Astronomy and Astrophysics – Astronomy
Scientific paper
Aug 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987apj...319..383o&link_type=abstract
Astrophysical Journal, Part 1 (ISSN 0004-637X), vol. 319, Aug. 1, 1987, p. 383-391.
Astronomy and Astrophysics
Astronomy
5
Late Stars, Red Giant Stars, Stellar Activity, Stellar Spectrophotometry, Supergiant Stars, Ultraviolet Spectra, Emission Spectra, Error Analysis, Iue, Line Spectra, Spaceborne Astronomy
Scientific paper
Chromospheric and transition region line activity is examined in apparently single red giants and supergiants using the IUE archives. Low-resolution, large-aperture spectra (mostly short-wavelength) were used to search for variations of emission-line fluxes in time. A series of automatic processing procedures were implemented 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 is offered to compute the overall error in the integrated flux, a critical measure of activity, independent of the observing and processing details. This processing was applied to above 120 images of 26 stars taken over a period of 7 yr (1978-1984). Four stars showed UV emission-line flux variations. Alpha Aqr, Beta Peg, and Sigma Oph showed a single enhanced-emission event in all detectable emission lines. Gamma Aql exhibited an increase in the flux level of the O I (1641 A) line in mid-1981 with no comparable change in any other lines. These four stars lie in a region of the H-R diagram in which time-dependent circumstellar absorption lines appear.
Gibson David M.
Oznovich I.
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