18.2. Flux conversions

HIFI data can be converted from temperature scale to Jy using the convertK2Jy task. The task works for spectra in ObservationContexts (obs), HifiTimelineProducts (htp), HifiSpectrumDatasets (ds), and in SimpleSpectrum format (spectrum). The conversion can be done assuming a disk-like (top-hat), a Gaussian source morphology, or an ad hoc source model morphology. In the first two cases, a source diameter needs to be entered (<size> ). The convertK2Jy task also allows you to convert data back from Jy to whatever temperature scale the data was originally on.

In the GUI, the convertK2Jy task is found under Applicable in the Tasks view panel when you have selected an ObservationContext in the Variables view panel. To open the convertK2Jy task GUI, double click on its name in the Task panel, the GUI will open with the ObservationContext you had selected in the Variables panel loaded into the obs parameter in the GUI. If you have selected an HTP, SpectrumDataset or SimpleSpectrum in the Variables panel, you can find the convertK2Jy task under By CategoryHifi or under All in the Tasks panel. You will need to drag the name of the variable containing the data you want to convert into the appropriate field in the GUI.

The simplest call to the task requires only the input data and the diameter of the source in arcsec (size):

MyConvertedObs = convertK2Jy(obs=obs, size=10.0)

By default, the output name from convertK2Jy is result. You can change this in the GUI by typing a different name into the Variable name for result field. In the command line, you can set the result name as you call the task, as was done in all the example above and other examples below.

All other parameters have default values, as described below. Depending on your science goals and your data, it is expected that you will to modify the defaults parameter values.

Beam coupling computation.

Figure 18.1. Illustration of the beam coupling computation in case of a user-provided source brightness distribution model. In this case, the model is passed as a PACS continuum image (background image) and the corresponding position of the HIFI observations where it is computed is shown as a circular footprint of the size of the HPBW.

The temperature values in the spectrum are converted by convertK2Jy from TA* or TMB to TA' using the forward and beam efficiencies available from the calibration tree or hard-coded values, as described above. The conversion to Jy is dependent on the size of your source, and is computed differently for point sources and extended sources.