6.3 Coordinated Parallel Containers

Text Proposal File

In the text proposal file format, coordinated parallel exposures are indicated with the exposure-level special requirement:

PAR <parallel-exp-list> WITH <primary-exp-list>

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. The PAR WITH special requirement must be specified on the first exposure in the <primary-exp-list>. Exposures in the <parallel-exp-list> have to appear immediately after the exposures in <primary-exp-list>. Parallel exposure numbers must follow this sequence as well.

The APT User Interface.

This special requirement has been replaced in the APT GUI with the use of Coordinated Parallel Exposure Containers. See 5.19 Exposure Containers: Exposure Groups, Coordinated Parallels and Patterns.

A Coordinated Parallel Container designates a set of one or more parallel exposures (<parallel-exp-list>) that will execute in parallel with a set of one or more primary exposures (<primary-exp-list) in the same visit. The SI used in the first exposure defines the primary SI (and therefore defines the <primary-exp-list>). All other exposures that use the same SI will also be considered primary.

All exposures using a different SI will be considered parallel. Parallel exposures using the same SI or NICMOS detectorwill be executed in the order specified in the container. 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.

6.3.1 Instrument Configuration

The exposures in <primary-exp-list> and <parallel-exp-list> are limited to the following instrument configurations and modes:

Configuration	Operating Mode
WFPC2	IMAGE
FGS2	POS
ACS/SBC 3,4	ACCUM
NIC1 or NIC2 or NIC35	ACCUM, MULTIACCUM

1 2FGS may only be used as primary, never parallel. 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 ORIENT (e.g., ORIENT 20D to 20D) is specified. Also, the coordinates of the parallel field must be determined and the parallel target or field must pass the same bright-object screening applied to SBC primary observations. 5The foci of NIC1 and NIC2 are close enough that they can be used simultaneously, whereas the focus of NIC3 is sufficiently different from the foci of NIC1 and NIC2 that it should not be used in parallel with either camera. See section 2.4.4 of the NICMOS Instrument Handbook. 6

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 ORIENT 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, or if there is no parallel target as such and the intent is just to sample whatever the parallel aperture happens to fall on, you should select the ANY target (which should not appear in your Target List).

6.3.3 Special Requirements

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:

END ORBIT

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 (replaced by the Exposure Group Container in APT; see 5.19 Exposure Containers: Exposure Groups, Coordinated Parallels and Patterns)

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 POS 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.

The parameters used with patterns for NICMOS may be used for coordinated parallels subject to the following restrictions and interpretations:

1. Only a single NICMOS exposure in a coordinated parallel container may use a pattern; this exposure must be the only exposure designated as primary. Background pattern parameters may not be used on a parallel exposure, because they involve pointing changes.
2. All NICMOS parallel exposures will be taken at each pattern position (defined in the primary exposure). Any parallel exposures using other SIs will also be taken at each pattern position.
3. If the primary is a NICMOS exposure that uses a pattern, no other exposure in the container may use the same configuration.
4. Background pattern parameters may be used on a parallel exposure only if OFFSET=FOM and the primary exposures use an SI other than NICMOS.
5. 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.
6. If OFFSET=FOM, each sequence of NICMOS exposures in the parallel exposure list using a different detector must take no longer to execute than the exposure with OFFSET=FOM.

In a Coordinated Parallel container, the NICMOS CAMERA-FOCUS, FOMXPOS, FOMYPOSoptional parameters (see Sections 12.2.4 and 12.3.4) may be used only by one NICMOS detector, referred to as the "primary detector," which is the SI detector used in the first exposure in the container. 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 the parallel exposures.

6.3.5 Ordering Restrictions and Interpretations

In Coordinated Parallel Containers, the SI used in the first exposure defines the "primary" SI.

If the exposures in the <parallel-exp-list> contain exposures that use different SIs or NICMOS detectors, an attempt will be made to execute each set of exposures with the same SI or NICMOS detector in parallel with the other sets. All exposures within a given set must be contiguous in the container. Also, sets of parallel exposures using different NICMOS detectors must be contiguous in the container. Within a set, exposures will be executed in the order they appear.

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 list, the parallel will be delayed. If two parallel exposures using different SIs or NICMOS detectors conflict, the exposure which appears later in the container will be delayed.

Following a set of exposures in a Parallel Container, subsequent exposures not in the container will be delayed until after all the primary and parallel exposures have completed.

Text Proposal File

In the Text Proposal File, the exposures in the <parallel-exp-list> of a PAR WITH special requirement must appear immediately after the exposures in <primary-exp-list>.

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 Container - with a new set of exposures - should be specified for each orbit.