Astronomy and Astrophysics – Astronomy
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.1304h&link_type=abstract
American Astronomical Society, AAS Meeting #212, #13.04; Bulletin of the American Astronomical Society, Vol. 40, p.206
Astronomy and Astrophysics
Astronomy
Scientific paper
Eighteen planetary nebulae, selected for their geometric simplicity, high brightness, and archival HST-WFPC2 images from 1996-1999 in F502N ([O III]5007Å) and F658N ([N II]6583Å), are being re-observed using the same camera and filters in 2007-2008 in order to monitor changes in their structures. As of this writing new data have been obtained for half the sample. After reducing and re-gridding all of the images in exactly the same way, we have aligned and subtracted the older and newer data in order to produce a "signal” image. This signal tracks changes in the locations of structure with sharp features such as rings, knots, and the leading edges of extended bubbles and shells. Our preliminary findings are these: (1) nebulae do not expand uniformly; (2) the leading edges of bubbles of a nebula generally change their size by a "magnification” factor M, but not their shape; (3) M is different for various extended features within the same nebula; (4) different nebulae are characterized by different average values of M; (5) sets of knots found within some of the targets have their own values of M; (6) knots with high Doppler shifts, called "FLIERs” do not have large proper motions (indeed, M is often smaller than it is for the surrounding nebula); changes in the surface brightness of [O III] and [N II] occur in almost every nebula by as much as %, even in some of the largest structures; (7) in general, the [O III] surface brightness increases and that of [N II] decreases. Whether the growth of large-scale structures is affected by the propagation of a D-type ionization front (rather than the actual motion of gas) is under study.
Balick Bruce
Huehnerhoff Joseph
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