J/A+A/709/A20 Star memberships and masses of 4 Ocls with BATC (Wang+, 2026)
Dynamical state of four open clusters
Wang S., Wang J., Ma J., Wu Z.-Y., Zhou R.
<Astron. Astrophys. 709, A20 (2026)>
=2026A&A...709A..20W 2026A&A...709A..20W (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Positional data ; Photometry ; Ultraviolet ;
Optical ; Stars, masses
Keywords: open cluster and association: general -
stars: fundamental parameters -
stars: luminosity function, mass function
Abstract:
Open clusters are vital laboratories for studying stellar dynamics and
evolution, with mass segregation-the preferential concentration of
massive stars toward cluster cores-serving as a key indicator of
internal dynamical processes. This study investigates four open
clusters (NGC 7243, NGC 2301, NGC 1528, and NGC 2281; ages 100-650
Myr) using deep multicolor photometry from the
Beijing-Arizona-Taiwan-Connecticut (BATC) Sky Survey, combined with
Gaia Data Release 3 (DR3), to explore their mass functions and
dynamical states.
The work seeks to characterize mass segregation patterns across
spatial scales to establish its origin (primordial vs. dynamical) and
to provide the first conclusive evidence of mass segregation in NGC
2281. Additionally, we analyze how cluster relaxation timescales and
evolutionary stages influence their dynamical architectures.
Fundamental parameters were derived via Bayesian methods. The tidal
radii were determined from the intersection of the observed cumulative
mass profiles and theoretical tidal mass curves, and mass functions
were analyzed through power-law fits (Φ(m)∝mα)
performed separately for the inner (bound) and outer (tidal) regions.
All clusters exhibit signs of mass segregation. However, only NGC 2281
shows a statistically significant steepening of the mass function
slope in its outer tidal region, indicating significant evaporation of
low-mass stars and providing the first clear evidence of strong,
dynamically evolved mass segregation in this cluster. For NGC 7243,
NGC 2301, and NGC 1528, the derived τ values
(τ=Age/trelax>3) suggest advanced dynamical evolution, yet their
outer regions contain too few stars to robustly confirm the expected
steepening of the mass function.
Description:
This work, we use observations carried out using the BATC photometric
system with the 60/90cm f/3 Schmidt telescope at the XinglongStation
of the National Astronomical Observatories, Chinese Academy of
Sciences (NAOC). For membership designations, we determined the
fundamental parameters of open clusters, we needed samples of
preliminary candidate cluster members. We chose preliminary candidate
cluster members based on the membership probabilities of stars and
cluster radii provided by the Milky Way Star Clusters (MWSC) catalog
of Kharchenko et al. (2012A&A...543A.156K 2012A&A...543A.156K, Cat. J/A+A/543/A156 and
2013A&A...558A..53K 2013A&A...558A..53K, Cat. J/A+A/558/A53). We ran BASE-9 on each open
cluster. For each open cluster, we ran the chain for 50000 steps and
used the last 20000 steps to infer the posterior distributions. We
studied mass function for each cluster based on the tidal radius Rt
obtained. Stars inside Rt are considered to be (presently) bound
members (i.e. see section 3).
As explicited in section 4, to obtain a relatively complete census of
cluster members across a larger spatial extent, we utilized the member
star catalogs from Hunt & Reffert (2023A&A...673A.114H 2023A&A...673A.114H, Cat.
J/A+A/673/A114), derived from Gaia DR3 data using a clustering
algorithm. We cross-matched our BATC sources with these data to the
necessary multicolor photometry for SED fitting. We derived the
individual mass for each member star by performing SED fitting with
procedure minimizes the Χ2 statistic, defined as equation 3 of
section 4. This catalog comprises all 2511 member stars properties
used in this study as their BATC/Gaia magnitudes, cluster memberships
and derived stellar masses.
Objects:
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RA (2000) DE Designation(s)
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22 15 15.99 +49 50 07.0 NGC 7243 = C 2213+496
06 51 51.00 +00 28 34.9 NGC 2301 = C 0649+005
04 15 27.39 +51 13 21.0 NGC 1528 = C 0411+511
06 48 19.69 +41 02 34.9 NGC 2281 = C 0645+411
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea3.dat 167 2511 Astrometric, photometry and SED fit masses of
member stars of the four open clusters
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See also:
J/A+A/558/A53 : Milky Way global survey of star clusters. II.
