The Pleiades star cluster (pictured here through a telescope) is a popular asterism in many cultures, frequently symbolizing a group of six or seven boys or girls, often sisters. In fact, the cluster numbers more than 1,100 members. And using the Gaia Early Data Release 3 archive, Jeremy Heyl, Ilaria Caiazzo and Harvey Richer not only refine the number of Pleiads but locate former members thanks to the proper motion and parallax data.
To identify the current members — 1,272 of them — the authors searched a volume of 8 million cubic parsecs to determine the cluster centre and centre-of-mass motion. They then searched for escapees by calculating the relative velocity of all the stars in their sample with respect to the cluster, and picking out the ones with a sufficiently large relative proper motion away from the Pleiades to have reached their current locations within the lifetime of the cluster. Heyl et al. identified 289 potential escapees — many of which were not previously associated with the Pleiades, such as 41 Tau and four δ Scuti variables — within the past 140 Myr. The cluster has lost 20% of its mass in the past 100 Myr, including three white dwarfs at the heavier end of the mass scale. White dwarf escapees can be used as a reliable age indicator as their cooling time is well-defined; in this case, the oldest white dwarf gives a firm lower limit of 60 Myr of the Pleiades cluster.
This is a preview of subscription content, access via your institution