J/MNRAS/490/2521 Fractal Statistics in Young Star Clusters (Hetem+, 2019)
Fractal Statistics in Young Star Clusters:
Structural parameters and dynamical evolution.
Hetem A., Gregorio-Hetem J.
<Mon. Not. R. Astron. Soc. 490, 2521-2541 (2019)>
=2019MNRAS.490.2521H 2019MNRAS.490.2521H (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Proper motions
Keywords: stars: pre-main sequence - ISM: clouds -
open clusters and associations: general
Abstract:
We used fractal statistics to quantify the degree of observed
substructures in a sample of 50 embedded clusters and more evolved
open clusters (<100Myr) found in different galactic regions. The
observed fractal parameters were compared with N-body simulations from
the literature, which reproduce star-forming regions under different
initial conditions and geometries that are related to the cluster'
dynamical evolution. Parallax and proper motion from Gaia-DR2 were
used to accurately determine cluster membership by using the Bayesian
model and cross-entropy technique. The statistical parameters Q,
and were used to compare observed cluster structure with
simulations. A low level of substructures (Q<0.8) is found for most of
the sample that coincides with simulations of regions showing fractal
dimension D∼2-3. Few clusters (<20 per cent) have uniform distribution
with a radial density profile (α<2). A comparison of Q with mass
segregation ({LAMBDA}MSR) and local density as a function of mass
({SIGMA}LDR) shows the clusters coinciding with models that adopt
supervirial initial conditions. The age-crossing time plot indicates
that our objects are dynamically young, similar to the unbound
associations found in the Milky Way. We conclude that this sample may
be expanding very slowly. The flat distribution in the Q-age plot
and the absence of trends in the distributions of {LAMBDA}MSR and
{SIGMA}LDR against age show that in the first 10 Myr the clusters did
not change structurally and seem not to have expanded from a much
denser region.
Description:
We used fractal statistics to quantify the degree of observed
substructures in a sample of 50 embedded clusters and more evolved
open clusters (<100Myr) found in different galactic regions. The data
herein presents structural results, mass segregation and local density
as a function of mass.
Notes: The flags represent the criteria used in the best sample which
members are noted by (0). The flag (1) indicates members with
selection of our bad quality of 2MASS photometry and/or large errors
in parallax, while flag (2) shows the sources falling out of CMD.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 106 50 Structural results based on spatial distribution
and fractal statistics (P50)
stars.dat 175 5974 Proper motions and membership for all clusters
--------------------------------------------------------------------------------
See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Cluster Cluster name
15- 21 F7.3 deg RAdeg Right ascension (J2000)
23- 27 F5.3 deg e_RAdeg rms uncertainty on RAdeg
29- 35 F7.3 deg DEdeg Declination (J2000)
37- 41 F5.3 deg e_DEdeg rms uncertainty on DEdeg
43- 48 F6.2 mas/yr pmRA Proper motion along RA, pmRA*cosDE
50- 53 F4.2 mas/yr e_pmRA rms uncertainty on pmRA
55- 60 F6.2 mas/yr pmDE Proper motion along DE
62- 65 F4.2 mas/yr e_pmDE rms uncertainty on pmDE
67- 69 I3 --- Npm Total number of P50 members identified on
the basis on proper motion
71- 75 F5.2 pc R Cluster radius (1)
77- 80 F4.2 pc e_R rms uncertainty on R
82- 86 F5.2 pc-2 n Stellar surface density (in stars/pc2)
88- 91 F4.2 pc rc Radius of the core
93- 96 F4.2 --- Mean edge length that is related to the
surface density of the point distribution
98-101 F4.2 --- Mean separation of the points in the
minimal spanning tree (2)
103-106 F4.2 --- Q Fractal Q parameter (3)
--------------------------------------------------------------------------------
Note (1): Cluster radius, defined as the mean between the minimal circle radius
and the radius of a circle having the same area as the convex hull
Note (2): Mean separation of the points in the minimal spanning tree, which is
defined as the unique network of straight lines that can connect a set of
points without closed loops, minimizing the sum of all the lengths of these
lines (or edges).
Note (3): Fractal Q parameter, describes the geometrical structure of the point
distribution and statistically quantifies the fractal substructures,
distinguishing fragmented from smooth distributions.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: stars.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 12 A12 --- Cluster Cluster name
14- 29 A16 --- 2MASS 2MASS identification
31- 32 I2 h RAh Right ascension (J2000), at Epoch=1989.0
34- 35 I2 min RAm Right ascension (J2000), at Epoch=1989.0
37- 44 F8.5 s RAs Right ascension (J2000), at Epoch=1989.0
47 A1 --- DE- Declination sign (J2000), at Epoch=1989.0
48- 49 I2 deg DEd Declination (J2000), at Epoch=1989.0
51- 52 I2 arcmin DEm Declination (J2000), at Epoch=1989.0
54- 61 F8.5 arcsec DEs Declination (J2000), at Epoch=1989.0
63- 68 F6.4 mas plx Parallax
70- 75 F6.4 mas e_plx Error in parallax
77- 84 F8.4 mas/yr pmRA Proper motion in RA direction, pmRA*cosDE
86- 91 F6.4 mas/yr e_pmRA Error in proper motion in RA direction
93-100 F8.4 mas/yr pmDE Proper motion in DEC direction
102-107 F6.4 mas/yr e_pmDE Error in proper motion in DEC direction
109-114 F6.3 mag JMAG Absolute J magnitude (MJ0)
116-121 F6.3 mag e_JMAG Error in absolute J magnitude
123-128 F6.3 mag J-K Absolute J-K colour
130-134 F5.3 mag e_J-K ? Error in absolute J-K colour
136-140 F5.3 --- Pmov Membership probability
142-146 F5.3 [yr] logAge ? Age
148-152 F5.3 [yr] e_logAge ? Error in age
154-159 F6.3 Msun Mass ? Mass
161-166 F6.3 Msun e_Mass ? Error in mass
168-173 F6.3 pc-2 SigmaLSD ? Local surface density
175 I1 --- Qual [0/2] Quality flag (1)
--------------------------------------------------------------------------------
Note (1): Quality flag as follows:
0 = good quality
1 = bad 2MASS photometry or big error in parallax
2 = out of CMD
--------------------------------------------------------------------------------
Acknowledgements:
Annibal Hetem, annibal.hetem(at)ufabc.edu.br
(End) Annibal Hetem [UFABC], Patricia Vannier [CDS] 25-Oct-2019