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After completion of the sky survey on 1 February 1991 all of the ROSAT observing time will be available to guest investigators. Pointed observation data are subject to proprietary data rights for a period of one year after the data has been made available to the Principal Investigator (PI) in a form suitable for scientific analysis.
There are no restrictions regarding the amount of observing time or the number of targets requested in guest observer proposals (see however § 3.5 ). In particular, proposals requesting large amounts of observing time will not be considered separately from proposals requesting only relatively modest amounts of time. Also, the percentage of observing time spent on long versus short investigations or the amount of observing time spent on various topical issues is not specified.
However, in order to avoid unnecessary duplications of scientific results and waste of observing time, no pointed observations will be approved and scheduled whose scientific output is not likely to exceed the all-sky survey results. Therefore, as a general rule, exposure times requested for pointed observations should considerably exceed the sky survey exposures. From figure the ROSAT all sky survey exposure times can be determined for any position on the sky. Pointings with durations not exceeding the all sky survey exposure by at least a factor of two will not be considered for scheduling unless a guest investigator explicitly demonstrates in her/his proposal that the proposed science cannot be extracted from the survey data.
Individuals interested in pursuing specific research projects using data from the all-sky surveys may contact Prof. J. Trümper with regard to the XRT data and Prof. K. Pounds with regard to the WFC data.
Time-critical observations, i.e., observations with scheduling constraints in addition to those described in Chapter 7 , impose a particular burden on ROSAT mission planning (for more discussion of such observations cf. § 9.5 ). In particular, for ``short-lived'' phenomena, i.e., phenomena where timing within a spacecraft orbit matters, the observability of an event may only be assessed a few weeks prior to scheduling. Too large a percentage of such time-critical observations would reduce the overall ROSAT observing efficiency since the observing schedule would then not be dominated by the visibility slots available for each target but rather by other requirements. Because all time-critical observations must receive highest priority in the scheduling process, their total share will not exceed five percent of the total available observing time. Guest investigators should carefully check whether the requested observations really need to be carried out in a time-critical fashion.