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The LAPLATE program.

The programme LAPLATE is a modification of the programme APLATE Starlink User Note SUN 89) developed at the Anglo-Australian Observatory (AAO).

This programme converts a list of equatorial coordinates (right_ascension and declination into focal plane positions (X and Y), for the fibre masks for the WHT.

LAPLATE runs starting from a user input file. This includes several parameters used by the programme and the equatorial coordinates of the observed objects.

The programme takes into account effects of precession and nutation of the rotational orientation of the field; for this, the equinox and observing date must be included in the input file. The effects of thermal contraction and expansion of the brass aperture plate are also considered; then, the input file must include information about the drilling temperature and the observing temperature. Though differential refraction effects cannot be calculated in advance, LAPLATE makes a first order correction using the zenith distance at which the field crosses the meridian. Regarding this last point, APLATE differs from LAPLATE because the latter uses the latitude of the La Palma Observatory.

LAPLATE Input file.

The following is an example for an input file (.DAT) for the LAPLATE programme:

M3 WHT-Aux


D 1992.27

E 1950.0

S 4.507320565

O 90.0

X 0.0,400.0

T 10.0,25.0

C 13 40 06.089 +28 32 12.41

F 13 40 38.120 +28 33 12.93 GS1

F 13 40 09.742 +28 27 15.30 GS2

F 13 39 55.393 +28 27 36.92 GS3

F 13 39 33.147 +28 32 51.73 GS4

P 13 40 25.376 +28 31 01.53 X1

P 13 40 23.213 +28 34 13.26 26

P 13 40 18.393 +28 34 45.30 50

P 13 40 18.568 +28 33 49.75 49

P 13 40 19.410 +28 32 50.81 43

P 13 40 19.231 +28 31 42.95 46 .

As can be seen, in this file each line starts with a keyword. Each keyword defines the data type given to the program. A brief description is provided below:

L is the plate label. Normally, the plate label will be the observed field. This label can contain up to 40 characters. It must identify clearly the field to avoid confusion in those cases where other fibre observing programmes use similar sky regions.

40ARCMIN defines the telescope field diameter. With the aid of this information, the programme checks if all the objects are on the telescope field; however, this command concerns the Anglo-Australian telescope and, actually, is has not been modified to be used for the La Palma telescopes. Then, the information obtained from this command is useless in this case.

D is the observing date in decimal years. This is required in order to correct for the rotational effects of precession and nutation. But, as this correction is a rotational correction, the plates can be used again at a later date (if the objects have no large proper motions). The rotational correction in this case is made adjusting the rotator and plate orientations (section 9.6.2).

E is the reference equinox for the objects equatorial coordinates. Also, this will be used to correct rotational effects.

S is the focal plane scale in units of ''/mm.. This value depends on the telescope and the telescope focal plane used.

T are two temperature value: the drilling temperature and an estimation of the observing temperature. These are used to correct effects of expansion or contraction of the brass aperture plate. Default values for these temperatures will be 20 and 5 degrees.

C is for the equatorial coordinates of the centre of the observed field. The telescope will be pointed to this position on the sky.

X is to insert two extra fiducial positions at the specified distances (in arcsec) from the nominal plate centre. In the example, these positions are the plate centre and a point 400 arcsec North. These holes are employed to connect the semi-coherent guiding bundles to be used for the rotator adjusting. In general, the plates must have two extra fiducial holes, one 400 arcsec North from the plate centre and another one 400 arcsec South.

F corresponds to the fiducial objects positions. These are the equatorial coordinates of the guide stars. A fiducial object position must be specified in the following format:

F right_ascension declination equinox comments

Each equinox and comment are optional arguments. The equinox must be specified if the object position is referred to a different equinox from the one defined in the E command.

P are the positions for the targets, with a similar format to that used for the fiducial objects:

P right_ascension declination equinox comments

A point '' .'' will be added on the line next to the last line containing positional data. This point indicates the end of file for the LAPLATE programme. After this ending point, other useful information not relevant for the programme, can be added.

LAPLATE Output file.

What follows is an example for an output file (.LOG) for the LAPLATE programme. It contains the corresponding output for each input parameter in the input file (as for the example shown before), and in the same order.

Comments on the Output file:

Previous: Details of the La Palma Sky
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Previous Page: Extinction at La Palma

Fri Jan 7 15:34:48 GMT 1994