The deadline for submitting proposals for Spanish CAT night observing time in semester 2026B (GTC, TNG, WHT, INT, NOT, Stella, LT, TCS, TTT, and Mercator) is Tuesday, 7 April 2026, at 22:59 WET (23:59 CET, 21:59 UT). The call for collaborative Spanish–University of Florida (UF) proposals at the GTC (Spanish/UF Time, see below) is also open with the same deadline. Proposals should be submitted via https://proposals.iac.es/ (see also sections “News for 2026B” and “How to submit”).
Each proposal within the Spanish CAT scheme should be led by a PI in a research institution based in Spain. As the scientific lead of the programme, the PI should be fully capable of executing the proposed research. Collaborators (co-Is) may be from institutions worldwide. For proposals with equal scientific merit, priority will be given to those with (1) a higher proportion of co-Is from Spanish institutions, and (2) a higher number of distinct Spanish institutions involved.
GTC Spanish/UF proposals can have either a Spanish or UF PI, and must include co-Is from both communities.
Proposals will be evaluated at the next CAT meeting in May 2026. Based on scientific criteria, the CAT will provide a recommendation to the Director of the IAC, who is responsible for making the final decision on proposal approval. Recommendations will then be sent to the Directors of the various observatories and telescopes by the end of June 2026.
Please read the following highlights and recommendations carefully, as there have been several changes since the last semester.
News for 2026B
- Starting from 2026B, proposals must be submitted via the new proposal submission service at https://proposals.iac.es.
Please note that this is a new service and that both PIs and co-Is need to be registered. It is advisable to register and start with the proposal preparation well ahead of the proposal submission deadline.
The previous submission service (http://cat.iac.es) will remain available until approximately summer 2026, but only to allow users to view and download their past proposals.
Requests for technical support with the new proposal submission service should be directed at helpdesk-cat[at]iac.es
- Starting in semester 2026B, a Fast Track scheme will be introduced at the NOT and TNG. This will also entail some changes to the previous Service Time scheme at these facilities.
Proposals requesting less than half a night per night that do not classify for a Fast Track scheme (see below) and that request observations during the months covered by 2026B will have to be submitted through the Standard Call for Proposals and identified as “Service” in the section “Observing mode” of the proposal. These observations will be carried out by telescope operators in service mode, during the nights scheduled as service nights. The dates (posted here) are established after the CAT meeting; however they are typically evenly spaced and distributed across bright, gray and dark time. A maximum of one service night per month per telescope is foreseen.
Suitable proposals for Fast Track are those that respect these conditions:
- unforeseen or urgent transitory phenomena
- a topic of particular impact or importance needing urgent action
- those with a high element of risk, but also having high impact if successful
- follow-up of previous observations, where urgent action might lead to a result of high impact or be of a decisive nature
- to demonstrate the viability of a given program or type of observations
- high impact programs initiated by the Director of the IAC
- The start and end dates of each semester depend on the telescope (see information at https://ocan.iac.es/night-cat/)
- Large programs requesting observing time with any telescope (except for the WHT, INT) are accepted. See details below.
- The following telescopes operate exclusively in visitor mode: TNG, TCS, NOT, and Mercator. An exception applies to proposals requesting less than half a night per night at TNG and NOT, provided that the observations are scheduled on nights specifically requested as Service Nights in this call (to be published here)
- The following telescopes operate in queue/service mode: GTC, WHT, INT, Stella, LT, and TTT. No backup program is required. The only exception is GTC, which also accepts visitor mode proposals. In such cases, the team must either include a backup program, following the same rules as for visitor-mode telescopes in this call, or explicitly state that any unused time will be returned to the Observatory for queue/service observations.
- Applicants should request total telescope time, including both on-source exposure time and overheads.
- All proposals must be written in English.
- ToO, Large Programs, and Fillers should be identified as such in the proposal submission form.
- The CAT will be instructed to evaluate proposals as they have been submitted, on the basis of scientific merit and the capacity of the team, led by the PI, to successfully meet the proposed objectives of the programme. No variation of the amount of requested time, target list, instruments, observing mode or observing constraints will be recommended by the CAT (e.g. Large Programs will either be granted time as Large Programs or not approved). Note that, due to scheduling constraints, approved programs might not be allocated.
- Since the time allocation is performed separately by telescope, proposals requesting multiple runs with different facilities should include a clear explanation of what scientific objectives can be reached with each facility and how they are impacted in case not all runs are granted.
