Related papers: Optical constraints on the coldest metal-poor popu…

In the past few years, astronomers have uncovered several very low-temperature, metal-poor stars with halo or thick disk kinematics and peculiar spectral and photometric properties, so-called ultracool subdwarfs. These include the first…

Recent discoveries from red optical proper motion and wide-field near-infrared surveys have uncovered a new population of ultracool subdwarfs -- metal-poor stars and brown dwarfs extending into the late-type M, L and possibly T spectral…

We present preliminary trigonometric parallaxes and proper motions for 22 L dwarfs and 18 T dwarfs measured using the ASTROCAM infrared imager. Relative to absolute parallax corrections are made by employing 2MASS and/or SDSS photometry for…

We presented 15 new T dwarfs that were selected from UKIRT Infrared Deep Sky Survey, Visible and Infrared Survey Telescope for Astronomy, and Wide-field Infrared Survey Explorer surveys, and confirmed with optical to near infrared spectra…

We report final results from our 2.5 year infrared parallax program carried out with the European Southern Observatory 3.5m New Technology Telescope and the SOFI infrared camera. Our program targeted precision astrometric observations of…

JWST has provided critical mid-infrared data for cold brown dwarfs. It has also provided low-resolution near-infrared spectra, and for faint sources these are the first spectra at these wavelengths. We use these data and other literature…

Accurate parallax measurements allow us to determine physical properties of brown dwarfs, and help us to constrain evolutionary and atmospheric models, break the age-mass degeneracy and reveal unresolved binaries. We measured absolute…

We present astrometric measurements of eleven nearby ultracool brown dwarfs of spectral types Y and late-T, based on imaging observations from a variety of space-based and ground-based telescopes. These measurements have been used to…

Extrasolar planet searches targeting very low-mass stars and brown dwarfs are hampered by intrinsic or instrumental limitations. Time series of astrometric measurements with precisions better than one milli-arcsecond can yield new evidence…

The survey of the mid-infrared sky by the Wide-field Infrared Survey Explorer (WISE) led to the discovery of extremely cold low-mass brown dwarfs, classified as Y dwarfs, which extend the T class to lower temperatures. Twenty-four Y dwarfs…

Our goal is to characterise the physical properties of the metal-poor brown dwarf population. In particular, we focus on the recently discovered peculiar dwarf WISE J1810055$-$1010023. We collected optical iz and near-infrared J-band…

We conducted a search for brown dwarf candidates in a James Webb Space Telescope deep field around A2744 to investigate the space density of these objects at kiloparsec distances. Our methodology employed an initial selection based on…

We present a new volume-limited sample of L0-T8 dwarfs out to 25 pc defined entirely by parallaxes, using our recent measurements from UKIRT/WFCAM along with Gaia DR2 and literature parallaxes. With 369 members, our sample is the largest…

We report parallax measurements for 70 ultracool dwarfs (UCDs). Using both literature values and our sample, we report new polynomial relations between spectral type and M$_{JHK}$. Including resolved L/T transition binaries in the…

The metal content of a galaxy's interstellar medium reflects the interplay between different evolutionary processes such as feedback from massive stars and the accretion of gas from the intergalactic medium. Despite the expected abundance…

Aims. We try to identify ultra-cool dwarfs from the seventh Data Release of the Sloan Digital Sky Survey (SDSS DR7) with SDSS i-z and r-z colors. We also obtain proper motion data from SDSS, 2MASS, and UKIDSS and improve spectral typing…

We report the discovery of 76 new T dwarfs from the UKIDSS Large Area Survey (LAS). Near-infrared broad and narrow-band photometry and spectroscopy are presented for the new objects, along with WISE and warm-Spitzer photometry. Proper…

We present ZJHKL'M' photometry of a sample of 58 late-M, L, and T dwarfs, most of which are identified from the Sloan Digital Sky Survey and the Two Micron All-Sky Survey. Near-infrared spectra and spectral classifications for most of this…

We present Spitzer IRAC photometry of twelve very late-type T dwarfs; nine have [3.6], [4.5], [5.8] and [8.0] photometry and three have [3.6] and [4.5] photometry only. We investigate trends with type and color for the planning and…

The evolution of brown dwarfs from L to T spectral types is one of the least understood aspects of the ultracool population, partly for lack of a large, well-defined, and well-characterized sample in the L/T transition. To improve the…