The tidal stream generated by the globular cluster NGC 3201

Abstract

ABSTRACT We detect a tidal stream generated by the globular cluster NGC 3201 extending over ∼140 deg on the sky, using the Gaia DR2 data, with the maximum-likelihood method we presented previously to study the M68 tidal stream. Most of the detected stream is the trailing one, which stretches in the southern Galactic hemisphere and passes within a close distance of 3.2 kpc from the Sun, therefore making the stream highly favourable for discovering relatively bright member stars, while the leading arm is further from us and behind a disc foreground that is harder to separate from. The cluster has just crossed the Galactic disc and is now in the northern Galactic hemisphere, moderately obscured by dust, and the part of the trailing tail closest to the cluster is highly obscured behind the plane. We obtain a best-fitting model of the stream which is consistent with the measured proper motion, radial velocity, and distance to NGC 3201, and show it to be the same as the previously detected Gjöll stream by Ibata et al. We identify ∼200 stars with the highest likelihood of being stream members using only their Gaia kinematic data. Most of these stars (170) are photometrically consistent with being members of NGC 3201 when they are compared to the cluster H–R diagram, only once a correction for dust absorption and reddening by the Galaxy is applied. The remaining stars are consistent with being random foreground objects according to simulated data sets. We list these 170 highly likely stream member stars.