A populous intermediate-age open cluster and evidence of an embedded cluster among the FSR globular cluster candidates

We study the nature of the globular cluster (GC) candidates FSR 1603 and FSR 1755 selected from the catalogue of \citet{FSRcat}. Their properties are investigated with 2MASS field-star decontaminated photometry, which is used to build colour-magnitude diagrams (CMDs), and stellar radial density profiles (RDPs). FSR 1603 has the open cluster (OC) Ruprecht 101 as optical counterpart, and we show it to be a massive intermediate age cluster (IAC). Relevant parameters of FSR 1603 are the age $\approx 1$ Gyr, distance from the Sun $\text{ds}\approx 2.7$ kpc, Galactocentric distance $\text{dgc}\approx 6.4$ kpc, core radius $\text{rc}\approx 1.1$ pc, mass function slope $\chi \approx 1.8$, observed stellar mass (for stars with mass in the range $1.27\text{ms}\le \mathrm{m}\le 2.03\text{ms}$) $\text{mObs}\approx 500\text{ms}$, and a total (extrapolated to $\mathrm{m}=0.08\text{ms}$) stellar mass $\text{mTot}\approx 2300\text{ms}$. FSR 1755, on the other hand, is not a populous cluster. It may be a sparse young cluster embedded in the H II region Sh2-3, subject to an absorption $\text{aV}\approx 4.1$, located at $\text{ds}\approx 1.3$ kpc. Important field-star contamination, spatially-variable heavy dust obscuration, even in \ks, and gas emission characterise its field. A nearly vertical, sparse blue stellar sequence shows up in the CMDs.