The nature of Hen 3-1312: A post-AGB star in a binary system ^*,**

Observatório Nacional, Rua José Cristino, 77, CEP 20921-400, São Cristóvão, Rio de Janeiro-RJ, Brazil

Corresponding author: claudio@on.br

Received: 29 April 2003
Accepted: 8 August 2003

Abstract

This work reports the low- and high-resolution spectroscopic diagnostic diagrams, radial velocity, stellar parameters and abundance analysis of the planetary nebula Hen 3-1312. The low- and high-resolution spectra reveal that Hen 3-1312 is in fact a very-low-excitation object, in a binary system with a supergiant as a cool central star. The analysis of the high-resolution spectrum shows the cool stellar component to have an effective temperature of  K and a surface gravity of log  corresponding to a spectral type of F(6-7)I. These parameters result in an estimated primary luminosity of , implying a distance of 4400 pc which is in agreement with previous determinations. The abundance analysis reveals Hen 3-1312 to be a metal-poor object having . The mean abundances of carbon, nitrogen and oxygen are found to be solar, however the α-elements (Mg, Si and Ca) are underabundant relative to the Sun. The abundance profile of Hen 3-1312 is analyzed and compared with other classes of stars with similar atmospheric parameters.