Runaway OB stars within 1 kpc of the Sun

Abstract

Runaway stars are high-velocity stars ejected from their birth environments that can provide insights into the kinematic history of the stellar cluster they were ejected from. We derived runaway star probabilities for 40 O-type stars and 24,487 B-type stars taken from a recently published volume-complete sample of OB stars within 1 kpc of the Sun. We fit a Galactic rotation model to the observed proper motions of these stars and identify runaway stars using both a fixed 2D peculiar velocity threshold of 23 km s−1 and by comparing individual peculiar velocities to the dispersion of the whole sample. We find runaway fractions of $17.5^{+0.1}_{-2.5}\%$ for O-type stars and $6.9\pm 0.1~{{\ \rm per\ cent}}$ for B-type stars; both using the fixed velocity threshold method. These values are consistent with previous studies, but with differences that are largely attributable to the underlying samples of OB stars used in various studies to identify runaway stars and to variations in the methods used to select them.