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1. Introduction

  Chromospheric and coronal heating on the Sun is highly concentrated into localised active regions of enhanced magnetic field. The distribution of such active regions with solar longitude is highly non-uniform, with the global brightness in high-temperature spectral features sometimes being dominated by a few very active regions. This is especially true near the maximum of the Sun's magnetic cycle.

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. tex2html_wrap_inline2085, 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.


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