VIMOS P2PP Tutorial (MOS)
This tutorial provides a step-by-step example of the preparation of one imaging and one MOS, Multi-Object Spectroscopy, OB with VIMOS, the VIsual Multi-Object Spectrograph at the ESO Cerro Paranal Observatory. Specifically, the resulting OBs will be targeted to a pre-imaging run and a follow-up spectroscopic run. The instructions given here for pre-imaging can be easily adapted to normal imaging.
To follow this tutorial you should have a P2PP installation on your computer and be familiar with the essentials of the use of P2PP. Please refer to the P2PP Web page for detailed installation instructions, and to the P2PP User Manual for a general overview of P2PP and instructions on the preparation of Observing Blocks.
In this tutorial we will prepare one pre-imaging OB with two filters, B and R, and one MOS OB with low resolution blue, LR_blue, grism. The targets will be a few well-known supernovae. The sample OBs will illustrate the use of a variety of features of P2PP and the kind of decisions to be taken at the time of preparing in advance an observing run, as well as some aspects that are specific to the preparation of OBs for VIMOS.
This tutorial has been prepared with the P2PP version currently available to Period 75 users (V.2.9). In the future, text and figures will be updated only when major changes in the instrument package and/or in P2PP have been included.
The Phase 2 process begins when you receive an email from the ESO Observing Programmes Office telling you that the allocation of time for the coming period has finalized and that you can view the results by logging into the User Portal and clicking on "Check the webletters." Note that the username and password that you need to use for the User Portal are the same as those you will use to prepare your OBs. You follow the instructions given by ESO and find that time was allocated to your run with VIMOS. Therefore, you decide to start preparing your Phase 2 material. First, collect all the necessary documentation:
- The VIMOS Manuals
- The Service Mode instructions for the VLT
- The P2PP Documentation referred to above
and proceed with the installation of P2PP in your machine if necessary. For the sake of this tutorial, we will hereafter use the following P2PP information:
- 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 data can still use P2PP and prepare example OBs and cannot be used to prepare actual OBs intended to be executed. After logging in using the tutorial account, the P2PP main GUI will appear as follows:
Runs for a number of instruments appear in the Folders area, since the same tutorial account is used for all of them. Similarly, if you log in with your own P2PP ID, you will get the list of all the runs for which you are PI. Now select the folder corresponding to the VIMOS Tutorial run, 60.A-9252(J). In this tutorial we assume that time was allocated in Service Mode. This is indicated by the SM letters that appear next to the Run ID of the VIMOS run. You can now start defining your OBs.
First, click on the New icon on the upper left side ofthe P2PP main GUI. This creates an entry under the Summaries area. The red dot next to the OB name means that it fails to pass some fundamental verification criteria, as may be expected from the fact that no template has been attached to the OB yet.
Click on the View icon. The View OB window appears:
This is the window where you will define the contents of your OB.
First, let us give a name to the OB in the Name field in the upper-left part of the window. Since this OB will be the pre-imaging observation of SN1987A, let us call it 'PRE SN1987A'
The Target Package, where the target information can be entered, is accessed by clicking on the Target tab at the bottom of the window:
- In the Name field under the Target tab at the bottom, type the target name (SN1987A)
- Type the coordinates of the object in the RightAscension and Declination fields, together with their epoch and equinox in the Epoch and Equinox fields, respectively.
- You can give also the Class to which this object belongs, for archival purposes. In this case, choose SNR (SuperNova Remnant).
- Finally, if appropriate, enter the proper motion of the object and the differential tracking rate for Moving Objects.
As stated in Section 2, we assume for the purposes of this tutorial that the program has been allocated time in Service Mode. Thus, you need to specify a constraint set for your OBs. You can do this by clicking on the Constraint Set tab next to the Target and filling the entries you find there:
Note that in your Phase 1 proposal you already specified some of these constraints (lunar illumination, seeing, transparency). You must make sure that none of the constraints specified in Phase 2 is more stringent than the corresponding one specified at Phase 1.
If appropriate, you can specify time windows where your OB can be executed by clicking on the Time Constraints tab. Click on the check-box at the far right next to the first row of the time interval to activate it.
If your observation can be executed in other, non-contiguous time windows, you could define up to five intervals in the same way as described. The User Comments and Calibration Requirements fields are free text fields whose contents is self-explanatory. We will leave them blank in this example.
The first template in any science OB is the acquisition template. In order to attach it to the OB, make sure that acquisition is highlighted in the Template Type list in the upper part of the OB window. This will list all the acquisition templates available for VIMOS in the Template section next to it. After reading the description of the templates in the VIMOS User Manual, you have determined that the VIMOS_img_acq_Preset template is the most suitable one for this particular observation. You, thus, click on this template in the Template list, and then on the Add button next to it. The keywords for the template will appear in the middle section of the window:
What this template does is, simply, to preset the telescope to the coordinates in the Target Package and, in the meantime, insert a filter in the light path. In order to save precious telescope time, it should be the same filter as in the first science template. Once the telescope reaches the selected target field, the guide star is acquired. Selection of a Guide Star for VIMOS observations is mandatory for MOS and IMG (including PRE-IMAGING) mode, to assess and control the amount and position of vignetting that may be introduced by the Guide Probe.Thus the user should provide a guide star by selecting the option SETUPFILE of Get Guide Star From parameter. It is requested that the users selecting a guide star for their observations use GUIDECAM to do it as well as to generate the finding chart which will be attached to the OB.
