Step Arguments

As discussed earlier, the input to the cube_build step can take many forms, containing data from one or more wavelength bands for each of the MIRI and NIRSpec IFUs. The following step arguments can be used to control which subsets of data are used to produce the output cubes. Note that some options will result in multiple cubes being created. For example, if the input data span several bands, but single-band cubes are selected, then a cube for each band will be created.

channel [string]

This is a MIRI only option and the valid values are 1, 2, 3, 4, and ALL. If the channel argument is given, then only data corresponding to that channel will be used in constructing the cube. A comma-separated list can be used to designate multiple channels. For example, to create a cube with data from channels 1 and 2, specify the list as --channel='1,2'. If this argument is not specified, the output will be a set of IFU cubes, one for each channel/sub-channel combination contained in the input data.

band [string]

This is a MIRI only option and the valid values are SHORT, MEDIUM, LONG, and ALL. If the band argument is given, then only data corresponding to that sub-channel will be used in constructing the cube. Only one value can be specified, so IFU cubes are created either per sub-channel or using all the sub-channels of the data. If this argument is not specified, a set of IFU cubes is created, one for each band. Note we use the name band for this argument instead of subchannel, because the keyword band in the input images is used to indicate which MIRI subchannel the data covers.

grating [string]

This is a NIRSpec only option with valid values PRISM, G140M, G140H, G235M, G235H, G395M, G395H, and ALL. If the option “ALL” is used, then all the gratings in the association are used. Because association tables only contain exposures of the same resolution, the use of “ALL” will at most combine data from gratings G140M, G235M, and G395M or G140H, G235H, and G395H. The user can supply a comma-separated string containing the names of multiple gratings to use.

filter [string]

This is a NIRSpec only option with values of Clear, F100LP, F070LP, F170LP, F290LP, and ALL. To cover the full wavelength range of NIRSpec, the option “ALL” can be used (provided the exposures in the association table contain all the filters). The user can supply a comma-separated string containing the names of multiple filters to use.

output_type [string]

This parameter has four valid options of Band, Channel, Grating, and Multi. This parameter can be combined with the options above [band, channel, grating, filter] to fully control the type of IFU cubes to make.

• output_type = band is the default mode and creates IFU cubes containing only one band (channel/sub-channel or grating/filter combination).
• output_type = channel combines all the MIRI channels in the data or set by the channel option into a single IFU cube.
• output_type = grating combines all the gratings in the NIRSpec data or set by the grating option into a single IFU cube.
• output_type = multi combines data into a single “uber” IFU cube. If in addition, channel, band, grating, or filter are also set, then only the data set by those parameters will be combined into an “uber” cube.

The following arguments control the size and sampling characteristics of the output IFU cube.

scale1

The output cube’s spaxel size in axis 1 (spatial).

scale2

The output cube’s spaxel size in axis 2 (spatial).

scalew

The output cube’s spaxel size in axis 3 (wavelength).

wavemin

The minimum wavelength, in microns, to use in constructing the IFU cube.

wavemax

The maximum wavelength, in microns, to use in constructing the IFU cube.

coord_system [string]

Options are ra-dec and alpha-beta. The alpha-beta option is a special coordinate system for MIRI data and should only be used by advanced users.

There are a number of arguments that control how the point cloud values are combined together to produce the final flux associated with each output spaxel flux. The first set defines the the region of interest, which defines the boundary centered on the spaxel center of point cloud members that are used to find the final spaxel flux. The arguments related to region of interest and how the fluxes are combined together are:

rios [float]

The radius of the region of interest in the spatial dimensions.

riow [float]

The size of the region of interest in the spectral dimension.

There are two arguments that control how to interpolate the point cloud values:

weighting [string]

The type of weighting to use when combining points cloud fluxes to represent the spaxel flux. Allowed values are STANDARD and MIRPSF. This defines how the distances between the point cloud members and spaxel centers are determined. The default value is STANDARD and the distances are determined in the cube output coordinate system. STANDARD is the only option available for NIRSpec. If set to MIRIPSF, the distances are determined in the alpha-beta coordinate system of the point cloud member and are normalized by the PSF and LSF. For more details on how the weight of the point cloud members are used in determining the final spaxel flux see the Algorithm section.

weight_power [float]

Controls the weighting of the distances between the point cloud member and spaxel center. The weighting function used for determining the spaxel flux was given in the Algorithm description: spaxel flux K = \(\frac{ \sum_{i=1}^n Flux_i w_i}{\sum_{i=1}^n w_i}\)

where n = the number of point cloud points within the region of interest of spaxel flux K

\(w_i =1.0 \sqrt{({xnormalized}^2 + {ynormalized}^2 + {znormalized}^2)}^{p}\)

by default currently p=2, but is controlled by the weight_power argument.