Toward understanding the 3.4 micron and 9.7 micron extinction feature variations from the local diffuse interstellar medium to the Galactic center
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Abstract
Observationally, both the 3.4 μm aliphatic hydrocarbon C-H stretching absorption feature and the 9.7 μm amorphous silicate Si-O stretching absorption feature show considerable variations from the local diffuse interstellar medium (ISM) to Galactic center (GC): both the ratio of the visual extinction (AV ) to the 9.7 μm Si-O optical depth ( 9.7 μm) and the ratio of AV to the 3.4 μm C-H optical depth ( 3.4 μm) of the solar neighborhood local diffuse ISM are about twice as much as that of the GC. In this work, we try to explain these variations in terms of a porous dust model consisting of a mixture of amorphous silicate, carbonaceous organic refractory dust (as well as water ice for the GC dust).