Observational $5-20μ$m Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS Spectra

M. K. McClure

doi:10.1088/0004-637X/693/2/L81

paper

Observational $5 - 20 μ$ m Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS Spectra

arXiv:0810.4561 · doi:10.1088/0004-637X/693/2/L81

Abstract

Using \emph{Spitzer} Infrared Spectrograph observations of G0--M4 III stars behind dark clouds, I construct $5 - 20 μ$ m empirical extinction curves for $0.3 \leq A_{K} < 7$ , which is equivalent to $A_{V}$ between $\approx$ 3 and 50. For $A_{K} < 1$ the curve appears similar to the \citet{mathis90} diffuse interstellar medium extinction curve, but with a greater degree of extinction. For $A_{K} > 1$ , the curve exhibits lower contrast between the silicate and absorption continuum, developes ice absorption, and lies closer to the \citet{wd01} $R_{V} = 5.5$ case B curve, a result which is consistent with that of \citet{flaherty07} and \citet{chiar07}. Recently work using \emph{Spitzer} Infrared Array Camera data by \citet{chapman08} independently reaches a similar conclusion, that the shape of the extinction curve changes as a function of increasing $A_{K}$ . By calculating the optical depths of the $9.7 μ$ m silicate and 6.0, 6.8, and 15.2 $μ$ m ice features, I determine that a process involving ice is responsible for the changing shape of the extinction curve and speculate that this process is coagulation of ice-mantled grains rather than ice-mantled grains alone.

Submitted to ApJ Letters, 5 pages, 4 figures, 1 table. Revised version published in ApJ Letters, with 5 pages, 3 figures, and 2 tables. Empirical extinction curves are available as online-only from ApJ

Observational $5 - 20 μ$ m Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS Spectra

Abstract

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Observational 5−20μm Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS Spectra

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References in corpus (5)

Cited by in corpus (116)

Observational $5 - 20 μ$ m Interstellar Extinction Curves Toward Star-Forming Regions Derived from Spitzer IRS Spectra