COMMISSION 27 OF THE I. A. U. INFORMATION BULLETIN ON VARIABLE STARS NUMBER 843 Konkoly Observatory Budapest 1973 October 31 ON THE PERIOD VARIATION IN RS CVn AND SS Cam There is an error in sign in the theory offered to explain the period variation in RS CVn (Hall, P.A.S.P. 84, 323, 1972) and SS Cam (Arnold, Hall, Montle, IBVS 796, 1973). Mass loss from the leading hemisphere of one star in a binary system would decrease the orbital period not increase it, as stated in the two papers). The correlation between the orientation of the fainter hemisphere of the cool peculiar star and the period variations, of course, unchanged. But the proper interpretation is that the mass loss is occurring preferentially from the brighter hemisphere not the fainter hemisphere, as was stated in the two papers. We still do not know why the mass loss should be anisotropic, nor why the one hemisphere should be brighter. CLIFFORD N. ARNOLD DOUGLAS S. HALL Dyer Observatory Astronomisches Institut Vanderbilt University Universitat Tubingen Nashville, Tennessee 37235 D-7400 Tubingen U.S.A. Germany PHOTOELECTRIC MAXIMA OF XZ Cyg The RR Lyrae-type variable XZ Cyg has been observed photoelectrically at the Odessa Observatory near Majaky, (USSR) with the 22- inch reflector, during the period from August 8 to September 12, 1972. Max.Hel. Max.Hel 2441... Cycles O - C 2441... Cycles O - C 541.5218 2348.853 -0.0686d 564.4270 2397.953 -0.0218d 542.4642 2350.873 -0.0592 565.3527 2399.938 -0.0291 The table shows the moments of four maxima in blue and the corresponding O-C's. The O-C values were calculated with the elements: Max.Hel.= 2440445,789+ 0.466497d * E; A more detailed analysis and reductions of the obtained 420 observations will be published later. University of Sofia, Bulgaria and Odessa Observatory, USSR. P. KUNCHEV THE ANALYSIS OF UBV OBSERVATIONS OF UV TYPE VARIABLES The method of brightness gradients (1) was applied to an analysis of UBV observations of YZ CMi, EV Lac and AD Leo. Brightness gradients are angular coefficients of regression lines of V,B and U,B- relations for simultaneous photoelectric observations: nabla_V= DeltaV/DeltaB, nabla_U= Delta U/Delta B In (2) nabla_U and nabla_V were obtained for the light variations between maxima and minima for two flares of YZ CMi and one flare of AD Leo. They are given in the table as well as nabla_U and nabla_V for one flare of EV Lac, obtained from observations (3). On Fig. 1. V,B and U,B relations are given for maxima of YZ CMi flares according to synchronous observations in (4). The relations are similar for the flares of EV Lac and AD Leo (photometric data taken from (5-8) and (9) correspondingly). All [FIGURE 1] the obtained nabla_U and nabla_V are given in the table with their errors and plotted on the (nabla_U, nabla_V) plane (Fig. 2). They are situated inside a narrow band determined by the equation: nabla_V= 1.09 - 0.31 nabla_U. The brightness gradients are determined by intensity variations in UBV regions of spectra. Therefore their values and the relation between them are directly connected with the nature of radiation. Taking this into account it can be said that the results of the analysis carried out are in agreement with the following conclusions about the basic continuous radiation of UV type flares that correspond to regression lines: 1. The nature of radiation is the same at all stages of brightness descent of a flare, so breaks are absent on the V,B, and U,B - relations. (2). 2. The nature of radiation in maxima is the same for flares of different intensity (Fig. 1). 3. The nature of radiation on the descending branches is the same as in the maxima, so the relation between nabla_U and nabla_V is described by the same equation. The reddening of flare radiation in early descent (10) has apparently a secondary nature as well as (11) other differences in continuous radiation in maxima of flares. [FIGURE 2] Table Flare nabla_V sigmanabla_V nabla_U sigmanabla_u Annot. to observations or calculations YZ CMi 1965,1 27.3264 0.82 0.13 1.03 0.06 (11) YZ CMi 1965,1 28.2499 0.72 0.04 1.02 0.04 " AD Leo 1965,11 110.1708 0.76 0.02 0.97 0.05 " EV Lac 1968,VIII 18 0.22 0.04 2.90 0.04 (3) YZ CMi 0.54 0.06 1.72 0.04 (4) EV Lac 0.80 0.01 1.00 0.06 (5-8) AD Leo 0.26 0.02 2.80 0.01 (9) Sum of bremsstrahlung and 0.91 0.94 (12) (square on fig.2) inverse Compton-effect rad. Hydrogen plasma optically thick in Balmer lines 0.48 1.28 (13) (triangle on fig.2) As here the results of the analysis made by a new method are presented it seems expedient to point out the advantages of this method comparitively with the widely used method of analysis of UBV observations by U-B and B-V color-indices. Delta_U and Delta_V do not depend on interstellar absorption, errors in magnitudes of comparison stars and intensities of spectral lines. They are unrandom parameters of irregular light variation processes and describe them in UB reasons by two numbers, for which the errors can be easily calculated. Different types of pure radiations (thermal, nonthermal of different types, hot gas of small optical thickness, hydrogen plasma optically thick in Balmer line frequencies and others) are represented by points on the (nabla_U, nabla_V) plane if only one parameter is variable. References : 1. F.I. Lukatskaya, Astron.and Astrophys. 17, 97, 1972 [BIBCODE 1972A&A....17...97L ] 2. F.I. Lukatskaya, Astron. Tsirk. No. 580, 1970 [BIBCODE 1970ATsir.580....5L ] 3. S. Cristaldy, L. Paterno, Non-periodic Phenomena in Variable Stars, Budapest, 1969 [BIBCODE 1969CoKon..65...51C ] 4. K. Osawa, K. Ichimura, I. Shimizu, E. Watenable, T. Okada, M. Jutani, H. Koyano, K. Okida, Inf.Bull.Comm. 27 IAU on Var.Stars No. 635, 1972 [IBVS 635] 5. S. Cristaldy, M. Rodono, Inf.Bull.Comm. 27 IAU on Var. Stars No. 525, 1971. [IBVS 525] 6. S. Cristaldy, M. Rodono, Inf.Bull.Comm. 27 IAU on Var. Stars No. 600, 1971 [IBVS 600] 7. S. Cristaldy, M. Rodono, Inf.Bull.Comm. 27 IAU on Var. Stars No. 759, 1973 [IBVS 759] 8. M. Rodono, Inf. Bull. Comm. 27 IAU on Var. Stars No. 802, 1973 [IBVS 802] 9. K. Osawa et al., Inf.Bull.Comm. 27 IAU on Var.Stars No. 790, 1973 [IBVS 790] 10. P.F. Chugainov, Izv.Krymskoj Astrofiz.Obs. 26, 171, 1961 11. W.E. Kunkel, An Optical Study of Stellar Flares, Austin, 1967 12. G.A. Gurzadyan, Astronomy and Astrophys. 20, 145, 1972 [BIBCODE 1972A&A....20..145G ] 13. R.E. Gershberg, Izv.Krimskoj Astrofiz.Obs. 46, 90, 1972 F.I. LUKATSKAYA Main Astronomical Observatory of the Ukrainian Academy of Sciences, Kiev-127 USSR