COS/FUV Spatial and Spectral Resolution at the new Lifetime Position
Abstract
In order to overcome gain-sag effects, the default position of spectra on the COS FUV detector was recently moved by 3.5" in the positive cross-dispersion direction, and by 0.05" in the dispersion direction. This move to the second "lifetime position", a fresh part of the detector which has not yet experienced significant gain sag, is potentially accompanied by changes in flux calibration, sensitivity, flat-field, and resolution. Hence, special calibration programs were undertaken to characterize the detector at this new lifetime position. In this ISR, we characterize the spatial and spectral resolution at the second COS FUV lifetime position. Code V Optical models of the COS LSFs are generated for modes of the M and L gratings, accounting for mid-frequency wavefront errors (MFWFE). In order to validate the modeling of the COS FUV LSFs, we perform a comparison of spectral line profiles between, on the one hand, COS FUV spectra of SMC O star AV75 acquired at the second lifetime position, and on the other hand previous STIS E140M spectra convolved with models of the COS FUV LSFs at the new lifetime position. Our analysis shows that the model LSFs are consistent with the observations within the measurement errors. In addition, we derive the spatial resolution of the COS FUV gratings at the new lifetime position, as a function of wavelength, from both observations and optical modeling. We show that the theoretical and observed cross- dispersion profiles are in very good agreement.
- Publication:
-
Instrument Science Report COS 2013-07
- Pub Date:
- June 2013
- Bibcode:
- 2013cos..rept....7R
- Keywords:
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- Hubble Space Telescope;
- Space Telescope Science Institute;
- STScI;
- HST