Astronomy and Astrophysics, volume 544A, 134-134 (2012/8-1)
VLT imaging of the β Pictoris gas disk.
NILSSON R., BRANDEKER A., OLOFSSON G., FATHI K., THEBAULT P. and LISEAU R.
Abstract (from CDS):
Circumstellar debris disks older than a few Myr should be largely devoid of primordial gas remaining from the protoplanetary disk phase. Tracing the origin of observed atomic gas in Keplerian rotation in the edge-on debris disk surrounding the ∼12Myr old star β Pictoris requires more detailed information about its spatial distribution than has previously been acquired by limited slit spectroscopy. Especially indications of asymmetries and presence of CaII gas at high disk latitudes call for additional investigation to exclude or confirm its connection to observed dust structures or suggested cometary bodies on inclined eccentric orbits. We set out to recover a complete image of the FeI and CaII gas emission around β Pic by spatially resolved, high-resolution spectroscopic observations to better understand the morphology and origin of the gaseous disk component. The multiple fiber facility FLAMES/GIRAFFE at the Very Large Telescope (VLT), with the large integral-field-unit ARGUS, was used to obtain spatially resolved optical spectra (from 385.9 to 404.8nm) in four regions covering the northeast and southwest side of the disk. Emission lines from FeI (at 386.0nm) and CaII (at 393.4 and 396.8nm) were mapped and could be used to fit a parametric function for the disk gas distribution, using a gas-ionisation code for gas-poor debris disks. Both FeI and CaII emission are clearly detected, with the former dominating along the disk midplane, and the latter revealing vertically more extended gas. The surface intensity of the FeI emission is lower but more extended in the northeast (reaching the 210AU limit of our observations) than in the southwest, while CaII shows the opposite asymmetry. The modelled Fe gas disk profile shows a linear increase in scale height with radius, and a vertical profile that suggests dynamical interaction with the dust. We also qualitatively demonstrate that the CaII emission profile can be explained by optical thickness in the disk midplane, and does not require Ca to be spatially separated from Fe.