Configurations

A configuration is the set of parameters needed to specify the search procedure for a given object and rotator position angle. The following combinations of telescope and focal station are supported initially (see Appendix A for further details):

WHT CASS

WHT Cassegrain focus (ISIS, FOS, Taurus, LDSS etc. )

WHT UESCOARSE

WHT UES Nasmyth focus (coarse guide fibre)

WHT UESFINE

WHT UES Nasmyth focus (fine guide fibre)

INT PRIME

WHT Prime focus (imaging CCD, photographic camera)

INT CASS

INT Cassegrain focus (IDS, FOS etc. )

JKT CCDE

JKT f/15 Cassegrain + CCD East of the pier

JKT CCDW

JKT f/15 Cassegrain + CCD West of the pier

JKT WFCE

JKT f/8 Cassegrain + wide-field camera East of the pier

JKT WFCW

f/8 Cassegrain + wide-field camera West of the pier

NONE

Nearest star search (this is independent of telescope, and is intended merely to locate the star(s) nearest to the target position, e.g. for use as references in blind offsetting).

The parameters included as part of a configuration are as follows:

Geometry

The descriptions of the search areas and the conversions between RA, Dec. and guide probe coordinates. These are not expected to change unless mechanical modifications are made and are not accessible to the user.

Magnitude

Each configuration is associated with a magnitude range, defining the brightest and faintest possible guide stars. The defaults have been set to suit the autoguiders, but may be overridden.

Observing aperture

This is specified as an (x,y) pair, in arcsec, and defines the position in the focal plane at which the target is to be observed. The origin of coordinates is at the intersection of the rotator axis with the focal plane and the x and y axes are defined in the same sense as those used by the telescope control system for aperture offsets.

WHT Cassegrain

The default aperture coordinates are set to zero, as the centre of rotation is almost on the ISIS slit.

WHT Nasmyth

Defaults are zero, pending further information.

INT Cassegrain

The defaults are set for a position corresponding to the intersection of the IDS slit and the central column of the EEV5 detector.

INT Prime

This is the only configuration for which the aperture is displaced by more than a few arcsec from the rotator axis. Some care is needed to ensure that self-consistent parameters are used by the GSS and the telescope control system. For CCD observing, the aperture used by the GSS should be the same as the nominal aperture determined for the chip centre (see INT Telescope Manual). For the plate camera, the aperture offset should be close to (0,0). The default is currently set for GEC3.1.

JKT Cassegrain

The default is set to (0,0), which should be close to the centre of the imaging CCD.

Note that accurate blind offsetting from an off-axis guide star will require precise specification of the observing aperture (this application will only become feasible once the proposed astrometric recalibration of the catalogue is completed). Default values are held as part of the configuration.

Minimum separation

This defines the minimum distance between a selected guide star and its nearest neighbour in the catalogue (whether or not the latter satisfies the selection criteria).

Number of stars

This is the maximum number of stars to be selected during a search.