COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1821 Konkoly Observatory Budapest 1980 July 23 HD39917: A NEW, PROBABLY NON-ECLIPSING RS CVn-TYPE VARIABLE In 1977 a four-colour uvby survey of the southern sky, designed to find F and early G stars belonging to the intermediate population II, was finished. Among many other object, HD 39917 (7.6mag., G0) was found to show photometric indications of low metallicity; cf. Olsen (1979), table 14, where it was tentatively predicted to be a G8 dwarf star with weak lines. It was consequently included in a spectroscopic programme by two of us (JA and BN) to determine the radial velocities of the presumed metal-poor stars identified in the photometric survey. These observations are made with the ESO 1.5 m telescope and coude spectrograph on La Silla, Chile, at a dispersion of 20 Angstr./mm. Baked IIa-O emulsion is used, and one spectrogram (0.4 mm wide) is taken of each star. The plate taken of HD39917 (F 6570, Oct.7 1978, HJD 2443789d8801) showed the spectrum to be double-lined, with both double absorption lines and double emission components in the Ca II H and K lines reaching almost to the continuum level. The two components show no gross difference in spectral type or rotation, the latter corresponding roughly to v sin i ~ 50 km/s, but they are clearly of different brightness, the measured line ratios corresponding to a luminosity ratio of 0.7-0.8. The spectral type given by Houk (1978) is G8V, in approximate agreement with our spectrum, although we cannot make precise classification at this dispersion of a spectrum with rather diffuse double lines. The measured radial velocities are V1 = 16.2 +- 1.2 km/s (brighter comp.) V2 = -63.1 +- 4.5 km/s (fainter comp.) The appearance of the spectrum seemed typical of RS CVn binaries in view of the dwarf classification and rather large rotation, the latter implying a period of the order of a couple of days. It was therefore natural to search for the light variations and possible eclipses characteristic of RS CVn systems. During 1979 additional uvby and B photometry was therefore obtained (by EHO). No eclipses were detected, but HD 39917 shows the intrinsic variations characteristic of RS CVn-type variables. The uvby photometry (standard system) is given in Table I with mean values and r.m.s. dispersions (one observation). Table I HJD V b-y m_1 c_1 2440000+ 3226d54547 7m895 0m508 0m232 0m320 3236.52057 7.895 0.516 0.234 0.304 3931.54434 7.969 0.511 0.236 0.303 3931.61838 7.963 0.519 0.234 0.316 3932.53845 7.869 0.520 0.236 0.326 3933.56253 7.910 0.513 0.242 0.299 3934.55934 7.883 0.509 0.256 0.282 3935.53944 7.856 0.511 0.244 0.300 3935.57493 7.854 0.510 0.243 0.305 3936.55226 7.962 0.512 0.244 0.301 3937.56892 7.856 0.508 0.259 0.296 3938.56645 7.924 0.509 0.246 0.312 3939.51807 7.895 0.507 0.249 0.309 3939.56293 7.886 0.510 0.241 0.317 3940.53901 7.847 0.515 0.237 0.319 3940.59465 7.869 0.509 0.252 0.291 3941.54215 7.942 0.525 0.222 0.338 3941.58864 7.950 0.523 0.229 0.310 4120.89730 7.811 0.514 0.236 0.311 4127.90271 7.855 0.516 0.225 0.328 4129.89667 7.879 0.515 0.217 0.308 4134.89047 7.867 0.519 0.223 0.297 Mean 7.893 0.514 0.238 0.309 Scatter 0.043 0.005 0.011 0.013 The corresponding over-all errors for the 3067 observations made with the same equipment in 1979 are 0m004, 0m007, and 0m007 for b-y, m_1, and c_1, respectively. Thus, b-y shows no indication of variation, while the variations in the u and v bands are somewhat larger than in b and y. This is not due to a lower-than-average number of counted photons in u and v since a minimum of 40000 photons was uniformly collected in u from all stars in the general programme. Four beta observations were made. The resulting value on the standard system is. 2m559 +- 0m010 (r.m.s. scatter). Generally, the r.m.s. error for 2626 beta observations made in 1979 is 0m007. We are tempted to suspect a slight change in the strength of H_beta from March 1979, where beta was 2m551 +- 0m001 (2 obs.) to October 1979, where beta was 2m568 +- 0m004 (2 obs.). The combined spectrographic and photometric evidence leave little doubt that HD 39917 is a RS CVn-type variable. No further work on this system is planned. JOHANNES ANDERSEN BIRGITTA NORDSTROM ERIK HEYN OLSEN Copenhagen University Observatory Brorfelde, Denmark References: Houk, N.,1978 Michigan Catalogue of Two-Dimensional Spectral Types for the HD Stars, Vol. 2 [BIBCODE 1978mcts.book.....H ] Olsen, E.H., 1979, Astron. Astrophys. Suppl. 37, 367 [BIBCODE 1979A&AS...37..367O ]