The 0.1X0.2 and 0.1X0.09 apertures were included as Cycle 7 supported apertures and included in the calibration plan for STIS since it was believed at the time that taller slits such as the 0.2X0.2 or 0.2X0.09 would result in order overlap in the E230H mode. On-orbit data shows, however, there is no problem with order overlap with the 0.2 arcsec high slits. Since the 0.2 high slit performs much better with respect to throughput and stability, as well as requiring a much shorter peakup time, and since we know that the 0.1 high slits are not needed for the order separation, we have therefore changed the supported single echelle slits for E230H to 0.2X0.2 and 0.2X0.09 for Cycle 8. Likewise, the 0.1X0.2 and 0.1X0.09 slits will become available-but-unsupported for Cycle 8 (this latter change is made in order to reduce our calibration overhead).

We are therefore recommending you consider changing your selected apertures from the 0.1 high slits to the 0.2 high slits for your Cycle 7 observations. You should take care in rechecking the counts predicted with the ETC for your targets. If you were already very close to the Bright Object Protection limit, it may be necessary to retain the 0.1 high slits to avoid exceeding the BOP limits.

You should also be aware when resubmitting your program with the change in apertures that a warning will be displayed indicating the aperture is not supported. You may ignore this warning and submit your program anyway in this particular case. RPS2 software for Cycle 8 currently being tested and used by your PC will process your proposal properly using the 0.2 high slits.

If you have questions about whether or how to implement the change in your proposal, please contact your CS or PC directly.

Sincerely,

Howard Lanning (STIS Instrument Scientist/User Support Coordinator,410-338-4486)

Stefi Baum (Spectrographs Group Lead - sbaum@stsci.edu, 410-338-4797)