Atmospheric Phase Correction for ALMA Phase correction & for - PowerPoint PPT Presentation

WVRGCAL B. Nikolic Atmospheric Phase Correction for ALMA Phase correction & for ALMA Introduction ALMA 183 GHz WVR The WVRGCAL program system The FP6 programme The WVRGCAL program B. Nikolic Results Good results Astrophysics Group, Cavendish Laboratory, University of Cambridge Effect on the beam Poor results http://www.mrao.cam.ac.uk/˜bn204/ “Dry” fluctuations Future work ALMA Software Development Workshop Summary NRAO/Charlottesville October 2011

Outline WVRGCAL B. Nikolic Phase correction Phase correction for ALMA for ALMA Introduction Introduction ALMA 183 GHz WVR system ALMA 183 GHz WVR system The FP6 programme The FP6 programme The WVRGCAL program The WVRGCAL program Results Good results Effect on the beam Results Poor results “Dry” fluctuations Good results Future work Effect on the beam Summary Poor results “Dry” fluctuations Future work Summary

Outline WVRGCAL B. Nikolic Phase correction Phase correction for ALMA for ALMA Introduction Introduction ALMA 183 GHz WVR system ALMA 183 GHz WVR system The FP6 programme The FP6 programme The WVRGCAL program The WVRGCAL program Results Good results Effect on the beam Results Poor results “Dry” fluctuations Good results Future work Effect on the beam Summary Poor results “Dry” fluctuations Future work Summary

ALMA WVRGCAL B. Nikolic Recent (but already out of date) photo of ALMA with 16 antennas Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

ALMA as a high resolution imager WVRGCAL B. Nikolic ◮ ALMA is aiming to improve the routinely available Phase correction for ALMA resolution at mm/sub-mm by 50 × from ∼ 0 . 5 to Introduction ALMA 183 GHz WVR system ∼ 0 . 01 arcseconds The FP6 ◮ Comparable to the improvement introduced by the programme The WVRGCAL Hubble space telescope at optical wavelengths program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary Images of M13 from http://hubblesite.org courtesy of NASA, ESA, and the Hubble Heritage Team (STScI/AURA). Approximately scaled by eye... Do not use for science!

ALMA as a high resolution imager WVRGCAL B. Nikolic ◮ ALMA is aiming to improve the routinely available Phase correction for ALMA resolution at mm/sub-mm by 50 × from ∼ 0 . 5 to Introduction ALMA 183 GHz WVR system ∼ 0 . 01 arcseconds The FP6 ◮ Comparable to the improvement introduced by the programme The WVRGCAL Hubble space telescope at optical wavelengths program Results Good results To achieve this: Effect on the beam Poor results “Dry” fluctuations ◮ ALMA will observe at λ ∼ 350 µ m on baselines up to Future work 15 km long Summary ◮ Will need to correct for the effects of the troposphere

Atmospheric Phase Fluctuations WVRGCAL B. Nikolic Astronomical Phase correction wavefront for ALMA Introduction ALMA 183 GHz WVR system The turbulent troposphere The FP6 programme The WVRGCAL program Results Corrupted Good results astronomical wavefront Effect on the beam Poor results “Dry” fluctuations Future work Summary R(t)

Atmospheric Phase Fluctuations WVRGCAL B. Nikolic Astronomical Phase correction wavefront for ALMA Introduction ALMA 183 GHz WVR system The turbulent troposphere The FP6 programme The WVRGCAL program Results Corrupted Good results astronomical wavefront Effect on the beam Poor results “Dry” fluctuations Future work Summary R(t)

Atmospheric Phase Fluctuations WVRGCAL B. Nikolic Astronomical Phase correction wavefront for ALMA Introduction ALMA 183 GHz WVR system The turbulent troposphere The FP6 programme The WVRGCAL program Results Corrupted Good results astronomical wavefront Effect on the beam Poor results “Dry” fluctuations Future work Summary R(t)

Path fluctuations due to the atmosphere WVRGCAL B. Nikolic Phase correction 0 . 009 for ALMA 750 Introduction ALMA 183 GHz WVR system 500 The FP6 programme 250 The WVRGCAL program δ L ( µ m) δ L ( µ m) 0 Results Good results Effect on the beam − 250 Poor results “Dry” fluctuations Future work − 500 Summary − 750 6 6 . 2 6 . 4 6 . 6 6 . 8 7 7 . 2 t (hours UT) t (hours UT) Path fluctuation on a baseline of ∼ 500 m inferred from ALMA observations of a quasar at λ = 3 . 3 mm.

