New molecules and star formation in the Milky Way

The first series of astronomical observations with GREAT on board of SOFIA were successfully completed in November 2011. Now, six months later, the scientific results have been published in a special issue of the European journal Astronomy & Astrophysics. In total, 22 articles by an international group of scientists report on the first astronomical results as well as the technologies employed in the GREAT instrument on board SOFIA.

As a joint project between NASA and the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt, DLR), SOFIA operates a 2.7-m telescope in a modified Boeing 747SP aircraft and is the world's largest ever airborne infrared observatory. SOFIA flies at altitudes as high as 13700 meters to provide access to astronomical signals at far-infrared wavelengths that would otherwise be blocked due to absorption by water vapour in the atmosphere. The SOFIA observatory and the GREAT instrument open the far-infrared skies for high-resolution spectroscopy, and GREAT pushes its technology to higher frequencies and sensitivities than ever reached before.

Many of the contributed papers study the star formation process in its earliest phases, first when the protostellar molecular cloud is contracting and condensing, and then when the embryonic star is vigorously interacting with its surrounding parental molecular cloud -tearing it apart and ionizing it. The high spectral resolution capabilities of GREAT enabled scientists to resolve the velocity field of gas in the parental molecular clouds traced by the important cooling line radiation of ionized carbon in several star forming regions.

GREAT detected the velocity signature of infalling gas motion ("collapse") in the envelopes of three protostars, directly probing the dynamics of a forming star. Two interstellar molecular species were detected for the first time ever: OD, an isotopic substitute of hydroxyl (OH) with the hydrogen atom replaced by the heavier deuterium, and the mercapto radical SH. Observations of the ground-state transition of OH at a frequency of 2.5 Terahertz (120 microns wavelength) explored new astrochemical territories while pushing the technological frontier.

The remnant envelope of an evolved star, ionized by its hot stellar core, was also investigated as was the violent shock interaction of a supernova remnant and the surrounding interstellar medium. Furthermore, the circumnuclear accretion disk, ultimately feeding the black hole in the centre of the Milky Way galaxy was studied, as well as star formation in the circumnuclear region of the nearby galaxy IC342.

"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" states the Deputy Director of the SOFIA Science Mission, Hans Zinnecker, from DSI. In parallel with Rolf Güsten from the Max-Planck-Institut für Radioastronomie, the Principal Investigator of the GREAT project, Zinnecker organized the selection process and ultimately selected some of the most exciting observing proposals from the German astronomical community.

"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," says Güsten. "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."

The "Deutsches SOFIA Institut" (DSI) of the University of Stuttgart coordinates SOFIA's science mission and operation on behalf of the German partners.

GREAT, the German Receiver for Astronomy at Terahertz Frequencies is a receiver for spectroscopic observations in the far-infrared spectral regime between frequencies of 1.25 and 5 terahertz (60-240 microns), which are not accessible from the ground due to absorption by water vapour in the atmosphere. GREAT is a first generation German SOFIA instrument, developed by the Max-Planck Institute for Radio Astronomy (MPIfR) and the KOSMA at the Universität zu Köln, in collaboration with the Max-Planck Institute for Solar System Research and the DLR Institute for Planetary Research. Rolf Güsten (MPIfR) is the Principal Investigator for GREAT.

SOFIA, the "Stratospheric Observatory for Infrared Astronomy" is a joint project of the National Aeronautics and Space Administration (NASA) and the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR; German Aerospace Centre, grant: 50OK0901).

Links to articles:

http://www.aanda.org/index.php?option=com_toc&url=/articles/aa/abs/2012/06/contents/contents.html

http://www.mpifr.de/div/submmtech/heterodyne/great/GREAT_science.html