ISAAC P2PP Tutorial
This tutorial provides a step-by-step example of the preparation of a set of OBs with ISAAC, the Infrared Spectrometer And Array Camera at ESO's Very Large Telescope (VLT). To follow it, you should have a P2PP installation in 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 generic instructions on the preparation of Observing Blocks.
In this tutorial we will prepare OBs for a simple example observing run, consisting of broad--band imaging and spectroscopy of the galactic young open cluster NGC 6611 (RA(2000) = 18:18:48.7, Dec(2000) = -13:46:29). 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 an observing run, as well as some aspects that are specific to the preparation of OBs for ISAAC.
The Phase II process begins when you receive an email from the ESO Observing Programmes Office (OPO) communicating to you that the allocation of time for the coming period has been finalized and that you can view the results by logging into the User Portal and clicking on "Check the web letters." 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 ISAAC. Therefore, you decide to start preparing your PhaseII material.
First, you collect all the necessary documentation:
- The ISAAC User Manual
- The Service Mode instructions for VLT/VLTI and VISTA.
- The P2PP Documentation referred to above.
and you proceed with the installation of P2PP on your machine if necessary. For the sake of this tutorial, we will hereafter use the following P2PP information:
- P2PP ID: 52052
- password: tutorial
You will be prompted for this information after you started P2PP by just typing p2pp
This is a special account that ESO has set up so that users who do now have their own P2PP login data can still use P2PP and prepare example OBs. You cannot use it 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.
Select the folder corresponding to the ISAAC Tutorial run, 60.A-9252(E). 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 ISAAC run.
You can now start defining your OBs.
First, click on the blue OB icon on the upper left side of the P2PP main GUI. This creates an OB entry under the ISAAC run ID folder. The red dot with white 'x' next to the OB name means that the OB fails to pass some fundamental verification criteria, as may beexpected from the fact that no template has been attached to the OB yet.
Double click on the OB name (by default 'No name'). The View OB window appears:
This is the window where you will define the contents of your OB.
Let this be the OB for Js, H and Ks-band imaging of your target. Since this OB will be the JsHKs observation of NGC 6611, you could choose a descriptive name like OB 'NGC 6611 - JsHKs'. Type this name in the OD Name entry near the top of the View window.
- In the Name field under the Target tab, type the target name (NGC 6611).
- In the Right Ascension, Declination fields, type the coordinates given above.
- Since the coordinates are given for both epoch and equinox J2000, leave these fields with their default values.
- You can give also the Class to which this object belongs, for archival purposes. In this case, choose Assoc* (stellar association).
- The proper motion of this target is negligible for the purposes of this example, and differential tracking of the telescope is not needed since this is not a moving Solar System target. Therefore, you can leave the last four fields in the Target tabset to their default values of zero.
As stated in Section 1, we assume for the purposes of this tutorial that the program has been allocated time in Service Mode. You thus need to specify a constraint set for your OBs. You can do this by clicking on the Constraint Set tab and filling the entries under it:
- 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 imaging observations, you type Imaging constraints in the Name field.
- Since you wish to be able to determine accurate fluxes from your images, you request Photometric conditions in the Sky Transparency entry.
- Since you need moderately good quality in your images, you specify 0.8 as the value of the Seeing field.
- Set the Airmass to 2.0, to ensure that your observations are not carried out at too low an elevation.
- Since you are doing broad band observations in the near-infrared, the lunar illumination has very little influence. You can thus leave the default values of 1.0 and 30 degrees for the Lunar Illumination and Moon Angular Distance fields.
Note that in your Phase I proposal you already specified some of these constraints (lunar illumination, seeing, transparency). You must make sure that none of the constraints specified in Phase II is more stringent than the corresponding one specified at Phase I.
We will assume now that the imaging observations that you are defining are part of a photometric monitoring program of NGC 6611 and that, to ensure that you have the light curves properly sampled, this particular OB needs to be executed between June and July 2009. You can specify this under the Time Intervals tab:
- Click on the box "New TI".
- Modify the lower boundary (start) of the time interval to the specified starting date of your time window, keeping the same format. In the present case, the entry should read 2009-06-01 and 00:00:00.
- In the same way, modify the upper boundary (end) of the time interval to 2009-08-01 and 00:00:00.
If your observation could be executed in other, non-contiguous time windows, you could define more intervals in the same way as described.
