IRAF help page for package noao.digiphot.daophot, program daofind

• image
• output
• starmap =
• skymap =
• datapars =
• findpars =
• boundary = nearest
• nearest
• constant
• reflect
• wrap
• constant = 0
• interactive = no
• verify = )_.display
• verbose = )_.verbose
• graphics = )_.graphics
• display = )_.display
• icommands =
• gcommands =

daofind image output

image

output

starmap =

skymap =

datapars =

findpars =

boundary = nearest

constant

reflect

wrap

constant = 0

interactive = no

verify = )_.display

verbose = )_.verbose

graphics = )_.graphics

display = )_.display

icommands =

gcommands =

DAOFIND searches the IRAF images image for local density maxima, with a full-width half-maxima of datapars.fwhmpsf, and peak intensities greater than findpars.threshold * datapars.sigma above the local background, and writes a list of detected objects in the file output. The detected objects are also listed on the standard output if the program is running in interactive mode or the verbose switch is turned on in non-interactive mode.

DAOFIND can be run either interactively or in batch mode by setting the parameter interactive. In interactive mode the user can examine, adjust and save algorithm parameters, change setup objects interactively, and finally write the coordinate list computed with the chosen parameter set. The verify parameter can be used to automatically confirm the critical parameters datapars.fwhmpsf and datapars.sigma when running with interactive = "no".

	     Interactive Keystroke Commands
?	Print help
:	Colon commands 
v	Verify critical parameters
w	Save the current parameters
d	Plot radial profile of star near cursor
i	Interactively set parameters using star near cursor
f	Find stars in the image
spbar	Find stars in the image and output results
q	Exit task
		Colon Commands
:show		[data/center]	List the parameters
		Colon Parameter Editing Commands
# Image and file name parameters
:image		[string]	Image name
:output		[string]	Output file name
# Data dependent parameters
:scale		[value]		Image scale (units per pixel)
:fwhmpsf	[value]		Full width half maximum of psf (scale units)
:emission	[y/n]		Emission feature (y), absorption (n)
:sigma		[value]		Standard deviation of sky (counts)
:datamin	[value]		Minimum good data value (counts)
:datamax	[value]		Maximum good data value (counts)
# Noise description parameters
:noise 		[string]	Noise model (constant|poisson)
:gain		[string]	Gain image header keyword
:ccdread	[string]	Readout noise image header keyword
:epadu		[value]		Gain (electrons per adu)
:readnoise	[value]		Readout noise (electrons)
# Observation parameters
:exposure	[string]	Exposure time image header keyword
:airmass	[string]	Airmass image header keyword
:filter		[string]	Filter image header keyword
:obstime	[string]	Time of observation image header keyword
:itime		[value]		Exposure time (time units)
:xairmass	[value]		Airmass value (number)
:ifilter	[string]	Filter id string
:otime		[string]	Time of observation (time units)
# Object detection parameters
:nsigma		[value]		Size of Gaussian kernel (sigma) 
:threshold	[value]		Detection intensity threshold (counts)
:ratio		[value]		Sigmay / sigmax of Gaussian kernel
:theta		[value]		Position angle of Gaussian kernel
:sharplo	[value]		Lower bound on sharpness
:sharphi	[value]		Upper bound on sharpness
:roundlo	[value]		Lower bound on roundness
:roundhi	[value]		Upper bound on roundness
# Plotting and marking commands
:mkdetections	[y/n]		Mark detections on the image display
The following commands are available from inside the interactive setup menu.
                    Interactive Daofind Setup Menu
	v	Mark and verify critical daofind parameters (f,s)
	f	Mark and verify the full-width half-maximum of the psf
	s	Mark and verify the standard deviation of the background
	l	Mark and verify the minimum good data value
	u	Mark and verify the maximum good data value

DAOFIND approximates the stellar point spread function with an elliptical Gaussian function, whose sigma along the semi-major axis is 0.42466 * datapars.fwhmpsf / datapars.scale pixels, semi-minor to semi-major axis ratio is ratio, and major axis position angle is theta. Using this model, a convolution kernel, truncated at nsigma * sigma, and normalized so as to sum to zero, is constructed.

The density enhancement image starmap is computed by convolving the input image with the Gaussian kernel. This operation is mathematically equivalent to fitting, in the least-squares sense, the image data at each point with a truncated, lowered elliptical Gaussian function. After convolution each point in starmap contains as estimate of the amplitude of the best fitting Gaussian function at that point. Each point in skymap, if the user chooses to compute it, contains an estimate of the best fitting sky value at that point.

After image convolution , DAOFIND steps through starmap searching for density enhancements greater than findpars.threshold * datapars.sigma, and brighter than all other density enhancements within a semi-major axis of 0.42466 findpars.nsigma * datapars.fwhmpsf. As the program selects candidates, it computes two shape characteristics, sharpness and roundness. The sharpness statistic measures the ratio of, the difference between the height of the central pixel and the mean of the surrounding non-bad pixels, to the height of the best fitting Gaussian function at the central pixel. The roundness statistics measures the ratio of, the difference between the height of the best fitting Gaussian function in x minus the height of the best fitting Gaussian function in y, over the average of the heights of the best fitting Gaussian functions in x and y. The default limits on these parameters findpars.sharplo, findpars.sharphi findpars.roundlo, and findpars.roundhi, are set to weed out non-astronomical objects and brightness enhancements that are elongated in x and y respectively.

