MIDI P2PP Tutorial

This tutorial provides step-by-step instructions for the preparation of a set of OBs for MIDI, the mid-infrared beam combiner for the VLTI. Since Period 90, MIDI OBs have had to be created as part of containers using the new P2PP Version 3. To follow this tutorial, you should have P2PP installed on your computer and be familiar with the essentials of the use of this software. Please refer to the instructions in order to install it, and to the P2PP User Manual for a general overview of P2PP and generic instructions on the preparation of Observing Blocks.

The Phase 2 process begins when you receive an email from the ESO Observing Programmes Office (OPO) informing you that the allocation of time for the coming period has been finalized and that you can view the results by logging into the UserPortal and clicking on "Check the webletters." Note that the username and password that you need to login to the User Portal are the same as those you need to provide to P2PP when preparing OBs for your own runs.

1: Goal of the run

Via the User Portal, you find out what time was allocated to your run. In this tutorial, we will therefore prepare a concatenation of two OBs, one for the science target and one for the calibrator. In our example, we had proposed at Phase 1 to observe Alpha Orionis with the prism on the UT2-UT4 baseline. Now, we have to provide more specific instructions for the observations, such as which filter to use for the target acquisition, finding charts, and which LST range to request.

2: Getting started

First, you should have available the following documentation:

Please start P2PP3 and login to the tutorial account with the following credentials:

  • P2PP ID: 52052
  • password: tutorial

This is a special account that ESO has set up so that users who do not have their own P2PP login can still use P2PP and prepare example OBs. You cannot use this account to prepare actual OBs intended to be executed. To do the latter, login to P2PP using your own User Portal credentials. You will then see a list of all the runs for which you are the PI.

The P2PP main GUI will then appear as follows (click on the MIDI folder to select it, this will also show the icons near the top in color).



3: Your First OB in a concatenation

All VLTI OBs must be part of concatenations, which is a type of container in which OBs are executed in sequence. For the VLTI, the allowed sequences are SCI-CAL, CAL-SCI-CAL, and CAL-SCI-CAL-SCI-CAL (waiver required).

First, click on the icon for a concatenation (labeled "C" in the icon bar). This creates an empty container of type concatenation in the MIDI folder. Select it with the mouse, hit <Enter> and type a name for your container, such as "Alpha Orionis 6-9" (the container names only serve to help you organize your observations).

Then, click on the icon for an OB (labeled "OB" in the icon bar), which will create an OB in your concatenation. (The red cross next to the OB name means that the OB fails to pass some fundamental verification criteria, as expected from the fact that no template has been attached to the OB yet.)

Select the OB, and enter a name just like you did this for the name of the concatenation. The name of the OB must follow the specific OB naming convention for MIDI: a science target OB must begin with SCI_ and should preferably contain the target name. In case the same target is also observed with another baseline (which implies that your program has several runs) the OB name could also include the run letter code. Assuming for this tutorial example that Alpha Ori shall indeed be observed on different baselines, the OB name in this tutorial shall be SCI_alfori-E, because the run ID for our MIDI run is 60.A-9253(E). Hence, type SCI_alfori-E in the Name field.

In the next step, we have to edit the OB information. To start this, click on the OD (observation description) button in the icon bar. This will display the "View OB" window, as shown below.


3.1: Filling in the Basic Information

OD Name

It may be useful in many cases to have an easy way of identifying an Observing Description (OD), like when having observations of a number of targets performed with identical instrument configuration and observation template parameters. The OD Name field in the View OB window allows you to define names for the ODs. The OD name appears in turn in the OB list area of the P2PP main GUI, thus allowing the identification at a glance of all OBs having ODs with the same name. In this tutorial, the observation description will define the use of the prism for the fringe observations.Thus, we enter the name Fringe_obs_prism in the OD Name field.

User Comments

The User Comments field can be used for any special requirements that you want the staff on Paranal to be alerted to (for example, to request taking an acquisition image), however, in most cases, this information should be part of the ReadMe attached to this OB, or should be included in the Calibration Requirements tab (see below). Since we don't have any special comments for this example, we leave this field blank.

Instrument Comments: Information on alternate baselines

For the VLTI instruments, the Instrument Comments field should be used if alternate baselines can be used in case the preferred baseline is unavailable. Please mention this also in the Readme.

