COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2737 Konkoly Observatory Budapest 30 May 1985 HU ISSN 0374 - 0676 THREE MODES OF VARIABILITY IN THE BRIGHT STAR HR 7428 We began photometry of HR 7428 = HD 184398/9 after it appeared on listings of bright suspected variable stars (Hall 1983ab). The literature contains rather many references to this bright spectroscopic binary, of which we mention about half. Radial velocity measures by Sanford (1925) showed the orbital period to be 108.5707d +/- 0.05d. Lucy and Sweeney (1971) later recomputed a circular orbit after concluding it was not significantly eccentric. The spectral type of the primary component has appeared in the literature as K2, cG6, K2 III, K2 (II-III), K2 II-III, and K2 II-III e; the secondary component has been designated variously as A3, A, A?, A0, and A0 V. Ca II H and K emission was first noted by Bidelman (Gratton 1950), the strength being 3 on Wilson's 0-to-5 scale (Glebocki and Stawikowski 1979), whereas H alpha appears in absorption (Bopp and Talcott 1978). Soft x-ray emission has been detected by Walter and Bowyer (1981). Argue (1966) gives the magnitudes as V = 6.36mag, B-V = 1.16mag, U-B = 0.91mag. As shown in Table I, we obtained differential photometry at eight different observatories in one or all three bandpasses of the UBV system. From the middle of 1982 through the end of 1984, we obtained 179 means of 2-to-5 individual differential measures between HR 7428 and the comparison star HD 184170. Inspection of our 2.5 years of photometry showed that HR 7428 was varying by about 0.05mag with a period around 55 days. Since this was so nearly half the known orbital period, we did Fourier analysis with the familiar truncated series which allows for terms in A1cos(theta) and A2cos(2theta). Repeated fits with different values assumed for the period, along with chi-squared analysis, indicated P = 108.85d +/- 1.15d. Application of the period-finding technique of Lafler and Kinman (1965) found values which were consistent. Thus both estimates (Fourier and Lafler-Kinman) are in agreement with Sanford's spectroscopically determined orbital period. Table I Tally of Observations Observer Location Telescope Means lambda Barksdale Florida 14-inch 2 V Boyd Arizona 10-inch 117 VBU Fried Arizona 16-inch 11 VBU Hoff Iowa 16-inch 3 V Ingvarsson Sweden 14-inch 21 V Nielsen Delaware 4-inch 5 V Stelzer Illinois 14-inch 14 V Wasson California 8-inch 6 V [FIGURE 1] Light curve of the K2 II-III + A spectroscopic binary HR 7428, where DeltaV is in the sense variable minus comparison and phase is based on the 108.6d orbital period of Sanford. Each point is a mean of 2-to-5 individual intercomparisons. The solid curve is a Fourier fit allowing for terms in cos(theta) and cos(2theta). Two points (0.38P,-0.43mag and 0.98P,-0.45mag) were off scale and are not plotted but were included in the Fourier analysis. We see evidence of an ellipticity effect and a smaller reflection effect. The 0.015mag difference between the two maxima, at 0.25P and 0.75P, indicates a possible RS CVn-type wave. The total range from minimum at 0.00P to the higher maximum at 0.25P is 0.045mag in V. Redoing the Fourier analysis with the 108.5707d period exactly, we found A2 = -0.017mag, A1 = -0.005mag, a mean light level of DeltaV = -0.522mag, and JD 2445062.88 +/- 0.05d for a time of the deeper minimum. The 179 mean values of DeltaV are plotted in Figure 1, where the curve represents the above Fourier coefficients and zero phase is at the deeper minimum. A reasonable interpretation of the light curve would be that the A2 coefficient indicates the ellipticity effect, not surprising in a binary with one very luminous (hence, large) star, and that the A2 coefficient indicates the differential reflection effect, not surprising in a binary composed of a large cool star and a smaller hot star. A residual asymmetry, not allowed for in our Fourier analysis which contained no sin(theta) terms, appears in Figure 1 as a 0.015mag difference in height between the maxima at 0.25P and 0.75P. This might be a manifestation of the "wave" seen in other chromospherically active stars, even ones with quite long rotational periods, the longest known being HR 1362 with P = 154 days (Boyd et al. 1985). We see that HR 7428 reaches maximum brightness around 0.25P (because of this asymmetry) and minimum brightness around 0.00P (because of the reflection effect), the full range being approximately 0.045mag in V. We acknowledge support from National Science Foundation research grant AST 84-14594. WILLIAM S. BARKSDALE 633 Balmoral Road Winter Park, Florida 32789 LOUIS J. BOYD RUSSELL M. GENET Fairborn Observatory 629 North 30th Street Phoenix, Arizona 85008 ROBERT E. FRIED Braeside Observatory P.O. Box 906 Flagstaff, Arizona 86002 DOUGLAS S. HALL WILLIAM T. PERSINGER Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 DARREL B. HOFF Hillside Observatory University of Northern Iowa Cedar Falls, Iowa 50614 STIG I. INGVARSSON Tjorn Island Astronomical Observatory Glashed 302 S-440 60 Skarhamn Sweden PAUL NIELSEN 1817 Shipley Road Wilmington, Delaware 19803 HAROLD J. STELZER 1223 Ashland Avenue River Forest, Illinois 60305 NORMAN F. WASSON Sunset Hills Observatory 15870 Del Prado Drive Hacienda Heights, California 91745 References: Argue, A. N. 1966, M.N. 133, 475. [BIBCODE 1966MNRAS.133..475A ] Bopp, B. W. and Talcott, J. C. 1978, A.J. 83, 1517. [BIBCODE 1978AJ.....83.1517B ] Boyd, L. J., Genet, R. M., Hall, D. S., Barksdale, W. S., Fried, R. E., Henry, G. W., Pearsall, J. E., and Wasson, N. F. 1985, I.B.V.S. No. 2696. Glebocki, R. and Stawikowski, A. 1979, Acta Astr. 29, 505. [BIBCODE 1979AcA....29..505G ] Gratton, L. 1950, Ap.J. 111, 31. [BIBCODE 1950ApJ...111...31G ] Hall, D. S. 1983a, I.A.P.P.P. Comm. No. 9, 47. [BIBCODE 1983IAPPP...9...47H ] Hall, D. S. 1983b, I.A.P.P.P. Comm. No. 13, 6. [BIBCODE 1983IAPPP..13....6H ] Lafler, J. and Kinman, T. D. 1965, Ap. J. Suppl. 11, 216. [BIBCODE 1965ApJS...11..216L ] Lucy, L. B. and Sweeney, M. A. 1971, A.J. 76, 544. [BIBCODE 1971AJ.....76..544L ] Sanford, R. F. 1925, Ap.J. 61, 326. [BIBCODE 1925ApJ....61..320S ] Walter, F. M. and Bowyer, S. 1981, Ap.J. 245, 671. [BIBCODE 1981ApJ...245..671W ]