GREAT Far-IR Spectrometer Opens Window to New Science Opportunities
4.7 Terahertz Spectroscopy with SOFIA, the airborne observatory
With successful commissioning of its high-frequency channel, the GREAT (German Receiver for Astronomy at Terahertz Frequencies) far-infrared spectrometer onboard SOFIA is ready to explore new realms.
The new so-called H-channel was first tested during SOFIA flights on May 14, 16, and 17, and confirmed to be working perfectly. It is based upon an extremely sensitive superconductive detector and a novel "quantum cascade" terahertz laser. With that receiver added, the GREAT instrument is now capable of high-resolution spectroscopy of astrophysically important lines of atomic neutral oxygen [OI] at a wavelength of 63 μm (frequency of 4.74 TeraHertz).
First-light spectra were obtained towards 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 constellation of Cygnus. The nebula has been extensively studied at other wavelengths, but only GREAT can resolve the velocities of the expanding envelope in the [OI] line. The spectrum (Figure 2) represents only 2 minutes of integration, illustrating the superb 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 at the University of Cologne (Co-I: Juergen Stutzki), in collaboration with the DLR Institute of Planetary Research (Co-I: Heinz-Wilhelm Huebers) and the Max Planck Institute for Solar System Research (Co-I: Paul Hartogh).
SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The aircraft is based at NASA Armstrong Flight Research Center that manages the program. NASA Ames Research Center at Moffett Field, Calif., manages the SOFIA science and mission operations in cooperation with the Universities Space Research Association (USRA) headquartered in Columbia, Md., and the German SOFIA Institute (DSI) at the University of Stuttgart.