JHKMagnitudes for L and T Dwarfs and Infrared Photometric Systems

L and T dwarfs emit most of their radiation in the near infrared and theirspectral energy distributions are dominated by strong molecular absorptionbands. These highly structured energy distributions lead to JHK magnitudes thatare extremely sensitive to the exact filter bandpass used. In the case of the Tdwarfs, the differences between commonly used photometric systems can be aslarge as 0.4 mag at J and 0.5 mag at J-K. To address this problem, we havesynthesized J,H and K magnitudes for some of the common photometric systems andpresent transformation equations. If the spectral type of the dwarf is known,our transformations allow data to be converted between systems to 0.01 mag,which is better than the typical measurement uncertainty. Transforming on thebasis of color alone is more difficult because of the degeneracy and intrinsicscatter in near-infrared colors of L and T dwarfs; in this case J magnitudescan only be transformed to < 0.05 mag and H and K to < 0.02 mag.Comment: 26 pages including 9 figures, uses aastex, to be published in PASP Jan 200