Standard call for proposals – semester 2024B

The deadline for the submission of GTC, TNG, WHT, NOT, Stella, LT, TCS, and Mercator proposals for Spanish CAT night observing time for semester 2024B is Monday, 8 April 2024, at 22:59 h Canarian local time (23:59 CEST, 21:59 UT). The call for collaborative proposals between Spanish and University of Florida astronomers at the GTC (Spanish/UF Time, see below) is also open, with the same deadline.

  • 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.  GTC Spanish/UF proposals can have either a Spanish or Florida PI, and must include co-Investigators (co-Is) from both communities (see below).

  • The start and end of the semester change with telescope as illustrated next:

    • Stella, TCS: August – January.

    • NOT, TNG, Mercator: October – March.

    • GTC:   September – February.

    • WHT: November – April.
    • 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 any telescope (except for the WHT) 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.

  • All proposals must be submitted using the application (more info at the end of this web page), with the only exception of WEAVE (WHT) proposals, which must be submitted using the specific ING platform created for the WEAVE instrument.

  • Proposals are evaluated at the next meeting of the CAT (May 2024). Recommendations will be made to the Director of the various Observatories/Telescopes by the end of June  2024.

Please, read carefully the following highlights and recommendations made for each telescope and for large programs. Pay special attention to the new (latex, word, pages) form for the preparation of proposals (except for the WHT).


What follows are the highlights of all seven telescopes managed by the CAT.


Detailed information about the feature of GTC for this semester is available here.

  • OSIRISEMIR, HiPERCAM, and MEGARA are offered in this call.
  • OSIRIS is offered at the Cassegrain focus station and with the new monolithic, blue-sensitive CCD.  
    • OSIRIS “imaging” (broad-band, SHARDS filters),  and “spectroscopy” (long-slit, MOS) modes are offered.
    • Tunable filters and “frame transfer and fast photometry” are not offered in 2024B.
    • 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. Because there is a new CCD, previous masks are no longer usable. All approved MOS proposals must build their new masks. 
    • OSIRIS new CCD is operating since January 2023.
  • EMIR is offered at the Nasmyth-A focal station with the new H2RG detector. 
    • EMIR broad- and narrow-band imaging, long-slit and MOS spectroscopy are the offered observing modes in 2024B. 
    • All applicants are recommended to read the instrument manual carefully.
    • 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.
    • EMIR new detector is operating since June 2023.
    • The new detector read-out overheads are as follows: 50% for imaging and 35% for spectroscopy. These overheads must be added to telescope presetting and instrumental configuration overheads.
  • MEGARA integral-field unit (IFU) is offered. The MOS mode will not be offered due to foreseen upgrades on the MOS positioners.
  • 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.
  • HiPERCAM is now permanently installed at the new Folded-CASS G focal station. It provides imaging capability in 5 channels (u’, g’, r’, i’, z’) simultaneously. Although offered to the GTC community, HiPERCAM is a visitor instrument (PI.Vik D hillon).
  • The Observatory encourages users to request Visitor Mode observations provided their programs benefit from this mode. Since 2020B, the Observatory has successfully implemented a “flexitime” mode intended to increase the efficiency of the visitor programs. Users interested in using this mode must declare it by ticking the “Visitor mode” button when filling in the electronic form of their proposal.
  • Actual visitor astronomers will be admitted only for proposals in bands A and B. C-band proposals requesting visitor mode will be included in the observing queue, but are not admitted as “visitor”. 
  • All visitor proposals must have a backup program for the case the observing conditions required by the main program are not met.  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 as regular programs (read carefully the ToO policy at GTC and as well as the GTC ToO page for further details). Large programs cannot contain ToO observations. 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.
  • Large programs requesting one, two, or three of the offered instruments (and offered observing modes) are accepted in semester 2024B. These programs must:
    • have the potential to lead to a major advance in a specific field of astrophysics,
    • require a minimum of 100 h of GTC CAT that can be distributed over 1 to a maximum of 4 semesters, with a limitation of a maximum of 100 h per semester,
    • must have a PI from any institute in Spanish soil (because the observing time is deduced from the CAT share), and 
    • must comply with the conditions, particularly those regarding dark, gray, and bright night time, described here.
  • SPANISH/UF TIME: Up to 1.25% of the GTC observing time is reserved for collaborative proposals between Spanish and University of Florida astronomers. To send proposals under this agreement, select the Special Agreement“Spanish/UF Time” in the CAT application tool
  • After publication of the GTC data, all PIs will be contacted by the CAB, CSIC-INTA, archive staff and invited to send their reduced data products for public release to the astronomical community through the GTC archive.

  • The Observatory announces that the R. A. ranges 0 – 2 h and 12 – 14 h are highly over-subscribed, whereas the R. A. interval 20 – 23 h and bright moon time are generally less demanded. Programs that can use bright moon time and/or have targets with R. A. between 20 and 23 h  will have higher probability of being executed at the telescope.
  • 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 (OSIRIS, EMIR, MEGARA, HiPERCAM) 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



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

  • Offered instrument: WEAVE (large integral-field unit, LIFU, mode): approximately 140 h.
  • Programs are sought for the semester November 2024 through April 2025.
  • NO Target of Opportunity (ToO) proposals are accepted in this call for proposals.
  • All WEAVE open-time observations in this semester will be queue-driven and will be done in service mode, sharing nights with the WEAVE surveys. ING welcomes astronomers from the teams of successful PIs being at the telescope during WEAVE observing nights, but note that there’s little chance of their own observations being carried out during their visit. Such visits should be organised well in advance in consultation with ING.
  • WEAVE open-time data will be processed with the standard WEAVE pipelines (CPS at CASU, APS at IAC). All raw and processed data will be made available to the PI teams through the WEAVE archive.
  • Following the WEAVE Data Policy agreed between ING and the WEAVE Surveys, prospective PIs should note that the surveys do not have reserved targets, or reserved science topics. However, any data which preempt or replicate survey data will be made available immediately to archive users in the same way as WEAVE survey data, and will be assigned a propietary period corresponding to survey data.

