The Phase 2 process begins when you receive an email from ESO 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 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 MUSE. Therefore, you decide to start preparing your Phase 2 material, which consists of a README file, and one or more OBs equipped with finding charts.

In what follows we will discuss and focus on concepts that are only specific to MUSE observations, therefore assuming you have read the p2 documentation and, as such, you are familiar with the general concepts of p2, and its features.  

Goal of the run

In this tutorial we will prepare an OB for a simple example observing run, consisting of IFU observations of distant galaxies in the Hubble Ultra Deep Field RA(2000)=03:32:39.0, DEC(2000)=-27:47:29.1, by using the WFM-NOAO-N mode. It is intended to provide an example of MUSE observations of a sparse field, therefore with no need for off-target sky monitoring, but the need of accurate target centering due to the assumption that we need to stack together multiple similar OBs.

The observing strategy based on the science requirements is:

• WFM-NOAO-N
• VLT Guide star selection
• Target centring through blind offset from a reference star
• Sky monitored on target (i.e., no need for off-target exposures)
• On-target integration split in multiple sub-exposures taken at different orientation and position (i.e., rotation + dithering).
  

Getting started

For the sake of this tutorial, we will use the p2 demo facility, which allows users who do not have their own p2 login data to still use p2 and prepare example OBs (for instance during the Phase 1 preparation to get the overheads right!).  You cannot use it to prepare actual OBs intended to be executed.  When you prepare OBs that should be executed in PARANAL you must use your ESO User Portal credentials to log into the p2 (with http://www.eso.org/p2).

After directing your browser to the p2, and creating an empty new OB under your SM MUSE run ID by clicking on the OB icon, the main p2 GUI will appear as follows (note that the p2 GUI is regularly updated and might look slightly different):

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OB general sections

Your newly created OB consists of general (Target, Time Intervals, Finding Charts, Ephemeris, Target Visibility) and instrument specific (Obs. Description, Constraint Set and ObsPrep) sections that in the figure below are highlighted in red and green, respectively. Each section is accessible through the corresponding tab that appears just below the OB name.  

Filling the general OB sections should be fairly straightforward (i.e. Target name, RA and DEC  etc..) because each field has its own mini help accessible to users when moving the mouse over it. However, should you need more detailed instructions please consult this page.

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OB instrument specific sections

1. Constraint Set

By clicking on to the Constraint Set tab you access the corresponding section, where you will have to provide constraints on airmass, Sky Transparency (i.e., Photometric, Clear, Variable thin cirrus, Variable thick cirrus), Lunar Illumination, Image Quality, Moon Angular Distance, Twilight (min) and Precipitable Water Vapor (mm). While defining the OB constraints you should always remember that Phase 2 constraint must agree with Phase 1 request. Details on each specific constraint (i.e., range and meaning) can be found in the general and specific observing conditions pages.

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2. Obs. Description: the Acquisition template

The Obs. Description section should be regarded as the core of any given OB bacause it contains the details of the observations, arranged in templates. Each OB must have an acquisition and one or more science templates.

Selecting the right acquisition template

The instrument mode is defined in the acquisition template, therefore each mode has its own dedicated acquisition template. As summarised in this table, for the case of seeing limited observations with the WFM there are two possible acquisition templates (MUSE_wfm-noao_acq_preset and MUSE_wfm-noao_acq_movetopixel) depending whether or not a precise (within ~0.3") target centering is required. 

In this example our target field is very sparse and we do not expect to see many sources after the short exposure taken during the acquisition. In addition, we assume that to fulfill the science goal we need to combine many identical (or very similar) OBs to that we are about to prepare here. Because the field does not contain many (i.e. > 5-10) point source like objects, an accurate stacking of multiple OBs might be problematic. Therefore, to circumvent this problem we must make sure that for all OBs the target (in this case the FoV center) is accurately centered in the same position, so that during the data processing we can rely on the accuracy and consistency of the coordinates and offsets stored in the header of all OB frames we will combine. The MUSE_wfm-noao_acq_movetopixel is the right acquisition template because it does allow us a fine target centering through interactive positioning. Indeed, thanks to this template, the instrument operator does have the option to manually center the target as we indicate in the OB (as opposed to the MUSE_wfm-noao_acq_preset).

Once you have decided which acquisition template matches your observational needs, click on to the Obs. Description tab to access the corresponding section and select the acquisition template as shown in the picture below. Then click on the "Add Template" button to access the content of the template.

