How to prepare TIME-LINK containers

This tutorial provides a step-by-step example of the preparation of a time-link scheduling container, one of the new features of P2PP version 3. To follow the tutorial you should have a P2PP installation on your computer and be familiar with the essentials of the use of P2PP (version 3). Please refer to the P2PP Webpage for detailed installation instructions and the latest P2PP version to be used. To the P2PP User Manual for a general overview of P2PP and generic instructions on the preparation of Observing Blocks.

Because the scope of this tutorial is to show how to prepare a time-link container in general, it is meant to be instrument independent hence it will not give you a detailed description on how to make an OB for a given instrument. Specifically devoted tutorial for each VLT instruments can be found in the Service Mode guidelines Webpage, under the Manuals and Tutorials tab section.

What is a time-link container?

The time-link container defines a sequence of OBs that has to be executed in a given order, respecting the relative time intervals specified for each linked OBs.

There are two kinds of time-link container:

  • OPEN time-link: only the lower limit - earliest after previous - of the separation interval is defined
  • CLOSED time-link: both lower - earliest after previous - and upper limit - latest after previous - are defined

Because there is a number of rules applied to the OBs belonging to a time-link container  the reader is strongly encouraged to consult the P2PP User Manual before making use of this type of container.

0. Goal of the run

Your goal here is to perform K-band multi-epochs monitoring of a star cluster using HAWK-I.For the sake of this tutorial, we will assume the following:

  1. The first epoch should be started between October 27th and November 10th;
  2. There will be 4 epochs in total;
  3. Each epoch will have a total execution window of 2 weeks;
  4. The time window between two consecutive epochs should be at least 3 weeks.

After checking the Exposure Time Calculator you find out that you need for each epoch about 45 minutes of exposure time to achieve the necessary signal-to-noise. Hence, you will create a closed time-link containing a total of 4 OBs, one for each epoch.

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1. Getting started

We assume that you have started the P2PP session, logged in and selected the run within the P2PP main GUI for which the OBs should be prepared. For the sake of this tutorial we will use the P2PP special tutorial account that ESO has set up so that users who do not have their own P2PP login data can still use P2PP and prepare example OBs. You cannot use this account to prepare actual OBs intended to be executed.

After starting P2PP and logging in using the tutorial account (i.e. login: 52052, password: tutorial), the P2PP main GUI will appear as follows:

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2. Create a time-link

In what follows we will create first a time-link container and then we will proceed to fill the container with 4 OBs.

The first step now is to create a time-link which will contain the OBs for the four epochs. To do so click on the T orange icon on the upper bar of the P2PP main GUI. This creates an entry under the Observing Runs area that look like as follow:

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Next step is naming the time-link and because there is no special requirement on the time-link's name we will called it t1. Select the time-link with the mouse, press Enter and type t1 in the New TimeLink field. The P2PP main GUI should then appear as follows:

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3: Define an OB within a time-link

To create an OB within the time-link t1, click on the OB blue icon on the upper left side of the P2PP main GUI. This creates an entry under the Observing Runs area. The red dot next to the OB name means that the OB fails to pass some fundamental verification criteria, as may be expected from the fact that no template has been attached to the OB yet. At this point your P2PP main GUI looks like the figure here below:

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3.1: Naming the OB

Because the first OB we will prepare corresponds to the first visit to the target we decide to name it epoch1, To do so - as done previously in case of the time-link container - select the OB, press Enter and type epoch1 in the field No Name.
The P2PP main GUI now looks like this:

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3.2 Define the OB acquisition template

Double click on the OB name to have access to the main OB window where you define the contents of your OB. Because this OB will define standard imaging observations through the K-band filter, we decide to name the Observing Description as imaK. Thus type imaK in the OD Name field.

In the case of HAWK-I, the Instrument Comments field refers to the IR magnitude of the brightest object in the sampled FoV, hence in order to provide that information you check the 2MASS catalog. In this tutorial we will assume that the brightest object has J=11, H=10.8, K=10, that are the values you need to enter.

The first template that must be part of any science OB is the acquisition template, so now you need to choose it and specify the appropriate parameters. In the Template Type field make sure that the acquisition entry is selected. This will list all the acquisition templates available for HAWK-I in the Template list below to it. In this example you do not need a very precise pointing, hence from the Template list select the HAWKI_img_acq_Preset template and then press add button to add it to the OB.

