The impact of main belt asteroids on infrared – submillimetre photometry and source counts ( Research Note )

Context. Among the components of the infrared and submillimetre sky background, the closest layer is the thermal emission of dust particles and minor bodies in the Solar System. This contribution is especially important for current and future infrared and submillimetre space instruments – like those of Spitzer, Akari and Herschel – and must be characterised by a reliable statistical model. Aims. We describe the impact of the thermal emission of main belt asteroids on the 5...1000 μm photometry and source counts, for the current and future spaceborne and ground-based instruments, in general, as well as for specific dates and sky positions. Methods. We used the statistical asteroid model (SAM) to calculate the positions of main belt asteroids down to a size of 1 km, and calculated their infrared and submillimetre brightness using the standard thermal model. Fluctuation powers, confusion noise values and number counts were derived from the fluxes of individual asteroids. Results. We have constructed a large database of infrared and submillimetre fluxes for SAM asteroids with a temporal resolution of 5 days, covering the time span January 1, 2000 – December 31, 2012. Asteroid fluctuation powers and number counts derived from this database can be obtained for a specific observation setup via our public web-interface. Conclusions. Current space instruments working in the mid-infrared regime (Akari and Spitzer Space Telescopes) are affected by asteroid confusion noise in some specific areas of the sky, while the photometry of space infrared and submillimetre instruments in the near future (e.g. Herschel and Planck Space Observatories) will not be affected by asteroids. Faint main belt asteroids might also be responsible for most of the zodiacal emission fluctuations near the ecliptic.