Abstract.From the light curve analysis of several semi-detached close binary systems, the exponent of the gravity-darkening (GDE) for the Roche lobe filling components has been empirically estimated. The analysis, based on Roche geometry, has been made using the latest improved version of our computer programme. The present method of the light-curve analysis enables simultaneous estimation of the systems' parameters and the gravity-darkening exponents. The reliability of the method has been confirmed by its application to the artificial light curves obtained with a priori known parameters. Further tests with real observations have shown that in the case of well defined light curves the parameters of the system and the value of the gravitydarkening exponent can be reliably estimated. This first part of our analysis presents the results for 9 of the examined systems, that could be briefly summarised as follows: 1) For four of the systems, namely: ZZ Cru, RZ Dra, XZ Sgr and W UMi, there is a very good agreement between empirically estimated and theoretically predicted values for purely radiative and convective envelopes. 2) For the rest five, namely: TT Aur, V Pup, TV Cas, LT Her, and VV UMa, the estimated values of the gravity-darkening exponents were deduced to be larger than theory expects for purely radiative or convective envelopes, respectively. Moreover, it is worthwhile to mention that these values -although greater than theoretical predictions-are: a) Smaller compared to those found by others. b) In two cases, (TV Cas & LT Her), they are normal if some kind of solar type activity (i.e. by employing the Roche model involving a spotted area on the surface of the secondary star) is assumed.3) The large values derived for the two early type systems TT Aur & V Pup, are very possibly connected with the effects of rotation laws, and in some degree with the large contribution of the radiative pressure in the total potential, leading by that to considerable deviations of the stellar surfaces from the assumed classical Roche geometry. 4) Finally, in the VV UMa case, the estimated value of the gravity-darkening exponent -although almost double than the expected for stars with convective envelopes -still it is low in comparison with that estimated by others who have analysed the same data. But, since for this particular binary the anomalous GDE is not supported by recent simultaneous uvby observations (Lazaro et al. 2002), the estimated higher value may be due to the old observational material used.

The subject of the present paper is the analysis of the orbital elements for nine binaries: WDS 00463–0634 = HDS 101, WDS 03264+3520 = HDS 430, WDS 03307–1926 = HDS 441, WDS 04025+0638 = HDS 510, WDS 09252+4606 = HDS 1353, WDS 09446+6459 = CHR 176, WDS 10294+1211 = HDS 1507, WDS 10596+1800 = HDS 1568, and WDS 14562+1745 = HDS 2108. The orbital elements are calculated for the first time for all of them. The eight binaries, denoted as HDS, were discovered during the Hipparcos mission. One binary, denoted as CHR, was discovered in the Center for High Angular Resolution Astronomy, CHARA, in 1988. These studied pairs have measured separations of less than 0.41 arcsec. For the eight pairs that have measured separations less than 0.3 arcsec, the resulting orbital periods fall within 16 and 55 years, and for the remaining one pair the orbital period is 94 years. In addition to the orbital elements, we also give (O − C) residuals in θ and ρ, masses, dynamical parallaxes, absolute magnitudes, spectral types, and ephemerides for the next five years. We also present one linear solution for the double star WDS 19218+7708 = HDS 2740 that has also been calculated for the first time. For this system we give (O − C) residuals in θ and ρ as well, along with ephemerides for the next five years.

This second part of our study concerning gravity-darkening presents the results for 8 semi-detached close binary systems. From the light-curve analysis of these systems the exponent of the gravity-darkening (GDE) for the Roche lobe filling components has been empirically derived. The method used for the light-curve analysis is based on Roche geometry, and enables simultaneous estimation of the systems' parameters and the gravity-darkening exponents. Our analysis is restricted to the black-body approximation which can influence in some degree the parameter estimation. The results of our analysis are: 1) For four of the systems, namely: TX UMa, β Per, AW Cam and TW Cas, there is a very good agreement between empirically estimated and theoretically predicted values for purely convective envelopes. 2) For the AI Dra system, the estimated value of gravity-darkening exponent is greater, and for UX Her, TW And and XZ Pup lesser than corresponding theoretical predictions, but for all mentioned systems the obtained values of the gravity-darkening exponent are quite close to the theoretically expected values. 3) Our analysis has proved generally that with the correction of the previously estimated mass ratios of the components within some of the analysed systems, the theoretical predictions of the gravity-darkening exponents for stars with convective envelopes are highly reliable. The anomalous values of the GDE found in some earlier studies of these systems can be considered as the consequence of the inappropriate method used to estimate the GDE. 4) The empirical estimations of GDE given in Paper I and in the present study indicate that in the light-curve analysis one can apply the recent theoretical predictions of GDE with high confidence for stars with both convective and radiative envelopes.

The influence of merging effects in the central part of an Active Galactic Nucleus (AGN) on the emission spectral line shapes are discussed. We present a model of close binary Broad Line Region. The numerical experiments show that the merging effects can explain double peaked lines. The merging effects may also be present in the center of AGNs, although they emit slightly asymmetric as well as symmetric and relatively stable (in profile shape) spectral lines. Depending on the black hole masses and their orbit elements such model may explain some of the line profile shapes observed in AGNs. This work shows that if one is looking for the merging effects in the central region as well as in the wide field structure of AGNs, he should first pay attention to objects which have double peaked lines.

Abstract. The CCD measurements for 123 double stars with ST-6 camera attached to the Zeiss 65/1055 cm Refractor of the Belgrade Observatory are communicated.