The ultracool-field dwarf luminosity-function and space density from the Canada-France Brown Dwarf Survey

Abstract

Context. Thanks to recent and ongoing large scale surveys, hundreds of brown dwarfs have been discovered in the last decade. The Canada-France Brown Dwarf Survey is a wide-field survey for cool brown dwarfs conducted with the MegaCam camera on the Canada-France-Hawaii Telescope. Aims. Our objectives are to find ultracool brown dwarfs and to constrain the field brown-dwarf luminosity function and the mass function from a large and homogeneous sample of L and T dwarfs. Methods. We identify candidates in CFHT/MegaCam i and z images and follow them up with pointed near infrared (NIR) imaging on several telescopes. Halfway through our survey we found ∼50 T dwarfs and ∼170 L or ultra cool M dwarfs drawn from a larger sample of 1400 candidates with typical ultracool dwarfs i − z colours, found in 780 square degrees. Results. We have currently completed the NIR follow-up on a large part of the survey for all candidates from mid-L dwarfs down to the latest T dwarfs known with utracool dwarfs' colours. This allows us to draw on a complete and well defined sample of 102 ultracool dwarfs to investigate the luminosity function and space density of field dwarfs. Conclusions. We found the density of late L5 to T0 dwarfs to be 2.0 +0.8 −0.7 × 10 −3 objects pc −3 , the density of T0.5 to T5.5 dwarfs to be 1.4 +0.3 −0.2 × 10 −3 objects pc −3 , and the density of T6 to T8 dwarfs to be 5.3 +3.1 −2.2 × 10 −3 objects pc −3 . We found that these results agree better with a flat substellar mass function. Three latest dwarfs at the boundary between T and Y dwarfs give the high density 8.3 +9.0 −5.1 × 10 −3 objects pc −3 . Although the uncertainties are very large this suggests that many brown dwarfs should be found in this late spectral type range, as expected from the cooling of brown dwarfs, whatever their mass, down to very low temperature.

Search and characterization of T-type planetary mass candidates in theσOrionis cluster

“…This density is a factor of 2-10 higher than the average volume densities published in the literature for similar spectral types (Reylé et al 2010;Metchev et al 2008;Burningham et al 2010), suggesting that either S Ori 70 or 73 is not a field object or that the density of field T dwarfs is higher in the direction towards the σ Orionis cluster. If only one of the S Ori objects were a field dwarf, our volume density determination for T4-T6 sources would decrease to values in better agreement with the literature, and the cluster mass function at planetary masses would resemble that depicted in Fig.…”

“…Unfortunately, the J − H color of these kind of "ultracool" objects is not known. Reylé et al (2010) provided volume densities for late-L and T-type dwarfs using astronomical observations of the CanadaFrance Brown Dwarf Survey. They quoted an object density of 1.4 +0.3 −0.2 × 10 −3 pc −3 for T0-T5.5, 5.3 +3.1 −2.2 × 10 −3 pc −3 for T6 to T8 dwarfs and 8.3 +9.0 −5.1 × 10 −3 pc −3 for dwarfs cooler than T8.…”

CFBDS J111807-064016: A new L/T transition brown dwarf in a binary system

“…Figs. 1 in Reylé et al 2010;Delorme et al 2012). In addition to confirming CFBDS 1118 as a brown dwarf, the photometry was used to flux-calibrate the spectrum (Sect.…”

Properties of ultra-cool dwarfs withGaia

“…We assumed them to be T6.5 (Kirkpatrick et al 2011), T6.5 (Reylé et al 2010), and T6 (Kirkpatrick et al 2011). Figure 8 shows a tendency to assign effective temperatures around 1700 K for sources with spectral type L. Table 2 lists the mean difference µ between the χ 2 T eff estimates and the effective temperatures derived from the SLC G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G G calibration and the spectral types cited in the spectral compilations (hereafter bias); the standard deviation with respect to the bias-corrected mean (σ) displayed by the four compilations; and the RMSE without correcting for the mean bias.…”