SONYC – Substellar Objects in Nearby Young Clusters – is a survey programme 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 ( \sim 1 Myr ) , nearby ( \sim 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 \sim 1.4 deg ^ { 2 } on the sky .
The i -band completeness limit of 20.3 mag is equivalent to 0.009 - 0.02 M _ { \odot } , for A _ { V } \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 T _ { \mathrm { eff } } \leq 3000 K , 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 H _ { \alpha } or forbidden lines associated with active accretion .
We derive a relation between the spectral type and effective temperature : T _ { \mathrm { eff } } = ( 4120 \pm 175 ) - ( 172 \pm 26 ) \times \mathrm { 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 .