49 new T dwarfs identified using methane imaging

Abstract

We present the discovery of 49 new photometrically classified T dwarfs from the combination of large infrared and optical surveys combined with follow-up TNG photometry. We used multi-band infrared and optical photometry from the UKIRT and Sloan Digital Sky Surveys to identify possible brown dwarf candidates, which were then confirmed using methane filter photometry. We have defined a new photometric conversion between CH 4 s -CH 4 l colour and spectral type for T4 to T8 brown dwarfs based on a part of the sample that has been followed up using methane photometry and spectroscopy. Using methane differential photometry as a proxy for spectral type for T dwarfs has proved to be a very efficient technique. Of a subset of 45 methane selected brown dwarfs that were observed spectroscopically, 100% were confirmed as T dwarfs. Future deep imaging surveys will produce large samples of faint brown dwarf candidates, for which spectroscopy will not be feasible. When broad wavelength coverage is unavailable, methane imaging offers a means to efficiently classify candidates from such surveys using just a pair of near-infrared images.

New Y and T Dwarfs from WISE Identified by Methane Imaging

“…If the estimated type that results is in "error" it is more likely to predict the object to be earlier, rather than later. (A similar result was found by Cardoso et al 2015). These results give us confidence in the T dwarf iden- tifications even for the eight T dwarfs in Tables 2 & 4 for which spectroscopy has not yet been obtained.…”

“…(The filters and detectors in both IRIS2 and NICS are identical, so the only the rest of the optical train can plausibly produce this difference.) The addition of further very late objects in our new sample of T and Y dwarfs brings our new calibration and that of Cardoso et al (2015) into much closer alignment for all objects later than T7, while the differences at earlier types now seem consistent with cosmic scatter about the calibration.…”

“…The lower left panel of Fig. 4 shows an expanded version of this plot, along with the calibration relations due to Tinney et al (2005) and Cardoso et al (2015). The authors of the latter have already noted that their calibration is systematically redder (in CH 4 s-CH 4 l) for a given spectral type than the earlier calibration.…”

“…An Updated CH 4 s-CH 4 l Spectral Type Calibration Tinney et al (2005) have presented a calibration between the IRIS2 CH 4 s-CH 4 l colour and spectral type. Cardoso et al (2015) have used very similar filters on the NICS instrument on the Telescope Nazionale Galileo and derived a calibration using the same functional form as Tinney et al (2005), but with slightly different values. With the additional methane imaging data for later-type objects available in Table 2 we have updated this calibration to derive the relation shown in the upper panel of Fig.…”

Primeval very low-mass stars and brown dwarfs - VI. Population properties of metal-poor degenerate brown dwarfs

“…Our candidates are primarily followed up with X-shooter spectrograph (Vernet et al 2011) on the Very Large Tele- (Skrzypek et al 2016). c Known T dwarf candidates identified by methane imaging (Cardoso et al 2015). d Known metal-poor T dwarf, HIP 73786B (Murray et al 2011).…”