J/A+A/710/A148 NGC 6866 isochrone-cloud and asteroseismology (Wang+, 2026)
Isochrone-cloud fitting and asteroseismology of the Kepler open cluster NGC6866.
Wang H., Li G., Fritzewski D.J., Van Reeth T., Aerts C.
<Astron. Astrophys. 710, A148 (2026)>
=2026A&A...710A.148W 2026A&A...710A.148W (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Models, evolutionary ; Photometry ;
Space observations ; Stars, variable
Keywords: asteroseismology - stars: early-type - stars: interiors -
stars: oscillations - stars: rotation -
open clusters and associations: individual: NGC 6866
Abstract:
Isochrone fitting is a classical method used to determine the ages of
open clusters. However, the derived ages depend strongly on the chosen
input physics of the stellar models used to deduce the isochrones.
Additionally, it remains an open question whether the isochronal ages
based on stellar surface parameters are consistent with the
asteroseismic ages derived from stellar interior properties.
Our aim was to investigate how isochrones based on different input
physics and computed for a variety of initial conditions affect the
age dating of the open cluster NGC6866. Using the four-year light
curves of its members assembled by the Kepler mission, we further
compared these results with asteroseismically derived ages.
We extracted 180 cluster members by applying a clustering algorithm to
Gaia DR3 data, and subsequently developed an isochrone-cloud fitting
method that simultaneously accounts for the range of free parameters
occurring in the input physics. Synthetic colour-magnitude diagrams
(CMDs) with various initial rotation rates were generated and compared
with the observations to determine the best-fitting rotation
distribution. Variable stars were then identified among the cluster
members. For the 19 gravity-mode (g-mode) pulsators, we performed
modelling using a dedicated grid of rotating stellar models. This
modelling was constrained by stellar surface parameters, the measured
asymptotic gravity-mode (g-mode) period spacing Pi0, and the
near-core rotation rate. Two approaches were considered: modelling the
pulsators individually and under the assumption that they share a
common age. Results-We found discrepant age estimates from PARSEC and
MIST isochrones, which yielded 690+140-30Myr and
467+70-50Myr, respectively. The isochrone-cloud fitting
indicates that NGC6866 has an initial rotation distribution peaking at
v/vcrit=0.6, which is a discrepancy with a factor of about two
compared to the asteroseismic values. The asteroseismic modelling of
the g-mode pulsators revealed agreement between seismic and isochronal
masses, whereas the derived ages differ substantially due to the
difference in internal mixing. When the g-mode pulsators were modelled
under the assumption of one shared cluster age, we obtained a value of
759+54-82Myr, in agreement with the PARSEC-based isochronal age.
We conclude that using different input physics and various initial
conditions impacts the age-dating results of open clusters. Our
findings point to the need for more carefully calibrated evolutionary
models. The seismic content of NGC6866 makes it a suitable middle-aged
cluster to achieve such calibrations.
Description:
The tables introduced in our paper. This includes the catalogue
containing the variability identification for the cluster member
stars, and the asteroseismic grid modelling results for the g-mode
pulsating members via two distinct approaches.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 288 85 Variability identification of the cluster member
stars within our region of interest
sep-age.dat 298 12 Asteroseismic grid modelling results using the
separate age approach
shar-age.dat 298 12 Asteroseismic grid modelling results using the
shared age approach
--------------------------------------------------------------------------------
See also:
V/133 : Kepler Input Catalog (Kepler Mission Team, 2009)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 19 I19 --- GaiaDR3 Gaia DR3 source id
21- 48 A28 --- Name Gaia designation
50- 67 F18.14 deg RAdeg Right ascension (ICRS) at Ep=2016.0
from Gaia DR3
69- 86 F18.15 deg DEdeg Declination (ICRS) at Ep=2016.0 from Gaia DR3
88-105 F18.16 mas plx Parallax given by Gaia DR3
107-125 F19.16 mas pmRA Proper motion in RA from Gaia DR3
127-145 F19.16 mas pmDE Proper motion in Dec from Gaia DR3
147-156 F10.7 mag Gmag Mean Gaia G magnitude
158-168 F11.9 mag BP-RP Colour index from Gaia bp minus RP
170-187 F18.16 --- MeanProb Mean value of the cluster membership
probability of this target from our
perturbative clustering algorithm
189-206 F18.16 --- MedianProb Median value of the cluster membership
probability of this target from our
perturbative clustering algorithm
208-230 E23.15 --- StdDevProb Standard deviation value of the cluster
membership probability of this target from
our perturbative clustering algorithm
232-238 I7 --- KIC Kepler input catalog ID
240-257 F18.16 arcsec Sep Separation from the KIC target to this Gaia
target when crossmatched
259-288 A30 --- Class Variability class (1)
--------------------------------------------------------------------------------
Note (1): The variability types are described as follows:
gamma_dor: target exhibits g-mode pulsations, with groups of peaks appearing
at frequencies typically below 5c/d. Some show period spacing
patterns.
