COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1798 Konkoly Observatory Budapest 1980 June 3 93 LEONIS: A NEW VARIABLE STAR The bright (V=4.5m) star 93 Leonis is a long-period RS CVn binary with a spectral type of A+G5IV-III according to Batten et al. (1978) and an orbital period of 71.70d according to Cannon (1910). Young and Koniges (1977) quote a spectral type of F8 IV but note that a secondary component in the spectrum, probably the cooler star, is responsible for the moderately strong Ca II H & K emission. To look for the photometric distortion wave characteristic of so many other RS CVn binaries, we observed 93 Leo photoelectrically in 1976 and in 1979. The 1976 observations, by Landis, revealed no variation larger than +-0.01m, as reported by Heiser (1978), but the 1979 observations did show 93 Leo to be variable, with an amplitude around 0.03m. We observed 93 Leo differentially with respect to the comparison star 92 Leo mostly in one color. Landis had observed on 14 nights in 1976 between JD 2,442,871.6 and 2,442,937.6. Louth, Montle, Skillman, and Vaucher observed on 44 nights in 1979 between JD 2,443,906.9 and 2,444,043.6, almost two cycles of the 71.7d orbital period. Details of the observations at Dyer are given by Vaucher (1979). The individual differential observations, generally three on each night, were corrected for differential atmospheric extinction with nightly extinction coefficients at Dyer but mean coefficients at the other observatories. Then they were transformed to V of the UBV system with known transformation coefficients and a mean color difference of Delta(B-V)=-0.41m, where Delta is in the sense 93 minus 92 Leo. At Dyer observations were obtained also in B of the UBV system, but they are not presented here. On 8 nights in 1979 at Dyer the comparison star 92 Leo was observed 17 times differentially with respect to the check star HR 4505. There was no indication of significant variability of one respect to the other, the standard deviation of a single observation from the mean being +-0.005m in V and +-0.009m in B. Nightly means of the 1979 Delta V magnitudes are plotted in the Figure versus phase computed with the ephemeris JD(hel.)=2,418,017.865+71.70d n, where the epoch is a time of conjunction (the A-type star behind) derived from the time of periastron given by Cannon (1910) and the period is that used by [FIGURE 1] Cannon in his determination of the spectroscopic orbit. We used Fourier analysis to express the light as l=A_0+A_1cos +A_2cos +B_1sin , where unit light corresponds to Delta V=-0.750m. The Fourier fit appears as the curve in the Figure. The resulting coefficients are given in the Table below. 1976 1979 A_0 0.9739+-0.0022 1.0000+-0.0019 A_1 +0.0055+-0.0033 +0.0122+-0.0025 A_2 +0.0012+-0.0032 +0.0015+-0.0028 B_1 +0.0011+-0.0031 -0.0038+-0.0028 The variation we see in 1979 is probably a distortion wave, with a full amplitude of a V=0.028m+-0.005m and a minimum at 0.452p+-0.034p. Seeing this variability prompted us to look again at the 1976 photometry. Fourier analysis of those observations resulted in the coefficients shown also in the Table. The distortion wave was probably there in 1976 also because, although its amplitude of Delta V=0.013m+-0.007m was smaller and significant at only the 2 sigma level, its minimum at 0.532p+-0.087p was at the same phase, within the uncertainties. A final curiosity is the smaller value of A_0 in 1976, indicating a mean light level almost 0.03m fainter than in 1979. Any uncertainty in the transformation of Landis' data should have produced a systematic error of only +-0.005m. We can probably say with confidence that the differential reflection effect cannot be producing this variation. For one reason, measurable reflection would be unlikely in such a long-period binary. For a second reason, its amplitude may be variable. And for a third reason, maximum light occurs around phase 0.0p, when the A-type (presumably the hotter) star is behind. In making this last statement we are assuming the uncertainty in Cannon's 71.70d period is around +-0.01d, in which case phases in our Figure would be uncertain by only +-0.05p. If the uncertainty is much larger, then we have lost our fix on the phasing, because the vanishingly small A_2 coefficients can provide no help. D.S.H. is happy to acknowledge that part of this work was supported by N.A.S.A. research grant NSG-7543. DOUGLAS S. HALL GREGORY W. HENRY CHRISTOPHER A. VAUCHER Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 HOWARD J. LANDIS ^* Price Road West RFD No. 2, Box 44ED Locust Grove, Georgia 30248 HOWARD LOUTH ^* 2199 Hathaway Road Sedro Woolley, Washington 98284 ROBERT E. MONTLE Veen Observatory 3308 Kissing Rock Road Southeast Lowell, Michigan 49331 DAVID R. SKILLMAN ^* 9514 48th Avenue College Park, Maryland 20740 References: Batten, A.H., Fletcher, J.M., Mann, P.J. 1978, P.D.A.O. 15, 158. [BIBCODE 1978PDAO...15..121B ] Cannon, J.B. 1910, J.R.A.S. Canada 4, 455. [BIBCODE 1910JRASC...4..452C ] Heiser, A.M. 1978, B.A.A.S. 10, 98. [BIBCODE 1978BAAS...10...98H ] Vaucher, C.A. 1979, M.A. Thesis, Vanderbilt University. Young, A. and Koniges, A. 1977, Ap. J. 211, 836. [BIBCODE 1977ApJ...211..836Y ] ^* of the A.A.V.S.O.