Name

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SUBSTAR

Purpose

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Subtract a scaled point spread function at specified star position(s).

Explanation

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Part of the IDL-DAOPHOT photometry sequence

Calling Sequence

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SUBSTAR, image, x, y, mag, [ id, psfname, /VERBOSE]

Input-output

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IMAGE - On input, IMAGE is the original image array. A scaled
PSF will be subtracted from IMAGE at specified star positions.
Make a copy of IMAGE before calling SUBSTAR, if you want to
keep a copy of the unsubtracted image array

Inputs

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X - REAL Vector of X positions found by NSTAR (or FIND)
Y - REAL Vector of Y positions found by NSTAR (or FIND)
MAG - REAL Vector of stellar magnitudes found by NSTAR (or APER)
Used to scale the PSF to match intensity at star position.
Stars with magnitude values of 0.0 are assumed missing and
ignored in the subtraction.

Optional Inputs

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ID - Index vector indicating which stars are to be subtracted. If
omitted, (or set equal to -1), then stars will be subtracted
at all positions specified by the X and Y vectors.
PSFNAME - Name of the FITS file containing the PSF residuals, as
generated by GETPSF. SUBSTAR will prompt for this parameter
if not supplied.

Optional Input Keyword

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VERBOSE - If this keyword is set and nonzero, then SUBSTAR will
display the star that it is currently processing

Common Blocks

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The RINTER common block is used (see RINTER.PRO) to save time in the
PSF calculations

Procedures Called

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DAO_VALUE(), READFITS(), REMOVE, SXOPEN, SXPAR(), SXREAD()

Revision History

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Written, W. Landsman August, 1988
Added VERBOSE keyword January, 1992
Fix star subtraction near edges, W. Landsman May, 1996
Assume the PSF file is in FITS format W. Landsman July, 1997
Converted to IDL V5.0 W. Landsman September 1997