The TELESCOP packet

The TELESCOP packet lists the header items which define the state of the telescope. The header records should be as follows:

CAT-NAME= CHAR              / Name of object
CAT-RA  = ' hh:mm:ss.ss'    / Catalogue RA of object
CAT-DEC = 'sdd:mm:ss.s '    / Catalogue Dec of object
CAT-EQUI= CHAR              / Equinox of catalogue coordinate system (e.g. 
J2000.0)
CAT-EPOC= CHAR              / Epoch of catalogue coordinates (e.g. 1992.1)
PMRA    = REAL              / Proper motion of object in RA (s/yr)
PMDEC   = REAL              / Proper motion of object in dec (arcsec/yr)
PARALLAX= REAL              / Parallax of object (arcsec)
RADVEL  = REAL              / Heliocentric radial velocity of object (km/s)
RATRACK = REAL              / Differential tracking rate in RA (arcsec/s)
DECTRACK= REAL              / Differential tracking rate in Dec (arcsec/s)
RA      = ' hh:mm:ss.ss'    / RA of telescope 
DEC     = 'sdd:mm:ss.s '    / Dec of telescope
EQUINOX = CHAR              / Equinox of telescope coordinates
EPOCH   = REAL              / Epoch of observation
STSTART = 'hh:mm:ss.ss'     / LST at approx. start of exposure
ST      = 'hh:mm:ss.ss'     / LST at approx. start of exposure
UTOBS   = 'hh:mm:ss.ss'     / UT at approx. start of exposure
AZIMUTH = REAL              / Azimuth at approx. start of exposure (degs)
ZDSTART = REAL              / ZD at approx. start of exposure (degs)
ZDEND   = REAL              / ZD at approx. end of exposure (degs)
AIRMASS = REAL              / Airmass averaged through the exposure
AMSTART = REAL              / Airmass at approx. start of exposure
AMEND   = REAL              / Airmass at approx. end of exposure
XAPOFF  = REAL              / Aperture offset in X (arcsec)
YAPOFF  = REAL              / Aperture offset in Y (arcsec)
ROTTRACK= LOGICAL           / Rotator tracking on ?
MNTPASTA= REAL              / Mount PA at approx. start of exposure (degs)
MNTPAEND= REAL              / Mount PA at approx. end of exposure (degs)
ROTSKYPA= REAL              / Sky PA of rotator at start of exposure (degs)
PARANGLE= REAL              / Parallactic angle at start of exposure (degs)
VIGNETTE= LOGICAL           / Beam vignetted by dome/shutter/mirror cover ?
DAZSTART= REAL              / Dome azimuth at start of exposure (degs)
DAZEND  = REAL              / Dome azimuth at end of exposure (degs)
TELFOCUS= REAL              / Telescope focus (mm)
AUTOMODE= CHAR              / Mode of autoguiding
AUTOX   = REAL              / Guiding position on autoguider, x
AUTOY   = REAL              / Guiding position on autoguider, y

Notes:

• We have provided both the input catalogue-coordinates initially used to point the telescope, and also the actual telescope-coordinates after offsetting onto the target object.

• The keyword CATNAME contains the name of the target as entered in the TCS catalogue. This should not be confused with the OBJECT keyword (in the OBSVATON packet) which holds a descriptive (and optional) title for the observation.

• A number of items in the header change during an exposure; in most cases we have specified that the value recorded is that at the start of the exposure. In a few cases (zenith distance, airmass, mount PA) there is a strong argument for saving the values at the start and end of an exposure, since the rate of change of these quantities is important for calibration.

• The FITS standard specifies that when RA and Dec are used to index the main data arrays ( e.g. if CTYPEn = RA or Dec), they should be scaled in degrees. However, where RA and Dec appear as header records we have adopted the more normal usage of hh:mm:ss.ss and dd:mm:ss.s. We do not believe that this violates the FITS standard, but we would be interested in hearing from anyone who does.

• The value of UTOBS is available from the time service and is highly stable. The clocks in the detector controllers, which determine the value of the UTSTART keyword, may not be synchronized with the time service and may drift. However, UTOBS is not a precise timing of the start of the exposure since the TCS cannot tell accurately when the shutter is opened.

• EPOCH and AIRMASS are required by IRAF.