Call for proposals – semester 2021B

The deadline for the submission of GTC, INT, Stella, Mercator, NOT, TNG, and LT proposals for Spanish CAT night observing time for semester 2021B is Sunday, 11 April 2021, at 22:59 h Canarian local time (23:59 CEST, 21:59 UT).

  • We recall that every proposal within the Spanish CAT scheme must be led by a principal  investigator (PI) affiliated to an Institution in Spanish soil. 
  • The start and end of the semester change with telescope as illustrated next:
    • INT, Stella: August – January.
    • NOT, TNG, Mercator: October – March.
    • GTC:   September – February.
    • Liverpool (LT):   July – February (a two-month overlap period is adopted at the start and end of each semester, when proposals from both semesters may be observed in order to reduce problems with under-filled observations queues).
  • Large programs requesting observing time with LT, Mercator, NOT, and/or Stella are accepted. See below.
  • Proposals requiring visitor mode (including GTC) should include a proper backup scientific program that does not demand good weather conditions. The backup program is also scientifically addressed by the CAT.
  • The application does allow to request multiple observations using different instruments and telescopes, including GTC. 
  • Proposals are evaluated at the next meeting of the CAT. Recommendations are made to the Director of the various Observatories/Telescopes in July 2021.

Please, read carefully the following highlights and recommendations made for each telescope and for large programsThere are IMPORTANT changes (e.g., instruments unavailability, remote observing at GTC) with respect to previous calls for proposals. Pay special attention to the new (latex, word, pages) form for the preparation of proposals.

To submit proposals, see “how to submit” at the end of this document.


Detailed information about the feature of GTC for this semester can be found on the GTC call for proposals. A short summary is provided next:


  • In semester 2021B, no Large Programs are offered.
  • OSIRIS (see below), EMIR, and MEGARA are offered in this call. 
  • OSIRIS is offered on a “shared-risk” basis between December 2021 and February 2022 (second half of the semester) on the Cassegrain focus station.OSIRIS “imaging” (broad-band, SHARDS filters, and tunable filters),  “spectroscopy” (long-slit, MOS), and “frame transfer and fast photometry” are offered, the latter only in visitor mode. Multi-Object Spectroscopy (MOS) observations will be part of the observing queue only if the proposals are ranked in bands A and B of the Spanish CAT final list. However, any proposal in band C that has the MOS masks already fabricated from previous semesters will be also included in the observing queue (still in band C). Applicants must indicate whether their MOS masks are to be fabricated or are available from previous semesters (there is a box named “masks” in the
  • The MEGARAintegral-field unit (IFU) is offered. The MOS mode will not be offered due to foreseen upgrades on the MOS positioners.
  • EMIR broad- and narrow-band imaging, long-slit and MOS spectroscopy are offered. All applicants are recommended to read the instrument manual carefully. Very importantly, the time needed to perform EMIR night-time calibrations (e.g., observations of telluric standard stars, wavelength calibration, etc.) will be charged to the observing programs. Therefore, applicants must include all the time needed to perform theses calibrations together with the time needed for the science observations in the total requested telescope time in their proposals.
  • For the calculation of overheads, the GTC Observatory strongly recommends the use of the following Phase 2 simulator. Further information on the calculation of overheads is provided in the GTC call for proposals.
  • Visitor programs are very welcome, but will only be admitted whenever they fall in bands A and B. In addition, a backup program (in visitor mode) has to be defined in the case the observing conditions for the main program are not met.  C-band proposals requesting visitor mode will be included in the observing queue, but are not admitted as “visitor”. The applicants must clearly indicate if they are applying for visitor mode or “remote visitor mode” (see below).
  • Target-of-opportunity (ToO) proposals are accepted (read carefully the ToO policy at GTC and as well as the GTC ToO page for further details). ToO proposals will be recommended with their corresponding priority whenever they fall in bands A and B of the ranked proposal list. ToO proposals in band C will not be approved. ToO proposals do not have carry-over status.
  • For all approved proposals (bands A, B, C, and filler), GTC Phase 2 information must be submitted to the GTC at the deadline corresponding to the semester in which the proposal is accepted.


