From Top to Bottom- The Multiwavelength Campaign of V824 Ara (HD 155555)

R. Dempsey, J. Neff, K. Strassmeier, J. Linsky, J. Lim, J-F. Donati, F. Walter, E. Budding, F. Marang, I. Jordan, S. Walker, D.G. Downing, D. Inwood, O. Petterson

Presentations at the 10th Cambridge Workshop ``Cool Stars, Stellar Systems and the Sun,'' Cambridge, MA, 1997 July 15-19


In the spring of 1996, we conducted a multi-wavelength campaign on V824 Ara (HD 155555, P=1d.68, G5 IV + K0 IV-V) covering one continuous, complete rotation cycle. At the core of this campaign were observations using the GHRS and HST. In all, ~46,000 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 EUVE. Radio observations (3.5 & 6 cm) were conducted at the Australian Telescope while ground based optical spectroscopic and photometric observations were made at ESO, CTIO, AAT, and SAAO. Additional amateur photometry were obtained from New Zealand before, during, and after the campaign. Our primary intent is to obtain a 3-D 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 preliminary results from turbulence model proposed by Gray (1976, The Observation and Analysis of Stellar Photospheres, Cambridge Astrophysics Series). Previous studies of TR lines in late-type active stars have used multiple gaussians to fit the observed line profiles, adding additional, 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 (Wood et al., 1995, ApJ, 458, 761). We discuss how anisotropic macroturbulence can also fit the Mg II profiles and, in some cases, with smaller residuals than is possible using only gaussians.

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