Introduction

Slee et al. (1987) have published data from microwave (predominantly 8.4 GHz) surveys of binary stars carried out at Parkes in the eighties. The present article revisits and extends the data on systems observed at Parkes, generally between mid-1981 and late 1989, with a few points added from more recent ATCA observations.

The stars concentrated on in this paper are those for which 3 detections were reported. They have been assigned to three groups as follows: (i) 16 RS CVn stars (AR Psc, AT Cap, BH Ind, CF Tuc, EI Eri, GT Msc, HD101309, IL Hya, IM Peg, IN Vel, RZ Eri, SZ Psc, TW Lep, V1379 Aql, V711 Tau & V824 Ara) (cf. Strassmeier et al., 1993); (ii) 8 classical Algol binaries ( Lib, KZ Pav, R CMa, RY Gem, S Cnc, V393 Sco, V505 Sgr & XZ Sgr) (EA2s, cf. Budding, 1985); and (iii) 6 early-type detached pairs ( Cap, TZ Men, V760 Sco, V822 Aql, V1647 Sgr & Phe) (ETBs, cf. Stewart et al., 1988). In the survey of Slee et al. (1987) there were 48, 25 and 18 stars altogether in these groups, respectively. All the binaries studied hereafter have known photometric ephemerides.

The original data samples consist of source intensity measurements over background measured at a specified offset position (`wags'), together with standard errors of the individual determinations. Precautions in procedure designed to eliminate the effects of possible source confusion were reported previously by Slee et al. (1987). The average value of this standard error over the whole data collection is a little over 2 mJy. There are 828 entries in our total subset, each a mean of 10 individual measurements, and 3, or greater, detections occur in about 41% of these entries. The most frequently detected sources are the RS CVn binaries, which account for almost 3/4 of the measurements, some of which (particularly V711 Tau = HR1099) are very frequently observable. In fact, both RS CVn stars and Algol binaries are well known radio emitters (cf. e.g. Linksy, 1994). Although the significance of early reported detections in certain other subsections of the Parkes stellar surveys (Slee et al., 1989) has been called into question (Beasley et al., 1992), on the basis of standard deviations some 20% lower than we apply here, the emissions we shall discuss carry internal evidence against spurious or accidental registration. Further informed discussion of the determination of appropriate significance measures was presented by Slee & Budding (1995).

All the observed sources have an irregular character to the emission, and the majority must be detected when an outburst is taking them, sporadically, above detection threshold. An inverse square law in distance would affect the threshold received power, but the evidence shows other factors to be also strongly at play in determining detection incidence. A (heliocentric) binary phase can be determined for each radio measurement, so one clear purpose is to look for any orbital phase dependence in such detections.

© Copyright Astronomical Society of Australia 1997