  • The Observatory announces that the R. A. range 10 – 12 h is highly over-subscribed, whereas the R. A. interval 3 – 8 h and bright moon time are generally less demanded. Programs that can use bright moon time and/or have targets with R. A. between 3 and 8 h do compete for less oversubscribed telescope time and regions of the sky. They will have higher probability of being executed at the telescope.
  • The Observatory encourages users to request Visitor Mode observations provided their programs benefit from this mode. The Observatory has successfully implemented a “flextime” mode intended to increase the efficiency of the visitor programs. 
  • Starting in semester 2020B, Remote Visitor Mode is also supported at GTC. Users interested in using this mode must declare it by ticking the “Remote visitor mode” button when filling in the electronic form of their proposal.
  • Starting in semester 2019A, all proposals (including ToO) will be ranked in bands A, B, C, and filler. Principal Investigators of A-, B-, and C-ranked proposals and filler projects must complete GTC Phase 2 of ALL approved observations in due time. The bands assigned to each proposal are defined as follows:
    • A-band proposals have very high priority and all possible efforts will be made to execute all of the required/approved observations in the requested semester. If for any reason, A-band proposals remain unfinished by the end of the corresponding semester, the existing GTC Phase 2 will be granted an extended life-time of two additional semesters, or until its completion, whichever comes first. Unfinished A-band proposals do not have to be re-submitted in the following two semesters because of their carry-over status. Approximately one quarter (according to the CAT ranking) of the total amount of GTC available observing time falls in this band.
    • B-band proposals will be executed on a best-effort basis during the requested semester, and do not have a carry-over status. Approximately three quarters (according to the CAT ranking) of the total amount of GTC available observing time falls in this band. 
    • C-band proposals will be executed in extraordinary cases when no A- or B-band objects are available but the good weather conditions permit observations during the requested semester. C-band proposals do have very little opportunity of execution until completion of the project, yet they are included in the GTC observing queue. 
    • Filler proposals, see below.

PROTECTED OBJECTS. Due to the execution of Guaranteed Time Observations (GTO) of various instrumental teams, all applicants are kindly requested to check the list of protected objects here (follow the links to the corresponding instrument). Protected objects cannot be proposed for observation by other users, unless an instrumental setup different to that of the GTO is required.

FILLER PROPOSALS: In order to have an efficient queue-scheduled observations scheme for the GTC, it is useful to have a set of “filler” programs that can be executed under adverse observing conditions (bad seeing, poor sky transmission, etc.). Filler proposals can request common-user instruments (EMIR, MEGARA) with simple instrumental configurations (filler proposals should not request complex observations that demand non-standard instrumental modes). These programs must contain targets spanning a wide range in right ascension (RA). Filler proposals will only be executed if the observing conditions do not permit observations of proposals in A-, B-, or C-bands. Proposers may request filler status for their program, and during the proposal selection process CAT will evaluate their suitability for this category. Such proposals can request a large number of observing hours. In order to be considered as filler proposals, they must fulfil the following requirements:

  • Their observing requirements should be very relaxed, i.e. little or no restrictions on seeing or cloud coverage. 
  • The chosen observing mode should be a frequently used mode .
  • There is a scientific gain even if only a small fraction of the requested observations are executed.
  • A list of targets with a broad R.A. coverage is provided or,  if only few targets are included, they must have good visibility during the semester.
  • Filler proposals cannot contain Target of Opportunity (ToO) targets.

Note that filler proposals have generally been highly successful in the last semesters. 

Filler proposals must be identified by ticking the “filler” box in the proposal submission tool


No time is offered at the WHT in 2021B. To learn about the status of the WEAVE instrument, see more information from the  ING call for proposals document and the web page particularly created for providing an update on the ING instrumentation.


