Observing with iLocater

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Overview

Following its delivery to the LBT, iLocater is being made available to the LBT community for science as a PI instrument. Current instrument status and observing constraints are listed below.

The process and details for proposing observations with iLocater is as follows:

• Well in advance of submitting a time request, proposers should email ilocater-obs-list@nd.edu with the information outlined below to allow the iLocater team to provide feedback regarding feasibility and observing support availability.
• All observations will be considered shared risk during ongoing instrument commissioning (expected through at least the end of 2026B and potentially continuing into 2027A).
• iLocater will only be available on the SX (left) hand side of the LBT. Simultaneous observations with other instruments on the DX (right) side of the telescope are possible (e.g. PEPSI, LUCI, SHARK-VIS), and observations in this mode should be noted in any iLocater observing requests.
  • Note: downstream instruments within LBTI (i.e. LMIRCam/NOMIC) cannot be used simultaneously with iLocater.
• The iLocater team will complete on-sky observations on behalf of the proposing team.
  • To support this mode of operation, it is expected that observations will be completed as part of the OSURC queue on the telescope schedule, with time being tracked and accounted to each LBT member.
• Reduced data products will be provided to the proposing team.
  • Data products will consist of one-dimensional wavelength-calibrated spectra, and radial velocity measurements.
  • Development of the data reduction pipeline is currently on-going and data products will be provided on a shared-risk basis. Reasonable efforts will be made to provide reduced data in a timely manner, however, given the ongoing development work, there may be delays in delivery to allow the iLocater team to validate the quality of the data.

Current Instrument Status (September 2026)

Status: iLocater is currently in operation at the LBT undertaking commissioning and shared-risk science operations in 2026B. For 2027A proposals, observers should assume the following instrument performance which is based on first-light observations of the instrument in June 2026.

Current instrument performance:

• Wavelength coverage, resolution, and spectral format: iLocater covers approximately 963.5 nm to 1310.8 nm over 41 spectral orders. The wavelength coverage is complete blueward of 1110 nm, with increasingly large gaps through the J band. The median resolving power is 207,000, but varies between approximately 150,000 and 250,000 over the length of each order.
• RV calibration stability: <1 m/s
• Spatial resolution on-sky: ~40 milli-arcseconds

Constraints for observation planning:

• Observing conditions: iLocater is an AO-fed instrument. Best performance is obtained in conditions with seeing <1.2 arcsec (targets with J≤7 have been demonstrated in these conditions). Degraded performance for bright targets may still be obtained in poorer seeing conditions depending upon the specific science program. Seeing <0.8 arcsec is necessary to obtain good performance for targets with J≤8. Further details regarding target magnitude can be found in the table below.
• Exposure times, detector readout and expected SNR: 
  • iLocater’s detector reads continuously up the ramp and thus has no inter-exposure gaps for readout. Exposure times are set in integer numbers of up-the-ramp frames (2.7 seconds per frame). The minimum recommended exposure time is 5 frames (13.5 seconds). The maximum exposure time at the present time 175 frames.
  • The signal recorded by the spectrograph depends upon the AO performance and efficiency of injection into the single-mode fiber. Work is ongoing during 2026B commissioning to better characterize performance with a goal to providing an exposure time calculator.
• Overheads:
  • AO Overheads: Typical LBT AO acquisition overheads will apply for observations with iLocater. These may be up to 10-15 minutes per target, but depends upon observing conditions.
  • Thermal background: Due to the small fiber size on-sky and the YJ-band coverage which does not include the thermal infrared, no nodding is necessary; observations are obtained in a continuous stare on target.
• Performance on binary stars: Initial estimates demonstrate that iLocater can achieve a suppression of flux from a central star of >10² at separations larger than ~200 milliarcseconds. Work is on-going to improve the quality of this performance assessment.

For 2027A observations, we recommend observers plan on the following source limits, which are based on the demonstrated LBTI/SOUL AO performance, combined with previous observations using iLocater's fiber injection system:

Target mag (Visible)	Target mag (J band)	Expected performance	Specific Comments	General Comments
R or I: < 8	J < 7	Optimal AO performance. Optimal beam-stabilization performance.	Acceptable fiber coupling/instrument throughput expected.	Fiber coupling efficiency (i.e. instrument throughput) is strongly coupled to AO system performance. Seeing of <1.2 arcsec is recommended for all observations, and tighter constraints (< 1.0 arcsecond) may be required depending on the observing program. For targets J>7, we recommend requiring seeing of <0.8 arcsec to minimize this impact.
	J > 7	Optimal AO performance. Limited beam-stabilization performance.	Increased risk of not obtaining acceptable fiber coupling and instrument throughput except in good seeing conditions.
R or I: 8 - 12	J < 7	Reduced AO performance. Optimal beam-stabilization performance.	Acceptable fiber coupling/instrument throughput expected.
	J > 7	Reduced AO performance. Limited beam-stabilization performance.	Increased risk of not obtaining acceptable fiber coupling and instrument throughput except in good seeing conditions.

For more information about expected LBT AO performance, please refer to the following references:

SOUL: https://ui.adsabs.harvard.edu/abs/2023aoel.confE..80P/abstract
LBTI AO Performance: https://scienceops.lbto.org/lbti/lbti-users-manual/

Current Instrument Status (July 2026)

iLocater was delivered to the LBT and achieved first light in June 2026. Characterization and optimization of the instrument is on-going in preparation for operations in 2026B.

Requesting time with iLocater

Scientists at LBT Member Institutions

Time requests for the use of iLocater should be handled through the time allocation process of the proposing members institution. Given the PI status of iLocater, of the time allocated for observations:

• 90% will be allocated to on-sky time for the science program;
•  10% will be allocated to a pool of time managed by the iLocater team to support engineering, key science programs, and to account for the time required by the team to support iLocater operations.

This breakdown of time should be accounted for in any time requests being made.

Prior to submitting a time request, proposers should email ilocater-obs-list@nd.edu with:

1. A brief overview of the type of program being proposed
2. Any specific precision requirements necessary for the observation/s
3. Any specific time constraints on the observation/s
4. Any simultaneous observations to be completed with another instrument on the DX side of the telescope

This will allow the iLocater team to ensure the instrument can support the proposed observation, prior to a time request being made.

Scientists outside the LBT Collaboration

At the present time, there is no direct path for iLocater time to be made available to scientists outside of LBT member institutions. We encourage scientists outside of the LBT Collaboration to build collaborative programs with scientists at LBT members institutions. For programs with compelling science cases requiring limited time, LBT Director's Discretionary Time may be requested however such requests are not guaranteed.

Use of iLocater Data/iLocater Collaboration Membership

Any person who supports and operates iLocater, or requests proprietary observations using iLocater is required to be a member of the iLocater Collaboration. This membership ensures that data products are used fairly, and their use is properly attributed. Proprietary data products may not be shared outside of the collaboration membership without explicit permission from the instrument Co-PIs.

If observing time with iLocater is awarded through a time allocation process, the proposing team will be invited to join the iLocater Collaboration prior to the observations being completed.

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Last updated: 29 September 2026