HST Phase II Proposal Instructions for Cycle 12 (RPS2)
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| HST Phase II Proposal Instructions for Cycle 12 (RPS2) | |||
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HST is, of course, a telescope with instruments that have relatively small apertures that must be accurately pointed to achieve useful scientific results. However, the value of "parallel" observations was recognized during the earliest stages of HST's design because by turning on other instruments one could discover new objects and new phenomena, or just acquire highly detailed images of random regions of the sky that are the equivalent of a survey. This parallel capability was present to a limited degree at launch, but it has become especially important since the fourth servicing mission because now WFPC2 and STIS can both work at the same time with ACS and NICMOS.
Parallel science refers to the use of two or more Science Instruments at the same time. The primary observation is the one that has determined the pointing of HST and it always takes precedence. The parallel observation is the one enabled to take place because the primary observation permits suitable conditions, but the parallel observation must never interfere with the primary. Although parallel observations are conceptually simple (e.g., "Turn on WFPC2 with the F555W filter while STIS is in use"), they are, in fact, complex to execute. Commanding the instruments for parallels and primaries at the same time requires strict observance of complex timing rules in order to avoid damage to instruments. Some special restrictions must be applied in order to effectively schedule and execute parallel observations.
From the point of view of the HST ground systems there are two types of parallel exposures: pure and coordinated parallels.
- Coordinated parallels are written to be part of the same proposal, with the intention of scheduling the primary and the parallels together. Coordinated parallels are inextricably linked with their primaries: both must be scheduled in order for either to be scheduled.
- Pure parallels are scheduled separately from primaries late in the scheduling process (essentially after the primary science schedule has been completely constructed). This type of parallel must be used whenever the primary and parallel exposures come from different proposals. The scheduling of pure parallels has no effect on the primary schedule: pure parallels will be placed on the schedule only when there are suitable opportunities available.
6.1 Parallel Science Limitations
These restrictions are to ensure that parallels can be scheduled and executed safely and efficiently:
- Parallel observations have some special restrictions on the targets that may be specified; see 6.2 "Pure Parallels" and 6.3 "Coordinated Parallels" for details.
- All scheduling constraints (pointing, orientation, and relative timing) that apply to coordinated primaries and parallels must be specified only on the primary exposure.
- No visit-level special requirements, and only a few exposure-level special requirements, are applicable to pure parallel visits.
- Exposures parallel with any instrument mode which permits interactive or autonomous motion of HST (e.g., interactive or onboard acquisitions) are not supported.
- Neither parallel exposures nor the primary of a coordinated parallel may have real-time (i.e., TDRS contact) requirements of any kind.
- Parallel observations may not be made while STIS MAMA TIME-TAG observations are being made.
These limitations are discussed further below.
6.2 Pure Parallels
Pure parallel visits are identified by a Proposal_Category (see 2.3.1 "Proposal Information [Proposal_Information]") that ends with /PAR (not the former PARallel visit special requirement). All visits in such proposals will be interpreted as pure parallel visits. Pure parallel proposals require additional information at the proposal level to specify pointing tolerances (see 2.3.2 "Parallel Information [Parallel_Pointing_Tolerance]"). At the visit level, the Visit_Priority (see 5.2 "Visit Priority [Visit_Priority]") must be specified to provide guidance for the scheduling system.
Parallel visits using the same target will be considered in order of Visit_Priority. A range of visits designed for opportunities of different lengths (say 1 to 10 orbits) is recommended, with the longer visits being given higher priority. At each opportunity on the calendar which matches the pointing of a set of parallel visits and whose pointing is stable within the proposal's Parallel_Pointing_Tolerance, STScI will schedule the highest-priority visit that fits in the opportunity. Exposures within a visit will be obtained consecutively and in the order specified, just as with primary visits.
How Pure Parallels Are Scheduled
Observer-defined visits correspond to scheduling units (SUs) in the HST ground system. An SU is a set of exposures which must be scheduled at the same time. An SU with coordinated parallel exposures is scheduled just like one without parallels. However, pure parallel SUs are scheduled through a separate process.
First the scheduling system builds a calendar from primary visits. Once the primary calendar is complete, a description of it is used to find appropriate parallel SUs to match the opportunities from the primary calendar. These parallels are then scheduled, subject to the constraints of the primary SUs already on the calendar.
While a primary visit is only scheduled once, a parallel visit may be scheduled many times (and generating a new SU each time) whenever it is the most appropriate use of an opportunity on the calendar. On the other hand, if a parallel visit never turns out to be the most appropriate, it will never be scheduled at all.
Instrument Configuration
Pure parallel exposures are limited to the following instrument configurations and modes:
Configuration Operating Mode WFPC2 IMAGE STIS/CCD ACCUM ACS/WFC ACCUM ACS/HRC ACCUM NIC1 or NIC2 or NIC3 ACCUM, MULTIACCUM
Every exposure in a pure parallel proposal must use the same instrument.
