In this first working example, we make use of the point-source photometry mode, get dual band photometry of an (almost) point-source: 3C273.

With any Herschel AOT the first step is to enter target information. The target of the observation can be entered in various ways (see The HSpot User's Manual), one of which is directly into the AOT that is being prepared via the "New Target" button near the top. Press the button and then enter your target coordinates or the target name and resolve with SIMBAD or NED.

The AOT opens with a unique AOR label at the top, however you can edit it to make it more meaningful to yourself if you so wish.

Figure 6.1. Photometer AOT : point-source mode, step 1 : Start up HSpot, select PACS Photometer AOT and provide target information, by clicking on the "New Target" button. The target can be resolved either with SIMBAD or NED.

As a second step, select the blue band (60-85 µm or 85-130 µm) and enter flux estimates is applicable.

Pressing the Source Flux Estimates button brings up a table in which you may enter details of your source. Note that it is optional to enter data here, if you do enter information then you will be presented with signal to noise (S/N) information in the Observation Estimates result panel and in the PACS Time Estimation report. This table depends on the observing mode selected, in Point-source photometry the fields for extended source are disabled.

Note for very bright sources the dynamic range for the bolometer detectors has to be changed via gain settings. If you specify a very bright source HSpot will warn you the gain settings will be changed. The low gain settings are not ideal for faint sources.

Figure 6.2. Photometer AOT : point-source mode, step 2 : Select one of the two bands of the blue photometer channel. Then click on button "Source Flux Estimates" and enter estimated flux densities in the 2 selected bands to later get signal-to-noise estimates (optional).

Clicking on the "Set the Observing Modes" button you have to select Point-source photometry tab in the pop-up window.

Figure 6.3. Photometer AOT : point-source mode, step 3 : Click on the "Set the Observing modes" button and select the Point-source photometry mode.

An accurate time estimate and associated noise is obtained by clicking the "Observation Est..." button to bottom left of the AOT window. The PACS Time Estimator calculates the time that the observation should take and calculates sensitivities. If flux estimates were provided the signal-to-noise calculation is done as well. The Time Estimation Summary gives the return information for the most essential performance numbers.

In this working case, we get 6 and 6.8 mJy (1-σ) for a repetition factor of 1. You can click further on "PACS Time Estimator Messages" to get further information on the AOR.

You can get an estimate of the local confusion noise in the bottom of the Time Estimator window. The confusion noise is specific for the AOR settings and is derived considering the two main astrophysical components in the far-infrared: the Galactic cirrus and the cosmic infrared background. How confusion noise estimator calculates the confusion noise is described in the "Herschel Confusion Noise Estimator Science Implementation Document"

The depth of the observation is controlled by the Repetition Factor. For a point source observation it increases the number of ABBA... nodding cycles.

Figure 6.4. Photometer AOT : point-source mode, step 4 : Click on the button "Observation Est..." to get the sensitivity in the 2 bands.

It is advisable to visualize the AOR on an already existing background image. Most of the available astronomical image servers can be accessed to download image in a relevant waveband. Our example shows the access to a DSS image.

Figure 6.5. Photometer AOT : point-source mode, step 5 : From the main HSpot panel, click on "Images" --> "DSS image" to download a DSS (or other) image.

The AOR you created can be overlayed now on the background image. From the main HSpot panel, navigate to "Overlays" and select "AORs on current image" from the pull-down menu. First, you have to select which AOR to visualize if more then one AORs are stored in the main HSpot panel. Select the current AOR. You will be prompted to specify the date of observation. If you do not have any preference than click "OK" with the default settings and the overlay image will appear in the HSpot window.

You may notice changing the observing day the overlay image will rotate on the sky. This is because the spacecraft position angle is locked at a certain Observing Day and varies from 0 degree to 360 degrees over a year. In case you want to avoid a certain region on the sky the chopper avoidance angle can be specified in the observing mode tab. To enter a chopper avoidance range of angles If you want to avoid chopping on to a region at 20-40 degrees east of north then you should enter 20 in the From box and 40 in the To box. Note if you want to avoid something to the North (say 350 to 10) then you should enter 350 in From and 10 in To. Also because of the nature of chopping the angles 180 degrees away from the pair you enter will also be avoided. It is very important that you visualize your observation at different dates to make sure that you observation is still possible.

