COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2543 Konkoly Observatory Budapest 27 June 1984 HU ISSN 0374-0676 HD 8358 AND HD 106225: TWO NEW VARIABLE STARS We began photometry and spectroscopy because there was spectroscopic evidence that they are chromospherically active stars of the RS CVn or BY Dra type. Bidelman (1981) reported spectral type G and slightly fuzzy spectral lines (suggestive of rapid rotation) for HD 8358 and spectral type gK and strong Ca II H and K emission (evidence of strong chromospheric activity) for HD 106225. HD spectral types and approximate V magnitudes are G0 and 8.43m for HD 8358 and K0 and 8.1m for HD 106225. Photometry was obtained in the UBV bandpasses with the 48-inch telescope at Cloudcroft Observatory and with the 30- and 36-inch telescopes at McDonald Observatory. The comparison star was SAO 109848 for HD 8358 and SAO 138628 for HD 106225. Radial velocity measures were obtained for Table I Photometry of HD 8358 JD (hel.) Delta V Delta B Delta U 2445153.949 -1.007 - - 167.970 -0.999 - - 168.946 -0.897 -1.124 - 187.866 -0.865 -1.106 - 188.959 -0.857 -1.089 - 191.948 -0.953 - - 320.664 -0.937 -1.190 -1.653 321.614 -0.941 -1.200 -1.676 325.607 -1.003 -1.274 -1.762 327.608 -0.931 -1.188 -1.656 332.612 -0.946 -1.196 -1.667 337.616 -0.991 -1.260 -1.744 338.624 -0.994 -1.264 -1.748 339.620 -0.968 -1.234 -1.717 340.599 -0.894 -1.149 -1.620 341.616 -0.874 -1.115 -1.580 342.631 -0.861 -1.103 -1.564 343.624 -0.879 -1.123 -1.589 344.649 -0.891 -1.140 -1.604 345.611 -0.943 -1.203 -1.662 357.626 -0.911 -1.168 -1.631 360.619 -0.950 -1.206 -1.696 2445361.615 -0.958 -1.217 -1.687 Table II Photometry and Spectroscopy of HD 106225 JD(hel.) Delta V Delta B JD(hel.) Vr 2445110.713 0.566 0.489 2444736.764 - 7.0 111.695 .588 .516 737.665 +13.3 113.696 .688 .623 738.685 +35.0 116.674 .834 - 2444739.757 +45.7 119.677 .631 - 2445075.814 -20.4 120.685 .577 - 076.786 -37.1 121.689 .600 - 077.814 -40.2 128.671 .811 - 078.762 -29.6 141.689 .577 - 079.834 + 0.5 146.639 .726 - 356.994 -41.1 2445153.639 .604 - 358.929 -41.7 360.922 + 8.2 361.954 +34.6 717.980 +21.9 720.000 -27.8 2445721.990 -51.8 HD 106225 at Kitt Peak National Observatory. The data are presented in Tables I and II. For the photometry delta means variable minus comparison, the differential magnitudes have been corrected for differential extinction and transformed differentially to the UBV system, and each value is a nightly mean of three separate differential measures between variable and comparison. Before JD 2445200 the photometry was obtained at Cloudcroft; after that date it was obtained at McDonald. When the delta V data for HD 8358 were analyzed by the method of Lafler and Kinman (1965), no satisfactory period was found. In subsequent analysis we excluded the six (Cloudcroft) nights which were obtained 130 days earlier than the other (McDonald) nights; the result was three periods which gave comparably good fits: 0.520d +- 0.001d, 1.805d +- 0.002d, and 12.75d +- 0.25d. Because the McDonald observations were made at very nearly the same time of night each night, i.e., they are separated by very nearly integral multiples of a day, we suspected those three values might be beat periods of each other. This is probably so, because they are related by the expression 1/0.520-1=1/1.085=1-1/12.75 to within their respective uncertainties. The early (Cloudcroft) photometry was not able to resolve the ambiguity, because it gave equally good light curves with all three periods. We also point out that its light curve shape was significantly different from that given by the McDonald photometry, and that the 130-day gap separating the two was too long to let the two be phased together reliably. In Figure 1 we plot the McDonald photometry from Table I versus phase computed with the ephemeris JD (hel.) = 2445214.7 + 0.520d n, where the initial epoch is arbitrary and the value of the period is not necessarily preferred over the other two. The total amplitude of the light variation is 0.14m in V and the shape is noticeably asymmetric. [FIGURE 1] When the Delta V data for HD 106225 in Table II were analyzed with the method of Lafler and Kinman (1965), the best light curves were obtained with periods of 0.91d +- 0.01d and 10.6d +- 0.1d. As with HD 8358, because the data were obtained at nearly integral-day multiples, we suspected these two values are beat periods of each other. Indeed they are related by the expression 1/10.6=1/0.91-1 to within their respective uncertainties. When the radial velocity data for HD 106225 in Table II were analyzed with the method of Lafler and Kinman (1965), the best fits were obtained with periods of 6.851d +- 0.001d and 10.389d +- 0.001d. We are inclined to rule out the smaller of these, because it produces a radial velocity curve very skewed in shape and hence indicative of an unreasonably large orbital [FIGURE 2] eccentricity. Figure 2 is a plot of the radial velocity values in Table II versus phase computed with the ephemeris JD(hel.) = 2445214.7 + 10.389d n, where the initial epoch is arbitrary. The Ca II H and K emission observed in HD 106225 makes us think it probably is an RS CVn binary. In most RS CVn binaries photometric variability results from rotational modulation as one of the two stars, its surface darkened unevenly by large-scale spot activity, rotates approximately synchronously with the orbital period. Consequently we believe the photometric (rotational) period should be close to the spectroscopic (orbital) period and on that basis prefer 10.6d rather than 0.91d as the correct photometric period. Figure 3 is a plot of the DeltaV values from Table II versus phase computed with the ephemeris JD(hel.) = 2445214.7 + 10.60d n, where the initial epoch is arbitrary. The total amplitude of the light variation is approximately 0.25m in V and the shape is very nearly sinusoidal. Comparing the photometric period (10.6d +- 0.1d) with the spectroscopic period (10.389d +- 0.001d), we see the rotation is synchronised with the orbital motion to within 2.0% +- 1.0%. [FIGURE 3] For HD 8358 we need more photometry, obtained throughout a single night, to determine whether 0.52d or 1.083d or 12.75d is the correct period; and we need radial velocity data to determine whether it is a close binary or a rapidly rotating single star. For HD 106225 we need more photometry, over a longer baseline of time, to improve the precision of the photometric period. FRANCIS C. FEKEL DOUGLAS S. HALL Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 GREGORY W. HENRY McDonald Observatory Fort Davis, Texas 79734 References: Bidelman, W. P. 1981, A.J. 86, 553. [BIBCODE 1981AJ.....86..553B ] Lafler, J. and Kinman, T.D. 1965, Ap.J. Suppl. 11, 216.[BIBCODE 1965ApJS...11..216L ]