Once the target is acquired, the science observations begin. They are defined in a set of one or more templates that form the Observation Description (OD). Let us attach the first of the science templates by selecting science as Template Type, VIMOS_img_obs_Offset as template and by clicking on the Add button:
Since the OB we are writing is meant as pre-imaging the Observation Category keyword should be set to PRE-IMAGE. Otherwise, the keyword should be set to SCIENCE. Clicking the Recalc Exec Time will compute the execution time of the OB, which is displayed in the top-left section of the window. It may be useful in many cases to have an easy way of identifying an OD, like when having observations of a number of targets performed with identical instrument configuration and exposure times. The OD Name field in the View OB window allows you to define names for the ODs. In this example, we assign to the OD the name BR offset. The OD name also appears in the Summaries area of the P2PP main GUI, thus allowing the identification at a glance of all OBs having ODs with the same name.
Let us now add to the OB observation in the R filter. We can either add another VIMOS_img_obs_Offset template or duplicate the one we have already completed by clicking on the DuplicateCol:4 button in the top-right corner of the window. In this case the values of the keywords in the newly added template will have the same values as in the one they were copied from, which is very convenient if you just want to edit a few of them.
In our case, in the second scientific template we just want to change the filter from B to R and the exposure time from 200 to 100 seconds. Again, hitting the Recalc Exec Time button will update the execution time of the OB:
If you followed all the indications given so far, the ViewOB window should look like the figure above, while the P2PPmain GUI now contains a summary of the OB we have created:
We now have to attach the relevant finding charts to the OB. This is accomplished by clicking on Finding Charts>Attach Finding Charts in the main P2PP window. This will cause another window to open, where the name of the chart can be specified.
The Finding Charts menu can also be used to clear, detach or view the charts.The number and names of the charts attached to a given OB are shown in the Finding Charts column in the main P2PP window (you can reshape the columns as indicated in the P2PP User Manual to view the full contents of each entry):
By repeating the steps described above we can create all the OBs we need for our run. In particular, the Duplicate button in the P2PP main GUI duplicates an entire OB. This is a convenient and easy way to make new OBs from existing ones by editing just a few parameters. When you are satisfied with the prepared OBs for your pre-imaging run go to Section 6 to see how to finish and submit them.
Let us assume that you now want to prepare the follow-up OB for multi-object spectroscopy (MOS) of stars in the field of SN1987A. First, using pipeline reduced R-band image from your pre-imaging run you should run the VIMOS Mask Preparation Software (VMMPS). Note that the use of the R filter is mandatory in order to minimize slit losses. VMMPS creates and manages the instrumental setup through the files containing the Aperture Definition in Pixels (ADP) of the MOS slitlets. These ADP files need to be attached to the acquisition template in the OB. For further information creating ADP files, please refer to the VMMPS Cookbook. We will assume that you have already prepared the pre-imaging OBs and that you are thus familiar with the basics of creating the new OB in P2PP. For details how to do that see above Sections 2 and 3. Click on the New icon in the main P2PP window to create the new OB. Then click on the View icon and in the newly opened View OB window set the appropriate target information, constraint set and time intervals as described above. Name the OB "MOS SN1987A", indicating already in the name the instrument setup.
As you know from the pre-imaging part, the first template in any science OB is the acquisition template. In order to attach the appropriate acquisition template make sure that acquisition is highlighted in the Template Type list in the upper part of the OB window. This will list all the acquisition templates available for VIMOS in the Template section next to it. After reading the description of the templates in the VIMOS User Manual, you have determined that the VIMOS_mos_acq_Preset template is the right one for this particular observation. You, thus, click on this template in the Template list, and then on the Add button next to it. The keywords for the template will appear in the middle section of the window:
This template inserts the correct mask with the MOS slit setup (ADP file) that you have defined using VMMPS, then preset the telescope to the coordinates in the Target Package and, in the meantime, insert the R-band filter in the light path. Finally it will take a through-slit image of the field. To attach the appropriate ADP file, click on the "ThisisADummyAdp.adp". This will open a new window in which you can select the appropriate ADP file to attach. To find the file browse through your folders using the Folders area on the left side or enter directly the name of the directory in the upper left. Then highlight the ADP file you wish to attach in the Files area in the middle of the window. The contents of this file will be displayed on the right side. Clicking the OK button in the lower left the file will be attached to the field in the View OB window.
Repeat the above procedure for each of the quadrants. Finally select the R-band filter and exposure time.To avoid slit losses due to dispersion correction the use of the R filter is mandatory in pre-imaging and in the acquisition of the MOS OB.
