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Early indications of performance

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

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Early indications of performance

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  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 1934-638 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 1934-638 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 1934-638! • 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 42951.47 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 1934-638 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. Contact Us Phone: 1300 363 400 or +61 3 9545 2176 Email: enquiries@csiro.au Web: www.csiro.au Thank you Australia Telescope National Facility Max Voronkov Software Scientist (ASKAP) Phone: 02 9372 4427 Email: maxim.voronkov@csiro.au Web: http://www.narrabri.atnf.csiro.au/~vor010

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