edwards by liamei12345

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									              DIVAS

      Phil Edwards (ISAS/ATNF)
H. Hirabayashi, J. Ulvestad, C. Salter,
  T. Ghosh, L. Gurvits, E. Fomalont
                 DIVAS is…
• The Deep Interferometric VSOP-Arecibo Survey

• A VSOP survey of faint(er) sources to compare size
  and brightness temperature distributions

• Preceded by VLBA observations of candidate
  sources to determine a source list for VSOP
  observations
V&A
DIVAS is not…




      DEVOS
      (Deep Extragalactic VLBI-Optical Survey)
      arXiv:0711.0862
      Frey, Gurvits, Paragi, Mosoni, Garrett, &
      Garrington
                 Arecibo
• 305m spherical dish
• Limited elevation
  range
• DIVAS observations
  made before surface
  refurbishment
• Sensitive!
• Equipped with a
  Canadian S2 recorder
          Pre-DIVAS survey
• 6.5 < RA < 17.5 hr
  (FIRST cut)
• 29 < dec < 34 deg
  (Arecibo cut)
• S(1.4GHz) > 25 mJy
• S(4.8GHz) > 50 mJy
• 161 sources observed
  with VLBA in Dec 1996   Offset of (RA,dec)=(0.342,-0.166)
                          applied to FIRST position to derive
                          coordinates for VSOP observation
            Pre-DIVAS results
                                            J0759+3010




                                            Peak 85 mJy/beam
                                            Lowest contour 2%



• Sources imaged
• Improved positions found by MBS (or phase referencing)
• 60 candidates with peak brightness > 75 mJy/beam
  selected for VSOP observations with small ground array


 Edwards, Ulvestad and Fomalont, 2005 PASP 340, 83
    DIVAS observations

*
*




*
*

*
J0949+2920   AR, GB, NT




70mJy, 0.9x0.4mas
T_B ~ 1x10^10 K
 J0919+3324 HALCA, AR, GB




160mJy component, 0.1 mas
T_B ~ 8x10^11 K
 J1228+3128 HALCA, AR, GB




150mJy, 0.24mas
T_B ~ 1x10^11 K
J1350+3034 HALCA, AR, NT




260mJy, 0.4mas
T_B ~ 9x10^10 K
J1442+3234 HALCA, AR, GB




?? 100mJy, 0.18mas ??
             Conclusions
• Limited observing time at Arecibo
  maximized by HALCA’s rapid movement
  through the (u,v) plane
• Model-fits of VSOP observations possible
  for simple sources
• A priori amplitude calibration important
• VSOP-2 phase-referencing capability
  would make observations much easier

								
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