Chromospherically active late-type stars exhibit most of the characteristics of the active Sun but on a globally much enhanced scale. RSCVn stars are close late-type binaries in which one component lies above the main sequence and, forced into corotation through tidal interaction, is chromospherically active as a result of dynamo generation of magnetic fields. RSCVn's exhibit a wide range of solar-like activity phenomena. These include non-radiatively heated chromospheres and X-ray emitting coronae (Doyle et al. 1991, 1992a,b), cool surface spots (Byrne 1992a,b) and frequent flares (Doyle et al. 1989b).
Based on the solar experience, it might be expected that non-uniform distributions of magnetic heating on RSCVn stars would lead to variability in the stars' detected flux in suitable chromospheric and coronal radiations as the star rotates, i.e. rotational modulation. Such effects have been very elusive, however, in spite of much observational effort (Rodonó et al. 1987; Andrews et al. 1988; Byrne et al. 1987, 1989, 1995 (hereafter Paper I), Doyle et al. 1989a, 1992a,b). However, since most previous efforts have been based on either sampling a single rotation of the active star, or random sampling during many different rotations, there is an obvious danger of any rotational modulation being masked by short-term variability, such as flaring, or longer-term variations, such as the growth and decay of active regions.
In this paper we describe observations of the 6.72d SB1 RSCVn K2IV binary,
IIPeg in the ultraviolet, optical and microwave spectral regimes, over
varying fractions of 2 stellar rotations, which are then used to examine these
issues. In this paper we present the data resulting from these observations.
In a forthcoming paper we will discuss their implications more fully (Byrne
et al. in preparation). Note that throughout this paper we use the orbital
ephemeris of Vogt (1981), i.e. , which we found in Paper I to be more accurate than any of the
other published ephemerides. We also assume, as have others, that II Peg's
axial rotation is tidally locked to the orbital motion of its companion.