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Filling the acquisition template  

The set of acquisition parameters appearing on the p2 GUI after loading the MUSE_wfm-noao_acq_movetopixel template can either be defined completely manually or in a more automatic way by using ObsPrep.

In what follows we first provide a short desciption of each parameter, and then we will use ObsPrep to fill in the template.

• Integration Time (seconds): it obviously defines the integration time of the acquisition exposure taken on the target field and used for the target centering. Generally it can be left to its default value (1 sec) unless there is a compelling reason (target field samples only very faint source and the centering is done by using a faint source in the field, which is anyway highly discouraged).
• Start slow-guiding?: The MUSE derotator produces a residual mechanical wobble, which produces a repeatable pattern as a function of the derotator position. The effect of this wobble can be compensated by the slow-guiding system (SGS) when point-sources are present in the metrology field outside the FoV (i.e., the four banana-shaped areas). Therefore, it is strongly recommended to enable the SGS if i) suitable sources are present in the metrology fields; ii) the target is neither a moving object nor a high proper motions source; and iii) the on-target exposures time is longer than 4 minutes. Four minutes is in fact the minimum interval of time after which offset corrections are sent from the slow guiding system to the telescope.
  
• Alpha offset for the target (arcsec): RA offset between the target and the reference star to be used for accurate target centering (i.e., optional as it applies only in case the blind-offset procedure is performed, see dedicated note below)
  
• Delta offset for the target (arcsec): DEC offset between the target and the reference star to be used for accurate target centering (see dedicated note below).
• RA of guide star: RA coordinate of the VLT guide star (VLT-GS, see dedicated note below)
  
• DEC of guide star: DEC coordinate of the VLT-GS
  
• Get Guide Star from: If left to CATALOGUE then the VLT-GS is selected by the telescope operator (see note below)
  
• Position Angle on Sky (deg): Orientation of the MUSE FoV
  
• Instrument Mode: Select the desired filter (i.e., Nominal or Extended)
  

Special Note on the VLT-GS:

Suitable VLT-GSs should not be closer than 4' from the MUSE field center but still within the VLT unvignetted FoV (i.e. within 11' radius) and should have a magnitude in the range: 11<R<13.5. The position of the selected VLT-GS is provided by the user in the acqusition template through the star absolute coordinate (i.e. RA of guide star, DEC of guide star). The parameter Get guide Star from must be set to SETUPFILE in case a specific star is given. Finally, the selection of the VLT-GS is optional, however users are encouraged to define a VLT-GS in the OBs in case the observing strategy requires: i) stacking together multiple OBs (i.e., by selecting for all similar OBs the same VLT-GS you can rely on the accuracy and consistency of the coordinates and offsets stored in the header of all raw frames you will combine); ii) mosaicking a large area; iii) performing very large offsets (i.e., for sky monitoring purpose).

Special Note on the Reference Star:

The reference object can be either within or outside the MUSE FoV. However, in the latter case one should check that both target and reference star are accessible by using the same VLT-GS. The position of the selected reference star is provided by the user through offsets in RA and Dec with respect to the target position (i.e. Alpha offset for the target, and Delta offset for the target). This is because the telescope will first point to the target coordinates, then, once the VLT-GS has been acquired, the telescope will move to the reference object after applying the provided alpha and delta offsets. The instrument operator centers the reference object in the MUSE field center, and then the telescope goes back to the target by applying the provided offsets but with reverted signs. In any case, the selection of a reference star is optional, however users are encouraged to define one in the OB in case the observing strategy requires: i) stacking together multiple OBs in very sparse fields; ii) accurate field centering.

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3. ObsPrep: the Acquisition template

Assuming that you have already partially filled in the Target section with at least the target coordinates RA and DEC, by clicking on the ObsPrep tab, the p2 main GUI appears as follows (note that the screenshots refer to the ObsPrep version in P105; additional functionalities were added later):

ObsPrep Pointing

ObsPrep Blind Offset

ObsPrep VLT Guide Star

Now, if you go back to the acquisition template under the Obs. Description section you will notice that all relevant template parameters have been properly propagated by ObsPrep (see figure below). Specifically, the Alpha/Delta offset from the target to the reference star and the RA/DEC of the VLT-GS.

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4. Obs. Desciption: the Science template

The only available science template for WFM-NOAO observation is the MUSE_wfm-noao_obs_genericoffset. To load it into the OB, first select the option science in the drop down menu "Template Type", then select the MUSE_wfm-noao_obs_genericoffset from the drop down menu on the right and click on the "Add Template" icon as shown in the figure below.

