J/ApJ/877/12 Coma Ber and a Neighbor Stellar Group tidal tails (Tang+, 2019)
Discovery of Tidal Tails in Disrupting Open Clusters:
Coma Berenices and a Neighbor Stellar Group.
Tang S.-Y., Pang X., Yuan Z., Chen W.P., Hong J., Goldman B., Just A.,
Shukirgaliyev B., Lin C.-C.
<Astrophys. J. 877, 12 (2019)>
=2019ApJ...877...12T 2019ApJ...877...12T (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Parallaxes, trigonometric ; Proper motions ;
Radial velocities
Keywords: stars: evolution -
open clusters and associations: individual (Coma Berenices) -
stars: kinematics and dynamic
Abstract:
We report the discovery of tidal structures around the
intermediate-aged (∼700-800Myr), nearby (∼85pc) star cluster Coma
Berenices. The spatial and kinematic grouping of stars is determined
with the Gaia DR2 parallax and proper motion data, by a clustering
analysis tool, StarGO, to map 5D parameters (X, Y, Z,
µ_α*cosδ, µδ) onto a 2D neural network. A
leading and a trailing tails, each with an extension of ∼50pc are
revealed for the first time around this disrupting star cluster. The
cluster members, totaling to ∼115+5-3M☉, are clearly mass
segregated, and exhibit a flat mass function with α∼0.79±0.16,
in the sense of dN/dm∝m-α, where N is the number of
member stars and m is stellar mass, in the mass range of
m=0.25-2.51M☉. Within the tidal radius of ∼6.9pc, there are 77
member candidates with an average position, i.e., as the cluster
center, of RA=186.8110°, and DE=25.8112°, and an average
distance of 85.8pc. Additional 120 member candidates reside in the
tidal structures, i.e., outnumbering those in the cluster core. The
expansion of escaping members lead to an anisotropy in the velocity
field of the tidal tails. Our analysis also serendipitously uncovers
an adjacent stellar group, part of which has been cataloged in the
literature. We identify 218 member candidates, 10 times more than
previously known. This star group is some 65pc away from, and ∼400Myr
younger than, Coma Ber, but is already at the final stage of
disruption.
Description:
Utilizing the high-precision Gaia DR2 astrometry, we
apply a new cluster finding method, StarGO, to identify
stellar structures around the Coma Ber in the 5-D
phase space of (X,Y,Z,µαcosδ,µδ).
Additionally to the previously published member candidates of Coma
Ber, here we identify for the first time, a leading and a trailing tidal
tails of Coma Ber, which extend ∼50pc from the cluster center, seven
times longer than cluster tidal radius, ∼6.9pc.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 80 197 Coma Ber Member Candidates
table2.dat 77 218 Group-X Member Candidates
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/197] Coma Ber member candidate, running number
5- 14 F10.6 deg RAdeg Right Ascension (ICRS) at epoch 2015.5 (G1)
16- 24 F9.6 deg DEdeg Declination (ICRS) at epoch 2015.5 (G1)
26- 30 F5.2 mas Plx Parallax (G1)
32- 35 F4.2 mas e_Plx Uncertainty in Plx (G1)
37- 42 F6.2 mas/yr pmRA Proper motion in Right Ascension, pmRA*cosDE (G1)
44- 47 F4.2 mas/yr e_pmRA Uncertainty in pmRA (G1)
49- 54 F6.2 mas/yr pmDE Proper motion in Declination (G1)
56- 59 F4.2 mas/yr e_pmDE Uncertainty in pmDEc (G1)
61- 66 F6.2 km/s RV ? Radial Velocity (G1)
68- 72 F5.2 km/s e_RV ? Uncertainty in RV (G1)
74- 78 F5.2 mag Gmag Gaia G band magnitude (G1)
80 A1 --- Memb [bt] Membership flag (2)
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Note (2): Membership flags as follows:
b = "bound" member candidates within tidal radius, see Section 4.3
t = "tail" member candidates
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/218] Group-X candidate, running number
5- 14 F10.6 deg RAdeg Right Ascension (ICRS) at epoch 2015.5 (G1)
16- 24 F9.6 deg DEdeg Declination (ICRS) at epoch 2015.5 (G1)
26- 30 F5.2 mas Plx Parallax (G1)
32- 35 F4.2 mas e_Plx Uncertainty in Plx (G1)
37- 42 F6.2 mas/yr pmRA Proper motion in Right Ascension, pmRA*cosDE (G1)
44- 47 F4.2 mas/yr e_pmRA Uncertainty in pmRA (G1)
49- 54 F6.2 mas/yr pmDE Proper motion in Declination (G1)
56- 59 F4.2 mas/yr e_pmDE Uncertainty in pmDEc (G1)
61- 66 F6.2 km/s RV ? Radial Velocity (G1)
68- 71 F4.2 km/s e_RV ? Uncertainty in RV (G1)
73- 77 F5.2 mag Gmag Gaia G band magnitude (G1)
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Global notes:
Note (G1): Astrometric and photometric data from Gaia DR 2, Cat. I/345.
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Acknowledgements:
Shih-Yun Tang, sytang(at)g.ncu.edu.tw
(End) Patricia Vannier [CDS] 30-May-2019