Pictoris during 1998
S.I. Barnes, William Tobin, K.R. Pollard
, PASA, 17 (3), 241.
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Title/Abstract Page: The Variable CaII Absorption
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The CaII absorption in 1998
New observations
The McLellan One-metre Telescope at MJUO was allocated to this research over 45 full and 39 shared nights during 1998. We were able to acquire 407 sets of spectra during 178 hours of observation on 50 nights between 1998 January 20 and December 2, where the southern declination of this star allows year-round observation. Reduced spectra were normalized by absorption-free photospheric profiles to isolate the circumstellar features, which, following earlier workers, we were able to well-fit with multiple Gaussian profiles. (We fitted a common velocity and width but separate depths and hence equivalent widths to corresponding H & K features.) For fuller details, see Barnes (1999). |
Results
A sample spectrum pair from 1998 November 27 is shown in Fig. 2. The deep, sharp central feature is always present and may be due to decelleration of Ca+ ions by a ring of HI surrounding 
Pictoris (Lagrange et al. 1998), in which case it may exhibit variability on the time scale of years. Fig. 3 shows the parameters of the individual variable features for the whole of that night. We have acquired a wealth of similar observational material. Some aspects of the entire data set are the presence of absorption activity on almost every night (in our 407 pairs of spectra we detect some 940 variable features--i.e. excluding the central absorption), the clear detection of blue-shifted absorption features, and the emergence of correlations between absorption velocities and absorption widths and depths. In addition, comparison of H & K line depths confirm that higher-velocity features obscure smaller fractions of the stellar disc. We feel we do not understand the scattered-light properties of our spectrograph sufficiently well to make any unequivocal statement concerning the stability or otherwise of the deep central absorption feature. Most interestingly, the H & K equivalent widths of the 
120 kms-1 feature on 1998 November 27 evolve jointly in a way evocative of the predictions of Beust & Lissauer (1994) for an FEB in a prograde equatorial orbit. Our observations are compared with one of their models in Figure 1: it must be emphasized that the strength and timescale of the predicted variation depend on assumed properties of the FEB and all that we are claiming is that there is a similarlity of form between model and observations. Though daylight occured at the moment when the H line strength might have been expected to exceed that of K, which would have provided a clear confirmation, this may have been the first detection of an FEB transit. Our data set now merits detailed modelling within the context of the FEB hypothesis. Next Section: Acknowledgements
Title/Abstract Page: The Variable CaII Absorption
Previous Section: Introduction
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