Call for Proposals
Semester S26B: August 1, 2026 -- January 31, 2027
Subaru Telescope, National Astronomical Observatory of Japan
Subaru Telescope invites observing proposals for Semester S26B. For the instruments available in S26B, please refer to Normal, Intensive or Service program pages. Since each instrument has its own specific restrictions/conditions, applicants are required to consult the relevant instrument page when preparing their proposals. Please also refer to Proposals, How to Submit via webform, Open-use Policy and Telescope webpage(s).
Open-use Schedule for S26B
| Deadline for Normal / Intensive / HSC Queue mode Filler Submission | March 3 (Tue), 2026 12:00 (Noon) in Japan Standard Time (i.e., March 3, 3:00 am in UT) |
|---|---|
| Deadline for Service Program and Phase 2 Submission for all HSC Queue Mode Program Submission | April 1 (Wed), 2026 12:00 (Noon) in Japan Standard Time (i.e., April 1, 3:00 am in UT) |
| Time Allocation Committee | Early May |
| Notification of Selection Results | Mid June |
Webform
the ProMS 2.0 page
How to Submit via webform?
Other instructions
Open-use Policy, and each instrument page
Frequently Asked Questions (FAQ)
We have compiled a list of frequently asked questions based on inquiries received by the Subaru Open-use Team. These FAQs provide practical clarifications on proposal submission, eligibility, observation styles, and system usage, and are intended to supplement the Call for Proposals and related policy documents.
Please refer to the FAQ page before contacting the Subaru Open-use Team.
Important Notice for S26B
| Notice | Description |
|---|---|
| Update on Scientific Justification | The policy for the Scientific Justification format has been updated. See: How to Prepare the Scientific Justification. An Overleaf template that complies with the new formatting policy is also available at: Overleaf template. Use of the template is not mandatory, as long as the proposal complies with the new formatting rules. For service programs, it is now no longer required to include an abstract at the top of the SJ file. The abstract should be entered as plain text in ProMS. |
| Telescope Downtime | Downtime for the S26B period is expected to be about 2.5 months. (1)Main shutter control panel refurbishment will require six nights on two separate three-night occasions, scheduled for October and December. (2) Replacement of the AZ and EL incremental encoders will take approximately 16 weeks, spanning mid-November to February. |
| Guaranteed Time | PFS development team will use 2.0 nights for GT in S26B. |
| Rubin time | Starting with S26A, we will reserve 2.5 nights per semester on Subaru for the Rubin community in return for Japanese PIs’ Rubin/LSST data rights. |
| Nasmyth Beam Switcher (NBS) | The NBS can be used for all IRCS, SCExAO, and REACH observations in shared-risk mode. For more information about the potential effects of the NBS, please visit the IRCS and SCExAO webpage(s). |
| PFS observations and allocation | The PFS observation period is planned for two dark night periods in September and November. The allocation of observation nights for each category during the PFS observation period, including the SSP, will be determined after consulting with the SAC/TAC. |
| Phase 2 Submission Period for HSC Queue Mode | Since S26A, the Phase 2 submission period for HSC Queue mode has been changed.Instead of the typical period following the TAC meeting, submissions are now accepted between the deadlines for Normal/Intensive and Service proposals. Phase 2 forms will be distributed within 1–2 weeks to PIs after the Normal/Intensive proposal deadline. PIs are requested to complete the form—such as preparing the OB list—based on the proposed observing time, and submit it by the Service proposal deadline. Please note that failure to submit the Phase 2 form by the deadline may result in disadvantage. |
| Deadline for Filler proposals for HSC Queue Mode | Since S26A, the Filler proposals must be submitted by the deadline for Normal/Intensive proposals, not for Service proposals. |
| LGS-mode of AO188 | The laser guide star (LGS) system for AO188 will be operated with TBAD (Transponder Based Aircraft Detector) . Please check the AO188 webpage(s) for the latest information. Please prepare for the NGS mode observation as a backup for when LGS performance issues are still standing. Please note that IRD will not be available in LGS-AO188 mode in S26B. |
| Notice for PFS Observation | The Prime Focus Spectrograph (PFS) will be operated in shared-risk mode in S26B. There are several important updates to the policies for Classical‑mode observations and the usage of flux standard stars. Please carefully review the PFS webpage. Please note that observations with science goals and target fields identical to those of the PFS‑SSP are not permitted. PFS applicants should clearly describe how their proposed program differs from the SSP in the PFS application form. For further details, please refer to the “Proposal and Observation Preparations” section on the PFS webpage(s) . |
| Rapid and Non-rapid ToO Programs | There are two types of ToO programs: Non-rapid ToO programs do not require immediate attention and can be executed after 24 hours or more. PIs need to submit their requests by 9:00 am Hawaii time one day before their observing night. Rapid Too programs require immediate attention and need to be executed within 24 hours. PIs can submit their requests within 24 hours. Considering the practical approval procedure, we recommend that PIs trigger several hours before the observation. In the case your proposal includes both rapid and non-rapid ToO, please select "rapid ToO". |
| On-site observation support for the student PI domestic proposals | As requested by the Subaru open-use community, the observatory will continue to accept the "on-site" observations for the student PI domestic proposals in S26B. Please refer to this document which was sent to the PIs of these programs in S26A, as a reference. |
