Applying for ESO observing time

The Call for Proposals for Period 115 has been announced (for observations between 1 April – 30 September 2025). 

Under the terms of the Strategic Partnership between ESO and Australia, Australian-based astronomers have access to the facilities of the La Silla and Paranal Observatories, specifically the:

• 3.6-m telescope (3.6);
• New Technology Telescope (NTT);
• Very Large Telescope (VLT); and
• Very Large Telescope Interferometer (VLTI).

Complete details on how to apply can be found at the P115 Call for Proposals web page. All applicants should consult the Call for Proposals document for Period 115, and are required to update their ESO User Portal accounts to submit or be on proposals.

Any questions about policies or the practical aspects of proposal preparation should be addressed to the ESO Observing Programmes Office, [email protected]. Applicants who may wish to seek advice on proposal or observing strategies, optimal choice of instrument, etc. are invited to contact AAL’s ESO Program Manager at [email protected].

What’s new in Period 115?

Applicants are strongly encouraged to review the expected changes in instrumentation offered and procedures for Period 115 given in Sec. 3 of the Call for Proposals. Among the items likely to be of most interest to the Australian community are:

1. Changes to Proposal Cycle: The Call for Proposals for the La Silla Paranal Observatory will move to a yearly cycle in 2025. To address the increased duty cycle resulting from this change, a Fast Track Channel with staggered deadlines throughout the year will be introduced simultaneously. The criteria and frequency for the Fast Track Channel are under discussion with the ESO advisory committees (Scientific and Technical Committee and Users Committee). The community will be informed regularly about the implementation of the yearly call and the Fast Track Channel through newsletter posts and direct emails to active Principal Investigators.
2. No Large Programme proposals accepted in P115: Large Programme proposals (those seeking >100 hrs over 1-4 Periods) are only accepted once per year. During the transition from the current six month Periods to the new yearly cycle, it is anticipated that new Large Programme proposals will be accepted in one of the Calls for Proposals in 2025.
3. Maximising your chances of being scheduled: In the interests of maximising their chances of being able to be scheduled even if highly ranked, applicants are strongly urged to consider the essential information provided in the Forecast of telescope pressure by telescope and by Right Ascension. Proposals exploiting less favourable weather constraints for UT1 are particularly encouraged. The telescope pressure at UT3 and UT4 for certain ranges of RA and observing conditions remains very high due to ongoing commitments (in particular Large Programmes). Proposals requesting time in the RA and constraint ranges listed below may be allocated time only if they are ranked particularly highly, and request complementary or more relaxed constraints:
   • UT3: 16h < RA < 19h with Turbulence Category ≤ 30% and any moon.
   • UT4: 9h < RA < 15h with Turbulence Category ≤ 50% and dark or gray time.
4. Joint VLT/I-ALMA proposals: ESO has a joint channel for scientific programmes requiring both VLT/I observations and ALMA observations. ESO may award a maximum of 50 hours of ALMA observing time on each of its arrays to Joint Proposals per year. Further details can be found on the Joint VLT/I-ALMA proposals page. ESO has confirmed that ALMA would always treat an Australian-led Joint VLT/I-ALMA proposal as “Open Skies”, regardless of whether they get their time allocated through ALMA’s own joint proposal process, or through a joint VLT/I allocation. If in doubt, users should contact the ALMA helpdesk.
5. FORS2: The FORS2 Absolute Photometry (FAP) is being decommissioned in early 2025, which means that users from P115 onwards can no longer rely on the zeropoints and extinction coefficients to photometrically calibrate their data. The pipeline is currently being prepared to calibrate imaging data observed with the standard BVRI filters using Gaia synthetic photometry. ObsPrep will allow users to verify the availability of Gaia stars with synthetic photometry during Phase 1. If none are available, the user is expected to request additional standard star observations if needed, as part of their allocated observing time. Under the FORS Upgrade project (FORS-Up) the original FORS1 will be refurbished and upgraded, while FORS2 will remain in nominal operation until the conclusion of Period 116.
6. VISIR: ESO plans to decommission VISIR in the coming semesters because the demand and allocations for this instrument have been very modest. Moreover, no further spare parts for maintaining the instrument are available. Proposers should take into account that VISIR will likely be decommissioned as early as P116.
7. Simultaneous usage of HARPS and NIRPS on the 3.6m: NIRPS and HARPS can be used simultaneously to collect spectra from 380nm to 1919nm (with a gap from 689nm to 974nm) in a single acquisition. Users requesting to use both NIRPS and HARPS should select NIRPS instrument in P1 and declare the intention of using both instruments in the Special Remarks field of the proposal. The NIR Laser Frequency Comb for NIRPS is not yet fully operational and might be available during Period 115 (after remaining issues are resolved).
8. NTT instrumentation: ESO plans to decommission EFOSC2 at the end of Period 115. The installation and commissioning of SoXS – the Son of X-SHOOTER – is expected to start by the end of Period 114, but the instrument is not planned to be offered until Period 117.

We remind applicants of the following important policies:

• Distributed Peer Review: ESO uses a Distributed Peer Review (DPR) process for proposals requesting a total time (including overheads) of less than 16 hours, with the exception of proposals including at least one ToO run; proposals for Calibration Programmes; Joint proposals; and DDT proposals. All other proposals submitted will be reviewed in the usual way by the OPC and its sub-panels. PIs of proposals qualifying for DPR accept that their proposals are reviewed by ten peers who have also submitted proposals in that Period, and consent to reviewing ten proposals submitted by their peers as laid out in the DPR rules and guidelines. The PI may elect to delegate the reviewer’s role to one of the co-Is listed in the proposal.

• Visitor Mode: Requests for Visitor Mode observations may be submitted (and are encouraged for new users in particular) for P114, although any scheduled runs may need to be executed in Designated Visitor Mode instead for operational reasons. Direct Qantas services between Sydney and Santiago operate 4 times per week, as well as daily services on LATAM via Auckland, and direct LATAM services between Melbourne and Santiago 3 times per week. ESO will pay for the costs of one visiting observer per run, and may also cover the costs of an accompanying student.
• Scientific keywords: From the p1 interface users must select at least two keywords, and at most five keywords (ten for Large Programmes). The keywords must be selected in decreasing order of relevance (i.e., the first selected keyword is the most relevant).
• Proposal anonymisation: Under the Dual-Anonymous Peer Review (DAPR) policy applicants must formulate the scientific rationales of their proposals following these anonymisation rules and examples, which includes a detailed description of the DAPR paradigm. Failure to abide by the DAPR rules may lead to the disqualification of the proposal.
• If Artificial Intelligence services are used to help write a proposal, the PI remains responsible for the content of the proposal and ensuring the text is properly referenced according to normal scientific standards.

Important Data Privacy Notice for all recent and intending Australian ESO applicants

ESO supplies AAL with telescope/instrument demand and time allocation data relating to Australian astronomers only. Australian ESO applicant data is used only for statistical purposes, and will only be published or made available to other third parties such as AAL member institutions, in aggregated and anonymised form. ESO’s data collection/use provisions are available on the AAL ESO Forum for reference. It may be necessary to use automated data matching from data provided to the Data Central Lens proposal database to confirm the identity of ESO applicants. Applicants may opt out of providing data for Australian statistical purposes (including those from previous Periods) by contacting [email protected].