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Observations

Observation modes

Queue mode

Queue mode is the default observation mode for PFS. In Queue mode, the investigator will not attend the observations. They will be carried out by the Subaru staff. The observation plan (including telescope pointing and fiber configurations) will be optimized by proposal rank, target priority, and target visibility to maximize the observation efficiency. The highly-ranked proposals will have higher priority in determining the telescope pointing and the fiber position, while the unused fibers can be assigned to other programs. Note that only highly-ranked proposals can drive the telescope pointing.

Important Queue mode policies for PFS

  1. The fibers will be shared among accepted Queue mode programs.
  2. The exposure time for a single frame is fixed to 15 min.
  3. All Queue mode targets must be fainter than 16 mag (AB mag) over the entire PFS wavelength coverage to avoid detector saturation and to reduce near infrared persistency effects.
  4. The investigators request their observing time for PFS Queue observation in units of "Requested Observing Time (ROT)". ROT is the time needed to complete the program by itself without sharing fibers with others. The ROT is calculated as "Number of PFS Pointing Centers (PPCs)" × 15 min + overhead.
    • ROT does not depend on how many fibers are assigned in a single PPC.
  5. The maximum ROT for a normal program is 35 hours (equivalent to 3.5 nights) within a semester. The ROT for an intensive program is limited to 280 hours (28 nights) over six consecutive semesters and to 140 hours (14 nights) per semester.
  6. Along with the ROT, the "Fiber Hour (FH)" is defined, which is the sum of the exposure time needed for each target.
  7. The observation time is allocated in FH. The allocated FH (FHalloc) can be reduced by the observatory, depending on the score of the proposal.
  8. The effectiveness of the exposure is evaluated in terms of "Effective Exposure Time (EET)". For details on EET, see also here. EET is the S/N-based estimation evaluated with respect to the nominal condition.
    • For example, if a 15 min exposure is taken with relative throughput=0.8 and relative noise=1.2 with respect to the nominal condition, the effective exposure time is calculated as (0.8 / 1.2)2 × 15 = 6.7 min.
    • If the observing conditions are better than nominal, a 15 min exposure may be counted as, e.g., 20 min. If the conditions are poor instead, it can be, e.g., 5 min.
    • However, when the sum of the EET for a target exceeds the required exposure time for that target, then the observatory does not charge the excess time to the program. For example, if the EET becomes 105 min for targets requesting 100 min, the extra 5 min is not charged to the program.
  9. The completion rate of the program is calculated by Σi EETi / FHalloc, where Σi EETi is the sum of the completed exposure time of all targets.
  10. The Queue proposal will be classified into the following categories.
    • Accepted
    • Non-accepted (used as a filler with higher priorities compared to community/observatory filler)
    • Rejected
  11. No carry-over, regardless of the category of programs.

Classical mode

In Classical mode observations, at least one investigator must attend the observations. Investigators can apply the Classical mode for the following cases where the requested observation does not fit the Queue mode scheme.

Example cases include:

  1. Individual exposures have to be shorter or longer than the default exposure time of Queue (15 min)
  2. The pointing centers have to be fixed by the investigator(s)
  3. Need to repeat several exposures with the same fiber configurations
  4. Time-critical observations
  5. The target list can only be fixed after the proposal deadline (e.g., transient target observations)

Proposers must explain the reason for requesting the Classical mode observations to achieve the science clearly in the proposal. During the review, the time allocation committee and the observatory will judge the necessity of the Classical mode. If the reason for Classical mode is not convincing, it may be switched to Queue mode.

Even with Classical mode, the complete target list must be submitted via PFS Target Uploader before the proposal submission, except for case 5 shown above. It is not allowed to update the target list during the observation preparation phase.

During the Classical mode observations, investigators can set/change the exposure time and repeat the exposure with the same fiber configurations, while the observatory determines the fiber allocations. The pointing centers of the telescope will also be determined by the observatory except case 2 shown above (the observatory still sets the fiber configurations). This is to efficiently use the open fibers for other targets such as community fillers and observatory fillers.

Target of Opportunity (ToO)

ToO observations with PFS will be conducted as Classical mode observations. Therefore, the observers must attend the observations. The ToO trigger must be accepted by the observatory beforehand by following the same procedures as with other instruments (see here), and the ToO targets have to be uploaded via PFS Target Uploader before 9 A.M. one day before the observing night. If a later submission is needed, please contact the observatory before the proposal submission. Open fibers may be used for Queue program targets, community fillers, and observatory fillers.

