J/AJ/153/57 Shape parameters for 154 Galactic open clusters (Zhai+, 2017)
The shape evolution of Galactic open clusters from observations under Galactic
external forces.
Zhai M., Abt H., Zhao G., Li C.
<Astron. J., 153, 57-57 (2017)>
=2017AJ....153...57Z 2017AJ....153...57Z (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, open ; Morphology
Keywords: Galaxy: stellar content - methods: statistical -
open clusters and associations: general
Abstract:
We present the Galactic characteristics of 154 open clusters using the
stellar statistics method with data from the WEBDA database. We find
that all clusters in our sample are elongated in shape, which
indicates that the spherical clusters are stretched out to be
ellipsoid as a function of age (log(age/year)=6.64–9.7). By dividing
a cluster into a central core and an outer part, we have computed the
apparent ellipticities of these two parts respectively. The scale
relations between ellipticities and age indicate that the outer parts
of open clusters become more elliptical while the central cores remain
circular. We suppose that the outer parts become more elliptical
because they are more subjected to the external forces, e.g., Galactic
differential rotation, while the central cores form a circular shape
under the domination of stellar dynamics. We have also performed an
analysis of the crucial influence of cluster mass and location on its
shape.
Description:
The data used are from database WEBDA
(http://www.univie.ac.at/webda/). We have found 946 open clusters with
equatorial coordinates for each cluster member. Since cluster members
are easily contaminated by field stars, we have only adopted stars
with membership probabilities higher than 70% as cluster members. It
is rarely possible to determine a cluster's shape with a small number
of members, so we have only considered relatively richer clusters,
which host more than 20 of the most probable member stars. After these
selections, there are 154 clusters left.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 109 154 Parameters of 154 objects used in this paper
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See also:
B/ocl : Optically visible open clusters and Candidates (Dias+ 2002-2015)
J/A+A/558/A53 : MW global survey of star clusters. II. (Kharchenko+, 2013)
J/A+A/495/807 : Shape parameters for 650 open clusters (Kharchenko+, 2009)
J/A+A/477/165 : Nearby open clusters tidal radii and masses (Piskunov+, 2008)
J/A+A/468/151 : Nearby open clusters radii and masses (Piskunov+, 2007)
http://www.univie.ac.at/webda/ : WEBDA
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- Name Cluster name (1)
15- 21 F7.3 deg GLON Galactic longitude (l) (1)
23- 29 F7.3 deg GLAT Galactic latitude (b) (1)
31- 35 F5.3 [yr] logAge [6.64/9.7] Logarithm of the cluster age (1)
37- 40 I4 pc Dist [150/5071] Distance of the cluster from Sun (1)
42- 46 F5.3 [Msun] logM [1/4.2]? Logarithm of the cluster mass
48- 53 F6.3 kpc Rgc [5.5/13.1] Distance of the cluster from the
Galactic center (dcen)
55- 61 F7.3 pc Zgc [1/780] Galactocentric vertical distance (H) (2)
63- 66 I4 --- Nc [20/1237] Total number of member stars of each
cluster
68- 72 F5.3 --- e [0.017/0.65] Cluster ellipticity (eall)
74- 78 F5.3 --- e_e [0.027/0.47] 1σ Uncertainty for e
(σall)
80- 84 F5.3 --- e-out [0.013/0.545]? Outer cluster ellipticity (eout)
86- 90 F5.3 --- e_e-out [0.021/0.21]? 1σ uncertainty for e-out
(σout)
92- 96 F5.3 --- e-in [0.003/0.5]? Inner cluster ellipticity (ein)
98-102 F5.3 --- e_e-in [0.03/0.42]? 1σ uncertainty for e-in
(σin)
104-109 F6.3 deg q [0.2/44.8] Orientation of open cluster (3)
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Note (1): Taken directly from WEBDA (http://www.univie.ac.at/webda/). We have
derived the Galactic coordinate positions of each member star from the
equatorial coordinates positions using the formulae of spherical
triangulation.
Note (2): The cluster distance from the Galactic plane.
Note (3): The orientation of open clusters is defined as q, which is the tilt
angle between the semimajor axis of the fitted ellipse and the Galactic
plane (also the direction of Galactic longitude in our analysis). See
Section 4.2 for further details.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 16-Jun-2017