- Targets included in Phase 2 for queue/service observations and visitor-mode runs should correspond to those originally proposed at the time of proposal submission. Only in exceptional and duly justified cases may target changes be considered. Such requests must be submitted to catiac[at]iac.es no later than two weeks before the Phase 2 deadline.
GTC
The complete GTC call for proposals for this semester is available at https://www.gtc.iac.es/observing/media/GTC_2026B_CallForProposals.pdf.
In 2026B, the time available to the Spanish community will be about 600h.
The instruments offered are:
GTC News and important notes
- New higher sensitivity detectors are available both for OSIRIS+ and EMIR+ instruments. In the case of EMIR+, using the new H2RG implies higher overheads than before (observing efficiency is now 50% in imaging mode and 75% in spectroscopic modes).
- HiPERCAM is operative at Folded Cass G focal station, including the new COMPO component
- MEGARA is recovered for scientific operations. However, due to pending upgrade works for MEGARA MOS positioners, MEGARA MOS mode will not be available for S26B.
- Large-Programs are offered in S26B for MEGARA (IFU mode), HiPERCAM, OSIRIS+ (imaging and longslit spectroscopy modes), and EMIR+ (imaging and longslit spectroscopy modes). A single instrument or a combination of the four instruments can be requested, accounting for a maximum of 100 h per semester in the present call. Note that ToO proposals are not accepted for GTC-LP, and it is also not allowed to request the use of diffuser/narrow band filters with HiPERCAM for GTC-LP.
- The 0 to 2 hours and 10 to 14 hours R.A. ranges are highly subscribed by ongoing high-priority large programmes, in particular during dark/grey time and under good seeing conditions; the 3 to 8 hours R.A. range is generally under-subscribed.
Bright moon time is under-subscribed (this time is mostly reserved for observations with EMIR+).
- For all approved proposals (bands A, B, C, and filler), GTC Phase 2 information must be submitted by the deadline corresponding to the semester of acceptance.
OSIRIS+
The OSIRIS optical spectrograph and imager will be available at the Cassegrain focal station with its new monolithic blue sensitivity CCD (OSIRIS+). Available observing modes are: Broad-band imaging; Medium-band imaging (SHARDS filters, http://www.gtc.iac.es/instruments/osiris+/osiris+.php#SHARDS_Filters); Long-slit spectroscopy; Multi-object spectroscopy.
Multi-object spectroscopy (MOS):
- MOS observations will only be carried out for proposals that are highly ranked by the TACs (i.e., A or B ranked bands). Proposals requesting MOS mode that are not sufficiently highly ranked will hence be rejected.
- Due to the change to a new OSIRIS CCD, previously produced masks are no longer usable. For further practical limitations we point the interested reader to http://www.gtc.iac.es/instruments/osiris+/osirisMOS.php.
- Slit widths as narrow as 0.63 arcsec are allowed, but users always must be aware of the 0.1 arcsec (r.m.s.) accuracy achievable in the slit positioning when defining the scientific goals of the program.
EMIR+
The EMIR near-infrared wide-field imager and medium-resolution spectrograph will be available in the Nasmyth-A focal station with its new higher sensitivity H2RG detector (EMIR+)
Observing modes offered in the present call are: Broad-band imaging (Y, J, H, Ks filters); narrow-band imaging ([FeII],[FeII]cont,Brγ, Brγcont,H2(1-0),H2(2-1)); long-slit spectroscopy (0.6”, 0.8”, 1,0”, 1.2”, 1.6”, and 5.0” slit widths); multi-object spectroscopy.
Note that with the new EMIR+ detector overheads are larger than before. The new detector overheads are as follows: 50% for imaging and 75% for spectroscopy. These overheads must be added to the on-source integration times. To optimize the telescope time for a predefined on-source integration time, applicants should use the EMIR efficiency calculator available at:
www.iac.es/proyecto/emir/pages/observing-with-emir/observing-tools/efficiency-calculator.php
All applicants are recommended to read the instrument manual (https://www.gtc.iac.es/instruments/emir/emir.php) 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.
MEGARA
For Semester 2026B MEGARA optical spectrograph will be available only for integral-field Unit (IFU) observations at intermediate-to-high spectral resolutions (R~5,500, 12,000 and 20,000 for the LR, MR and HR modes respectively).
HiPERCAM
The HiPERCAM high-speed, multi-band imager is a GTC visitor instrument (P.I. Vik Dhillon) that has been permanently installed at the new Folded-Cass G focal station. HiPERCAM provides simultaneously imaging in 5 channels (u’, g’, r’, i’, z’), at (windowed) rates over 1 kHz in a FOV of 2.8’ x 1.4’ with a 0.081”/pix plate scale.
