Petr Harmanec

Evolutionary changes in the eclipsing binary β Lyrae

Abstract An attempt at the first direct test of the theory of large-scale mass transfer between the components of a binary system is discussed. It is argued that β Lyr is the only binary in the sky for which such a test is presently possible.

VEGA: A Visible Spectrograph and Polarimeter for the VLTI

The ESO/VLTI has now clearly a position of world leader in the domain of ground-based optical interferometry. With four 8.2 m telescopes and two (four) 1.8 m telescopes, the Paranal Observatory is without any doubt the best optical interferometric facility in the world. Since many years, it has attracted the major part of the European interferometric community and with the opening of MIDI and AMBER, the astronomers have now access to ’general user’ interferometric instruments in the thermal and near infrared. This paper describes a project for a second generation focal instrument of the VLTI, named VEGAfor Visible spEctroGraph and polArimeter. The goal is to give access to the visible wavelength region, with spectroscopic and polarimetric capabilities, taking advantage of the coherent field of view of the VLTI. It is a unique scientific field for the VLTI. For example, a 200m interferometer operating in the visible will be able to resolve structures of the order of 0.5 mas or 0.1 AU at the distance of the Ophiuchus cloud.

Observations of the Close Binary System ß Lyrae with the GI2T Interferometer

We present the results of the 1994 international multitechniques campaign of observations of the well-known binary system s Lyrae, emphasizing on the interfer-ometric observations and results obtained with the GI2T interferometer.

Spectroscopic and Photometric Support for Interferometric Observations of Be Stars

The nature of Be stars and true physical causes of their spectral and brightness variations on several timescales remain largely unknown. It is argued that real progress in their understanding may come from systematic spectro-interferometric observations supplemented by simultaneous spectroscopy and photometry. Several unsolved problems and existing hypotheses to be addressed this way are discussed. It is argued that the present-day interferometers can mainly help to understand the geometrical structure of the circumstellar matter around Be stars and the nature of the long-term (years and longer) and (in some cases) medium-term (weeks to months) changes. Studies of rapid changes on timescales shorter than about 2 d and (in most cases) investigation of possible duplicity of Be stars will require a much higher angular resolution to be only achieved by future interferometers or by application of the promising technique of differential interferometry. It is clear, however, that Be stars are very suitable and challenging objects to be studied by means of interferometry.

An Improved Model of the B0.5e + Be Binary System φ Per

ϕ Per (HD 10516) is a spectroscopic binary with a 126.699-day period (Ludendorff 1910, Cannon 1910, Harmanec 1985). However, most of the published RV curves of the primary are based on H I shell lines and exhibit a typical distortion with a sharp maximum, shallow minimum and a bump at 0.P4 after the RV maximum (c.f., e.g., Harmanec 1985). There has been controversy on the nature of the secondary. Hynek (1940) and Hendry (1976) concluded that the binary was composed of two B stars. Peters (1976) suggested that the secondary of ϕ Per is a Roche-lobe filling K giant. Poeckert (1981) reported the discovery of a weak He II 4686 emission which moved in antiphase to the Be primary and suggested that it originated in the disk around the secondary. In his interpretation, the secondary is a helium star, a remnant of an originally more massive star which in the past transferred its mass to the present Be star. There is now no mass tranfer in the system according to Poeckert. Using RVs of the broad absorptions for primary, and of the He II 4686 emission for the secondary, Poeckert obtained two roughly sinusoidal RV curves and M1sin3i = 21.1 m⊙ and M2sin3i = 3.4 m⊙.

Line-Profile Variable ε Per: Spectroscopic Binary and (?) Mild Be Star

e Per (45 Per, HR 1220, HD 24760, ADS 2888A) is a star which was used for years as a spectrophotometric and MKK classification standard. Nowadays it is known as an archetype of early-type line-profile variables (LPV). The variations are so pronounced that they were misinterpreted for a composite spectrum (B0.5+A2) and the star was even reported to be a double-lined spectroscopic binary (Petrie 1958). Since 1983, the characteristics of line-profile variability in the spectrum of e Per have been intensively studied (Bolton 1983, Smith 1985, Gies & Kullavanijaya 1988). The recent investigations of RV variations of e Per led to the conclusion that e Per is a spectroscopic binary with a period of about 14.05 days and a rather eccentric orbit (Harmanec & Tarasov 1990). The issue of the binary nature (with a very eccentric orbit) is of utmost importance since it could be causally related to the extremely large observed line-profile variations (e.g., Polfliet & Smeyers 1990, Tassoul & Tassoul 1992).

70 Years of Observations of 4 Her: Changes through Three Shell Episodes

4 Her (HD 142926, HR 5938; V=5 m .75, v.sini=300 km s-1) is a well known and rather frequently observed Be and shell star. It was recognized as a Be star by Heard (1939) and Mohler (1940). The estimates of its spectral type by different authors vary between B7 IV-V and B9e. Hubert(1971) reported remarkable spectral changes of 4 Her which occurred between 1953 and 1970. Harmanec et al.(1973) discovered periodic radial-velocity variations of the hydrogen shell lines with a period 46.023 days and suggested the object is a single-line spectroscopic binary. The system elements were later refined by Heard et al.(1975) to P=46.194 days, K=12 km s-1 and e=0.3. In a subsequent paper, Harmanec et al.(1976) studied the variations of emission and absorption components of the hydrogen lines and concluded that 4 Her is an interacting binary and that the observed eccentricity of the orbit is spurious, caused by the effects of circumstellar matter.