Low mass star and brown dwarf formation in the Orion B molecular cloud

I present an extensive near-infrared imaging and spectroscopic survey of young, low mass objects in the Orion B molecular cloud. Results of this survey are used to investigate the shape of the low mass initial mass function (IMF) and examine the stellar and substellar populations of three young clusters in Orion B, ultimately placing observational constraints on models of brown dwarf formation.;Classical star formation theory predicts that the minimum mass required for the birth of a star is roughly one solar mass. However, studies of Galactic field stars have revealed many smaller objects, including significant populations of sub-solar mass stars (M≃0.2-0.3 M⊙ ) and brown dwarfs (M<0.08 M⊙ ). The origin of these objects remains an unsolved problem in modern astrophysics. Using FLAMINGOS on the Kitt Peak National Observatory 2.1 and 4 meter telescopes, I have completed a new J, H, and K-band imaging survey of ∼6 square degrees of Orion B and compiled a new library of ∼200 JH spectra of M stars in the young clusters NGC 2024, NGC 2068, and NGC 2071. I combine the photometry and spectroscopy to construct Hertzsprung-Russell diagrams, inferring masses and ages for cluster members using pre-main sequence evolutionary models. Median ages, substellar disk frequencies, IMFs, and the abundance of brown dwarfs (R ss) are determined and the spatial distribution of M stars is discussed. The results show the IMF peaks for the Orion B clusters (M peak≃0.2-0.3 M⊙ ) are consistent with each other but different from isolated star forming regions such as Taurus. There is also evidence for a dependence of the peak mass on local gas density. A significant fraction of brown dwarfs are shown to have an infrared excess, indicative of circumsubstellar disks. Finally, I find that the Rss is not universal but varies from region to region. After examining the dependence of Rss on local physical properties, I find no clear trend with cluster mass, but some dependence on stellar and gas density and the spectral type of the most massive star in each region. I conclude that the outcome of the brown dwarf formation process appears to be dependent on the local star-forming environment.