The user selects the applicable wavelength ranges (defined by the grating diffraction orders) via the first pull-down menu. There are two possibilities:

As a result of the selection, the (redshifted) wavelengths of line centres have to be specified in the "PACS Line Editor" table, either within the 72-210 micron band, or within the 55-72 and 105-210 micron band.

	Note
	As it is indicated in the options above, irrespective the blue order selection spectral lines can be always requested in the 105-210 micron band (1st diffraction order) of the red spectrometer array.

	Tip
	The observer has a choice of creating an observation of spectral lines located along the entire PACS wavelength range (55-210 micron) by grouping AORs. In this case at least two AORs have to be filled with flipped grating order options. See chapters 5.5.3 and 5.5.4 (grouping and timing constraints) for further information.

When setting up the list of spectral lines to be observed the PACS Line Editor is used. The AOT allows a maximum of ten lines to be entered into the table, although the use of "Repetition factor" parameter could result a further restriction on the number of observable lines (see below).

	Tip
	If your observation requires more than the allowed number of lines consider to set up a group of AORs. See chapters 5.5.3 and 5.5.4 (grouping and timing constraints) for further information.

The table gives a summary of spectral line dependent attributes of your AOR. You cannot enter, modify or remove values in the table directly. The three buttons at the bottom of the table allow the following:

Figure 11.2.  Window to add- and modify spectral line entries

The "Add Lines to the Observation Request" dialogue is a shopping basket which filters PACS detectable transitions from the HSpot "Manage Lines" facility (see Chapter13).

Figure 11.3.  "Add Lines to the Observation Request" dialogue

The "Add Lines to the Observation Request" dialogue has some rules applied to it:

	Note
	Default lines included in the "Add Lines to the Observation Request" dialogue provides a handful set of most often requested strong lines.

	Tip
	An extended list of lines can be added to the "Add Lines to the Observation Request" window from online catalogues and/or individual line information provided by the user (see Chapter 13 and functionalities of the "Manage Lines" dialogue).

The redshift selection menu allows the observer to make adjustments to the observing wavelength. The input can be specified either in known radial velocities or redshifts. Once any area in the PACS Line Editor is clicked on the "Redshifted Wavelength" field turns to show the wavelength to be observed.

On the left hand side of the observing mode settings area a text box labelled "Nodding or wavelength switching cycles" can be found. The absolute sensitivity of the observation can be controlled by entering an integer number between 1 and 100. The on-source time is increased by repeating the nodding pattern the number of times that is entered. For each of the nod positions the sequence of line scans is repeated with the relative depth specified in the PACS Line Editor (see "Line Repetition" above). In case wavelength switching is used the on-source time is increased by switching with the grating the number of times that is entered. No nodding is applyied in this latter case.

This mode is offered for taking data for a point-like object. The integral-field concept allows simultaneous spectral and spatial multiplexing, for the most efficient detection of weak individual spectral lines, with sufficient baseline coverage and high tolerance to pointing errors, without compromising spatial resolution. The PACS spectrometer arrays have 5 by 5 spatial pixels covering a square field of view of 49 by 49 arcseconds. Both channels view identical positions on the sky. The line flux from a point source object will always be collected with the filled detector array. Therefore, for the simple detection of a line source, one pointing is sufficient.

Figure 11.5.  Options for the Pointed observing mode

Background subtraction can be achieved either through a standard chopping/nodding, or through 'wavelength-switching technique.' These modes are mutually exclusive.

Chopping/Nodding

This mode allows a classic three-position nodding observation to eliminate inhomogeneities in to the telescope and sky background. The PACS focal plane chopper is moved between the on-target and the off-positions during a grating scan and the whole sequence of spectral line scans is repeated in the nod position. One half of the total integration time is spent on-source. This mode can be selected by clicking on "Chopping/nodding" in the "Observing mode selection" field.

Observing mode parameters - Chopping/Nodding

The chopper throw and chopper avoidance angle can be selected. The choice of "Small", "Medium" and "Large" refer to 1.5, 2.0 and 4.0 arcminutes chopper throws respectively on the sky. The chop direction is determined by the date of observation; the observer has no direct influence on this parameter. If an emission source would fall in within the chopper throw radius around the target the observer may consider setting up a chopper avoidance angle constraint. The angle is specified in Equatorial coordinates anticlockwise with respect the celestial North (East of North). The avoidance angle range can be specified up to 345 degrees.

