PG1323-086 and PG1704+222 - two post-AGB stars at high galactic latitudes

TL;DR

This study analyzes two high galactic latitude B-type stars, revealing their low metallicity and post-AGB evolutionary status, consistent with Population II membership, through spectral and photometric analysis.

Contribution

It provides detailed abundance and evolutionary analysis of two previously uncharacterized high galactic latitude post-AGB stars, confirming their evolutionary stage and population membership.

Findings

Both stars have near-solar helium abundance.

Metal underabundances of about 1.2-1.3 dex are found.

Stars are consistent with low-mass post-AGB evolutionary tracks.

Abstract

Two high galactic latitude B-type stars, PG1323-086 and PG1704+222, are analysed from low and medium resolution optical spectra and Stroemgren photometry. A differential abundance analysis for He, C, N, O, Mg, Al, and Si reveals that the He abundance is close to solar while metal underabundances relative to the solar value of typically 1.3 and 1.2 dex for PG1323-086 and PG1704+222, respectively, are found. For both stars, carbon is even more depleted. The atmospheric parameters are consistent with evolutionary tracks for stars evolving from the asymptotic giant branch (AGB) with a stellar mass of 0.55 solar masses. The anomalous compositions are compatible with those of other high galactic latitude post-AGB stars. Hence, PG1323-086 and PG1704+222 are low mass post-AGB stars in an evolutionary stage between those of A- and F-type supergiants of low mass and central stars of planetary nebulae. From kinematic data and distances a population II membership is probable for both stars.