Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007acs..rept...11f&link_type=abstract
Instrument Science Report ACS 2007-11, 21 pages
Astronomy and Astrophysics
Astrophysics
Ramp Filters, Acs, Advanced Camera For Surveys, Hst, Hubble Space Telescope
Scientific paper
Ramp filters provide ACS users with the equivalent of tunable narrow and medium-width passband filters. Here we analyze images taken under calibration programs CAL 9671 and CAL 10742 to measure the wavelength calibration of the ACS ramp filters by observing standard stars with the ramp filters crossed with the ACS G800L grism. We find that the tested HRC ramp filters are relatively well centered on the requested wavelengths. A number of the WFC filters, however, display significant offsets from the desired central wavelength. While the WFC direct images show large image offsets (wedges) due to the crossed filters, we have attempted to remove these offsets. Our results suggest we have reduced these offsets to one pixel or less both in images taken with the ramps crossed with wideband filters and in the spatial direction of images taken with the ramps crossed with the grism. Offsets in the spectral direction of the grism images cannot be distinguished from a wavelength miscalibration. Data taken of line emission from an astrophysical source through the FR782N filter and compared to ground-based imaging suggest that this filter is well calibrated, in contrast to the result of the crossed filter observations reported here. Ray tracing simulations, deeper second order grism spectra, and further observations of astrophysical targets with known strong spectral features should be able to determine the extent to which the wavelength offsets reported here are real or an artifact of the calibration method.
Fruchter Andrew S.
Pirzkal Nor
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