Actions

BLIND

Determine the positions of guide stars suitable for a closed-loop blind offset between two named objects. The reference and target objects must be included in the current catalogue. This command will then select guide stars which are within the accessible field for both objects and will write the probe positions and displacements to the current output file. It does not work if the CONFIG NONE or ROTATOR ANY options are specified.

2=to: 2!:}Format: BLIND reference$>$ target$>$

2=to: 2!:}Example: BLIND THREE MICE

CATSEARCH

Search for guide stars around all objects in a named catalogue. The catalogue name follows standard VMS syntax and the default extension is .CAT.

2=to: 2!:}Format: CATSEARCH catalogue_name$>$

2=to: 2!:}Examples: CATSEARCH MACAVITY.CAT

2=to: 2!:} CATSEARCH U3:[GUEST01.CAT]BASKET

DO

Filename. Search the GSC using GSS commands from the specified file rather than interactive input. Defaults to .COM extension and the current directory. Nesting of GSS commands is not supported.

2=to: 2!:}Format: DO filename$>$

2=to: 2!:}Example: DO STARS.CMD

HELP

Access to help on GSS commands and abbreviations via a VMS HELP library with the usual hierarchical structure.

2=to: 2!:}Format: HELP [topic$>$]

2=to: 2!:}Examples: HELP

2=to: 2!:} HELP OUTPUT

EXIT

Stop the GSS program. If using the CD-ROM version of the catalogue, also dismount the disks.

2=to: 2!:}Format: EXIT

OFFSET

Determine the positions of guide stars for a closed-loop blind offset of a specified amount from a named reference object. The reference object must be included in the current catalogue. The offsets are specified in arcsec in the tangent plane parallel to RA ($\xi$) and Declination ($\eta$). An optional rotation, in degrees, may also be included (this is intended primarily for alignment of multislit fields on the WHT and has the same parameters as the TCS TWEAK command). OFFSET selects guide stars which are within the accessible field before and after the offset and will write the probe positions and displacements to the current output file. It does not work if the CONFIG NONE or ROTATOR ANY options are specified.

2=to: 2!:}Format: OFFSET reference$>$ $\xi$ $\eta$ [rotation$>$]

2=to: 2!:}Examples: OFFSET ALPHACEN 3.4 -23.4

2=to: 2!:} OFFSET REF 4.5 0.0 1.3

OUTPUT

Filename. Creates and opens a new output file to be used until superseded by another OUTPUT command, and closes any previous output file. Standard VMS syntax, defaulting to OUTPUT.GS in the current directory.

2=to: 2!:}Format: OUTPUT filename$>$

2=to: 2!:}Examples: OUTPUT WHT.GS

2=to: 2!:} OUTPUT DISK$USER1:[GUEST01.CATS]TARGETS.GUIDE

PLOT

Plot the positions of the selected guide stars on the selected device. The plot is centred on the rotator axis and shows the positions of the selected guide stars in the focal plane coordinate system (x left-right; y up-down; PA $0o$ vertical). The target position is marked by an open star, and the rotator axis (if the target is not on it) is marked by an open circle and dot. The outline of the field is drawn, together with an ``L'' indicating North and East. An open circle indicates that the object is classified as stellar on all available plates. An x represents an object with a non-stellar classification on all plates and a circle with a superposed x represents an ambiguous classification. Larger symbols correspond to brighter objects.

2=to: 2!:}Format: PLOT

SEARCH

Search the catalogue for guide stars around a target position specified explicitly. The RA, Dec and Equinox are required; other positional information can be entered using optional qualifiers, as follows:

/RAPROPER

proper motion in RA (seconds of time per year)

/DECPROPER

proper motion in Dec (arcseconds per year).

/EPOCH

(year). Defaults to equinox.

/PARALLAX

(arcsec). Defaults to zero.

/RADVEL

radial velocity (kms$-1$; defaults to zero).

Examples:

SEARCH 20 12 13.33 -30 45 55.2 B1950
SEARCH 19 57 57 30.233 04 06.77 J2000 /RAP=0.001 /DECP=-0.12 /EP=1945.5

This command is for use when a catalogue has not been specified (e.g. for small numbers of objects).

SHOW

displays the parameters of the currently-selected configuration (SHOW CURRENT) or lists all the available configurations (SHOW CONFIG). The former is the default.

2=to: 2!:}Format: SHOW keyword$>$

2=to: 2!:}Examples: SHOW

2=to: 2!:} SHOW CONFIG

SOURCE

causes the GSC to be searched around the position of a named object in the current catalogue, using the current configuration and rotator PA. The name should follow the requirements of the WHT TCS (up to 20 characters; embedded spaces require double quotes).

2=to: 2!:}Format: SOURCE sourcename$>$

2=to: 2!:}Example: SOURCE M87