.. C-Munipack - User's manual
Copyright 2012 David Motl
Permission is granted to copy, distribute and/or modify this document under the
terms of the GNU Free Documentation License, Version 1.2 or any later version published
by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and
no Back-Cover Texts.
$Id: getting_started.rst,v 1.2 2012/09/01 12:47:00 dmotl Exp $
.. _getting-started:
Getting started
===============
The following text describes the basic procedure for processing an
observation of a short-periodic variable stars by means of the Muniwin.
The package with demo data used in the example is available on the project's
web pages. Download and unzip the archive to an empty folder at your hard disk
(e.g. :file:`~/c-munipack/sample`. The archive has the following structure:
.. object:: dark / 20s / masterdark.fts
master-dark frame (20 seconds exposure)
.. object:: dark / 20s / raw / dark*.fts
set of raw dark frames (20 seconds exposure)
.. object:: flat / v / masterflat.fts
master-flat frame (optical filter V)
.. object:: flat / raw / flat-v*.fts
set of raw flat frames (optical filter V)
.. object:: data / v / frame*.fts
sample CCD frames (optical filter V)
General overview
----------------
In general, the reduction of CCD data consists of the several steps:
#) Creating a new project and populating it with input files (source CCD frames)
#) Calibration of the source frames
#) Photometry and matching
#) Selection of stars
#) Selection of aperture
Creating a new project
----------------------
Launch the :program:`Muniwin` program - a way how to launch an application depends on your operating system and desktop environment.
For example, on the MS Windows platform, the Muniwin program can be run from the menu :menuselection:`Start --> Programs --> C-Munipack 2.0`
folder.
Using the main menu, select item :menuselection:`Project --> New`. A new dialog appears.
.. figure:: images/newproject.png
:align: center
:alt: "New project" dialog
The dialog for making a new project.
Fill in a name that will be assigned to the project. Because the name of the file that keeps track of the data related
to the project, the project file, is derived from the name, some characters cannot appear in the project name, do not use: / \ ? % * : | " < and >
In our example, let us use the designation of the variable star ``CR Cas``.
The field :guilabel:`Location` shows a path to the directory where a new project will be created. Edit the path to
change the location, you can also click the :guilabel:`Browse` button to select a directory in a separate dialog.
The dialog also displays a list of available project types. Project types were designed to limit the amount of control
that are shown in application. Select the :guilabel:`Variable star observation`, please.
Confirm the dialog, yet another dialog appears.
.. figure:: images/newproject2.png
:align: center
:alt: "Load profile" dialog
The dialog for specifying an initial set of configuration parameters
Using the second dialog, you can load an intial set of configuration parameters into a new project. If this is a fresh
installation, you have one choice only - use factory defaults. The choice :guilabel:`Load factory defaults` should be
automatically selected and make sure that the options below are unchecked. Confirm the dialog.
You should be in the main window again now. The table of input files shown there is empty.
.. figure:: images/main.png
:align: center
:alt: Main application window
The main application window with the table of input files, now empty.
Selecting source frames
-----------------------
Now, we're going to populate the project with source files. Open the :guilabel:`Frames` menu and click on :guilabel:`Add frames from folder`.
Go to the folder which contains the source CCD frames. The demo data is stored in the :file:`data/v` subfolder. You should
see the list of files in the center navigation pane. This dialog allows you to add all frames from folders and subfolders.
If you need to specify only a subset of files from a particular folder, you the :guilabel:`Add individual frames` choice.
.. figure:: images/addfolder.png
:alt: "Add folder" dialog
:align: center
The dialog with the place selection box (left), the file selection box (middle)
and the preview panel (right).
Push the :guilabel:`Add` button. If you want to process data taken in several nights at once, use the same procedure to add
those files to the table. After inserting all the files you want to process, close the dialog by pushing the :guilabel:`Close`
button.
.. figure:: images/inputfiles.png
:alt: Main application window
:align: center
The main application window with the sample frames inserted.
