If a science project requires observations with both HST and XMM-Newton, then a single proposal may be submitted to request time on both observatories to the XMM-Newton Announcement of Opportunity, so that it is unnecessary to submit proposals to two separate reviews. The proposal should be submitted to the observatory that represents the primary science.
By agreement with the HST Project, the XMM-Newton Project may award up to 30 orbits of HST observing time. Similarly, the HST Project may award up to 150 ks of XMM-Newton time. The time will be awarded only for highly ranked proposals that require use of both observatories and shall not apply to usage of archival data. The only criterion above and beyond the usual review criteria is that both sets of data are required to meet the primary science goals. Proposers should take special care in justifying both the scientific and technical reasons for requesting observing time on both missions. It is not essential that the project requires simultaneous XMM-Newton and HST observations. No observations with a reaction time of less than 5 working days from an unknown triggering date will be considered for this cooperative programme. Target of opportunity (ToO) proposals must state explicitly whether the HST observations require a disruptive ToO (observations within 14 days of notification). No more than one (1) disruptive ToO will be allocated to the HST Cycle 20 time awarded jointly with XMM observations. It is the responsibility of the PI to inform both observatories immediately if the trigger criterion is fulfilled. For this solicitation, no HST time will be allocated without the need for XMM-Newton time on the same target to complete the proposed investigation.
Establishing technical feasibility is the responsibility of the PI, who should review the XMM-Newton and HST Calls for Proposals and Instrument Handbooks and/or contact the HST Helpdesk at STScI (firstname.lastname@example.org). All standard observing restrictions for both observatories apply to joint proposals. For proposals that are approved, both projects will perform detailed feasibility checks. Both projects reserve the right to reject any approved observation that is in conflict with safety or mission assurance priorities or schedule constraints, or is otherwise deemed to be non-feasible.
Scientists can apply for joint XMM-Newton/HST programme time by selecting the proposal type ``HST/XMM-Newton''. The ``Remarks'' field, which is offered in the RPS should be used to briefly describe the instrument modes and observing time requests for HST.