As for the acquisition case, the set of science parameters appearing on the p2 GUI after loading the MUSE_wfm-noao_obs_genericoffset template can either be defined completely manually or in a more automatic way by using ObsPrep.

In what follows we first provide a short desciption of each parameter, and then we will use ObsPrep to fill in the template.

• Number of offset positions: Number of positions at which you want to take exposures
  
• Number of exposures per offset position: Number of exposures to be taken at any defined position
  
• Observation type list, O/S: Each defined exposure must be tagged either as 'O', for on-target observations, or as 'S', for sky monitoring (see sec. 5.4 of User Manual).
  
• Offset coordinate type selection: The offsets pattern can be defined either in DETECTOR or SKY coordinates system (see sec. 5.4 of User Manual).
  
• List of relative offsets in position angle (deg): The field orientation at each defined offset position (offsets in position angle are cumulative).
  
• List of relative offsets in RA or X (arcsec): Offset in RA/X of each defined position (offsets are cumulative).
  
• List of relative offsets in DEC or Y (arcsec): Offset in DEC/Y of each defined position (offsets are cumulative).
  
• Return to origin?: This flag is set always to "Yes", meaning that the telescope returns to the original position after the defined offsets pattern is completed. Note that the original position matches the telescope pointing before the science template has started (i.e., after the acquisition). Should you need to set this keyword to "No" you must submit a waiver.
  
• List of UITs: Integration time (in seconds) of each defined exposure. If all defined exposures must be taken with the same integration time you can just type in a single value.
  

Note on offsets and field orientation:

To improve the flat-fielding of the slicer and channel patterns during the data reduction we strongly advise the observer to always split the on-target observation in multiple exposures taken at least at two different position angles (separated by 90 degrees) and with a small offsets pattern. The size of each on-object offset should at least be larger than a spaxel (i.e. >0.2" for the WFM).

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5. ObsPrep: the Science template

To prepare the science observing sequence we will make use of ObsPrep. To this end go back to the ObsPrep section and click on the Observing Offsets tab. The main P2 GUI will appear as follows:

ObsPrep Observing Offsets

Because the target field is very poorly populated there are enough spaxels from which a sky background estimate can be derived (i.e., no need for off-target sky monitoring), therefore we decide to perform on-target (i.e. offset type 'O') observations only. In addition, to obtain the best results in terms of cosmics rejection and to improve the flat-fielding of the slicer and channel patterns during the data reduction, we plan to split the total integration time on source into 3 exposures, each one rotated by 90 degrees and taken at different position.  Note that the number of exposures and their exposure time should be defined with the help of the ETC to ensure the requested S/N is reached with respect to the total integration time on source.

Now, if you go back to the science template (i.e., in the Obs. Description section) you will notice that most of the parameters have been properly propagated by ObsPrep (see figure below).  Specifically, all but the list of UITs that you must fill in manually.  

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Finding charts

At this point you must create finding charts compliant with ESO general and MUSE specific requirements. The easiest and quickest way to do that is by using the finding charts generator embedded in the p2 environment. Once the OB templates content has been fully provided, click on the "Generate Finding Chart" button you find under the Finding Charts section. In doing that 2 finding charts will be created and automatically attached to the OB. Specifically, the tool produces a finding chart showing the position of the selected VLT-GS with respect to the telescope pointing (i.e., large field of view chart showing the telescope patrol field), and a second one showing the MUSE FoV footprint centred on the reference star selected for the accurate target centering onto the target field showing the final centering.

Alternatively, you can provide your own-made finding charts (please consult this page to check all the requirements), which you must manually attach to the OB (i.e., click on the "Upload Finding Chart" button you find in the Finding Charts section).

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Access to the final OB

The ascii version of the OB just created, together with the corresponding finding charts can be downloaded here.

Alternatively, by logging into p2 demo, under the programme ID 60.A-9253(R) you can access to the USD-Tutorials folder where this OB has been created and stored. In the same folder you can also find a sample of OBs designed for different modes and observing strategies. The example OBs are not editable but can be exported if needed. We kindly ask you to please refrain from creating new OBs in the USD-Tutorials folder.

MUSE p2 tutorial

• Goal of the run
• Getting started
• OB general sections
• OB instrument specific sections
  • Constraint Set
  • Obs. Description: Acquisition template
    
  • ObsPrep: Acquisition template
  • Obs. Description: Science template
  • ObsPrep: Science template
• Finding charts
• Access to final OB
• Back to MUSE p2 tutorial main page
  

P2 documentation

• Introduction
• New features
• Demo

Useful links

• MUSE User Manual
• ETC
• Service Mode Guidelines