Observations of Debris Disks
The focus of my previous research projects have been optical- and submillimeter observations of debris disks. In one study we observed optical light scattered from dust grains in nearby debris disks (chosen from IRAS, ISO, and Spitzer IR-excess samples) using the polarimetric coronagraph PolCor-2, developed at Stockholm Observatory. The instrument used a high-speed CCD in conjunction with a coronagraphic technique, where the direct light from the star is blocked out and the stellar point-spread-function wings are suppressed, making the faint scattered optical light from the disk detectable. By also inserting a polarizing filter in different orientations, the angle and degree of polarization can be calculated and used to further enhance the contrast. Our high-contrast imaging of low surface brightness features successfully captured the AU Mic debris disk and produced interesting results for the controversial circumbinary disk around BD+31°643 (Olofsson et al. 2012).
In another project we performed a submillimeter survey of a sample of IR-excess main-sequence stars with the LABOCA bolometer array, observing at 870 μm on the APEX telescope, to determine the existence, extent, mass, and evolution of Kuiper Belt-like disk structures. Studies at mid- to far infrared wavelengths have shown excess emission in the spectral energy distribution (SED) of many young main-sequence stars, indicating warm circumstellar dust extending out to some tens of astronomical units (AU). Probing more extended, cold dust components, in Kuiper-Belt analogues reaching out to some hundreds of AU, requires sensitive submillimeter observations. Results from a precursor study of the β Pictoris Moving Group were presented in Nilsson et al. (2009). Out of the observed sample of stars in the larger survey, we detected 10 submillimeter disks with at least a 3σ significance, increasing the number of currently known exo-Kuiper-Belts (inferred from cold extended dust disks detected in the submillimeter) from 27 to 32 (Nilsson et al. 2010).
A third project involved spectroscopic observations of the disk around the young (∼12 Myr old) star β Pictoris. We imaged the disk in three emission lines using integral-field spectroscopy at the Very Large Telescope, and obtained the first complete image of Fe Ⅰ emission (probing the neutral gas in the disk plane) and Ca Ⅱ (probing vertically more extended gas) (Nilsson et al. 2012). We concluded that the paucity of mid-plane Ca
Much of this work was summarized in my PhD thesis.