J/A+A/645/A116 NGC 2808, NGC 6266 and NGC 6397 Gaia DR2 sources (Kundu+, 2021)
The search for extratidal star candidates around the Galactic globular clusters
NGC 2808, NGC 6266 and NGC 6397 with Gaia DR2 astrometry.
Kundu R., Navarrete C., Fernandez-Trincado J.G., Minniti D., Singh H.P.,
Sbordone L., Piatti A., Reyle C.
<Astron. Astrophys. 645, A116 (2021)>
=2021A&A...645A.116K 2021A&A...645A.116K (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Proper motions ; Photometry ; Optical
Keywords: globular clusters: general -
globular clusters: individual: NGC 2808 -
globular clusters: individual: NGC 6397 -
globular clusters: individual: NGC 6266
Abstract:
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.
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.
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.
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.
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.
Description:
In this work, we used Gaia DR2 astrometry to find candidate
extra-tidal stars around the Galactic globular clusters NGC 2808,
NGC 6266 and NGC 6397. We used the mean proper motions and the
color-magnitude diagram of the clusters to select the extra-tidal
candidates up to five times the nominal tidal radii of each cluster.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
ngc2808.dat 108 126 Extra-tidal candidates around NGC 2808
ngc6266.dat 108 107 Extra-tidal candidates around NGC 6266
ngc6397.dat 108 120 Extra-tidal candidates around NGC 6397
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: ngc2808.dat ngc6266.dat ngc6397.dat
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Bytes Format Units Label Explanations
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1- 19 I19 --- Source Gaia DR2 ID
21- 35 F15.11 deg RAdeg Right ascension (ICRS) at Ep=2015.5
37- 51 F15.11 deg DEdeg Declination (ICRS) at Ep=2015.5
53- 58 F6.3 mas/yr pmRA* Proper motion in RA*cos(DE)
60- 64 F5.3 mas/yr e_pmRA* Error in proper motion in RA*cos(DE)
66- 72 F7.3 mas/yr pmDE Proper motion in DE
74- 78 F5.3 mas/yr e_pmDE Error in proper motion in DE
80- 88 F9.6 mag Gmag Gaia DR2 G-band magnitude
90- 98 F9.6 mag BPmag Gaia DR2 BP-band magnitude
100-108 F9.6 mag RPmag Gaia DR2 RP-band magnitude
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Acknowledgements:
Richa Kundu, Richa.Kundu(at)eso.org
(End) Patricia Vannier [CDS] 24-Nov-2020