Query : 2021A&A...645A.116K

2021A&A...645A.116K - Astronomy and Astrophysics, volume 645A, 116-116 (2021/1-1)

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


Abstract (from CDS):

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.
Methods. The extratidal stars for the clusters were selected on the basis of: their distance from the cluster center, similarity in their proper motions to the cluster population, and their position on the color-magnitude diagram of the clusters. Each cluster was explored in an annulus disk from the tidal radius up to five times the tidal radii. The significance level of the number of selected extratidal stars was determined on the basis of the distribution of Milky Way stars according to the Besancon Galaxy model and Gaia data. To understand the observed extratidal features, the orbits of the clusters were also determined using GravPot16.
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.

Abstract Copyright: © ESO 2021

Journal keyword(s): globular clusters: general - globular clusters: individual: NGC 2808 - globular clusters: individual: NGC 6397 - globular clusters: individual: NGC 6266

VizieR on-line data: <Available at CDS (J/A+A/645/A116): ngc2808.dat ngc6266.dat ngc6397.dat>

Status at CDS : All or part of tables of objects could be ingested in SIMBAD with priority 2.

Simbad objects: 9

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Number of rows : 9
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NGC 2808 GlC 09 12 03.10 -64 51 48.6           ~ 1365 0
2 M 4 GlC 16 23 35.22 -26 31 32.7           ~ 1785 0
3 M 10 GlC 16 57 09.05 -04 06 01.1     4.98     ~ 755 0
4 M 62 GlC 17 01 12.60 -30 06 44.5           ~ 580 0
5 NGC 6397 GlC 17 40 42.09 -53 40 27.6     5.17     ~ 1912 0
6 NAME Galactic Center reg 17 45 39.60213 -29 00 22.0000           ~ 13455 0
7 NGC 6535 GlC 18 03 50.51 -00 17 51.5     9.85     ~ 274 0
8 NAME Gaia Enceladus-Sausage St* ~ ~           ~ 353 0
9 NAME Galactic Bulge reg ~ ~           ~ 4018 0

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