6th Announcement of Opportunity (AO-6) for participation in the CHEOPS Guest Observers (GO) Programme

This 6th Announcement of Opportunity (AO-6) marked another opportunity to participate in CHEOPS' first extended mission. AO-6 opened on 18 March 2025 and closed on 8 May 2025, soliciting proposals for observations to be carried out as part of the CHEOPS Guest Observers (GO) Programme, with the observation window spanning from 1 October 2025 to 30 September 2026 (inclusive). CHEOPS offers its GO users space-based ultra-high precision photometry for the observation of exoplanet transits, eclipses, occultations, phase-curves, and more. Science cases may range from exomoons, ring structures, stellar activity, and trans-Neptunian objects to other topics beyond the exoplanet field. The timely overlap of several space- and ground-based missions can provide opportunities for synergies with NASA/ESA/CSA JWST, NASA/ESA HST, NASA TESS, ESO ground-based facilities, and more.

Modern & user-friendly

The CHEOPS AO-6 Call provided several updated and user-friendly tools to enhance community access and the GO experience:

• Zero-installation tools: our modern Visibility Tool and streamlined Scheduling Feasibility Checker (SFC) were powered by ESA Datalabs
• Streamlined proposal submission: users could follow our simple step-by-step guide and use our agile Proposal Handling Tool for Phase 1 (PHT1)
• Community contributions: the scientific community developed many useful tools that could be helpful for proposal preparation, observation simulation, and data analysis

It also repeated the successful novelties introduced with the first extended mission:

• More targets: only 50 GTO reserved targets, with all the rest generally being open to the entire Community, including a larger fraction of the sky with a reduced Sun Exclusion Angle of 117 degrees
• More time: up to 30% science observing time dedicated to the GO Programme
• Modern approach: double-anonymous peer-review of proposals

Milestones

Important Notes

Prospective observers were asked to take note of the following points:

• Read the Policies and Procedures document carefully before starting any proposal preparation, as it is the definitive document for this opportunity. It highlights details of CHEOPS' science programme, available time for the community, observing strategy and constraints, and required contents of observing proposals. It also lists the tools and documents available to support observers in their proposal preparation and submission. Remember that all proposal material and file names must be fully anonymous, and that failure to comply will result in rejection on formal grounds. Also thoroughly consult the Observers Manual and all relevant documentation on this website.
• Follow 7 easy steps
  1. Registration: Register immediately if you do not already have a user account. Waiting with this step until the deadline might cause you to miss the opportunity.
  2. Coordinates: Familiarise yourself with the correct coordinate system to use. Use the Target Checker, Simbad, or MAST. Do not copy & paste from ExoFOP, as it uses a different format.
  3. Visibility Checks: Get familiar with the visibility maps to see which targets might be in reach. Then verify if and when your targets are observable with the brand-new Visibility Tool or, optionally, the Scheduling Feasibility Checker.
  4. Target Status Checks: Make sure your target is eligible by checking the publicly available list of all of CHEOPS' targets, both reserved and unreserved, and the GTO programme information. Ensure that your observations will contribute something new by checking the CHEOPS Mission Archive to see what data CHEOPS has already gathered.
  5. Exposure Time Calculation: Make sure you can achieve the desired signal-to-noise by using the exposure time calculator.
  6. Proposal Templates: Download, fill in, and you are all set up.
  7. Submission: Phase 1: Submit your proposal via the Proposal Handling Tool for Phase 1 (PHT1).

Please also note that:

• Updates related to this AO Call and its material were published on this webpage.
• Note the special case of Alpha Cen, including Alpha Cen A and Alpha Cen B: the system was on the Reserved Target List (RTL), but due to its high proper motion and orbital motion, the Target Checker did not resolve its RTL coordinates if queried by name. Alpha Cen’s RTL coordinates were given in the RTL csv file and had to be used for any Target Checker queries for this system.
• Detailed examples helping users make their proposals dual-anonymous were listed on the FAQ pages.
• The CHEOPS team does everything possible to observe and complete awarded programmes. However, it is important to appreciate that an award of observing time does not guarantee that the observations can be conducted, even if a programme is considered to be high-priority science. Due to the nature of the science that CHEOPS addresses, time pressure can be high, unforeseen events can occur, and some observations might not be feasible to schedule.
• CHEOPS is a small mission, with a correspondingly small team to support the GO Programme. Observers are encouraged never to leave proposal preparation to the very last moment, as it may take a couple of days to answer questions.

Phase-1 step-by-step tutorials

Hands-on tutorials were run in March and April 2025 across various time zones to guide users through the proposal preparation and submission process and answer their questions. Please find below the presentation shown with the seven simple steps to follow, a video with the process, and a video recording of the last hands-on tutorial.

Presentation (pdf, 4.4 MB)

4-minute video tutorial on how to submit a CHEOPS GO observing proposal:

Video recording of the hands-on tutorial (30 min):

Key Documentation

• Announcement of Opportunity (AO-6) - invitation letter by the Director of Science
• Policies and Procedures (AO-6 & DP)
• Observers Manual (AO-6 & DP)
• GTO Programme (AO-6)
• GTO Reserved Target List (AO-6)