COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2546 Konkoly Observatory Budapest 6 July 1984 HU ISSN 0374-0676 FIVE BRIGHT NEW VARIABLE STARS We report UBV photometry obtained during the first quarter of 1984 with the 10-inch automatic photoelectric telescope at Fairborn Observatory West in Phoenix, Arizona, which shows five bright stars to be variable: HR 4430, HD 25893, HD 28591, HD 116204, and HD 136901. We suspected variability because all five have characteristics which marked them as possible RS CVn binaries. HD 4430 is a known SB1 (Northcott 1947) containing a late-type giant. The other four, though not known binaries, were of late spectral type and Bidelman (1983) reported Ca II H and K in emission. Heard (1956) did, however, report "variable velocity" for HD 136901 on the basis of nine radial velocity measures. HD 116204 was included in the list of 20 suspected variables published by Hall (1983). Table I lists the approximate V magnitude of each variable, the comparison star we used, the spectral type, and the source of the spectral type. Table I Star V Comparison Sp. Tp. Source HR 4430 6m4 HD 101133 K2 III Y.B.S.C. HD 25893 7.1 HD 25975 G5 HD HD 28591 6.7 HD 28620 G5 HD HD 116204 7.2 HD 116010 K2 HD HD 136901 7.4 HD 136643 K1 III Heard (1956) Our photometry is described by Boyd, Hall, and Genet (1984) and the data have been sent to the I.A.U. Commission 27 Archive for Unpublished Data on Variable Stars (Breger 1982) where they are available as file no. 136 . HD 25893 is ADS 2995 but, since the two visual components are separated by only about 1.5 arcseconds, both components were included in the diaphragm during photometry. We determined photometric periods by estimating times of well-defined minima and maxima and using least squares to fit those times with a linear ephemeris. If maxima did not occur midway between successive minima, we shifted their times accordingly by a constant amount. For HD 28591 we added 4.0d to times of maxima; for HD 116204 we subtracted 3.0d. The resulting ephemerides are given in Table II, where integer values of n refer to minimum light and half-integer values of n refer to maximum light. Table II Star Ephemeris V HR 4430 2445704.1+ 39d0 n 0.13m +-2.2 +-1.3 HD 25893 2445701.0+ 7.37 n 0.03 +- .4 +- .06 HD 28591 2445698.9+ 21.3 n 0.07 +-1.0 +- .4 HD 116204 2445700.3+ 21.7 n 0.06 +- .5 +- .2 HD 136901 2445705.9+ 9.63 n 0.16 +- .2 +- .05 Light curves are plotted in Figures 1 through 5. Each point is a mean of three individual observations of the variable, each of these three flanked by comparison star measures; each mean corresponds to one line in [FIGURE 1] Figure 1 Light curve of HR 4430 . [FIGURE 2] Figure 2 Light curve of HD 25893. [FIGURE 3] Figure 3 Light curve of HD 28591. [FIGURE 4] Figure 4 Light curve of HD 116204. [FIGURE 5] Figure 5 Light curve of HD 136901. file no. 136 . Except for one case, phases are computed with the ephemerides in Table II. For HR 4430 the photometric period is very nearly half the spectroscopically determined orbital period of Northcott (1947), so we used her ephemeris JD(hel.) = 2430852.014 + 74.861d n, where the initial epoch is a time of periastron. The approximate total range of the brightness variation in V is given in the last column of Table II. The corresponding ranges in B and U are similar. Because Lucy and Sweeney (1971) judged the orbit of HR 4430 circular, we ignored the eccentricity and estimated a time of conjunction (the K1 III star behind) to be JD 2430826.0 +- 1.0d. Extrapolating this forward to the epoch of our photometry, we concluded that the two minima seen in Figure 1 coincide with the two conjunctions and the two maxim coincide with the two quadratures, all to within the cumulative uncertainty of about +- 0.05p. Such a light curve could be a result of ellipticity and/or shallow eclipses, similar to that of the giant eclipsing binary 5 Ceti (Lines and Hall 1981). On the other hand, we note that the two maxima are not equally bright and the two minima are not equally faint, suggesting similarity to the double- humped light curve of the RS CVn binary HD 185151 (Bopp et al. 1982), although the absence of Ca II H and K emission (Lloyd-Evans 1977) suggests HR 4430 is not an RS CVn binary. The other four stars, because of the Ca II H and K emission, probably are RS CVn binaries. Therefore the photometric periods in Table II are probably rotational periods for the brighter star in each, which we presume are unevenly darkened with starspots. Moreover, since rotation in virtually all known RS CVn binaries is synchronous to within a very few percent, these photometric periods provide useful estimates of what future spectroscopic observations may prove the orbital period to be. LOUIS J. BOYD Fairborn Observatory West 629 North 30th Street Phoenix, Arizona 85008 RUSSELL M. GENET Fairborn Observatory East 1247 Folk Road Fairborn, Ohio 45324 DOUGLAS S. HALL Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 References: Bidelman, W. P. 1983, A.J. 88, 1182. [BIBCODE 1983AJ.....88.1182B ] Bopp, B. W., Fekel, F. C., Hall, D. S., Henry, G. W., Noah, P. V., Africano, J., Wilkerson, M. S., and Beavers, W. I. 1982, A.J. 87, 1035. [BIBCODE 1982AJ.....87.1035B ] Boyd, L. J., Genet, R. M., and Hall, D. S. 1984, I.B.V.S., No. 2511 Breger, M. 1982, I.B.V.S. No. 2246. Hall, D. S. 1983, I.A.P.P.P. Comm. No. 13, 6. [BIBCODE 1983IAPPP..13....6H ] Heard, J. F. 1956, P.D.D.O. 2, 107. [BIBCODE 1956PDDO....2..107H ] Lines, R. D. and Hall, D. S. 1981, I.B.V.S. No. 2013. Lloyd-Evans, T. 1977, M.N.A.S.S.A. 36, 41. [BIBCODE 1977MNSSA..36...41L ] Lucy, L. B. and Sweeney, M. A. 1971, A.J. 76, 544. [BIBCODE 1971AJ.....76..544L ] Northcott, R.J. 1947, P.D.D.O. 1, 369. [BIBCODE 1947PDDO....1..369N ] [DATAFILE 3]