PFS ToO observations can only be triggered on the nights when the PFS observations are scheduled. In the semester S25B, the execution time of ToO observations will be in a unit of 0.5 nights.

Fillers

The filler targets for PFS are used to fill up the open fibers where targets were not assigned in the Queue/Classical/ToO observations.

Warning: PFS fillers will not affect the telescope pointing!

PFS filler is a completely different category from HSC fillers, which are used to fill the observation time in poor weather conditions. PFS fillers will be used only to assign targets to surplus fibers, and therefore the telescope pointing will not be determined by the fillers. Basically, a filler target that is located at a field where no other Queue/Classical/ToO programs look at will not get observed.

Community fillers

We are not calling for proposals of community fillers for S25B semester. The next call will be for S26A.

Investigators can submit a proposal for community fillers to request observations as a filler. An international call for community filler proposals is issued every two semesters, and the accepted programs run for two consecutive semesters.

  • The duplicated submission of the same proposal to the normal program and the community filler program is not allowed.
  • The investigator must explain the reason for applying for the community filler and why it cannot be done with the normal program.
  • The proposals are reviewed by the distributed peer review process, i.e. investigators (either the PI or the Co-I) review each other’s proposals.
  • The upper limit on the target sample size and source brightness may be imposed for technical reasons.
    • If the investigator requests more than 100K targets, the observatory may ask the investigator to reduce targets for technical reasons. Prepare the proposal with this possibility in mind.
    • All targets have to be fainter than 17th magnitude over the entire PFS wavelength coverage.

The target of the accepted program has a standard proprietary period (1.5 years). Investigators cannot access the raw data during the proprietary period, but will receive the fully reduced and calibrated spectra data through the PFS science platform.

If a target included in a community filler program is also targeted in accepted normal programs or other community filler programs that have higher priorities, it will be excluded from its list. The investigators of this filler program cannot access to the data even if the target is observed.

Observatory fillers

Observatory fillers are the targets that are prepared by the observatory, to fill the remaining fibers after assigning community filler targets. The PS1 sources with iP1 = 18–21 mag will be used in Observatory filler. If a source is targeted in accepted normal proposals or community filler programs, it will be excluded from the observatory filler program.

The fully reduced and calibrated spectra of the observatory filler targets will be made public after every observing run or every semester from the PFS science platform. The raw data will be released to the public after 1.5 years.

Proposal and observation preparations

Duplication restrictions with PFS Subaru Strategic Program (SSP) targets

The submission of Normal (Queue/Classical) and Community filler programs that duplicate the PFS SSP is prohibited. Any proposal with both science goals and observation fields identical to those of the SSP will be considered a duplicate. Even if the observation targets or required sensitivity differ, it may still be regarded as a duplicate if both criteria match. Observing any of the seven dwarf galaxies that are targets of the SSP will be considered a duplicate. In any case, please clearly specify the differences from the SSP in the section "17. Justify Duplications with the ongoing SSP" of the proposal format. See here for the PFS SSP proposal.

Please read the instructions below very carefully when applying for PFS observations.

Tutorial materials

Tutorial materials are available for the proposal preparation.

Queue mode preparations

  1. Prepare the target list and submit it via PFS Target uploader

    The PI must first upload the complete target list through PFS Target Uploader before proposal submission. Through the process of uploading the target list, the total Fiber Hour (FH) and the Requested observing time (ROT) will be calculated. The basic procedure to upload the target list is as follows.

    • Prepare the target list which contains all of the targets to be observed in csv format, including all mandatory fields.
    • Validate the target list. Check the output message and revise the target list if needed.
    • Simulate the required observation time and the number of "pointing centers" to complete the observations.
    • Submit and record the Upload ID which will be issued upon completion. See here when the ID is lost.

    Please check the PFS Target Uploader User Guide for the detailed procedure for each step. PFS Target Uploader Demo is also available.

    Calibration for targets at low Dec. or low galactic latitudes

    If an investigator plans to target at Dec. < -30 deg or |Galactic latitude| < 10 deg, please contact the observatory in advance. The observatory does not have calibration objects (sky objects in particular) there, and we may ask investigators to prepare the objects by themselves.

