Simultaneous observations of variability at all atmospheric levels of V824Arae (HD 155555)

We conducted a multiwavelength campaign observing V824 Ara (HD 155555, G5 I V + K0 IV-V) continuously throughout one complete orbital cycle (similar to 1.7 days) in early May of 1996. At the core of this campaign were observati ons using the GHRS on the Hubble Space Telescope (HST). In all, about 48,00 0 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. S imultaneous observations were made with the Extreme Ultraviolet Explorer (E UV E). Radio observations (3.5 and 6 cm) were conducted at the Australian T elescope, while ground-based visual spectroscopic and photometric observati ons were made at European Southern Observatory, Cerro Tololo Inter-American Observatory, the Anglo-Australian Telescope, and South African Astronomica l Observatory. Additional ground-based observations were obtained before, d uring, and after the campaign. Our primary intent was to obtain a three-dim ensional model of the atmosphere extending from the photosphere to the coro na. Variability was clearly detected, including several flares observed in the HST, EUV E, and radio data. We present results from modeling the ultrav iolet transition region lines using an anisotropic macroturbulence model. P revious studies of transition region lines in late-type active stars have u sed multiple Gaussians to fit the observed line profiles, adding broad comp onents to account for the extended wings observed in several active systems , including V711 Tau (HR 1099). This broad component has been interpreted a s arising from the continuous presence of microflaring. We demonstrate that anisotropic macroturbulence models can also explain the observed Mg II pro files.