HiPERCAM was installed at FCass G focal station in mid-April 2023, including the new COMPO subsystem.
The use of the narrowband filters and of the diffuser is only accepted for A-band ranked regular programs (but not accepted for Large Programmes and for ToO programmes).
Further information about the instrument is found in the GTC web pages at http://www.gtc.iac.es/instruments/hipercam/hipercam.php and/or contacting the instrument PI at vik.dhillon[at]sheffield.ac.uk
Target-of-opportunity (ToOs)
- GTC accepts ToOs override proposals. GTC´s procedure for triggering ToO observations can be found at http://www.gtc.iac.es/observing/too.php.
- ToO proposals are accepted for service observations.
- ToO proposals are not accepted for Large Programmes (or as part of Large Programmes) at GTC.
- ToO regular programs can request HiPERCAM observations without narrow-band filters and the diffuser.
- ToO proposals will be recommended with appropriate priority only if ranked in bands A or B; those in band C will not be approved. ToO proposals do not carry over to the next semester.
GTC Large Programmes (GTC-LP)
- For S26B, Large Programmes can be requested at GTC. These programs can request a maximum of 100 hours per semester of the CAT observing time at the GTC in the present call.
- A GTC-LP is defined as a program with the potential to lead to a major advance in a specific field of astrophysics, requiring a minimum of 100 hours of GTC time which can be distributed during 1 to 4 semesters. In addition to a strong scientific justification, proposers should have the necessary person-power and tools for a quick and comprehensive analysis of the data and publication of the results.
- By the time of this announcement, only MEGARA (IFU mode), HiPERCAM, OSIRIS+ (imaging and longslit spectroscopy modes) and EMIR+ (imaging and longslit spectroscopy modes) can be requested for the execution of a GTC-LP. A single instrument or a combination of the four instruments can be requested.
- ToO proposals are not accepted for Large Programmes at GTC and it is also not allowed to request the use of diffuser/narrow band filters with HiPERCAM for GTC-LP
- LP should comply with the conditions, particularly those regarding dark, gray, and bright night time, described here.
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.
Overheads
Applicants should request total telescope time, including both on-source exposure time and overheads. For the calculation of observing overheads, the GTC Observatory strongly recommends using the Phase 2 simulator (http://gtc-phase2.gtc.iac.es/science/F2/). Please also consult the GTC call for proposals and http://www.gtc.iac.es/observing/ for further details and see notes about oveheads in EMIR+ in the relevant section of this call.
When observing with EMIR, for reasons of overall efficiency and since these calibrations are specific for each observing program, we require that applicants define their night-time calibrations also as observing blocks. The time necessary for these calibrations will be charged to the observing program and should therefore be included in the time request.
See http://www.gtc.iac.es/observing for further details.
Spanish-UF time
Up to 1.25% of the GTC observing time is reserved for collaborative proposals between Spanish and University of Florida astronomers. Proposals to be sent under this agreement will need to be submitted though the specific “Night time calls” at https://proposals.iac.es
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.
Telescope Support Model
Observations at GTC can be either carried out in queue-scheduled service mode by trained GTC support astronomers, or in visitor mode. The appropriate option should be clearly specified in the proposal form.
Users are encouraged to request Visitor Mode when beneficial for science programs. GTC offers some flexibility in the scheduling of this mode to increase the chance of success of the proposal.
Visitor programs will only be admitted for A- or B- ranked proposals. Lower ranked programs will automatically be placed in the observing queue, except for those requesting observing modes that are only admitted in visitor mode (e.g. programs using high-speed readout modes of OSIRIS). GRANTECAN will aim to follow the preference of the PI when drawing up the observing schedule, but no guarantee can be given that all preferences can and will be honored.
If requesting visitor mode, the team must either include a valid backup program, following the same rules as for visitor-mode telescopes in this call, that can be carried out if the observing conditions required for the principal program are not met or explicitly state that any unused time will be returned to the Observatory for queue/service observations.
In visitor mode, the PI will normally be present at the telescope during the observations. Remote visitor mode is also supported in GTC. If on the scheduled dates the PI cannot travel to the observatory, then the GTC support astronomer will carry out the observations in service mode, with the possibility of remote connection of the PI that allows real-time assessment of the data quality and the opportunity to adjust the observing parameters (remote visitor mode functionality has been enhanced during the last year, providing a better access to the scientific data and telescope status).
