hopkins, J. L., Krisciunas, K., Landis, H. J., Louth, H., Olsen, E. H., Renner, T. R., Stelzer, H. J. 1983, Astrophys. Space Sci. 93, 271. [BIBCODE 1983Ap&SS..93..271E ] Eggen, O. J. 1978, I.B.V.S. No. 1426. Glebocki, R. and Stawikowski, A. 1979, Acta Astr. 29, 505. [BIBCODE 1979AcA....29..505G ] Harper, W. E. 1926, P.D.A.O. 3, 341. [BIBCODE 1926PDAO....3..341H ] Harper, W. E. 1935, P.D.A.O. 6, 207. Lloyd Evans, T. 1977, M.N.A.S.S.A. 36, 41. [BIBCODE 1977MNSSA..36...41L ] Percy, J. R. and Welch, D. L. 1982, J.R.A.S.C. 76, 185. [BIBCODE 1982JRASC..76..185P ] Young, A. and Koniges, A. 1977, Ap. J. 211, 836. [BIBCODE 1977ApJ...211..836Y ]