Frequently Asked Questions (FAQ)

for Announcements of Opportunity (AOs)

This webpage shows a collection of Frequently Asked Questions (FAQ) and answers related to the preparation and submission of Anouncements of Opportunity (AO) proposals for the CHEOPS Guest Observer (GO) Programme. The page will be continuosly updated throughout current and future AO Calls.


Q1) WHY Do I have to REGISTER FOR THE CHEOPS GO PROGRAMME, and How do I do it?

You will need to register for the Guest Observers Programme to (a) download the scheduling feasibility checker and (b) submit your GO proposals. The latter is required to make a detailed assessment of the visibility of your targets with CHEOPS. Instructions on how to register can be found here.


Q2) which targets (i.e., lines of sight) are already reserved and Not accessible for the GO Programme?

There are two ways in which you can find out which targets (i.e, lines of sight) are already reserved, and thus may not be included in GO observing proposals: 

  1. Target by target, one-by-one, using the so-called reserved target list checker tool which is available here. This provides access to the most up-to-date version of the target list.
  2. A table which contains the target name and coordinates for all targets on the reserved target list will be made available on these pages at the time the AO Call opens.


Q3) Are there any restrictions or quotas on science topics/areas?

Observations can be proposed that cover any science topic/area, including exoplanets. There are no quotas for time that will be allocated to different science topics. All proposals will be evaluated by the Time Allocation Committee according to the following criteria:

  • The scientific excellence and relevance of the proposed observations;
  • The uniqueness and applicability of CHEOPS to achieve the proposed scientific objectives of the proposal;
  • The technical feasibility and robustness of the proposed observations and data analysis.

There are some constraints on the types of observations that CHEOPS can be used to do. These are summarised below and elaborated on in more detailed in the Policies and Procedures document for each AO Call:

  • Simultaneous CHEOPS observations with other facilities can be done in exceptional cases but might be challenging to schedule and thus might pose a risk of non-completion.
  • CHEOPS does not support non-sidereal tracking. Solar system objects may be observed in exceptional circumstances by providing static time-dependent RA and Dec values. This approach is definition extremely time-critical and makes scheduling of such observations correspondingly challenging.

In both cases above the scientific justification for the request needs to be made in the proposal and will be considered by the TAC in the proposal evaluation process. 


Q4) Are there limits to the number of orbits that CAN Be requested?

There is no maximum number of orbits that can be requested in a single proposal. However, there are restrictions on the number of orbits that can be requested for a single observation/visit:

  • There is a minimum visit duration of 5 orbits outside of transit which is enforced to ensure that efficient and effective detrending of the resulting lightcurves is possible.
  • There is a maximum visit duration of around 100 orbits (around 1 week) which is set by the length of the observing schedule that is uplinked to the satellite. Longer duration observations can be made by scheduling two consecutive visits.


Q5) I am UNABLE TO run the scheduling feasibility checker on a virtual machine on the UBUNTU OS

A user has reported difficulties using the scheduling feasibility checker (SFC) in combination with the Ubuntu OS. They were able to isolate the issue to the Virtual Box installation based on the solution proposed here. They could solve the issue by removing the VirtualBox version downloaded from the VirtualBox website, and using that provided in the Ubuntu software source (reply 8 in the link above):

sudo apt-get install --reinstall virtualbox


Q6) When is it useful to use CHEOPS imagettes rather than subarrays, and how do I do so?

Photometry on imagettes typically performs as well as photometry on subarrays, with the added advantage of the higher cadence. This can be advantageous when detrending but also for resolving rapid phenomena such as flares in active stars and for timing measurements (e.g. better resolution of ingress and egress). PIPE is a photometric extraction package, developed by members of the CHEOPS Science Team, that uses PSF photometry on 60 pixel diameter CHEOPS imagettes. The package complements (but does not replace) the official Data Reduction Pipeline (DRP), which uses aperture photometry on the 200 pixel diameter subarrays. Details of the PIPE package can be found at this link (GitHub). The package currently requires detailed tuning - interested users are therefore advised to contact the author of the package directly to discuss possible collaborations.  


Q7) How do I make sure my proposal complies with the dual-anonymous Guidelines?

Importantly, remember what the goal of dual-anonymous peer-review is. The goal is to shift the focus of the review onto the science case - and away from the PI and their team (and their names, genders, etc.). The goal is not to make it completely impossible to guess who the team is.

For example, proposals should say "A recent study showed that the period of this planet is 42.0 days (Adams et al., 1978)" instead of saying "We showed that the period of this planet is 42.0 days (Adams et al., 1978)".

To this end, it is crucial to not claim nor indicate ownership of past work, work in preparation, or proprietary data sets. If referencing such points, proposers must indicate this as "private communication" without including the names of the respective individuals or teams. It can help to use third person neutral wording for this. In most cases, it can be as simple as saying "Previous CHEOPS programmes on this target have ruled out several period aliases, leaving only the options outline here (private communication)".

Sometimes the proposers may have access to unique facilities or skills. Stating this is not against any principles of the dual-anonymous peer review as long as the identities of the team are not explicitly revealed. For example, proposals should say something like "These observations will be performed simultaneously with JWST, for which the project has been awarded 365 days of telescope time." or "The target's stellar activity will be monitored with 1-metre class ground-based facilities before/after the event."

Note that the Management Plan section of the proposal is not anonymised. This section will be removed from all proposals before the science evaluation by the TAC. Thus, it gives an excellent opportunity to add specific details to back up certain claims in the main part of the proposal. For example: "The relevant JWST programme has the number 123456 (link)." or "The proposing team leads the Tiny-ELT consortium of 1-metre class telescopes."

If in doubt, please do not hesitate nor overthing - simply send an email and examples to cheops-support at, and we will be happy to help.


Questions about CHEOPS or the GO Programme? Please email cheops-support at and we will be happy to help!
This website was last updated on 12 March 2024.