Frame reduction
---------------
Reduction of CCD frames is a process that takes source CCD frames, performs their conversion and calibration,
detects stars on each frame and mearures their intensity and finally finds correlation (match) between objects
that were found in the data set. The process of reduction prepares the data that are necessary for making a light
curve or a variable star.
The reduction consists of several steps - conversion, calibration, photometry and matching. They can be invoked
step-by-step manually. The preferred way is to use the :guilabel:`Express reduction` dialog that allows to perform
these steps in a batch. Using the menu, activate the :menuselection:`Reduce --> Express reduction` item.
A new dialog appears. The dialog has several options aligned to the left, Each of them relates to an optional
step in the reduction process.
.. figure:: images/express.png
:alt: "Express reduction" dialog
:align: center
The dialog for setting parameters of the reduction process
Check the :guilabel:`Fetch/convert files`.
In this step, the program makes copy of the source CCD frames. This is necessary, because the following
calibration steps will modify them and we don't want the program to change our precious source data.
.. figure:: images/express_convert.png
:alt: "Express reduction" dialog
:align: center
A raw CCD frame consists of several components. By the calibration process, we get rid of those
which affect the result of the photometry. In some literature, the calibration is depicted as the
peeling of an onion. There are three major components which a raw frame consists of - the current
made by incident light, current made thermal drift of electrons (so-called dark current) and
constant bias level. In standard calibration scheme, which we will demonstrate here, the dark-frame
correction subtracts the dark current and the also the bias. Because of the nature of the dark current,
it is necessary to use a correction frame of the same exposure duration as source files and it must
be carried out on the same CCD temperature, too. Thus, the properly working temperature regulation
on your CCD camera is vital. Our sample data needs to perform the dark-frame correction, so check
the :guilabel:`Dark-frame correction` option. Click the :guilabel:`Browse` button and find the file
with the dark frame. For the sample data, use the file :file:`dark / 20s / masterdark.fts`.
.. figure:: images/express_dark.png
:alt: "Express reduction" dialog
:align: center
Then, we have to compensate the spatial non-uniformity of a detector and whole optical
system. These non-uniformities are due to the fabrication process of a CCD chip and they are
also natural properties of all real optical components, lenses in particular. The flat-frame
correction uses a flat-frame to smooth them away. The flat-frame is a frame carried out
while the telescope is pointed to uniformly luminous area. In practice, this condition is
very difficult to achieve, the clear sky before dusk is usually used instead. Our sample data
needs to perform the flat-frame correction too, so check the :guilabel:`Flat-frame correction`
option. Click the :guilabel:`Browse` button and find the file with the flat frame. For the sample data,
use the file :file:`flat / V / masterflat.fts`.
.. figure:: images/express_flat.png
:alt: "Express reduction" dialog
:align: center
The photometry is a process that detects stars on a CCD frame and measures their brightness. Unlike the previous
steps, the result is saved to a special file, so-called the photometry file. There are a lot of parameters which
affect the star detection and also the brightness computation. In this example, the default values work fine,
but I would suggest you to become familiar with at least two of them - FWHM and Threshold - before
you start a real work. Check the :guilabel:`Photometry` option.
.. figure:: images/express_photometry.png
:alt: "Express reduction" dialog
:align: center
The previous command treated all source files independently. As a result of this, a star #1
in one file is not necessarily the same as a star #1 in another file. The matching is a process
which finds corresponding stars on source frames and assigns an unique identifier. Check the
:guilabel:`Matching` option.
It is necessary to select one frame from the set of source frames that all other frames are matched
to, this frame is called a reference frame. In my experience, the frame with the greatest number of
stars works the best. Back to our example, let's pick up the first one.
.. figure:: images/express_matching.png
:alt: "Express reduction" dialog
:align: center
In previous steps, we have configured parameters of the reduction process and we are ready to start
it. Click the :guilabel:`OK` button. During the execution a new window appears displaying the state
of the process; all the information is also presented there. This window will be automatically
closed after finishing the process. Wait for the process to finish.
.. figure:: images/progress.png
:alt: Progress dialog
:align: center
The dialog displayed during time demanding operations.
