An IUE survey of activity in red giants and supergiants
We examine chromospheric and transition region line activity in apparently single red giants and supergiants using the ME archives. Low resolution, large aperture spectra (mostly short-wavelength ones) were used to search for variations of emission line fluxes in time. We implemented a series of automatic processing procedures in order to uniformly calibrate a large number of spectra, fit continua to each of them, determine the fluxes of as many as 18 emission lines and compare them at different epochs. A method to compute the overall error in the integrated flux (being the crucial activity measure used) independent of the observing and processing details is offered. The data-base consisted of ∼120 images taken over a period of seven years. We detected UV emission line flux variations in four stars, comprising 15% of the tracked stellar set. All four stars lie in a region of the HR diagram in which time-dependent circumstellar absorption lines appear.
KeywordsEmission Line Line Flux Hybrid Star Standard Calibration Procedure Variability Magnitude
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