Mg II h&k line diagnostics of IM Pegasi *
K. Oláh 1,
D. Marik 1,
E.R. Houdebine 2,
*** , 3 and
E. Budding 4
Received 18 December 1996 / Accepted 8 October 1997
We have analysed the Mg II h&k resonance lines of IM Peg (KII-III) on 14 high resolution IUE LWR spectra and compared the results coming from visual spectroscopic and photometric data. The `clean' spectra (free from interstellar absorption) were modelled using a convolution of the rotational profile with a Gaussian profile, that represents macroturbulence and broadenings of other origin, the former dominating.
Significant variations in the h&k line fluxes and widths were found throughout the orbital phase range. A line broadening effect is found at maximum spot visibility both in the k and h lines. The Mg II line widths increase linearly with the flux of the transition region lines as a function of rotational phase. Anticorrelations as a function of phase were found between the Mg II line fluxes and the higher temperature lines. The k line is broader than the h line, correlated with a slope greater than unity, in keeping with a greater radiation transfer effect in the k line, and a non-optically thin medium at all phases. We observe a systematic asymmetry in the ratio of the h to k line profiles at all phases. The spectral diagnostics thus suggest the appearance of a plage region on the stellar disc.
We obtained new orbital elements of the IM Peg system, deriving a small, but non-zero eccentricity.
Key words: stars: individual: IM Peg stars: activity stars: chromospheres stars: binaries: spectroscopic stars: late-type
* The authors would like to dedicate this paper to their late referee, Dr. P.B. Byrne.
Send offprint requests to: K. Oláh
© European Southern Observatory (ESO) 1998
Online publication: January 16, 1998