Published February 18, 2023 | Version v1
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A novel water-band technique to identify brown dwarfs and planetary mass objects in the Solar neighbourhood

  • 1. Department of Physics and Electronics, CHRIST (Deemed to be University), Bangalore, India
  • 2. Indian Institute of Science Education and Research (IISER), Tirupati, India
  • 3. SUPA, Institute for Astronomy, University of Edinburgh, UK
  • 4. Institut de Recherche sur les Exoplanètes (iREx), Université de Montréal, Canada
  • 5. Department of Physics and Astronomy, Bucknell University, USA
  • 6. Department of Astronomy & Astrophysics, University of California, USA
  • 7. Institute for Astronomy, University of Hawai'i, USA
  • 8. Institute of Astronomy, National Central University, Taiwan


In star-forming regions, the low-mass brown dwarfs and free-floating planets are vital tracers of the low mass end of star formation and are key analogues to exoplanets around stars. The complete census of a star-forming cloud, to masses well below the deuterium-burning limit, will also constrain the very low-mass end of the IMF. Our team surveys various nearby young star-forming regions in the solar neighborhood like Taurus, Serpens, IC348 etc. in search of brown dwarfs and planetary mass objects using a novel and robust technique which photometrically identifies these ultra cool objects. Here we present the study of one such nearby young star-forming region, Sigma Orionis located at a distance of ~400pc with very low extinction (Av<1mag). We use the near-IR WIRCam data from the 3.6m Canada-France Hawaii Telescope (CFHT) in the custom W-band filter (centred at 1.45µm water absorption feature) combined with the data from the J and H broadband filters to classify brown dwarfs based on a reddening insensitive index (Q). The Q-index distinguishes the sub-stellar objects below the hydrogen burning limit (i.e. M6 spectral type) and the sub-stellar objects thus identified were then spectroscopically followed-up using the SpeX spectrograph on the 3.2m NASA Infrared Telescope Facility (IRTF). All our candidate brown dwarfs are found to have spectral types M5-M8.5 and along with data from previous studies we have the complete census of spectroscopically confirmed members of the region up to ~15MJup. This shows that with our novel approach we can efficiently identify low-mass objects. Studying these brown dwarfs enables us to probe the IMF down to the sub-stellar regime and aid in understanding their formation mechanism in one of the well-known young clusters in the solar neighborhood for the first time. Our study explores the potential environmental influence on the brown dwarf formation scenario by performing a comparative analysis with the nearby well-studied star-forming regions.



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