Here we show in Nasmyth coordinates the instantaneous calibrated maps obtained during the sequence On Off where the Off is still in the array. The Off position is 25 arcsec. away in Az and 25 in El. Each subscan is 10 seconds. There are 18 subscans. Analysis is on progress to assess the pointing jitter from these data.
Scan 60 in 20111018.
Once analyzed with a Gaussian fitting of constant width (19, 12 arcseconds) and in the AzEl (trueHorizon) coordinate system we obtain these curves:
The off position is a bit at the edge of the array (we'll try to find another scan). The jitter of the telescope is well within one arcsecond on the On position. More precisely the jitter is of typically 0.1 arcsecond over 1 second and after big motions (going back and forth to the off position) the repointing accuracy is of 1 arcsecond peak-to-peak.
RZ, May 25 2012: this analysis ignores the anomalous refraction of the atmosphere, i.e. it says nothing about the jitter of the telescope coordinates ! The accuracy of the telescope coordinates is given by the encoders and is available in the telescope files. Note that the existence and importance of the anomalous refraction in the mm-range was proven with this telescope. This analysis turns upside down the last 25 years of mm-astronomy !
This analysis turns upside down the last 25 years of mm-astronomy !