Next: Sky Subtraction Up: Construction of Flat Previous: Standard construction . For a number of projects where very deep integrations and accurate flat fields are required, and the targets are point sources or much smaller than the frame size, the sky background itself can be used to calculate the flat field. ... Use STATISTICS/IMAGE to calculate the image median, and COMPUTE/IMAGE to divide by this to get the normalised flat field. ...

... The amount of energy encircled by an aperture used for stellar photometry will depend on both the aperture size, and also on any variations in the PSF with field position, time, etc. ... The differences in photometric magnitude between apertures with various radii (i.e. aperture corrections), and their mean and standard deviations for the F555W filter, are presented in Table 5.5 . ... Variations in the PSF with field position will, of course, cause a position dependence in the aperture corrections. ...

Magnetic field measurements onboard the Interball Tail spacecraft are carried out by the FM-3I instrument which consists of two flux-gate magnetometers covering two different ranges: [-200, +200] nT and [-1000, +1000] nT. Besides scientific goals, the FM-3I experiment data is used to perform the attitude control of the Interball Tail spacecraft. ... August 22, 1995 . ... October 18, 1995 . Top of the page . ... Back to the Interball Home Page . ...

... The improvement will be more pronounced in our crowded Wide Field Camera (WFC) images, and may be increased further through use of a more sophisticated method of combining the individual dithered images. Our analysis allows us to check for point spread function shape variations in the HST Planetary Camera (PC) field. ... In crowded field images, we are deriving information about the faint end of the luminosity function (LF) from the texture of the image background. ...

Program: GETVAL Purpose: Get image values at given positions in a set Category: UTILITY File: getval.c Author: M.G.R. Vogelaar Keywords: INSET= Give set (,subset): Maximum number of subsets is 1. ... The image values are formatted according the string entered in FORMAT= APPEND= Ok to append? ... The flag characters and their meanings are: - The result of the conversion is left- justified within the field. ... If the result of a conversion is longer than the field width, an asterisk is returned. ...

IBIS Data Analysis . ... IBIS . ... Flat Fielding - Introduction . The images obtained by IBIS will have intensity variations across the field of view that are not due to the solar image, but rather caused by instrumental effects that alter the observed intensity in each point of the field of view. ... IBIS Flat Fielding Techniques . ... Therefore, it is desirable to obtain the flat field measurements center on a point along the equator near the heliographic center of the solar disk. ...

... 09.11.2007 (VNY) Fixed a bug that could result in a crash of the task when processing crowded fields (SSC-SPR-3700); Restoring the omgsource flag when extracting the target spectrum: in the case when omgrism is called from the interactive tool omgsource the target spectrum shouldn't be extracted (fixing the SSC-SPR-3702); Added a parameter enabling the output of an additional region file that contains newly detected point-like sources (zero-order features); . ...

... Armagh Observatory, College Hill, Armagh BT61 9DG, +44 (0)28 3752 2928 . ... The low-resolution, Cassegrain mounted, FORS spectropolarimeter of the ESO Very Large Telescope is being extensively used for magnetic field surveys. Some of the new discoveries suggest that relatively strong magnetic fields may play an important role in numerous physical phenomena observed in the atmospheres as well as in the circumstellar environments of certain kinds of stars. ...