Outline WVRGCAL B. Nikolic Phase correction Phase correction for ALMA for ALMA Introduction Introduction ALMA 183 GHz WVR system ALMA 183 GHz WVR system The FP6 programme The FP6 programme The WVRGCAL program The WVRGCAL program Results Good results Effect on the beam Results Poor results “Dry” fluctuations Good results Future work Effect on the beam Summary Poor results “Dry” fluctuations Future work Summary

Water Vapour cm/mm/sub-mm lines WVRGCAL B. Nikolic 1 mm precipitable water vapour Phase correction for ALMA 300 Introduction ALMA 183 GHz WVR system 250 The FP6 programme The WVRGCAL 200 program Results T b (K) T b (K) Good results 150 Effect on the beam Poor results “Dry” fluctuations 100 Future work Summary 50 0 200 400 600 800 1000 ν (GHz) ν (GHz)

Water Vapour cm/mm/sub-mm lines WVRGCAL B. Nikolic 1 mm precipitable water vapour Phase correction 183 GHz Water Line – for ALMA 300 Introduction ALMA WVR system ALMA 183 GHz WVR system 250 The FP6 programme The WVRGCAL 200 program Results T b (K) T b (K) Good results 150 Effect on the beam Poor results “Dry” fluctuations 100 Future work Summary 50 0 22 GHz Water Line – 200 400 600 800 1000 ν (GHz) ν (GHz) previous WVR systems

The 183 GHz Water Vapour Line WVRGCAL B. Nikolic Blue rectangles are nominal WVR filters Phase correction for ALMA Introduction 250 ALMA 183 GHz WVR system The FP6 programme 200 The WVRGCAL program 150 Results Good results T b (K) T b (K) Effect on the beam Poor results 100 “Dry” fluctuations Future work Summary 50 0 175 177 . 5 180 182 . 5 185 187 . 5 190 ν (GHz) ν (GHz)

WVR in the ALMA receiver cabin WVRGCAL B. Nikolic Phase correction for ALMA Introduction ALMA 183 GHz WVR system The FP6 programme The WVRGCAL program Results Good results Effect on the beam Poor results “Dry” fluctuations Future work Summary

Sky brightness observed by WVRs WVRGCAL B. Nikolic Phase correction 250 250 for ALMA Introduction 200 200 ALMA 183 GHz WVR system T B (K) T B (K) T B (K) T B (K) The FP6 150 150 programme 100 100 The WVRGCAL program 50 50 Results 6 6 . 25 6 . 5 6 . 75 7 7 . 25 6 6 . 25 6 . 5 6 . 75 7 7 . 25 Good results t (hours UT) t (hours UT) t (hours UT) t (hours UT) Effect on the beam Observed brightness Poor results “Dry” fluctuations 250 temperatures of WVR Future work on the three antennas 200 Summary involved in this test T B (K) T B (K) 150 observation. The four 100 colours in each panel 50 are the four channels 6 6 . 25 6 . 5 6 . 75 7 7 . 25 of the WVRs. t (hours UT) t (hours UT)

Correlation between WVRs and paths WVRGCAL B. Nikolic 8 Phase correction for ALMA 1 . 5 8 1 Introduction 1 6 ALMA 183 GHz WVR 0 . 5 system 6 0 . 5 The FP6 ∆ T B , 1 (K) ∆ T B , 1 (K) ∆ T B , 2 (K) ∆ T B , 2 (K) 4 0 0 programme 4 − 0 . 5 The WVRGCAL − 0 . 5 2 program − 1 2 − 1 − 1 . 5 Results 0 0 Good results − 200 − 100 0 100 200 300 − 200 − 100 0 100 200 300 Effect on the beam δ L ( µ m) δ L ( µ m) δ L ( µ m) δ L ( µ m) Poor results 8 “Dry” fluctuations 1 8 1 Future work 6 0 . 5 Summary 0 . 5 6 ∆ T B , 3 (K) ∆ T B , 3 (K) ∆ T B , 4 (K) ∆ T B , 4 (K) 4 0 0 4 − 0 . 5 − 0 . 5 2 2 − 1 0 0 − 200 − 100 0 100 200 300 − 200 − 100 0 100 200 300 δ L ( µ m) δ L ( µ m) δ L ( µ m) δ L ( µ m)

Outline WVRGCAL B. Nikolic Phase correction Phase correction for ALMA for ALMA Introduction Introduction ALMA 183 GHz WVR system ALMA 183 GHz WVR system The FP6 programme The FP6 programme The WVRGCAL program The WVRGCAL program Results Good results Effect on the beam Results Poor results “Dry” fluctuations Good results Future work Effect on the beam Summary Poor results “Dry” fluctuations Future work Summary

About the FP6 programme WVRGCAL B. Nikolic Phase correction for ALMA ◮ ‘European Union Framework 6 Programme for Introduction ALMA 183 GHz WVR Enhancement of ALMA Early Science’ system ◮ Aim to enhance ALMA over-and-above the already The FP6 programme planned/funded capabilities The WVRGCAL ◮ Funded entirely separately from ALMA program ◮ Wide range of community groups (universities + ESO Results Good results + IRAM) Effect on the beam ◮ “No drag” on the project Poor results “Dry” fluctuations ◮ Proposal to the EC in March 2004, work packages Future work commenced Mid-2006 Summary ◮ Six Band-5 receivers, OTF interferometry software, and (this talk) Advanced Radiometric Phase Correction Techniques ◮ Similarities to the ALMA Development programme