| Status of Visiting Instruments/devices (PI Instrument/devices) | Following instruments/module are offered for open-use in S26B: - CHARIS: NGS-AO188 or NIRWFS-AO3k mode with SCExAO (including spectro-polarimetric mode) - VAMPIRES: NGS-AO188 or NIRWFS-AO3k mode with SCExAO (cameras have been upgraded for improved sensitivity, speed, and dynamic range. A new multi-band imaging mode is available.) - Fast PDI: NGS-AO188 or NIRWFS-AO3k mode with SCExAO (under shared-risk mode) - REACH (combination of SCExAO and IRD for single-mode fiber spectroscopy) - IRD: NGS-AO188 mode - NsIR Wave Plate Unit (a visiting device for IRCS/SCExAO polarimetry mode) - NIR WFS (a near-infrared wavefront sensor inside the AO188 instead of the visible wavefront sensor) - FIRST-PL: NIRWFS-Ao3k mode with SCExAO The laser guide star (LGS) system can be used with IRD under shared-risk mode. CHARIS, FastPDI and VAMPIRES can be used together at the same time as the modules of SCExAO. Please check the relevant webpage(s) for the latest information. Proposals to use visiting instruments/devices must include the relevant PIs as Co-investigators. Visiting instruments may be used in intensive programs if necessary conditions are fulfilled. Please check the Intensive webpage(s). |
Reminder About Basic Information
| Reminder | Description |
|---|---|
| One Proposal for One Project | The description of the ‘One Proposal for One Project’ principle in the Normal Program has been revised to provide a more specific and precise explanation. |
| Dual Anonymous (DA) Review System | Subaru SAC and TAC decided to implement a DA review system for Subaru proposal review from S23B (see Subaru Open-use Policy for more details). Please prepare proposals following the DA writing style described in How to Submit via webform?. |
| Requested time for queue-mode proposals | According to the SAC decision, the allocation time of HSC/PFS Queue-mode proposals will consider 30% bad weather factor in order to increase the observation completion rate by ensuring sufficient observation time. To keep the limitation of the maximum nights, the requested time in HSC/PFS Queue-mode should not exceed 3.5 nights for the normal program and 28 nights for the intensive program. |
| PFS Community Filler | The PFS Community Filler program is open for proposals only during "A" semesters. Users applying through the Subaru Open-Use framework, the Keck/Gemini–Subaru time exchange program, as well as UH-affiliated users, must submit their proposals via ProMS. The deadline is the same as that for Normal and Intensive programs. For further details, please refer to the PFS page. |
| Programs that use both HSC and PFS | Because of the operational constraints, exchanging HSC and PFS within each run is not recommended. |
| Classification of ToO Programs: Rapid and Non-rapid ToO | There are two types of ToO programs: Non-rapid ToO programs do not require immediate attention and can be executed after 24 hours or more. PIs need to submit their requests by 9:00 am Hawaii time one day before their observing night. Rapid Too programs require immediate attention and need to be executed within 24 hours. PIs can submit their requests within 24 hours. Considering the practical approval procedure, we recommend that PIs trigger several hours before the observation. |
| Instrument Switching between IRD, REACH, CHARIS, VAMPIRES and Fast PDI | Instrument switching between IRD, REACH, CHARIS, VAMPIRES and Fast PDI in one or half observation night for one observing proposal is possible. The required time for switching is, - REACH <=> VAMPIRES: 0 (REACH can be used with VAMPIRES simultaneously) - IRD <=> REACH: ~20 minutes (if the laser frequency comb is required for both IRD and REACH, otherwise 5 minutes) - CHARIS, VAMPIRES and FastPDI can run simultaneously: See SCExAO webpage(s) - Other combination: <5 minutes Note that IRD <=> REACH switching with laser frequency comb for both IRD and REACH is allowed up to twice per one night per one observing proposal. |
| Simultaneous use of REACH and CHARIS | REACH can be used simultaneously with CHARIS with any dispersion modes, but the wavelength coverage of CHARIS will be from 1850 nm to the longest wavelengths shown in the REACH and the CHARIS webpage(s). |
| Observation w/o the Windscreen | The windscreen of the Subaru Telescope is continuously out of operation in S26A, and thus tracking accuracy of the telescope may be degraded by high winds. Since observations may be interrupted by high winds, it is recommended that you prepare backup targets with different azimuth angles. |
| Description of Acceptable Observing Date Range | Even though your preferred observing dates are rather limited, you should make your acceptable date range as wide as possible. Half night allocation could be made if necessary. Your proposal would be automatically rejected, in case that we cannot find any observing slot for your program in your acceptable range (even if your proposal is above the borderline of acceptance). |
| Moon-affected Unacceptable Dates | If the Moon is close to the target, the observation could be severely affected by the Moon light and such condition should be avoided. Applicants are responsible to avoid such condition to occur by specifying the inconvenient/unacceptable dates in Hawaii Standard Time. Those inconvenient or unacceptable dates should be explicitly indicated in Entry 13 (Scheduling Requirements). |
| 2nd Choice Instruments | If your science goal could (fully or partly) be achieved by other instruments (of Subaru/Keck/Gemini) instead of your 1st choice instrument, we recommend that you describe such alternative instruments, which may be usable/acceptable to achieve your science goal, as 2nd choice instrument(s). If you choose a PI-Type instrument as a 2nd choice instrument, you need to get approval from the PI of PI-Type instrument. |
| Duplicated Submission Unallowable | Any identical proposal of the same science and targets using the same instrument and telescope should not be submitted at the same time through different TAC processes. For example, if a proposal using Keck or Gemini was once submitted to Subaru time-exchange program, it should not be applied to the ordinary proposal selection on Keck or Gemini side in the same semester (and vice versa). |
updated on February 3, 2026