RR Lyrae Stars Belonging to the Candidate Globular Cluster Patchick 99

Abstract

Patchick 99 is a candidate globular cluster located in the direction of the Galactic bulge, with a proper motion almost identical to the field and extreme field star contamination. A recent analysis suggests it is a low-luminosity globular cluster with a population of RR Lyrae stars. We present new spectra of stars in and around Patchick 99, targeting specifically the three RR Lyrae stars associated with the cluster as well as the other RR Lyrae stars in the field. A sample of 53 giant stars selected from proper motions and a position on the color–magnitude diagram are also observed. The three RR Lyrae stars associated with the cluster have similar radial velocities and distances, and two of the targeted giants also have radial velocities in this velocity regime and [Fe/H] metallicities that are slightly more metal-poor than the field. Therefore, if Patchick 99 is a bona fide globular cluster, it would have a radial velocity of −92 ± 10 km s ^−1 , a distance of 6.7 ± 0.4 kpc (as determined from the RR Lyrae stars), and an orbit that confines it to the inner bulge.

Keywords

• Stellar populations
• Stellar astronomy
• Galactic archaeology
• Milky Way dynamics
• Galactic bulge
• Galaxy bulges