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

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 $T_{\rm eff}=6500\pm100$ K and a surface gravity of log $g=0.8\pm0.2$ corresponding to a spectral type of F(6-7)I. These parameters result in an estimated primary luminosity of $4100~L_{\odot}$, 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 $\rm [Fe/H]=-1.1$. 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