ToO Policy

CTIO Blanco 4-m Telescope
Target-of-Opportunity Observing Program Policies

For the attention of: CTIO staff, Blanco 4-m telescope observers, CTIO Blanco 4-m telescope ToO program principal investigators.

Updated on: 3 August 2020

CTIO follows the NOIRLab Target of Opportunity observing program policy ( with the addenda given below for the V. M. Blanco 4-m telescope. We thank observers for their forbearance and co-operation with these policies

A) Before triggering your first interrupt

Communications with the observatory regarding your ToO program should be made by email to; please always include the propid of your program in the subject line of any messages.

This email alias includes the CTIO Director and Deputy, the DECam Instrument scientist, and the other members of the CTIO scientific staff comprising the DECam support team. It also includes members of the Telescope Operations Staff, in Chile, and the data management staff in Tucson who are responsible for handling and pipeline processing the data. Communicating through the DECamToO alias is the only way to ensure that everyone who needs to know about your ToO program is kept in the loop.

At the beginning of the semester well before triggering your first interrupt please send an e-mail to in order to:

  • Check communication
  • Identify the individuals authorized to trigger ToO events. Only the PI of the program or their deputy previously authorized by the PI, are allowed to trigger observations. Requests from others will not be acted upon until we are able to confirm the request with the PI.
  • Touch bases with the Support Scientist assigned for your program (hereinafter referred to as the ToO Support Scientist). They will work with you to plan your observations to the extent possible in advance, and in particular will help you develop a template DECam observing script which can be edited according to the specific circumstances of an event and then executed in order to carry out the required observations.
  • Make contact with the data management folk to discuss any special data processing needs for your program (e.g. moving object detection)

B) Call-up Procedure

ToO events can only be triggered during NOIRLab community access time. That is they cannot be triggered on nights assigned through the Chilean or AAO TACs

The regular observer and observatory support staff should hear about a ToO as soon as possible, preferably no later than the afternoon of the observing night. This allows time for email back and forth with the PI of the ToO program, and for making any necessary preparations.

To initiate the process of triggering an observation for their Target of Opportunity Program, the approved program PI or specified deputy must send e-mail to

For each night when DECam is in operation a member of the DECam Scientific support team (all of whom are included in the DECamToO alias) is "on duty" to support the scheduled observer either on the mountain, or remotely in la Serena. On receiving the email the support scientist "on duty" will inform the scheduled observer about the ToO, and will work with the PI's of the ToO and scheduled program to coordinate the collection of the required observations. The ToO Support Scientist for your run may also become involved, but, given the unpredictability of timing, should not be assumed to be available for any given event, hence the importance of careful coordination via the email alias.

C) Data taking

  1. The current observer will be asked to take the ToO data by executing an observing script. This observing script should be prepared by the ToO team with the help of the DECam support scientist on duty, using the template observing script developed in advance as a starting point. The ToO PI or deputy must send this script and any supporting information and instructions to the alias.
  2. Any images taken specifically for a ToO program must be identified with the NOIRLab propid of the ToO program to ensure that the data is correctly labelled in the NOIRLab data archive. Fixing incorrect propids post facto is possible in an emergency but very time consuming. 
  3. The scheduled observer should note in their night report whenever a ToO observation is requested, and record the amount of time that was dedicated to the ToO
  4. To access data please read ToO Data Files

Updated on July 8, 2021, 4:41 am