Xselect_guide
guide to xselect and the ds9 environment

    To begin open a unix command prompt, the guide will then instruct you in the order that Xselect will run.
    Text in [ ] is the default, pressing enter with nothing entered will put in the default.  


The information within brackets
[ ] is either the default value or the last value selected.

Pressing <Enter> without typing anything automatically selects this value.



Command
Command Description
Machine response to Command
Information returned after Command execution and before machine response
Type xselect to begin
Launches xselect program
>Enter session name [xsel]
[xsel] Designates file save location when you exit xselect

Displays that xselect is
setup for ASCA, time keyword
is TIME in units seconds, and the
default bin size
Type read events at the
new prompt
Tells xselect that you want to open an Events ("evt") file.
>Enter the Event file dir [./]
[./] Specifies the location of the Events file to be analyzed
>Enter the Event file list [acis...fits]
 [acis..._evt2.fits]
Selects Event file you want to open. 
Got new mission [axaf)
> Reset the mission ? [yes]

[yes]

Resets the (observatory) mission.

Displays that xselect is now setup for AXAF (aka Chandra), time units, and Default Binsize.
Also displays settings commands, and the location of the file, object name, date it was observed, exposure time ( = LIVETIME).
[note: mission can also be reset by typing set mission and then by typing AXAF in response to which mission?]

Default Binsize (or minimum time resolution) should match that in image header.
If minimum time resolution is not recognized, execute next command
Type set binsize
Manually resets the minimum time resolution
Give bin size in seconds [16.000]

1.24104



Image Analysis
At the new prompt type
extract image
Extracts the image you selected from the Events file.

Shows total events (photon counts) written for the exposure time period;
reports average counts/sec ;
a high rate means the image is bright, a low rate means the image is faint.
Type saoimage
Opens the extracted file in ds9.
For more help with ds9 visit short guide to ds9.
  • To select a small Region of the image:
  • Click on the center of your object and drag out the radius, enclosing the area you want to observe/
  • Click on the button labeled Region at the top of the screen.
    • Click on File Format.
    • Click on SAOimage.
  • Now Click on the Region button directly above the image.
    • Click Save As
    • Click OK
  • Return to xselect window.
Type filter region ds9.reg
Takes the region you just selected in ds9 and blocks out surrounding image


Type extract events
Extracts events from the Event File.

equivalent to "extract image";
see above
Examining light curves
Type extract curve
Extracts light curve data.

equivalent to "extract image";
see above
Type set device /xw
Sets device to /xw, just as in lcurve routine


Type plot curve
Opens plot window with graph.


                         To rescale graph on x axis type rescale x xmin xmax , with xmin and xmax being the numbers you want for the scale.
                         To rescale graph on y axis type rescale y ymin ymax.
Type exit
Exits out of PLT> window, and returns to xselect prompt.


Type save curve
Tells xselect you want to save your light curve.
Give output file [lcurve]

Designates file path to save in, default is last save name.
lcurve88

Extracting a power spectrum
(these commands are nearly the same as those for the powspec routine)
Type $
Temporarily leaves xselect.
(type exit to return to xselect)


Type powspec filename.lc
Opens the light curve file you just saved, filename being whatever
you named it.
Name of the window file ('-'
for default window). 

Type -
Tells xselect what window file you want to use.
Newbin Time or negative
rebinning [3.241]
Displays Minimum Newbin Time(s);
this should match time resolution

Displays Default Newbin Time
(which must be an integer multiple of the Minimum Newbin Time); Default Newbin Time chosen so that number of bins is close to an integer power of 2 (helpful for Fourier transform?)
3.2410400 Tells xselect what you want the Newbin Time to be, enter the minimum.
Number of Newbins/Interval [14433] Confirms the Newbin Time entered.
Displays number of Newbins covering the exposure time interval.
14433
Tells xselect what you want the Number of Newbins per Interval
to be, enter the maximum.
Number of Intervals/Frame [1] Confirms number of Newbins and Newbin TIme interval.
1
Tells xselect that all data should be collected in one inteval of time
Rebin results?
Confirms that all data will be collected in 1 interval.
0
(allows another opportunity for rebinning?)
Name of output file?
[powspec_objectname]

powspec_objectname write powerspectrum filename
Do you want to plot your results? [yes] power spectrum file has .fps extension
yes
plots power spectrum
Enter PGPLOT device
[/xw]

/xw
Power Spectrum Ready!

Under the PLT> type hardcopy
Saves the power spectrum file and closes the window


Type exit
Exits PLT> and returns to xselect prompt


Extracting an energy spectrum from the light curve
Type xselect
Re-enters the xselect prompt.


Enter session name [xsel] Will designate file save location when you exit xselect xsel
Displays that xselect is
setup for ASCA, time keyword
is TIME in units seconds, and the
default bin size
Type read events in the
new prompt
Tells xselect that you want it to open a file.

Enter the Event file dir [./] Designates where the Event file you want analyzed is located,
enter the same as before.
./
Enter the Event file list [acis...fits] Selects Event file you want to open.  Default is the last opened
event file in xselect, use the same as before.
acisf00088N001_evt2.fits
Reset the mission? [yes]
Type yes
Resets the mission.

Displays that xselect is now setup
for AXAF, time units again, and
Default Binsize again.
Also displays settings commands,
and finally, it shows the location
of the file, object name, and date
it was observed.
Now type extract spectrum
Extracts the data needed for the energy spectrum.


Type plot spectrum
Plots the spectrum on a graph.


Type exit
Exits PLT> prompt.


Type save spectrum
Tells xselect you want to save the spectrum.


Give output file name?
Enter a file name.  This file is saved as filename.pha, filename
being whatever you pick.
powspec1943

Type exit to quit xselect.
Tells xselect you want to quit.


Save this session?
Type yes






Time Filter with cursor
After a light curve graph has been plotted type exit under the PLT> prompt.
Exits out of the plot window and returns to xselect


Type filter time cursor.
Tells xselect you want to break down the file into intervals of your choosing.

Opens plot window again.
At PLT> type quit again
Re-opens plot window with a cursor selector.  Click once where the left boundary will be and click again where the right boundary will be.


Type x in the plot window.
Sets the points.


Type exit in the PLT> prompt.
Exits back to xsel prompt.


Type save curve.
Tells xselect that you want to save your curve.


Give output file [default]
Type the filename that you want to save it as.
1943split1





Time Filter with numbers
After you have a light curve extracted and plotted type exit at the PLT> prompt.
Exits out of the plot window and returns to xselect.


Type filter time scc under the xsel prompt.
Tells xselect you want to select times by numbers.


When the plot window opens type quit.
To quit the plot screen.

Brings up prompt asking what starting and stopping times you want.
Prompt asks what your starting and stopping times are.
Enter starting time, and then enter your stopping number, with a , separating the two times.
0, 928
xselect will save the file
Type save curve.
Tells xselect that you want to save your curve


Give output file [default]
Type the filename that you want to save it as.
1943split1