L dwarfs and the substellar mass function

I. Neill Reid, J. Davy Kirkpatrick, J. Liebert, Adam S. Burrows, J. E. Gizis, A. Burgasser, C. C. Dahn, D. Monet, R. Cutri, C. A. Beichman, M. Skrutskie

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172 Scopus citations


Analysis of initial observations sky surveys has shown that the resulting photometric catalogs, combined with far-red optical data, provide an extremely effective method of finding isolated, very low-temperature objects in the general field. Follow-up observations have already identified more than 25 sources with temperatures cooler than the latest M dwarfs. A comparison with detailed model predictions (Burrows & Sharp 1999) indicates that these L dwarfs have effective temperatures between ≈ 2000 ± 100 K and 1500 ± 100 K, while the available trigonometric parallax data place their luminosities at between 10-3.5 and 10. Those properties, together with the detection of lithium in one-third of the objects, are consistent with the majority having substellar masses. The mass function cannot be derived directly, since only near-infrared photometry and spectral types are available for most sources, but we can incorporate VLM/brown dwarf models in simulations of the solar neighborhood population and constrain Ψ(M) by comparing the predicted L dwarf surface densities and temperature distributions against observations from the Deep Near-Infrared Survey (DENIS) and 2 Micron All-Sky Survey (2MASS) surveys. The data, although sparse, can be represented by a power-law mass function, Ψ(M) ∝ M, with 1 < α < 2. Current results favor a value nearer the lower limit. If α = 1.3, then the local space density of 0.075 > M/M > 0.01 brown dwarfs is 0.10 systems pc-3. In that case, brown dwarfs are twice as common as main-sequence stars but contribute no more than ∼15% of the total mass of the disk.

Original languageEnglish (US)
Pages (from-to)613-629
Number of pages17
JournalAstrophysical Journal
Issue number2 PART 1
StatePublished - Aug 20 1999

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxy: stellar content
  • Stars: low-mass, brown dwarfs
  • Stars: luminosity function, mass function
  • Stars: statistics


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