β Pictoris: observations of the Ca ii H&K absorptions in 1997 and 1998

Abstract

ABSTRACT We present spectroscopy with resolution R ∼ 33 000 of the circumstellar Ca ii H&K absorptions in the star β Pictoris during 1997 and 1998. From 1997 April onwards, both lines were observed simultaneously. A total of 688 spectra were obtained over 95 nights in order to characterize the lines’ behaviour. Near-continuous Falling Evaporating Body (FEB) variable absorption activity was seen, including additional strong, blueshifted features besides the one on 1997 June 19–20 already reported by others. Temporal coverage is more even than in the HARPS spectra from 2004–11 that have been analysed for FEB orbital parameters via a model of FEB evaporation. Our observations likely encompass the 1997–98 Hill-sphere transit by β Pic b, but we have found no clear signature of transiting material. Lower velocity FEB absorptions tend to be deeper, narrower and longer lived, in confirmation of earlier studies. The ratio of line strengths for one absorption on 1998 November 27 is evocative of the variations expected for a single FEB making a transit perpendicular to the stellar rotation axis. Analysis with the evaporation model produces similar distributions of orbital parameters to those obtained from the HARPS observations, but when the derived orbital parameters are fed into a model based solely on gravitational dynamics of point masses, the predicted FEB accelerations do not agree with observed values. More sophisticated modelling is called for. There is no convincing intrinsic variation in the central circumstellar absorption such as might be expected if an H i ring is responsible for the confinement of circumstellar Ca+ ions. Our observations are available electronically for further analysis by others.