Call for Proposals
PERIOD 73:   April 1 -- October 1, 2026

The Nordic Optical Telescope (NOT) invites applications for observing time in Period 73, April 1 -- October 1, 2026.

The deadline for receipt of the applications is: Monday, November 10, 2025, at UT 12:00 noon.

Information for applicants

The applicants are reminded of the following:

The share of observing time for applicants will be proportional to the contributions from the different Partners. Regular visitor-mode observing is the basic mode provided to researchers affiliated with the Partner institutions, and does not require any user contribution. For any services requested beyond basic access (visitor mode), a contribution to the operational cost will be required. The detailed rules for the allocation of observing time and the related user contributions can be found at
  http://www.not.iac.es/observing/rules/ObservingTimeAndContributions.pdf

Only 75% of the science time can be scheduled by NOT; the rest is Spanish time (20%) and ITP time (5%).
The total time allocated to non-partner programs will be limited to ~15% of the Nordic time. For such external/foreign projects, the full financial user contribution for 'External projects' is expected in order to compensate for the operational cost of NOT.

Applicants will be informed of the outcome of their proposal as soon as possible after the evaluation by the NOT Observing Programs Committee and preparation of the observing schedule by the Director and NOT staff. Brief explanatory notes are provided to proposers, especially for rejected proposals. Awards of observing time do not imply any financial support from NOT.

Late applications are not accepted. However, proposals for short programs (≤ 4 hours) are welcome at any time (see http://www.not.iac.es/observing/service/). This Fast-Track program is a service that is provided free of cost to researchers affiliated with a Partner institution.

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Applicants should carefully read the following instructions:

1: Proposals for projects of all sizes are welcome, large and small as well as medium-size. Pooling of related and synergistic proposals by consortia of groups with similar interests is encouraged.

Visitor-mode observing is the basic mode provided. Programs requiring service mode observing, or propose a Monitoring, Target-of-Opportunity (ToO) or similar projects, should so indicate this in the proposal. In principle, compensation is provided in service mode for any observing time affected by Monitoring or ToO observations.

Applicants for regular observing programs (in visitor mode or service mode) who consider that having ToO programs possibly overriding their observations, or having Monitoring observations scheduled in nights allocated to their program, is a (potential) problem for their program, should state so in the proposal, indicating the reasons.

Applicants having particular, or complex scheduling requirements should contact the Director (directorate@not.iac.es) in advance in order to discuss optimum strategies.

Proposals requesting more than one observing run in the period (using different instruments on a project counts as separate runs) should specify them individually in the proposal as indicated in the LaTeX template form.

2: With a Large Observing Proposal one can apply for observing time for multi-semester programs. A separate proposal form has been prepared for Large proposals, which can be downloaded together with the regular proposal form. The proposal submission is the same for both regular and Large proposals. The detailed rules applicable to these Large Proposals can be found at http://www.not.iac.es/observing/largeproposals/LargeProposalsRules.pdf

3: The proposal submission procedure is electronic. The Latex template and style files for Period 73 are available at the NOT web site: http://www.not.iac.es/observing/proposals/P73/. Detailed instructions are provided in the template file itself and in a README file; they should be followed carefully. Applicants should process and view the output of their files before submission, in order to check that they process properly. Proposals using modified style files will not be accepted.

As of Period P73 the LaTeX version to be used for compiling your proposal is 'PDFlatex'. This implies that not only PS figures can be used for illustration, but also other image formats (PDF, JPG, EPS, PNG), as supported by 'PDFlatex'.

4: Regular and Large proposals should be submitted by e-mail before the above deadline to: proposal@not.iac.es, with the word "Proposal" as Subject. Automatic e-mail acknowledgement of receipt, with notification of any problems encountered in processing, is provided. Before the deadline, questions on proposal preparations or procedures may be sent to the same address with "Question" as the Subject.

5: Up-to-date information on instruments at NOT (ALFOSC, FIES, NOTCam, StanCam) is found at
      http://www.not.iac.es/instruments/.

Please note the following features for Period 73:

• The double-image polarimeter DIPol-UF remains available as a visitor instrument at the NOT. It allows for high-speed and high-precision broad-band polarimetry simultaneous in 3 pass-bands (BVR), but can also be used as a high-speed 3-band photometer. DIPol-UF is not a common-user instrument, but is only supported during specific periods. See for more information: http://www.not.iac.es/instruments/dipol-uf

• The SOFIN high-resolution Echelle spectrograph is also available. It only is offered 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.

• Please contact our Director well in advance of the application dead-line if you are making plans to use your own instrument at NOT.

• We do not offer the direct-imaging instrument MOSCA anylonger.

6: We offer two recently added observing modes in Period 73:

• Rapid-response mode:
  From the end of P70 onward, we intend to perform full and final on-sky testing of our Rapid-response mode (RRM) that has been under development for some time. The purpose of this observing mode is to allow ToO triggers to start observations of fast transient phenomena as early and rapidly as possible. It is planned and envisaged, that no human interaction will be needed to pass on a trigger from a user at their own research facility to our NOT observing system, and to, possibly then also override ongoing observations. To allow these automatically processed triggers to set the NOT in motion, dedicated software has been developed in-house, while that also needs to be set up by the prospective users remotely. As for any RRM/ToO observation, affected observing programs may claim Payback time to compensate the time lost to other RRM observations.

  While the NOT Council and OPC are yet to define the exact rules under which the RRM observations are be executed, we are confident that the RRM mode can be offered in a way that is safe for staff, students and astronomers that may be present in the telescope.

  For P73 in particular, we offer the RRM mode for ALFOSC only.

  Applicants should indicate their wish to use the RRM mode in boxes on the application form that detail scheduling information and in the technical case.

• Filler mode:
  As of P70, some of the lowest-ranked service-mode programs, based on the scientific ratings given by the OPC, will be given a 'Filler-mode' status in case this does not hamper the scientific goal of the proposed observations. Such a designation, by decision of the NOT Director, gives us more flexibility to make sure that telescope time is used optimally from night to night, in addition to executing fully scheduled higher-ranked priority programs.

  Programs that have Filler-mode status will be executed in Queue-mode scheduling, but with low priority, in particular when there otherwise would be gaps of scheduled observations during the night, for any reason. Observing blocks have to be prepared in advance, and should be flexible, with only minor constraints on the observing-date window and/or other observing conditions.

  At this point we do not yet offer a dedicated way to request Filler mode on the application form, as new more formal policies regarding it, and service mode in general, are being developed for upcoming semesters. Nevertheless, applicants are free to indicate such wishes in boxes that detail scheduling information and/or in the technical case, while applying for the general case of service-mode observations (i.e., for example, whether the PI considers the program to be suitable, in principle, as a Filler mode program, should it become relevant).