COMMISSION 27 OF THE I.A.U. INFORMATION BULLETIN ON VARIABLE STARS Number 1459 Konkoly Observatory Budapest 1978 August 16 HR 5110: A NEW VARIABLE STAR We obtained photoelectric photometry of the bright (V=5.0m) non-eclipsing RS CVn binary HR 5110 (=HD 118216) to see if there is a distortion wave in its light curve. We did discover it to be a variable star, but the light variation was very small, DeltaV=0m.010. Ironically , we are probably not seeing a distortion wave afterall but rather just the familiar reflection effect. Relevant recent references on HR 5110 are Conti (1967), Popper and Ulrich (1977), and Eggen (1978). Because we expect a light variation in a short period binary to be a function of orbital phase, we computed phases with the ephemeris JD (hel.) = 2,417,021.60 + 2d.6131738 * E. (1) The initial epoch here is a time of conjunction with the F-star behind and the K-star in front; it was derived from the time of periastron given by Harper (1938). The orbit is not necessarily eccentric, because the eccentricity is within one standard deviation of zero. The period is the value derived recently by Conti (1967). On 54 different nights between 1-2 March and 23-24 June 1978, we obtained a total of 181 differential magnitudes at 6 different observatories. Several nights were observed at more than one observatory. A tally is given below, where n is the number of individual observations and m is the number of nights. Observatory Aperture n m Dyer 24-in. 38 14 Kitt Peak 16 28 12 Hickox 10 33 10 Landis 8 32 12 Louth 11 42 26 Schlegel-McHugh 20 8 4 Most of the observations were made in one color (V of the UBV system) and were made differentially with respect to the same comparison star (25 CVn, including the faint visual companion 1.5 arcseconds away). All individual differential magnitudes were corrected for atmospheric extinction with mean extinction coefficients and transformed to the UBV system with known transformation coefficients and a mean value of delta(B-V) between the variable and the comparison. Then we formed normals of all those observations made at one observatory on one night. The normals were analyzed separately in two groups: the first two observatories in Group A and the last four observatories in Group B. Group A included observations between JD 2,443,606.8 and 2,443,673.7; Group B included observations between 2,443,569.7 and 2,443,683.7. The light was expressed as a truncated Fourier series, l = A_o + A1cosTheta + A2cosTheta + B1sinTheta, (2) with l = 1 fixed at DeltaV = 0m.145. The resulting coefficients and their errors are given below. Group A Group B A0 1.0012 1.0019 +-0.0006 +-0.0010 A1 -0.0040 -0.0051 +-0.0009 +-0.0016 A2 -0.0016 -0.0001 +-0.0009 +-0.0014 B1 -0.0024 -0.0001 +-0.0008 +-0.0014 Theta(min.) 0.08p 0.00p +-0.03 +-0.05 DeltaV(max. 0.010m 0.011m to min.) +-0.002 +-0.003 DeltaV at l=A_o +0.1437m +0.1429 +-0.0006 +-0.0010 Also given are (1) the value of Theta(min), the phase of the minimum of the distortion wave/although in this case we do not believe it is a distortion wave/, (2) the value of DeltaV, the amplitude of the wave from maximum to minimum, in magnitude units, and (3) the mean magnitude, DeltaV at l=A_o. Although the variation we have found is quite small, total amplitude only 0m.010, we believe it is real because the agreement between Groups A and B so close. Notice that the amplitude, the mean magnitude, and Theta(min) all agree within their respective errors. Because the variation has its maximum so near the phase when the facing hemisphere of the cooler star is towards earth, we are most probably seeing the differential reflection effect. It should be mentioned that there is some question about the constancy of the orbital period, with Harper (1938) having found 2d.61312 and 2d.61314 at two different epochs and Conti (1967) having derived 2d.6131738 at a later epoch. The accumulated effect of a 0d.00002 or 0d.00003 error in equation (1) would produce an uncertainty of ~0p.1 in our phases. Although HR 5110 has never been listed as a variable or suspected variable in any of the editions of the General Catalogue of Variable Stars or its supplements, we point out that the 3 values of V listed in the U.S. Naval Observatory UBV Catalogue show a range of 0m.05. Therefore HR 5110 perhaps ought to be reobserved from time to time in case a distortion wave of variable amplitude does exist and we happen to have observed it at minimum amplitude. DOUGLAS S. HALL LARRY P. LOVELL GREGORY W. HENRY* CHRISTOPHER A. VAUCHER Hickox Observatory 18410 Munn Road Dyer Observatory Chagrin Falls, Ohio 44022 Vanderbilt University Nashville, Tennessee 37235 HOWARD J. LANDIS HOWARD LOUTH 2395 Wood Hill Lane East Point, Georgia 30344 2199 Hathaway Road Sedro Woolley, Washington 98284 PETER BROOKS RALPH SCHLEGEL RICK WASATONIC Schlegel-McHugh Observatory East Rock Road Allentown, Pennsylvania 18103 * Guest Investigator, Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, Inc., under contract with the National Science Foundation. References: Conti, P.S., 1967, Ap.J. 149, 629 [BIBCODE 1967ApJ...149..629C ] Eggen, O.J., 1978, I.B.V.S. No. 1426 Harper, W.E., 1938, P.D.A.O. 7, 141 [BIBCODE 1938PDAO....7..141H ] Popper, D.M. and Ulrich, R.K., 1977, Ap.J. 212, L131 [BIBCODE 1977ApJ...212L.131P ]