Ranking
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, observations of A-band proposals are not completed 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; hence, during this carry-over period, the proposal does not need to be resubmitted. Approximately the top 25% (according to the CAT ranking) of the total amount of GTC available observing time will be allocated in this band.
- B-band proposals fall in the remaining 75% of the total amount of GTC available observing time falls. B-band proposals will be executed on a best-effort basis during the requested semester, and do not have a carry-over status.
- C-band proposals will be executed only when no observations from A- or B-band programmes can be executed. C-band proposals do have very little opportunity of execution until completion of the project, yet they are included in the GTC observing queue.
- Fillers 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 with simple instrumental configurations. These programs must contain targets spanning a wide range in right ascension (R. A.). 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 the CAT will evaluate their suitability for this category. Such proposals can request a large number of observing hours. Note that filler proposals have generally been highly successful in the last semesters. In order to be considered as filler proposals, they must fulfill the following requirements:
- The 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.
TNG
- Available telescope time for the Spanish community: approximately 31 nights.
- The polarimetric mode with DOLORES will be unavailable during the semester 2026B. The TNG polarimeter is mounted at the GTC; TNG encourages to ask for observations using the GTC when it will be available.
- The execution of the observations related to the long-term program A53TAC_69 “Follow-up of the electromagnetic counterparts of gravitational wave sources at TNG during O4b” may have a significant impact on the schedule of the semester 2026B.
- 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 the telescope observing time and scientific return in exoplanets observations, time sharing (TS) with Large Programs is necessary.
- Starting from the semester 2025A, new rules on the time-sharing among programs of exo-planetary science are in force. It is essential that researchers who would like to submit a proposal on exo-planetary science needing monitoring of Radial Velocities over a wide range of dates take into account the important considerations on TS. These are reported below, with some additional considerations (but please make sure to consult also the URL https://www.tng.iac.es/observing/time_sharing_policy.html):
- There are several Large Programs (LPs) on exoplanetary science ongoing at the TNG, with granted time until AOT57 (or 2028A). To optimize the scientific return for their science goals, the two main scientific groups with approved LPs (HARPS-N and GAPS collaborations) already agreed on sharing the observing time at the telescope.
- Exoplanetary science (with HARPS-N and/or GIANO-B) is not the only observing mode of the TNG. Other science cases with different instruments have been approved which means that dense monitoring with frequent observations every few days is not possible, even in case of TS. TS is only available when exoplanetary science programs are scheduled and even so, on a best effort basis.
- At the earliest time or at least two weeks before the closure of a new call for Observing time (TAC, CAT, ITP, ORP), the researchers who know that their science goal could only be attained with TS should properly fill the form available at the following form.
- The above form will only be available on-line until one week before the deadline of the call. Failure to submit the compiled form in due time will imply that the program is technically unfeasible.
- The final acceptance of the TS by the other groups with already approved time is subjected to the following constraints:
- Programs requesting to join the TS group must have scientific goals that do not overlap with those of existing TS group members. Applicants in such cases may still submit their proposals to the Spanish CAT call but should refrain from requesting inclusion in the TS group.
- The target list should not encompass targets for which one of the programs in the TS has already expressed interest. In case of a strong and justified interest on the same target, a spirit of collaboration is encouraged and a policy on the use and publication of the data should be agreed before submitting the proposal. The time allocation committees judging the proposal should be informed of the possible conflict due to mutual interest and know in advance if the groups already agreed on collaborating.
- The scheduling of the targets of the new proposal will be organized on a best effort basis and in any case will not be detrimental for other programs already in the TS. Asking for TS is accepting the scheduling of the targets organized by one of the two main groups.
- PIs of the proposal accept to provide observers for the scheduled nights who: [1] will follow the scheduled observations from the schedulers of the two main groups (HARPS-N Collaboration and GAPS) and [2] will accept that the observing shift could be larger than the assigned time to their proposal (i.e. assigned 1 night to the proposal, but could be observing for 3 consecutive nights).
- PIs of the proposal accept that the calculated percentage of shared time will be based on the allocated time by the TAC and that the bad weather loss will be equally distributed with the same percentage.
- Time Constraint observations (transits) are typically not included in the TS, however the hours of the night outside the transit could be used for TS.
- PIs and observers of programs within the TS will respect a no disclosure of the data from other programs.
