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EXES, the echelon-cross-echelle spectrograph for SOFIA

Learn about EXES, a high spectral resolution mid-IR spectrograph on the SOFIA telescope. Explore its capabilities and potential for scientific research.

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EXES, the echelon-cross-echelle spectrograph for SOFIA

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  1. EXES, the echelon-cross-echelle spectrograph for SOFIA Matthew J. Richter (UC Davis) with Mark McKelvey (NASA Ames Research Center) Andreas Seifahrt (UC Davis) special notice to John Lacy, UT Austin Richter - UC Davis

  2. SOFIA • SOFIA is 747 with 2.5m aperture • 6-8 hour flights at 39-45,000 feet • PWV 5-10 micron • first science in 2010 • Impact of SOFIA for mid-IR • new spectral windows • large instruments (600 kg) • EXES is PI instrument • collaborative proposals Richter - UC Davis

  3. EXES and SOFIA 8 10 7 10 6 GREAT 10 CASIMIR 5 10 EXES Spectral resolution 4 10 3 FLITECAM 10 FIFI LS 2 10 HIPO FORCAST 1 10 HAWC 0 10 1 10 100 1000 Wavelength [µm] Richter - UC Davis

  4. Atmospheric comparison SOFIAvsMauna Kea Richter - UC Davis

  5. Forward EXES • High spectral resolution, mid-IR, grating spectrograph • Operates between 4.5 and 28 mm • R =100,000 (3 km/s) at 10 mm • 0.7% spectral coverage with 15” long slit (depending on telescope) • medium (R=10,000) and low (R=3000) modes available • 10242 pixel Si:As IBC detector designed for space backgrounds • Preparing for ground-based telescope proposal for 2010B • fly on SOFIA in 2013 Richter - UC Davis

  6. Propane Importance of High Spectral Resolution Propane on Titan • measure weak lines • measure features in crowded regions Roe et al. 2003 • Resolve disk radii • Separate multiple velocity components Richter - UC Davis

  7. Importance of High Spectral Resolution • Complements Spitzer (Herschel, JWST, ALMA) • more later • Reduce impact of telluric features ±100 km/s Mauna Kea SOFIA Richter - UC Davis

  8. Echelon Grating • 40 inches long • 0.3 inch groove spacing • 0.131 grooves / mm • Diamond machined Al 6061 • 0.03 inch groove height • 84.3 degree angle of incidence 0.3” 0.3” Richter - UC Davis

  9. Selected Science Potential of EXES • Solar System • mapping Martian disk in CH4 • SO2 on Io • H2O, CO2, and other molecules in comets • Star formation regions • H2O rotational and vibrational lines in circumstellar disks • pre-biotic molecules in absorption Richter - UC Davis

  10. Spitzer IRS Spectrum of a Typical T Tauri Star Carr & Najita (2008) S/N ~ 250[NeII], other atomic lines and molecular bands

  11. H2O Rotational Emission Line Resolved 13mm • Gemini/TEXES R=100,000 • Water emission resolved: • 90 km/s FWHM • From r = 0.3--1 AU Carr, Najita, Richter, Lacy, Knez, etc.

  12. Molecular absorption toward a low-mass PMS star • Spitzer found molecular band absorption toward a T Tauri star with IR companion • C2H2, HCN, CO2 (T=550 K for HCN) • Absorption against mid-IR continuum • star or disk Courtesy IRS GTOs

  13. Molecular absorption toward a low-mass PMS star • Molecular lines resolved with TEXES (R=80,000) • warm gas • asymmetric lines • offset from cloud velocity • probes origin (disk,wind, infall) Other molecules without strong, overlapping bands also detected e.g. NH3 Richter - UC Davis

  14. IRC +10216 (Fonfria et al. 2008) Richter - UC Davis 1 of 6 panels

  15. IRC +10216 (Fonfria et al. 2008) Richter - UC Davis 1 of 6 panels

  16. Slit stepping observations provide data cube (spatial, spatial, spectral) Sky subtraction comes from edge of scan [NeII] map of the Galactic Center region Richter - UC Davis

  17. EXES detector • 10242 pixel array on long term loan from NASA • intermediate step toward MIRI arrays for JWST • Designed for space backgrounds • very low read noise: ~30 e- • shallow well (roughly linear up to 100,000 e- ) Richter - UC Davis

  18. EXES C2H2 Q-branch spectrum Q(1) Q(3) • Gas cell with low-pressure, room temperature C2H2. The features are mostly from Q-branch at 13.7 microns. • R = 60,000 (FWHM of 12.5 pixels). • Expect to reach R=100,000 when EXES is properly focused. • The wavelength coverage is 0.6% at this wavelength: • 15% more than TEXES • no gaps between echelon orders. Q(5) Q(7) Q(9) Q(8) Q(10) Q(11) Q(9) Q(10) Q(11) Q(12) Q(13) Q(14) Q(15) Q(15) Q(16) Q(19) Q(20) Pixels Q(22) R(0) Q(23) Q(23) Q(25) Spatial Direction Q(27) Spectral Direction R(1) Pixels

  19. Summary • EXES on SOFIA will provide truly unique data because of resolution and atmospheric transmission • EXES is nearly ready for first ground-based run • working 10242 Si:As array • still some work to be done, but on track for first flight in 2013 Richter - UC Davis

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