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Subaru/Keck Time Exchange Program

Last Updated with S26B information on February 13, 2026.

1. Definition

According to the agreement between Directors of Subaru Telescope and Keck Observatory, Subaru users can apply to Keck time through this Subaru-Keck time exchange program. This time exchange program is coordinated so that astronomers in each community can mutually access unique instruments of each telescope. Scientific merits of the proposals are reviewed and determined in each TAC independently (namely, proposals from the Subaru community using Keck are reviewed by Subaru TAC).

2. Eligibility

Only Japanese or Taiwanese researchers (i.e., those belonging to institutes in Japan or Taiwan, or those of Japanese nationality) or EACOA/EAO fellows are eligible for this Subaru -> Keck application.

3. Observing Mode

Observations with Keck Telescope will be executed in a 'classical' mode. Keck observations are always executed remotely, either from the Keck office at Waimea or approved remote sites. At-home observing will continue to be available to observers. Please see the Keck webpage for information about remote observing, including at-home observing.

We note that Keck observations from the Mitaka remote observing room is available for Subaru-Keck time exchange users. We have some experience of successful Keck observations from Mitaka remote observing room without fatal problems, but please be reminded that the support is provided only with a best-effort basis, and thus we cannot always guarantee safe/stable Keck observations.

Proposals requesting Target of Opportunity (ToO) observations and intensive programs are not accepted.

4. Telescope Downtime

Keck I and Keck II facility downtime:
Each of Keck I and Keck II will have two five‑night shutdown periods during bright time in the 26B semester to complete dome, shutter, and high priority infrastructure work. The dates will be finalized during May telescope scheduling, taking into account scientific demand and the requirements of the infrastructure projects.

Keck I and Keck II bottom shutters:
The Observatory anticipates a period of 2 weeks on each of Keck 1 and Keck 2 where the bottom shutter will be fixed at 25 degrees elevation in order to replace wire ropes on the bottom shutters. Targets below 40 degrees elevation would experience vignetting. Please note on your coversheet if this restriction would be a significant impact to your science.

5. Instruments

Keck I telescope:

  • LRIS
  • MOSFIRE
  • OSIRIS

  • HIRES

  • KPF: KPF had an operations review in January 2026 that identified reduced detector thermal control and increased detector noise as key issues. Planning is under way to address the hardware causes of these issues, likely beginning in 2027A and lasting several months. During 2026B, proposers and time allocation committees should be aware that the Green and Red CCDs in the main spectrometer are likely to experience thermal events of a few degrees C (or more) above the -100 C detector setpoints lasting a few hours. While the number and timing of these are difficult to predict, it is likely that KPF will not maintain long-term RV stability over 2026B. Thus, time series RV measurements over long periods (weeks or months) are likely to be compromised by changing RV zero points at the ~10 m/s level. Experience has shown that these zero-point changes are difficult/impossible to calibrate out and are different for each star observed. Science projects that rely on a time series of KPF RVs or spectra over a short timescale (a night to a few nights) are unlikely to be affected by the warmups (which would have to occur during the observing sequence). Projects in this category include obliquity measurements (Rossiter-McLaughlin, etc.), exoplanet transit spectroscopy, (astero)seismology, and ultrashort-period mass measurements (using the floating-chunk offset method). For the detector noise issue, KPF users should be advised that the Green/Red CCDs have a per-pixel read noise of 8.5/4.3 RMS electrons as of February 5, 2026. (The expectation is < 3.5 RMS electrons per CCD pixel.) Read noise is variable due to environmental factors and updates will be posted on Instrument Status. Proposers are encouraged to use the KPF exposure time calculator and note that the added noise is non-Gaussian, causing it to degrade RV performance more significantly for low-SNR spectra than would be expected based on the RMS values above in a way that is difficult to quantify.

  • KPF-CC: Due to the issues detailed above regarding long term RV stability with KPF, KPF-cc will not be offered in 26B.
  • Keck I AO: The following AO modes will be available for the full 26B semester:
    • NGS and single star LGS
    • KAPA in LTAO mode with STRAP or TRICK
    • KAPA in GLAO mode with STRAP or TRICK

There are no changes to the tip-tilt star magnitude limits for STRAP or TRICK. Users can expect higher Strehl ratios with LTAO than with SLGS, or improved uniformity across the field with GLAO, under the same observing conditions. Performance info will be posted online by the end of February.

Keck II telescope:

  • Keck II AO: Keck 2 AO with the new HAKA DM will be available in NGS mode with guide stars brighter than R=12, and in LGSAO mode with no restrictions.

One of the Keck II AO rotator mirrors is planned to be recoated in 26B.
Note that science proposals may be pushed into their acceptable timeframes in order to facilitate downtime for this work.

  • SCALES: SCALES will not be offered in 26B for the Subaru-Keck time exchange program due to uncertainty in its arrival and commissioning at the Keck Observatory. Depending upon a successful pre-ship review in April 2026, SCALES is anticipated to install and commission at the end of the 26A semester and the first few months of the 26B semester. For more information on SCALES, see SCALES Home Page.

  • DEIMOS: DEIMOS will be unavailable in August and September for commissioning of a new science detector DEIMOS is expected to be available for science beginning in October.