- Proposals that fail to demonstrate that an agreement of TS has been reached will be considered as technically unfeasible by the TNG staff
- There are no protected targets.
WHT
Detailed information provided by the ING Observatory can be found in the ING call for proposals. Below we provide an extended summary. 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 also summarized here.
WEAVE
The instrumental capabilities of WEAVE are summarised at
https://www.ing.iac.es/astronomy/instruments/weave/weaveinst.html
In semester 2026B all three WEAVE observing modes are offered: MOS, LIFU and mini-IFUs (mIFU).
As the mIFU mode is not yet fully commissioned, mIFU observations are offered on a shared-risk basis, and users should assume design specifications rather than as-built performance when preparing proposals.
Prospective applicants should note that this call is for observations to be carried out during 1st November 2026 – 30th April 2027. The 3-month shift relative to the usual semesters is imposed by the long lead time for preparation of the WEAVE observing blocks.
Approximately 30% of the available WHT night-time during this period is offered for open-time proposals, following the standard UK, Dutch and Spanish shares.
Information about applying for WEAVE Open Time Programme can be found on:
https://www.ing.iac.es/astronomy/observing/WEAVE-OT.html
All observations will be queue‑scheduled, executed in service mode, and carried out alongside WEAVE Survey operations (see ING call for more details).
WEAVE data will be processed with the standard CPS and APS pipelines and made available through the CamCEAD Operational Repository and the WEAVE archive.
Following the WEAVE Data Policy agreed between ING and the WEAVE Project, 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 proprietary period corresponding to Survey data.
WEAVE Open-Time Target of Opportunity observations
In semester 2026B, ING will offer Target of Opportunity (ToO) observations using the WEAVE LIFU mode.
ToO proposals will be evaluated in the same manner as regular open-time proposals, though only Band A programmes are likely to be attempted. ING anticipates executing at most one ToO trigger per night, on a first-come, first-served basis.
The observing strategy must follow that approved in the proposal, and triggers must remain within the allocated time.
At present, ING supports “next-day” triggers: triggers must be received by 12:00 UT on the preceding day. ING will attempt shorter-notice triggers on a best-effort basis.
Guidelines for LIFU Proposals and Filler Observations
- Non-sidereal observations are now possible with the LIFU and can be executed as part of both regular open-time and ToO programmes.
- ING encourages PIs to submit LIFU proposals designed for poor observing conditions during bright time. See the ING call for proposals for more information.
- Given the large fibre diameters for LIFU, 2.6 arcsec, PIs should usually not specify seeing < 2 arcsec for LIFU proposals. Any requests for seeing < 2 arcsec must be clearly justified and will be scrutinized at the technical-assessment stage.
- Observers requiring dark sky are recommended to request sky brightness V < 21.5 mag/arcsec2 to improve the chance that proposals get observed.
INT
Detailed information provided by the ING Observatory can be found in the ING call for proposals. Below we provide an extended summary. 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 also summarized here.
HARPS3 Status and Shared-Risk Open Time
HARPS3 is currently undergoing integration at the INT, with commissioning activities expected to begin shortly.
In anticipation of scientific operations, the ING invites the community to submit shared-risk open-time proposals for HARPS3 for semester 2026B. A detailed overview of specifications, operations and expected performance will follow shortly. At this stage, the polarimetric mode is not offered.
Shared-risk conditions are as follows:
- HARPS3’s primary operational priority is the Terra Hunting Experiment (THE). Open-time proposals must be operationally compatible with THE scheduling constraints; final assessment of compatibility will occur during Phase 2.
- Open-time execution depends on confirmed operational funding. Operational funding to support management of open-time HARPS3 proposals by the Terra Hunting consortium is anticipated but not yet confirmed. While it is expected that this support will be in place, open-time observations cannot proceed if the necessary STFC funding is not available at the start of the semester.
It is anticipated that a maximum of 40% of the available time for science could be devoted to open-time programmes, following the standard UK, Dutch and Spanish shares. Detailed information about the HARPS3 open-time programme can be found here:
https://www.ing.iac.es/astronomy/observing/HARPS3-OT.html
NOT
Offered common-user instruments:
Available telescope time for the Spanish community in 2026B will be approximately 29 nights due to a planned stand-down over next Christmas.
Please note that ALFOSC spectro-polarimetry is not offered in ToO mode.
STELLA
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.
Available telescope time for the Spanish community is: ~140 h with WiFSIP and ~140 h with SES.
Liverpool Telescope (LT)
The offered instruments are IO:O, RISE, SPRAT, MOPTOP, and LIRIC.
