Catalogue of ISO LWS observations of asteroids ^*

¹ Centro Astronómico Hispano Alemán, C/ Jesús Durbán Remón 2-2°, 04004 Almería, Spain
² Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany e-mail: hormuth@mpia.de
³ Max-Planck-Institut für extraterrestrische Physik (MPE), Giessenbachstrasse, 85748 Garching, Germany e-mail: tmueller@mpe.mpg.de

Received: 11 October 2006
Accepted: 28 January 2009

Abstract

Context. The long wavelength spectrometer (LWS) onboard the infrared space observatory (ISO) observed the four large main-belt asteroids (1) Ceres, (2) Pallas, (4) Vesta, and (10) Hygiea multiple times. The photometric and spectroscopic data cover the wavelength range between 43 and 197 μm, and are a unique dataset for future investigations and detailed characterisations of these bodies.

Aims. The standard ISO archive products, produced through the last post-mission LWS pipeline, were still affected by instrument artefacts. Our goal was to provide the best possible data products to exploit the full scientific potential of these observations.

Methods. For all asteroid observations we analysed in detail the dark current, the calibration reference flashes, the space environment effects (glitches), memory effects, tracking influences, and various other sources of uncertainty. We performed a refined reduction of all measurements, corrected for the various effects, and re-calibrated the data. We outline the data reduction process and give an overview of the available data and the quality of the observations. We apply a thermophysical model to the flux measurements to derive far-IR based diameter and albedo values of the asteroids. The measured thermal rotational lightcurve of (4) Vesta is compared to model predictions.

Results. The catalogue of LWS (long wavelength spectrometer) observations of asteroids contains 57 manually reduced datasets, including seven non-standard observations, which as such did not have final pipeline products available before. In total, the archive now contains 11 spectral scans and 46 fixed grating measurements with a simultaneous observation at 10 key wavelengths distributed over the full LWS range. The new data products are now accessible via the ISO data archive as highly processed data products (HPDP).

Conclusions. The quality of the data products was checked against state-of-the-art thermophysical model predictions and an excellent agreement was found. The absolute photometric accuracy is better than 10%. The calibrated spectra will serve as a source for future mineralogical studies of dwarf planets and dwarf planet candidates.