Australia Telescope National Facility

The Active Algol Binary KZ Pavonis
E. Budding,
S. C. Marsden ,
O. B. Slee
, PASA, 18 (2), in press.

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Introduction

Microwave emission has been observed with large radio telescopes from a few dozen Algols and RS CVn binaries with periods of several days. The flux density correlates with rotation rate (Slee & Stewart, 1989) and is related to strong magnetic fields in convective outer envelopes and consequent gyrosynchrotron emission (Owen et al., 1976; Dulk, 1985). This is generally associated with the cool subgiant components. Both RS CVn and Algol systems contain such subgiants, though the evolutionary states of Algols and RS CVns are quite different. The subgiants in RS CVn binaries have expanded beyond the Main Sequence, but not yet reached the surrounding `Roche-lobe' (cf. Popper and Ulrich, 1976). Algols, however, are already into an era of mass transfer, where the subgiant sheds matter from its Roche-lobe filling surface (cf. Lubow & Shu, 1975). The Algol type, eclipsing binary star KZ Pavonis (=HD 199005; RA 20h 58.6m, dec -70 $^\circ$ 25 $^\prime$ [2000], $V_{\rm max}$ = 7.71) is some 99pc distant from the Earth (HIPPARCOS), and has an orbital period of 0.9499d. It consists of a mid-F type dwarf, of mass 1.2

$M_{\hbox{$\odot$}}$ , separated a little over 5

$R_{\hbox{$\odot$}}$ from a mid-K type subgiant. The main parameters are summarized in Table 1. (cf. Walker & Budding, 1996). The system's net brightness variation is about 0.6 in V mag. It has been detected previously with the ATCA at a level of about 0.4mJy (cf. Stewart et al., 1989; Walter et al., 1990). It has relatively low mass compared with most better known Algols, and may resemble the R CMa subgroup (Kopal, 1959; Budding, 1989). There is also at least one lower-brightness companion within a few arcseconds of the optical position (Kholopov, 1987; Chambliss, 1992). It appears to be at an early stage of semi-detached life, so that the inter-binary stream is still relatively vigorous, entailing possible observational consequences (cf. Budding et al., 1998a). The measured rate of period increase over recent decades verifies the scale of such interaction.

**Table 1:** Astrophysical Parameters of KZ Pav
Parameter	Value
Primary (F6V) Luminosity L₁	3.6 $L_{\hbox{$\odot$}}$
Secondary (K4IV) Luminosity L₂	1.5 $L_{\hbox{$\odot$}}$
Primary Mass M₁	1.2 $M_{\hbox{$\odot$}}$
Secondary Mass M₂	0.8 $M_{\hbox{$\odot$}}$
Primary Radius R₁	1.50 $R_{\hbox{$\odot$}}$
Secondary Radius R₂	1.66 $R_{\hbox{$\odot$}}$
Primary Temperature T₁	6500 K
Secondary Temperature T₂	5000 K
Orbital inclination i	86.0 $^\circ$
Separation A	5.05 $R_{\hbox{$\odot$}}$
Abs. Mag. (system) M_V	2.31

Recently, Gunn et al. (1999), have studied flux variations of the Algol system V505 Sgr, which they related to an intercomponent emission region. Uncovering source structure is a key aim in their work. The spatial incidence of Algols is, however, generally less than that of RS CVns, so that observed Algol radio fluxes tend to be less than those from RS CVns. Consequently, the available information for studying Algol emission geometry is less. Budding et al. (1998a) found weak indications of a maximum detectability of Algols at orbital phase $\sim$ 0.4. That study was based on isolated observations, mainly from Parkes (e.g. Slee et al., 1987), covering most orbital phase ranges. The present small multi-site, multi-wavelength campaign, planned in mid-1998, involved the ATCA and photometric facilties of the University of Southern Queensland in an effort to probe this potentially active binary. Orbital-phase-related data was sought to clarify comparisons with RS CVn binaries, or distinguish any factors reflecting the particular Algol status, as well as retrieve an accurate astrometric position.

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