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 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