Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001aj....122..332d&link_type=abstract
The Astronomical Journal, Volume 122, Issue 1, pp. 332-348.
Astronomy and Astrophysics
Astronomy
4
Stars: Activity, Stars: Chromospheres, Stars: Coronae, Stars: Individual (V824 Arae), Stars: Late-Type
Scientific paper
We conducted a multiwavelength campaign observing V824 Ara (HD 155555, G5 IV+K0 IV-V) continuously throughout one complete orbital cycle (~1.7 days) in early May of 1996. At the core of this campaign were observations using the GHRS on the Hubble Space Telescope (HST). In all, about 48,000 spectra, many in rapid readout mode, were obtained with the GHRS covering the C IV, Mg II, and Fe XXI wavelength regions at 11-15 separate phases. Simultaneous observations were made with the Extreme Ultraviolet Explorer (EUVE). Radio observations (3.5 and 6 cm) were conducted at the Australian Telescope, while ground-based visual spectroscopic and photometric observations were made at European Southern Observatory, Cerro Tololo Inter-American Observatory, the Anglo-Australian Telescope, and South African Astronomical Observatory. Additional ground-based observations were obtained before, during, and after the campaign. Our primary intent was to obtain a three-dimensional model of the atmosphere extending from the photosphere to the corona. Variability was clearly detected, including several flares observed in the HST, EUVE, and radio data. We present results from modeling the ultraviolet transition region lines using an anisotropic macroturbulence model. Previous studies of transition region lines in late-type active stars have used multiple Gaussians to fit the observed line profiles, adding broad components to account for the extended wings observed in several active systems, including V711 Tau (HR 1099). This broad component has been interpreted as arising from the continuous presence of microflaring. We demonstrate that anisotropic macroturbulence models can also explain the observed Mg II profiles. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Dempsey Robert C.
Lim Jeremy
Neff James E.
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