A Deep Infrared Photometric Survey for Very Low Mass Brown Dwarfs in the Pleiades

This paper presents the results of a deep infrared survey for low-mass brown dwarfs in the Pleiades cluster. By comparing J -band (1.25 μm) and I -band (0.83 μm) photometry of an ∼450 arcmin 2 area with the latest theoretical models of pre-main-sequence substellar evolution, a number of candidates were identified with J -band magnitudes and I - J color limits consistent with Pleiades membership. The mean 10 σ completeness limits of J = 19.25 and I = 23.25 mag correspond to an age-dependent (80–125 Myr) effective depth of (23–28) M J at which Pleiades members of late L spectral types and temperatures near ∼1650 K ( I - J color ∼4 mag) are predicted to begin making a transition to methane-dominated spectra. Of the preliminary candidates, three are more likely field stars, one is a previously known Pleiades brown dwarf (BPL 81), and the remaining are new substellar candidates, all ranging in membership-dependent mass (again for 80–125 Myr ages) from (22–26) M J to (46–57) M J . Follow-up infrared photometry and higher resolution image profile analysis with the Keck telescopes have eliminated all except about five new substellar Pleiades candidates as likely cluster members. Additional follow-up observations including proper-motion and spectral analysis, as well as more comprehensive multiband imaging, will be required to clarify membership likelihood for these Pleiades candidates. Any of the remaining new substellar candidates presented herein, if confirmed as cluster members, would be the lowest mass brown dwarfs discovered in the Pleiades by any survey to date.