Luminosity Functions of Young Clusters: Modeling the Substellar Mass Regime

Abstract

We predict near-infrared luminosity functions of young (5 Myr to 1 Gyr) star clusters by combining evolutionary models of very low-mass ($1M_J$ to $0.15M_{\odot }$) dwarfs with empirical bolometric corrections. We identify several characteristic features in our results. These can be attributed to three causes: (1) deuterium burning in the most massive substellar objects; (2) methane absorption in bodies with $T_{eff}$ less than 1300 K, the temperature of the L/T transition; and (3) the formation of dust clouds and the rainout of dust at roughly the same effective temperature as methane formation. Accurate reconstruction of the substellar mass function from luminosity function observations requires that these phenomena are taken into account. At present, few observational studies extend to sufficient sensitivities to allow detection of these effects. However, the luminosity function of the young open cluster IC 2391 shows a clear peak at $M_I\sim 14$ which we attribute to the result of deuterium burning in substellar objects. The location of this feature is a strong function of age, and we estimate an age of 35 Myr for IC 2391. This is significantly younger than the 53 Myr derived from the location of the lithium depletion boundary but agrees with the main sequence turnoff age. We consider the implications of this result and our multi-band luminosity functions for future observational studies. All predicted luminosity function features are, or will be, accessible to observations using new wide-field IR imagers and the Space Infrared Telescope Facility.

arXiv commentAccepted for publication in The Astrophysical Journal, V595 #2, Oct 2003; 24 pages, 10 Figures

References in corpus (16)

• On the variation of the Initial Mass Function
• Evolutionary models for very-low-mass stars and brown dwarfs with dusty atmospheres
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• Astrometry and Photometry for Cool Dwarfs and Brown Dwarfs
• Sixty-seven Additional L Dwarfs Discovered by the Two Micron All Sky Survey (2MASS)
• Towards Spectral Classification of L and T Dwarfs: Infrared and Optical Spectroscopy and Analysis
• Keck Spectra of Pleiades Brown Dwarf Candidates and a Precise Determination of the Lithium Depletion Edge in the Pleiades
• The Spectra of T Dwarfs I: Near-Infrared Data and Spectral Classification
• Infrared Photometry of Late-M, L, and T Dwarfs
• L Dwarfs and the Substellar Mass Function
• A Survey for Low-mass Stars and Brown Dwarfs in the Upper-Scorpius OB Association
• The Lithium Depletion Boundary and the Age of the Young Open Cluster IC~2391
• Modeling the Near-Infrared Luminosity Functions of Young Stellar Clusters
• Very Low Mass Stars and Brown Dwarfs of the Young Open Cluster IC2391
• Lithium Depletion Boundary in a Pre-Main Sequence Binary System
• 5-micron photometry of late-type dwarfs

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• The Substellar Mass Function: A Bayesian Approach
• Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions
• New Photometry and Spectra of AB Doradus C: An Accurate Mass Determination of a Young Low-Mass Object with Theoretical Evolutionary Tracks
• The possiblity of detection of Ultracool Dwarfs with the UKIRT Infrared Deep Sky Survey
• A Close Companion Search around L Dwarfs using Aperture Masking Interferometry and Palomar Laser Guide Star Adaptive Optics
• AB Doradus C: Age, Spectral Type, Orbit, and Comparison to Evolutionary Models
• DECam Survey for Low-Mass Stars and Substellar Objects in the UCL and LCC Subgroups of the Sco-Cen OB Association (SCOCENSUS)
• The Cohesive Object Sequence: The Mass-Density Distribution of Astronomical Objects from Asteroids to Stars