Herschel celestial calibration sources
Journal article, 2014

Celestial standards play a major role in observational astrophysics. They are needed to characterise the performance of instruments and are paramount for photometric calibration. During the Herschel Calibration Asteroid Preparatory Programme approximately 50 asteroids have been established as far-IR/sub-mm/mm calibrators for Herschel. The selected asteroids fill the flux gap between the sub-mm/mm calibrators Mars, Uranus and Neptune, and the mid-IR bright calibration stars. All three Herschel instruments observed asteroids for various calibration purposes, including pointing tests, absolute flux calibration, relative spectral response function, observing mode validation, and cross-calibration aspects. Here we present newly established models for the four large and well characterized main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (21) Lutetia which can be considered as new prime flux calibrators. The relevant object-specific properties (size, shape, spin-properties, albedo, thermal properties) are well established. The seasonal (distance to Sun, distance to observer, phase angle, aspect angle) and daily variations (rotation) are included in a new thermophysical model setup for these targets. The thermophysical model predictions agree within 5 % with the available (and independently calibrated) Herschel measurements. The four objects cover the flux regime from just below 1,000 Jy (Ceres at mid-IR N-/Q-band) down to fluxes below 0.1 Jy (Lutetia at the longest wavelengths). Based on the comparison with PACS, SPIRE and HIFI measurements and pre-Herschel experience, the validity of these new prime calibrators ranges from mid-infrared to about 700 mu m, connecting nicely the absolute stellar reference system in the mid-IR with the planet-based calibration at sub-mm/mm wavelengths.

Celestial standards






Herschel Space Observatory




T. Muller

Max Planck Society

Z. Balog

Max Planck Society

M. Nielbock

Max Planck Society

T. Lim


D. Teyssier

European Space Astronomy Centre (ESAC)

Michael Olberg

Chalmers, Earth and Space Sciences, Onsala Space Observatory

U. Klaas

Max Planck Society

H. Linz

Max Planck Society

B. Altiéri

European Space Astronomy Centre (ESAC)

C. Pearson


G. Bendo

Jodrell Bank Centre for Astrophysics

E. Vilenius

Max Planck Society

Experimental Astronomy

0922-6435 (ISSN) 1572-9508 (eISSN)

Vol. 37 2 253-330

Subject Categories

Astronomy, Astrophysics and Cosmology



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