THE PHOTOSPHERE AND CHROMOSPHERE OF THE RS CANUM-VENATICORUM STAR, II-PEGASI .1. SPOTS AND CHROMOSPHERIC EMISSION IN 1991

We report on high-resolution spectroscopy of the RS CVn binary II Peg, along with contemporaneous UBV(RI)(KC) photometry, including partly s imultaneous U-band flare monitoring, during the third quarter of 1991. The spectroscopy was taken at two epochs separated by more than 61/2 weeks or seven rotations of II Peg. At the first epoch we have observe d the three chromospheric lines, H alpha, H beta and HeI D-3, over a s ingle rotation and at the second epoch we observed almost the entire v isible region, for a substantial fraction of one rotation, including H alpha-H epsilon and CaII H. Our photometric results show that there w as an unusually complicated spot distribution at this epoch, with at l east three centres of activity discernable. We demonstrate, for the fi rst time on a spotted late-type star, that these centres of spot activ ity have significantly different mean temperatures from one another. F urthermore, our derived spot temperatures are markedly lower than thos e previously derived from such multicolour photometry and more similar to those derived spectroscopically. Using multiple repeat exposures o n each spectral line within each night, we are confident that we have derived a mean, non-flaring spectrum at each observational phase. Furt hermore, the line flux variations at the two epochs repeat very well, suggesting that the mean global chromospheric structures are stable on a 11/2 months time scale. We discuss the implication of the mean spec tra for the non-flaring atmosphere of II Peg and conclude that, in the region of formation of the H alpha line, velocity fields are required to account for the line profile. These results suggest upward motions of the deep chromosphere with a less dramatic downflow in the high ch romosphere. We examine the variation of the chromospheric line fluxes as a function of spot visibility and conclude that there is only a ver y loose spatial correlation of chromsopheric heating with spots. The m otions suggested from the Her profile variations appear to be spot-ass ociated.