Discovery of new nearby L and late-M dwarfs at low Galactic latitude from the DENIS data base



N. Phan-Bao; M. S. Bessell; E. L. Martin; G. Simon; J. Borsenberger; R. Tata; J. Guibert; F. Crifo; T. Forveille; X. Delfosse; J. Lim;B. de Batz


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Abbreviated Journal Title

Mon. Not. Roy. Astron. Soc.


techniques : photometric; techniques : spectroscopic; stars : low-mass, ; brown dwarfs; stars : luminosity function, mass function; solar; neighbourhood; DIGITAL SKY SURVEY; LOW-MASS STARS; PROPER MOTION SURVEY; ULTRACOOL; DWARFS; T-DWARF; COOL NEIGHBORS; BROWN DWARFS; SPECTROSCOPIC; CLASSIFICATION; SPECTRAL CLASSIFICATION; OPTICAL SPECTROSCOPY; Astronomy & Astrophysics


We report on new nearby L and late-M dwarfs (dphot <= 30 pc) discovered in our search for nearby ultracool dwarfs (I-J >= 3.0, later than M8.0) at low Galactic latitude (vertical bar b vertical bar < 15 degrees) over 4800 deg(2) in the Deep Near Infrared Survey of the Southern Sky (DENIS) data base. We used late-M (>= M8.0), L and T dwarfs with accurate trigonometric parallaxes to calibrate the M(J) versus I-J colour-luminosity relation. The resulting photometric distances have standard errors of similar to 15 per cent, which we used to select candidates d(phot) <= 30 pc. We measured proper motions from multi-epoch images found in the public archives ALADIN, DSS, 2MASS and DENIS, with at least three distinct epochs and time baselines of 10-21 yr. We then used a maximum reduced proper motion cut-off to select 28 candidates as ultracool dwarfs (M8.0-L8.0) and to reject one as a distant red star. No T dwarf candidates were found in this search, which required an object to be detected in all three DENIS bands. Our low-resolution optical spectra confirmed that 26 were indeed ultracool dwarfs, with spectral types from M8.0 to L5.5. Two contaminants and one rejected by the maximum reduced proper motion cut-off were all reddened F-K main sequence stars. 20 of these 26 ultracool dwarfs are new nearby ultracool dwarf members, three L dwarfs within 15 pc with one L3.5 at only similar to 10 pc. We determine a stellar density of <(Phi)over bar>(J cor) = (1.64 +/- 0.46) x 10(-3) dwarfs pc(-3) mag(-1) over 11.1 <= M (J)<= 13.1 based on this sample of M8-1-3.5 ultracool dwarfs. Our ultracool dwarf density value is in good agreement with the measurement by Cruz et al. of the ultracool dwarf density at high Galactic latitude.

Journal Title

Monthly Notices of the Royal Astronomical Society





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