Special Requirements
No visit-level special requirements are allowed in pure-parallel visits. Exposure-level special requirements are limited to the following:
MAXimum DURation; MINimum DURation;
PARallel <parallel-exp-list> WITH <primary-exp-list>1 (Restricted)
SEQuence <exposure-list> NON-INTerruptible
We recommend that MINimum DURation, plus either MAXimum DURation or EXPAND, be specified on all pure-parallel exposures, except with NICMOS, where no adjustment of exposure time is possible. If MIN DUR is omitted, the default minimum exposure time is set to 80% of Time_Per_Exposure. If MAX DUR is omitted, the default maximum exposure time is unlimited if EXPAND is specified, and is otherwise set to 120% of Time_Per_Exposure.
For visits intended to span multiple orbits, END ORBIT should be specified on the exposure that is intended to end each orbit in order to provide STScI with better guidance in matching parallel visits to the sizes of opportunities.
Optional Parameters
Dithering parameters and wavelength scans with the WFPC2 linear ramp filter are not permitted with pure parallels because the pointing is determined by the primary observation.
For ACS pure parallels, no automatic image exposures in conjunction with HRC prism observations will be scheduled. The usual default of AUTOIMAGE=YES does not apply, and the AUTOIMAGE optional parameter may not be specified.
6.3 Coordinated Parallels
Coordinated parallel exposures are indicated by the exposure-level special requirement:
This designates a set of one or more parallel exposures which will execute in parallel with a set of one or more primary exposures in the same visit. Parallel exposures using the same SI or NICMOS detectorwill be executed in the order specified on the Visit/Exposure Logsheet. The first parallel exposure which uses a given instrument or NICMOS detector will be executed as early as possible, but not before the first primary exposure.
The PARallel WITH special requirement must appear on the first exposure in the <primary-exp-list>. Exposures in the <parallel-exp-list> must appear on the Visit/Exposure Logsheet immediately after the exposures in <primary-exp-list>. Parallel exposure numbers should follow this sequence as well.
6.3.1 Instrument Configuration
The exposures in <primary-exp-list> and <parallel-exp-list> are limited to the following instrument configurations and modes:
WFPC2 IMAGE STIS/FUV-MAMA1 ACCUM STIS/NUV-MAMA1 ACCUM STIS/CCD ACCUM FGS2 POS ACS/WFC3 ACCUM ACS/HRC3 ACCUM ACS/SBC3,4 ACCUM
1In order to protect the STIS MAMA detectors from inadvertent overillumination, they may be used as coordinated parallels only if an exact spacecraft orientation (ORIENTation) is specified, the coordinates of the parallel field are determined, and the parallel target or field passes the same bright-object screening applied to MAMA primary observations.
2FGS exposures may only be used in the <primary-exp-list>, never in the <parallel-exp-list>.
3ACS exposures cannot be used in both the <primary-exp-list> and the <parallel-exp-list>, and all ACS exposures in the <parallel-exp-list> must use the same configuration.
4In order to protect the ACS SBC detector from inadvertent overillumination, the ACS/SBC configuration may be used for coordinated parallels only if an exact spacecraft orientation (see ORIENTation <angle1> TO <angle2>) is specified, the coordinates of the parallel field are determined, and the parallel target or field passes the same bright-object screening applied to SBC primary observations.
All exposures in <primary-exp-list> must have the same Instrument Configuration (Config) and the same Aperture or Field of View (Aperture). Except for the NICMOS, no exposure in <parallel-exp-list> may use the same SI as the primary exposures. NICMOS parallel exposures may use the same SI but only in a different configuration.
6.3.2 Targets
Coordinated parallels may specify fixed, generic, or solar system targets; the special target ANY; or internal targets. However, the pointing of HST will be determined only by the primary exposures. Any pointing conditions to be applied on the primary+parallel combination must be specified on the primary exposures via exposure-level special requirements, or on the visit as a whole via visit-level special requirements. All external exposures in a given <primary-exp-list> must have the same pointing (this generally means the same target, aperture, and POS TARG), except for NICMOS background patterns (see the discussion of optional parameters below).
If a parallel exposure specifies a fixed target, it should be a different target from the primary ones and should appear in the Target List. In this case, an ORIENTation special requirement is required to ensure that the parallel target is in the aperture. It is the observer's responsibility to verify that the specified orientation will place the parallel target in the aperture; STScI will not check the geometry. Contact your Program Coordinator if you need assistance.
If the parallel target is diffuse and the orientation does not matter, a generic target specification should be used. If there is no parallel target as such, and the intent is just to sample whatever the parallel aperture happens to fall on, the ANY target (which should not appear in the Target List) should be used. Generic targets or target ANY should only be used in one of these three cases:
- The exposure is PARALLEL WITH or SAME POS AS another exposure (so that the pointing is determined by the other exposure), or
- The visit is a pure parallel (in which case the target will be matched against already-scheduled observations), or
- The visit is ON HOLD (as with Targets of Opportunity, for example). In this case the target should be replaced by a fixed target when the ON HOLD is removed.
Coordinated parallels and their primaries may not use the WFPC2 UVFLAT or VISFLAT internal targets.
