EXES, the Echelon-Cross-Echelle Spectrograph, made
its first light flight on April 7, 2014. The instrument is a mid-infrared
spectrograph and is shown mounted to SOFIA's telescope.
Image Credit: NASA/SOFIA/EXES/Mathew Richter
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:
or
For information about SOFIA's science mission, visit:
or
NASA
Guillermo Gonzalo Sánchez Achutegui
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