S5 - Spectroscopy of the ISM

Question 1

What is an unreddened star?

Answer 1

A star with very little ISM between it and the observer.

Question 2

What are dust grains made of? How was this composition determined?

Answer 2

Silicate, as shown by high amounts of absorption (reduced flux) at sharp region around infrared wavelength corresponding to silicate, and carbonaceous compounds, as shown by high amounts of absorption/extinction at sharp region around UV wavelength corresponding to carbonaceous compounds.
Dense clouds also contain water and CO ices as shown by infra-red absorption spectra.

Question 3

What wavelength light spectroscopy is used for measuring the atomic and molecular composition of dust?

Answer 3

Optical and UV for atomic composition. Infrared for molecular composition due to the vibrational excitation effect of infrared on bonds within molecules.

Question 4

What are PAHs?

Answer 4

Poly-aromatic-hydrocarbons. They are large carbon-bearing molecules which have been found in space by emission spectra in the infrared. The C60+ buckminsterfullerene is proposed to be a DIB carrier.

Question 5

What are DIBs?

Answer 5

Diffuse interstellar bands (DIBs) are absorption features found in the optical spectra of reddened stars and other objects.

Question 6

At what wavelengths do stars have their largest flux?

Answer 6

At optical and UV wavelengths.