Detailed information provided by the ING Observatory can be found in the ING call for proposals. All potential applicants must become familiar with the series of changes in instrument availability and of observing time at the WHT and INT driven by the arrival of new survey instruments. The changes are summarized here

The main changes for 2021B are:

  • See the complete list of ING instruments here. Offered instruments are: 
  • Applicants are encouraged to submit proposals for large time allocations within the semester.
  • Large programs (covering various semesters) are not offered in semester 2021B.
  • Users should be aware of the instrument changes that will take place in coming semesters for a proper preparation of their INT proposals.
  • In response to the current pandemic situation, and associated travel restrictions, the ING has increased its capacity to carry out regular INT programs in service mode for those science teams that are unable to send an observer. The request for service-mode observing must be done at least one month before the start of the run.
  • There will be no observing support assistant at the INT. Therefore, inexperienced INT observers MUST be accompanied by an experienced observer. ‘Inexperienced’ here means unable, alone, to make efficient (and safe) use of the observing night, whether from general lack of observing experience, or from lack of experience with the specific techniques/instruments to be used. Observers will be responsible for all aspects of operation, from opening the dome in the evening and operating the telescope and instrumentation throughout the night to parking the telescope and closing the dome at the end of the night. 


Offered common-user instruments (ALFOSC, StanCam, MOSCA, NOTCam, and FIES) and non-common user instruments are listed here. Updates with respect to previous semesters are as follows:

  • A set of two holographic diffuser are available to do high-precision photometry with ALFOSC. The diffuser effectively scrambled the incoming light, providing a more constant and optimal (`top-head’) shape, with minimal light loss, significantly reducing any systematic effects in the photometry. The diffusers provides a very stable stellar image with a width (~FWHM) of 5 and 7 arcsec, respectively. Read here for more information.
  • The SOFIN high-resolution Echelle spectrograph is again available. It is offered only to do circular spectro-polarimetry with the medium-resolution (R~80,000) camera. SOFIN is not a common-user instrument: only limited support is provided, and explicit approval for a proposal should be obtained. 


Offered instruments (GIANO-B, HARPS-N, Nics, Dolores, GIARPS = GIANO-B+HARPS-N, SiFAP2) are summarized here.

  • Objects included in the TNG Protected Target List (GAPS collaboration, AOT44=2021B/AOT45=2022A) cannot be requested.
  • The execution of the observations related to the long-term program A41TAC_18, “Follow-up of electromagnetic counterparts of gravitational wave sources at TNG”, may have a significant impact on the schedule of the semester 2021A.


The instruments WiFSIP and SES are offered:

  • WiFSIP: the small-band filters and H-beta narrow and wide are not available. 
  • SES has no change with respect to previous calls for proposals. 

LIverpool Telescope (LT)

The offered instruments for 2021B are IO:O, RISE, SPRAT, and MOPTOP. (For other LT instrumentation NOT OFFERED this semester, see here). Note the following points:

  • In addition to applying for telescope time through the CAT twice-yearly process, LT now also allows observers to apply for PriorityZ time via:
    PriorityZ time is defined as time when there is no A, B or C-ranked science group available for the scheduling software to pick, and so the telescope would otherwise sit idle. This can occur during periods of poor seeing during full moon, or during times of instrument failure. We estimate approximately 10-15 hours of such time are available per month, although this can of course vary significantly. PriorityZ time is well-suited to long-term proposals of bright targets with no significant time constraints. We would typically expect to approve a PriorityZ proposal for a period of two years. Observers can apply via the web form available at the above link, and proposals will be assessed internally by LT staff. Proposals can be submitted at any time.
  • Check the restrictions and guidance notes for the Liverpool Telescope.
  • IO:I and FRODOspec currently have some technical issues and are not offered.

