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Hubble Space Telescope Call for Proposals for Cycle 22 > Chapter 4: Observation Types and Special Requirements > 4.2 Parallel Observations

4.2 Parallel Observations
Since the scientific instruments are located at fixed positions in the telescope focal plane, it is possible to increase the productivity of HST by observing simultaneously with one or more instruments in addition to the primary instrument. Those additional observations are called parallel observations.
Since each instrument samples a different portion of the HST focal plane (see Figure 2.2 of the HST Primer), an instrument used in parallel mode will normally be pointing at a “random” area of sky several minutes of arc away from the primary target. Thus parallel observations are usually of a survey nature. However, many HST targets lie within extended objects such as star clusters or galaxies, making it possible to conduct parallel observations of nearby portions of, or even specific targets within, these objects.
Depending on whether a parallel observation is related to any specific primary observation, it is defined either as a Coordinated Parallel or Pure Parallel. Coordinated Parallel observations are related to a particular primary observation in the same proposal. Pure Parallel observations are unrelated to any particular primary observation (i.e., the primary observation is in another program). Investigators interested in proposing for parallels must consult the Parallel Observations User Information Report, which provides further details on how coordinated and pure parallels are defined, implemented and scheduled.
Parallel observations are rarely permitted to interfere significantly with primary observations; this restriction applies both to concurrent and subsequent observations. Specifically,
4.2.1 Coordinated Parallel Observations
Coordinated Parallels use one or more instruments, in addition to and simultaneously with the primary instrument in the same proposal, e.g., to observe several adjacent targets or regions within an extended object. Proposals that include Coordinated Parallel observations should provide a scientific justification for and description of the parallel observations. It should be clearly indicated whether the parallel observations are essential to the interpretation of the primary observations or the science program as a whole, or whether they address partly or completely unrelated issues. The parallel observations are subject to scientific review, and can be rejected even if the primary observations are approved.
Proposers are generally not allowed to add Coordinated Parallel observations in Phase II that were not explicitly included and approved in Phase I. Any such requests will be adjudicated by the Telescope Time Review Board (TTRB). Coordinated Parallel Observations will ordinarily be given the same proprietary period as their associated primary observations.
4.2.2 Pure Parallel Observations
The Pure Parallel observing process is designed to take advantage of the full complement of instruments installed in SM4. Similar to primary science planning, the parallels process provides a reliable estimate, in advance of observations, of the number of orbits that will be executed on accepted parallel programs during the cycle. The Parallel Observing User Information Report provides a complete description of this observing mode and is required reading if you are considering submitting a Pure Parallel Proposal. It is anticipated that up to 500 Pure Parallel observations will be available in Cycle 22.
Restrictions
Pure Parallel observations are currently restricted to orbits where COS and STIS are the primary instruments. Consequently, parallel opportunities will be limited by the actual number of orbits allocated to these instruments and to the corresponding regions of sky being observed. Past experience shows that the final allocation of Pure Parallel orbits also depends on the science goals of the parallel programs (e.g. desired targets may not be available and multiple Pure Parallel Programs can compete for the same primary opportunities.) STScI continues to investigate ways to expand the number of Pure Parallel observing opportunities.
For the purpose of Pure Parallel orbit allocation, an orbit is defined as having visibility of at least 2500 seconds. The number and types of parallel observing opportunities will vary depending on the mix of primary GO Programs each cycle. Additionally, the total number of Pure Parallel orbits actually executed could be less than planned due to changes to the Primary Programs or on-board execution failures. For Cycle 21, opportunities totaling 515 orbits were found to satisfy the 350-orbit TAC allocation to one Pure Parallel Program. Time not requested but potentially also available included 60 one-orbit and 39 two-orbit pure parallel opportunities.
PIs with accepted Pure Parallel Programs will be given a list of parallel science opportunities that STScI has identified as being suitable for their program. The PI then selects and submits a final list of opportunity matches to STScI in the Phase II Pure Parallel Program submission.
The process of matching Pure Parallel observations to Primary Programs will occur during the planning and implementation phase (Phase II) so that it can be known in advance when and how the parallel observations can be executed. Proposals for Pure Parallel observations may specify either particular or generic targets, although the latter are more common and provide more flexibility for matching parallel observations to actual opportunities.
Review and Execution
The review panels and the TAC will select the programs based on the proposed science. The TAC will consider all accepted programs and produce a ranked list as an aid for resolving potential conflicts. The proprietary period for a GO Pure Parallel Program will depend on the number of orbits requested, as is the case for Primary GO Programs. Small (1-34 orbits) and Medium (35-74 orbits) Pure Parallel Programs will have a default proprietary period of 12 months; Large (75 orbits or more) Pure Parallel Programs will have no proprietary period by default. Pure Parallel observations are assigned to specific primary observations, and the parallel observations will be carried over to subsequent cycles if the primary observations are not executed in Cycle 22.
4.2.3 Restrictions and Limitations on Parallel Observations
Parallel Observations with ACS
The ACS/SBC may not be used for either Pure or Coordinated Parallel observations in any mode.
The ACS/WFC detector may be used for Coordinated Parallel observations with any other instrument as primary.
The ACS/WFC may be used for Pure Parallel observations with the COS and STIS instruments as primary (see Section 4.2.2).
Parallel Observations with COS
The COS/FUV MCP detector may be used for Coordinated Parallel observations with any other instrument as primary, provided that the telescope orientation is specified exactly and the parallel field passes bright-object checking.
The COS/NUV MAMA detector may be used for Coordinated Parallel observations with any other instrument as primary, provided that the telescope orientation is specified exactly and the parallel field passes bright-object checking.
COS may not be used for Pure Parallel observations in any detector mode.
Parallel Observations with FGS
The FGS cannot be used for either Pure or Coordinated Parallel observations.
Parallel Observations with STIS
The STIS/CCD detector may be used for Coordinated Parallel observations with any other instrument as primary.
Neither the STIS/NUV-MAMA PRISM mode nor any STIS/MAMA imaging mode can be used for Coordinated Parallel observations.
STIS/MAMA spectroscopic modes (other than the NUV/PRISM) may be used for Coordinated Parallel observations, but only if an exact ORIENT is specified.
STIS may not be used for Pure Parallel observations in any detector mode.
When STIS is the primary instrument and another instrument is used for a Coordinated Parallel, STIS auto-wavecals will never be done during an occultation. Instead these calibration exposures have to be scheduled when the external target is visible, leading to a slight reduction in the observing efficiency.
Parallel Observations with WFC3
WFC3 may be used for Coordinated Parallel observations with any other instrument as primary. WFC3 may only be used for Pure Parallel observations with COS or STIS as primary (see Section 4.2.2).
Pointing Accuracy for Parallel Observations
The spacecraft computers automatically correct the telescope pointing of the primary observing aperture for the effect of differential velocity aberration. This means that image shifts at the parallel aperture of 10 to 20 mas can occur during parallel exposures.

Hubble Space Telescope Call for Proposals for Cycle 22 > Chapter 4: Observation Types and Special Requirements > 4.2 Parallel Observations

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