The search for extratidal star candidates around Galactic globular clusters NGC 2808, NGC 6266, and NGC 6397 with {\textit{Gaia}} DR2 astrometry

Abstract

Context. Extratidal stars are stellar bodies that end up outside the tidal radius of a cluster as a result of internal processes or external forces acting upon it. The presence and spatial distribution of these stars can give us insights into the past evolution of a cluster inside our Galaxy. Aims. Previous works suggest that globular clusters, when explored in detail, show evidence of extratidal stars. We aim to search for possible extratidal stars in the Galactic globular clusters NGC 6397, NGC 2808, and NGC 6266 using the photometry and proper motion measurements from Gaia DR2 database (Gaia Collaboration et al. 2018). Results. Finally, 120, 126, and 107 extratidal candidate stars were found lying outside the tidal radius of the globular clusters NGC 6397, NGC 2808, and NGC 6266, respectively. 70%, 25.4%, and 72.9% of the extratidal stars found are located outside the Jacobi radius of NGC 6397, NGC 2808, and NGC 6266, respectively. The spatial distribution of the extratidal stars belonging to NGC 6397 appears S-like, extending along the curved leading and trailing arms. NGC 2808 has an overdensity of stars in the trailing part of the cluster and NGC 6266 seems to have overdensities of extratidal stars in its eastern and northern sides. Conclusions. Proper motions and color-magnitude diagrams can be used to identify extratidal candidate stars around GCs. Nonetheless, depending on how different the kinematics and stellar populations of a cluster are compared to the Milky Way field, the fraction of contamination can be larger. All three clusters are found to have extratidal stars outside their tidal radii. For NGC 6397 and NGC 2808, these stars may be the result of a combined effect of the disc shocks and tidal disruptions. For NGC 6266, the distribution of extratidal stars is symmetrical around it, most likely indicating that the cluster has an extended stellar envelope.

Accepted for publication in Astronomy and Astrophysics

References in corpus (19)

• Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc
• The life cycle of star cluster in a tidal field
• Globular cluster number density profiles using Gaia DR2
• The Outer Envelopes of Globular Clusters. II. NGC 1851, NGC 5824 and NGC 1261
• Kinematics of the local disk from the RAVE survey and the Gaia first data release
• Variations in the width, density, and direction of the Palomar 5 tidal tails
• The eye of Gaia on globular clusters structure: tidal tails
• Quasar and galaxy classification in Gaia Data Release 2
• Chemodynamics of newly identified giants with globular cluster like abundance patterns in the bulge, disk, and halo of the Milky Way
• Tails and streams around the Galactic globular clusters NGC1851, NGC1904, NGC2298 and NGC2808
• On the tidal tails of Milky Way globular clusters
• The discovery of tidal tails around the globular cluster NGC 7492 with Pan-STARRS1
• Purveyors of fine halos. II. Chemodynamical association of halo stars with Milky Way globular clusters
• A Spectroscopic Survey for Omega Centauri Members at and beyond the Cluster Tidal Radius
• Searching for tidal tails around $\omega$ Centauri using RR Lyrae Stars
• Development of multiple tidal tails around globular clusters and dwarf satellite galaxies
• Formation of N-rich field stars in the high-density building blocks of the Galactic bulge
• Star Streams and the Assembly History of the Galaxy
• Tidal stripping stellar substructures around four metal-poor globular clusters in the Galactic bulge

Cited by in corpus (9)

• galstreams: A Library of Milky Way Stellar Stream Footprints and Tracks
• Galactic ArchaeoLogIcaL ExcavatiOns (GALILEO) I. An updated census of APOGEE N-rich giants across the Milky Way
• APOGEE discovery of a chemically atypical star disrupted from NGC 6723 and captured by the Milky Way bulge
• CAPOS: the bulge Cluster APOgee Survey II. The Intriguing "Sequoia" Globular Cluster FSR 1758
• Simulations of globular clusters within their parent galaxies: Metallicity spreads and anomalous precursor populations
• Extra-tidal star candidates in globular clusters of the Sagittarius dwarf spheroidal galaxy
• Existence of Tidal Tails for the Globular Cluster NGC 5824
• Identifying substructure associations in the Milky Way halo using chemo-kinematic tagging
• Robust ellipticity measurements of 29 Galactic globular clusters