EUROPEAN SOUTHERN OBSERVATORY
Policy for Target of Opportunity Observations
Policy for Target of Opportunity
||Olivier Hainaut, 2002-May-20
||J. Melnick, J.Breysacher 2002-Jul-01
||J. Melnick, 2002-Jul-04
2003-apr-09/2.2.3/clarified compensation, ohainaut
2003-jan-18/2.2.2/clarified dead line, ohainaut
2002-nov-08/2.2.1/link updated, ohainaut
2002-sep-24/2.2.0/minor changes for Web Form, ohainaut
2002-jul-15/2.1.0/minor changes, visas
2002-may-20/2.0.0/update for SciOp
1999-jan-1/1.0 first official version
1997/0.0/ internal La Silla policy, Ch.Lidman
1. Preliminary Remarks and Definitions
Target of Opportunity Observations (ToO) are needed to follow-up transient phenomena
of great scientific interest. There are basically two types of events
that trigger ToO:
- Unpredictable sudden astronomical events which require urgent or immediate
observations. Those should be submitted as Director Discretionary Time (DDT)
proposals, following the procedure described in the DDT
Proposal web page. In this document, we refer to these ad DDT ToOs.
- Events predictable in a generic sense only. This is typically (but not limited
to) transient phenomena, and follow-up or co-ordinated observations of targets
of special interest. Telescope time to observe these events is obtained using
the normal proposals for observing time that go through the OPC review. In
this document, we refer to these as OPC ToOs.
Because the support scientist on La Silla are already fully occupied with normal
observing programmes, ToO impose an additional, often heavy, work load on them.
ToO can also consume a significant fraction of a scheduled observing programme.
Therefore, it is necessary to restrict ToO's in order to limit their effect
on staff and scheduled programmes, while preserving their scientific return.
This document describes the restrictions to be applied at La Silla to achieve
Also, to ensure the success of the ToO observations, it is critical that La
Silla receives all the information needed in the shortest possible time. This
document describes the information needed and the procedure to make it available
to La Silla.
2. Delegation of Authority
2.1- DDT ToOs
DDT ToO's can only be authorized by the following
The normal procedure is that the proponent sends a request to Director's Discretionary
Time Committee (DDTC) following the procedure described in the DDT
Proposal Page. The DDTC transmits its decision to La Silla. During holiday
periods, week-ends, or after working hours in Garching, the proposals are transmitted
automatically to La Silla. For these cases, upon receipt of a proposal, the La
Silla Shift Leader must contact the La Silla Director to request approval of the
observations. When the Director cannot be reached, his authority is automatically
delegated to the Head of SciOp, then to the Head of Astro, then to the Shift Leader.
- The Director General or his delegate (the DDTC)
- The Director of La Silla
2.2- OPC ToOs
Only the PI of a OPC ToO program can trigger an observation for that program.
For large consortia, the PI can send in advance a list of authorized triggerer.
An observation triggered by a Co-I not included in that list will be rejected.
Once a trigger is received from an authorized person, the SciOp Shift Leader will
check that the requested observations fit within the available time quota for
3.0 Dead line
ToO trigger must reach La Silla before 16:00 local time.
3.1 ToOs on National Telescopes
ToO observations on national telescopes during national time must be requested
through the chairpersons of the corresponding committees, to be executed either
by the scheduled observers, or by La Silla staff. In the latter case, the
La Silla Shift Leader must be kept fully informed, and s/he will follow the rules
3.2 Trigger of ToO observations
An OpC ToO trigger must be submitted using the ToO Web Form available on the SciOp
Web Page, and it must include the name of the Observation Block(s) (OBs)
to be executed. In case these OBs cannot be updated for coordinates of the objects,
the coordinates must be included in the form.
A DDT ToO trigger must by submitted following the procedure listed on the DDT
page. Once the program is accepted, you will receive further instructions.
In case of extreme emergency, a request can be sent to email@example.com. Ideally,
this should include the name of the OB to be executed. However, considering the
urgency of the observations, this can be relaxed to a detailed description of
3.3 Time spent on ToO
The OPC recommends programmes for telescope time (TT) allocation for OPC ToO observations.
The Director (or DDTC) allocate shutter time (ST) for emergency DDT ToO observations.
- Telescope Time (TT) is the total time spent for the observations.
TT includes time to change configuration, point the telescope, acquire guide
stars, expose, read-out, calibrate, etc. It is measured from the time
the telescope is taken over by the ToO observer, until the time the scheduled
observer begins the first exposure after the ToO.
