We present and analyze two seasons of intense photometric monitoring in the Stroemgren uvbyH{beta} system of {eta} Carinae (October 1992-August 1994). The luminous blue variable (LBV) in the core did not show much S Dor activity, i.e. it was in a relatively quiescent stage. This situation was very favourable for studying its optical micro variations. It appears that the central LBV pulsates (presumably in a non-radial mode) like other massive evolved stars, the {alpha} Cyg variables. The quasi-period is 58.56d. The linear ephemeris is: JD_max_=2448875.0 +58.56 E. Support was found for the existence of the presumed periodicity of 52.4d of the so-called "dimples", shallow dips in the light curve which only last for a few days. The cause may be the eclipse of a small companion or of a hot spot in an accretion disk. The H{beta} index became bluer by ~0.07mag during the last 11/2 years and shows an oscillation in anti-phase with the 58.56d pulsation, suggesting that the HII region(s) responsible for the hydrogen line emission has a relatively high luminosity. This is another reason to suppose that a second luminous source, perhaps a luminous disk (with a hot spot), may be present in the {eta} Car system.
Recent studies have shown that stellar chromospheric activity, and its effect on convective energy transport in the envelope, is most likely the cause of significant radius and temperature discrepancies between theoretical evolution models and observations. Accurate mass, radius, and abundance determinations from solar-type binaries exhibiting various levels of activity are needed for a better insight into the structure and evolution of these stars. We aim to determine absolute dimensions and abundances for the solar-type detached eclipsing binary EF Aqr, and to perform a detailed comparison with results from recent stellar evolutionary models.
Complete uvby light curves of the detached double-lined early B-type eclipsing binary LZ Centauri are presented. They contain 916 points in each color and were obtained 1982-84. A detailed photometric analysis based on these observations and on new spectroscopic material will be published separately (Vaz et al. 1995)
Accurate uvby light curves of the southern, detached, double-lined eclipsing binary V539 Ara (HR 6622A, HD 161783, V=5.71mag , B3V+B4V, P=3.17d) are presented. They contain 1409 observations in each colour, collected 1982-1984. Typical mean errors are 0.003-0.004mag. Observations for 8 additional times of minima from 1985-1994 are included. The secondary component belongs to the group of slowly pulsating B (or SPB) stars. An analysis of V539 Ara based on the new photometry and the spectroscopic orbit by Andersen (1983A&A...118..255A) is published separately (Clausen 1995).
Table 1 contents 852 simultaneous measurements collected in each of the four uvby colours of the Stromgren photometric system for the eclipsing binary system V2154 Cyg. The data are magnitude differences (Du,Dv,Db,Dy,D(b-y),Dm1,Dc1) of the variable star minus comparison star in the standard system versus Heliocentric Julian Day. The comparison star is HD 204626. The observations were carried out (by E. Rodriguez, J.M. Garcia, S. Martin and A. Claret) through the year 1998 using the 0.90m telescope at Sierra Nevada Observatory, Spain. This telescope is equipped with a six-channel uvby-Hbeta spectrograph photometer for simultaneous measurements in uvby or in the narrow and wide Hbeta channels, respectively.
We carried out a Stroemgren photometric survey of thirteen southern bright stars, including {beta} Pictoris itself, during three years, d'Astrophysique de Paris, in order to detect possible weak photometric variations. {beta} Pictoris presents a small long-term variation with a change of brightness by -2.1x10^-3^mag per year, over about two years from beginning of 1996, a situation relatively similar to the one about 18 years ago. Among the other stars, only HD 38392 presents weak photometric variations with a period of 21.4 days, probably related to the star rotation period. The negative result concerning photometric variations of all other stars suggests that those stars are actually really stable and strengthens the reality of the variations discovered in the case of {beta} Pictoris and HD 38392.
We have obtained Stromgren b and y differential photometric observations of the solar-type eclipsing binary HD 74057 plus follow-up high-resolution, red wavelength spectroscopic observations. The system has an orbital period of 31.2198 days, a high eccentricity of 0.47, and is seen almost exactly edge on with an inclination of 89.8{deg}. The two main-sequence G0 stars are nearly identical in all physical characteristics. We used the Wilson-Devinney program to obtain a simultaneous solution of our photometric and spectroscopic observations. The resulting masses of the components are M1=1.138+/-0.003M_{sun}_ and M2=1.131+/-0.003M_{sun}_, and the radii are R1=1.064+/-0.002R_{sun}_ and R2=1.049+/-0.002R_{sun}_. The effective temperatures are 5900K (fixed) and 5843K, and the iron abundance, [Fe/H], is estimated to be +0.07. A comparison with evolutionary tracks suggests that the system may be even more metal rich. The components rotate with periods of 8.4 days, significantly faster than the predicted pseudosynchronous period of 12.7days. We see evidence that one or both components have cool spots. Both stars are close to the zero-age main sequence and are about 1.0Gyr old.
We have obtained uvby data of a sample of 232 stars in Baade's Window. These observations are presented along with the corresponding diagrams. For a description of the uvby photometric system, see e.g. <GCPD/04>
The open cluster NGC 7419 is known to contain five red supergiants and a very high number of Be stars. However, there are conflicting reports about its age and distance that prevent a useful comparison with other clusters. We intend to obtain more accurate parameters for NGC 7419, using techniques different from those of previous authors, so that it may be used as a calibrator for more obscured clusters. We obtained Stroemgren photometry of the open cluster NGC 7419, as well as classification spectroscopy of ~20 stars in the area. We then applied standard analysis and classification techniques.
