High-mass X-ray binaries as members of open clusters

Traditionally, high-mass X-ray binaries (HMXBs) are considered atypical products of close binary evolution where the primary component of the progenitor binary has formed a compact object through a supernova explosion, shedding a significant portion of the overall binary mass in the process. This rapid mass loss from the system results in an extra peculiar systemic velocity with respect to the system's local standard of rest. Moreover, there is also a contribution to the peculiar systemic velocity from a natal velocity kick, which is imparted to the compact object upon formation. Provided that the binary remains bound, both the rapid mass loss and the natal kick cause the system to gain a significant systemic velocity of typically several tens of kilometers per second with respect to its standard of rest. This makes the system rapidly leave the environment where it was born. This classical picture has now been challenged by discoveries of systems with low or negligible peculiar systemic velocities, arising from more exotic supernova types, such as electron-capture or ultrastripped supernovae. These supernovae explode with a low degree of asymmetry and only eject a small amount of mass, yielding low peculiar systemic velocities. We investigate the occurrence of HMXBs in open clusters and, if they are present, use the cluster parameters to constrain the system properties and the physics of the supernovae that produced them. We used Gaia astrometry data and derived catalogs to examine whether known HMXBs are physical members of open clusters, using membership criteria based on positions, parallaxes, and proper motions. We identify four HMXB and HMXB candidates that are members of open clusters: IGR J16465-4507 in CWNU 2672, SGR 0755-2933 in HSC 1981, HD 119682 in NGC 5281, and NGC 6649 9 in NGC 6649. Their presence in open clusters implies that they were born without significant systemic kick, which provides important constraints to supernova explosion mechanisms in close binary systems. The residual tangential velocities we derive (0.9 ± 0.4 km/s for SGR 0755-2933 and 2.6 ± 0.5 km/s for IGR J16465-4507) provide direct observational evidence for the ultralow kick mode recently identified in Be X-ray binary populations, demonstrating that such systems can remain gravitationally bound to their parent clusters