Pointing of VISIR
=================

Please, be aware that this is work in progress. Final results shall be posted when available.

To assess pointing of VISIR I analyzed observations of the imaging standard star obtained in 2008, 2009 and 2010.

The VISIR pipeline recipe visir_img_phot, used to process the imaging standard stars, writes to the log file information about target-pointing difference, e.g.

[WARNING] visir_img_phot: The location of the standard star 'HD189831' in the FITS header (RA,DEC)=(300.89,-37.9425) and the catalog (RA,DEC)=(300.889,-37.9407) differ by 0.00182087 degrees

Such information is easy to "harvest" and was used to produce the following histogram:

The results show that the difference between the standard star catalog and observed coordinates is around 0.00129595 deg ~ 4.665 sec.

There was a comment that the accuracy of the coordinates to only the 3-rd decimal may affect the final results. However, I performed independent checks on the differences estimated from the values in the header keywords (accuracy to the 6-th decimal) and the results are consistent.

In addition, I have also performed spot check on the data obtained in 2011 (see report attached below).

The pipeline products of the imaging standard star were displayed (with ds9), and coordinates of the upper left positive target, read from the display, were compared with coordinates of the target extracted from SIMBAD. The blurry images were not considered.

FK5 coord. (ep=J2000 eq=2000)
file, target, data coord., catalog coord., diff.
------------------------------------------------------------------------------------------------------------------
VR_MSIC_111107A_px0.075_fNEII_1.fits HD12524 02 01 42.532 -44 42 49.53 02 0 1 42.377 -44 42 48.62 1.8863 sec

VR_MSIC_111107A_px0.075_fNEII_2.fits HD12524 02 01 42.603 -44 42 49.67 02 01 42.377 -44 42 48.62 2.6279 sec

VR_MSIC_111108A_px0.075_fPAH1.fits HD216149 22 51 02.489 -39 09 25.15 22 51 02.159 -39 09 24.61 3.876 sec

VR_MSIC_111108B_px0.075_fPAH1.fits HD216149 22 51 02.487 -39 09 25.11 22 51 02.159 -39 09 24.61 3.848 sec

VR_MSIC_111111A_px0.075_fSIC.fits HD22663 03 37 05.931 -40 16 29.78 03 37 05.682 -40 16 28.36 3.184 sec

VR_MSIC_111111B_px0.075_fSIC.fits HD22663 03 37 05.931 -40 16 29.78 03 37 05.682 -40 16 28.36 3.184 sec

VR_MSIC_111111F_px0.075_fSIC.fits HD61935 07 41 14.833 -09 33 04.07 blurry

VR_MSIC_111111G_px0.075_fSIC.fits HD71095 blurry

VR_MSIC_111106C_px0.075_fSIC.fits HD39425 05 50 57.956 -35 46 02.18 05 50 57.592 -35 46 05.92 5.798 sec

VR_MSIC_111106C_px0.075_fNEII_2.fits HD12524 02 01 42.606 -44 42 49.65 02 01 42.377 -44 42 48.62 2.649 sec

VR_MSIC_111011B_px0.075_fSIC.fits HD39425 05 50 57.852 -35 46 02.08 05 50 57.592 -35 46 05.92 4.976 sec

VR_MSIC_111015A_px0.127_fSIC.fits HD177716 19 06 56.674 -27 40 16.50 19 06 56.409 -27 40 13.52 4.612 sec

VR_MSIC_111015B_px0.127_fSIC.fits HD177716 blurry