Improvements to the COS FUV G130M and G160M Wavelength Solutions at Lifetime Position 1
Abstract
The wavelength dispersion coefficients and zero points of the COS FUV G130M and G160M gratings at each lifetime position (LP1, LP2, LP3, LP4) have been re-derived. In this document we present the analysis behind the improvements of the wavelength solutions for data obtained at LP1 (i.e., before July 2012). Discussions of the methodology used to derive updated wavelength solutions at lifetime positions 2, 3, and 4 are presented in separate documents. In this analysis, we have used archival data of objects that were observed with both COS and an overlapping STIS echelle mode to determine the dispersion coefficient and an initial measurement of the zero point for each standard cenwave setting. The zero points were then refined using archival COS programs where multiple cenwaves were used within a single visit, which provided a better relative alignment between COS modes. The wavelength solution accuracy has been improved from 15 km/s (1 resolution element) to 7.5 km/s (0.5 resolution element), with the greatest correction occurring for each grating at the longest cenwaves (i.e., 1327 and 1623).
- Publication:
-
Instrument Science Report COS 2018-22
- Pub Date:
- November 2018
- Bibcode:
- 2018cos..rept...22P
- Keywords:
-
- Hubble Space Telescope;
- HST;
- Space Telescope Science Institute;
- STScI;
- Cosmic Origins Spectrograph;
- COS