COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1902 Konkoly Observatory Budapest 1980 December 31 HU ISSN 0374-0676 12 CAMELOPARDALIS: A NEW VARIABLE STAR In this note we announce our discovery of the photometric variability of the long-period (P = 80.^d2) RS CVn binary 12 Cam = HR 1623. The most important reference is that of Abt et al. (1969), who provide the following information. The blue-violet spectrum shows a K0 III star but no trace of a secondary star. Radial velocity variations show 12 Cam to be a spectroscopic binary with an orbital period of 80.174469d +- 0.000003d and a surprisingly large orbital eccentricity of e = 0.35 +- 0.02. There is strong Ca II H & K emission associated with the K0 III star. To search for photometric variability such as is characteristic of so many other RS CVn binaries, Eaton obtained photoelectric observations in 1979 between JD 2443960.60 and 2444001.56 and saw the first indication of variability, with an amplitude well over 0.1m. Subsequent photoelectric photometry in 1980 between JD 2444287.61 and 2444336.63 Henry, Landis, McFaul, and Renner confirmed the variability and showed a comparably large amplitude. Eaton made his observations with a 24-inch telescope and Henry made his with a 16-inch, their equipment having been described by Burke et al. (1980). Landis and Renner made their observations with 8-inch and 10-inch telescopes, respectively, their equipment having been described by Bartolini et al. (1978). McFaul made his observations with an 8-inch telescope and described his equipment in McFaul (1979). All observed with a filter chosen to match V of the UBV system and all used HR 1688 as the comparison star. The 1979 and 1980 observations are plotted separately in the figures below. Each point is a nightly mean of 2 or 3 or 4 individual differential measures. The ordinate DeltaV is differential magnitude (in the sense variable minus comparison) corrected for differential atmospheric extinction and transformed to V of the UBV system with known transformation coefficients. [FIGURE 1] In applying the transformation correction, we used an assumed constant color difference of Delta(B-V) = -0.059m, determined from Henry's B observations, which is so small that we are confident there is very little residual error related to transformation problems. On 12 of his 13 nights Henry obtained individual differential measures of the check star BD + 59d850 with respect to the same comparison star. Those measures yielded mean values of DeltaV = +2.0372m +- 0.0012m and DeltaB = +1.0365m +- 0.0010m, with standard deviations of single measures from those means being +-0.0041m in V and +-0.0035m in B, indicating very little if any variation in either the comparison star or the check star. Although we did not analyze these data to search explicitly for the photometric period, they appeared to be in phase approximately with the orbital period found by Abt et al. Fourier analysis of the two sets of data, with a period of 80.174469d and a sinusoidal shape assumed, yielded amplitudes (max. to min.) of DeltaV = 0.129m +- 0.011m in 1979 and DeltaV = 0.140m +- 0.004m in 1980 and epochs of light minimum of 2443959.6 +- 1.0d in 1979 and 2444288.8 +- 0.9d in 1980. These two light minima are separated by 4.13 cycles of the 80.2d period, implying that the photometric period is close to but a bit longer than the orbital period, in other words, P(phtm.) = 82.8d. In the jargon of RS CVn binaries this would correspond to a photometric wave migrating towards increasing orbital phase with a migration period of about 7 years. Also noteworthy is the fact that the mean light level (defined by the A_0 term in the Fourier analysis) changed apparently in one year. The mean level was DeltaV = -0.003m +- 0.004m in 1979 and DeltaV = +0.017m +- 0.003m in 1980 Because, as we said before, the transformation should be very secure in this particular study, this change in mean level can be believed with some confidence, provided the comparison star did not change brightness between 1979 and 1980. It came out during discussions at the N.A.T.O. Advanced Study Institute on "Solar Phenomena in Stars and Stellar System" that 12 Cam is important as the longest-period RS CVn binary in which approximate synchronization between the stellar rotation (deduced from the photometric wave) and the orbital motion has been established. Moreover, 12 Cam is important also as the RS CVn binary with the largest known orbital eccentricity. The wave migration towards increasing orbital phase is interesting for two reasons. First, it is opposite in sense from that in most other RS CVn binaries. Second, for true synchronization in a highly eccentric orbit, the components should rotate significantly faster, not slower, than the orbital period. This interesting matter should be studied further by additional photometry in subsequent years. It will also be helpful if this subsequent photometry can define the shape of the descending as well as the ascending branch of the light curve. The matter of the changing mean light level can be investigated further at the same time but only if the photometry is carefully standardized to V of the UBV system. JOEL A. EATON DOUGLAS S. HALL GREGORY W. HENRY (a) Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 HOWARD J. LANDIS (b) Price Road West RFD No. 2 - Box 44 ED Locust Grove, Georgia 30248 THOMAS G.McFAUL East Hook Cross Road Hopewell Junction, New York 12533 THOMAS R. RENNER Scuppernong Observatory 4512 Deerpark Drive Dousman, Wisconsin 53118 REFERENCES: Abt, H. A., Dukes, R. J., Weaver, W. B 1969, Ap. J. 157,717. [BIBCODE 1969ApJ...157..717A ] Bartolini C., et al. 1978, A. J. 83, 1510. [BIBCODE 1978AJ.....83.1510B ] Burke, E. W. et al. 1980, A. J. 85, 744. [BIBCODE 1980AJ.....85..744B ] McFaul, T. G. 1979, J.A.A.V.S.O. 8, 64. [BIBCODE 1979JAVSO...8...64M ] a) Guest investigator, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. b) of the A.A.V.S.O.