Revealing the stellar population of the ultra-obscured Galactic globular cluster 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 $\approx$ 10 magnitudes, enabling the first identification of the cluster's main sequence turnoff. Due to the extreme reddening affecting the region, a differential reddening correction was necessary. The resulting reddening map reveals variations up to $\delta E(B-V)\approx 2.5$ mag. From isochrone-fitting of the differential reddening corrected color-magnitude diagram, we derived a mean color excess $E(B-V)=6.33_{-0.04}^{+0.05}$, and a distance modulus $(m-M{)}_0=14.00_{-0.11}^{+0.26}$, corresponding to a distance of $d=6.3_{-0.3}^{+0.8}$ kpc from the Sun, and a Galactocentric distance of $2.6_{-0.7}^{+0.6}$ kpc. 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. We obtained a photometric metallicity estimate of [Fe/H]$=-0.30_{-0.08}^{+0.10}$ and the first absolute age determination for Glimpse-C02, resulting in $t=11.9_{-0.6}^{+0.7}$ Gyr, as typically measured for Galactic globular clusters at this metallicity. We also derived 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 $r_c=8.72_{-0.35}^{+0.40}$ arcsec. Finally, from the surface brightness profile of the system, we derived an integrated $H$-band magnitude $M_{\mathrm{H}}=-7.9$, corresponding to a mass of $M=3.57_{-0.19}^{+0.22}\times 10^4{M}_{\odot }$. Thus, our work classifies Glimpse-C02 as an old and metal-rich globular cluster that is in an advanced stage of its dynamical evolution.

9 pages, 8 figures. Accepted for publication in A&A

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