We report on high-resolution spectroscopy of the RS CVn binary II Peg, along with contemporaneous UBV(RI)(KC) photometry, including partly simultaneous 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 observed the three chromospheric lines, H alpha, H beta and HeI D-3, over a single rotation and at the second epoch we observed almost the entire visible region, for a substantial fraction of one rotation, including H alpha-H epsilon and CaII H. Our photometric results show that there was an unusually complicated spot distribution at this epoch, with at least three centres of activity discernable. We demonstrate, for the first time on a spotted late-type star, that these centres of spot activity have significantly different mean temperatures from one another. Furthermore, our derived spot temperatures are markedly lower than those previously derived from such multicolour photometry and more similar to those derived spectroscopically. Using multiple repeat exposures on each spectral line within each night, we are confident that we have derived a mean, non-flaring spectrum at each observational phase. Furthermore, 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 spectra 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 chromosphere. We examine the variation of the chromospheric line fluxes as a function of spot visibility and conclude that there is only a very loose spatial correlation of chromsopheric heating with spots. The motions suggested from the Her profile variations appear to be spot-associated.
|Titolo:||THE PHOTOSPHERE AND CHROMOSPHERE OF THE RS CANUM-VENATICORUM STAR, II-PEGASI .1. SPOTS AND CHROMOSPHERIC EMISSION IN 1991|
|Data di pubblicazione:||1995|
|Appare nelle tipologie:||1.1 Articolo in rivista|