Di-Sheng Zhai

Radial velocity observations and physical activities of the contact binary system SW lacertae

Abstract We present our 1984 radial velocity observations of the W UNa system SW Lac. These give a new spectroscopic mass ratio qsp = 1.255 ±0.011. A joint solution of the velocity and light curves give the following revised absolute parameters: M 1 = 0.78 M⊚, M 2 = 0.96M⊚, R 1 = 0.91R⊚ , and R 2 = 1.00 R⊚ . Based on our new results, together with a detailed review of the period changes, probable mass transfer, mass loss, spot activity and other physical properties of SW Lac are discussed.

The short period eclipsing binary V 361 Lyrae and near-contact detached systems

Abstract The short period eclipsing binary V 361 Lyr with a period of 0.3096 d has probably the shortest period among known near-contact binaries made of non-degenerate matter. In this paper a detailed photometric analysis is made using the V and I light curves observed by Kaluzny in 1989. Considering that any hot spot on the secondary component from accretion is likely to be extended in the longitude direction, we adopted a multi-spot model and succeeded in obtaining a good fit to the observed, distorted light curve. The photometric solution shows V 361 Lyr to be a near-contact detached system, with a photometric mass ratio q = 0.696 ± 0.005. The secondary is an evolved subgiant and the mean temperature of three hot spots is about 7340 K. The absolute masses and radii were estimated and the hot spots were found to have an accretion luminosity of about 1.07×1033 erg/s, corresponding to a probable mass exchange rate of about 7.0×10−7 yr−1. A discussion is made on the statistical properties of 15 known A-K type, near-contact, detached systems.

Spot Solutions for Two RS CVn Systems: ER Vul and V711 Tau

Based on spot model and Roche approximation for binary stars, the photometric analysis was carried out for the BV light curves of both the eclipsing system ER Vul and the non-eclipsing V711 Tau. The preferable spot parameters were obtained by using differential correction adjustment and least squares technique.

Near infrared spectrophotometry of the chromospherically active binary HR 1099

Abstract This paper presents the results of near infrared spectrophotometry of the chromospherically strongly active binary HR 1099 before and after the extra energetic white-light flare of December 1989. Low-dispersion, CVF spectra between 2.3–4.2 μm for this star are given here for the first time. The effects of starspots at the time of the observation are calculated and an approximate blackbody spectrum is given. Comparison with multi-wavelength photometry and the IRAS measurements revealed strong emission band at 2.3 μm and absorption band at 3.1 μm by circumstellar matter. A preliminary discussion is made on the probable composition and distribution of the circumstellar matter.

UBV photometric study of the extra large flare of HR 1099

Abstract This paper presents observation and analysis of the extraordinarily energetic white-light flare of the solar-like active binary HR1099 (=V 711 Tau) on 1989 December 14. The flare luminosities in U, B, V were found to be 3.00, 6.49, 3.44 × l032erg/s, respectively, and the total flare energy in the optical region, to be greater than 1037 erg. The colour indices of the pure flare radiation near the maximum phase were (B − V) ƒ = 0.35, (U − B) ƒ = −0.65 , similar to events in classical flare stars. Under the assumption of quasi black body radiation the flare area was found to be about 3% of the apparent disk of the K1 IV component star, and the maximum temperature, 7000–8000 K. This event shows that it is possible for active subgiants more massive than the sun to produce super luminous white light flares, and provides an important datum in the study of the chromospheric activity of such stars.

Photoelectric photometry of the early-type semi-detached binary UW Orionis

Abstract We give a photoelectric light curve of UW Ori for the first time and a new epoch formula. A preliminary photometric solution was obtained using the Wilson-Devinney method of light curve synthesis. The reuslts show that it is an early-type, almost contact, semi-detached binary of large mass, with a mass ratio 0.513. If the large mass component is a zero age main sequence star, then the small mass component is no longer such. The O-C in the time of minimum suggest a possibly increasing period.