Interacting Magnetospheres in RS CVn Binaries – Coronal Heating and Flares

Abstract

Coronae and flares of RS CVn systems are interpreted as due to gradual and sudden releases of magnetic free energy which is built up throught the interaction of magnetic fields of stars in these close binary systems. X RAY AND RADIO OBSERVATIONSRecent observations of RS CVn binaries in soft X-rays (Walter et al 1980) and in radio wavelengths (Gibson et al 1978, Feldman et al 1978 indicate the presence of vigorous coronae and the occurrence of flares. These, combined with the starspot hypothesis based on the "Photometric Wave" (PW) in the light curves (Hall 1972, Eaton andHall 1979), strongly suggest that these high temperature or high energy phenomena may be due to activated magnetic fields in the outer atmospheres of the component stars, as already found in the case of the Sun (e.g., Sheeley et al 1974, Sakurai and. In the present paper, we look into this possibility by examining the magnetic field configuration and various distorting effects. ACTIVE-LONGITUDE-BELT MODELIn presenting our argument we first introduce a new aspect into the starspot hypothesis. We propose that the PW may correspond to the stellar analogue, in an extreme form, of an "Active-Longitude-Belt" on the Sun (ALB) in which active spot-groups are seen to emerge, drift across and disappear, rather than being due to a gigantic, long-lived starspot, or aggregate of spots. Introduction of the notion of an ALB relieves us of the somewhat unnatural, though very fascinating, assumption of a gigantic spot or aggregate of spots, staying almost fixed on 629 [629][630][631][632] P. B. Byrne and M. Rodond feds.), Activity in

Synchrotron emission from the T Tauri binary system V773 Tauri A

“…Such intruding loops have indeed been observed on the Sun in high-resolution maps obtained with the Nobeyama Radio Interferometer (Nishio et al 1996); 2. in protostars or young (pre-main sequence) stellar systems, which are still surrounded by a dense accretion disk, flares can occur because of stretching, disruption, and reconnection of magnetic field lines between the star and its disk (Feigelson & Montmerle 1999); 3. in close binary systems consisting of late spectral type stars, much higher magnetic activity is expected compared to the Sun (because tidal synchronism increases the rotation rate and therefore the dynamo efficiency). Moreover, the coronal loops of the two stars can interact with each other, as for RS CVn (close) binaries (Uchida & Sakurai 1983;Graffagnino et al 1995). Observational evidence for inter-binary loop "collisions" was also recently found for the young binary system V773 Tau A, which shows a high rate of radio flares around the periastron passage (Massi et al 2002).…”

“…In close binary systems consisting of late spectral type stars, much higher magnetic activity is expected compared to the Sun (because tidal synchronism increases the rotation rate and therefore the dynamo efficiency). Moreover, the coronal loops of the two stars can interact with each other, as for RS CVn (close) binaries (Uchida & Sakurai 1983;Graffagnino et al 1995). Observational evidence for inter-binary loop "collisions" was also recently found for the young binary system V773 Tau A, which shows a high rate of radio flares around the periastron passage (Massi et al 2002).…”

Simulations of the periodic flaring rate on YY Gem

“…So, whenever the closed loops bulge, a current sheet forms natually, and magnetic reconnection is ready to commence (if the polarity of one magnetic system expressed in equation ( 16) is flipped, the two loop systems become to repel each other, and no reconnection can happen). Similar magnetic connectivity with a null point was also computed for the active RS CVn system (Uchida & Sakurai 1983;Uchida & Sakurai 1985;Beasley & Güdel 2000).…”

“…For example, observations revealed large-scale strong X-ray sources between the two stars of the RS CVn binary AR Lac (Siarkowski 1992;Siarkowski et al 1996), as well as of the RS CVn binary TY Pyx (Culhane et al 1990;Pres, Siarkowski & Sylwester 1995). At the same time, it is probable that the two stars are magnetically connected, as illustrated by Uchida & Sakurai (1983). Uchida & Sakurai (1985) proposed that the interstellar activities are intimately affected by the differential rotations of both stars.…”

Very long baseline interferometry of evolved binary systems

“…Previous VLBI observations of active binaries have revealed extended coronal emission (e.g., Beasley and Güdel, 2000;Massi et al, 1999;Mutel et al, 1984;Massi et al, 1999). Various models have been used to explain this emission (e.g., Kellett et al, 2002;Uchida and Sakurai, 1983). However, a polar-aligned X-ray and radio plasma provide the best explanation of the observations (Mutel et al, 1998;Favata et al, 2000).…”