Generally it is useful to mention in the User Comments any peculiarities concerning the execution of an OB. You may also enter here requests for specific calibration requirements. If this is lengthy or complicated, add a reference to the README file, where you should explain it in detail.
The User Comments field (in top section) is a free text field and can be used to mention any peculiarities concerning the execution of an OB. If this is lengthy or complicated, add a reference to the README file, where you should explain it in detail. Here, we do not have any special information or requirements and leave this field blank.
Instrument Comments: Magnitude of the brightest object in the field
The ISAAC specific field Magnitude of the brightest object in the field must be used to insert the J, H, and K-magnitude of the brightest star present in the 2.5arcmin x 2.5arcmin ISAAC field. In order to retrieve this information you query the 2MASScatalogue. When querying the catalogue you do not provide a search box size of 2.5 x 2.5 arcmin only, but an even larger size of 2.7 x 2.7 arcmin to account for the fact that you will define (see below) also a jitter box width of 20arcsec in your science template. The query result tells you that the brightest object in the whole field has the magnitudes: J=12.3, H=11.9, K=11.7mag. You verify on the ISAAC service mode specific webpage that this is not too bright for ISAAC observations (Note:imaging observations leading to strong detector saturation are not schedulded in service mode) and you continue with typing J=12.3H=11.9 K=11.7 into the Instrument Comments field
The first template that must be part of any OB that requires adefinite pointing is the acquisition template, so let us define it next. In the Template Type list, make sure that the acquisition entry is highlighted. This will list all the acquisition templates available for ISAAC in the Template list below to it.
After reading the description of the templates in the ISAAC User Manual, you have determined that the ISAACSW_img_acq_MoveToPixel template, suitable for imaging with the Hawaii (Short wavelength) array, 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.
You need to decide now on the acquisition parameters. This acquisition template sets a filter and takes an OFF frame at an offset of Alpha offset and Delta offset arcseconds from the target position for sky subtraction purposes. Then it takes exposures in open loop presenting on the Real Time Display at the telescope console the image obtained after DET.NDIT integrations of DET.DIT seconds each, minus the OFF frame. This allows the identification of the target field. Since you have decided to obtain the images in the Js, H and Ks filters in this order, some time will be save if you set the Js filter already in the acquisition template, so that the filter setup is already done by the time that the first science observation starts. Moreover, since the brightest stars in this field are fairly bright, the images for acquisition do not need to go very deep, meaning that DET.DIT and DET.NDIT can be small; say, 5 sec and 1exposure respectively. As to the other parameters, you decide that the default orientation of the frames, which is North at the bottom (in imaging mode), is perfectly fine for your purposes. The set of parameters that you choose in your acquisition template is thus:
- DET.DIT (sec): 5
- DET.NDIT: 1
- Alpha offset (arcsec): 10
- Delta offset (arcsec): 10
- Position Angle on Sky (degrees): 0. (i.e. North on bottom of the ISAAC array display)
- Preset Telescope ? (T/F)checked (i.e., True)
- SW Filter wheel 1: Js
- SW Filter wheel 2: open
If you specify one of the parameters outside the allowed range, it turns red. The OB is not considered valid and you will not be allowed to check it in, unless all parameters are defined within allowed ranges. The acquisition template is now complete.
Once the acquisition is completed, the science observation begins. The science observation is defined in a set of one or more templates that form the Observation Description, or OD for short.
In this example OB, the OD will consist of a sequence of three jittered exposures through the Js, H and Ks filters.
Next, the templates need to be attached. After checking with the manual and considering the scientific requirements of your program, you have decided to execute the observations with the Hawaii (SW) array (you selected the detector already during your submission of the Phase1 proposal). You will apply a random jitter pattern within a 20arcsec box, using the object frames themselves to construct a skyframe for background subtraction. You conclude that the ISAACSW_img_obs_AutoJitter template is the most suitable one. On Template Type, select now science. The existing ISAAC science templates will appear. Select the chosen one, ISAACSW_img_obs_AutoJitter, and click on Add. The template will be attached to the grid below next to the acquisition template selected and filled previously.
