Deep Very Large Telescope Photometry of the Faint Stellar System in the Large Magellanic Cloud Periphery YMCA-1

Abstract

Abstract We present FORS2@VLT follow-up photometry of YMCA-1, a recently discovered stellar system located 13° from the Large Magellanic Cloud (LMC) center. The deep color–magnitude diagram (CMD) reveals a well-defined main sequence (MS) and a handful of stars in the post-MS evolutionary phases. We analyze the YMCA-1 CMD by means of the automated isochrone-matching package ASteCA and model its radial density profile with a Plummer function. We find that YMCA-1 is an old ( 11.7 − 1.3 + 1.7 Gyr), metal-intermediate ([Fe/H] ≃ − 1.12 − 0.13 + 0.21 dex), compact (r h = 3.5 ± 0.5 pc), low-mass (M = 102.45±0.02 M ⊙), and low-luminosity (M V = −0.47 ± 0.57 mag) stellar system. The estimated distance modulus ( μ 0 = 18.72 − 0.17 + 0.15 mag), corresponding to about 55 kpc, suggests that YMCA-1 is associated with the LMC, but we cannot discard the scenario in which it is a Milky Way satellite. The structural parameters of YMCA-1 are remarkably different compared with those of the 15 known old LMC globular clusters. In particular, it resides in a transition region of the M V –r h plane, in between the ultrafaint dwarf galaxies and the classical old clusters, and close to SMASH-1, another faint stellar system recently discovered in the LMC surroundings.