WEAVE open-time proposals must be submitted via the ING platform. In the ING form, you must select “Spain” country.



Offered instruments (GIANO-B, HARPS-N, NICS, DOLORES, GIARPS = GIANO-B+HARPS-N) are summarized here.

  • The polarimeter PAOLO will move to GranTeCan in the next months, thus the polarimetric mode with DOLORES will be unavailable during the semester 2024B.
  • The execution of the observations related to the long-term program A47TAC_44, “Follow-up of electromagnetic counterparts of gravitational wave sources at TNG during O4”, may have a significant impact on the schedule of the semester 2024B.
  • Monitoring mode is subjected to severe limitations at TNG. The schedule is dominated by long blocks of full-nights belonging to Large Programs dedicated to Exoplanetary Science.
  • Proposals requesting high frequency monitoring of exoplanets or other targets should clearly specify the ideal and the minimum rate needed to get the expected scientific results. In any case, too dense cadence (like 1 visit per week or less) will be probably considered not feasible due to scheduling issues. Moreover, to optimize telescope observing time and scientific return in exoplanets observations, time sharing with Large Programs is necessary. A time sharing agreement will be requested after the proposals are accepted.
  • There are no protected targets. 



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.


The instruments WiFSIP and SES are offered.

The telescope control software has been upgraded to allow for non-sidereal tracking and guiding for solar-system observations with WiFSIP/Stella-1.

LIverpool Telescope (LT)

The offered instruments for 2024A are IO:O, RISE, SPRAT, MOPTOP, and LIRIC. Highlights are the following:

  • A new instrument, LIRIC, is available in 2024B. It replaces the now-decommissioned IO:I camera.
  • 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.

Mercator Telescope

Offered instruments (HERMES) can be found at Mercator. Instrument MAIA is not offered in 2024A.
  • 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.
  • An upgrade of the wavelength calibration system of HERMES is foreseen in the period 2023-2024.
  • 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.
  • There is a remote observing system, although CAT observers may find it more useful to perform the observations at the Observatory.
  • 2022 was a very successful year for the Mercator telescope and 36 refereed publications were published based on Mercator data. A wide spread of stellar astrophysical themes are covered and, while HERMES is not in vacuum, also exoplanet science is performed. This can be appreciated on Please, let the team know if you have more publications based on Mercator data so that they can keep track of the science output of Mercator (by email to or

Telescopio Carlos Sánchez (TCS)

Offered instruments on the TCS are MuSCAT2 and FastCAM.
  • About 90 nights are offered to the CAT community. 
  • Target of Opportunities proposals are accepted in 2024B.
  • Observations are sought for the semester between August 2024 and January 2025.
  • Technical information about the instruments and their pipelines are given at the MuSCAT2 and FastCAM webpages.

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 2024B the following time is available for Large Programs:

  • TNG:  5 n in 2024B, 10 n in 2025A, 2025B and 2026A.
  • WHT: no large programs are accepted in 2024B.
  • INT: no large programs are accepted in 2024B.
  • NOT:  10 nights per semester (up to 4 semesters).
  • Mercator: 17 nights per semester (up to 4 semesters).
  • Liverpool: 90 h per semester (up to 4 semesters).
  • Stella-SES: 120 h per semester (up to 4 semesters).
  • Stella-WiFSIP: 80 h per semester (up to 4 semesters).
  • TCS: 30 n per semester (up to 4 semesters).
  • GTC: These projects should require a minimum of 100 hours that can be distributed over up to four semesters, with a limitation of  100 h per semester. These 100 hours follow the standard division into dark, grey and bright time (50-30-20). This limits the maximum allocation to GTC Large programs per semester to 50 hours in dark time, 80 hours in dark/grey conditions, and 100 hours without any moon restriction. Given these limits, a GTC Large program can request up to a total of 200 hours of dark time distributed over 4 semesters, 320 hours in grey time, and 400 hours with no moon restrictions. Execution of a GTC-LP will be preferentially done in service/queue mode.  Requests to conduct it (partially or completely) in visitor mode will be considered if it significantly improves the efficiency of the proposed observations. Note, however, that payback for bad weather or technical failure in visitor mode will no be offered. As the observing time is deduced from the CAT share, only GTC Large Program applications with PIs and a large part of team from Spanish institutions will be accepted.

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, TCS, 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

  • WEAVE proposals on the WHT. Applicants must use the ING platform and select Spain country. Page/word limits and instructions are given on the electronic form.
  • For all other telescopes (GTC, TNG, NOT, LT, Mercator, Stella, TCS), all applicants must use the night time CAT application tool at, A simple manual to learn how to deal with this CAT application is available in this pdf document. Please, select properly the Committee to which you will submit your proposal: Spanish CAT, Spanish/UF, TAC China, TAC Florida, or TAC Mexico. 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.

ALL proposals must be written in English. 

Applicants must ensure that their proposals comply with the required page limits and layout indicated below. If your proposal is a ToO and/or Large Program proposal, this must be clearly identified by ticking the corresponding labels on

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, the SpanishCAT 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 3 Apr 2024

Contact: catiac at