E. Budding

The interpretation of cyclical photometric variations in certain dwarf Me-type stars

A method of determination of parameter sets characterizing models of starspots is described. The method makes use of a systematic integral notation in the description of the darkening due to spots and optimization procedures to evaluate appropriate parameters. The method is applied to light curves of YY Gem and CC Eri. In the latter case a comparison is made with the results of Bopp and Evanss (1973) study. The physical meaning of the derived parameter set and possibly correlated effects are considered for YY Gem.

Analysis of eclipsing binary light curves on automatic computers

A direct method of analysis of the light curves of eclipsing binary systems is proposed, which, as an alternative to numerical integration methods, adopts the associated alpha functions of Kopal as the means of description of eclipses. Alpha functions can be internally generated, corresponding to given trial parameters and orbital phase, in a computer program which then goes on to optimize the trial parameter set. The method has been applied to a number of light curves including those of YZ Cas, WW Aur, YY Gem and SZ Cam. Second order coefficient of limb darkening have been determined for the YZ Cas stars. Finally, a comparative discussion is given of various methods of light curve analysis.

The system VV Ori and the consistency of photometric analysis of eclipsing binary light curves

The extensive, homogeneous and automatically obtained OAO-2UV data on VV Ori at six different wavelengths, as presented by Eaton (1975), are subjected to detailed numerical analysis, and the extent of derivable information on this star from such photometry is critically assessed.An economic (analytical integration) fitting function which can depend on up to 16 independently specifiable parameters is introduced. The use of frequency domain techniques along previously described lines is also discussed.The determination of sought parameter values is examined in some generality, and it is shown that a simultaneous unique optimal specification of more than six or seven such parameters is highly unlikely. An eight-parameter simultaneous specification for the quantities considered by Eaton would not be unique, rendering the conclusions of that author on relatively indeterminate parameters to be considered sceptically. By adopting means from all the solution sets of a five-element specification for basic parameters and carrying out statistical tests for self consistency it is possible to then investigate gravity darkening and reflection coefficients. We find that there is no great departure in the corresponding values from simple standard theory.

Analysis of red and infrared wide-band photometry of Algol

The basic physical picture of the Algol system is reviewed, and, using collected red and infrared observations, photometric curve fits are investigated by applying numerical quadratures to determine theoretical light curves appropriate to Roche model stars. The ‘contact’ nature of Algol B appears to be confirmed, and effective temperatures of the three components areTA=11 400°,TB=5300°,TC=7600°. In terms of a Lamberts law approach to the ‘reflection effect’, the effective heat-albedo is required to be reduced from unity to one half; and it is also found that the averaged ‘gravity-darkening coefficient’ is close to a value appropriate for a diffusion type of heat-transfer mechanism operating in sub-photospheric layers.

Calculations of proximity effects in close binary systems

The proximity effects in the light curves of close binary systems are investigated with the aid of facilities provided by a high-speed, digital computer. The treatment follows, to a large extent, that summarized by Kopal (1959) and makes extensive use of the alpha-functions and related integrals provided by that author. The ‘ellipticity’ and ‘reflection’ effects are studied individually and different expressions are checked and compared. Test data are drawn continually from the well known system SZ Cam for which a ‘rectified’ (in a more realistic sense) light curve is ultimately produced.

Gravity darkening of the secondary component of Algol

An analysis of the infrared light curve of the secondary minimum of the Algol system — when the contact subgiant component of spectral class K0 undergoes eclipse by its nearly spherical and early-type mate — for the gravity-darkening of the distorted contact star has disclosed that the monochromatic coefficient τλ of this darkening at λ=1.6 μ is some three to four timeslarger than that resulting from von Zeipels theory. This is in agreement with recent photometric studies of gravity darkening in WUMa-type systems, but in flagrant contrast with the consequences of theories requiring deep sub-surface convection zones for subgiants of advanced spectral types. The origin of this discrepancy remains unresolved, and underlines the need of further observations of the secondary minima in semi-detached eclipsing systems in the infrared.

The system WY Cnc and derivation of absolute information at the lower end of the Main Sequence

Photometric and spectrographic observations of the system WY Cnc are presented and analysed. It is concluded that the system consists of two Main Sequence stars: a G5 primary and a low mass secondary star with a mass of about 0.4M⊙, corresponding to a spectral type of around M2. The possibility of deriving absolute information on this low mass Main Sequence object lends significance to this study.Also there is evidence concerning the role of scattering by the atmosphere of the cool comparison.

Optimization analysis of the light curves of eccentric eclipsing binary systems

The iterative optimization procedures described in a previous paper by the author have been extended to cover unrectified light curves of eccentric eclipsing binary systems. Two stars have been studied in detail: namely, α Coronae Borealis and V477 Cygni. In both cases improved element sets have been obtained. Moreover, in the case of V477 Cygni the obtained values of the longitude of periastron for three different light curves are found to provide a useful basis for discussion of the apsidal motion of this system.

Analysis of the light curves of SZ Cam using automatized fourier techniques

UBV light curves of the early type close eclipsing binary system SZ Cam have been investigated using recently developed frequency-domain techniques. The combination of both minima in the analysis results in a distinct methodological improvement over the single minimum method discussed hitherto. This improvement has two aspects: (i) increased accuracy of the determined elements, (ii) agreement of the results of the two-minimum method with those of the single-minimum method provides a criterion whereby the self-consistency of the underlying model with its representation of the light curve in the regions between minima by a cosine series and the empirically determined coefficients of such a series may be assessed. Such a ‘self-consistent’ solution is found, and a further step towards a realistic representation is made by including the ‘photometric perturbations’. It is confirmed from these three light curves that the less massive star is overluminous. A probable tendency for the limb-darkening coefficient of the more massive star to increase with decreasing wavelength is also noted.

IUE observations of certain short period RS CVn-like stars

Nine low and one high resolution IUE (LWR) spectrograms for the short period subgroup RS CVn-like stars have been studied, particularly in connection with the MgII 2800 Å feature. Clear emission contributions can be easily seen for some of these stars, while all nine of them appear to have the feature filled by emission to some extent.If surface flux in emission is considered as a measure of ‘activity’ (and not just equivalent width) the short period subgroup is as active as the main group. The activity is not as obvious because of the generally higher photospheric temperatures.Correlations of such activity with angular velocity and the scale of irregular photometric distortions (‘starspots’) are present, though the sample size is low.