1 Introduction

The main goal of the DENIS survey (Deep Near-Infrared Southern Sky Survey, see Epchtein et al. ([1994]) for a complete introduction to DENIS) is to bridge the gap between the optical surveys on Schmidt plates and the far-infrared IRAS survey. Many aspects of astrophysics will benefit from such a survey, particularly studies of cool stars and heavily obscured regions.

Each night, roughly 1 million stars are detected by at least one of the 3 cameras of the DENIS instrument. Photometric calibration is derived by observation of standard star fields. In order to compare our magnitude system to published ones, we need a precise definition of our photometric bands and an absolute calibration of the DENIS photometric system.

In Sect. 2, we describe the DENIS instrument and show the response curve for the complete system in the three bands. In Sect. 3, we estimate the conversion factors (ADUs to electrons) from the typical characteristics of DENIS images. Absolute calibration, based upon a synthetic Vega spectrum, is performed in Sect. 4, and observed and theoretical zero-points are compared.