New Y and T Dwarfs from WISE Identified by Methane Imaging

Abstract

We identify new Y-and T-type brown dwarfs from the WISE All Sky data release using images obtained in filters that divide the traditional near-infrared H and J bands into two halves -specifically CH 4 s & CH 4 l in the H and J2 & J3 in the J. This proves to be very effective at identifying cool brown dwarfs via the detection of their methane absorption, as well as providing preliminary classification using methane colours and WISE -to-near-infrared colours. New and updated calibrations between T/Y spectral types and CH 4 s-CH 4 l J3-W2, and CH 4 s-W2 colours are derived, producing classification estimates good to a few spectral sub-types. We present photometry for a large sample of T and Y dwarfs in these filters, together with spectroscopy for 23 new ultra-cool dwarfs -two Y dwarfs and twenty one T dwarfs. We identify a further 8 new cool brown dwarfs, which we have high confidence are T dwarfs based on their methane photometry. We find that, for objects observed on a 4m-class telescope at J band magnitudes of ∼20 or brighter, CH 4 s-CH 4 l is the more powerful colour for detecting objects and then estimating spectral types. Due to the lower sky background in the J-band, the J3 and J2 bands are more useful for identifying fainter cool dwarfs at J 22. The J3-J2 colour is poor at estimating spectral types. But fortunately, once J3-J2 confirms that an object is a cool dwarf, the J3-W2 colour is very effective at estimating approximate spectral types.

Spectroscopic Follow-up of Discoveries from the NEOWISE Proper Motion Survey

“…Additionally, two objects have published spectral types estimated using photometry. Tinney et al (2018) used methane imaging to spectral type WISE0309−5016 as a T7, which agrees with our spectral type. Kirkpatrick et al (2019) note that, because this object is much brighter in M H than other objects of similar H − W 2 color, and much brighter in M W 1 and M ch1 than other objects of similar Spitzer ch1−ch2 color, it is likely an un-resolved binary.…”

The Field Substellar Mass Function Based on the Full-sky 20 pc Census of 525 L, T, and Y Dwarfs

“…WISE 1112−3857: This T9 dwarf falls along the subdwarf locus in the color-type plots of Figure 16(e), (f), and the color-color plot of Figure 18(d). The nearinfrared spectrum presented in Tinney et al (2018) does not extend to the K-band but appears to show excess flux on the blueward side of Y-band, as seen in other T subdwarfs (see Section 7.2). A more complete spectrum at higher S/N is needed to confirm the subdwarf hypothesis.…”

Ross 19B: An Extremely Cold Companion Discovered via the Backyard Worlds: Planet 9 Citizen Science Project

“…The coldest spectral class of brown dwarfs, the Y dwarfs (Cushing et al 2011;Kirkpatrick et al 2012), have estimated temperatures (T eff < 450 K) and masses (20 M Jup ) approaching those of the gas giants of our own Solar System. The population of known Y dwarfs is scarce-to date, only 25 Y-type objects have been spectroscopically confirmed (Cushing et al 2011;Kirkpatrick et al 2012;Liu et al 2012;Tinney et al 2012;Kirkpatrick et al 2013;Cushing et al 2014;Luhman 2014;Pinfield et al 2014;Dupuy et al 2015;Schneider et al 2015;Leggett et al 2017;Martin et al 2018;Tinney et al 2018). Benchmark companions at these extremely cold temperatures and low masses are rarer still.…”