(Proposal ID) S17B-096

(PI) Oasa, Yumiko

(Proposal Title)
[EAO time] Spectroscopic Determination of Young Brown Dwarfs, Planetary-Mass 
Objects and IMFs

(Abstract)
We are executing NIR surveys of nearby young clusters to search for young brown
dwarfs and planetary-mass objects and to examine their formation mechanisms and
IMFs. Hundreds of such substellar-mass objects with NIR excesses have been 
newly identified using Subaru/MOIRCS and UKIRT/WFCAM. Comparison of the derived
IMFs implies that there is not any cutoff at low-mass end. On the other hand, 
it would not be universal and substellar IMFs may be dependent on the forming 
cloud gas and dust density. However, the mass estimate from JHK photometry 
alone is somewhat uncertain due to the age assumption. We propose NIR multi-
object spectroscopy of our previously identified substellar YSO candidates in 
Serpens using MOIRCS. We will determine their temperature from depths of water 
absorption bands, and equivalent widths of metallic lines if possible, from HK 
spectra. Together the derived temperature with our previously determined 
luminosity, we will place the substellar-mass YSOs on the HR diagram to 
characterize the mass and age with the evolutionary models.  Our goal is to 
clarify whether substellar IMFs are not universal and to search possible 
environmental differences.