Substellar Objects in Nearby Young Clusters (SONYC) VIII: Substellar
  population in Lupus 3
  SONYC -- Substellar Objects in Nearby Young Clusters -- is a survey program
to investigate the frequency and properties of substellar objects in nearby
star-forming regions. We present a new imaging and spectroscopic survey
conducted in the young (~1 Myr), nearby (~200 pc) star-forming region Lupus 3.
Deep optical and near-infrared images were obtained with MOSAIC-II and NEWFIRM
at the CTIO-4m telescope, covering ~1.4 sqdeg on the sky. The i-band
completeness limit of 20.3 mag is equivalent to 0.009-0.02 MSun, for Av \leq 5.
Photometry and 11-12 yr baseline proper motions were used to select candidate
low-mass members of Lupus 3. We performed spectroscopic follow-up of 123
candidates, using VIMOS at the Very Large Telescope (VLT), and identify 7
probable members, among which 4 have spectral type later than M6.0 and Teff
\leq 3000K, i.e. are probably substellar in nature. Two of the new probable
members of Lupus 3 appear underluminous for their spectral class and exhibit
emission line spectrum with strong Halpha or forbidden lines associated with
active accretion. We derive a relation between the spectral type and effective
temperature: Teff=(4120 +- 175) - (172 +- 26) x SpT, where SpT refers to the M
spectral subtype between 1 and 9. Combining our results with the previous works
on Lupus 3, we show that the spectral type distribution is consistent with that
in other star forming regions, as well as is the derived star-to-BD ratio of
2.0-3.3. We compile a census of all spectroscopically confirmed low-mass
members with spectral type M0 or later.