3.2: Defining the acquisition template

The first template that must be part of any science OB is the acquisition template, so let us define it next. In the TemplateType list, select MIDI_starintf_acq. Click the Add button next to it. The window should now look like this (with some fields already set to values we enter later).



Now, you need to decide on the acquisition parameters, and if necessary, modify the default values given in the acquisition template.

The first fields to fill out in the acquisition template are the correlated and uncorrelated infrared (12 micron) fluxes of the target in the fieldsCorrelated magnitude (Jy) and Uncorrelated magnitude (Jy), as well as the H magnitude of the target in the field Magnitude in H-band. The latter is used for the settings of the IRIS laboratory guiding system. Our target, Alpha Ori, has an IRAS 12 micron flux of 4682 Jy. We expect avisibility amplitude of 0.6 with the chosen baseline. So, the correlated flux for this observation is 0.6*4682 Jy = 2809 Jy.The H magnitude of Alpha Ori is -4.0.So, we enter:

  • Correlated magnitude (Jy): 2809. (Note: despite the label, it is really the flux what is meant!)
  • Magnitude in H-band: -4.0.
  • Uncorrelated magnitude (Jy): 4682.

The next two parameters of the acquisition template are related to the direction and amplitude of the secondary mirror chopping. If you notice that the default direction of chopping (chop north, i.e. move target north) would result in taking the background in an area contaminated with other objects, you should change the parameter Amplitude of chopping and/or Angle of chopping. In our example, we choose to chop east (i.e. use blank sky to the west of the target), but leave the chopping amplitude at its default value, and therefore enter:

  • Angle of chopping:90
  • Amplitude of chopping : 15 (Default value)

Then you have to enter the filter that should be used for acquisition. Because you know that Alpha Ori shows a strong emission feature at 11.3 micron, while showing strong absorption at 8.7 micron, the default filter (please note this is just an example and doesn't have to be true for Alpha Ori at all) you choose from the filter drop-down menu:

  • Filter: N11.3

Since your science target, Alpha Ori, is visually sufficiently bright, it can be used for Coude guiding itself. Therefore you choose the following parameters in your acquisition template:

  • Coude guide star alpha: 0. (Default value)
  • Coude guide star delta: 0. (Default value)
  • Coude guiding type: SCIENCE (Default value)
  • Coude guide star magnitude in V: 1.1

The values for "Coude guide star alpha/delta " are used in cases where the science target is not bright enough to serve for coude guiding and an off-axis guide star within a radius of 1 arcmin is provided. In that case "Coude guiding type: SETUPFILE" is chosen. The parameter "Coude guide star magnitude in V" is set to the V magnitude of the target that is used for Coude guiding, whether it is the target itself or an off-axis guide star.

The next field to fill out in the acquisition template is Science or calibrator, which obviously must be Science since this is your science OB.



3.3: Defining the Observation Description/Science templates

From the Template Type menu, select now science. The only existing MIDI science template will appear. The template will be attached to the grid next to the acquisition template that we filled previously.

Six parameters have to be defined in the template MIDI_starintf_obs_fringe, which are the Number of frames per photometry exposure, the Fringe tracking at zero OPD, Angle of chopping, Amplitude of chopping, Dispersive element, and the Beam Combiner parameters. (Please note that the correlated flux mode first introduced in P88 is not available in service mode. Therefore, there should be no check mark in the corresponding box.) In this tutorial, we choose the recommeded Fringe tracking at zeroOPD=True fringe tracking mode, and PRISM as Dispersive element. Since your target is very bright (in correlated and uncorrelated flux) it is sufficient to obtain 2000 frames per photometry exposure, which is actually the minimum value. If your target would be much fainter it would be advisable to select 4000 or 6000 frames per photometry exposure (please consult the template manual). The brightness of the target also allows you to use the SCI_PHOT mode, which provides better accuracies on the fringe measurements, and hence, you chose SCI_PHOT as BeamCombiner from the drop-down menu. Finally, you define the same chopping parameters as you had defined in the acquisition template, namely:

  • Angle of chopping: 90
  • Amplitude of chopping : 15 (Default value)

3.4: Inserting Target Information

At the top of the view window you find the Target field where to insert your target name and coordinates. Please insert the target name here, which should be the same name as used in the OB naming, in other words, insert Name: alfori. Also, enter the right ascension and declination for Alpha Ori. If your target exhibits high proper motion, it is very important to enter this information in the proper motion RA and proper motion DEC fields respectively, unless the proper motion is not available. You may check the Hipparcos catalogue for these values. Please remember to insert the proper motion in RA and DEC in units of arcsec/year. For Alpha Ori one enters

  • proper motion RA: 0.0281
  • proper motion DEC: 0.0101

Furthermore, edit the entry in the Target-tabbed subpanel Class. In our case , choose Supergiant.

