Infrared aperture photometry at ESO (1983-1994) and its future use

Abstract

We describe the infrared (IR) photometric system for the single channel photometers at ESO, which have been used from 1983 until 1994. In addition to the broadband near infrared (NIR, 1-5 μm) photometric system presented in 1991 by Bouchet et al. and Bersanelli et al., we describe a narrow-band NIR photometric system and a mid infrared (MIR, 7-20 μm) photometric system. We also extend the set of NIR standard stars by Bouchet et al. towards fainter objects (K≃9). The photometric data of the standard stars in these systems were extracted from the complete IR photometric data archive of ESO, covering 10 years. The zeropoints of the NIR photometry are set by assuming that HR 3314 has a V-magnitude of 3.89, and that V - K=-0.05, J - K=-0.01, H - K=-0.01, K - L′=0.00, K - M=0.00. The zeropoints of the MIR photometry are set by assuming that the colours of β Hyi (HR 0098) and α CenA (HR 5459) are equal to the colours of the Sun. We adopt the absolute calibration of Mégessier (1995) for the NIR and we argue that this calibration can be extrapolated to 20 μm, using the MIR calibrations by Rieke et al. (1985) and Cohen et al. (1992). The definition of the zeropoints is consistent with the absolute calibration. We obtained accurate (σ ≃ 0.02 mag.) NIR photometry of about 240 standard stars and MIR photometry of about 40 standard stars (σ ≃ 0.04 mag). Comparison of our NIR photometric system with other well established systems shows that there are some small colour dependencies and zeropoint offsets which are always smaller than about 0.02 mag. except for the L′ band.