1. Early indications of performance
Max Voronkov
Software Scientist – ASKAP
13th May 2009

2. Performance tests - Main questions
Typical delay scatter in vis plot and its stability
Wide bandwidth allows to estimate delays better
May see weak effects we have never seen before
Flux scale calibration
Bandpass shape, spectral indices and software can affect it
Using at 7mm?
Astrometric accuracy
Systematic effects (e.g. baseline solution)?
Accuracy of the pointing solution
Greater sensitivity may improve the solution
Bandpass shape and spectral indices can make it worse
Could we use weaker sources?

3. Delays in vis plot

4. Delays in vis plot (cont’d)

5. Flux scale calibration
We didn’t have a chance to study this in detail
More information will probably come from the calibrator monitoring
Be prepared to see systematic effects
Wide bandwidth effects are more serious for CX-band (3 and 6 cm).
Probably the uncertainty is not worse than a few per cent for CX-band, 10% for 12mm, a few tens per cents for 7mm and 3mm bands.
Paddle measurement at 3mm
Frequency-dependent Tsys measurement
Does not converge amplitudes in vis.
Can be used instead of the planet at 7mm?
The source is easily detectable at the level of about 0.3 Jy
There is a factor of 1.8 difference in fluxes if calibrated on Uranus and !
The difference is present for narrow bandwidth too. Flux model?
Previous such experiments with the old system at 36 GHz gave a factor of about 1.3.

6. Interference spikes
Things improved a lot since this picture was taken!

7. Observations of G19.61-0.23 at 7mm

8. Recombination lines in G19.61-0.23 at 7mm
H53
MHz

9. Pointing accuracy
Important for mm bands where wide band effects are small (for general users)
Pointing solution is done at 3/6cm after reconfig (staff)
Wide-band effects (spectral index and primary beam dependence on frequency) are not taken into account
Iterative solution for pointing should converge
Did a number of pointing scans with a 10’’ offset in positions
Compared solutions with 10’’

10. Pointing accuracy (contd.)
Antennas 3 (technical problems) and 6 were excluded from the analysis
Found 3.9 arcsec accuracy
This is similar to the accuracy obtained with the old system
Strangely enough, the pointing procedure always underestimates the offset
It would be interesting to repeat the same experiment in C/X and/or with narrower tvch
It is advisable to use the old strategy to choose pointing calibrators.

11. W33 - combining old and new data
Blue contours - old system, 6km array
Red contours - the same 6km array data combined with the new CABB data (using H168)
Grayscale - VLA ammonia data (Keto & Ho, 1989)
CABB data completely outweigh the data from the old system

12. Summary Usually delays are spread by less than 10 ps or so
Baseline errors can give a residual delay of the order of tens of picoseconds (especially 6km baselines at 7mm). This should not be a problem for a typical science experiment
The weather and other effects we don’t yet understand usually give a smaller delay
Flux scale calibration and ATCA astrometry need further study
Calibration on and Uranus at 7mm gives different result
There are interference spikes and lines in the spectra (flagging)
Always observe bandpass calibrator for every frequency setup
Pointing accuracy is no better than before
Use the same strategy as before (1 Jy or brighter source close to the target)
Merging old correlator data with CABB data is non-trivial

13. Thank you Australia Telescope National Facility Max Voronkov
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Australia Telescope National Facility
Max Voronkov
Software Scientist (ASKAP)
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Thank you