The acquisition template including the target information is now complete, and the window should look like this.


3.5: Setting the Constraint Set

Here you specify a set of constraints, which indicate under which conditions only your OB should be executed. You can do this by clicking onthe Constraint Set tab and filling the entries under it. Please make sure that none of the constraints specified here is more stringent than the corresponding ones you specified at Phase 1!


First, give a descriptive name to the constraint set about to be defined. Since you have decided that this constraint set will be applied to all the fringe observations, you type Fringe_obs_constraints in the Name field.

Sky transparency:

Since we assume that your observations are typical MIDI mid-IR observations and do not need exceptional atmospheric conditions you request Clear conditions in the Sky Transparency entry.


Let's assume that time has been allocated for your programme on the baselines UT2-UT4 and UT2-UT3, but this run here uses the baseline UT2-UT4. You must therefore choose UT2-UT4 from the baseline drop-down menu.



3.6: Setting the Sidereal Time

Click "Time intervals" and then select the "Sid. Time Intervals" tab where you can constrain the LST range within which your OB should be executed. In this tutorial you wish to prepare an OB that should be executed between 06h < LST < 09h, hence you do the following:

  • Click on the "New TI" button.
  • Modify the lower boundary of the sidereal time range to the specified starting LST of your LST range, keeping the same format. In the present case, the entry should read 06:00.
  • In the same way, modify the upper boundary of the sidereal time range to 09:00.
  • To edit an existing range, click on it in the display, and click the "Edit" button.
  • In case your intervals crosses midnight, you enter, e.g., 22:00 - 02:00

In the same way you could define one more alternative(!) LST range, in case the OB cannot be executed during your prefered LST range setting or you want to define two ranges before and after meridian. Please remember that defining more than one sidereal time ranges in this field does NOT mean that the OB will be executed at all these LST ranges. The number of alternative LST ranges must be the same for all OBs of a concatenation.


3.7: Verifying the OB

Once you finished with the complete entry of observation description, you should verify the OB by clicking on the "Verify" button to the right of the "OD" button in the P2PP main GUI. A pop-up window will inform you whether or not the OB parameters you entered are consistent with the requirements given in the MIDI Template Manual. In the example below, a container level error is displayed because we have not created and defined the required calibration OB yet. The warning shown in our example on the target missing in the proposal is normal when using the tutorial account, as the runs do not refer to actual OPC approved runs. However, when preparing OBs for your own runs, such a warning should not occur if you prepare OBs just for the targets you proposed at Phase 1. (OB names prefixed with CAL_ and declared as CALIB in the acquistion template are not checked with respect to Phase 1 information.)

Keep in mind that container or OB errors will prevent you from checking in the corresponding OBs, therefore these need to be fixed. 


3.8: Attaching Finding Charts

The next thing to do is to attach the respective Finding Chart(s) to the OB. The Finding Charts must be prepared as jpeg-files and must fulfill all general requirements for finding charts, as well as the specific requirements for MIDI Finding Charts.You can use any tool of your choice to create the Finding Charts in jpeg-format. P2PP itself, however, does not contain such an option.

Let's assume you have prepared a jpeg-Finding Chart for this tutorial run [remember:run ID 60.A-9253(E)], which you called 60.A-9253E.alfori01.jpg, and which is saved in a folder of your home directory.

Now, in the P2PP main GUI click on the OB which you want to associate with this finding chart, then select Finding Charts from the top menu bar, which opens a drop-down menu:

From the drop-down menu select Attach Finding Charts, which will open up a new window that allows you to enter path and filename of the Finding Chart you wish to attach to the selected OB. In our example you choose 60.A-9253E.alfori01.jpg and finally click on the Attach Finding Charts button (you could select more than one Finding Chart). The pop-up window will close and the Summaries area of the P2PP main GUI will show the entry

  • FindingCharts: (1) 60.A-92..

If you are interested in a more comprehensive explanation on howto create and attach or detach finding charts, you should have a look at this page.


