J/A+A/674/A146 Asteroseismic age constraints on NGC2477 (Palakkatharappil+ 2023)
Asteroseismic age constraints on the open cluster NGC 2477 using oscillating
stars identified with TESS FFI.
Palakkatharappil D.B., Creevey O.L.
<Astron. Astrophys. 674, A146 (2023)>
=2023A&A...674A.146P 2023A&A...674A.146P (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, open ; Photometry, CCD ; Stars, variable
Keywords: asteroseismology - stars: fundamental parameters -
open clusters and associations: individual: NGC 2477 -
stars: evolution - stars: oscillations - dust, extinction
Abstract:
Asteroseismology is one of the few methods to derive ages of
individual stars due to the high precision of their observations.
Isochrone fitting is a powerful alternative method for deriving ages
by studying clusters of stars. Pulsating stars in clusters should
therefore allow for detailed studies of the stellar models.
Our objectives are to exploit the NASA TESS data along with ESA Gaia
data to search for and detect oscillations in cluster member stars. We
analyse the intermediate-age open cluster NGC 2477, known to suffer
from differential extinction, to explore if asteroseismology and
cluster characteristics can help us understand the metallicity and
extinction, as well as result in better age determinations than
isochrone-fitting alone.
We combined a multitude of recent observations from Gaia,
high-resolution spectroscopy, and extinction maps to analyse the
cluster and then search for and detect variability in the member stars
using TESS full frame images (FFIs) data. To interpret all of these
data, we used stellar structure, evolution and oscillation codes.
We conducted an in-depth analysis of the extinction and metallicity of
NGC 2477, using the most recent spectroscopic, photometric, and
extinction observations for the cluster. Analysis of dust and
extinction maps confirmed that the differential extinction in the
direction of the cluster is not due to the background. The cluster's
metallicity from high-resolution spectroscopy varies from 0.06 to
0.16dex. We performed an isochrone fitting to the cluster using
publically available isochrones (BASTI, MIST, and PARSEC), which
provides a cluster age of between 0.6 to 1.1Ga. Then using TESS FFI,
we analysed the time dimension of the members of this cluster. We
created optimised pixel light curves using the tessipack package which
allows us to consider possible contamination by nearby stars. Using
these light curves, we identified many interesting levels of
variability of stars in this cluster, including binaries and
oscillating stars. For the asteroseismic analysis, we selected a few
uncontaminated A-F type oscillating stars and used the MESA and GYRE
codes to interpret the frequency signals. By comparing the theoretical
and the observed spectra, we identified frequency separations,
{DELTA}ν, for four stars. Then using the identified {DELTA}ν and
imposing that the best matched theoretical models have the same age,
metallicity, and background extinction, we constrained the cluster's
age to 1.0±0.1Ga.
We conclude that using the TESS FFI data, we can identify oscillating
stars in clusters and constrain the age of the cluster using
asteroseismology.
Description:
This work focuses on the analysis of the cluster NGC2477. We
aimed to combine the most recent observations available in the
literature with those from Gaia and then to use the TESS FFI to search
for and analyse the oscillating stars in the cluster.
The variable stars identified are given in table 1, with the star's
ID, G magnitude, and membership probability.
Table A1 contains identified individual frequencies in Hz for
oscillating stars.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 84 2047 Position, magnitude, membership probability and
variability of stars
tablea1.dat 28 448 Identified individual frequencies for
oscillating stars
lc/* . 26 Individual light curves
pr/* . 26 Individual periodogram
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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- 8 A8 --- ID Identification for each star (N77-NNNN)
10- 13 A4 --- --- [DR2-]
14- 32 I19 --- GaiaDR2 Gaia DR2 source identification
34- 40 F7.3 deg RAdeg Right ascension (ICRS) at Ep=2015.5
42- 48 F7.3 deg DEdeg Declination (ICRS) at Ep=2015.5
50- 54 F5.2 mag Gmag Gaia G magnitude
56- 59 F4.2 mag BP-RP ? Gaia BP-RP colour
61- 78 F18.16 --- PMemb Membership Probability (1)
80- 82 A3 --- Code [OBDRU ] Type of variability (2)
84 A1 --- More [*] * indicates data in table A1, lc and pr
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Note (1): Membership probability is from Cantat-Gaudin et al.
(2018A&A...618A..93C 2018A&A...618A..93C, cat. J/A+A/618/A93)
Note (2): Code indicates the type of variability we detect as follows:
O = Oscillating stars
B = Candidate binaries
D = Stars contaminated by nearby source
R = Oscillating red-giants
U = Unknown variable Stars
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- ID Star identification (N77-NNN)
9- 15 F7.3 uHz Freq Frequency
17- 22 F6.3 --- S/N Signal to Noise ratio
24- 28 F5.3 --- fdet The fraction of times that the signal is
above the S/N
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Byte-by-byte Description of file: lc/*
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 18 F18.13 d BJD Time (BJD-2457000)
25- 42 F18.16 --- Flux Normalized Flux
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Byte-by-byte Description of file: pr/*
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Bytes Format Units Label Explanations
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1- 23 F23.19 uHz Freq Frequency
25- 46 F22.19 --- S/N Signal to Noise ratio
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Acknowledgements:
Dinil Bose Palakkatharappil, dinil-bose.palakkatharappil(at)oca.eu
(End) Patricia Vannier [CDS] 04-Apr-2023