The vmmosobsstare recipe

vmmosobsstare

Synopsis

Reduce a MOS science exposure.

Description

This recipe is used to apply basic reduction steps to one exposure made in MOS mode, to locate objects, and to optimally extract their spectra.

Input files

DO category:             Type:       Explanation:         Required:
MOS_SCIENCE              Raw         Science exposure        Y
MASTER_BIAS              Calib       Master bias             Y
MASTER_DARK              Calib       Master dark             .

MOS_MASTER_SCREEN_FLAT   Calib       Normalised flat field   .

EXTRACT_TABLE            Calib       Extraction table        .

GRISM_TABLE              Calib       Grism table             Y
EXTINCT_TABLE            Calib       Atmospheric extinction  .

MOS_SPECPHOT_TABLE       Calib       Response curve          .

CCD_TABLE                Calib       Bad pixel table         .

Output files

DO category:             Data type:  Explanation:
MOS_SCIENCE_REDUCED      FITS image  Extracted objects spectra
MOS_SCIENCE_FLUX_REDUCED FITS image  Flux calibrated objects spectra
MOS_SCIENCE_EXTRACTED    FITS image  Sky subtracted slit spectra
MOS_SCIENCE_SKY          FITS image  Sky spectra
MOS_SKY_REDUCED          FITS image  Extracted sky spectra
OBJECT_TABLE             FITS table  Objects spectra identification
WINDOW_TABLE             FITS table  Objects positions in slit

A flat field correction is applied only if a normalised master flat field (produced by the recipe vmspflat) is specified.

The extraction table is the product of the local spectral distortions modelling performed by the recipe vmspcaldisp. If an extraction table is not specified, then the global distortion models read from the science frame header are used.

The grism table contains necessary information to control the way spectra are extracted, starting from the reference wavelength (header entry PRO WLEN CEN), on a specific range of pixels above and below its position on the CCD (header entries PRO SPECT LLEN LO and PRO SPECT LLEN HI). Other parameters, used in the extraction of the science slit spectra, are the start and the end wavelength of the image of the extracted slit spectra (header entries PRO WLEN START and PRO WLEN END), and the step of the sampling along the dispersion direction (header entry PRO WLEN INC). Finally, the wavelengths of the sky lines used in the alignment of the spectral distortion models, necessary to keep into account the possible coordinates shifts introduced by a variation of the instrument flexures between the science and the calibration exposures, are listed in the header keywords PRO SKY WLENi, with i ranging from 1 to the number specified in the keyword PRO SKY NO.

A CCD table must be specified in input only if a bad pixel cleaning is requested.

The slit spectra are remapped with the instrument distortions removed and at a fixed wavelength step. A sky value is estimated for each wavelength and then subtracted from the data. The result is stored in the MOS_SCIENCE_EXTRACTED image, while the image MOS_SCIENCE_SKY contains the subtracted sky model. The 1D extracted spectra are stored in the MOS_SCIENCE_REDUCED image, while the corresponding sky spectra extracted with the same method are stored in the MOS_SKY_REDUCED image.

The positions of the extracted slit spectra and of the detected objects that they may contain are listed in the window table.

If a spectro-photometric table (produced by the recipe vmmosstandard) is specified together with an atmospheric extinction table, and a flux calibration is requested, then a MOS_SCIENCE_FLUX_REDUCED image is also created. This image is identical to the MOS_SCIENCE_REDUCED, but the spectra it contains are flux calibrated, and expressed in units of erg/cm/cm/s/Angstrom.

For more details, please refer to the VIMOS Pipeline User’s Guide.

Constructor

cpl.Recipe("vmmosobsstare")

Create an object for the recipe vmmosobsstare.

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

Parameters

vmmosobsstare.param.BiasMethod

Bias removal method. (str; default: ‘Zmaster’) [default=”Zmaster”].

vmmosobsstare.param.SkyMethod

Sky level determination method. (str; default: ‘Median’) [default=”Median”].

vmmosobsstare.param.PolyOrder

Degree of polynomial used when the SkyMethod is set to Fit. (int; default: 0) [default=0].

vmmosobsstare.param.SkyKSigmaLow

Low threshold for K-sigma rejection in sky fitting. (float; default: 1.0) [default=1.0].

vmmosobsstare.param.SkyKSigmaHigh

High threshold for K-sigma rejection in sky fitting. (float; default: 1.0) [default=1.0].

vmmosobsstare.param.Fuzz

Extra pixels from expected position of spectrum edge in extraction. (int; default: 5) [default=5].

vmmosobsstare.param.SlitMargin

Number of excluded pixels at slit ends in object search or in sky level determination. (int; default: 2) [default=2].

vmmosobsstare.param.LineWidth

Size of spectrum to extract around any skyline. (int; default: 16) [default=16].

vmmosobsstare.param.DetectionLevel

Object detection level in units of sigma. (float; default: 2.0) [default=2.0].

vmmosobsstare.param.WatershedLevels

Number of levels in the watershed method in object detection. (int; default: 32) [default=32].

vmmosobsstare.param.WatershedFraction

Flux fraction to use in watershed. (float; default: 0.01) [default=0.01].

vmmosobsstare.param.MinObjectSize

Minimal size for an object candidate to be considered an object. (int; default: 2) [default=2].

vmmosobsstare.param.MaxObjectSize

Maximal size for an object candidate for not trying deblend into sub- objects. (int; default: 7) [default=7].

vmmosobsstare.param.CleanBadPixel

Bad pixel correction on MOS science exposure. (bool; default: False) [default=False].

vmmosobsstare.param.CalibrateFlux

Extracted spectra are flux calibrated. (bool; default: False) [default=False].

vmmosobsstare.param.HorneExtraction

Use 1D Horne extraction. (bool; default: False) [default=False].

vmmosobsstare.param.ModelSlit

Model wavelength solution within each slit. (bool; default: True) [default=True].

vmmosobsstare.param.ModelSlitOrder

Order of polynomial for wavelength solution modeling within each slit. (int; default: 0) [default=0].

vmmosobsstare.param.UseSkylines

Use sky lines to refine the wavelength calibration (bool; default: True) [default=True].

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

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

vmmosobsstare.param.BiasMethod = "Zmaster"
vmmosobsstare.param.SkyMethod = "Median"
vmmosobsstare.param.PolyOrder = 0
vmmosobsstare.param.SkyKSigmaLow = 1.0
vmmosobsstare.param.SkyKSigmaHigh = 1.0
vmmosobsstare.param.Fuzz = 5
vmmosobsstare.param.SlitMargin = 2
vmmosobsstare.param.LineWidth = 16
vmmosobsstare.param.DetectionLevel = 2.0
vmmosobsstare.param.WatershedLevels = 32
vmmosobsstare.param.WatershedFraction = 0.01
vmmosobsstare.param.MinObjectSize = 2
vmmosobsstare.param.MaxObjectSize = 7
vmmosobsstare.param.CleanBadPixel = False
vmmosobsstare.param.CalibrateFlux = False
vmmosobsstare.param.HorneExtraction = False
vmmosobsstare.param.ModelSlit = True
vmmosobsstare.param.ModelSlitOrder = 0
vmmosobsstare.param.UseSkylines = True

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

import cpl
vmmosobsstare = cpl.Recipe("vmmosobsstare")
[...]
res = vmmosobsstare( ..., param = {"BiasMethod":"Zmaster", "SkyMethod":"Median"})

See also

cpl.Recipe for more information about the recipe object.

Bug reports

Please report any problems to ESO VIMOS Pipeline Team and VIMOS Consortium. Alternatively, you may send a report to the ESO User Support Department.