Figure 6.6. Photometer AOT : point-source mode, step 6: From the main HSpot panel, click on "Overlays" --> "AORs on current image" to overlay the footprint of the AOR on the sky.

In this example we create an AOR targeting the galaxy cluster Abell 2218. A relatively small area is to be observed on the cluster core of 7x7 arcmin. For this purpose the appropriate mode is the raster mode. The idea here is to make very small step sizes along the chopping direction to chop out of the raster map as much as possible, but larger step sizes in the perpendicular direction in order to achieve a square map.

By repeating the rasters several times in the AOR with the repetition factor, but also repeating the AOR for slightly different raster map centre coordinates (drizzling), the sensitivity will increase.

With any Herschel AOR, the first step is to enter target information. The reference position provided in the target dialogue has to refer to the required geometrical central position of the map with the chopper on footprints (in green on Figure 6.14). The coordinates of the galaxy cluster can be resolved from one of the online available catalogues.

Figure 6.7. Raster map, step 1 : start up HSpot, select PACS Photometer AOT and provide target information.

Figure 6.8. Raster map, step 2: Select blue channel filter and provide flux estimates

Figure 6.9. Raster map, step 3: Observing mode and raster map settings

Figure 6.10. Raster map, step 4: Provide map repetition factor and run the PACS Time Estimator and the Herschel Confusion Noise Estimator

Figure 6.11. Raster map, step 5: Check the PACS Time Estimator Message

Figure 6.12. Raster map, step 6: Select and download background image

Figure 6.13. Raster map, step 7: Create AOR overlay

Figure 6.14. Raster map, step 8: Pointing table

	Note
	The raster map is centered in the middle of the grid of the chop-on positions (displayed in green Figure 6.14). As the position angle rotates by about 1 degree a day on this high ecliptic latitude target, the orientation of the chop-off area cannot be controlled, unless a constraint is put on the on the raster line direction with the orientation constraint.

The first AOR example attempts to illustrate how to design a large area deep mapping measurement using the PACS Photometry AOT. Our goal is to make a two band extragalactic scan map on the COSMOS field. For such a wide area (2 square degrees) the only suitable mode is the scan map mode.

Figure 6.15. Scan map, step 1: A scan map is entered in array coordinate system, with a low scan speed (10"/s), a scan leg length of 85 arcmin, and an orientation angle of 70 degrees. As the field is close to the ecliptic plane, the position angle of the array is constrained to a small range and this effectively hence an array-to-map angle of 70 degrees constrain the orientation of the scan legs to be north-south. An homogeneous coverage is selected to get a homogeneous exposure map.

Figure 6.16. Scan map, step 2: The observation duration is computed and the sensitivity estimated for the chosen scan map configuration, in our case 12 mJy- 1σ in the 100 micron band.

Figure 6.17. Scan map, step 3 : Overlay of the above scan map AOR on the sky. Changing only the orientation angle to 160 degrees allows an orthogonal coverage, in a second AOR (to be concatenated) with all other parameters identical

Figure 6.18. Scan map, step 4 : An alternative is to define the scan map in sky coordinates with scan legs oriented north-south in equatorial coordinates (orientation angle = 0) and a cross-scan distance of 51 arcsec ('magic distance') that allows a rather homogeneous exposure map in all cases.

In this example we define a point source observation on planetary nebulae NGC 7027. Three spectral lines are requested: the OI line at 63 microns, NII at 122 microns and C+ at 158 microns.

Figure 6.19. Line spectroscopy, step 1 : Open Line Spectroscopy AOT window and select target coordinates.

Select from the pull-down menu of "Wavelength settings" the combination of grating orders in which the set of line can fit (3rd and 1st orders in this example).

HSpot provides an easy way to include spectral line transitions from online catalogues. You have to click on "Add line from database" button to show the default selection of lines selected for PACS. In case this selection does not include the transition you wish to observe, under the "Lines" option on the HSpot main page additional lines can be retrieved from CDMS/JPL servers. The "Manage Lines" facility allows you to modify line attributes if necessary and save your own line database. This tool can be used to merge line databases saved in the same HSpot format.

