Target of Opportunity (ToO) Observations

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Observers who expect to observe unpredictable events ("Targets of Opportunity", ToO) with the 2.2- or/and 3.5-m telescopes at Calar Alto are required to submit a general application for observing time, like for standard observations. In this application, the scientific case, the aim, and the method of the proposed observations should be presented. The application will be discussed by the Calar Alto Time Allocation Committee (
TAC). In order to be approved, the proposal should obtain a high grade.

Should the proposed observations be approved by the TAC, the approval is limited to one semester. Should it be necessary to continue observations after this period, a new application is required, together with a status report presenting the results obtained thus far.

ToO observations generally have an override status. Exceptions will be defined beforehand by the director of CAHA (e.g. for time critical programmes). In case more than one ToO occurs in the same night, CAHA staff reserves the right to restrict the observations. Follow-up observations (if approved by the TAC) shall be scheduled in advance, once the initial trigger is performed.

When possible, a compensation of the observing time lost for the current observer will be attempted (in service mode for ToOs triggered during visitor mode runs).

How to trigger a ToO?

The PI of the accepted proposal should contact CAHA staff ( sending the additional material (expected brightness, details of the observations, finding chart, etc.). CAHA staff will confirm the reception of the material ASAP (feedback at night is insured quickly all year long, but it might be slower at day during the week-ends/holidays). The observations will then be attempted if possible. In exceptional cases, the night observers (CAHA staff only) may be alerted by phone at the observing rooms (+34 950 632 500, ext. 572 or 575), but only after the written request has been sent. The maximum number of triggers accepted by the TAC might be extended, after agreement by the CAHA staff and/or CAHA director, until the total time allocated to a given is reached (e.g. addtn'l triggers at the end of a semester, if there is time left from the one allowed by the TAC).

Who can trigger a ToO?

Under any circumstances, a researcher WITHOUT an approved ToO program must NOT contact the CAHA staff, specially the night observers (including visitor programmes), to conduct an observation which has not been approved by the TAC or the director under a DDT program.

Guidelines for the visitor astronomers:

When a ToO program is activated during a visitor program, the CAHA staff will communicate it to the visiting astronomer and the time lost, when possible, will be compensated (most likely in service mode during available buffers). Visitor astronomers cannot begin any ToO on their own, or any other observation which is not described in the approved proposal by the TAC, without the consent of the CAHA staff and/or the CAHA director.

Programs not approved as ToO by the TAC will not be approved as DDT by the director during the same semester.

Last updated: September 2020