The exposure time in the acquisition template is the time used to obtain the image of the field with the spectroscopic masks inserted in the light-path. The masks have slits cut at the position of the spectroscopic targets and these objects are the only ones that should be visible in the acquisition image. This image is used to check if the pointing is correct, i.e. to check that the targets are well centered in the slits, and, after the comparison of the acquisition image with the finding chart, the observer will decide if it is necessary to correct the pointing of the telescope and the centering of the targets. Thus the exposure time in the acquisition template should be short, to save the precious telescope time, but not too short, because the targets (or at least the brighter ones) should be visible in the through-slit image.
Once the target is acquired, the science observations begin. They are defined in a set of one or more templates that form the Observation Description (OD). In the MOS mode only one science template is typically used. Let us attach it by selecting science as Template Type, VIMOS_mos_obs_Offset as template and by clicking on the Add button:
Set the appropriate parameters by clicking on the fields in the last column on the right.The second keyword Number of Exposures per Telescope Offset (NEXPO) defines how many exposures are taken at each telescope offset. The keyword in the third row Number Telescope Offset (NOFF) will define at how many telescope positions the above selected NEXPO is taken. Selecting for example NEXPO=3 and NOFF=1 will take 3 exposures all in the same position of the telescope, without regard to the list of offsets specified! If instead one wants to take 3 exposures, but each at a different offset, NEXPO should be set to 1 and NOFF to 3 as shown here:
It may be useful in many cases to have an easy way of identifying an observation description (OD), like when having observations of a number of targets performed with identical instrument configuration and exposure times. The OD Name field in the View OB window allows you to define names for the ODs. In this example, we assign to the OD the name LR_blue 3offsets. The OD name also appears in the Summaries area of the P2PP main GUI, thus allowing the identification at a glance of all OBs having ODs with the same name.
In order to minimize the flat field residuals and wavelength calibration offsets due to instrument flexures the use of nightcalib template is highly recommended for MOS (at least for the arc calibration) and from P76 attached arcs exposure is mandatory for MOS observations using LR_blue and HR_blue grisms. During the VIMOS upgrade (since October 2010, i.e. since P87) the attached night-time calibrations are mandatory for all VIMOS setups.
The night-time MOS calibration template is used right after a science observation. This template doesn't contain any setup definitions and the data will be taken with exactly the same instrument setup as used in the previous observation template. Thus it has to be the last part of an OB containing an acquisition and observation templates. To attach the night-time calibration template select calib as Template Type, VIMOS_mos_cal_NightCalib as template and then click on the Add button. If you only want to have wavelength calibrations executed during the night, unselect Night Flat Field by clicking on the tick-mark button. Again, hitting the Recalc Exec Time button will update the execution time of the OB:
As described above in Section 4.7. finding charts should be attached to the OB by clicking on Finding Charts>Attach FindingCharts in the main P2PP window. This will cause another window to open, where the name of the chart can be specified.
In the case of MOS OB, 4 finding charts, for the 4 quadrants have to be attached and they can be all attached at once as follows: first select the first finding chart and then, while simultaneously holding down the SHIFT key, click on the last of the 4 finding charts. Release the SHIFT key and click on the Attach Finding Charts button in the lower left part of the window. In the main OB window you can see now a list of finding charts attached to your MOS OB.
This finishes the preparation of the MOS OB. How to make additional MOS OBs, by duplicating this one and changing only few of the parameters is analogous as described for the imaging OBs in Section 4.8.. To submit the MOS OBs follow the same procedure as described in Section 6. for pre-imaging. Remember that your Phase 2 submission is final only after you have prepared the README file and submitted it via Readme button in the main P2PP window. Then finalize the Phase II submission by pressing the p2pp-submit button.
Once you are satisfied with the OBs you have made, in Service Mode you should submit them to the ESO database for revision and, finally, scheduling and execution.The P2PP main GUI displays the OBs that you have prepared. Highlight the ones you wish to submit with Ctrl+LeftButton and click on File->Check-in, or, in short, Ctrl+K, to enter them into the ESO database (you will be prompted for confirmation):
The complete Phase 2 material includes also a README file for each run. As of P75, the README file is an integral part of P2PP, it is written within the P2PP environment and also submitted along with the OBs by using the p2pp tool. A tutorial for the README file is available here. When all the OBs and the README file for a given run are submitted, the Phase 2 submission is finalized by pressing the p2pp-submit button.
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. The P2PP User Manual gives you detailed indications on how to do this. In short,
- Select Check-out... from the File menu in P2PP
- In the Database Browser window that opens, type 60.A-9252(J) 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 four 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
After removing the OBs from the ESO Database they will be left in your Local Cache only. From there you can delete them if you like by selecting them and choosing the Delete option under the File menu in the P2PP main GUI.
VIMOS P2PP Tutorial
- 1: Goal of the Run
- 2: Getting Started
- 3: Creating the first OB - starting with P2PP
- 4: PreparingPRE-IMAGING OBs with P2PP
- 5: Preparing MOS OBswith P2PP
- 6: Finishing the preparation and submitting the OBs