Search

L, T, and Y brown dwarf (BD) exploration is a topical issue. First, the transition boundary between planets and BDs is not fully understood yet. Second, there is a phenomenon called the L/T-transition. The observed properties of cooler BDs differ significantly from the less cool ones, namely, colors of BDs shift much bluer and, simultaneously, dwarfs become brighter with a decrease in temperature. Models of this phenomenon are now being actively developed, for which reason BDs observed in a wide range of spectra are needed. Our goal is to refine the position of BDs in the parameter space of colors and magnitudes in order to effectively search for them in photometric surveys (without involving spectroscopic observations). For that reason, we crossmatched about 500 known L, T, and Y BDs with large photometric surveys. We paid special attention to the problem of identifying objects near the Sun because the crossmatching by default is made by searching for the closest object in a particular survey, which can be inappropriate concerning the high proper motions of our dwarfs. We have determined the color indices that can be used to search for these objects in large photometric surveys, and we have pointed out the color indices that are inappropriate for this purpose. We also made preliminary estimates of the radius matching to search for objects in the modern photometric surveys, given their proximity to the Sun and, consequently, their high proper motion.

We determine the interstellar extinction in the selected high-latitude areas of the sky based on Gaia EDR3 astrometry and photometry and spectroscopic data from RAVE survey. We approximate the results with the cosecant law in each area thus deriving the parameters of the barometric formula for different lines of sight. The distribution of the parameters over the entire sky is described using spherical harmonics. As a result, we get a mathematical description of the interstellar visual extinction for different lines of sight and distances from the Sun which can be used for estimating interstellar extinction.