Warning

Specifying the chopper avoidance angle place restrictions on when the observation can be scheduled. This constraint might reduce the chance that your observation will be carried out, especially targets at low ecliptic latitudes could be inaccessible for certain chopper angles. You should use chopper avoidance angle only for observations where it is absolutely necessary. (You may check your observation's footprint orientations by clicking in the HSpot menu: Overlays -> AORs on current image...)

Wavelength Switching

If by chopping a maximum of 4 arcminutes the field-of-view would not be placed in an emission-free area, the observer should consider wavelength switching as an alternative of the chopping mode. There may be be other reasons in a number of science cases to use this option. For very bright objects (typically solar system targets) chopping to off-source could introduce a high contrast, resulting in memory effects in the spectrometer's Ge:Ga detectors. Such an effect would lead to data that can only be poorly calibrated.

In wavelength switching mode three spectra are taken with sufficient overlap in between. The grating is frequently switched between the on-line and the two symmetrically placed of-line positions. There is no observing parameter the user can access for this mode. You can select wavelength switching by clicking on the "Wavelength switching" option button in the "Observing mode selection" field.

	Note
	The continuum information is eliminated when using wavelength switching technique. This mode is very unefficient if significant continuum gradients are expected over the covered wavelength range. More information can be obtained in the PACS Observers Manual.

This mode is offered to take data for a point-like object in a very similar way to "Pointed" observing mode (see above). The underlying pointing mode is slightly different; dithering will be done by small spacecraft movements perpendicular to the chopper direction. In such a configuration this observing mode can compensate for image slicer effects, especially important for faint targets (see further explanation in the PACS Observer's Manual). User parameters are identical to the "Pointed" mode.

Figure 11.6.  Options for the Pointed with Dither observing mode

Setting up the instrument mode parameters on the "Mapping" screen is identical to that for the "Pointed" or "Pointed with dither" modes. The one difference can be seen at the bottom of the tab under "Raster map parameters".

Figure 11.7.  Options for the Mapping observing mode

The breakdown of the observation is provided in the "PACS Time Estimation" screen (see figure above). It indicates the on-source time, calibration time, overheads and the total observing time.

More detailed information can be obtained by clicking the "Messages" button on the "PACS Time Estimation" screen.

Figure 11.9.  PACS Time Estimator messages window

The message window presents information of two kinds: (1) a summary of the data entered in HSpot (line wavelengths and observing mode parameters); and (2) several relevant pieces of timing information, as well as the RMS noise and signal-to-noise for the resulting times.

This first pull-down menu gives the choice to select between two scan modes:

In SED mode parameters stored in the PACS Range Editor are ignored by the AOT backend except the reference wavelength and continuum flux density parameters if given. The observation will cover the blue or the red SED domain as defined by the selected grating order combination (see next option). In this mode, the observer has no control over the grating sampling density; the "Instrument settings" field is disabled for this purpose.

The user selects the applicable wavelength ranges (defined by the grating diffraction orders) via this pull-down menu. There are two possibilities if "Range scan" mode has been selected previously:

As a result of the selection, the spectral ranges to observe have to be specified in the PACS Range Editor as being within either the 72-210 micron band, or within the 55-72 and 105-210 micron bands.

	Note
	As is indicated in the options above, irrespective of the blue order selection, PACS always observes a part of the [105-210] microns range (1st order) in the red spectrometer array. See more information about the covered ranges in the PACS Observers Manual.

	Tip
	The observer has a choice of creating an observation comprising of spectral ranges spread along the entire PACS wavelength range (55-210 micron) by grouping AORs. In this case, at least two AORs have to be requested, one with each of the grating order options. See chapters 5.5.3 and 5.5.4 (grouping and timing constraints) for further information.

Available options if "SED" mode has been selected previously:

As a result of the selection, the blue or red part of the PACS wavelength range is observed.

