TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 65 (No. 3), pp. 129-138, 2013

Revisiting astronomical crystalline forsterite in the UV to near-IR

Karly M. Pitman1, Anne M. Hofmeister2, and Angela K. Speck3

1Planetary Science Institute, 1700 East Fort Lowell Road, Suite 106, Tucson, AZ 85719-2395, USA
2Department of Earth & Planetary Sciences, Washington University, Campus Box 1169, 1 Brookings Drive, St. Louis, MO 63130-4899, USA
3Department of Physics & Astronomy, 223 Physics Bldg., University of Missouri, Columbia, MO 65211-7010, USA

(Received December 31, 2011; Revised May 8, 2012; Accepted May 11, 2012; Online published March 12, 2013)

Abstract: Optical functions (n and k) of cosmic dust species like forsterite (Mg2SiO4) are required at all wavelengths to quantify the temperature and amount of dust. Astronomers combine optical functions of forsterite and olivine in different ways, which will affect radiative transfer models. We investigated what recent updates to the ultraviolet-visible-near-infrared (UV-VIS-NIR) laboratory spectra of forsterite and the choice of forsterite n, k dataset will have on radiative transfer models. We measured the UV-VIS-NIR transmission spectra of synthetic forsterite, MgO, SiO2, olivine (Fo90), and meteoritic olivine (pallasite). We derived optical functions for these and compared the UV-IR behavior of our k, absorption cross-section 〈Cabs〉, and total flux to that of "astronomical silicate" and olivine. Laboratory-derived k is substantially lower than "astronomical silicate" k at λ ∼ 0.2-5 μm. In the IR, different laboratory n and k produce equivocal 〈Cabs〉, whereas total flux is different for "astronomical silicate" versus laboratory n, k. From 0.35-5 μm, the choice of "forsterite" k values has the most effect on modeled quantities. For environments with significant UV flux, astronomers should use recent UV-VIS-NIR laboratory n, k.
Key words: Dust, extinction, forsterite, optical constants, ultraviolet, near-infrared, laboratory spectroscopy.

Corresponding author E-mail: pitman@psi.edu

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