NAME

targets -- Find coordinates of selected targets in the Guide Star Catalog.

USAGE

targets ra dec width exttab image

DESCRIPTION

This task will extract guide stars from the CD-ROM catalog in a field, overlay the guide stars on an image, interactively determine a plate solution and read back image coordinates.

The user defines a region of the sky by specifying a center position and a width. Guide star tables are then copied from the CD-ROM whenever they contain fields that overlap this region. Guide stars within the specified region---and optionally within specified brightness limits---are selected from the Guide Star Catalog (GSC) and written to an output table.

The specified region is assumed to overlap an image provided by the user. With an estimate of the transformation between equatorial and pixel (image or plate) coordinates, the coordinates of the selected guide stars are overlaid on a copy of the user's image. This produces a marked image that is displayed; the user can then interact with the displayed image to improve the positions of selected stars, compute a plate solution fit, and print the coordinates of selected targets.

PARAMETERS

ra [real, min=0, max=24]

Right ascension (in hours) of the field center. Stars within a region of size width, centered around ra and dec will be selected from the guide star catalog.

dec [real, min=-90, max=90]

Declination (in degrees) of the field center. Stars within a region of size width, centered around ra and dec will be selected from the guide star catalog.

width [real, min=0, max=180]

Field width, in degrees.

exttab [file name]

Name of the output table that will contain extracted guide stars, their magnitudes, equatorial and pixel coordinates, and validity flags.

image [file name]

The image (plate) containing the user's target(s). This image is assumed to overlap the field specified by ra, dec, and width. To obtain an initial estimate of the guide star positions on the image, define the coordinate transformation parameters below.

(mag1) = INDEF [real]

Lower magnitude limit---stars dimmer than mag1 will be ignored. If mag1=INDEF, do not apply a lower magnitude limit; otherwise, only stars between the limits will be extracted from the guide star catalog.

(mag2) = INDEF [real]

Upper magnitude limit---stars brighter than mag2 will be ignored. If mag2=INDEF, do not apply an upper magnitude limit; otherwise, only stars between the limits will be extracted from the guide star catalog.

(allcols = no) [boolean]

Use all GSC columns?

If this parameter is set to "yes", the task will copy all table columns for selected stars from the GSC catalog table(s) to the output merged table. Otherwise, copy only coordinates and brightness, the default.

(plot = no) [boolean]

Plot a chart of the extracted guide stars in the selected region?

(index = "scidata$index.tab") [file name]

Name of the CD-ROM index table file for the region.

(onestar = yes) [boolean]

Select stars from one plate only?

If more than one original guide star plate contains this star, select only one. If plateid is specified, select stars from that plate only, otherwise, take the first star in the table.

(plateid = "") [string]

Plate ID from which stars will be selected from the guide star catalog.

(pixval = INDEF) [real]

The pixel value to use in overlaying guide star positions in the image. If pixval=INDEF, the task will use a value that is 10% higher than the highest value in the image. Caution: if you do not specify a value, it will take a substantial amount of time to determine the extreme pixel values.

(crpix1) [real]

X reference pixel (i.e., the pixel coordinate corresponding to RA,DEC).

(crpix2) [real]

Y reference pixel (i.e., the pixel coordinate corresponding to RA,DEC).

(xpxsize) [real]

X pixel size in microns; this is used to convert pixel coordinates to plate coordinates (in millimeters).

(ypxsize) [real]

Y pixel size in microns; this is used to convert pixel coordinates to plate coordinates (in millimeters).

(pltscl) [real]

Plate scale in arcseconds per millimeter; this is used to convert pixel coordinates to plate coordinates (in millimeters).

(crota) [real]

Rotation angle, in degrees, used to convert pixel coordinates to plate coordinates (in millimeters).

(ctype= "RA") [string]

X coordinate type.

(ctype= "DEC") [string]

Y coordinate type.

(boxsize = 7) [integer, min=3]

Size of the box in which to search for the star center.

EXAMPLES

BUGS

SEE ALSO

strfits, skymap, display, pltsol, xyeq