Call for Proposals
Semester S26A: February 1, 2026 -- July 31, 2026
Subaru Telescope, National Astronomical Observatory of Japan
Subaru Telescope invites observing proposals for Semester S26A. For the instruments available in S26A, 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 S26A
| Deadline for Normal / Intensive / HSC Queue mode Filler / PFS Community Filler Program Submission | September 2 (Tue), 2025 12:00 (Noon) in Japan Standard Time (i.e., September 2, 3:00 am in UT) |
|---|---|
| Deadline for Service Program and Phase 2 Submission for all HSC Queue Mode Program Submission | October 1 (Wed), 2025 12:00 (Noon) in Japan Standard Time (i.e., October 1, 3:00 am in UT) |
| Time Allocation Committee | Early November |
| Notification of Selection Results | Mid December |
Webform
the ProMS 2.0 page
How to Submit via webform?
Other instructions
Open-use Policy, and each instrument page
Important Notice for S26A
| Notice | Description |
|---|---|
| National Astronomical Observatory of Japan (NAOJ) Summer Holidays | The National Astronomical Observatory of Japan (NAOJ) will be closed from Wednesday, August 13 to Sunday, August 17 (Japan Standard Time). During this period, we will be unable to respond to inquiries. |
| Telescope Downtime | Downtime for the S26A period is expected to be up to 11 nights (2 nights for recoating the infrared 3rd mirror, 6 nights for updating the main shutter control panel, and 3 nights for testing the dome rotation motor). |
| Guaranteed Time | PFS development team will use 0.5 night for GT in S26A. |
| Nasmyth Beam Switcher (NBS) | Once installed, the NBS will 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). |
| SSP in S26A | PFS SSP will use about 30 nights and IRD SSP has 0.5 night compensation in S26A. |
| Change in Phase 2 Submission Period for HSC Queue Mode | 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. |
| Change in deadline for Filler proposals for HSC Queue Mode | 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. |
| Hour base ToO trigger in HSC queue mode | Since S25A, ToO observations can be triggered with more than 2 hours in hourly increments during HSC Queue mode observation periods. However, ToO observations with other instruments and classical mode observation periods should be conducted in half-night increments like now. PI or observers should attend ToO observations. Please see the ToO policy (English/Japanese). |
| Intensive Programs that involve a Target of Opportunity (ToO) observation | Eligibility for intensive programs that involve a ToO observation is under discussion. We do not open this mode in S26A. |
| Notice for PFS Observation | The Prime Focus Spectrograph (PFS) will be available for open-use in S26A under shared-risk mode. For the latest information and application procedures, please refer to the PFS webpage(s). We note that it is prohibited to conduct observations with both science goals and observation fields identical to those of the PFS-SSP. For PFS applicants, please describe the differences between your program and the SSP in the application form for PFS applicants. Please visit the “Proposal and observation preparations” section on the PFS webpage(s) for more details. |
| 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 S26A. Please refer to this document which was sent to the PIs of these programs in S25B, as a reference. |
| New Filters for MOIRCS | Three new Medium-band filters (J2, H2, and K2) and two narrow-band filters (BrG_ON amd BrG_OFF) are available for use with some conditions. Please check the MOIRCS page for more details. |
| Status of Visiting Instruments/devices (PI Instrument/devices) | Following instruments/module are offered for open-use in S26A: - 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 or LGS-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) 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). |
| 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). |
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. |
| 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. |
| 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 August 5, 2025