SOFIA Completes GREAT Science Flight

The German Receiver for Astronomy at Terahertz Frequencies (GREAT) experiment onboard the Stratospheric Observatory for Infrared Astronomy (SOFIA) has completed its first observations, and scientists at the National Aeronautical and Space Administration (NASA) and the German Aerospace Center (DLR) have published the first round of results.

SOFIA makes its observations from a 2.7-m telescope contained within a modified Boeing 747SP flying in the upper atmosphere (as high as 13700 m). Cruising at this height reduces the amount of atmospheric turbulence it would have to look through and increases the amount of far-infrared wavelengths that would otherwise be absorbed by water vapor in the lower atmosphere.

Optical color image of the rho Ophiuchi star formation region, about 400 light-years from Earth, with dark dusty filamentary gas clouds. The position of the optically obscured low-mass protostar IRAS16293-2422 toward which interstellar deuterated hydroxyl OD has been detected is marked with a red circle. The absorption line spectrum, observed with GREAT onboard SOFIA, displays the molecule’s fingerprint at a frequency of 1.3915 terahertz, or 0.215-mm wavelength. The inset shows the OD molecule (red: oxygene; gray: deuterium), an isotopic substitute of hydroxyl (OH) with the hydrogen atom replaced by heavier deuterium. This deuterated molecule is an important marker in the formation of interstellar water and may serve as a chemical clock in the early star formation process. The bright-yellowish star in the bottom left is Antares, one of the brightest stars in the sky. Below and to Antares’ right is the globular cluster Messier 4. (Credits: Spectrum: MPIfR/B. Parise, Photo: ESO/S. Guisard)

GREAT's primary focus was studying the formation of stars at the earliest point in their evolution, the formation of protostars out of the great protostellar molecular clouds that are remnants of ancient supernovae. GREAT allowed scientists to detect the cooling line of the ionized carbon in several stellar nurseries and to resolve the velocity field of the gas, showing how the embryonic star interacted with its parent cloud.

The GREAT far-infrared spectrometer (the vertical structure in the foreground) is mounted to the telescope counterweight flange inside the pressurized cabin. During observations GREAT rotates ±20º from the vertical, while the telescope (invisible on the far side) and its counterweight (seen here in blue at an angle of 45º) move between roughly 25º and 65º from the vertical. (Photo: R. Güsten)

“The high resolving power of the GREAT spectrometer is designed for studies of interstellar gas and the stellar life cycle, from a protostar’s early embryonic phase when still embedded in its parental cloud to an evolved star’s death when the stellar envelope is ejected back into space,” said Rolf Güsten, principal investigator of the GREAT project. “This stunning collection of first scientific results is reward for the many years of development work and underlines the huge scientific potential of airborne far-infrared spectroscopy.”

GREAT also observed the collapse of three protostars, discovering two interstellar molecular species in the process: OD, an isotopic substitute of hydroxyl with the helium replaced with deuterium, and SH, a mercapto radical.

“The rich harvest of scientific results from this first observing campaign with SOFIA and the GREAT instrument gives a first glimpse of the tremendous scientific potential of this observatory and promises unique astronomical observations for years to come, particularly in the topical research areas of star formation and astrochemistry,” said Hans Zinnecker, deputy director of the SOFIA science mission.

SOFIA, the "Stratospheric Observatory for Infrared Astronomy" cruises above Southern California with its large cavity door wide open; the 2.7-m German-built telescope is visible. At altitudes of up to 45000 ft (14 km) the observatory operates above 99.8% of the atmospheric water vapor. (Photo: NASA)

The results of the mission were published in the May 10 edition of Astronomy and Astrophysics.

SOFIA, a joint project of NASA and the DLR, is funded by the Federal Ministry of Economics and Technology. Operation is coordinated by the German SOFIA Institute (DSI) in Germany and the Universities Space Research Association (USRA) in the United States. GREAT was developed by the Max Planck Institute for Radio Astronomy (MPIfR) and KOSMA at the University of Cologne. Development was financed by the Max Planck Society (MPG), and the Deutsche Forschungsgemeinschaft (DFG).

For more information, visit: www.uni-stuttgart.de