You may notice, the default line list includes all three lines we want to observe in this AOR. Only one line can be selected once, to include more lines you have to repeatedly click on the "Add Line from Database" button.

The PACS Line Editor allows to set up to 10 spectral lines but this limit might be reduced if line repetition is applied.

Figure 6.20. Line spectroscopy, step 2 : Retrieve spectral line from database or add a line manually

Once the Line Editor is filled, spectral line parameters can be modified by clicking on "Modify Line" button. An editable window will appear and show the current settings for the selected line.

The black mandatory fields have to be provided in order to get a valid line request. Optional parameters are highlighted in green, leaving default zero values mean the observer does not want to specify these values.

Figure 6.21. Line spectroscopy, step 3 : Modify spectral line parameters if necessary

The observing mode has to be selected, click on the "Pointed" tab. You have access to the chopper angle, set it to "Medium".

Figure 6.22. Line spectroscopy, step 4 : Select Pointed observing mode and chopper throw to "Medium"

The PACS Time Estimator message includes sensitivity estimations for each line and for the continuum at the line centre. Sensitivities can be improved by two ways: increase the number of grating repetitions per line or increase the number of nodding cycles.

The relative line strength (fraction of on-source time per line) is taken into account by specifying the grating scan repetition factor for each line. This number can be specified in the line editor window. A maximum of 10 repetitions in total can be given in the table. For instance, in the case that 10 lines are selected, the "Line repetition" factor has to be 1 for each line; if 3 lines are selected then the total of the 3 repetition factors has to be less or equal to 10 (e.g. 4+5+1 or 2+3+3 ...). If the sum of repetitions exceeds 10 then you must either remove spectral line(s), or reduce the scan repetition factor(s).

Figure 6.23. Line spectroscopy, step 5 : Run the time estimator by clicking on "Observation Est..." button. Check time estimation details in the PACS Time Estimator Message.

Similar as described in the photometer case, the AOR overlay can be visualized on a background image. Click on "Images" and select the image database from which you want to retrieve the background, then navigate to option "Overlays" and "AORs on current image".

Figure 6.24. Line spectroscopy, step 6 : Download a background image and create the overlay of the AOR.

In this example we define a point source observation on planetary nebulae NGC 7027. Full spectral energy distribution (SED) measurement is requested using the combination of "SED Red" and "SED Blue" range scan options. The grating performs only one up-down scan, the measurement time is the shortest possible for the entire 55 to 210 microns spectral range in this fast scanning mode (see Section 4.2.2 for details). Two AORs have to be created for the complete range coverage, these AORs are being concatenated in the last step.

The measurement time with only one repetition (single AB nodding cycle) is 2065 seconds in the "SED Red" mode and 1119 seconds in the "SED Blue" mode. In total, the shallow full SED spectrum with overheads takes 53 minutes respectively. The best continuum sensitivity at 132 microns is 464 mJy.

Figure 6.25. Range spectroscopy, step 1 : Start PACS Range Spectroscopy AOT and select "SED Red" range mode.

In the second step by clicking on "Add Range" button the "Range Id", "Reference wavelength" and "Continuum flux density" optional parameters appear in enabled mode. The range Id is a mandatory field, the other two are optional parameter and used for point-source continuum signal-to-noise calculation only. Accepting the default zero values means the Time Estimator will not perform S/N calculation.

	Note
	In SED mode it is not mandatory to add a range manually. If the range line is missing from the PACS Range Editor then HSpot will apply default SED values.

Figure 6.26. Range spectroscopy, step 2 : Click on button "Add Range" to set up optional parameters for S/N calculation.

Figure 6.27. Range spectroscopy, step 3 : Select "Pointed" observing mode and set up the appropriate chopper throw.

Figure 6.28. Range spectroscopy, step 4 : Run the PACS Time Estimator for the "SED Red" AOR by clicking on "Observation Est..." button on the bottom of the main AOT window.

Figure 6.29. Range spectroscopy, step 5 : Create the "SED Blue" AOR and run the PACS Time Estimator.

Figure 6.30. Range spectroscopy, step 6 : Concatenate the two AORs. Select from the main HSpot menu "Tools" and option "Group/Follow-on Constraints". In the pop-up window you have to first click on "Concatenation" button, then select the two AORs by clicking on "Get AOR" two times.