Kazimierz J. Borkowski

Interaction of planetary nebulae with the interstellar medium

Interaction of planetary nebulae (PNe) with the interstellar medium (ISM) is quite common, in accord with our understanding of the large-scale structure of the ISM. The characteristic signature of the interaction is a dipole asymmetry resulting from a distortion and compression of the nebula in the direction of stellar motion. Studies of interacting PNe provide us with information on the structure of the ISM, and on the evolution of old PNe and PN halos.

Interaction of a Stellar Wind with Clumpy Stellar Ejecta in A30

Clumpy, hydrogen-depleted material in the planetary nebula Abell 30 was ejected by its central star ~1000 yr ago. We present observations of Abell 30 showing compact, hydrogen-poor knots with wind-blown tails, obtained with the Wide Field Planetary Camera (WFPC2) on board the Hubble Space Telescope, which offer an unprecedented view of the interaction of a stellar wind with an ambient inhomogeneous medium. We can see how dense clumps of material, left within an expanding bubble blown by a stellar wind, are being photoevaporated by the stellar radiation and then swept back and accelerated by the wind. This accelerated material mixes with the wind, slowing it and increasing its density. The observed extent of this mass loading in Abell 30 supports claims that the mass-loading process is generally important in highly inhomogeneous astrophysical flows. In particular, mass loading of the magnitude observed in Abell 30 may explain the detection of X-ray-emitting gas in planetary nebulae.

HST Measurements of the Angular Expansion, Kinematics and Distance of the Planetary Nebula Bd+30°3639

The HST WFPC2 camera was used to obtain images of the planetary nebula BD+30°3639 at two epochs separated by 5.66 years. The expansion of the nebula in Hα and [N II] has been measured using several methods. Detailed expansion maps for both emission lines were constructed from nearly 200 almost independent features. There is good agreement between the (independent) Hα and [N II] proper motions. There are clear deviations from uniform radial expansion, with higher expansion rates in regions where the shell is faintest, such as the south-west quadrant. HST STIS echelle spectra obtained in the C II] λ2326 multiplet provide well-resolved expansion velocities at two position angles. We find that the central velocity split is ±36.3 km s -1 at a position angle of 99°. To determine the distance of BD+30°3639 by comparison of the angular expansion and the radial expansion, we must address the problem of the three dimensional shape of the nebula. We measured the angular expansion along the position of the 99° echelle slit, finding displacements of 4.25 mas yr -1 at the shell edge (2″.47 from the center). If the nebula were spherical, this would imply a distance of 1.80 kpc. But there is evidence that the nebula is elongated along the line of sight, which suggests that the actual distance is less. Radio continuum images from 5 and 15 GHz VLA observations provide information on the extent of the radial elongation. We fit the radio brightness variation and the echelle data by approximating the nebula as an ellipsoid. Our model has an axial ratio of 1.56, is inclined to the line of sight by 9°.7, and exhibits an expansion in the plane of the sky which is 2/3 that in the radial direction, leading to a distance of 1.2 kpc. Based on a recent model atmosphere (Crowther et al., these proceedings), this distance implies a stellar luminosity of 4250 L ⊙ .