(Kharchenko+, 2013)
J/A+A/543/A156 : Milky Way global survey of star clusters (Kharchenko+, 2012)
J/A+A/531/A92 : Deep all-sky census of the Hyades (Roeser+, 2011)
J/A+A/438/1163 : Catalogue of Open Cluster Data (COCD) (Kharchenko+, 2005)
J/A+A/401/531 : Proper motions in NGC 7243 (Jilinski+, 2003)
J/AJ/134/1368 : Proper motions in NGC 2244 and NGC 6530 (Chen+, 2007)
J/AJ/132/1669 : Wide-field CCD phot. around nine open clusters (Sharma+, 2006)
J/AJ/112/628 : BATC Color Survey of M67 (Fan+ 1996)
J/A+A/656/A49 : Decoding the morphological evolution of open clusters
(Hu+, 2021)
J/A+A/673/A114 : Improving the open cluster census. II. (Hunt+, 2023)
Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- Cluster Name of the open cluster (Cluster) (1)
9- 15 F7.3 deg RAdeg Right ascension (J2000) (RA)
17- 22 F6.3 deg DEdeg Declination (J2000) (Dec)
24- 42 I19 --- GaiaDR3 Unique Gaia DR3 source identifier
(GaiaDR3Source_ID)
44- 49 F6.3 mag amag ?=99.999 BATC a-band magnitude the effective
wavelength of 3360 Å and bandwidth FWHM
of 360 Å (a_mag)
51- 56 F6.3 mag bmag ?=99.999 BATC b-band magnitude the effective
wavelength of 3890 Å and bandwidth FWHM
of 340 Å (b_mag)
58- 63 F6.3 mag cmag ?=99.999 BATC c-band magnitude the effective
wavelength of 4194 Å and bandwidth FWHM
of 309 Å (c_mag)
65- 70 F6.3 mag dmag ?=99.999 BATC d-band magnitude the effective
wavelength of 4540 Å and bandwidth FWHM
of 332 Å (d_mag)
72- 77 F6.3 mag emag ?=99.999 BATC e-band magnitude the effective
wavelength of 4925 Å and bandwidth FWHM
of 374 Å (e_mag)
79- 84 F6.3 mag fmag ?=99.999 BATC f-band magnitude the effective
wavelength of 5267 Å and bandwidth FWHM
of 344 Å (f_mag)
86- 91 F6.3 mag gmag ?=99.999 BATC g-band magnitude the effective
wavelength of 5790 Å and bandwidth FWHM
of 289 Å (g_mag)
93- 98 F6.3 mag hmag ?=99.999 BATC h-band magnitude the effective
wavelength of 6074 Å and bandwidth FWHM
of 308 Å (h_mag)
100-105 F6.3 mag imag ?=99.999 BATC i-band magnitude the effective
wavelength of 6656 Å and bandwidth FWHM
of 491 Å (i_mag)
107-112 F6.3 mag jmag ?=99.999 BATC j-band magnitude the effective
wavelength of 7057 Å and bandwidth FWHM
of 238 Å (j_mag)
114-119 F6.3 mag kmag ?=99.999 BATC k-band magnitude the effective
wavelength of 7546 Å and bandwidth FWHM
of 192 Å (k_mag)
121-126 F6.3 mag mmag ?=99.999 BATC m-band magnitude the effective
wavelength of 8023 Å and bandwidth FWHM
of 255 Å (m_mag)
128-133 F6.3 mag nmag ?=99.999 BATC n-band magnitude the effective
wavelength of 8484 Å and bandwidth FWHM
of 167 Å (m_mag)
135-140 F6.3 mag omag ?=99.999 BATC o-band magnitude the effective
wavelength of 9182 Å and bandwidth FWHM
of 247 Å (o_mag)
142-147 F6.3 mag Gmag ?=99.999 Gaia G-band magnitude
149-154 F6.3 mag BPmag ?=99.999 Gaia BP-band magnitude
156-161 F6.3 mag RPmag ?=99.999 Gaia RP-band magnitude
163-167 F5.3 Msun M* Stellar mass derived from SED fitting
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Note (1): Open cluster memberships are as follows:
ngc1528 = NGC 1528, 463 occurences in our sample
ngc2281 = NGC 2281, 717 occurences in our sample
ngc2301 = NGC 2301, 828 occurences in our sample
ngc7243 = NGC 7243, 503 occurences in our sample
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Acknowledgements:
Wang S., scwang(at)nao.cas.cn
License: CC-BY-4.0 [see https://spdx.org/licenses/]
(End) Luc Trabelsi [CDS] 10-Apr-2026