Astrometry with TheHubble Space Telescope: A Parallax of the Central Star of the Planetary Nebula NGC 6853

We present an absolute parallax and relative proper motion for the centralstar of the planetary nebula NGC 6853 (The Dumbell). We obtain these withastrometric data from FGS 3, a white-light interferometer on {\it HST}.Spectral classifications and VRIJHKT$_2$M and DDO51 photometry of the starscomprising the astrometric reference frame provide spectrophotometric estimatesof their absolute parallaxes. Introducing these into our model as observationswith error, we find $\pi_{abs} = 2.10 \pm 0.48$ mas for the DAO central star ofNGC 6853. A weighted average with a previous ground-based USNO determinationyields $\pi_{abs} = 2.40 \pm 0.32$. We assume that the extinction suffered bythe reference stars nearest (in angular separation and distance) to the centralstar is the same as for the central star. Correcting for color differences, wefind $<$A$_V>$ = 0.30 $ \pm $ 0.06 for the central star, hence, an absolutemagnitude M$_V = 5.48^{-0.16}_{+0.15}$. A recent determination of the centralstar effective temperature aided in estimating the central star radius,$R_{*}=0.055 \pm 0.02R_{\sun}$, a star that may be descending to the whitedwarf cooling track.Comment: To appear in The Astronomical Journal, November 2003. CS absolute position (Table 2) changed to 2MASS positio