COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1928 Konkoly Observatory Budapest 1981 February 26 HU ISSN 0374-0676 HD 178450: A NEW RS CVn VARIABLE The G6 V spectrum of 8.1m HD 178450 displays strong Ca II H & K emission lines (Joy and Wilson 1949) and variable radial velocity (Wilson and Joy 1950). Fekel (1980), who is observing HD 178450 to determine its spectroscopic orbital elements, suggests it as a good candidate for RS CVn-type optical variability. HD 178450 was observed photometrically between JD 2444506 and 2444513 with the No. 4 0.4-meter telescope at Kitt Peak National Observatory and between JD 2444526 and 2444569 with the 0.6-meter telescope at Dyer Observatory. BD +31d3457 was used as the comparison star. Means of the three individual differential magnitudes obtained each night are shown in the table, where Delta is in the sense variable minus comparison. The observations have been corrected for differential atmospheric extinction and transformed to the standard UBV system. The Hel. J.D. Phase DeltaV DeltaB (2,44.4,500+) 06.6490 0.2970p 0.026m -0.207m 09.7431 .7131 -0.005 10.6632 .1342 0.021 -0.217 11.6727 .5962 0.079 12.6400 .0389 0.012 -0.218 13.6448 .4988 0.027 26.5868 .4219 0.022 35.5967 .5454 0.023 36.5459 .9798 0.011 38.6025 .9211 0.001 45.5476 .0996 -0.003 49.5298 .9221 0.000 50.5104 .3709 0.023 54.5178 .2049 0.024 55.5667 .6850 -0.010 56.5194 .1210 0.012 69.4993 0.0615 0.003 standard deviation of the individual nightly magnitudes was usually +-0.005m. Phases were computed with the ephemeris JD(hel.) = 2,444,506.0 + 2.185d E where the epoch is arbitrary and the period is the photometric period as determined below. [FIGURE 1] The nightly means in V are plotted in the figure with filled circles for Kitt Peak and open circles for Dyer. The photometric period was determined by fitting the data with the truncated Fourier series l = A_0 + A_1 * cos Theta + A_2 * cos 2Theta + B_1 * sin Theta, varying the period (and thus recomputing the phases) until the smallest errors in the coefficients resulted. The period which best fit the data was 2.185d with an estimated uncertainty of +-0.005d. The sine curve resulting from the use of this period had an amplitude ( maximum to minimum) of DeltaV = 0.033m +-0.005m and a minimum at 0.348p +- 0.024p, which would correspond to JD 2,444,506.76 +-0.05d. The light curve is only approximately sinusoidal and suggests some cycle-to-cycle changes in shape. These changes in the light curve, along with the small amplitude of the variation, may imply an uncertainty in the period larger than estimated above from the Fourier coefficients. In fact, the variation may not even be strictly periodic. More nearly continuous photometry over fewer cycles would be needed to define the shape of the light curve more accurately. The author acknowledges that this work was supported in part by N.A.S.A. research grant NSG-7543. GREGORY W. HENRY * Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 References: Fekel, F.C. 1980, private communication. Joy, A.H. and Wilson, R.E. 1949, Ap. J. 109, 231. [BIBCODE 1949ApJ...109..231J ] Wilson, R.E. and Joy, A.H. 1950, Ap. J. 111, 221. [BIBCODE 1950ApJ...111..221W ] * Guest Investigator, Kitt Peak National Observatory, which is operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation