Observing at WMKO

Instruments Available for Semester 2026B


For detailed information about the instruments, please check the Instruments Home Page
For information about which instruments can be used on the same night, please check Instrument Sharing
For a Resolving Power vs. Wavelength comparison of Keck instruments, please check this Instrument Comparison graph.

Keck I Instruments are:


        HIRESb (blue x-disperser) scheduled for hibernation no earlier than the conclusion of semster 27A 
        HIRESr (red x-disperser) scheduled for hibernation no earlier than the conclusion of semster 27A
        KPF
        KPF-CC unavailable in 26B, see below
        LRIS-ADC (red and blue, with ADC)
        LRISp-ADC (polarimeter, with ADC)
        MOSFIRE
        OSIRIS-NGS
        OSIRIS-LGS
       

Keck II Instruments are:


        DEIMOS - limited availability, see below
        ESI - hibernated after 26A
        ESIi (ESI with the Integral Field Unit) - hibernated after 26A
        KCWI
        NIRSPEC (without AO)
        NIRC2-NGS
        NIRC2-LGS
        NIRC2p-NGS/LGS non-facility visitor mode, see below
        SCALES - limited availability, see below

      

Subaru Time Exchange Instruments are:

FOCAS, HDS, Hyper Suprime-Cam, IRCS, MOIRCS, PFS, CHARIS, VAMPIRES, REACH, Fast PDI, NsIR, NIR-WFS, FIRST-PL, and IRD. See below for limitations.
       

Telescope Limits

Please note that Keck I and Keck II have different eastern and western telescope limits. This affects the times objects will be available for observing. Objects can be acquired earlier on Keck II and followed later on Keck I.

Special Notes for Semester 2026B:

Keck I and Keck II facility: 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 I and Keck II 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.

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 KPF Status . Proposers are encouraged to use the KPF exposure time calculator ETC 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 throughout the 26B semester:

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 information will be posted online by the end of February.

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: 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. Shared risk science is offered from Sept-Oct with routine science operations anticipated starting in November 2026 following an operations handover review in Oct. The imaging channel and low-resolution IFS are expected to be commissioned during the first few nights on-sky and are considered lower risk in 26B. The medium-resolution IFS will be commissioned next, followed by coronagraphy, which is expected to extend the furthest into the shared risk time in 26B. Due to some schedule uncertainty, SCALES proposers shall have a backup program with a preference for observing with NIRC2. For more information on SCALES, see SCALES homepage

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-polarimeter: NIRC2 in polarmetric 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:

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 nirc2_info@keck.hawaii.edu and we will put you in touch with the polarimetry team.

ZWFS, CRED2 and ORKID: These technology demonstrators are available for use after May 17, when Keck II AO returns to service. 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.

Instrument Hibernation: :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:

At-Home (pajama mode) Observing: At-home observing will continue to be available to observers. Please see https://keckobservatory.atlassian.net/wiki/spaces/MOSD/overview for information about remote observing, including at-home observing.

Time Domain Astronomy: Observers will continue to have the ability to propose both cadence and ToO programs using the cover sheet. Policies related to Target of Opportunity or Cadence proposals can be found at Too Policies and Cadence Policies. These policies are not applicable to Subaru Exchange time. TAC-approved Cross-institutional ToO (TDA) projects will continue to be able to interrupt observers at any Institution, to increase the utility of the ToO process.

Twilight Cadence Observing: The twilight cadence program will continue this semester, with NIRC2-NGS and OSIRIS-NGS available for use. Each institution may allocate one twilight cadence program per telescope. Please note that due to ongoing AO upgrades, there will be times in the semester when AO is unavailable for cadence observations (see above). 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. More details can be found in the Cadence Policy.

FOCAS, HDS, Hyper Suprime-Cam, IRCS, MOIRCS, PFS, CHARIS+SCExAO, REACH, FastPDI, VAMPIRES, NsIR, NIR-WFS, FIRST-PL and IRD will be available at Subaru. Please check the Subaru web site http://www.subarutelescope.org/Observing/index.html for detailed descriptions of these instruments. Please visit https://subarutelescope.org/Observing/Proposals/call.html for instrument restrictions, particularly for visiting (PI-type) instruments SCExAO+CHARIS, IRD, VAMPIRES, Fast PDI, REACH, NIR-WFS, NsIR, FIRST-PL and for filter availability of HSC. The SUBARU-KECK exchange will continue to have flexibility with regard to the number of nights available for exchange with the number of nights exchanged determined based on the demand from each community. Subaru ToO observers will continue to be able to interrupt Keck observers on the Subaru Telescope, and Keck ToO observers will be able to interrupt Subaru observers on the Keck Telescope. Compensation will be according to the policy of each observatory.

Subaru observations are executed in "classical" observing mode, except for HSC and PFS observations. Queue observing is the default observing mode for HSC; applicants who desire classical mode with HSC must justify their request. For all classical observations, Subaru may support half night allocations, but whole night allocations are preferred. Please check the HSC queue mode website https://subarutelescope.org/Observing/queue/index.html for more details on HSC observations.

Subaru facility/instrument related restrictions for the 2026B semester:

  1. 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.
  2. 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).
  3. Filler Proposals: Keck users can apply for the HSC Queue Filler without a time exchange cost. All Filler proposals must be submitted directly to Subaru TAC by Subaru’s normal and intensive proposal deadline. The PFS Community Filler program is not open during "B" semesters.
  4. LGS-mode of AO188: The LGS system for AO188 will be operated with TBAD. 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.
  5. 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.
  6. Available facility instruments: Adaptive Optics (AO188-mode/AO3k-mode), FOCAS, HDS, HSC, IRCS, MOIRCS, PFS
  7. Status of PI-type instruments/devices:
    • 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 mliti-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.
  8. Proposals to use visiting instruments/devices must include the relevant PIs as Co-investigators

LGS-AO: A detailed set of guidelines for LGS-AO nights and information on the capabilities of the systems may be found on the LGS-AO page. Backup programs for LGS proposals are essential. Backup programs for LGS on Keck II may be either NGS programs or NIRES. On Keck I, either NGS-OSIRIS and non-AO HIRES may serve as a backup.

KOA (Keck Observatory Archive): Data from all instruments will be archived in the Keck Observatory Archive (KOA). The default proprietary period for data is 18 months except for data taken with NASA as the allocating institution which has a default proprietary period of 12 months. If observers desire a different proprietary period they may request this through the Keck coversheet. Please see the KOA homepage for information on the archive. Please also see the KOA proprietary period policy.

For detailed information about the instruments, please check the Instruments Home Page

  (further observing information)

This page last updated 04 February 2026 ccj.
Telescope-scheduling@keck.hawaii.edu