Your decision for the values of DIT and NDIT depends on the brightness of the target. Since we assume here that in your field there are fairly bright stars that are easily identifiable in a short exposure of 5 seconds long, you type 5 in the DIT field and 1 for the NDIT values. You then select the following parameters:

  • Alpha offset for the target (arcsec): 115 (to prevent the target center from falling within the detectors gap)
  • Delta offset for the target (arcsec): 115(to prevent the target center from falling within the detectors gap)
  • Filter Name: Ks

The remaining parameters can be left as their Default values.
At this point the OB main GUI should appear as follows:

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3.3: Define the OB science template

Now it is time to insert the science template. On Template Type select now science and the existing HAWK-I science templates will appear. In this tutorial we will use the HAWKI_img_obs_AutoJitter template that allows you to randomly move the target within a given box whose width is defined by the user. In our example we will choose a jitter box width of 60" to get rid of the detectors gap. Select the aforementioned template from the list and then click on the Add button on the right side. After consulting the Exposure Time Calculator you decide to use a DIT of 10 sec, NDIT of 20 and to take 13 exposures. The science template has thus the following parameters:

  • DIT: 10
  • NDIT: 20
  • SATLEVEL: 25000 (Default)
  • Number of exposures per offset position: 1
  • Return to Origin? (T/F): True (Default)
  • Observation Category: SCIENCE (Default)
  • Jitter box width: 60
  • Number of offset within a box:13
  • Filter Name: Ks

The OB main window should look like this:

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3.4: Inserting the Target information

To access the view window where the Target information are, click on the Target icon in the top left of the main OB window. In this example we assume that the target name is cl01 and it has the following coordinates: (RA;DEC)=(07:08:09 -29:30:31). You hence fill these values in the corresponding fields. The Target OB view window should then look like as follow:

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3.5: Filling the constraints set

Click on the Constraint Set icon in the upper bar of the OB view window to access the fields related to the observing constraints. Here we assume that the observation can be performed in clear condition, with a seeing of 0.8", airmass not below 1.6. The rest of the parameters can be left as their default values. Now the Constraint Set OB view window appear as follow:

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3.6: Setting the Time Intervals

Click on the Time Intervals icon in the upper bar of the OB view window to access the fields related to the observing time constraints.

As mentioned in section 0 we want the first epoch to be executed between October 27th and November 10th, hence to do so click on the New TI button in the right part of the Time Intervals OB view window. This will open a pop-up window where you should provide the time window suitable for the observation of this OB. Select 2012-10-27 and 2012-11-10 in the Start and End date field, as shown below:

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Once you click on the OK button in the pop-up window, the OB view window should look like as follow:

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Now, if you go back to the P2PP main GUI, in the Schedule tab, you can check under the Abs. Time Interval column that the first OB just prepared has indeed 1 absolute time critical window.

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3.6.1: Setting the Relative Time Intervals

Once the first OB of our time-link is completed, the next step is to create the second epoch OB. Because in this tutorial we assume that for all epochs the observing strategy (i.e. mode, filter, exposure time) is the same, the easy and quick way to proceed is to duplicate the first OB. To do so, select with the mouse the OB and then click on the green arrow icon in the upper bar of the P2PP main GUI, which at this point looks like this:

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As you see, duplicating a time-link OB which has an absolute time interval triggers a pop-up window which warns you that only the first OB of the container can have a given absolute time interval.

Click on the Yes button to proceed with the OB duplication. The P2PP main GUI should then appear as below.

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The duplicated OB, automatically named epoch1_2, is hence a copy of the first OB (epoch1) with the exception for the time interval. If you double click on the second OB to have access to the main OB view window you will noticed that unlike the first OB, the second does not show the Time Intervals icon in the upper bar. This is also reflected in the P2PP main GUI under the Schedule tab area. In case of the second OB the field under the Abs.Time Interval column is empty. However, unlike the first OB, now it is possible to set some Relative Time Intervals by filling the fields under the Earliest After Prev. and Latest After Prev. columns.
In section 0 we have assumed that the time between to consecutive epochs should be at least 3 weeks but not exceeding 5 weeks, hence under the Earliest After Prev. column select 21d (i.e. 21 days) and type 35d (i.e. 35 days) in the Latest After Prev. field. For convenience, rename the OB epoch1_2 as epoch2 as done previously in section 3.1.
Now that the second epoch OB is finished we can create the third and fourth epoch OBs by duplicating OB epoch2. As done previously, select with the mouse the second OB and click twice on the green arrow to have two identical copies of such OB. When done you notice that this time the duplication did not trigger any warning message pop-up window. This is because you have duplicated an OB which does not have the absolute time interval.
If you have followed all the instructions given so far, then the P2PP main GUI should appear as below:

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Finally as done in section 3.1 you can re-name the last two OBs as epoch3 and epoch4.

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4: Time-link and OBs priority

If you have followed all the instructions given so far, then in your P2PP main GUI you should see four OBs within a time-link as shown here below:

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As can be seen in the P2PP main GUI, under the Schedule tab and priority column, the priority is associated only to the container and not to the OBs within that given container. This implies that all the OBs of a given time-link share a unique priority although the sequence of their execution is given by the absolute and relative time intervals.

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5. README, Finding Chart and Package Submission

With the completion of the time-link we consider this tutorial to be finished. However, the Phase 2 package preparation is completed only after providing the finding charts and the README file. The reader can refer to the following pages for a more detailed description of the final three steps:

  1. Attaching the Finding Chart
  2. Filling the README file
  3. Submitting OBs and containers

 

Click here to return to the general P2PP documentation page.

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