The HARPS3 Open-Time Programme

Time allocations and priority bands are shown on the time allocations page when phase 1 is over. Time awarded can lie in one of the following observing priority bands:

A-band proposals have very high priority. If an A-band proposal remains unfinished at the end of the applied semester, it will be granted an extended life-time over a number of additional semesters, or until its completion, whichever comes first. Unfinished A-band proposals do not have to be re-submitted in the additional semesters because of their carry-over status. A proposal is considered as complete when the quality of the obtained data meets the applied requirements.

B-band proposals have lower priority and they will be attempted only during the applied semester, after which they will be removed from the observing queue.

C-band proposals have an even lower priority and we anticipate only a small fraction of these targets will be observed, unless they use poor conditions. C-band proposals are not carried over semesters.

6. Phase 2: observing preparation

All open-time observations go through a phase-2 system to generate "groups", which the robotic scheduler uses to create observing blocks (see below). The THE Consortium provides and maintains the Phase 2 submission tool, and ING organises the submission by open-time applicants of Phase 2 to the observations database.

7. HARPS3 observations

A HARPS3 observation block consists of a target acquisition followed by a series of exposures.

Target acquisition

Targets can be acquired in two ways. The simplest is the bright star acquisition where the brightest star in the roughly two arcminute acquisition field is placed on the fibre. There is also a blind acquisition for fainter targets where several stars are used to create an astrometric solution for the acquisition image, and a given set of co-ordinates are placed in the aperture. The decision as to which to use is made at Phase 2, by which time we hope to have more information about which approach is optimal for a given target.

Guiding

There are two guiding modes. The first is using the light from the star around the edge of fibre aperture to maintain the star centrally in the aperture. The second is offset guiding, where the system is supplied with the position of a nearby star which is held a given position in the focal plane. Again, the decision as to which mode to use is made a Phase 2, at which time we will have identified which approach is best for a given target magnitude.

Note than non-sidereal tracking (i.e. moving targets) is not possible.

Exposures

In 2026B all exposures in a block must be of the same length. The required exposure time can be calculated using the HARPS3 Exposure-time Calculator.

Wavelength calibration, flatfields and darks

During commissioning we will establish the best calibration procedures, and the calibration frames required each night will be obtained by the observatory and applied to the data, giving the user a science-ready data-product. In Phase 2 the observer will decide whether the fibre not being used for the object is to be used

(i) for a simultaneous observation of a wavelength calibration source, or
(ii) for observing the sky so it can be subtracted from the object or
(iii) with no light from the calibration lamps or the sky.

We expect the first of these to give the best radial velocities.

Total time required

The system has a concept of "chargeable time" which is a nominal observation time which is used for both estimating the time requirement for a programme, and calculating the time used. The chargeable time for an observation is the sum of all the exposure times, plus the acquisition time (which includes a nominal slew time), plus the CCD readout times for all the exposures except the last one. (This is because the final CCD readout will occur whilst the telescopes is slewing to the next target.) In 2026B observers should use a CCD readout time of 34s and an acquisition time of two minutes when calculating the time requested (use the HARPS3 Total Time Estimator).

Spectropolarimetry will not be offered in 2026B.

8. HARPS3 scheduling

Observations are arranged in groups. A group is a set of observations of a target which share the same scheduling mode and observing setup. For example, an observer wishing to observe HD123456 every night for 4 weeks months might create a block of 28 identical observations using “monitoring mode�. The modes available in 2026B are as follows.

Single observations

A group of just one observation, where the sole time constraint is that it must be carried out between two given times (technically the “group enable� and “group disable� times), which are set in Phase 2. If the times are the beginning and end of the semester the observation can be carried out at any time, but much tighter constraints (for example to force overlap with observations from another facility) can be given. If the observations are highly time constrained (to less than a one-month period) please state this in the technical section of the proposal.

Phased observations

This scheduling mode is primarily intended for programmes where observations of a transit or eclipse are required, and the event in question lasts significantly less than a night. However, it can be used for any periodic phenomenon. The timing of the observations is defined by three parameters set in Phase 2. The first two are a phase zero time and a period with which the event recurs at the Solar System barycenter, in Barycentric Dynamical Time (TDB). The final parameter is the half width of a window within in which the observation must occur. The entire observation must lie within the window.

Monitoring observations

This scheduling mode is intended for programmes which want to observe a source regularly, for example every hour or once a week. In Phase 2 a monitoring period is set, and an allowed range around the period defined by a window half-width. The differences between this and phased observations are as follows.

1. The timing is in UT as opposed to TDB.
2. An observation can be carried out after the window has closed if it has not occurred within the window.

For example, consider a target with a four-day monitoring period but a window which is only a night long. If a given night is missed, the scheduler carries on attempting to make an observation, rather than waiting three more nights for the next slot. Once the observation is made (maybe after a five-night gap) the scheduler will next try to observe on the fourth night after the successful observation. Note that the mid-point for the observation window is always moved to the nearest occurrence of 01:12UT (roughly local midnight) to allow the user to set sensible window widths which cover entire nights.

This scheduling mode behaves rather differently if the period is set to less than a day. If, for example, the period is set to be 2 hours then at the beginning of the night windows will be set centered on 17:12, 19:12 etc, and the scheduler will attempt to place observations close to each of those times.

Targets of opportunity

Entry of targets after the start of the semester will not be possible in 2026B.

Additional Constraints

In Phase 2, in addition to the above scheduling modes observers should be able to request additional constraints. Below we list those ones that we hope to implement for 2026B.

1. That a target is not observed when it is lower in the sky than a given altitude.
2. That a target is not observed if
   1. the Moon is in the sky and
   2. brighter than a given fractional illumination.
3. That a target is not observed if
   1. the Moon-target distance is smaller than a given value and
   2. the Moon is brighter than a given fractional illumination.
4. That a target is not observed if
   1. the difference between the radial velocity of the target and that of scattered moonlight is smaller than a given value and
   2. the Moon is brighter than a given fractional illumination and
   3. the Moon is higher in the sky than a given altitude.
5. That a target is not observed unless the Sun is a given distance below the horizon.
6. That a target is not observed if the seeing is worse than a given value.

Observation length

Observations requiring more than 3 consecutive hours on the same night are not possible given the scheduling constraints imposed by the THE survey.

9. Data availability

Our aim is that HARPS3 observations will be passed through a data reduction pipeline the morning after they were taken. The data products should include a radial velocity and its photon-noise uncertainty, as well as extracted, wavelength- and flat-field-calibrated, two-dimensional echelle spectra. There should also be a flux calibrated spectrum, although the instrument response function will not be derived on a nightly basis. These data products and the raw data will be made available to users via the HARPS3 archive.

10. Data ownership and publication

The open-time applicants own their HARPS3 data, following ING standards. The data are available to the THE Consortium but only for the specific purpose of data quality control checks. Public availability for HARPS3 raw and DRSP processed data starts one year after observations, except for those data obtained for the THE Consortium Core Survey.