A. V. Raveendran

Orbital period modulation and spot activity in the RS CVn binary V711 Tauri

Aims. We attempt to establish the real nature of the orbital period variation and its relation to the spot activity of V711 Tau, and determine why the (B −V) colour of the star appears to be nearly independent of its V magnitude. We wish to verify whether existing predictions in the literature for the long-term spot activity of the star are true or not by making extended photometric observations, and whether the broad component of Hα emission originates in more localised active regions, as suggested by some chromospheric models, by searching for any correlation between the base-line width of the emission and the light modulation. Methods. We obtained new radial velocities of the G-type component of V711 Tau on 42 nights during 2004−09, and BV photometry of V711 Tau on 202 nights during the years 1993−2009. We measured the equivalent widths of two well resolved lines of the G-type component from 13 of the spectra obtained by us. We also measured the equivalent widths and base-line widths of Hα emission from 21 spectra obtained during 2008−09. We analyse these along with relevant information available in the literature. Results. The available radial velocity data of V 711 Tau are consistent with a sinusoidal modulation of its orbital period; the period of modulation is found to be 36.3 ± 1.9 yr. The fractional light-loss over a photometric cycle is found to vary with an average period of 14.1 ± 0.3 yr. It appears that physical processes linked to the magnetic activity of the spotted star are responsible for the variation in the orbital period. The excess reduction in the B band flux relative to that in V band caused by spot activity is almost compensated for by the fractional increase in the contribution by the hotter companion to the total light in the blue spectral region, and thereby makes the (B − V) colour of the binary system nearly independent of its V magnitude. We find that the ratio of the radii of the components derived from their v sin i values, which is usually quoted in the literature, is substantially larger than that implied by the ratio of their brightnesses in V band. There is a slight indication from the V band data that the spot activity in V711 Tau has a component that is fixed in the orbital frame of reference. The equivalent width and base-line width of Hα emission do not show any obvious correlation with the V band light curve.

BV photometry of UX Arietis

DifferentialBV photometry of UX Ari obtained on 58 nights during 1984-85, 1985-86, 1986-87, and 1987-88 observing season is presented. We find that (B-V) is phase dependent with the system being reddest at the light maximum and we interpret this as due to the variable fractional contribution by the G5 V component to the total light at shorter wavelengths. An analysis of the available data indicates that at larger amplitudes of the photometric wave the brightness at maximum increases and that at minimum decreases and both converge to δV ≃ −1.0 mag at very low amplitudes. It implies that the low wave amplitudes are essentially due to more homogeneity in the surface distribution of spots rather than due to low levels of spot activity. The variation in wave amplitude is found to be near-sinusoidal with a period around 13–14 years

Spot activity in the RS CVn binary HR 1099

UBV photometry of HR 1099 obtained during the 1979-80 and 1980-81 observing seasons is presented. An analysis of the available data shows that the brightness at the light curve maximum increases as the wave amplitude increases, while the brightness at the light minimum remains almost the same. In terms of the starspot model it implies that there is always a hemisphere of the active component that is nearly ’saturated’ with spots and that spots occupy a larger fraction of the stellar surface when the wave amplitude is smaller. The continuous migration attributed to the photometric wave by various authors is far from certain. The amplitude of the wave has a sharp rise followed by slow decay with a period around 5–6 yr. It is found that the two-spot model proposed by Dorren and Guinan (1982) is inadequate to describe all the observed photometric peculiarities of HR 1099.

Evolution of starspot regions in DM UMa

B andV photometry of DM UMa obtained between January, 1980 and June, 1984 is presented. Analysis yields a mean photometric period 7d.478±0d.010, compared to the known oribital period of 7d.492±0d.009. Light curves obtained during any two seasons do not agree in any of the following: shape, amplitude, phases of the light maxima and minima, mean light level, or brightness at the light maxima and minima. From the change inB-V over the photometric period, we concludethat the hemisphere visible during the light minimum is cooler than that seen during light maximum. The mean colorB-V=1m.065±0m.002 is consistent with K1 III or K2 IV. Phases of light minima lie on two well-separated groups with different slopes; the corresponding periods are 7d.471±0d.002 and 7d.481±0d.001, in dicating that both migrate linearly towards decreasing orbital phase. In terms of the starspot model this indicates that two respective centers of activity were situated at different longitudes and latitudes on a differentially rotating star. From circumstantial evidence we infer that the dark region seen from 1979 onwards disintegrated sometime between the 1982 and 1983 observing seasons, leaving behind an area of relatively high surface brightness. We can put a lower limit of about four years on the lifetime of a center of activity.

RS CVn-type variables

Photometric observation of HR 1099 inV andB obtained on 18 nights between January and March 1977 is presented. The amplitude of the asymmetric light curve is found to be 0m.10±0m.004 both inV andB. On three occasions—namely, JD 2443164. 17, JD 2443176. 14 and JD 2443177.12—the star brightened by ∼ 0m.05. Four Hα spectrograms at 42 Å mm−1 dispersion were obtained during October–November 1978. The profile and equivalent width of Hα of 14 November, 1978 suggest a probable major outburst.Analysis of all available photometry shows that (1) the amplitude and shape of the light curve change in a few orbital periods, (2) the phase of the minimum light migrated towards decreasing orbital phase during the interval JD 2442720 to JD 2443000 and from JD 2443200, there is almost a linear increase of the phase of the minimum light and (3) the phase of the light minimum sometimes shows to and fro behaviour suggesting the migration of the wave is not taking place smoothly.

Photometry of the RS CVn Binary II Peg

B and V photometry of II Peg obtained at Kavalur on 39 nights during 1980–81, 1981–82 and 1984–85 observing seasons is presented in Fig. 1. From an analysis of the available data on this object we find that no two light curves agree in any of the following: shape, amplitude, phases of the light maxima and minima, mean light level, or brightness at the light maxima and minima.