You want the brightest source in your field to remain within the linear part of the response of the Hawaii array, but still want to obtain a sufficient signal to detect fainter sources. After consultation of the manual and the Exposure Time Calculator you find that you will approximately need a total on-source time of 700s per filter, and that DITs should not exceed 45s in Js and 12s in H and K (see the ISAAC User Manual). The time spent at a jitter position (=DIT * NDIT) should not exceed 180s in Js and 120s in Ks,respectively. You decide to set DIT to 28s and NDIT to 3 for Js band, which results in 8 jitterpositions (Number of Exposures), a reasonable number (it should not be too low). For H and K band, you rather want to set DIT to 11s, NDIT to 8, which again results in 8 jitter positions.
Furthermore, you decide to start the jitter in each filter at the reference position given by the preset coordinates, rather than at the last position observed in the previous template. The first ISAACSW_img_obs_AutoJitter template (the observation in Js) thus has the following parameters:
- DET.DIT (sec): 28
- DET.NDIT: 3
- Observation category: SCIENCE
- Number of Exposures: 8
- Jitter Box Width (arcsec): 20
- Return to Origin ? (T/F): checked (i.e., True) (the telescope will thus return to the initial position after the execution of the template)
- SW Filter wheel 1: Js
- SW Filter wheel 2: open
For the observations in H and Ks, you could select again the same template, Add it, and fill the parameters in the same way as done for the template in Js. However, since the parameters of these other two templates will be very similar to those of the one just defined, you can speed up the preparation by clicking on any entry of the template for the Js-band observation, then clicking on the Duplicate Col button on the right. In this way, you will have produced an identical copy of the first science template in which you should now only edit the parameters that change from template to template:
- DET.DIT (sec): 28 must be changed to DET.DIT (sec): 11
- DET.NDIT: 3 must be changed to DET.NDIT: 8
- SW Filter wheel 1: Js must be changed to H
In a similar manner, you create your Ks-band OD by duplicating the H-band OD and modifying the filter entry.
This completes your first OB! If you followed all the instructions given so far, the View OB window should look like this now:
and you should see an entry under the ISAAC run folder in the P2PP main GUI with the following contents:
- Name: No name
- Local Id: 666 (or any other number)
- Status: (P)artiallyDefined
- Target: NGC 6611
- OD: NGC 6611 - JsHKs
- CS: Imaging constraints
- Acquisition: ISAACSW_img_acq_MoveToPixel
You can reshape the columns as indicated in the P2PP User Manual to view the full contents of each entry.
You should now give a name to the OB by clicking with the right-hand mouse button on "No name", a pop-up appears, select 'rename' and enter, e.g.: NGC6611 JHK imaging.
You should next check the execution time of your OB, to make sure it is shorter than 1 hour. This is done by clicking on the Recalculate button in the OB "View" GUI window (or by selecting Reports -> Execution Time -> in the main GUI window). The calculated time includes overheads, and it is 00:59:48.
Now is maybe also the time to check if your OB contains any errors which are easy to find via a coded script. This is done by selecting Reports -> Verify -> Selected in the main P2PP GUI window, and it checks for template mismatches, filter settings, and the like. If it reports an "ERROR", this will prevent you from checking in the OB to the ESO database, and you will have to correct it. A "WARNING" or information means that you set a parameteror combination of parameters in an unusual way. You should confirm for yourself that this is what you really want. If the reason for this unusual setup is not obvious to the future observer from the context, it might be useful to add a remark to the "README" file.
The result of running the verification is shown here:
The WARNING about the target seems missing from the target list can be ignored, because this tutorial run is not associated with a real phase2 proposal and hence the check for target consisistency between Phase1 and Phase2 is irrelevant.
The REMARK about several distinct filters was implemented to warn users who might inadvertently changed a filter in their OB. In your case, this is exactly what you want to do, so you can ignore it. Otherwise, the OB is fine.
The REMARK about specifying the exact positioning of the field in the ReadMe file reminds you, that you will need to inform the Paranal astronomer to put the center of the cluster NGC 6611 on pixel 530/530 (this is just a fictive example for this tutorial). You place respective instructions in the ReadMe file (see below).
To complete this ISAAC tutorial with an exercise on another instrument mode, we will add a spectroscopic OB to our hypothetical run.
The purpose of this OB will be to obtain a medium resolution spectrum of the core of NGC 6611 in the region around the Brackett alpha line of Hydrogen at 4.05 microns. We start by generating a new OB from scratch (icon New in the P2PP main GUI) and get ready to edit its contents (icon View). We can name this OB NGC6611 spectrum, and its OD spectroscopy.
