Discovery of 22 GHz Water Masers in the Serpens South Region
  Using the Karl G. Jansky Very Large Array (VLA), we have conducted a survey
for 22 GHz, 6_{1,6}-5_{2,3} H2O masers toward the Serpens South region. The
masers were also observed with the Very Long Baseline Array (VLBA) following
the VLA detections. We detect for the first time H2O masers in the Serpens
South region that are found to be associated to three Class 0-Class I objects,
including the two brightest protostars in the Serpens South cluster, known as
CARMA-6 and CARMA-7. We also detect H2O masers associated to a source with no
outflow or jet features. We suggest that this source is most probably a
background AGB star projected in the direction of Serpens South. The spatial
distribution of the emission spots suggest that the masers in the three Class
0-Class I objects emerge very close to the protostars and are likely excited in
shocks driven by the interaction between a protostellar jet and the
circumstellar material. Based on the comparison of the distributions of
bolometric luminosity of sources hosting 22 GHz H2O masers and 162 YSOs covered
by our observations, we identify a limit of L_Bol ~ 10 L_Sun for a source to
host water masers. However, the maser emission shows strong variability in both
intensity and velocity spread, and therefore masers associated to
lower-luminosity sources may have been missed by our observations. We also
report 11 new sources with radio continuum emission at 22 GHz.
