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Molecular Imager: Focal Plane Array

Molecular Imager: Focal Plane Array. Glen Langston Motivation: Molecular discoveries Focal Plane Arrays important for all observing bands First 7 pixel Array for 18 to 26 GHz. NRAO. Molecular Discoveries: 100m. World’s most sensitive Telescope in frequency range 10 to 50 GHz

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Molecular Imager: Focal Plane Array

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  1. Molecular Imager: Focal Plane Array Glen Langston • Motivation: Molecular discoveries • Focal Plane Arrays important for all observing bands • First 7 pixel Array for 18 to 26 GHz NRAO Glen Langston: KFPA CDR: Jan 2009

  2. Molecular Discoveries: 100m • World’s most sensitive Telescope in frequency range 10 to 50 GHz • Discovered >7 new large interstellar molecules, including propenal and propanal • Widely distributed, not exclusively in compact cores Hollis, Snyder, Remijan and Jewell 2004-2008 Langston, Turner 2007 Glen Langston: KFPA CDR: Jan 2009

  3. Molecular Line Surveys Science goals require wide instantaneous bandwidths Prime targets have many widely spaced narrow lines. Widely separated (Delta nu > 1 GHz) Glen Langston: KFPA CDR: Jan 2009

  4. 1st Pixel Tests Completed • September 11, 2008 – Single Pixel Tests on GBT • October 6, 2008 – IDM1 IF Spur studies – Measure versus feed position • October 12, 2008 – Comparison of Current GBT K-band (K0) and Single Pixel (K1) • December 28, 2008 – IDM 2 – Check of System temperature and compare K0 with K1 • https://safe.nrao.edu/wiki/bin/view/Kbandfpa/SinglePixelTesting Glen Langston: KFPA CDR: Jan 2009

  5. First Astronomical Tests • Peak and Focus results good. • Obs revealed IF spurs, that are now understood. • Extensive tests of interfaces. • Web based monitor http://172.23.1.79/ • CLEO /Astrid scripts worked for test obs. • Obs on Sept 11, 2008 Glen Langston: KFPA CDR: Jan 2009

  6. 1st Pixel Tests: Frequency Range • Orion A 18-26.5 GHz • H and He Recombination Lines • Water Line and molecules • Negative features are IF spurs • Initial tests showed IF spur problems (now fixed) Glen Langston: KFPA CDR: Jan 2009

  7. Gain and Tsys Tests • Performed intensity measurements as a function of pixel offset from center location. • Gain versus Position Offset 3.8’ in Azimuth and Elevation directions (LCP and RCP) Frequency Offset-Azimuth Offset-Elevation (GHz) Average Average 19 97.7 +/- 2.5 % 95.2 +/- 2.5 % 25 99.4 +/- 4.4 % 89.4 +/- 4.5 % • Performed a sequence of obs with K0 Feed system followed by K1 sequence. • Found higher system temperatures • Cause: Low gain and IF spurs • Obs Oct 6, 2008 • https://safe.nrao.edu/wiki/bin/view/Kbandfpa/TKfpa08Oct06 Glen Langston: KFPA CDR: Jan 2009

  8. Spectral Line Tests • Configured for TMC • NH3 1-1 and 2-2 Lines, plus HC7N • Baseline Performance Good, similar to K0 Glen Langston: KFPA CDR: Jan 2009

  9. Baseline Stability Check • Comparison of twenty five 90 second observations • Obs. Sig-Ref/Ref calibrated with same average reference scan • No significant baseline structure changes. No baseline fit subtracted, only single average value plus an offset to separate spectra Glen Langston: KFPA CDR: Jan 2009

  10. 1st Pixel Tests: Line Mapping Taurus Molecular Cloud HC7N NH3 Simultaneous Maps of several lines Note High GBT Sensitivity: Only 2 seconds per pixel! Glen Langston: KFPA CDR: Jan 2009

  11. RMS noise Versus Time • RMS decreases roughly as expected with time. • Plot shows measured RMS in spectra and sqrt(T) model. • Common Reference may add to systematic noise. Glitch may be due to weather or Processing (?) Glen Langston: KFPA CDR: Jan 2009

  12. K0/K1 Tsys Comparison • K0/K1 Comparisons at 19, 21, 23 and 25 GHz show comparable performance • Weather Variations limit comparison accuracy • All obs show increasing Tsys with time. • 23 GHz results typical • Obs on Dec. 28, 08 Glen Langston: KFPA CDR: Jan 2009

  13. Efficiency Estimate at 23 GHz • Efficiency estimated by comparison of 3C123 peak intensities (K) for K0 and K1. • Two K0 measurements and one K1 Measurements at 23 GHz. • Weather dominates uncertainty (and cal values) • https://safe.nrao.edu/wiki/bin/view/Kbandfpa/KbandTests08Dec28 K1/K0 Efficiency LCP RCP ==== === 99% 84% 95% 79% 96% 81% 88% 75% Ratio of 3C123 Peak Heights Glen Langston: KFPA CDR: Jan 2009

  14. Mapping Tests: Multiple Beams HC7N HC5N Software for Mapping Tests using Current GBT Rx: Two Beam mapping works, must write software for 7 beams. Glen Langston: KFPA CDR: Jan 2009

  15. IDM 2 Tests • 2nd IDM showed no IF spurs • Tsys performance similar to K0 Glen Langston: KFPA CDR: Jan 2009

  16. Summary: Planned Tests Accomplished • First On Telescope tests showed good basic performance, and identified engineering tasks • Tests of gain offsets versus feed position were consistent with predictions. • Second IDM seems free of IF Spurs • Baseline stability seems good • Comparison of K0/K1 is good (Weather limits accuracy) • RMS decreasing with integration time. Further observations needed for firm conclusions • Wide frequency (18 to 26 GHz) observations are critical for study of important large molecules and Chemistry. Glen Langston: KFPA CDR: Jan 2009

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