COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 2110 Konkoly Observatory Budapest 1982 March 17 HU ISSN 0374-0676 HD 26337: A NEW RS CVn VARIABLE STAR According to Bidelman and MacConnell (1973) HD 26337 (= SAO 130994) is a G5 IV star with Ca II H & K in emission. This made us suspect it was an RS CVn binary and (as most members of that class are) variable in light as well. As part of a program to obtain spectroscopic observations of the Ca II H & K emission stars listed by Bidelman and MacConnell (1973) Fekel observed HD 26337 with the 91-cm reflector at Goddard Space Flight Center and with the 2.7-m and 2.1-m reflectors at McDonald Observatory of the University of Texas. The 5 Goddard observations with a dispersion of 40 A/mm and a resolution of 2.5 A showed moderate strength Ca II H & K emission lines. On 8 nights between JD 2444179.9 and 2444627.6 red spectrograms were obtained at McDonald with dispersions of 4.4 A/mm or 9 A/mm. A preliminary orbital element solution with 10 radial velocities, 8 from McDonald and 2 from other observatories, indicates an orbital period of 2.04414d +-0.00047d and a velocity amplitude of about 50 km/sec. The observations show only one component, whose lines are substantially broadened by rotation with V sin i ~ 40-45 km/sec. The H alpha line appears to be a relatively weak absorption feature. Spectroscopic observations are being continued to improve the orbital elements. Differential photoelectric measurements were made at four different observatories on a total of 27 different nights between JD 2444287.55 and 2444660.60. Landis observed with the 8-inch reflector of Landis Observatory in Locust Grove, Georgia; Henry observed with the 24-inch Seyfert reflector at Dyer Observatory and the No. 4 16-inch reflector at Kitt Peak National Observatory; Renner observed with the 10-inch reflector at Scuppernong Observatory near Dousman, Wisconsin. All observed with filters chosen to match V of the UBV system, although Henry obtained also a few observations at Kitt Peak with a filter selected to match B. All used 37 Eridani as the comparison star. The individual differential magnitudes, corrected for differential atmospheric extinction with mean coefficients appropriate for each observatory and transformed to the UBV system with coefficients determined previously, have been deposited in the I.A.U. Commission 27 Archive for Unpublished Observations of Variable Stars (Breger 1979), where they are available as file [FIGURE 1] no. 95. In the reductions we used a mean color difference of Delta(B-V) = -0.27m, in the sense variable minus comparison. Our photometry is best fit by a period close to but very slightly shorter than the orbital period. The light curve in V is plotted in the figure below, with a period of 2.038d. Each point is a mean of the two or three individual magnitudes obtained on each night. The total range is Delta V = 0.19m, but the shape seems to be somewhat variable from one year to the next. The four observations of Landis (dots), from the 1979-80 season, do not fit very well the other observations (crosses), all from the 1980- 81 season. A recent epoch of minimum light would be JD 2444635.65, which corresponds to zero phase in the figure. For our comparison star 37 Eri, Nicolet (1978) gives V = 5.44m and B-V = 0.94m. Our light curve then indicates that HD 26337 varies over the range 6.95m < V < 7.15m. The color index, probably constant, is around B-V = 0.67m. It is characteristic of most RS CVn binaries that the light is variable and that the photometric period is very close to but slightly shorter than the orbital period. Such is the case with this newly discovered RS CVn binary HD 26337, for which P(phtm.) is shorter than P(orb.) by about 0.3%. D.S.H. is happy to acknowledge support from N.A.S.A. research grant NSG-7543. FRANCIS C. FEKEL Code 685 Goddard Space Flight Center Greenbelt, Maryland 20771 DOUGLAS S. HALL ^a GREGORY W. HENRY ^a Dyer Observatory Vanderbilt University Nashville, Tennessee 37235 HOWARD J. LANDIS ^b Landis Observatory Route 2, Box 44ED Locust Grove, Georgia 30248 THOMAS R. RENNER Scuppernong Observatory 4512 Deerpark Drive Dousman, Wisconsin 53118 References: Bidelman, W.P. and MacConnell, D.J. 1973, A.J. 78, 687. [BIBCODE 1973AJ.....78..687B ] Breger, M. 1979, I.B.V.S. no. 1659. Nicolet, B. 1978, Astr. Astrophys. Suppl. 34, 1. [BIBCODE 1978A&AS...34....1N ] a) Guest Observer, Kitt Peak National Observatory, operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation. b) of the A.A.V.S.O. [DATAFILE 1]