Presentation on theme: "MmVLBI in the Future: technical/experimental Shep Doeleman Haystack Observatory."— Presentation transcript:
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 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.
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.
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
Mark 5A VLBI Data System Mk5 cost ~ $15K 700 GB disks expected ~2005 – 24 hours @ 1 Gbps unattended (comparable to ~19 VLBA tapes)
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.
v=1 J=3-2 SiO Masers in VY CMa 30 AU First 129GHz VLBI image using all phase and amp information. Relative astrometry small fraction of beam.
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 – 49 as –SiO Masers 2003: Carried out 129, 230GHz VLBI using Pico, KittPeak, SMTO, Plateau de Bure –Detected Pico-SMTO 1.3mm fringes – 34 as on 3C279 –World Record: equivalent to 5 R SCH of SgrA* MBH –Used new generation of VLBI recorders. Very promising, but future depends on funding.
UltraVLBI Proposal Submitted to ATI program at NSF Outfit largest cm antennas (Effelsberg, Arecibo, GBT, WSRT, Jodrell bank) with 4Gb/s recording systems: <1 Jy/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 …
230GHz VLBI Observations Proposed VLBI on JCMT-HHT baseline. Just a detection will provide a firm upper size limit.
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 y (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.
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.