The distance to the Serpens South cluster from H2O masers

Abstract

In this Letter we report Very Long Baseline Array observations of 22 GHz water masers toward the protostar CARMA–6, located at the center of the Serpens South young cluster. From the astrometric fits to maser spots, we derive a distance of 440.7±3.5 pc for the protostar (1% error). This represents the best direct distance determination obtained so far for an object this young and deeply embedded in this highly obscured region. Taking depth effects into account, we obtain a distance to the cluster of 440.7 ± 4.6 pc. Stars visible in the optical that have astrometric solutions in the Gaia Data Release 3 are, on the other hand, all located at the periphery of the cluster. Their mean distance of 437−41+51 pc is consistent within 1σ with the value derived from maser astrometry. As the maser source is at the center of Serpens South, we finally solve the ambiguity of the distance to this region that has prevailed over the years.