Praesepe (NGC 2632) and its tidal tails

Abstract

Aims: Within a 400 pc sphere around the Sun, we search for Praesepe's tidal tails in the Gaia Data Release 2 (DR2) data set.
Methods: We used a modified convergent-point method to find stars with space velocities close to the space velocity of the Praesepe cluster.
Results: We find a clear indication for the existence of Praesepe's tidal tails, both extending up to 165 pc from the centre of the cluster. A total of 1393 stars populate the cluster and its tails, giving a total mass of 794 M_⊙. We determined a tidal radius of 10.77 pc for the cluster and a tidal mass of 483 M_⊙. The corresponding half-mass radius is 4.8 pc. We also found a clear indication for mass segregation in the cluster. The tidal tails outside 2 tidal radii are populated by 389 stars. The total contamination of our sample by field stars lies between 50 and 100 stars or 3.6-7.2%. We used an astrometrically and photometrically clean subsample of Gaia DR2, which makes our Praesepe sample incomplete beyond M_G ≈ 12.0 mag; this corresponds to about 0.25 M_⊙. A comparison with an N-body model of the cluster and its tails shows remarkably good coincidence. Three new white dwarfs are found in the tails.

Data of stars shown in Figs. 2 and 3 are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/627/A4