AAS 196th Meeting, June 2000
Session 3. Dwarf Stars
Display, Monday, June 5, 2000, 9:20am-6:30pm, Empire Hall South

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[3.10] An Efficient Survey for Faint L Dwarfs, T Dwarfs, and z\gtrsim5.5 Quasars

P.B. Hall, M. Gladders (U. Toronto), F. Barrientos (U. Catolica), H. Yee (U. Toronto), M. Sawicki (Caltech)

The discovery of L and T dwarfs has opened a new window on the study of brown dwarfs, the physics of their atmospheres, and their mass function, which can be constrained through modelling of magnitude-limited samples.

We have in hand 35\sq\arcdeg\ of a planned 100\sq\arcdeg\ of deep (Rz)AB imaging from which we can identify candidate L and T dwarfs and z\gtrsim5.5 quasars to z'=22 through IR followup of r'-z'\geq4 objects. These three populations of objects are well separated in the r'-z'/z'-J color-color diagram, and are relatively bright (L & T dwarfs, J<20; quasars, J<21.5). Pilot J imaging of 28 z'<22 targets sparsely sampled from ~4\sq\arcdeg\ demonstrates our efficient selection: 23 have colors consistent with M7-L8 dwarfs, 2 with L8 or T dwarfs, 1 with a T dwarf, and 2 with z\gtrsim5.5 quasars (undetected in J). Thus we have proposed a JHK snapshot survey to rapidly and efficiently assemble a large sample of L and T dwarfs complete to 2\fm5 fainter in J than 2MASS or Sloan. We may be able to determine spectral classes for our entire sample from colors alone, if further spectroscopy confirms the suggestion, based on Sloan L dwarf colors, that z'-J for L dwarfs depends monotonically on spectral class.

Despite covering only 1/400 the area of 2MASS, we probe ~1/12 its volume and our fainter brown dwarf sample will have lower \em eff>, plus we may be more sensitive to L-T transition objects since we do not select on IR-IR colors.

The full 100\sq\arcdeg\ survey could find more than 50 J<18.5 T dwarfs, 450 J<19.5 L dwarfs and 1000 J<20 M7-M9 dwarfs, plus up to 100 z\gtrsim5.5 quasars.

We will present candidate counts over \geq6.5\sq\arcdeg\ and compare to predictions of brown dwarf + z\gtrsim5.5 quasar surface densities.

The author(s) of this abstract have provided an email address for comments about the abstract: hall@astro.utoronto.ca

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