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The Variable CaII Absorption in Pictoris during 1998

The Variable CaII Absorption in $\beta $
Pictoris during 1998

S.I. Barnes, William Tobin, K.R. Pollard
, PASA, 17 (3), 241.
Next Section: Introduction
Contents Page: Volume 17, Number 3

The Variable CaII Absorption in $\beta $
Pictoris during 1998

S.I. Barnes - William Tobin - K.R. Pollard

Mount John University Observatory & Department of Physics and Astronomy,
University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand
s.barnes, w.tobin, k.pollard@phys.canterbury.ac.nz

Abstract:

Variable absorption features were observed in the visible and ultraviolet spectrum of $\beta $ Pictoris soon after this star gained attention in the early 1980s due to its large IRAS infrared excess and the discovery from optical imaging of an edge-on dust disc. The absorption has been attributed to the evaporation of infalling planetesimals or comet-like bodies (the Falling Evaporating Bodies, or FEB, hypothesis). With a view to confronting this hypothesis with fuller observations, we monitored the CaII H & K lines in $\beta $ Pictoris simultaneously during 1998, obtaining sequences of spectra on 50 nights. Variable absorption was usually present. The different oscillator strengths of the H & K lines permit the determination of covering factors, but detailed modelling is required to test whether all features can be explained by the FEB hypothesis. The blend of CaIIб H with Balmer H$\varepsilon$ means that the H & K photospheric profiles are different and that the variable absorption features do not evolve in parallel. The behaviour of the variable absorption on November 27 is evocative of a body passing in front of the stellar disc in a prograde equatorial orbit.

Keywords: circumstellar matter -- line: profiles -- stars: individual ($\beta $ Pictoris)





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