Extinction-independent determination of temperatures for central stars of planetary nebulae.

Abstract

A method to determine temperatures for central stars of planetary nebulae from ultraviolet color indices which are essentially extinction-independent is described and applied. Using a standard extinction law (Seaton, 1979) and assuming that the continuum emission from the nuclei of planetary nebulae can be approximated by black-body distributions, It is shown that the color indices m(1225-1475) -m(1910-2140), m(1225-1475) -m(2195-2395), and m(1475-1725) -m(1738-1951) satisfy the condition of extinction independence for EB-V between the values of 0 and 1.0 for all temperatures T between 20,000 and 100,000 K within an accuracy of a few percent. Using data retrieved from the Unified Low Dispersion Archive of the IUE database for 40 planetary nebulae, their UV color indices were determined, and, from these, their color temperatures were found.