  2. Submit the proposal with the Upload ID

    The proposal for openuse of Subaru Telescope must be submitted via ProMS following the steps below. For time-exchange and UH proposals, please follow their instructions.

    • Use the application form for the PFS Queue mode.
    • All of the information including the Upload ID must be specified clearly. Observatory staff must be able to conduct observations without further interaction with PI.
    • Attach the template shown below at section 15 "Technical Justification" of the proposal.

    Warning: No adjustments allowed after submission!

    Submitting the proposal means that the preparation for the observation is also completed. All targets/configurations must be uploaded through the PFS Target Uploader before proposal submission.

Classical mode preparations

Proposal preparation

The proposal preparation procedure is basically the same as Queue mode. Use the application form for 'Normal+Intensive' program. All of the targets must be uploaded before submitting the proposal. Please follow the steps shown above.

  • To fix the pointing centers (telescope pointing coordinates), create an additional list following the instructions here and upload it through "User-defined pointing list" at the "config" tab of PFS Target Uploader.
  • When the target can only be fixed before the observations, the investigator should use PFS Spectral Simulator and PFS Target Uploader to simulate exposure time and the pointing centers.
  • After the pointing simulation, convert the estimated ROT to the number of nights to fill out the Total Requested Number of Nights and the Minimum Acceptable Number of Nights in Section 12 of the proposal form. The conversion is given as 10 hours (ROT) = 1 night. The maximum number of nights that can be requested is 5 nights, which is the same as the Classical programs of other instruments. That is, the maximum applicant ROT is 50 hours (= 10 hours x 5 nights). Please IGNORE the warning message about ROT in PFS Target Uploader if the planning ROT is greater than 35 hours.
  • In Section 14 of the proposal form, along with Upload ID, please summarize the property of the target list (i.e., observing area, number of targets, etc.) If the target list cannot be fixed at the time of the proposal, please contact us before the proposal submission.
  • Attach the template shown below at section 15 "Technical Justification" of the proposal.

Observation preparation

The telescope pointing centers will be determined by the observatory, by taking into account the target information for the Classical mode, while the open fibers may be allocated to targets of Queue program targets, community fillers, and observatory fillers. The pfsDesign file (which contains detailed information of the targets, fiber assignment, allocated standard stars, etc.) will be sent to the investigator before the observations, and should be reviewed by the investigator. The investigator can modify the exposure time for each pfsDesign file, but not the targets and fiber allocations. The exposure time can also be modified during the observation.

In the case that the targets are not fixed at the proposal submission phase, investigators must fix and upload the targets 1 week before the PFS run of the scheduled night and submit the target list via PFS Target Uploader. The observatory will inform investigators how to review the pfsDesign files.

ToO preparations

Proposal preparation

Use the application form for the 'Normal+Intensive' program. The investigator should use PFS Spectral Simulator and PFS Target Uploader to simulate exposure time and the pointing centers to describe the observation plan when the ToO is triggered (e.g., number of targets (or density), required S/N, exposure time for the typical object that is assumed to be observed, total required nights, etc.).

Observation preparation

The investigator must receive an approval from the observatory first, and upload the target information via PFS Target Uploader. No changes to the target list are allowed after sending the trigger request. The telescope pointing centers will be determined by the observatory, by taking the target information for the ToO into account, while the open fibers may be allocated to targets of Queue program targets, community fillers, and observatory fillers. The pfsDesign file (which contains detailed information on the targets, fiber assignment, allocated standard stars, etc.) will be sent to the investigator before the observations. The observers must review the created pfsDesign files.

Community filler preparations

We are not calling for proposals of community fillers for S25B semester. The next call will be for S26A.

The proposal preparation for the community filler is basically the same as Queue mode, however, the simulation of the pointing centers and the observation time are not needed. Please follow the steps shown above to upload the target list. Use the application form for PFS Community Filler.

  • Note that the reason for applying for the community filler (instead of the normal programs) must be clearly specified.
  • It is not allowed to change/modify the target list after the proposal submission.
  • Community filler proposal does not require the description of Technical justification.

Template of Technical Justification

The observatory will check consistency between the description in the proposal and uploaded PPC plans through section 15 "Technical Justification" of the proposal for Queue and Classical (including ToO) modes. Please include the information below at this section. Descriptions of technical justification is not required in a community filler proposal.

