J/A+A/709/A186 The Globular cluster Glimpse-C02 (Loriga+, 2026)
Revealing the stellar population of the ultra-obscured Galactic globular cluster
Glimpse-C02.
Loriga M., Cadelano M., Pallanca C., Ferraro F.R., Lanzoni B., Chiappino L.,
Crociati C., Dalessandro E., Giusti C., Leanza S., Massari D., Origlia L.,
Vesperini E.
<Astron. Astrophys. 709, A186 (2026)>
=2026A&A...709A.186L 2026A&A...709A.186L (SIMBAD/NED BibCode)
ADC_Keywords: Milky Way ; Clusters, globular ; Photometry, infrared
Keywords: Hertzsprung-Russell and C-M diagrams - stars: Population II -
Galaxy: stellar content - globular clusters: individual: Glimpse-C02
Abstract:
In this paper, we present the results of a detailed photometric
analysis of Glimpse-C02, one of the most extincted globular clusters
of the Milky Way. We built a deep color magnitude diagram spanning ∼10
magnitudes and enabling the very first identification of the main
sequence turnoff of the cluster. Due to the extreme reddening
conditions of the region where the stellar system is located, a
differential reddening correction was necessary. The resulting
reddening map shows color excess variations up to δE(B-V)∼2.5mag
in the direction of the target. From isochrone-fitting of the
differential reddening corrected color-magnitude diagram, we obtained
a new estimate of the mean color excess, E(B-V)=6.33+0.05-0.04,
and a distance modulus (m-M)0=14.00+0.26-0.11, corresponding to
a distance of d=6.3+0.8-0.3kpc from the Sun, and a Galactocentric
distance of 2.6+0.6-0.7kpc. This distance value, within the
associated uncertainties, suggests that the cluster may be located
closer to the Galactic Center compared to previous estimates, possibly
supporting its classification as a bulge globular cluster.
Furthermore, we obtained a photometric metallicity estimate of
[Fe/H]=-0.30+0.10-0.08 and the first absolute age determination
for Glimpse-C02, resulting in t=11.9+0.7-0.6Gyr, as typically
measured for Galactic globular clusters at this metallicity. We also
obtained a new estimate of the center of gravity of the cluster and
determined its projected density profile from resolved star counts,
finding a high King concentration parameter (c=1.97-0.67+0.51) and
a core radius rc=8.72+0.40-0.35arcsec. Finally, from the surface
brightness profile of the system, we derived an integrated H-band
magnitude MH=-7.9, corresponding to a mass of
M=3.57+0.22-0.19x104M☉. Thus, our work classifies
Glimpse-C02 as an old and metal-rich globular cluster that is in an
advanced stage of its dynamical evolution.
Description:
The photometric investigation of Glimpse-C02 presented in this study
is based on the analysis of the first HST epoch of this stellar system
(proposal GO 17918, PI: Loriga). It is composed of high-resolution
images obtained from the IR channel of the WFC3/HST. This instrument
provides a spatial resolution of ∼0.13 arcsec/pixel in a nominal
136x123 arcsec2 field of view (FoV). The data were acquired on March
30, 2025 and they are composed of four images obtained in F110W
(2x399s, 2x299s) and four images in F160W with an exposure time of
199s.
Catalogue of the globular cluster Glimpse-C02.
It includes the stars ID, the x and y coordinate, the right ascension
and declination, the calibrated magnitudes, relative errors, chi,
sharpness and roundness parameters in the F160W, F110W, the
differential reddening dE(B-V) values. 99.999 stands for no measured
data.
Objects:
----------------------------------------------------
RA (2000) DE Designation(s)
----------------------------------------------------
18 18 30.49 -16 58 37.9 Glimpse-C02 = GLIMPSE C02
----------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 121 23100 Catalog of the globular cluster Glimpse-C02
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See also:
J/A+A/489/583 : JHKs photometry of GLIMPSE-C02 (Kurtev+, 2008)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 5 I5 --- ID [1/23100] Star ID
7- 14 F8.3 pix Xpos X coordinate
16- 22 F7.3 pix Ypos Y coordinate
24- 34 F11.7 deg RAdeg Right ascension (J2000)
36- 46 F11.7 deg DEdeg Declination (J2000)
48- 53 F6.3 mag F160W ?=99.999 Magnitude in F160W filter
55- 59 F5.3 mag e_F160W ?=9.999 Uncertainty on the F160W magnitude
61- 65 F5.3 --- chF160W ?=0 Chi parameter in F160W filter
67- 72 F6.3 --- shF160W ?=0 Sharpness parameter in F160W filter
74- 80 F7.3 --- rdF160W ?=0 Roundness parameter in F160W filter
82- 87 F6.3 mag F110W ?=99.999 Magnitude in F110W filter
89- 93 F5.3 mag e_F110W ?=9.999 Uncertainty on the F110W magnitude
95- 99 F5.3 --- chF110W ?=0 Chi parameter in F110W filter
101-106 F6.3 --- shF110W ?=0 Sharpness parameter in F110W filter
108-114 F7.3 --- rdF110W ?=0 Roundness parameter in F110W filter
116-121 F6.3 mag dE(B-V) Differential reddening dE(B-V) value
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Acknowledgements:
Martina Loriga, martina.loriga2(at)unibo.it
License: CC-BY-4.0
(End) Patricia Vannier [CDS] 31-Mar-2026