  • NIRC2

  • NIRC2-polarimeter: NIRC2 in polarimetric imaging mode, in both NGS and LGS AO, will be offered in a non-facility visitor mode for 26B. NIRC2 has an internal Wollaston prism and the K2AO system has two external half waveplates (HWPs) that are optimized for JHK- or L-band science. To swap between the JHK-HWP and L-HWP is a daytime task such that we cannot support both modes on a single night. NIRC2 polarimetry and non-polarimetry are supportable on a single night. To organize polarimetry nights based upon the science need for a specific HWP, there will be four additional instruments to select on the coversheet:

    • NIRC2pJHK-NGS
    • NIRC2pL-NGS
    • NIRC2pJHK-LGS
    • NIRC2pL-LGS

In polarimetry mode, LGS tip/tilt stars must be within 30 arcseconds of the science object.
We ask observers interested in proposing for NIRC2p to reach out to WMKO and we will put you in touch with the polarimetry team.

  • ZWFS, CRED2 and ORKID: These technology demonstrators are available for use throughout the semester. PIs who wish to use these should consult with the Keck AO team before proposing and PIs should select NIRC2-NGS on their coversheet, with a clear description of what mode they will be using in their coversheet summary.

  • KCWI

  • NIRSPEC

  • Adaptive Optics with LGS / NGS

LGS-AO backup program:
Those who request LGS-AO time must prepare backup programs, because cloudy conditions may hinder propagation of laser. For OSIRIS + LGS-AO applicants, OSIRIS with NGS-AO is available as a backup instrument. For NIRC2 + LGS-AO applicants, NIRC2 with NGS-AO, and NIRSPEC without AO, are available.

Instrument Hibernations:

WMKO, in consultation with the Science Steering Committee after the receipt of the findings of the Instrument Suite Evolution task force (comprised of members of the WMKO community and WMKO science staff), is undergoing a process of hibernation and eventual decommissioning of instruments in the coming years as new capabilities arrive and to be responsive to pressures on WMKO resources. A hibernated instrument is not available for community use unless there is a significant emergent scientific and strategic need. After a year's hibernation, the hibernated instrument will be completely removed from service and decommissioned. The community should begin planning for the following:

  • NIRES: NIRES will be hibernated after May 07, 2026. Unless a compelling scientific or strategic need emerges, NIRES will be decommissioned at the end of the 27A semester.
  • ESI: ESI will be hibernated after July 08, 2026. Unless a compelling scientific or strategic need emerges, ESI will be decommissioned in at the end of the 27A semester.
  • HIRES: HIRES will be decommissioned no earlier than the conclusion of 2027A. Due to the nature of the instrument and need to free the Keck I Nasmyth platform for future instrumentation, HIRES will not undergo a hibernation period and will instead transition directly to decommissioning. The final decommissioning timeline will depend on both the readiness of Zshooter, which is set to occupy HIRES’s current Nasmyth location, as well as the stability of KPF. A comparison of HIRES and KPF capabilities can be found on the "Comparing KPF to HIRES" page. As per instrument evolution process, WMKO is soliciting feedback from the community regarding the HIRES planned hibernation. Please provide feedback through Keck Science Steering Committee members or address them to instrument_retirement@keck.hawaii.edu

Additional instruments are under consideration for hibernation and eventual decommissioning in later semesters, with a focus on those instruments whose capabilities are being significantly superseded by new instrumentation.

  • Twilight Cadence Observing: In 2026B, institutions will continue to be able to allocate one twilight observing program per telescope, for a total of up to two programs. On Keck I, OSIRIS-NGS (imager only) will be available, and on Keck II, NIRC2-NGS will be available. Please note that due to ongoing AO upgrades, there may be times in the semester when AO is unavailable for cadence observations. Cadence program PIs are responsible for development of instrument scripts, providing documentation, and training of staff needed to make the cadence program a turnkey operation.

  • Please be sure to refer to the Keck instruments webpages for more details.

6. Available Amount of Time

In S26B, up to several Keck I nights and up to several Keck II nights are available to the Subaru community. The number of exchange nights will be determined based on the demand of each community.

7. Proposal Preparation for Programs using Keck Telescopes

Table 1. Guide for Applicants for Keck Time
Phase-I Subaru Submission Step 1. Applicants should submit their proposals via the webform by the deadline in Subaru Call for Proposals.


7-1. Step 1. Phase-I Submission to Subaru ProMS

Applicants intending to apply Keck observations via this Subaru Call for Proposals should access the ProMS 2.0 page to fill the webform. Proposals from the Subaru community to use Keck are treated as a part of Subaru Open Use Programs and are reviewed in the same way as other Subaru proposals.

How to complete the Application Form:

Please follow the instructions detailed in 'How to Submit'.

  • "1-12"(Observing Run):
    If your science goals can be achieved with any Subaru (or Gemini) instruments, please give the name(s) of your backup instrument(s) in the "2nd choice instruments" box. Please note that you need to contact the instrument PI in advance if your 2nd choice instrument includes a PI-type instrument of Subaru.
  • "1-15"(Observing Method and Technical Details):
    Describe by referring to Keck Instrument page.
    Please describe observing methods such as mode, grism, slit width etc. using the backup instruments, too.
    If you want to use FOCAS as the back up instrument, please check whether you need pre-image observations for your MOS masks. Please describe "I need preimage observations" in this section if you need pre-image observations.
    Please refer this page about the pre-image observations.

7-2. Step 2. Submission of Keck Coversheet (Approved Programs)

The PIs of approved proposals will be asked to submit the Keck Proposal Coversheet.

8. Phase-I Contact

Please contact cfp_consult_at_naoj.org.

updated on February 13, 2026