GREAT: the SOFIA high-frequency heterodyne instrument

Abstract

We describe the design and construction of GREAT (German REceiver for Astronomy at Terahertz frequencies) operated on the Stratospheric Observatory For Infrared Astronomy (SOFIA). GREAT is a modular dual-color heterodyne instrument for highresolution far-infrared (FIR) spectroscopy. Selected for SOFIA's Early Science demonstration, the instrument has successfully performed three Short and more than a dozen Basic Science flights since first light was recorded on its April 1, 2011 commissioning flight. We report on the in-flight performance and operation of the receiver that -in various flight configurations, with three different detector channels -observed in several science-defined frequency windows between 1.25 and 2.5 THz. The receiver optics was verified to be diffraction-limited as designed, with nominal efficiencies; receiver sensitivities are state-of-the-art, with excellent system stability. The modular design allows for the continuous integration of latest technologies; we briefly discuss additional channels under development and ongoing improvements for Cycle 1 observations. GREAT is a principal investigator instrument, developed by a consortium of four German research institutes, available to the SOFIA users on a collaborative basis.

Dynamics and photodissociation region properties in IC 1396A

“…The forward efficiency is 0.95, and the beam efficiency is 0.54 and 0.51 for L1 and L2, respectively (Heyminck et al 2012). Because the emission line is sufficiently narrow, only a linear baseline was fitted between −30 and −20 km s −1 , and between 0 and 20 km s −1 .…”

“…After excluding data suffering from strong standing waves and discarding spectra with excess noise, the data were spectrally resampled to a 0.5 km s −1 resolution and spatially to 25 (0.09 pc at the distance of 750 pc) to obtain a better signal-to-noise ratio (S/N). In the following, we use Article published by EDP Sciences L10, page 1 of 4 A&A 542, L10 (2012) (a) the data from the XFFTS-backend, because the other backends show fully consistent and hence redundant data (see Heyminck et al 2012, for details of the spectrometers). Figure 1 shows the integrated line intensity, summed over the velocity range from −5 to −15 km s −1 .…”

“…Considering the spatial distribution discussed above, it seems that the gas emitting [C ii] is blown away from the rim. The numerical simulations of the evolution of cometary globules by Lefloch & Lazareff (1994) suggest that such a cometary regime lasts ∼90% of the cloud's lifetime, and numerous small clumps that are ejected and accelerated along the globule appear as "fuzz" on the blue side of Lefloch & Lazareff's model position-velocity diagram. The observed structures match this cometary regime.…”

“…There are additional cavities associated with YSOs, and Reach et al (2009) suggested that the globule is being reshaped from the inside, with each protostar residing in a "compartment" that it has blown out via its outflow. Therefore, high spatial resolution, as provided by the German REceiver for Astronomy at Terahertz frequencies (GREAT 1 ; Heyminck et al 2012) Astronomy (SOFIA; Becklin & Gehrz 2009;Young et al 2012) at THz-frequencies is essential for understanding the structure and evolution of the IC 1396A globule.…”

[CII] gas in IC 342

“…6. The observations were performed with the German REceiver for Astronomy at Terahertz frequencies (GREAT 1 , Heyminck et al 2012) on board the Stratospheric Observatory For Infrared Astronomy (SOFIA). In Sect.…”