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Extending the ICRF to Higher Radio Frequencies: 24 and 43 GHz Astrometry Overview

This presentation discusses the motivation for extending the International Celestial Reference Frame (ICRF) to higher radio frequencies, specifically 24 GHz and 43 GHz. Key aspects include initial observations, results, accuracy, and future plans. It highlights benefits such as more compact sources, stable positions, and higher telemetry rates that can improve astrometry, geodesy, and deep space navigation. Collaborated by experts from JPL, NRAO, and other institutions, the findings indicate significant potential for enhanced precision in celestial measurements.

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Extending the ICRF to Higher Radio Frequencies: 24 and 43 GHz Astrometry Overview

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  1. IVS General Meeting 2004 Extending the ICRF To Higher Radio Frequencies: 24 and 43 GHz Astrometry C.S. Jacobs JPL (Caltech/NASA) P. Charlot, E.B. Fomalont, D. Gordon, G.E. Lanyi, C.Ma, C.J. Naudet, O. J. Sovers, L.D. Zhang, and the KQ VLBI Survey Collaboration 9 Feb 2004

  2. Outline • Motivation for a radio frame above 8 GHz (X-band) • Game plan • Initial Observations • Results • Accuracy • Future Plans/Conclusions

  3. Collaborators on Astrometry • P. Charlot Observatory of Bordeaux • E. B. Fomalont NRAO-Charlottesville • D. Gordon Goddard/NASA • C. S. Jacobs JPL/Caltech NASA • G.E. Lanyi JPL/Caltech NASA • C. Ma Goddard/NASA • C.J. Naudet JPL/Caltech NASA • O.J. Sovers RSA Systems/JPL • L.D. Zhang JPL/Caltech NASA This team is a subset of the larger KQ VLBI Collaboration which includes: National Radio Astronomy Observatory -Socorro U.S. Naval Observatory

  4. Motivation • Astrometry, Geodesy and Deep Space navigation, now at 8.4 GHz (X-band) Going to Higher radio frequencies allows • Potentially more compact sources Potentially more stable positions • Higher Telemetry Rates to Spacecraft • Avoid 2.3 GHz RFI issues • Ionosphere &solar plasmadown 16X !! at 32 GHz (Ka-band) compared to 8 GHz. Picture credit: SOHO/ESA/NASA

  5. Why Ka-band? Valleys are microwave windows The three curves show absorption in a dry atmosphere, in the same atmosphere with 20 kg/m2 of added water vapour, and with both water vapour and 0.2 kg/m2 of stratus cloud added. . Murphy, R. et al., 1987, Earth Observing System Volume IIe: HMRR High-Resolution Multifrequency Microwave Radiometer. Published by NASA, Goddard Space Flight Centre, Greenbelt, Maryland 20771, USA, 59pp. Murphy, R. et al., 1987, Earth Observing System Volume IIe: HMRR High-Resolution Multifrequency Microwave Radiometer. Published by NASA, Goddard Space Flight Centre, Greenbelt, Maryland 20771, USA, 59pp.

  6. Basis of VLBI: Point source at infinity How Does VLBI work? Extragalactic “nebulae” idea goes back to 18th c. ? • Relies on point source at infinity - Active Galactic Nuclei Concept: Nav by “fixed” stars • Advantages: Parallax unobservable Proper Motions < 0.1 nrad/yr BUT . . . • Price to be paid is Very weak sources 1 Jy = 1.0E-26 watt/m**2/Hz need lots of square meters => 34 - 70m Antenna lots of Hz bandwidth => 100 Mbps – 1Gbps low system temp => Tsys = 20-40 Kelvin (Hubble Deep Field STScI/NASA)

  7. AGN schematic Schematic of Active Galactic Nuclei Redshiftz~ 0.1 to 5 Distance: billions light years Parallax = 0 Proper motion < 0.1 nrad/yr (Credit: C.M. Urry and P. Padovani ) http://heasarc.gsfc.nasa.gov/docs/objects/agn/agn_model.html

  8. AGN Cen-A in X-ray, Optical, Radio Credits: X-ray (NASA/CXC/M. Karovska et al.); Radio 21-cm image (NRAO/VLA/Schiminovich, et al.), Radio continuum image (NRAO/VLA/J.Condon et al.); Optical (Digitized Sky Survey U.K. Schmidt Image/STScI)

  9. Game Plan • Long term - simultaneous 8.4 and 32 GHz (X/Ka-bands) at present instrumentation not all in place • Interim plan: Bracket 32 GHz with currently available 24 GHz (K-band) 43 GHz (Q-band) - Interpolate behavior at 32 GHz (Ka-band) identifies likely detectable sources • Now: Exercise short baseline Ka-band instrumentation at Goldstone California (DSS 13 - DSS 25) • Exploring potential single baseline Goldstone CA to Kashima • Ka-band Soon - Goldstone-Spain (March ‘04) and Goldstone-Australia (April ‘05) VLBA ?? Others??

  10. Initial Observations Mauna Kea OVRO Brewster N. Liberty Hancock Ft. Davis Los Alamos St. Croix Kitt Peak Pie Town • VLBA ten 25m antennas 5 sessions each 24 hours ~ 60 sources per session 3-5 snapshots, 2 min each 400 MHz spanned bandwidth 128 Mbps record rate • Simultaneous astrometry and imaging • more sessions planned for 2004 (photos credit NRAO/NSF/AUI http://www.aoc.nrao.edu/vlba/html/vlbahome/thesites.html)

  11. Results: 24 GHz Celestial Frame

  12. Results: 43 GHz Reference Frame

  13. ∆RA accuracy: K vs. S/X ICRF ext “1.5”

  14. ∆Dec accuracy: K vs. S/X ICRF ext “1.5”

  15. Internal consistency: K - Q ∆RA

  16. Internal Consistency: K - Q ∆Dec

  17. Zonal Errors: ∆RA vs. Dec

  18. RA-RA corr. vs. Arc: Minimal constraint • 3-D orientation set by fixing 1.5 sources • RAs not well separated by least squares • Only 3 days data

  19. RA-RA correlations: 4 source constraint • 3-D orientation set by fixing 4 sources • RAs now better separated by least squares • Still only 3 days data • Cost: Impose 5 pieces of external information from S/X ICRF

  20. Conclusions • ICRF now extended to K and Q-bands at sub mas accuracy ! 24 and 43 GHz observations: 5 sessions ~ 230 sources at K-band, 24 GHz ~132 sources at Q-band, 43 GHz ~ 250 µas formal precision systematics at 500 µas level or less Source parameters not yet well separated with only few days data - more data needed. • Future Plans More K and Q-band data on the way. Planning for simultaneous 8.4 / 32 GHz (X/Ka) data

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