A Novel Survey for Young Substellar Objects with the W-band filter II.
  The Coolest and Lowest Mass Members of the Serpens-South Star-forming Region
  Given its relative proximity (~430 pc), compact size (< 20'), young age (~
0.5 Myr) and rich number of young stellar objects, the Serpens-South star
forming region is a promising site for studying young sub-stellar objects, yet
the low-mass members of this region remain largely undiscovered. In this paper
we report on a deep photometric survey using a custom 1.45 um filter (W-band),
as well as standard J and H near-IR filters, in order to identify candidate
low-mass young brown-dwarfs in the Serpens-South region. We constructed a
reddening-insensitive index (Q) by combining J, H and W-band photometry for
survey objects, in order to identify candidate low-mass members of Serpens
based on the strength of the water absorption feature at 1.45 um in the
atmospheres of mid-M and later objects. We then conducted spectroscopic follow
up to confirm youth and spectral type for our candidates. This is the first
survey to identify the very low-mass and coolest members of Serpens-South. We
identify 4 low-mass candidate Serpens members, which all display IR excess
emission, indicating the likely presence of circumstellar disks around them.
One of the four candidate low-mass members in our list, SERP182918-020245,
exhibits Pa_beta and Br_gamma emission features, confirming its youth and
ongoing magnetospheric accretion. Our new candidate members have spectral types
>M4 and are the coolest and lowest mass candidate members yet identified in
Serpens-South.
