GREAT Far-IR Spectrometer’s H-channel Offers New Science Opportunities

With successful commissioning of a new “H” (high-frequency) channel, SOFIA’s GREAT (German Receiver for Astronomy at Terahertz Frequencies) far-infrared spectrometer is ready to open new celestial windows for the world’s scientific community.

The H-channel was first tested during SOFIA flights on May 5, 6, and 7, and was confirmed to be working perfectly. Its operation is based upon an extremely sensitive superconducting detector plus a novel “quantum cascade” laser that operates at frequencies of trillions of cycles per second, or terahertz. With the addition of that new channel, the GREAT instrument is now capable, for example, of high-resolution measurements of the spectral line of atomic neutral oxygen [O I] at a frequency of 4.74 terahertz (wavelength of 63.2 microns). That spectral line is important in determining the energy balance of the interstellar medium.

First-light spectra were obtained toward planetary nebula NGC 7027 (Figure 1). That nebula is an expanding bubble of gas expelled by a dying star with approximately twice the mass of our Sun, 3,000 light-years away in the direction of the constellation Cygnus. The nebula has been extensively studied at other wavelengths, but only GREAT can resolve the velocities of the expanding envelope in the [O I] line. The spectrum obtained (Figure 2) represents only two minutes of observation, illustrating the sensitivity of the GREAT instrument carried into the stratosphere by SOFIA.

GREAT is a Principal Investigator-class instrument for SOFIA, developed and maintained by the Max Planck Institute for Radio Astronomy (PI: Rolf Guesten) and KOSMA (Kölner Observatorium für SubMillimeter Astronomie) at the University of Cologne (Co-I: Juergen Stutzki), in collaboration with the Institute of Planetary Research (Co-I: Heinz-Wilhelm Huebers) and the Max Planck Institute for Solar System Research (Co-I: Paul Hartogh). The GREAT instrument, including the H-channel, will be available to the world astronomical community via the SOFIA Cycle 3 Call for Proposals.

SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The aircraft is based at NASA Armstrong Flight Research Center's Palmdale, California. NASA Armstrong Flight Research Center manages the program. NASA Ames Research Center at Moffett Field, California, manages SOFIA’s science and mission operations in cooperation with the Universities Space Research Association (USRA) headquartered in Columbia, Maryland, and the German SOFIA Institute (DSI) at the University of Stuttgart.

For information about GREAT, visit:

Read about the GREAT Far-IR spectrometer's H-channel (in English) on the Max Planck Institute for Radio Astronomy's website:

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Points of Contact

Web feature U.S. Point-of-Contact:
Dr. Dana Backman
Outreach, SOFIA Science Center
NASA Ames Research Center
Moffett Field, CA 94035-0001

News release German Point-of-Contact:
Dr. Norbert Junkes,
Press and Public Outreach,
Max-Planck-Institut für Radioastronomie.
Fon: +49(0)228-525-399

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