JHKLM photometry: Standard systems, passbands and intrinsic colors

Abstract

The relations between colors of the JHKL systems of SAAO, ESO, CIT/CTIO, MSO, AAO and Arizona have been examined and linear relations derived to enable transformation between the J-K, J-H, H-K, and K-L colors in the different systems. A homogenized system, essentially the Johnson-Glass system is proposed and its absolute calibration derived based on the Bell model atmosphere fluxes for Alpha Lyrae. The homogenized colors of the standard stars were used to derive intrinsic colors for stars with spectral types between B7V and M6V, and G7III and MSIII. The JHKL passbands of the MSO IR system, derived from measured filter passbands and estimated atmospheric transmission values, were used to compute synthetic colors from relative absolute fluxes of some stars (including the sun). The reasonable agreement with the standardized JHKL colors indicates that these passbands can be adopted as representing the homogeneous system, and used to compute broad band IR colors from theoretical or observed fluxes. The passbands of other IR systems were similarly estimated from published data, and the synthetic colors were intercompared using black-body and stellar fluxes. These passbands were then adjusted in wavelength to produce agreement with the observed relations between different systems, enabling the effective wavelengths of the different natural systems to be established. Better effective wavelengths could be determined were spectrophotometry available for the very red stars with known broad band colors. The full text of this paper is published in Bessell and Brett (1988).