Open Access10‐μm absorption spectra of silicates for two new diffuse interstellar medium sightlines
Author(s) -
Bowey J. E.,
Rawlings M. G.,
Adamson A. J.
Publication year - 2004
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2004.07497.x
Subject(s) - physics , astrophysics , spectral line , interstellar medium , absorption spectroscopy , astronomy , emissivity , galaxy , optics
We present low resolution 10‐μm spectra of the newly identified diffuse interstellar medium (ISM) sightlines towards StRS 217 and StRS 371 and a new spectrum of Cyg OB2 no. 12 obtained at the UK Infrared Telescope (UKIRT) with the Michelle imager/spectrometer. As previously, the μ Cephei emissivity better represents the profile of diffuse medium silicates than does the broader Trapezium emissivity which is characteristic of dust in molecular clouds. These spectra together with seven spectra published by Roche & Aitken comprise the majority of the silicates data set for the diffuse ISM. The observed sample includes sources in the first galactic quadrant at heliocentric distances of about 1.0–4.2 kpc. We find the silicate optical depth, c sil = A V /(19.2 ± 0.6) and the ratio of c sil to heliocentric distance, d , is in the range 0.1 ≲ c sil / d ≲ 0.7 kpc −1 ; for StRS 217 the ratio could be as high as c sil / d ≲ 1.2 kpc −1 . However, this ratio is dominated by uncertainties in the distance estimates and does not indicate the degree of clumping in the diffuse interstellar medium.