Kam-Ching Leung

Evolved Contact Systems of Spectral Type A: Au Puppis, V535 Arae, and V1073 CYGNI

The photoelectric observations of AU Pup, V535 Ara, and V1073 Cyg were reanalyzed with Wilson and Devinneys approach. All three systems are found to be contact configurations. AU Pup has an unusually large degree of overcontact, 72y0. V1073 Cyg is found to be an evolved contact system since the radius of the primary is twice that of a zero-age main-sequence star of corresponding mass. All three systems are found to be evolved according to their locations in the period-spectral-type diagram. Improved photometric parameters are reported for all three systems. Subject heading: stars : eclipsing binaries

The astrophysics of emission-line stars

Stellar Atmospheres and Formation of Emission Lines.- Stellar Spectra and Radiation Fields.- Dynamic Processes in Stellar Atmospheres.- Formation of Emission Lines.- Emission-Line Stars.- Early-type Emission-line Stars.- Late-Type Stars and Close Binaries.- Pre-main Sequence Stars.

An explanation of light-curve asymmetries in contact binaries by means of the coriolis effect

In this study, it is proved that the isothermal surface is not identical with the isobaric surface in a static model of a contact binary system based on hydrostatic and thermal equilibrium equations. Therefore, there is a baroclinic structure in a contact binary atmosphere, and the development of circumfluence is thus inevitable. It is suggested that a static model should not be adopted in modeling a contact binary atmosphere. The asymmetry (different brightness between the maxima) commonly found among the light curves of W UMa binary systems can be explained in terms of the asymmetry of circumfluence in the contact binary stars due to the Coriolis effect. 8 refs.

Spectroscopy of IY Ursae Majoris during Superoutburst

We report time-resolved spectroscopic observations of the recently discovered dwarf nova, IY Ursae Majoris, over 2 days during its 2000 January superoutburst. The spectra show prominent, broad, and double-peaked emission lines of Hα, Hβ, Hγ, Hδ, and He II and weaker He I lines. The radial velocity curve of the peaks of Hα and Hβ has an amplitude of 93 ± 7 km s-1 and a phase offset of 0.12 ± 0.03. From clear evidence for a precessing disk, we obtain a solution to an eccentric outer disk consistent with theoretical works, which demonstrates the validity of the relation between superhumps and tidal effects. The γ velocity of the binary is derived as -4 ± 32 km s-1 according to the solution. The inner part of the disk is also eccentric as evidenced by asymmetric wings in the lines. Therefore, the whole disk is eccentric. Finally, we find that a simple model can explain all asymmetric features of the emission lines.

The influence of radiation pressure on equipotential surfaces in high-temperature binary systems

In this paper we considered the effect of the radiation pressure from both components of the high-temperature binary systems in terms of a modified Roche potential. Usually, the parameters of radiation pressures δ1, δ2 can be written as a function of radiiR, effective temperatureTeff, and massM of components. The simulation calculation shows that the positions of saddle pointsL1,L2,L3 and shape of critical surface are changed with radiation pressure factors δ1, δ2. Consequently, use of the conventional critical Roche model to estimate value of radii and mass ratios may be completely unwarranted if effective temperature of both componentsTeff≥30 000 K.These conclusions are applied to Wolf-Rayet binary systems V444 Cygni,v2 Velorum, and O-type binary system Y Cygni. The modified critical potentials are calculated and discussed.

Analysis of the evolved contact system V367 Cygni

Three groups of observations of V367 Cyg - Fresas blue light curve (1957-1960, group I), Heisers UBV light curves (1960-1961, group II), and BV light curves of Kalv and Pustylnik (1967-1973, group III) - were analyzed separately with the Wilson and Devinney approach. An appropriate value of the mass ratio of the system was derived from a q-search procedure. Three contact solutions were obtained with over-contact of 0.0 percent (critical contact), 4.5 percent, and 8.8 percent, corresponding to the observations of group I, group II, and group III respectively; and no third lights were found in the light curves. Absolute dimensions of the system were calculated with the photometric mass ratio. The observed radii are found to be about a factor of six greater than the zero-age main-sequence values for stars of corresponding masses. It is suggested that V367 Cyg is at an evolved contact phase with active mass transfer or mass loss or both. 19 references.

A Photometry Campaign for IR Geminorum in Quiescence

We report a V band photometry of the SU UMa star IR Gem at quiescence in January 2002. The observations were made with two telescopes spaced ~ 160° apart in longitude. Several photometric modulations have been found. One gives a period of 98.50(13) min, exactly equal to the orbital period determined spectroscopically. Two others occasionally strengthen and seem to be positive and negative superhumps with periods of 103.6(4) and 95.4(4) min, 5.2 % longer and 3.1 % shorter than the orbital period, respectively. A signal at ~ 0.6 c/d in the power spectrum is roughly consistent with the expected period of nodal precession of the disk. There is a puzzling peak at 0.21(3) c/d corresponding to the ~ 4.3 d sine wave seen in the raw light curve. We suspect it to be a beat frequency between the frequencies of apsidal and nodal precessions of the disk. Quasi-periodic cycles with amplitudes 0.15–0.6 mag can be seen in the light curve. The mechanism underlying this modulation is not clear.

DETECTION OF A SECOND-GENERATION BINARY IN THE GLOBULAR CLUSTER ω CENTAURI

omega Centauri is the largest globular cluster in the Milky Way; it is composed of multiple stellar populations. Photometric solutions for the EA-type eclipsing binary NV364 in this cluster indicate that NV364 is a well-detached binary and that both of its components are early-type normal main-sequence stars. There is no evidence for mass transfer between the two components, which are at an early stage in their evolution. Using the luminosity-color relation with optical (BV) observations, we obtain the distance modulus of (m - M) = 14.05 for NV364, which confirms that it is a member of omega Centauri. The ages of the binary components and the first-generation stars in omega Centauri are about 1.19 Gyr and 16 Gyr, respectively. Thus, the binary components are much younger than the first-generation stars. There is therefore a strong basis for considering NV364 to be a second-generation binary in this globular cluster.

UBV observations of short-period close binary V392 Orionis

The eclipsing binary V392 Ori was observed photoelectrically, from November 1984 to January 1985, inUBV bands using the P34B photometer attached to the 0.91 m reflector at the McDonald Observatory. Four-hundred eighty-six observations in each band were obtained. Six primary and 4 secondary minimum were observed during this period. The light curves show a typical Beta Lyrae-type variation instead of an Algol-type light curve reported earlier.

Photometric solution for the eclipsing binary system AO Camelopardalis

UBV light curves of AO Cam were analyzed with Wilson and Devinneys model. The system was found to be a contact configuration with a degree of overcontact of 1.4%. The mass ratio of the system is about 1.30, and the inclination is 75.09. The primary eclipse appears to be an occultation. Thus AO Cam has the characteristics of a W-type W UMa system. Its location in a period-spectral type diagram suggests that the system may be a zero-age contact system.