Metal-containing amorphous silicate grains are expected to be a major component of interstellar dust. Amorphous silicate grains containing magnesium, iron, and calcium have been synthesized in the IWU chemistry department. I have contributed to the construction and testing of an instrument that will be used to measure terahertz absorption spectra of cold samples at astronomically interesting temperatures.
To study cosmic dust analogs, we installed dust samples, embedded in low-density polyethylene (LDPE) pellets, in a sample-exchanger and cooled it down within a cryostat to 3.0 Kelvin. Using a blackbody radiation source, we measured the transmission of terahertz light through those samples using a semiconductor bolometer. Light from the blackbody radiation source travelled through a Fourier Transform Spectrometer which allowed us to obtain the frequency dependence of the absorption of the dust sample. By using the Bruggeman eective-medium approximation, we accounted for the high density of dust in our pellets compared to the negligible density in the interstellar medium (ISM). Then we can use the mass of the dust contained in each sample pellet to calculate (frequency dependent) absorptivity per unit mass of dust from the absorption spectra. We obtained spectra at several interesting astronomical temperatures between 4-30 Kelvin.
From the summer of 2018, we have carried out two cool-downs with several sets of data for different dust analogs. Using the data that we have gathered, I fitted the absorptivity with a power law in frequency (goal 2), following the work of other groups. Finally, I measured any variation of the power law indices as a function of dust temperature (goal 3).
Phan, Binh, "Terahertz Absorption Spectra of Silicate Cosmic Analog Dusts Using a Novel Spectrometer" (2019). Honors Projects. 19.