The fors_subtract_sky recipe

fors_subtract_sky

Synopsis

Subtract sky from scientific spectra

Description

This recipe is used to subtract the sky emission from unrebinned slit spectra. This is obtained by robust fitting (i.e., excluding the signal from possible point-like objects in slit) of the emission along the CCD columns within each spectrum). This method doesn’t work if extended objects are in slit (it really destroys the object spectra), and is not applicable to LSS data. The input scientific frames are produced by the recipes fors_remove_bias and fors_flatfield.

This recipe cannot be applied to LSS or long-slit like data (MOS/MXU with all slits at the same offset). No automatic recipe is available for this.

Please refer to the FORS Pipeline User’s Manual for more details.

In the table below the MXU acronym can be alternatively read as MOS, and SCI as STD.

Input files

DO category:               Type:       Explanation:         Required:
SCIENCE_UNBIAS_MXU
or SCIENCE_UNFLAT_MXU
or STANDARD_UNBIAS_MXU
or STANDARD_UNFLAT_MXU     Calib       Frame with sky lines    Y
CURV_COEFF_MXU             Calib       Spectral curvature      Y
SLIT_LOCATION_MXU          Calib       Slit location on CCD    Y
GRISM_TABLE                Calib       Grism table             .

Output files

DO category:               Data type:  Explanation:
UNMAPPED_SCI_MXU
or UNMAPPED_STD_MXU        FITS image  Sky subtracted scientific frame
UNMAPPED_SKY_SCI_MXU
or UNMAPPED_SKY_STD_MXU    FITS image  Subtracted sky frame

Constructor

cpl.Recipe("fors_subtract_sky")

Create an object for the recipe fors_subtract_sky.

import cpl
fors_subtract_sky = cpl.Recipe("fors_subtract_sky")

Parameters

fors_subtract_sky.param.dispersion

Expected spectral dispersion (Angstrom/pixel) (float; default: 0.0) [default=0.0].

fors_subtract_sky.param.startwavelength

Start wavelength in spectral extraction (float; default: 0.0) [default=0.0].

fors_subtract_sky.param.endwavelength

End wavelength in spectral extraction (float; default: 0.0) [default=0.0].

fors_subtract_sky.param.cosmics

Eliminate cosmic rays hits (bool; default: False) [default=False].

The following code snippet shows the default settings for the available parameters.

import cpl
fors_subtract_sky = cpl.Recipe("fors_subtract_sky")

fors_subtract_sky.param.dispersion = 0.0
fors_subtract_sky.param.startwavelength = 0.0
fors_subtract_sky.param.endwavelength = 0.0
fors_subtract_sky.param.cosmics = False

You may also set or overwrite some or all parameters by the recipe parameter param, as shown in the following example:

import cpl
fors_subtract_sky = cpl.Recipe("fors_subtract_sky")
[...]
res = fors_subtract_sky( ..., param = {"dispersion":0.0, "startwavelength":0.0})

See also

cpl.Recipe for more information about the recipe object.

Bug reports

Please report any problems to Carlo Izzo. Alternatively, you may send a report to the ESO User Support Department.