6.3.3 Special Requirements
All the fields on the Visit/Exposure Logsheet should be filled out as for primary exposures. However, the following exposure-level special requirements are disallowed for both primary exposures (any exposure in a <primary-exp-list>) and parallel exposures:
EXPAND MAXimum DURation [<time or percentage>] MINimum DURation [<time or percentage>] RT ANALYSIS
The following exposure-level special requirements are allowed for primary exposures, but not for parallels:
LOW-SKY PHASE <number1> TO <number2> POSition TARget <x-value>, <y-value> REQuires EPHEMeris CORRection <id> REQuires UPLINK SAME POSition AS <exposure> SAVE OFFSET <id> SHADOW USE OFFSET <id>
The following exposure-level special requirements are allowed without restriction:
SEQuence <exposure-list> NON-INTerruptible SAA CONTOUR (WFPC2 only)
No parallel exposure may appear in the <exposure-list> of an RT ANALYSIS FOR Special Requirement, or be the <exposure> referenced by a SAME POSition AS special requirement.
6.3.4 Optional Parameters
The WFPC2 READ=NO option is not allowed, because the WFPC2 CCDs are erased during delays between exposures to avoid cosmic-ray effects.
For ACS coordinated parallels, no automatic image exposures will be scheduled when in conjunction with HRC prism observations. In this case the usual default of AUTOIMAGE=YES does not apply, and the AUTOIMAGE optional parameter may not be specified.
The parameters used with patterns for NICMOS may be used for coordinated parallels subject to the following restrictions and interpretations:
- Only a single NICMOS exposure in the PARallel WITH Special Requirement may use a pattern. This exposure must be the only exposure in <primary-exp-list>. Background pattern parameters may not be used on a parallel exposure, because they involve pointing changes.
- All NICMOS parallel exposures will be taken at each pattern position. Any parallel exposures using other SIs will also be taken at each pattern position.
- Only a single NICMOS exposure in the PARallel WITH special requirement may use a pattern, and no other exposure in the list may use the same configuration. This exposure must be either the only exposure in <primary-exp-list> or the first exposure in <parallel-exp-list>.
- Background pattern parameters may be used on a parallel exposure only if OFFSET=FOM and the primary exposures use an SI other than NICMOS.
- All other NICMOS parallel exposures will be taken at each pattern position. If the exposure using the background patterns is the primary, parallel exposures using other SIs will also be taken at each pattern position.
- If OFFSET=FOM, each sequence of NICMOS exposures in <parallel-exp-list> using a different detector must take no longer to execute than the exposure with OFFSET=FOM.
Within a PARallel WITH special requirement, the NICMOS CAMERA-FOCUS, optional parameter may be used only by one NICMOS detector, referred to as the "primary detector." If the primary exposures use the NICMOS, the primary detector is the one used in those exposures. Otherwise, the primary detector is determined by the configuration used for the first NICMOS exposure in <parallel-exp-list>.
Within a PARallel WITH special requirement, the NICMOS FOMXPOS, FOMYPOS optional parameters may be used only by one NICMOS detector, referred to as the "primary detector." If the primary exposures use the NICMOS, the primary detector is the one used in those exposures. Otherwise, the primary detector is determined by the configuration used for the first NICMOS exposure in <parallel-exp-list>.
6.3.5 Ordering Restrictions and Interpretations
The exposures in the <parallel-exp-list> of a PARallel WITH special requirement must appear on the Visit/Exposure Logsheet immediately after the exposures in <primary-exp-list>.
If the <parallel-exp-list> contains exposures which use different SIs or NICMOS detectors, an attempt will be made to execute each group of exposures with the same SI or NICMOS detector in parallel with the other groups. All exposures within a given group must be contiguous on the logsheet.Groups of parallel exposures using different NICMOS detectors must be contiguous on the logsheet. Within a group, exposures will be executed in the order in which they appear on the logsheet.
Due to readout conflicts and limits on the number of SIs which may execute simultaneously, parallel exposures sometimes have to be delayed. If a parallel exposure conflicts with an exposure in its <primary-exp-list>, the parallel will be delayed. If two parallel exposures using different SIs or NICMOS detectors conflict, the exposure which appears later on the logsheet will be delayed.
Following a set of exposures in <primary-exp-list> and <parallel-exp-list>, subsequent exposures not part of either list will be delayed until after all primary and parallel exposures have completed.
Example 1: Three WFPC2 exposures parallel with three STIS exposures
6.3.6 Efficiency Considerations
Within a set of coordinated-parallel exposures, the ground system will not break up sequences of exposures that are too long to fit in an orbit, as it does for non-coordinated-parallel exposures. Each group of exposures with the same SI or NICMOS detector must be short enough to fit in one orbit. If it is necessary to take coordinated-parallel data over multiple orbits, a separate PARallel WITH special requirement - with a new <primary-exp-list> and <parallel-exp-list> - should be specified for each orbit.
1Coordinated parallel exposures are allowed in pure-parallel visits only to support observing with different NICMOS detectors, not different SIs.
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