The planetary nebula (PN) K 648 is a member of the Galactic globular cluster M15, and is the archetype of PNe produced by the oldest stellar populations. Due to the long transition lifetimes of single low-mass stars between the AGB and the hot nuclei of PNe, it has been proposed that PNe can arise in old populations only through binary-star mass-transfer processes. In order to test whether the central star of K 648 is a close binary, we obtained Hubble Space Telescope observations with the WFPC2 camera and UByRI filters. Frames were taken in December 1998 on 10 different HST orbits, spaced so that we can test for variability over timescales from 45 minutes up to about 10 days. Preliminary analysis indicates that no significant photometric variability of the central star of K 648 was detected. However this does not necessarily rule out the binary hypothesis, since the orbit could be viewed at low inclination, or the stars could have coalesced as a result of a common-envelope interaction. We also obtained deep narrow-band images of K 648 in the light of Hα , [O III], and [N II], in order to study the nebular morphology. The PN shows an extended faint halo surrounding a bright inner elliptical shell. The shell exhibits a remarkable limb-brightening at one end of its major axis, suggestive of an interaction with the interstellar medium.
American Astronomical Society Meeting Abstracts #194
- Pub Date:
- May 1999