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

We present FORS2@VLT follow-up photometry of YMCA-1, a recently discovered stellar system located 13 degrees 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 packae 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] similar or equal to -1.12(-0.13)(+0.21) dex), .45 +/- 0.0 compact (r(h) = 3.5 +/- 0.5 pc), low-mass (M = 10(2.45 +/- 0.02) M-circle dot), and low-luminosity (M-V = -0.47 +/- 0.57 mag) stellar system. The estimated distance modulus (mu(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.