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
Telescope Downtime	There is a possibility of three(3) weeks of downtime after October for repairs to the dome's main shutter.
NsIR Downtime	Due to the delay of the Nasmyth Beam Switcher (NBS) installation work, all instruments except for IRD on the NsIR focus - including IRCS, SCExAO(CHARIS, VAMPIRES, FastPDI), and REACH - will be unavailable for about 2-3 months from August. After the installation, all IRCS, SCExAO, and REACH observations will be done with the NBS under shared-risk mode. Please see the IRCS and SCExAO webpage(s) for the possible impacts of the NBS.
SSP in S26A	In S25B, PFS-SSP will be assigned about 10-20 nights (TBD) over 3-4 observing runs (TBD).
LGS-mode of AO188 with TBAD system	The laser guide star (LGS) system for AO188 will be operated with TBAD (Transponder Based Aircraft Detector) under shared-risk mode. Please check the AO188 webpage(s) for the latest information.
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).
Updates in Scientific Categories	There have been changes to the Scientific Categories since the last semester. Please refer to How to Submit via webform? and select the appropriate category for your proposal.
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 S25A, as a reference.
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.
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?.
Upgrade project of the deformable mirror (DM) for AO188	As part of the AO3k project, the DM has been upgraded from a 188-element bimorph mirror to a 3228-actuator magnetic mirror. AO188 provides three modes: NGS-AO188 mode (uses 188-element WFS + 3k-element DM), LGS-AO188 mode (uses 188-element WFS + 3k-element DM), and NIRWFS-AO3k mode (uses NIR WFS + 3k-element DM). While NIR WFS provides high-performance AO correction, NGS and LGS mode performance is unchanged because they use 188-element WFS. Please refer to the AO188 webpage(s) for more information.
Status of Visiting Instruments/devices (PI Instrument/devices)	Following instruments/module are offered for open-use in S26A: - CHARIS with SCExAO+AO188 (including spectro-polarimetric mode) - VAMPIRES with SCExAO+AO188 (cameras have been upgraded for improved sensitivity, speed and dynamic range. A new multi-band imaging mode is available.) - Fast PDI with SCExAO+AO188 (under shared-risk mode) - REACH (combination of SCExAO and IRD for single-mode fiber spectroscopy) - IRD with AO188 (NGS-AO188 mode or LGS-AO188 mode under shared-risk 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 CHARIS webpage(s).

Reminder About Basic Information

Reminder	Description
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 S25B, 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