Highlights:
- Available telescope time for the Spanish community is: 150 h (band A+B) + 50 h (band C).
- In addition to applying for telescope time through the CAT twice-yearly process, LT now also allows observers to apply for PriorityZ time via: http://telescope.livjm.ac.uk/PropInst/PriorityZ
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. Approximately 10-15 hours of such time are available per month, although this can 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
Highlights:
- Available telescope time for the Spanish community is: 29 nights.
- It is strongly recommended to request long runs and full nights since the Observatory will reduce the number of introduction due to limited local person-power.
- 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.
- There is a remote observing system, although CAT observers may find it more useful to perform the observations at the Observatory.
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 not offered.
- Large Programmes are offered.
- Technical information about the instruments and their pipelines are given at the MuSCAT2 and FastCAM
Two-meter Twin Telescope (TTT)
Offered imaging instruments on two 80-cm telescopes TTT1 (MPC Y65) and TTT2 (MPC Y66) are the following:
- TTT1 – FERVOR-L (sCMOS) SDSS filters Lum, g’, r’, i’, zs (FOV 0.56º x 0.42º, 0.28 arcsec/pix)
- TTT2 – FERVOR-M (sCMOS) SDSS filters Lum, g’, r’, i’, zs, Ha, OIII (FOV 0.38º x 0.25º, 0.28 arcsec/pix)
Highlights:
- The Observatory offers observing time on a shared-risk basis.
- Available telescope time for the Spanish community is: ~511 h.
- Service mode observations (no visitors).
- Exposure time calculator is available.
- On this link there is a video indicating how to prepare phase 2 for approved programs.
- This is thelink for the preparation of phase 2 (called DTO using TTT terminology).
Large Programmes (LP)
Large programs are expected to accommodate projects that require long-term or synoptic coverage, and large-size projects. They must satisfy these requirements:
- Involve novel ideas, opportunities for great advance, or have a strong legacy value,
- Span between two and four semesters (except for GTC, see section below),
- Publicly release their final high-level products in an appropriate format
- Be led by a Spanish institution (a large fraction of the team – co-Is – should be affiliated to a Spanish institution).
All large programs will be evaluated by the non-conflicted members of the panel to which they are assigned; should it be deemed necessary, advice from external reviewers will be requested. It is expected that LPs rank at the top of their specific panels. This list of grades will be used to decide which LPs will be elevated for discussion at the meeting of the chairs and vice-chairs of all the CAT panels and of the President and vice-President of the CAT. During this meeting, the final decision will be taken on which LPs to recommend to the IAC Director.
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, TTT, 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.
Considering the time allocated to on-going large-programs, in 2026B the following time is available for Large Programs:
- TNG: 14 n per semester (up to four semesters).
- WHT: no large programs are accepted in 2026B.
- INT: no large programs are accepted in 2026B.
- 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: 30n for 2026B
- TTT: 100 h per semester and per unit (up to 4 semesters).
- GTC:
- For S26B, GTC-LP programs can request a maximum of 100 hours per semester of the CAT observing time at the GTC in the present call.
- A GTC-LP is defined as a program with the potential to lead to a major advance in a specific field of astrophysics, requiring a minimum of 100 hours of GTC time which can be distributed during 1 to 4 semesters. In addition to a strong scientific justification, proposers should have the necessary person-power and tools for a quick and comprehensive analysis of the data and publication of the results.
- By the time of this announcement, only MEGARA (IFU mode), HiPERCAM, OSIRIS+ (imaging and longslit spectroscopy modes) and EMIR+ (imaging and longslit spectroscopy modes) can be requested for the execution of a GTC-LP. A single instrument or a combination of the four instruments can be requested.
- ToO proposals are not accepted for Large Programmes at GTC and it is also not allowed to request the use of diffuser/narrow band filters with HiPERCAM for GTC-LP
- GTC-LP should comply with the conditions, particularly those regarding dark, gray, and bright night time, described here (https://ocan.iac.es/night-cat/regular-and-large-proposals/)
- 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 Note, however, that payback for bad weather or technical failure in visitor mode will not be offered.
How to submit
Starting from 2026B, proposals will need to be submitted through the new proposal submission service (https://proposals.iac.es/).
Please note that both PIs and Co-Is need to be registered. It is advisable to proceed to registration and proposal preparation well in advance of the proposal submission deadline.
Requests for technical support on the proposal submission service should be directed at helpdesk-cat[at]iac.es