  1. Brightness range of the target in the target list that the investigator uploaded via PFS Target Uploader: Averaged, Faintest, and Brightest values in AB magnitudes or nJy.
  2. obj_id: the ‘obj_id’ of the target used for the estimation with PFS Spectral Simulator.
    • The ‘obj_id’ is at the 2nd column in the target list to be uploaded via PFS Target Uploader.
    • Input “N/A” if target list is not available at submission of the proposal (e.g., transient, ToO).
  3. Attach the parameters used in PFS Spectral Simulator, which can be downloaded as shown below.
    • Attach for just one of the representative (highest prioritized) targets in the target list. Attaching this information for all targets is not required.
    • If it is necessary to show estimations of multiple targets for scientific justification (e.g., there are special requirements for observation plans because of different object types/classes), list the “[16] Simulation ID” recorded in TJ_template file with the “obj_id” only for representative targets. Even in this case, please keep the number to the minimum required.

  4. Justifications for specific cases:

    For Queue mode:

    • If the target location is Dec. < -30 deg or |Galactic latitude| < 10 deg, please describe whether the investigator have communicated in advance with the observatory regarding the assignment of calibration stars.

    For Classical mode:

    • Justify why the investigator requires the observation to be in Classical mode.
    • Explain why the target list is not available when the proposal is submitted (e.g., transient, ToO).
    • If the target location is Dec. < -30 deg or |Galactic latitude| < 10 deg, please describe whether the investigator has communicated with the observatory in advance regarding the assignment of calibration stars and the communication outline (same as Queue mode).

How to get parameters

After running the PFS Spectral Simulator, the “TJ template (.txt)” button will appear in "Download Results" as shown in the figure below.

TJ_template

Click this button to get all parameters that is used in the exposure time calculation. Please copy and paste the information below to "Section 15. Technical Justification".

[1] Template spectrum: Flat in frequency;
[2] AB mag: 20.0;
[3] Wavelength: 550.0;
[4] Redshift: 0.0;
[5] (1) Emission line flux: 1e-17, (2) Emission line width 70.0;
[6] (1) Galactic extinction: 0.0, (2) Effective radius: 0.3;
[7] Seeing FWHM: 0.8;
[8] Throughput degradation factor: 1.0;
[9] Moon zenith angle: 30;
[10] Moon-target separation: 60;
[11] Moon phase: 0.0;
[12] Exposure time: 900;
[13] Number of exposures: 1;
[14] Distance from FoV center: 0.0;
[15] Zenith angle: 45;
[16] SimulationID: 20240726-185758-35b997982c5cb62e

Additional information

Overheads

Overhead time will be approximately 1.2 hours per night for calibration and focusing, in addition to 5 min per pointing. This is taken into account in the ROT calculation in PFS Target Uploader. Therefore, investigators do not need to consider overheads separately during preparations.

In addition to the above default overheads, there is a possibility of conducting additional calibration (once or a few times) to check fiber throughput during observations. Each calibration takes approximately 25 minutes. The decision will be based on the condition of the instrument in each run.

Fiber allocation of standard and sky objects

Flux standards and sky objects must be observed in the same exposure as science objects. Those exposure times are, therefore, the same for the science objects. The figure shows an example of a fiber-allocated field of view.

Fiber_allocation_map

Possible contamination by bright objects in neighboring fibers

Wings of a fiber trace overlap with those of adjacent fibers. The data processing pipeline attempts to "deblend" the wings, but a faint spectrum next to a bright spectrum may be contaminated. To avoid such contamination for high-priority targets, the observatory may remove very bright targets from low-priority programs.

Cautions and known issues of the exposure time calculator function

Cautions and known issues of the Exposure Time Calculator (ETC) function used in PFS Spectral Simulator are summarized here.

Note on long exposures

The PFS data processing pipeline is still under active development, and the observatory have not confirmed if the S/N increases as 'sqrt(Texp)', especially with long exposures. For S25B (the same as S25A), we encourage investigators to focus on bright objects with relatively short exposures.

Note on fiber throughput

Careful analyses of recent engineering observations indicate that the throughputs of the fibers are not completely stable with time. This can be a major problem for sky subtraction; we use the sky fibers for sky subtraction, and the variation in fiber throughputs results in over/under-subtraction of the sky lines in science fibers. Work is in progress to understand and mitigate the effect. The investigator interested in (narrow) emission/absorption lines should be aware of this problem.

Relevant documents