Next, we proceed to adding the acquisition template. Since we want to observe at wavelengths longer than 2.5 microns, we will have to use the Aladdin (Long Wavelength) Array for both the acquisition and the observation itself. You may note at this point that, unlike you may have expected, there is no ISAACLW_spec... template for spectroscopic acquisition. This is due to the fact that placing the object at the position of the slit (which is known to the instrument from calibration procedures carried out by the observatory staff) is done by imaging the field, and thus the acquisition template isactually of the img type. As described in the ISAAC manual,the template to be used for spectroscopic acquisition with the Aladdin array is ISAACLW_img_acq_MoveToSlit.
Some of the parameters to be defined in this template are already familiar from previous examples. We will assume that the acquisitionis made with images through the M_NB filter with chopping with a chopthrow of 20 arcseconds parallel to the slit, and that the slit to be used is the one with 0.6 arcsec width (slit_0.6).
The parameters Alpha Offset from Ref. Star and Delta Offset from Ref. Star offer the possibility of accurately presetting the telescope on a bright reference target close to the position of the science target, and then giving an offset to the telescope before the science observation starts so that it moves to the position of the science target. This isuseful in case of faint targets that may not be visible in the acquisition image or require an excessively long acquisition time. In our example, the science target is bright enough and we do not need to use this indirect acquisition, so we leave these offset fields at their default zero values.
For practical purposes, this template also offers the possibility of actually presetting the telescope to the desired position, or just performing the setup of the instrument without sending the preset order to the telescope (parameter Preset Telescope ? (T/F)). Skipping the telescope preset saves some time at execution if the telescope was already at the target position. At the time of preparing the observations, either in Visitor or Service Mode, this flag should always be set to True.
- Preset Telescope ? (F/T): checked (i.e., True)
- Chop Throw (arcsec): 20
- Number of chop cycles: 1
- ChopNod PARA or PERP to Slit: PARA
- Alpha offset from Ref. Star: 0
- Delta offset from Ref. Star: 0
- Position Angle on Sky (degrees): 0.
- LW Filter wheel 1: M_NB
- LW Filter wheel 2: open
- Slit: slit_0.6
As explained in the ISAAC User Manual, there are three templates for LW spectroscopic observations with ISAAC, each one allowing the use of either of two detector readout modes. AutoChopNod, suitable for automatic chopping and nodding along the slit, moves the target between the proximities of two positions along the slit and will be our choice here (the ISAACLW_spec_obs_AutoChopNod template).
After considering the spatial extent of our target, we decide to carry out our observations using a chop throw of 20 arcseconds parallel to the slit (which keeps the object in the slit during all exposures and therefore optimizes the SNR), and decide on a jitter boxwidth of 10 arcseconds. The dispersion element to be used is defined in the Instrument Mode entry: in our case, we select LWS3-MR, which will produce a medium resolution spectrum. For the Central Wavelength, we select the wavelength of the Brackett alpha line, 4.05 microns. The slit to be used must be consistent with the one selected in the acquisition template, as different slits project on different positions on the detector. Since the individual detector integration times are dominated by the (variable) skybackground at the long wavelength at which we are observing, the only other parameter we have to specify is the total Integration time in minutes. Using the information found in the ISAAC User Manual, we decide that a total integration of 30 minutes should produce a sufficient S/N to achieve our scientific goals.
This is thus the contents of the science template that composes the OD:
- Jitter Box Width (arcsec): 10
- Return to Origin ? (T/F): checked (i.e., True)
- Chop Throw (arcsec): 20
- ChopNod PARA or PERP to Slit: PARA
- Integration time (minutes): 30
- Instrument Mode: LWS3-MR
- Slit ?: slit_0.6
- Central Wavelength (microns): 4.05
Let us consider first the Constraint Set of this spectroscopic OB, and assume that the spectroscopic part of our program can be done under less favourable conditions than the imaging one, as is usually the case with spectroscopy. We define a new Constraint Set under the corresponding tab, that we name Spectroscopicconstraints. We specify there Sky Transparency: Variable,thin cirrus, Seeing: 1.0, Airmass: 2.0, Lunar Illumination: 1.0, Moon Angular Distance:30.
