Stellar properties
The primary star, designated HD 159062 A, is a G-type main-sequence star slightly cooler than the Sun with 80% the mass and 76% the radius. It has the spectral type G9V Fe−0.8, where the "Fe−0.8" suffix indicates a slight but anomalous deficiency of metals like iron.[12] Indeed, it has a low metallicity of [Fe/H]=−0.31±0.06 dex. The star is thought to be ancient, somewhere between 9-13 billion years old, and has been marked as a population II star and a candidate blue straggler.[13] It rotates on its axis at roughly 2 km/s, about the same as the Sun's equatorial rotational velocity (1.997 km/s[14]).
Based on stellar kinematics, it is very likely (88% probability) a part of the thick disk population, and has been measured to have a europium abundance typical of thick disk stars. However, it is highly enhanced in s-process elements, such as barium, lanthanum, and cerium.[15] Fuhrmann et al. (2017) noted that the barium overabundance is particularly extreme at [Ba/Fe]=0.40 dex, which they argued was almost certainly the result of stellar wind accretion from a distant (orbital period 10-1,000 years) former asymptotic giant branch primary, which would have shriveled up into a cool white dwarf companion.[16]
As predicted, a white dwarf, HD 159062 B, was discovered in 2019 by Hirsch et al.[8] in a near-circular orbit around HD 159062 A at a distance of approximately 62 AU with a period of 411 years. The low eccentricity and large separation of the orbit implies that a Roche lobe overflow never took place.[7] It was once a ~1.5 M☉ star, whose lifespan came to an end roughly 8 billion years ago and has been radiating away heat as a stellar remnant ever since.[9] It has now cooled to an effective temperature of 4,580 K (4,310 °C; 7,780 °F). Its mass, together with its orbital parameters, was determined precisely using a Python script devised in 2021.[7]
