J/A+A/696/A221 NGC 6397 WFC/ACS and NIR/WFC3 photometry (Milone+, 2025)
Exploring multiple stellar populations in globular clusters with Euclid:
A theoretical overview and insights from NGC 6397.
Milone A.P., Cordoni G., Marino A.F., Altomonte V., Dondoglio E.,
Legnardi M.V., Bortolan E., Lionetto S., Marchuk A.V., Muratore F.,
Ziliotto T.
<Astron. Astrophys. 696, A221 (2025)>
=2025A&A...696A.221M 2025A&A...696A.221M (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, globular ; Populations, stellar ; Photometry, HST ;
Infrared ; Optical
Keywords: stars: population II - globular clusters: general -
globular clusters: individual: NGC 6397
Abstract:
We investigate the behavior of multiple stellar populations in
globular clusters (GCs) using photometric diagrams constructed with
Euclid photometry. By employing synthetic spectra and isochrones that
incorporate the chemical differences between first-population (1P)
stars (resembling field stars) and second-population (2P) stars
(enriched in helium and nitrogen, but depleted in carbon and oxygen)
we have identified, from a theoretical perspective, the
color-magnitude diagrams and the chromosome maps most effective at
distinguishing these populations within GCs. Euclid photometry has
proven to be a powerful tool for identifying multiple populations
among M-dwarfs, as 1P and 2P stars form distinct sequences in
well-chosen photometric diagrams, driven by differences in the
strength of oxygen-based molecular features, such as water vapor. To
validate our theoretical findings, we analyzed Euclid photometry and
astrometry of the GC NGC 6397, complemented by photometric and
astrometric data from the Hubble Space Telescopeand James Webb Space
Telescope, enabling a comprehensive study of its stellar populations
across a wide field of view (FoV). We find that the 1P constitutes
∼30% of the M-dwarfs in NGC 6397, with the fraction of 1P stars
remaining consistent across different stellar masses and throughout
the entire FoV. Next, 2P stars exhibit an [O/Fe] depletion of about
0.3dex relative to 1P stars and both populations display isotropic
proper motions. This study represents the first comprehensive analysis
of multiple populations among M-dwarfs across a wide FoV,
demonstrating that Euclid photometry is a powerful instrument for
investigating multiple populations in GCs.
Description:
To evaluate the potential of Euclid for identifying and characterizing
multiple stellar populations in GCs, we analyzed photometry and
astrometry of stars within the field of view of NGC6397. This analysis
was complemented with additional data from Gaia DR3 (Gaia
Collaboration et al., 2021A&A...649A...1G 2021A&A...649A...1G, Cat. I/350, , Cat. I/355),
JWST, and HST. The footprints of the JWST and HST images, shown in
Figure 1, include six fields: the central field and fields A to E.
Most observations are concentrated in the central field and field A.
The central field includes images from WFC/ACS (GO-10755, Sarajedini
et al. 2007AJ....133.1658S 2007AJ....133.1658S, Cat. J/AJ/133/1658; Anderson et al.,
2008AJ....135.2055A 2008AJ....135.2055A) and UVIS/WFC3 (GO-13297, Piotto et al.,
2015AJ....149...91P 2015AJ....149...91P), used to identify 1P and 2P stars along the MS
and RGB. Infrared images from WFC3 (IR/WFC3, Correnti et al.,
2018ApJ...864..147C 2018ApJ...864..147C) analyze multiple populations among M-dwarfs,
supplemented by UVIS/WFC3 and WFC/ACS data for proper motions.
Objects:
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RA (2000) DE Designation(s)
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17 40 42.08 -53 40 27.5 NGC 6397 = [KPS2012] MWSC 2662
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fielda.dat 67 3729 Photometry and astrometry of stars in the field A
(see Section 2 and Figure 1 of the paper)
cen.dat 71 3123 Photometry and astrometry of stars in the central
(see Section 2 and Figure 1 of the paper)
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See also:
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
J/AJ/133/1658 : ACS survey of galactic globular clusters (Sarajedini+, 2007)
Byte-by-byte Description of file: fielda.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 mag F606W WFC/ACS F606W magnitude
9- 14 F6.4 mag e_F606W WFC/ACS F606W magnitude rms uncertainty
16- 18 I3 --- o_F606W Number of exposures where the F606W magnitude
is well measured
20- 26 F7.4 mag F814W WFC/ACS F814W magnitude
28- 33 F6.4 mag e_F814W WFC/ACS F814W magnitude rms uncertainty
35- 37 I3 --- o_F814W Number of exposures where the F814W magnitude
is well measured
39- 52 F14.10 deg RAdeg Right ascension (ICRS) at Ep=2016.0
54- 67 F14.10 deg DEdeg Declination (ICRS) at Ep=2016.0
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Byte-by-byte Description of file: cen.dat
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Bytes Format Units Label Explanations
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1- 7 F7.4 mag F110W NIR/WFC3 F110W magnitude
9- 14 F6.4 mag e_F110W NIR/WFC3 F110W magnitude rms uncertainty
16 I1 --- o_F110W Number of exposures where the F110W magnitude
is well measured
18- 24 F7.4 mag F160W NIR/WFC3 F160W magnitude
26- 31 F6.4 mag e_F160W NIR/WFC3 F160W magnitude rms uncertainty
33 I1 --- o_F160W Number of exposures where the F160W magnitude
is well measured
35- 41 F7.4 mag E(B-V) Amount of differential reddening E(B-V)
43- 56 F14.10 deg RAdeg Right ascension (ICRS) at Ep=2016.0
58- 71 F14.10 deg DEdeg Declination (ICRS) at Ep=2016.0
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Acknowledgements:
Antonio Milone, antonino.milone(at)unipd.it
(End) Patricia Vannier [CDS] 25-Mar-2025