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mmVLBI in the Future: technical/experimental

mmVLBI in the Future: technical/experimental. Shep Doeleman Haystack Observatory. In Defense of Theory. Do I contradict myself? Very well then I contradict myself, (I am large, I contain multitudes.) --Walt Whitman, "Song of Myself". High Frequency VLBI Challenges.

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mmVLBI in the Future: technical/experimental

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  1. mmVLBI in the Future:technical/experimental Shep Doeleman Haystack Observatory

  2. In Defense of Theory Do I contradict myself? Very well then I contradict myself, (I am large, I contain multitudes.) --Walt Whitman, "Song of Myself"

  3. High Frequency VLBI Challenges • Sensitivity: limited by atmospheric coherence, telescope apertures, bandwidth, weather (opacity and coherence). • Past observations limited to brightest sources. • Baseline coverage: limited by relatively small number of high demand sub/mm telescopes. • LO quality: phase noise in electronics increases – loss of fringe amplitude. • First VLBI at new mm sites requires effort.

  4. Challenges cont’d • Scheduling: mm/submm telescopes difficult to schedule. • Array phasing: all antennas must be phased prior to summing (you only get one chance). • Hydrogen masers: if atmosphere is good, maser should not limit coherence time. • Amplitude calibration is difficult: array phasing, pointing, atmosphere, gain curves. • BBCs have limited Bandwidth • Major improvements can be expected in some of these areas.

  5. Sensitivity: a solution. • Old conventional wisdom: collecting area. • New technical developments – new wisdom • 1983 VLBI BW: 224Mb/s, • 2004 VLBA BW: 512Mb/s. • New disk based VLBI recording systems will allow multi Gb/s data rates

  6. Mark 5A VLBI Data System Mk5 cost ~ $15K 700 GB disks expected ~2005 – 24 hours @ 1 Gbps unattended(comparable to ~19 VLBA tapes)

  7. Sensitivity: a solution. • Old conventional wisdom: collecting area. • New technical developments – new wisdom • 1983 VLBI BW: 224Mb/s, • 2004 VLBA BW: 512Mb/s. • New disk based VLBI recording systems will allow multi Gb/s data rates. • Leverages COTS technology and industry demand for affordable, high capacity, high speed hard disks. • Units can be used in parallel for N Gb/s.

  8. Tape vs. Disc Price Comparison X

  9. mmVLBI at Haystack • 2001-present: focus on 1-2mm VLBI • 2002: Carried out successful 129, 147GHZ VLBI on Pico Veleta, KittPeak12m, SMTO triangle: • High resolution: Pico-SMTO fringes – 49mas • SiO Masers • Collaborators: MPIfR, IRAM, Onsala, Metsahovi, Arizona Radio Observatory

  10. mmVLBI In the News

  11. v=1 J=3-2 SiO Masers in VY CMa • First 129GHz VLBI image using all phase and amp information. • Relative astrometry small fraction of beam. 30 AU

  12. mmVLBI at Haystack • 2001-present: focus on 1-2mm VLBI • 2002: Carried out successful 129, 147GHZ VLBI on Pico Veleta, KittPeak12m, SMTO triangle: • High resolution: Pico-SMTO fringes – 49mas • SiO Masers • 2003: Carried out 129, 230GHz VLBI using Pico, KittPeak, SMTO, Plateau de Bure • Detected Pico-SMTO 1.3mm fringes – 34mas on 3C279 • World Record: equivalent to 5 RSCH of SgrA* MBH • Used new generation of VLBI recorders. • Very promising, but future depends on funding.

  13. Evolution of 3mm Capability 3-5 years: 1Gb/s Present: 256Mb/s 5-10yrs: 10Gb/s VLBA-VLBA = 0.13Jy ALMA-LMT = 0.004Jy ALMA-VLBA = 0.014Jy Resolution (8000km)=90mas Tcoh = 20 seconds VLBA-VLBA = 0.4Jy GBT-LMT = 0.032Jy GBT-LMT = 0.016Jy* LMT-VLBA = 0.1Jy VLBA-VLBA = 0.8Jy PicoV-PdeB = 0.25Jy PicoV-PdeB = 0.13Jy* PicoV-VLBA = 0.5Jy Higher recording rates.

  14. Evolution of 1mm Capability 3-5 years: 4Gb/s Present: 0.5Gb/s 5-10yrs: 10Gb/s ALMA-LMT = 0.008Jy ALMA-SMT = 0.042Jy Resolution (8000km)=34mas Tcoh = 10 seconds PicoV-PdeB = 0.4Jy PicoV-KittPeak = 1.15Jy LMT-CARMA = 0.06Jy LMT-SMT= 0.15Jy

  15. UltraVLBI Proposal • Submitted to ATI program at NSF • Outfit largest cm antennas (Effelsberg, Arecibo, GBT, WSRT, Jodrell bank) with 4Gb/s recording systems: <1mJy/beam rms. • Outfit best mm sites with 4Gb/s systems: JCMT, SMTO (CARMA, LMT, SMA, ALMA, APEX) • Target science requiring sensitivity: SNR in Galactic mergers, GRBs, Grav. Lenses, Stellar VLBI, SgrA*!! • Waiting to hear …

  16. 230GHz VLBI Observations Proposed VLBI on JCMT-HHT baseline. Just a detection will provide a firm upper size limit.

  17. Next Generation VLBI System • Multiple Digital BBC units (500MHz each). • Cost: 20K each. • Multiple MK5b units (1Gb/s each). • Cost: 16K each. • H-maser with sy(10sec)<=3e-14. • Cost: 175K. • Rack with power supplies, backplane, GPS clock, • Cost: 20K • Total: $270K/new station, much less if maser is already available.

  18. Summary • Over next decade: BW x40, Element area x25, means capable 230GHz imaging arrays. • Phase stability of mm/submm arrays is very important: CARMA, ALMA, PdeBure. • Creating low phase noise LO systems for submm VLBI is necessary. • VLBI arrays up to 345 and 450GHz are possible. • ‘Widebanding’ IFs and receivers will be a requirement. • Scheduling: need turn-key operation from single dish to VLBI. • Current proposed work: 4Gb/s VLBI on SgrA* in 3 years.

  19. END

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