paper

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

arXiv:0712.2692 · doi:10.1111/j.1365-2966.2008.12863.x

Abstract

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 Gyr, distance from the Sun $\ds\approx2.7$ kpc, Galactocentric distance $\dgc\approx6.4$ kpc, core radius $\rc\approx1.1$ pc, mass function slope , observed stellar mass (for stars with mass in the range $\rm 1.27 \ms\leq m\leq2.03 \ms$) $\mObs\approx500 \ms$, and a total (extrapolated to $\rm m=0.08 \ms$) stellar mass $\mTot\approx2300 \ms$. 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 $\aV\approx4.1$, located at $\ds\approx1.3$ 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.

9 pages and 6 figs. Accepted by MNRAS

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