HD 69686: A Mysterious High Velocity B Star

TL;DR

This paper reports the discovery and analysis of a high velocity B star, HD 69686, reconstructing its trajectory and suggesting an unusual birthplace in the outer Galaxy, along with a potential stellar group with similar properties.

Contribution

It presents the first detailed analysis of HD 69686's trajectory and origin, proposing a novel scenario for its formation in an unusual Galactic location.

Findings

HD 69686 was born 73 million years ago in the outer Galaxy.

The star's trajectory traces back to a location well below the Galactic plane.

A group of about 12 stars with similar properties was identified along its path.

Abstract

We report on the discovery of a high velocity B star, HD 69686. We estimate its space velocity, distance, surface temperature, gravity, and age. With these data, we are able to reconstruct the trajectory of the star and to trace it back to its birthplace. We use evolutionary tracks for single stars to estimate that HD 69686 was born 73 Myr ago in the outer part of our Galaxy ($r \sim 12$ kpc) at a position well below the Galactic plane ($z \sim -1.8$ kpc), a very unusual birthplace for a B star. Along the star's projected path in the sky, we also find about 12 other stars having similar proper motions, and their photometry data suggest that they are located at the same distance as HD 69686 and probably have the same age. We speculate on the origin of this group by star formation in a high velocity cloud or as a Galactic merger fragment.