Pointing Data Format under TPOINT
Pointing Data Format under TPOINT
The acquisition of data in the
new TCS
produces a file called yyyymmdd-hhmmss.pnt in the summit
directory /jac_logs/yyyymmdd/yyyymmdd-hhmmss.pnt.
The format is TPOINT input version 1,
recording RAs & Decs and the LST rather than the multitude of telescope
parameters recorded under the
old TCS system.
Data is collected at the issuance of each heterodyne log.
An
example of the resulting pointing file, with a name like
         
20090128-235843.pnt
is shown below :
JCMT Pointing Test - 2009/01/28
: ALTAZ
+19 49 22.30 2009 01 29 -2.25 621.00 4120.00 0.827 866.963
09 48 29.174 +13 14 02.63 09 48 35.756 +13 15 09.01 08 12.04958 4.760 108.775 HARPB 0.00 0.00 1.9 2.6
09 48 29.174 +13 14 02.63 09 48 36.988 +13 14 31.52 08 37.90685 -1.266 124.686 HARPB 0.00 0.00 2.5 0.4
07 23 22.817 -25 47 11.45 07 23 37.834 -25 49 16.26 09 1.52885 -1.400 53.730 HARPB 0.00 0.00 -0.3 5.1
07 23 22.816 -25 47 11.46 07 23 38.266 -25 50 07.28 10 6.12021 -1.400 40.427 HARPB 0.00 0.00 -2.2 0.3
09 48 29.175 +13 14 02.63 09 48 25.106 +13 11 47.59 10 31.05245 -1.400 142.134 HARPB 0.00 0.00 2.9 3.6
05 18 04.613 +53 35 58.94 05 18 20.552 +53 31 13.78 10 52.60965 -1.400 29.219 HARPB 0.00 0.00 -1.2 -0.5
05 18 04.612 +53 35 58.95 05 18 22.694 +53 31 15.81 10 59.29623 -1.400 28.202 HARPB 0.00 0.00 -2.1 4.6
12 45 35.318 +45 23 03.10 12 45 24.203 +45 24 20.18 12 21.49399 -1.400 105.967 HARPB 0.00 0.00 1.5 -0.1
12 45 35.321 +45 23 03.11 12 45 21.284 +45 21 46.28 14 9.76879 -1.400 95.100 HARPB 0.00 0.00 3.0 1.8
The 3rd line shows the observatory latitude, the UT date, the
atmospheric
temperature and pressure (mb), the observatory altitude in metres, local humidity
(%/100),
and the effective wavelength in microns.
Subsequent lines give the pointing data. The parameters displayed are as follows,
using the last entry as an example :
12 45 35.321 +45 23 03.11 12 45 21.284 +45 21 46.28 14 9.76879 -1.400 95.100 HARPB 0.00 0.00 3.0 1.8
-- RA & Dec of source --- --RA & Dec of telescope-- --- LST --- SMU-colln-offsets FE Instr.Ap.Offsets uaz uel
Note: uaz and uel are the offsets from the current pointing model in azimuth and elevation.
The following five Notes regarding the derivation of these terms were
provided by Russell Kackley (20071219):
- The following two steps are performed prior to computing the telescope
coordinates:
- Apply the pointing offsets computed by the POINTING_FOCUS task
- Examine the current instrument aperture in the TCS. If the aperture
involves the use of a tracking receptor, change the instrument
aperture
to the (0,0) aperture location. We do this because TPOINT cannot
handle aperture offsets. The aperture is reset to the original
location after recording the information in the .pnt file.
- The observatory latitude has been corrected for polar motion, using:
lat = lat + xpmr*cos(longit) - ypmr*sin(longit)
where the uncorrected latitude is 0.346026069 radians, longitude is
-2.713633073 radians, and (xpmr, ypmr) are from the IERS tables.
- The RA & Dec of the source is computed as follows:
- Start with demand RA & Dec supplied by TCS configuration file
- Correct RA & Dec for proper motion using slaPm with ep0 = the epoch
in which the source coordinates were supplied and ep1 = current
barycentric dynamical time
- Transform to geocentric apparent RA & Dec using slaMapqkz and the
current target-independent mean-to-apparent parameters.
- The RA & Dec of the telescope is computed as follows:
- Start with the demand Az/El coordinates as sent to the telescope
hardware interface task
- Use the observatory location and slaDh2e to transform Az/El to
HA/Dec
- Use the HA and current sidereal time to compute RA
- The demand Az/El coordinates sent to the telescope are computed by
starting with the demand RA & Dec supplied by TCS configuration file,
transforming to Az/El, and applying corrections for the Earth rotation,
diurnal aberration, refraction, the telescope pointing model, and current
pointing model offsets.
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