Volume 629, September 2019
|Number of page(s)||12|
|Section||Atomic, molecular, and nuclear data|
|Published online||12 September 2019|
Broadband spectroscopy of astrophysical ice analogues
I. Direct measurement of the complex refractive index of CO ice using terahertz time-domain spectroscopy⋆
Max-Planck-Institut für extraterrestrische Physik, Gießenbachstrasse 1, 85748 Garching, Germany
2 Prokhorov General Physics Institute of the Russian Academy of Sciences, 119991 Moscow, Russia
3 Bauman Moscow State Technical University, 105005 Moscow, Russia
4 Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany
5 Excellence Cluster Origin and Structure of the Universe, Boltzmannstr. 2, 85748 Garching bei München, Germany
6 INAF – Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy
Accepted: 22 July 2019
Context. Reliable, directly measured optical properties of astrophysical ice analogues in the infrared and terahertz (THz) range are missing from the literature. These parameters are of great importance to model the dust continuum radiative transfer in dense and cold regions, where thick ice mantles are present, and are necessary for the interpretation of future observations planned in the far-infrared region.
Aims. Coherent THz radiation allows for direct measurement of the complex dielectric function (refractive index) of astrophysically relevant ice species in the THz range.
Methods. We recorded the time-domain waveforms and the frequency-domain spectra of reference samples of CO ice, deposited at a temperature of 28.5 K and annealed to 33 K at different thicknesses. We developed a new algorithm to reconstruct the real and imaginary parts of the refractive index from the time-domain THz data.
Results. The complex refractive index in the wavelength range 1 mm–150 μm (0.3–2.0 THz) was determined for the studied ice samples, and this index was compared with available data found in the literature.
Conclusions. The developed algorithm of reconstructing the real and imaginary parts of the refractive index from the time-domain THz data enables us, for the first time, to determine the optical properties of astrophysical ice analogues without using the Kramers–Kronig relations. The obtained data provide a benchmark to interpret the observational data from current ground-based facilities as well as future space telescope missions, and we used these data to estimate the opacities of the dust grains in presence of CO ice mantles.
Key words: astrochemistry / methods: laboratory: solid state / ISM: molecules / infrared: ISM
The data plotted in Fig. 6 are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/629/A112
© B. M. Giuliano et al. 2019
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Open Access funding provided by Max Planck Society.
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