Lastly the x and y centroids of the detected objects are computed by estimating the x and y positions of the best fitting 1D Gaussian functions in x and y respectively; a magnitude is estimated by computing the ratio of the amplitude of the best fitting Gaussian function at the object position to findpars.threshold * datapars.sigma, and the object is added to the output coordinate file.

If verbose = yes, the following quantities are written to the terminal as each object is measured.

	xcenter  ycenter  mag  sharpness  roundness  id
			where
	mag = -2.5 * log10 (peak density / detection threshold)

Xcenter and ycenter are the computed x and y coordinates in pixels. Mag is a measure of the intensity ratio of the amplitude of the best fitting Gaussian function at the object position to the detection threshold. Sharpness is typically .5 to .8 for a star with fwhmpsf identical to the pattern star and roundness is approximately zero for round stars. Id is the sequence number of the star in the list.

In both interactive and batch mode the full output is written to the text file output. At the beginning of each file is a header listing the values of the parameters current when the first stellar record was written.

1. Run daofind on an image of n2264 using the default setup.

	da> daofind n2264 default
	... answer the verify prompts
	... the output will appear in n2264.coo.1

2. Run daofind interactively on n4147 using the image display and display cursor. Set the fwhmpsf and sigma parameters with the graphics cursor, radial profile plot, and the interactive setup key i.

	da> set stdimcur = stdimage
	... define the image cursor
	da> display n4147 1 fi+
	... display the image
	da> daofind n4147 interactive+
	... move display cursor to a setup star
	... type i to enter the interactive setup menu
	... enter maximum radius in pixels of the radial profile
	... set the fwhmpsf and sigma using the graphics cursor and the
	    radial profile plot
	... typing  leaves the parameters at their default values
	... type the v key to verify the critical parameters
	... type the w key to save the parameters in the parameter files
	... type the space bar to detect stars in the image
	... a 1 line summary of the answers will appear on the standard
	    output for each star measured
	... full output will appear in the text file n4147.coo.1

3. Run daofind interactively on a single image using the contour plot and graphics cursor. Set the fwhmpsf and sigma parameters with the graphics cursor and radial profile plot and the interactive setup key i.

	da> set stdimcur = stdgraph
	... define the image cursor to be the graphics cursor
	da> contour m92 >G m92.plot1
	... store the contour plot of m92 in the file m92.plot1
	da> daofind m92 display=stdgraph interactive+
	... type :.read m92.plot1 to load the contour plot on the screen
	... move graphics cursor to a setup star
	... type i to enter the interactive setup menu
	... enter maximum radius in pixels of the radial profile
	... set the fwhmpsf and sigma using the graphics cursor and the
	    radial profile plot
	... typing  leaves the parameters at their default values
	... type the v key to confirm the critical parameters
	... type the w key to save the parameters in the parameter files
	... type the space bar to detect stars in the image
	... a 1 line summary of the answers will appear on the standard
	    output for each star measured
	... full output will appear in the text file m92.coo.1

4. Run DAOFIND interactively on a SUN workstation using the imtool window, setting the parameters interactively with the i key as in example 2, but without using cursor readback.

	da> set stdimcur = text
	... set the image cursor to the standard input
	da> display m92 1
	... display the image in the imtool window
	... move the mouse to the imtool window
	... press the F6 key to enter cursor readback mode
	... return to the text window
	da> daofind m92 interactive+
	... move the mouse to the imtool window
	... move the cursor cursor to a setup star, press the center mouse
	    button to freeze the coordinates of the star, and return
	    to the text window
	... type "x y 1 i" in response to the image cursor query where
	    x and y are the coordinates of the star to be used as setup,
	    1 is the default world coordinate system, and i enters the
	    interactive setup menu.
	... enter maximum radius in pixels of the radial profile
	... set the fwhmpsf and sigma using the graphics cursor and the
	    radial profile plot
	... typing  leaves the parameters at their default values
	... type the v key to verify the parameters
	... type the w key to save the parameters in the parameter files
	... type the space bar to detect stars in the image
	... a 1 line summary of the answers will appear on the standard
	    output for each star measured
	... full output will appear in the text file m92.coo.2

5. Run daofind on a list of 3 images contained in the file imlist in batch mode. The program will ask the user to verify that the fwhmpsf, sigma, and threshold are correct before beginning execution.

	da> daofind @imlist default 

6. The user can submit the same job to the background after satisfying himself/herself that the parameter values are correct by appending an & at the end of the command and turning off the parameter queries with the verify switch.

	da> daofind @imlist default verify- &

It is currently the responsibility of the user to make sure that the image displayed in the frame is the same as that specified by the image parameter.

Commands which draw to the image display are currently disabled. The TVMARK task in the proto package can be used to draw simple marks on the display. All the DAOPHOT marking commands will however function if a contour plot is used in lieu of the image display.

Users should not be confused by the normally enabled markcur option in the SUN/IMTOOL setup window. This feature is under the control of the IMTOOL window and the DAOPHOT package has no control over it.