The Angular Expansion and Distance of the Planetary Nebula BD +30°3639

The WFPC2 camera aboard the HST was used to obtain images of the planetarynebula BD+30 3639 at two epochs separated by 5.663 years. The expansion of thenebula in the H-alpha and [N II] bands has been measured using several methods.Detailed expansion maps for both emission lines were constructed from nearly200 almost independent features. There is good agreement between the(independent) H-alpha and [N II] proper motions. The central velocity split ismeasured from the STIS echelle spectra of the C II] 2326A multiplet to be+/-36.3 km/s at a position angle of 99 degrees. The angular displacement alongthis slit position was measured to be 4.25 mas/yr at 2".47 from the center. Weconstructed a tilted ellipsoidal shell model by fitting the radio brightnessvariation of the 5 and 15 GHz VLA observations, and making use of theground-based echelle spectra from Bryce & Mellema (1999), to estimate distance.Our model has an axial ratio of 1.56, is inclined to the line of sight by 9.7degrees, and exhibits an expansion in the plane of the sky which is 2/3 that inthe radial direction, leading to a distance of 1.2 kpc. Not all the kinematicdata fits this simple model, so the distance must still be regarded asuncertain. Based on the recent model atmosphere of Crowther et al. (2002), adistance of 1.2 kpc implies a stellar luminosity of 4250 L_sun. The kinematicage of the nebula varies somewhat from region to region; a good average valueis 800 years, while the expansion along the position of the echelle slit givesabout 600 years.Comment: 21 pages, 9 figures, accepted by AJ, May 200