COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS Number 1811 Konkoly Observatory Budapest 1980 July 1 ON THE VARIABILITY OF THE OLD NOVA HR DELPHINI 1967 Photometry Photoelectric observations of the old nova HR Del 1967 were carried out with the 61cm Bochum telescope at the European Southern Observatory in Chile on May 28 and 31, 1979. The photometer was furnished with standard Johnson UBV filters. In order to improve the time resolution, the nearby field star HD 197397 (=BD+18deg4591 = SAO 106418; Sp=A0 V) was used as comparison star. As the separation of both stars is less than eight arcminutes, no extinction correction was applied; the brightness of the postnova was determined by means of differential photometry. The individual measurements were obtained with an integration time of 20 seconds. Means of observations with the V, B, and U filters are presented in columns 2 to 4 of Table l, respectively; the Julian dates corresponding to the times of mid-observation are given in the first column. The standard deviations from the mean value of n measurements, and the number n are given in the last two columns. Continuous observations with the B filter conducted on May 28, 1979 revealed variations between B=12m38 and 12m51, obviously covering a brightness minimum of the old nova. During the UBV measurements obtained on May 31, 1979 the B magnitude of the postnova was brighter by at least 0m20; B-V ~ -0m06, and U-B ~ -0m90. Table l: UBV Photometry of HR Del JD (mid-obs.) V B U Error n 244.... 4021.8028 12m383 0m019 6 .8045 12.406 .011 6 .8099 12.449 .017 6 .8116 12.436 .011 6 .8167 12.444 .014 6 .8184 12.481 .020 6 .8311 12.501 .015 6 .8327 12.515 .011 6 .8381 12.485 .018 6 .8397 12.515 .023 6 .8452 12.462 .008 6 .8469 12.460 .011 6 .8802 12.378 .005 4 .8815 12.397 .006 5 4024.8164 12.270 12.205 11.328 .011 2 .8259 12.209 12.166 11.268 .011 2 .8350 12.219 12.161 11.249 .008 2 Optical Spectroscopy From optical spectroscopic data, Hutchings (1979) found evidence that HR Del is a close binary system with a 0.5 M_sun main-sequence star and a 1.0 M_sun white dwarf as probable components, and with a fairly high inclination close to i ~ 45deg. Thus, only sight photometric variability can be expected. Our observations might have covered a shallow eclipse; the combination with further photoelectric data is useful for an improvement of Hutchings' ephemeris. Light variations with an amplitude of 0m2 are also reported by Tempesti (1979), but do not fit the spectroscopic period of 0.17 days. UV Spectroscopy Variations in the line intensities are noticeable in IUE satellite spectra of HR Del. A comparison of our low resolution short wavelength (1100-2000 Angstrom) spectrum taken on Juy 10, 1979, with the one obtained by Hutchings (1979), shows a varying intensity ratio of the He II (1640 Angstrom) to C IV-(1550 Angstrom) emission lines, as well as variations in the Si III (1303 Angstrom) absorption; the relative strengths of the Si III (1368 Angstrom) line and Si IV doublet (1398 Angstrom), however, appear to remain essentially constant. Phase-dependent spectroscopic observations have recently been made by Hutchings (1980). Simultaneous photometry and spectroscopy of the classical nova V 603 Aql (1918) with the FES-instrument and UV spectrometer aboard the IUE satellite, revealed correlated periodic variations in the optical light curve and the UV spectra (Boggess et al., 1980). Additional comprehensive photometry of HR Del might similary yield new information on the binary nature of this system. HORST DRECHSEL and JURGEN RAHE Remeis-Sternwarte Astronomical Institute University Erlangen-Nurnberg D-8600 Bamberg / FRG Present Address: Laboratory for Astronomy and Solar Physics NASA-Goddard Space Flight Center Greenbelt, Md. 20771 / USA References: Boggess, A., Drechsel, H., Holm, A., and Rahe, J, 1980, I.A.U. Circ. 3485. [BIBCODE 1980IAUC.3485....2B ] Hutchings, J.B. 1979, Ap.J., 232, 176 [BIBCODE 1979ApJ...232..176H ] Hutchings, J.B. 1979, P.A.S.P., 91, 661. [BIBCODE 1979PASP...91..661H ] Hutchings, J.B. 1980, preprint. Tempesti, P. 1979, I.A.U. Circ. 3340. [BIBCODE 1979IAUC.3340....4T ]