Previous
abstract 
Next
abstract
We present results of a NLTE model atmosphere analysis of Keck $10\,$m HIRES echelle spectra of the star K648, the central star of the planetary nebula Ps1 in the globular cluster M15. The high resolution ($R=\lambda/ \Delta\lambda=35,000$\ [4 pixels] for a 1.1-arcsec slit width), high S/N ($S/N=140$\ per resolution element at H$\gamma$\ in 2 hours of exposure) Keck spectra of K648 reveal HI Balmer, HeII, CIII, and CIV absorption lines, among others. By fitting the observed line profiles to ``unified'' model atmosphere line profiles, we derive accurate, distance-independent estimates of T$_{\rm eff}$, $\log (g)$, and helium abundance $y$\ in the stellar photosphere. Comparison to post-AGB theoretical evolutionary tracks through the $\log (g)$\ -- $\log {\rm T}_{\rm eff}$\ plane yield distance-independent estimates of the stellar mass and post-AGB evolutionary age. Finally, from the observed $V$\ magnitude (corrected for interstellar extinction) and the best-fit model atmosphere flux, we derive a spectroscopic distance to K648. When compared against the well-established distance to M15, the reliability of our spectroscopic distances to this and other central stars of planetary nebulae (CSPN) can be verified.