delta_scuti: target exhibits p-mode pulsations, with frequencies above 10c/d
gdordscthybrid: target with both p- and g-mode pulsations
surface_modulation: target with surface spot rotational modulations at low
frequencies.
dsctsurfacemodulation_hybrid: target with both p-mode pulsations and
surface modulations.
eclipsing_binary: target showing eclipses.
solarlikewithclearpattern: Post-main-sequence oscillators with an
amplitude spectrum displaying a bell-shaped group of frequencies centred
around nu_max. Mixed l=1,3 modes can be distinguished.
solarlikeonly_numax: Post-main-sequence oscillators with an amplitude
spectrum displaying a bell-shaped group of frequencies centred around
nu_max. No mixed mode can be distinguished.
No_data: target do not have Kepler light curve data.
not_found: target show no variable signal.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: sep-age.dat shar-age.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 I7 --- KIC Kepler input catalog ID
9- 25 F17.15 [yr] logAge Median fitted log10 age
27- 44 F18.16 [yr] e_logAge Lower uncertainty range of logAge
46- 63 F18.16 [yr] E_logAge Upper uncertainty range of logAge
65- 82 F18.16 Msun Mass Median fitted stellar mass
84-101 F18.16 Msun e_Mass Lower uncertainty range of stellar mass
103-120 F18.16 Msun E_Mass Upper uncertainty range of stellar mass
122-139 F18.16 --- fov Median fitted overshoot
141-158 F18.16 --- e_fov Lower uncertainty range of fov
160-177 F18.16 --- E_fov Upper uncertainty range of fov
179-196 F18.16 --- omegai Median initial rotation rate over critial rate
198-215 F18.16 --- e_omegai Lower uncertainty range of omegai
217-234 F18.16 --- E_omegai Upper uncertainty range of omegai
236-254 F19.17 --- MccM Median convective core mass ratio
256-276 F21.19 --- e_MccM Lower uncertainty range of Mcc/M
278-298 F21.19 --- E_MccM Upper uncertainty range of Mcc/M
--------------------------------------------------------------------------------
Acknowledgements:
From Haotian Wang, haotian.wang(at)kuleuven.be
The research leading to these results has received financial
support from the Flemish Government under the long-term structural
Methusalem funding program by means of the project SOUL: Stellar
evolution in full glory, grant METH/24/012 at KU Leuven, Belgium, as
well as from the European Research Council (ERC) under the Horizon
Europe programme (Synergy Grant agreement No.101071505: 4D-STAR).
While partially funded by the European Union, views and opinions
expressed are, however, those of the authors only and do not
necessarily reflect those of the European Union or the European
Research Council. Neither the European Union nor the granting
authority can be held responsible for them. G.L. acknowledges the
support of the Australian Research Council through the DECRA project
DE250100773. This research has made use of NASA's Astrophysics Data
System Bibliographic Services and of the SIMBAD database, operated at
CDS, Strasbourg, France. The computational resources and services used
in this work were provided by the VSC (Flemish Supercomputer Centre),
funded by the Research Foundation Flanders (FWO) and the Flemish
Government.
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 06-May-2026