After finishing, the icon in the file table changes; the information about the time of observation,
the length of the exposition and the used filter is filled in. In case some of the frames could not be
processed successfully, the entry is be marked with a special icon and in the :guilabel:`Status` column
the error message is indicated.
.. figure:: images/inputfiles3.png
:alt: Main application window
:align: center
The main application window after the recution.
Making a light curve
--------------------
The sample data is the observation of an eclipsing binary star. For most of such observers,
the goal is to make a light curve. A light curve is usually represented as a table, which consists
of at least two columns - time stamps expressed as Julian dates and differential instrumental
brightness of a variable star in magnitudes. The magnitudes are called differential, because they
are differences between two stars - a variable star and a comparison star. A variable star is a
star that is subject of brightness variation and a comparison star is supposed to be constant.
To check that the comparison star is really constant, it's advisory to use one or two additional
stars, so-called check stars. They are supposed to be constant too and thus the difference between
any check star and the comparison star should be constant.
The Muniwin program is designed to guide you through the process of making a light curve.
Open the :guilabel:`Make` menu and select the :guilabel:`Light curve` item. A new dialog appears, all
fields in this dialog are optional, they allows you to include only subset of frames to the curve,
apply the heliocentric correction or include the air mass coefficients to the output. Let all options
unchecked and just confirm the dialog by the OK button.
.. figure:: images/makelightcurve.png
:alt: Make light curve
:align: center
The dialog for making a light curve.
Another dialog appears. The next dialog allows you to pick up a variable star, a comparison star and one or more
check stars. In this dialog, the reference frame is displayed. Find a variable star and click on
it using the left mouse button. A context menu appears. Select the :guilabel:`Variable`
item. The star is drawn in red color now and the label ``var`` is placed near to it. Using
the same procedure, select one comparison star and one or more check stars. I would recommend
you to use two check stars. If you are using the sample data, use the stars according to the
following screenshot. Confirm the selection by the :guilabel:`OK` button.
.. figure:: images/stars.png
:alt: Choose stars
:align: center
The dialog for selection of a variable star (red), a comparison star (green)
and check stars (blue).
In the next dialog, we have to choose the aperture. You can image the aperture as a virtual circular pinhole,
placed on each star on a frame to measure its brightness. All pixels that are inside
the pinhole are included in computation leaving out the background pixels. The best
aperture should be big enough to include most of the star's light, on the other hand,
the bigger aperture is used the more background is included and the more noisy the
result is. Because of this, the photometry process computes the brightness of each
star in a set of predefined apertures of radius in the range of 2 and 30 pixels.
The programs allows you to select an aperture in the following dialog, the program
displays a graph of standard deviation of data for each aperture. The curve has U-like
shape usually and the best aperture is in the minimum of the curve. For the sample data,
select the aperture #2 and confirm the dialog by the :guilabel:`OK` button.
.. figure:: images/aperture.png
:alt: Choose aperture
:align: center
The dialog for selection of an aperture.
Now the program has got enough information to make a light curve of the
selected variable star. The light curve is presented in a new window. Please keep
in mind that the magnitudes displayed in the light curve are differential with
respect to the selected comparison star.
.. figure:: images/lightcurve.png
:alt: Light curve graph
:align: center
The dialog with a light curve graph.
In the light curve window, open the :guilabel:`File` menu and select
the :guilabel:`Save` item. A new dialog appears. Locate the folder
where you want to save the results and fill in the name of the output file. Confirm
the dialog by the :guilabel:`Save`.
The light curve is saved to a text-based file. On its first line, the
names of the columns are stored. The second line shows the aperture and color
filter used. The data are stored on the followin lines. Each line corresponds
to a single source frame. In the first column, there is a time of observation
(center of exposure) expressed as a Julian date. The second column consists
of differential instrumental brightness of the variable stars with respect
to the comparison star in magnitudes (V-C). The error estimation is stored
in the next column. Following columns consist of differential magnitudes
of comparison star and check stars and their error estimations.
.. figure:: images/output.png
:alt: Output file
:align: center
The light curve of a variable from the sample data stored to a file.