	Tip
	The observer has a choice of creating an observation comprising of SED scans spread along the entire PACS wavelength range (55-210 micron) by grouping AORs. In this case two AORs have to be requested, one with "SED Red" and a second observation with "SED Blue" option. See chapters 5.5.3 and 5.5.4 (grouping and timing constraints) for further information.

The PACS Range Editor is used to set up the list of spectral ranges to be observed. The AOT allows a maximum of ten ranges to be entered into the table, although the use of the "Repetition factor" parameter could result in a further restriction of the number of observed ranges (see below).

	Tip
	If your observation requires more than the allowed number of ranges consider setting up a group of AORs. See Chapters 5.5.3 and 5.5.4 (grouping and timing constraints) for further information.

The table gives a summary of spectral range dependent attributes of your AOR. You cannot enter, modify, or remove values directly in the table. The three buttons at the bottom of the table allow the following:

Figure 11.11.  Window to add- and modify spectral range entries

On the left hand side of the observing mode settings area there is a button labelled "Nodding or map repetition cycles". The absolute sensitivity of the observation can be controlled by entering an integer between 1 and 100. This parameter has the effect of increasing the on-source time by repeating the nodding pattern the number of times that you specify. For each of the nod positions the sequence of range scans is repeated with the relative depth specified in the PACS Range Editor (see "Range Repetition" above). In SED mode this parameter has a very similar effect, the entire spectral range is repeated the number of times that is specified. In case crowded-field observation with mapping with off-position is used the on-source time is increased by repeating the map the number of times that is entered. No nodding is applyied in this configuration.

This mode is for observing point sources, i.e. sources that are not extended at the wavelength of observation. The integral-field concept allows simultaneous spectral and spatial multiplexing for the most efficient detection of weak individual spectral lines, with sufficient baseline coverage and high tolerance to pointing errors, without compromising spatial resolution. The PACS spectrometer arrays have 5 by 5 spatial pixels covering a 49 x 49 arcsecond field of view. Both channels view identical positions on the sky. The line flux from a point source object will always be collected with the filled detector array. Therefore, for a simple detection of a line source, one pointing is sufficient.

Figure 11.13.  Options for the Pointed observing mode

Background subtraction can be achieved through standard chopping/nodding technique.

Chopping/Nodding

This mode allows a classical three position nodding observation to eliminate inhomogeneities between the telescope and sky background. The PACS focal plane chopper is moved between the on-target and the off-positions during a grating scan. The whole sequence of spectral line scans is then repeated in the nod position. In total, one half of the integration time is spent on-source. This mode is always enabled.

Observing mode parameters -Chopping/Nodding

The chopper throw and chopper avoidance angle can be selected. The choice of throws "Small", "Medium" and "Large" refer to 1.5, 2.0 and 4.0 arcminute chopper throws on the sky respectively. The chopping direction is determined by the date of observation, the observer cannot directly influence this parameter. If a source of emission falls within the chopper throw radius around the target, the observer should consider setting up a chopper avoidance angle constraint. The angle can be specified in Equatorial coordinates, anticlockwise with respect the celestial North (East of North). The avoidance angle range can be specified up to 345 degrees.

Warning

Setting up a chopper avoidance angle requires an additional constraint on mission planning, therefore this parameter should have to be used only for observations where it is absolutely necessary. Specifying the chopper avoidance angle place restrictions on when the observation can be scheduled. This constraint might reduce the chance that your observation will be carried out, especially targets at low ecliptic latitudes could be inaccessible for certain chopper angles. You should use chopper avoidance angle only if a constraint is essential for your observation. (You may check your observation's footprint orientations by clicking in the HSpot menu: Overlays -> AORs on current image...)

This mode is offered for taking data on a point-like object in a similar way to the "Pointed" observing mode (see above). The underlying pointing mode is slightly different, as dithering will be carried out by small spacecraft movements perpendicular to the chopper direction. In this configuration the observing mode can compensate for image slicer effects, especially important for faint targets (see further explanation in the PACS Observer's Manual). The user parameters are identical to the "Pointed" mode.

Figure 11.14.  Options for the Pointed with Dither observing mode

Setting up the instrument mode parameters on the Mapping screen is identical to that for the "Pointed" or "Pointed with dither" modes. The difference can be seen at the bottom of the tab under "Raster map parameters" and the "Off-position" settings.

