Knowledge Bank

Infrared spectrosocpy in astronomy at mid-infrared wavelengths often requires resolving powers $\nu /\Delta \nu$ as high as $105$. Molecular lines in stars, planets and the sun can be very narrow, with widths produced by doppler broadening due to the temperatures or velocities in the source. Completely resolved line profiles can yield dynamics, composition, temperatures and magnetic fields in atmospheres and circumstellar shells. Spectral resolutions near $0.01cm-1$ are achievable using Fourier transform spectrometers. Until recently, however, such high resolution has been impractical because of detector or background noise. A postdisperser has been developed at Goddard Space Flight Center to improve the sensitivity of FTS's used for astronomy. This instrument, a cryogenic grating monochromator, permits $0.01cm-1$ resolution on a variety of sources. By narrowing the spectral bandwidth to $0.6-3cm-1$, the background noise is greatly reduced. Examples will be shown of Mg lines in $stars1,C2H2$ and HCN in circumstellar $shells2,CCH6$ detected in $Jupiter3$ and Zeeman splitting in $sunspots4$. Observations were performed using the facility FTS's at the McMath and Mayall telescopes at Kitt Peak.