COS Lifetime Position.
In the Summer of 2017, the COS FUV spectra will be moved from lifetime position 3 (LP3) to lifetime position 4 (LP4) in order to alleviate the continuing effects of gain sag. Typical spectral resolution (λ/Δλ) is expected to decline by about 15% for observations with the primary science aperture (PSA). Changes in the COS extraction and calibration pipeline have improved the calibration of point-source observations. COS/FUV observations at LP3 and LP4 targeting extended objects or using the Bright Object Aperture (BOA) are more complex. In these cases the standard pipeline calibration will not always produce the flux accuracy achieved for point sources observed with the PSA, and it will be the responsibility of the user to evaluate the adequacy of the spectral extraction and, if necessary, undertake any customized extractions. See Chapter 3 of the COS Data Handbook
for more information.
For Cycle 25 STIS/CCD imaging observations.
Observations with the BAR5 coronagraphic position in concert with specific observing strategies can obtain contrasts for faint point sources of 10-6
beyond 0.55”. For more information, see Section 4.6.4
, and Section 12.11
of the STIS Instrument Handbook
For Cycle 25 STIS spectroscopy with aperture widths smaller than 0.2”.
There is some evidence that in recent years the STIS instrument focus has changed. Because the STIS corrector mechanism has not been moved since 1997, it is unlikely that the focus will be adjusted unless the performance suffers from additional degradation.