Figure 11.15.  Options for the Mapping observing mode

This mode allows the observer to set up a raster map observation in combination with chopping/nodding or off-position. If the field of view would not be placed in an emission-free area by chopping 4 arcminutes away, a selected off-position on the sky can be given as a reference position. Note that the reference position must be within 2 degrees of the target. The frequency of calibration blocks at the off-position is optimised by the AOT backend; the user has no control over it.

The breakdown of the observation is provided in the "PACS Time Estimation" screen (see figure above). It gives the on-source time, calibration time, overheads and the total observing time.

More detailed information can be obtained by clicking the "Messages" button on the "PACS Time Estimation" screen.

Figure 11.17.  PACS Time Estimator messages window

Figure 11.18.  PACS Time Estimator messages window (cont.)

The message window presents information of two kinds: (1) a summary of the data entered in HSpot (line wavelengths and observing mode parameters); and (2) several relevant pieces of timing information, as well as the RMS noise for the resulting times.

The first step to create a PACS Photometry AOR is the filter selection in the blue channel. The two mutually exclusive options are [60-85] or [85-130] microns bands. Irrespective the blue filter selection, parallel data are always obtained in the red channel.

Clicking on the "Source Flux Estimates" action button a pop-up window will offer four entry fields:

Figure 11.20.  The Photometry AOT main window

These are optional AOR parameters, source estimated data used only for S/N calculation except if very a bright source is specified. In case "Point source photometry" observing mode is selected the extended source entry fields get disabled.

	Warning
	Specifying a very bright source will induce a change in gain settings. Check the applicable flux limits in the HSpot Users Manual.

On the right hand side of the observing mode settings area a text box labelled "Repetition factor" can be found. The absolute sensitivity of the observation can be controlled by entering an integer number between 1 and 100. The on-source time is increased by repeating the nodding pattern the number of times that is entered in case "Point Source Photometry" or "Small Source Photometry" modes are used. For each of the nod positions the minimum 64 seconds chopped exposure sequence is repeated. In case "Chopped Raster" or "Scan Map" large area mapping options are used the number of map coverages increased the number of times that is entered.

Figure 11.22.  Point Source Photometry tab

This mode is reserved for observers who want to target a source that is completely isolated and point-like, or smaller than one blue matrix (approx. 85 arcseconds). It uses chopping and nodding, both with amplitude of 1 blue matrix, and dithering with an amplitude of a single pixel.

The point-source photometry mode is using a classic 4-position chopping, with dithering along the chopper axis, combined with nodding in the perpendicular direction. This setup compensates for the different optical paths in the most efficient way since the source is always kept on-array.

The observer specifies a repetition factor that is used to adjust the number of nod cycles to reach the requested integration time. The minimum time per nod position is 64 seconds. This is to block very short observations that have a poor observing efficiency, but is done at the expense of a stepwise behaviour in the AOR total time.

Depending on the user specified source flux level, the photometer gain is adjusted by the backend logic to provide a comprehensible dynamic range.

Observing mode parameters

Chopper avoidance angle

The chop direction is determined by the date of observation; the observer has no direct influence on this parameter. If an emission source would fall in within the chopper throw radius around the target the observer may consider setting up a chopper avoidance angle constraint. The angle is specified in Equatorial coordinates anticlockwise with respect the celestial North (East of North). The avoidance angle range can be specified up to 345 degrees.

Warning

Specifying the chopper avoidance angle place restrictions on when the observation can be scheduled. This constraint might reduce the chance that your observation will be carried out, especially targets at low ecliptic latitudes could be inaccessible for certain chopper angles. You should use chopper avoidance angle only for observations where it is absolutely necessary. (You may check your observation's footprint orientations by clicking in the HSpot menu: Overlays -> AORs on current image...)

Dithering

A predefined set of dithering positions can be observed by clicking on this parameter.

	Note
	In the Photometry AOT dithering is performed only along the spacecraft Y-axis using the PACS focal plane chopper for beam modulation. More complicated two-axis dithering patterns are not allowed in the current design.

