2.6 Prime and Parallel Observing: MAMA Bright Object Constraints

The STIS ultraviolet MAMA detectors are subject to damage at high illumination rates, as explained in greater detail in Section 7.6. To protect the instrument, we have established limits on the maximum count rate at which the detectors may be illuminated. These count-rate limits translate into a set of configuration dependent bright-object screening magnitudes. The spectroscopic bright-object screening magnitudes are summarized in Table 13.44, and the imaging counterparts in Table 14.39.

STScI will perform screening of all MAMA exposures prior to scheduling. Targets not established as safe for the configuration in which they are being observed will not be scheduled. Observations that pass screening but are lost in orbit due to a bright-object violation will not be rescheduled. Observers are responsible for assuring that their observations do not violate the MAMA count-rate limits. A detailed description of the MAMA bright-object limits and the observers' responsibility is presented in Section 7.6. and in STIS ISR 2000-01.

To assure that STScI can adequately screen observations, special constraints are imposed on parallel observing with the MAMAs:

• No pure parallels are allowed using the MAMA detectors.
• Coordinated parallels are allowed with the MAMA detectors only if an exact spacecraft orientation (ORIENT) is requested and the RA and Dec of the parallel field determined. Note that the specification of an exact orient usually limits the scheduling of observations to a ~4-8 week period each year. The observer is responsible for assuring that observations do not violate the MAMA count rate limits both for coordinated parallel MAMA observations and for primes.

Targets that are one magnitude or more fainter than the magnitude limits in the screening tables generally automatically pass screening. For a target that is within one magnitude of the screening limits after correction for extinction and slit losses, observers must provide a spectrum of the source at the intended observing wavelength. If such a spectrum is not available, the prospective General Observer (GO) must request an orbit in Phase 1 for a pre-qualification exposure, during which the target spectrum must be determined by observation in an allowed configuration (see Section 7.6 for more details).

Normal MAMA bright object limits apply to all objects that may be within 5 arc-seconds of the entrance aperture. In addition, there are special limits that apply to any extremely bright object that may be within 13.5 arc-seconds of the aperture. Full details are given in Section 7.6.4.

Please also note that if you are proposing MAMA target-of-opportunity observations, we ask you to provide an explanation in your Phase 1 proposal of how you will ensure that your target can be safely observed.