SPATIAL OR SPECTRAL INTEGRATION
Integrate over a wavelength interval :
integrate spectra
Principles
- For a given datacube, for all the spectra, a given wavelength
interval is scanned. Output may be the integral of the energy
over this domain, or the mean, or the RMS dispersion.
- The data are recorded into a column created into the table
associated with the datacube, or directly mapped as an image
of the spatial repartition of the computed parameter.
Use
- Click on [Analyse] in the main menu, then on [Integrate spectra].
The [Integrate spectra] window pops up.
- Enter the name of the Input datacube. You can type it in
directly, or use the browse
icon at the end of the field, or drag and drop it from the
Reduction
folder.
- Enter the Spectral range (Å) of the spectral region
to be
scanned, or check the [Full range] button to scan the complete
spectral domain.
Options description
- Save output as a table column : the computed result will
be recorded
into a column which will be created (if it does not already exist) in
the table associated with the input datacube; remember that this table
is known by the software, as it has been associated with the creation
of the datacube. the user is requested to fill in the Column name
input field.
- Output in an image : the computed result will be recorded
into an image. This image may be later viewed (button [View result]
in the result window). The user is requested to give the
Image name.
- Compute : the user has to choose between [Sum]
(the spectra will be integrated over the given wavelength range),
[Average] (the spectra will be averaged over the given
wavelength range), and [RMS dispersion] (the spectra will be scanned
over the given wavelength range, and the RMS dispersion computed).
- Optional parameters : the user may filter the spectra
using a given wavelength transmission curve. This curve may be given as
a 1D-image (a spectrum) or as a couple of table columns [lambda,trans].
- Save values :
All the input values (files names, coordinates) are saved,
and become the new default values for this user. They can
be recalled at will, and are used each time the Check frame
offset job window is opened.
- Recall values :
The values (files names, coordinates) saved by the user,
are loaded to the various input fields.
- Default values :
The input fields are set to the general defaults values;
for instance, the file names are set to blank.
Integrate over a circular spatial area :
sum aperture
Principles
- A circular area is defined in the field, by giving a center and
a radius.
- The spectra of the spatial pixels included into this area are
summed up and the resultant spectrum recorded as a 1D-image.
Use
- Click on [Analyse] in the main menu, then on [Sum aperture].
- Give the names of the Input datacube and of the
Output spectrum.
You can type it in directly, or use the browse
icon at the end of the field, or drag and drop it from the
Reduction
folder.
- Give the [Center] and the [radius] of the area of interest.
- Click on [Accept].
Options description
- CCD coordinates : the [Center] and [Radius] are interpreted
as given in CCD pixel units.
- Sky coordinates : the [Center] and [Radius] are interpreted
as given in arcseconds on the sky [alpha,delta].
- Other coordinates : the [Center] and [Radius] are
interpreted as given in the units of the [X] and [Y] columns
of the associated table. The names of the columns are entered by the
user in the two [X] and [Y] input fields.
- Save values :
All the input values (files names, coordinates) are saved,
and become the new default values for this user. They can
be recalled at will, and are used each time the Check frame
offset job window is opened.
- Recall values :
The values (files names, coordinates) saved by the user,
are loaded to the various input fields.
- Default values :
The input fields are set to the general defaults values;
for instance, the file names are set to blank.
The user's interface for this function is Not yet implemented (please
wait for release 4),
BUT the function may already be used. Yes, that is XOasis...
Just use the Sky, Define sky area, and
Compute sky spectrum functions described in the
Sky subtraction section of this manual
to build the spectrum of any part of the field, connex or not.
Principles
- This operation can be performed either on an isolated spectrum
or on all the spectra recorded into a datacube.
- A polynomial fit is performed over the spectra, and the resulting
fit is taken as an image of the underlying continuum of each spectrum.
- The continua maybe saved as such, or used to divide the associated
spectra, or subtracted from the spectra.
Use
- Click on [Analyse] in the main menu, then on [Continuuum
subtraction]. The [Continuum subtraction] window pops up.
- Choose between On spectrum and On datacube.
- Give the Input spectrum (or Input datacube)
and Output spectrum (or Output datacube) names.
You can type them in directly, or use the browse
icon at the end of the field, or drag and drop it from the
Reduction
folder.
- Choose the degree for the polynomial fit. The default, 7, is
often OK, but it depends on the object observed.
- Click on [Accept]. The continuum (continua) is (are) computed,
and recorded into the output spectrum (datacube).
Options description
- Operation :
This paragraph presents the datacube case; in the spectrum
case, just switch to singular form...
- Save : The computed continua are saved in the output
datacube.
- Subtract : The computed continua are subtracted from the
spectra of the input datacube, and the results are stored into
the output datacube.
- Divide : The spectra of the input datacube are divided by
the computed continua, and the results are saved in the output
datacube.
- Divide-1 : The spectra of the input datacube are divided
by the computed continua, 1 is subtracted from every spectrum
to bring the mean around zero, and the results are saved in the
output datacube.
- Rejection factor : this is the N-sigma rejection level
for the polynomial fit over the number of iterations given (see
below). The user may introduce a dissymetry in the
rejection process by choosing different absolute values for the
Inf and Sup coefficients.
- Maximum number of iterations : does what you expect
regarding the continuum fit with bad points rejection...
- Discarded intervals table : the user may tell the program
to ignore some wavelength intervals for the continuum fit. The interval
limits are recorded in a table which is most conveniently created
using the standard XOasis graphical display :
- Using function [Display]/[Spectrum and Table]/[Open]/[Plot
spectrum], plot some
nice typical spectrum where the zones to be avoided are
clearly spotted.
- Click on [Curs] at the bottom left of the window, then,
starting with short wavelengths, left-click on all the points
where you would like the program to switch from
take care of the following pixels to
ignore the following pixels;
you note that the cursor positions are displayed in the
result window.
- When done (there must be an even number of points),
click on [Save], and give a name for the save file.
- Debug : as a first step, the user may choose to fit a
single spectrum of the datacube, to fine tune the above parameters.
The [Lens number] has to be given, as well as the name of the
the temporary [Lens spectrum] (which will be automatically extracted
from the datacube), and the name of the [Output spectrum].
- Save values :
All the input values (files names, numerical values) are saved,
and become the new default values for this user. They can
be recalled at will, and are used each time the Check frame
offset job window is opened.
- Recall values :
The values (files names, numerical values) saved by the user,
are loaded into the various input fields.
- Default values :
The input fields are set to the general defaults values;
for instance, the file names are set to blank.
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Last update: 11/01/1999. Send comments to
martin@cfht.hawaii.edu