EDP Sciences
Free access
Volume 391, Number 2, August IV 2002
Page(s) 641 - 645
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20020892

A&A 391, 641-645 (2002)
DOI: 10.1051/0004-6361:20020892

IUE-newsips spectra of $\sigma$ Geminorum

F. Ekmekçi and O. Karakus

Ankara University, Science Faculty, Dept. of Astronomy and Space Sciences 06100 Tandogan, Ankara, Turkey
(Received 6 March 2002 / accepted 15 May 2002 )

The IUE spectra of $\sigma$ Gem have been taken from the NASA IUE archive using IDL (Interactive Data Language). The spectra have been observed in 1979-1986 period. All the spectra analysed in the present study have NEWSIPS reductions and consist of 25 LWP, 8 LWR and 5 SWP images in high resolution, and 2 LWP and 14 SWP images in low dispersion. The emission lines, identified as activity indicators and originating in the chromosphere and transition region, are seen in the spectra. The emission line fluxes and equivalent widths are computed based on Gaussian profile fitting procedures to examine the existence of any line flux variation that depends on time or orbital phase. It was found that there is a flux variation with time and orbital phase that is in good agreement with the photometric light curve variation. By comparing the flux variation with simultaneous light curve variation, it can be shown that there is a relation between the ultraviolet flux variation and the spot activity of the system, as shown by Ayres et al. (1984) and Engvold et al. (1988) based on their IUE (with IUESIPS reduction) spectral analysis. Moreover, it was inferred that there is no ultraviolet excess in $\sigma$ Gem by comparing the spectra of $\beta$ Gem taken as a comparison star. The Mg II h and k radial velocity curves of $\sigma$ Gem were in a good agreement with data obtained by Eker (1986) and Duemmler et al. (1997). The sinusoidal Mg II radial velocity curve solutions of the system give e = 0, $P_{\rm orb.} = 19.607\pm0.008$ days, $K = 34.86\pm 2.33$ km s -1, $\gamma = 49.42\pm 1.87$ km s -1 and $T_{\rm o} =
2445972.53\pm 0.28$ . Since the ultraviolet flux data are not conveniently distributed and are insufficient to determine the activity cycle, the evaluation of the ultraviolet flux activity cycle was not successful.

Key words: stars: activity -- stars: atmospheres -- stars: binaries: spectroscopic -- stars: chromospheres -- stars: individual: $\sigma$ Gem -- stars: late-type

Offprint request: F. Ekmekçi, ekmekci@astro1.science.ankara.edu.tr

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