|COS Instrument Handbook for Cycle 25|
The COS photon-counting detectors can be harmed by exposure to bright light. Because all COS observations must be checked at STScI by a Contact Scientist to confirm that both the intended target and all nearby objects lie within safe-brightness limits, the total number of targets accepted for all COS and STIS MAMA SNAP programs will be limited to 150 per cycle.For similar reasons, when planning Target of Opportunity (TOO) observations COS observers must ensure that sufficient time is available to allow for STScI screening of targets for compliance with safety limits. Ultra-rapid TOOs, (< 2 days), are not allowed with COS. No COS observations will be performed until the bright object screening has been completed. This process can be greatly accelerated by preliminary discussions with the assigned Contact Scientist to clarify the information that the observer will need to provide to STScI and the criteria that will be used to determine if the target is safe to observe.In the case of irregular variables that are either known to undergo unpredictable outbursts, or belong to classes of objects that are subject to outbursts, the proposer must determine whether the target will violate the bright object limits during outburst. If a violation is possible, the proposer must outline a strategy that will ensure that the target is safe to observe with COS. The observing strategy might include additional observations, obtained over a timescale appropriate to the particular type of variable object, with either HST or ground-based telescopes. If HST data are to be used for this purpose, the required orbits must be requested in Phase I (see Section 4.1.3 of the Call for Proposals). STScI reserves the right to limit the number of visits requiring quiescence verification observations within 20 days or less of an HST observation to no more than 12 such visits per Cycle. Further details about these procedures are presented in ACS ISR 06-04. The general policies described there apply to the STIS/MAMA and COS detectors as well, with suitable scaling for the differences in the exact Bright Object Protection (BOP) limits for each detector and mode. These limits are described in the individual instrument handbooks.For more information on these and other policies pertaining to HST observing, please see the Call for Proposals.