Figure 11.23. Small Source Photometry tab

Here the term "small source" refers to sources that are smaller than the array size, yet larger than a single matrix. To be orientation invariant, sources must fit within approximately 2 by 2 arcminutes. Classic three-position nodding is performed in a 2 by 2 raster minimap (with fixed map parameters), in this configuration the source cannot be kept on the array at all times. The chopper is moving along the long size of the field of view with largest possible 4 arcminute throw. Again, as in the point-source photometry mode, the unit is one nod cycle, and the total duration is computed as multiples of this cycle. The only option of this observing mode is the "Chopper avoidance angle". For detailed description of this parameter see "Point Source Photometry" above.

If the source is significantly larger than the array, or the objective is to cover a large contiguous area of the sky, there are two possible observing modes: chopped raster and unchopped scan mapping.

Figure 11.24. Chopped Raster tab

The raster map option, combined with on-array chopping, preserves the PACS highest spatial resolution without degrading the point spread function. Maps can be specified in instrument coordinates, the chopper axis is perpendicular to the raster lines. The observing unit is the chopper cycle; the total duration is computed by multiples of this cycle.

Observing mode parameters

Raster map parameters

The four parameters have to be specified:

• m - Number of raster points, range: [2-32]

• n - Number of raster lines, range: [1-32]

• X - Raster point step (arcseconds), range: [2-480]

• Y - Raster line step (arcseconds), range: [2-480]

Map orientation parameters

The observer can select the map orientation reference coordinate system and map orientation angle through the following parameters:

• Position angle reference frame, options: Array or Array with sky constraint

• Position angle (degrees)

• Constraint angle from (degrees)

• Constraint angle to (degrees)

Warning

Specifying the chopper avoidance angle or selecting a map orientation constraint place restrictions on when the observation can be scheduled. These constraints might reduce the chance that your observation will be carried out, especially targets at low ecliptic latitudes could be inaccessible for certain chopper or map angles. You should use constraint angle only if it is essential for your observation. (You may check your observation's footprint orientations by clicking in the HSpot menu: Overlays -> AORs on current image...)'

Line scan maps are the suggested default to map large areas of the sky, for Galactic as well as extragalactic surveys. In this mode the signal modulation is provided by the spacecraft motion. The extended emission is filtered out by fitting the temporal signal, but point sources can be detected without losing sensitivity. Line scan maps can be performed in spacecraft coordinates, or in sky coordinates, although there is no direct control of the homogeneity of the map coverage when performed in sky coordinates. The observer has the choice of selecting the scan speed (low, medium and high), which determines the on-source time and the depth of the observation.

Figure 11.25. Scan map tab

Observing mode parameters

Scan map parameters

The following five parameters have to be specified:

• Map scan speed, range: [high, medium, low]

• Scan leg lengths (arcminutes), range: [1-120]

• Number of scan legs, range: [1-240]

• Select homogeneous coverage

• Cross-scan step (arcseconds), range: [2-480]

Map orientation parameters

The observer can select the map orientation reference coordinate system and map orientation angle through the following parameters:

• Position angle reference frame, options: Sky, Array, Sky with constraint, Array with constraint

• Position angle (degrees)

• Constraint angle from (degrees)

• Constraint angle to (degrees)

Warning

Specifying the chopper avoidance angle or selecting a map orientation constraint place restrictions on when the observation can be scheduled. These constraints might reduce the chance that your observation will be carried out, especially targets at low ecliptic latitudes could be inaccessible for certain chopper or map angles. You should use constraint angle only if it is essential for your observation. (You may check your observation's footprint orientations by clicking in the HSpot menu: Overlays -> AORs on current image...)'

The breakdown of the observation is provided in the "PACS Time Estimation" screen. It indicates the on-source time, calibration time, overheads and the total observing time.

More detailed information can be obtained by clicking the "Messages" button on the "PACS Time Estimation" screen.

Figure 11.27.  PACS Time Estimator messages window

The message window presents information of two kinds: (1) a summary of the data entered in HSpot (instrument settings and observing mode parameters); and (2) several relevant pieces of timing information, as well as the RMS noise and signal-to-noise for the resulting times.

The breakdown of calculated confusion noise in the "PACS Time Estimation" screen. It indicates the confusion noise specific for the AOR configuration. On startup this table is kept empty, in order to receive a confusion noise estimation the "Update confusion noise estimates" button has to be pushed.