4. Editing the Readme

The Readme information is used by support astronomers to know any special instructions or requirements which cannot be coded in the observations description of the OB. These instructions must however be compliant with the service mode rules, e.g. they cannot require the execution of several containers in a row.

Please fill the different sections of the Readme with concise and brief information, avoiding duplication. Enter e.g. "No constraints" in sections if applicable.

Remember to also go through the checklist (select the corresponding tab) and confirm the questions. A special tutorial is available for the Readme file.


5: Defining the Calibrator OB

Since each science OB must be followed by a calibration OB we will briefly demonstrate how to define the calibrator OB. The necessary steps are very similar to the definition of the science OB.

To select for each science target a calibration target, it is recommended to use the CalVin tool developed by ESO and based on a list of calibrators provided by the MIDI consortium. CalVin selects suitable calibrators according to different user criteria. Optimally you would wish to have a calibrator star as close as possible to and of similar brightness as your science target. Consulting the CalVin tool you find that the star HD39400 is a suitable calibrator for your science target alf Ori.

You can either repeat the steps as outlined above, i.e. you start defining your calibrator OB by clicking on the OB button after having selected the container you are working on, or you can duplicate the science OB by clicking on the Duplicate button. By duplicating your existing OB, the only fields that you need to modify are of course the ones related to the target, but not the instrumental setup.

Make sure the calibrator target name is updated in the OB name (and prefixed with CAL_) and CALIB is selected in the acquisition template. In the target tab, update the target name and enter the correct target coordinates and proper motions for the calibrator.

The LST intervals for SCI and CAL OBs in a concatenation must follow specific rules. As shown in the figure below, a CAL preceding a SCI OB must have an LST interval which starts 30 minutes before that of the SCI OB. It must end exactly at the end of the SCI LST interval, or extend it exactly 30 minutes (optionally). The same rules apply vice versa, as shown below, if the CAL follows the SCI OB. The figure below also shows the relationships between the LST intervals in a CAL-SCI-CAL sequence.

In a CAL-SCI-CAL-SCI-CAL sequence (which requires a waiver), as in a CAL-SCI-CAL sequence, the above rule implies that the LST interval of the last CAL must end exactly 30 minutes after the LST interval of the SCI OB, and the SCI OB LST intervals must be equal.


6: Finishing the preparation and submitting the OBs

At this point, after having defined and placed two OBs in a concatenation, it is recommended to verify the concatenation as whole. Also make sure that the sequence of the OBs in the concatenation is correct, as they will be executed in that same sequence.

We will now submit these OBs to the ESO Database: select the container in the main OBs view window, go to the File menu, and select the Check-in option. A dialog box will appear asking for confirmation and, if you click on OK, they will be saved in the ESO Database along with all OBs belonging to the container ("lock" symbols will be displayed). Now, you can no longer modify the OBs unless your support astronomer at ESO releases them for check-out again.

When all the OBs and the ReadMe file for a given run have been submitted, the Phase II submission for each run is finalized by pressing the "Whistle" button. This will notify the User Support Astronomer that you have completed your submission of all material related to this run.

As a courtesy to the next user who follows this tutorial, we would like to ask you to finish these exercises by removing the OBs form the ESO Database. (By the way, the same procedure would have to be followed should you need to modify your OBs after checking them in.) The P2PP User Manual gives you detailed indications on how to do this. In short,

  • Select (i.e. highlight) the container to check out
  • Select Check-out from the File menu in P2PP.
  • The lock symbol in front of the OBs disappear

Alternatively, the following procedure can be used in a real life case when the OBs are not displayed in p2pp because you are not running p2pp on the same computer with which you prepared the OBs

  • Under the File menu, select View ESO Database...
  • In the Database Browser window that opens, type 60.A-9253(E) in the Prog ID selection criterion
  • Click on the Query button on the lower left.
  • Select all the OBs that appear in the display area after the query. Normally there should be your two submitted OBs only, but if another user has submitted other OBs from this same account without removing them afterward you will see them as well.
  • Under the File menu in the View OB window, select Check-out
  • The lock symbol in front of the OBs will disappear, or the OBs will show up in p2pp if they had not been there before

In this way, the OBs will be transferred from the ESO Database to your P2PP local cache. For the purpose of this tutorial, you delete them by selecting them and choosing the Delete option under the File menu in the P2PP main GUI.

If you have any questions or problems regarding your Phase 2 preparation, please don't hesitate to contact usd-help@eso.org.

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