- Shutter time (ST) is the time during which the telescope is collecting
photons on the ToO target. ST does not include pointing, acquisition, or calibrations.
- ToO observations cannot exceed the following limits of telescope time:
- OPC ToOs: 3 hours of TT per run (i.e.
scheduled programme) or per 3 nights in the case of longer runs (within
the limit of the total OT approved by the OPC).
- DDT ToOs: 2 hours of TT per run
or per 3 nights for longer runs.
The above restrictions can only be over-ridden by the Director General or the
Observatory Director, and this approval will be granted only in very exceptional
- No ToO observations can be scheduled during 1-night runs.
- ToO observations requiring more time than specified above must be spread
over consecutive observing runs, if justified.
- ToO cannot be imposed over time-critical scheduled observations as established
in the OPC-approved proposal (e.g. occultations).
- Follow-up and monitoring ToOs must be scheduled in Service, Reserved, Technical
or Idle nights. If not at all possible, the timing of the follow-up or monitoring
observations must be adjusted in order to minimize the impact on regular programs.
To summarize, the table below lists the maximum number of hours that can be allocated to ToOs.
Observers of Visitor Mode programs interrupted by a ToO for more than 1 hour
TT (per run or 3-night period) may request compensatory observations in "Queue
Scheduling" Service Mode by the La Silla Science Operation Department., for a
total telescope time less than or equal to the time they lost minus 1h (e.g. a
program that has lost 2.5h can request 1.5h compensation). Whenever possible,
SciOp will schedule and execute these observations during special nights reserved
for this purpose. The affected visitor will have to submit a reduced "Phase
II" package using the ToO Web Form, including
SciOp will attempt to schedule the lost OT on a best effort basis, subject
to the usual astronomical constraints (weather, coordinates, moon, etc.).
Since in general it may not be feasible to compensate all the lost time, priority
will be given to the observers who lost the largest fractions of their scheduled
time. The pending compensations will be declared obsolete and removed from the
queue at the end of the visibility period of the OBs.
- list of OBs to be executed, totalling to the TT lost.
- finding charts, mandatory for spectroscopy
- Strategy instructions
5- Requirements to ToO PI's
5.1- OPC ToO
In order to be scheduled, an OPC-approved ToO PI must provide the following
- Phase II package, as described in the Phase
II instructions, including
- a README
- a set of OBs with dummy coordinates
This Phase II package has to be submitted before the Phase II deadline
defined by SciOp, and has to be approved by the corresponding support astronomer.
- With ToO Web Form triggering the alert, the PI must submit
- a list of the OBs to be executed. Ideally, the OBs should be updated in
the Repository, but if that is not possible, the coordinates can be included
in the email
- a list of calibrations to be acquired (either generic "standard calibrations",
or a list of pre-defined OBs).
- Upon reception of the confirmation email from the ToO Web Form, a finding
chart of the target if it is identified must be sent following the instructions
in the confirmation email.
5.2- DDT ToOs
For DDT ToO proposals, an effort should be made to provide as much as possible
of this information, and the PI must be available for questions before and during
the observations. The following information must be included in the ToO Web Form
- A description of the observing strategy
- A set of OB descriptions:
- Precise coordinates precessed to J2000 and integrated to the epoch of
- Filters with ESO numbers for non-standard filters
- Wavelength range and resolution. Grism or grating ESO number and central
wavelength when applicable.
- Slit position angle if relevant.
- Detector setup (readout speed, binning, windowing)
- Any constraints such as time, seeing, photometric conditions, moon distance,
airmass, etc., must be clearly specified. For example, for transient
sources such as GRB it is critical to observe the sources as soon
as possible after the alert. This and any other science constraints
must be clearly specified in order to preserve the scientific value of the
- Calibrations in addition to those provided by the calibration plans must
be specified completely. Photometric and spectro-photometric standards
will be selected by the observer unless indicated otherwise by
- A finding chart must always be provided for spectroscopy.
For imaging, it should be clearly indicated whether the field is to be checked,
and a finding chart provided accordingly. The scale and field of the
finding chart should be appropriate to the crowding and magnitude of
the targets and correspond approximately to the wavelength of the ToO observations.
The finding chart must be submitted as a PostScript file (no other
format accepted), emails following the instructions given in the confirmation
email sent by the ToO Web Form.