Early Results from the COS Spectroscopic Sensitivity Monitoring Programs

Details Early Results from the COS Spectroscopic Sensitivity Monitoring Programs Early Results from the COS Spectroscopic Sensitivity Monitoring Programs

Aug 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010cos..rept...15o&link_type=abstract

Instrument Science Report COS 2010-15 (v1), 37 pages

Physics

Hubble Space Telescope, Hst, Space Telescope Science Institute, Cos, Cosmic Origins Spectrograph

Scientific paper

We report initial results from the Cosmic Origins Spectrograph spectroscopic sensitivity monitoring calibration programs. For the NUV channel we use both internal and external measurements to determine the time dependence of any sensitivity changes, while for the FUV channel we use only external targets. Time-dependent sensitivity (TDS) trends for the NUV channel appear to be wavelength-independent but gratingdependent. Internal Grating Efficiency Tests (GETs) performed in the NUV show that the bare-Al gratings G225M and G285M are exhibiting declines in efficiency, while the Al+MgF2-coated G185M and G230L gratings appear to be quite stable. The changes in efficiencies for the bare-Al gratings were first noted on the ground and continue in orbit. GET data obtained on the ground indicate efficiency declines relative to the G230L grating of -1.8 ± 0.9%/year for G225M and -5.4 ± 0.6%/year for G285M. The onorbit NUV TDS data obtained using external targets confirms the trends seen with the internal wavecal exposures. In the first 9 months of Cycle 17, the weighted means of the TDS slopes using external targets for G230L and G185M are -1.1 ± 0.4%/year and -0.8±0.4%/year, respectively, while the G225M and G285M gratings on the NUV channel have exhibited on-orbit declines of -3.3 ± 0.3%/year and -10.8 ± 0.2%/year, respectively. We have considered the effect which potentially inaccurate target acquisition had on early FUV monitoring observations. The absolute values of the corrections are small (generally <1%) and the uncertainty in their values is larger than the value of the correction itself, and so we do not apply them. All gratings on the FUV channel are experiencing wavelength-dependent sensitivity degradation, which is worse at longer wavelengths. The behavior is slightly different for each detector segment, possibly reflecting differences in the photocathodes. The G130M grating is exhibiting an average decline in sensitivity of -4.6 ± 0.3%/year for segment A, and -6.3 ± 0.2%/year for segment B, while the G160M grating is on average declining in sensitivity at a rate of -11.2 ± 0.8%/year for segment A, and -12.0 ± 0.4%/year for segment B. Sensitivity degradation of the G140L grating ranges from -4.9±2.3%/year in the interval 955-970 Å, to -10.9±3.5%/year in the interval 1700-1800 Å. The implications of the observed sensitivity changes for Cycle 17 and 18 COS users are presented. A discussion of the cause of the sensitivity degradations is deferred to a later document, as analysis and investigation is still ongoing.

Affiliated with

Also associated with

No associations

Rating

Early Results from the COS Spectroscopic Sensitivity Monitoring Programs does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Early Results from the COS Spectroscopic Sensitivity Monitoring Programs, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Early Results from the COS Spectroscopic Sensitivity Monitoring Programs will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-979323