A PHOTOMETRIC AND ORBITAL ANALYSIS OF GT MUSCAE

GT Mus is a quadruple system comprising a long-period RS CVn-type bina ry (HD 101379) and a pair of eclipsing A dwarfs (HD 101380). Six and a half years of UBV(RI)(c) photometry obtained at the Mt John Universit y Observatory has enabled identification of four distinct types of pho tometric variability in this system. These are (1) a slowly changing m ean magnitude, which probably arises from an activity-cycle-like effec t in the active component of HD 101379, (2) a periodic variation (P-ro t similar to 64 d), which is attributed to rotational modulation due t o spots on the active star, (3) a periodic variation (P-eclipse = 2.75 46 d) due to the eclipses of HD 101380, and (4) an excess in the I ban d, which occurs on a short time-scale (<1 d) and is probably associate d with HD 101379 activity. The evolution of the light curve of HD 1013 79 is fast with respect to the rotational period, suggesting rapid spo t evolution for which we anticipate a possible model. The colours of H D 101379, even at maximum brightness, are excessively red for its spec tral type, unless there is significant reddening by dust. Radial veloc ity measurements of HD 101379 are also presented, along with an improv ed determination of the orbit of this somewhat long-period (P-orb = 61 .448 d) system.