We present new photometric observations in Johnson V and B of WR30a, revealing relative dramatic changes in brightness of 0.2mag. These variations occur on a time scale of hours, and are only seen in V. We argue that they are not caused by dust extinction, but either by a dramatic change in the strength of the C IV 5801-12{AA} emission line doublet due to a de-excitation process, or by some unknown continuum effect.
The photoelectric observations in v and b bands for YY Eri are presented. These observations were obtained during four nights in November, 1984, with the 35-cm Cassegrain reflector of the Yunnan Observatory in China.
TT Ari was observed in the 5 passbands VBLUW (544, 430, 384, 362 and 324nm) during 3 nights on the 90cm telescope at ESO (La Silla), between July and November 1988, with an integration time of 16s.
VBLUW photometric observations of 13 eclipsing binary stars carried out by C.J. van Houten with the Walraven 5-color photometer between 1965 and 1978 are presented together with a first analysis of the orbital periods.
The 1982-1985 photometry (VBLUW system) of the O3V+O8V close binary HD 93205 has been rediscussed because of new insights into its true nature and orbital changes. By comparing this data set with the one obtained by Antokhina et al. (2000ApJ...529..463A) in 1993, and using the same ephemeris to construct the light curve in the phase diagram, the effect of the apsidal motion became obvious: a phase shift between the two light curves and a small change of the shape. A phase-locked light variation in the L passband (containing the higher Balmer lines) is clearly present in the 1982-1985 data set and is presumably due to absorption if the O8 star is seen through cooler inter-binary gas, e.g. the bow-shock between the two colliding winds.
We have obtained photometric observations in a 182arcmin^2 area, 25' to the north of the center of the globular cluster {omega} Centauri. The Stroemgren vby and broadband BI filters were used to obtain measurements for some 2500 stars. Preliminary examinations of parts of the data have been presented previously (Hughes & Wallerstein, 2000, Cat. <J/AJ/119/1225>; Hughes, Wallerstein, & van Leeuwen, 2002, in ASP Conf. Ser. 265, 73). Here we present the complete data set, study the giant branches, and use the B-I color index as a tool for assessing the ages of the populations within {omega} Cen.
We present a detailed study of an eclipsing binary which had been classified Ap SrCrEu (Hartoog, 1976ApJ...205..807H) before being known as a binary. Radial velocities measured at the times of both quadratures allow us to obtain precise masses for both components, while the light curve yields the radii. The following ephemeris and fundamental parameters of the system were obtained: HJD=(2447999.7656+/-0.0041) +(3.174990+/-0.000001) E, e=0.00, i=81.9+/-0.1{deg}, M_1_=1.90+/-0.02M_{sun}_, M_2_=1.85+/-0.02M_{sun}_, R_1_=1.63+/-0.03R_{sun}_, R_2_=1.60+/-0.03R_{sun}_, vsini_1_=27.6+/-3.5km/s, vsini_2_=23.6+/-3.6km/s. The projected rotational velocities were determined by fitting a synthetic spectrum convolved with a rotational profile to the observed spectrum. A comparison of the spectra of V392 Car and of the normal A star Cox 98, which has the same colour indices, shows that Sr is not overabundant and the metallicity of V392 Car is the same as that of the other cluster members. Therefore, V392 Car is a normal A2 star rather than an Ap star. The position of V392 Car in the HR diagram is entirely consistent with membership of the cluster NGC 2516. An independent estimate of the distance to this cluster was done using the parameters of the eclipsing system, and found to be in agreement with the Hipparcos one. A comparison of the parameters obtained from observations with predictions of internal structure models leads to a metallicity estimate [M/H]=0+/-0.10dex for NGC 2516. This estimate is completely independent of any spectroscopic or photometric method (except for the T_eff_ determination) but relies on stellar structure models.
Using extended multicolour CCD photometry of the triple-mode radial pulsator V823 Cas we studied the properties of the coupling frequencies invoked by nonlinear processes. Our results support that a resonance connection affects the mode coupling behaviour. The P1/P0 period ratio of V823 Cas has an "out of range" value if compared with the period ratios of the known double mode pulsators, while the P2/P1 period ratio is normal. The periods and period ratios cannot be consistently interpreted without conflict with pulsation and/or evolution models. We describe this failure with the suggestion that at present, the periods of V823 Cas are in a transient, resonance affected state, thus do not reflect the true parameters of the object. The anomalous period change behaviour of the fundamental and second overtone modes supports this idea. We have also raised the possibility that a f0+f2=2f1 resonance may act in triple mode pulsators.
The cool, overcontact, close binary, V523 Cassiopeiae was observed with the 1 m reflector at the US Naval Observatory, Flagstaff Station. The photometry was very good, with a precision on the order of a few millimagnitudes, but not numerous enough for complete light-curve analyses (e.g., differential corrections). A conventional published synthesis has been found acceptable as a fiducial model, and most of the observational weight has been used to develop a spot model for the stars and to support the validity of theoretical limb-darkening coefficients. Both photospheres and chromospheres contribute to the model. This result indicates that multifilter measures of this and similarly cool binaries are necessary for fuller descriptions of stellar activity cycles. A number of newly determined times of minimum light solidify the published rate of period variability.