Mercator Telescope

Offered instruments (HERMES and MAIA) can be found at Mercator.
  • It is strongly recommended to request long runs and full nights since the Observatory will reduce the number of introduction due to limited local man/womanpower.
  • The low-resolution, high stability mode of HERMES is no longer available.
  • The high-resolution mode is more efficient, and a double mode in which the object’s spectrum is interleaved with a simultaneous ThArNe exposure is offered. The double mode is intended only for radial velocity work : the background cannot be corrected so if you are interested in the extracted 1D spectrum, you cannot use this mode.
  • The exposure time calculator on the web has been updated accordingly with respect to the efficiency of HERMES.
  • A new guiding mode on the spectrographic telescope is introduced, which allows now guiding in close visual binaries separated by at least 3 arcsec (the spectrograph’s entrance pinhole diameter). This works for faint companions as well.

Large programs

Large programs are expected to accommodate projects that require long-term or synoptic coverage, and large-size projects. They must satisfy these four requirements: 

  • involve novel ideas, opportunities for great advance, or legacy programs, 
  • span between two and four semesters, 
  • publicly release their final high-level products in an appropriate format, and 
  • be led by a Spanish institution (a large fraction of the team should be affiliated to a Spanish institution).

Considering the time allocated to on-going large-programs, in 2021A the following time is available for Large Programs:

  • TNG:  no large program is offered in 2021B.
  • WHT: this telescope is not offered in 2021B.
  • INT: no large programs are offered in 2021B.
  • NOT:  10 nights per semester (maximum of 4 semesters)
  • Mercator: 20 nights per semester (maximum of 4 semesters).
  • Liverpool: 20 h  in 2021B, and 70 h in next three semesters.
  • Stellar-SES and Stella-WiFSIP: 60 h per robotic telescope and semester (maximum of 4 semesters).
  • GTC: not offered for large programs in 2021B.

All large programs will be evaluated by the CAT and advised by external expert referees, based on the above criteria. Yearly progress reports are expected, and a final report to the CAT is due at the end of the project.  Raw data from long-term programs will follow the same proprietary period as regular proposals. Up to 66% of the time distributed by the CAT on the Liverpool (LT), Mercator, STELLA, and INT, up to 33% of the time on NOT and TNG, and up to 15% of the time on the WHT may be assigned to large programs.

How to submit

Applicants must ensure that their proposals comply with the required page limits and layout indicated below. ALL proposals must be written in English. To send proposals, use the night time CAT application tool at  A simple manual to learn how to deal with this application is available in this pdf document. To submit a proposal, the PI and co-Is need to be registered. If you are already registered but you do not remember your password, please do NOT register twice (in order to avoid confusions for statistical purposes). You can find instructions about how to reset your password in the same webpage or contact the CAT for additional help.

THERE IS A NEW FORM to build the scientific case of the CAT proposals. All applicants of standard and large proposals are kindly requested to use this new form, which is available here  (a “tar” file will be downloaded; read the README file first).  Please note that applications forms are different for LARGE (long-term) and REGULAR programs. Note also that the time request in the on-line application tool has changed, as one should now specify the  time requested for each semester by creating as many “Observations” as needed.

In the evaluation of proposals, CAT will take into account the publications derived from previous observations with the CAT telescopes. Therefore, in the BIBCodes menu of the application tool, remember to update the fields Comment and Bibliographic code  for all proposals approved in the last two years.

Before the deadline expires, please check that the uploaded pdf file (created with the new form) contain the latest version of your proposal, and that it prints correctly. No replacement or updating of the proposal content will be made after the deadline, and those proposals which do not correctly print out or lack relevant sections will be automatically withdrawn from the evaluation process. Those proposals where the font size (12pt) has been reduced or the text of the scientific justification exceeds limitations (one page for common/regular proposals and two pages for large programmes) will also be withdrawn. Figures and Tables cited in the scientific justification should fit a maximum of one page (normal proposals) and two pages (large programs). It is advised to follow the instructions described at

UPDATED on 15 Mar 2021.

Contact: catiac at