Fred Lahuis | SRON, Netherlands Institute for Space Research (original) (raw)

Papers by Fred Lahuis

The Astrophysical Journal, 2008

The Astrophysical Journal Supplement Series, 2004

The Astrophysical Journal, 2008

Astronomy & Astrophysics, 1996

Astrophysical Journal Supplement Series, 2004

Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded l... more Sensitive 5-38 um Spitzer Space Telescope (SST) and ground based 3-5 um spectra of the embedded low mass protostars B5 IRS1 and HH46 IRS show deep ice absorption bands superposed on steeply rising mid-infrared continua. The ices likely originate in the circumstellar envelopes. The CO2 bending mode at 15 um is a particularly powerful tracer of the ice composition and processing history. Toward these protostars, this band shows little evidence for thermal processing at temperatures above 50 K. Signatures of lower temperature processing are present in the CO and OCN- bands, however. The observed CO2 profile indicates an intimate mixture with H2O, but not necessarily with CH3OH, in contrast to some high mass protostars. This is consistent with the low CH3OH abundance derived from the ground based L band spectra. The CO2/H2O column density ratios are high in both B5 IRS1 and HH46 IRS (~35%). Clearly, the SST spectra are essential to study ice evolution in low mass protostellar environments, and to eventually determine the relation between interstellar and solar system ices.

We present a summary of all ground based SWS instrument tests and calibrations together with a de... more We present a summary of all ground based SWS instrument tests and calibrations together with a description of test equipment and environment. The contents and results of the SWS ground calibration are discussed and their value for the in-flight calibration of SWS is demonstrated.

Astronomy & Astrophysics, 1996

Astrophysical Journal, 2008

With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spect... more With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]

Icarus, 1995

Page 1. Icarus 114, 197-202 (1995) IRAS LRS Spectra of Comets Tempel 1 and Tempel 2* David K. Lyn... more Page 1. Icarus 114, 197-202 (1995) IRAS LRS Spectra of Comets Tempel 1 and Tempel 2* David K. Lynch, John A. Hackwell, and David Edelsohn Space and Environment Technology Center, Aerospace Corporation M2I266 ...