Trinity Astrophysicist Flies on the NASA and German Space Agency Airborne Observatory SOFIA to Observe Supergiant Star Betelgeuse

Posted on: 24 November 2011

Trinity College Dublin astrophysicist Dr Graham Harper  flew on board the NASA and German Space Agency, DLR’s new SOFIA Airborne Observatory to make far-infrared observations of the massive red supergiant star Betelgeuse in an all night expedition on November 9th  last.  Dr Harper travelled to Palmdale California, on the edge of the Mojave Desert, to be a guest Investigator on the SOFIA flight during the observation.

Betelgeuse (also known as Alpha Orionis) is the second brightest star in the constellation Orion, the eighth brightest star in the northern night sky, and one of the largest stars ever measured.

SOFIA is a converted Boeing 747-SP that has a 2.5 metre diameter reflecting telescope which points through an opening in the side of the plane. SOFIA flies at up to 45,000 feet where it is above 99.8% of the Earth’s atmosphere water vapour and this permits astronomers to make far-infrared observations that are otherwise impossible to make from the ground.

Flight 86 – view of science crew, GREAT instrument, and telescope pressure bulkhead taken during the flight. Shows the working environment.

Betelgeuse is shedding its extended outer layers and no one is really sure why. Dr Graham Harper, from Trinity College’s School of Physics led an international team consisting of Dr Matthew Richter (University of California – Davis), Dr Alexander Brown (University of Colorado at Boulder), and Dr Joanna Brown (Harvard-Smithsonian Center for Astrophysics) on the flight. Their observation was designed to help solve this riddle that has puzzled astronomers for over 50 years.

For his observations on board SOFIA, Dr Harper used the German Receiver for Astronomy at Terahertz Frequencies, or GREAT, an infrared heterodyne spectrometer developed by a team led by Rolf Güsten from the Max-Planck-Institute for Radio Astronomy in Germany. Dr Harper’s investigation called for an examination of the 217 and 163-micron cooling lines of carbon monoxide molecules in the gas flowing away from the red supergiant star. Gas expelled from the star will be recycled over the next several thousand millennia to form future generations of stars and planets. SOFIA and GREAT were chosen for this research as the spectral line Dr Harper was observing cannot be detected by any ground-based telescope because it is at a wavelength completely blocked by water vapour in Earth’s atmosphere.

The SOFIA Flight #86 lasted about 9 hour and 40 minutes. When the plane reached 43,000 feet the observations of Betelgeuse commenced with the German Receiver for Astronomy at Terahertz Frequencies (GREAT). Major telescope computer software problems, however, were encountered just after the initial data was collected but with some excellent team work by the telescope and instrument scientists, and with help from the pilots, the faulty system was by-passed and they were able to collect spectra of Betelgeuse’s warm carbon monoxide.  Initial inspection of the data reveal that this carbon monoxide emission arises from an outflow travelling at  up to 9 km per second and which is approximately symmetrical about Betelgeuse.

The SOFIA data are now being analysed by Dr Harper’s research group at Trinity College, PhD students Sarah Kennelly and Eamon O’Gorman and Neal O’Riain, as part of an SFI RFP research programme.  The data will be combined with ultraviolet spectra obtained from the Hubble Space Telescope (in collaboration with Drs  T. R.  Ayres, University of Colorado at Boulder, and Kenneth Carpenter, GSFC), millimetre radio interferometry (Joanna Brown, and Trinity PhD student Eamon O’Gorman), and ground based infrared spectra (in collaboration with Dr. Nils Ryde, Lund University, Sweden).

NASA’s Stratospheric Observatory for Infrared Astronomy 747SP flies over California’s Mojave Desert.
(NASA photo / Jim Ross)