For the target, we could in principle click on the Target tab and type in again all the information (name, coordinates, type). But since we have already typed the information for this same target in the imaging OBs, we can just cut-and-paste information between OBs:
- Go to the P2PP main GUI, and select under Summaries (top bar) one of the imaging OBs for NGC 6611 (such as for instance NGC 6611 - JsHKs)
- Under the Synchronise menu, select Copy Target
- Go to the Summaries list, and click on the new spectroscopic OB to select it
- Go again to the Synchronise menu, and select now Paste to Selected OBs
You will see a dialog box asking you for confirmation of the synchronise operation. Upon clicking on Yes, the Target information in the entry corresponding to NGC 6611- Spectrum is updated. If you go to the View OB window, you will see the Target information updated there as well, thus making the OB complete. The appearance of that window should be as follows:
When planning your observing run, you realized that the accuracy that you need for the telluric corrections makes it advisable to observe, next to the standard calibrations provided by ESO, a specific standard star near your scientific target in the sky. For this purpose you have selected the A-type star HD 170902 located at RA(2000) = 18:32:20.8, Dec(2000) = -14:38:39, and applied for time within your proposal to obtain an extra observation of this specific spectroscopy standard star. Now you must prepare the OB for this star.
In principle, this observation can be very similar to the science spectroscopic observation described in detail before. Note however that now you are defining an OB for telluric calibration purposes, and that as a consequence the appropriate ISAAC templates to use in the OD must be calibration templates, rather than science templates like before. The steps that you should follow to define the OB are analogous to those that you followed when preparing the NGC 6611spectrum OB before (see Section 4). Since the target coordinates and the template contents of this OB are both rather different from those of the previous two, you create it from scratch by clicking on the New icon in theP2PP main GUI while still being in the ObsBlock tab (we do not define a day-time calibration). We get ready to edit its contents with the icon View. The name of this OB must start with the prefix CAL according to the service mode OB naming conventions. Hence, you name the OB CAL_HD 170902, and its OD cal spectroscopy. We can use the same acquisition template as before and make use again of the Synchronise button, this time choosing Copy Acquisition Template. For the science observation, however, we need now the ISAACLW_spec_cal_AutoChopNod template instead of ISAACLW_spec_obs_AutoChopNod. If we synchronised the acquisition template, we first must, therefore, delete the column with ISAACLW_spec_obs_AutoChopNod. Then, we choose the ISAACLW_spec_cal_AutoChopNod template under the calib menu in the Template Type list.
The standard is a rather bright star (J=5.9, H=5.8, K=5.8), a total integration time of five minutes will produce a spectrum of this standard star with much better S/N than our science spectrum, and thus be suitable for calibration purposes. All other parameters in the ISAACLW_spec_cal_AutoChopNod template can/should be identical to the ones from the ISAACLW_spec_obs_AutoChopNod template used for the science observation.
In addition to selecting, adding, editing, and duplicating templates as described in detail in Section 2 and making the necessary adaptations as outlined above, you must enter the Target and Constraint Set information relevant for this case. After doing this, the contents of your OB should look as follows:
and we will assume that this completes your run.
Starting in P74 and P75, respectively, the submission of Finding Charts and the README file are not via ftp any more, but they are directly attached to the OBs. Please, see the respective tutorials on Finding Charts and README for instructions on how to do that.
With the completion of the spectroscopic OB, we consider the examples developed in this tutorial to be finished. Now it is time to run the Verification Module again (see above) to make sure the OBs do not contain any errors, and to determine the total execution time of all OBs by selecting them all in the main GUI window and then running Reports - > Execution Time from the top bar pulldown menu. Make sure the total execution time stays within the time allocated by the OPC.
The P2PP main GUI displays the four OBs that we have prepared:
You have the possibility to influence the order in which your OBs are executed by assigning "User Priorites". Let us assume that yours pectroscopy is useless if you do not get the images first. The default for the User Priority (in the top left section of the View window) is 1, the highest priority, and we leave it at the default value. For the spectroscopy and the standard star, we decrease the priority by setting it to 2. It is advisable to add a note on this in the README file, otherwise it might get overlooked.
We will now submit these OBs to the ESO Database: select all of them in the Summaries list, go to the File menu in the P2PP main GUI, 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.
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(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 four submitted OBs only, but if another user has submitted other OBs from this same account without removing them afterwards you will see them as well.
- Under the File menu in the View OB window, select Check-out
In this way the OBs will be removed from the ESO Database and 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.
ISAAC P2PP Tutorial
- Goal of the run
- 1- Getting started
- 2- Creating the first OB
- 3- Defining a spectroscopic OB
- 4- Attaching the Finding Charts and the README file
- 5- Finishing the preparation and submitting the OBs