[meteorite-list] NASA Begins Testing of New Spectrograph on Agency's Airborne Observatory

[Ron Baalke]

June 3, 2014
     
NASA Begins Testing of New Spectrograph on Agency's Airborne Observatory

Astronomers are eagerly waiting to begin use of a new instrument to study 
celestial objects: a high-resolution, mid-infrared spectrograph mounted on 
NASA's Stratospheric Observatory for Infrared Astronomy (SOFIA), the world's 
largest flying telescope.

This new instrument, the Echelon-Cross-Echelle Spectrograph (EXES), can 
separate wavelengths of light to a precision of one part in 100,000. At the 
core of EXES is an approximately 3-foot (1 meter) bar of aluminum called an 
echelon grating, carefully machined to act as 130 separate mirrors that split 
light from the telescope into an infrared "rainbow."

SOFIA is a heavily modified Boeing 747 Special Performance jetliner that 
carries a telescope with an effective diameter of about 8-feet (2.5-meters) 
at altitudes of 39,000 to 45,000 feet (12 to 14 km), above more than 99 
percent of Earth's atmospheric water vapor. Lower in the atmosphere, at 
altitudes associated with most ground-based observatories, water vapor 
obscures much of what can be learned when viewed in the infrared spectrum.

"The combination of EXES's high spectral resolution and SOFIA's access to 
infrared radiation from space provides an unprecedented ability to study 
celestial objects at wavelengths unavailable from ground-based telescopes," 
said Pamela Marcum, a program scientist at the SOFIA Science Center and 
Program Office in Moffett Field, California. "EXES on SOFIA will provide data 
that cannot be obtained by any other astronomical facility on the ground or 
in space, including all past, present or those observatories now under 
development."

EXES successfully carried out its first two flights on SOFIA on the nights of 
April 7 and 9, according to Matthew Richter, leader of the team that is 
developing the instrument at the University of California, Davis, Physics 
Department. EXES is a collaboration between U.C. Davis and NASA's Ames 
Research Center in Moffett Field.

"During the two flights, EXES made observations to investigate and 
characterize the instrument's performance. All the main goals of these 
observations were successful, although further commissioning flights are 
required to test EXES in all of its modes," said Richter.

On the first commissioning flight, EXES observed emissions from Jupiter's 
atmosphere in two molecular hydrogen lines. These observations will be used 
to understand how gas rises from deep in Jupiter's interior and mixes into 
the planet's upper atmosphere.

During the second commissioning flight, EXES observed a young, massive star 
in the constellation Cygnus that is still embedded in its natal cocoon. The 
star, known as AFGL 2591, warms up the surrounding interstellar dust and 
causes ice coatings on the dust to evaporate. The warmed dust provides an 
excellent background infrared "lamp" to probe the chemical make-up of the 
intervening gas.

New stars and planets are forming from that material through processes 
similar to the ones that made the sun and Earth. These observations are 
designed to study water vapor around the protostar, and demonstrate that EXES 
can detect absorption from the lowest energy level of water molecules despite 
interference from water vapor from Earth's atmosphere.

"Of the observations obtained during the instrument's first flights, only one 
can be done from the ground, albeit with some difficulty, and the others are 
impossible from even the best ground-based telescope sites because the water 
in Earth's atmosphere is opaque at these wavelengths," Richter said. "While 
space observatories are above Earth's atmosphere, the massive optical 
equipment required to separate the light as finely as EXES does – EXES 
weighs almost 1,000 pounds – would be a challenge to launch into space. In 
these observations, the spectral features we are studying are narrow, and 
finely dividing the infrared spectrum to detect them is exactly what EXES was 
designed to do."

SOFIA is a joint project of NASA and the German Aerospace Center (DLR). The 
aircraft is based at and the program is managed from NASA Armstrong Flight 
Research Center's facility in Palmdale, California. NASA's Ames Research 
Center, manages the SOFIA science and mission operations in cooperation with 
the Universities Space Research Association (USRA) headquartered in Columbia, 
Maryland, and the German SOFIA Institute (DSI) at the University of 
Stuttgart.

For more information about SOFIA, visit:

http://www.nasa.gov/sofia 

or

http://www.dlr.de/en/sofia 

For information about SOFIA's science mission, visit:

http://www.sofia.usra.edu 

or

http://www.dsi.uni-stuttgart.de/index.en.html 

end

J.D. Harrington
Headquarters, Washington
202-358-5241
j.d.harrington at nasa.gov 

Nicholas A. Veronico
SOFIA Science Center and Program Office, Moffett Field, Calif.
650-604-4589
nicholas.a.veronico at nasa.gov