| xgphot | xapphot | xgphot |
xgphot -- Do aperture photometry on a list of objects through circular, elliptical, rectangular, or polygonal apertures interactively using xgterm or non-interactively
xgphot images objects results
Xgphot computes accurate center, sky values, shape statistics, fluxes, magnitudes, and magnitude errors for selected astronomical objects in the input images images . The object coordinates and /or geometry are either: read from the skypars and photpars parameter sets, specified interactively with the image cursor, or read from the input text files objects . The results are logged in the output text files results . In non-interactive mode all measurements are logged automatically. In interactive mode logresults is normally disabled on task startup in order to give the user time to set the parameter values and make test measurements.
Xgphot supports multi-aperture circular, elliptical, rectangular, and polygonal object and sky apertures. The sky apertures may be concentric with or offset from the object apertures.
The xgphot algorithm parameters are grouped into parameter sets by function. The image data and image display parameters are defined in the impars and dispars parameter sets respectively. The automatic object list generating and marking algorithms are controlled by the findpars and omarkpars parameters respectively. The cenpars , skypars , and photpars parameters control the centering, sky fitting, and photometry algorithms respectively. The contour and surface plotting algorithm parameter sets control the action of the results viewing code. If update is yes the algorithm parameter sets on disk will be updated to the latest values.
Xgphot can be run: interactively with the default gui (the default), interactively without the gui, or non-interactively. All three modes are discussed briefly below.
See the help page for xguiphot.
If interactive is "yes" xgphot activates the xgterm window, initializes the parameters, displays the first images, and waits for user input. The user interacts with xgphot via the xgterm graphics window, using a series of keystroke and colon commands, to communicate with the program.
The default gui in this case is the xgterm window. The xgterm window is used to display the current image, enter keystroke and colon commands, and display both printed and graphical results. Full IRAF cursor mode is supported so users can zoom, pan, etc the displayed image just as they can any other graph. However the usual image mouse button functions such as interactive image display contrast and brightness windowing are not available in this mode as they are with the default gui.
Users can edit the algorithm parameters individually using colon commands or in groups using the epar mechanism.
By default results logging is disabled. Users should adjust the algorithm parameters by making trial measurements, and only turn results logging on when an optimal set has been chosen.
The complete set of cursor keystroke and colon commands for use with the xgterm window is listed below.
Xgphot Keystroke Commands
? Print help Q Quit task
: Colon command CR Erase status line
$ List input and output files
n Display next image p Display previous image
i Redisplay current image h List current image header
x Fit model to object \X Refit model to object
y Fit and plot model \Y Enter model plotting submenu
] Read next objects file [ Read previous objects file
r Reread current objects file l List current objects list
@ Autofind objects list z,a Draw objects list
m Mark objects list e Erase objects list
^ Rewind object list ~ Move to nearest list object
f Move to next list object b Move to previous list object
z Delete entire objects list d Delete nearest list object
u Undelete nearest list object a Add object to list
v Draw object and sky polygons
Sp Measure nearest object * Find and measure objects
# Measure entire object list
o Measure next list object - Measure previous list object
+ Measure rest of object list . Measure nearest list object
; Print last result g Plot object analysis results
G Plot shape analysis results , Plot sky analysis results
j Enter object display submenu k Enter sky display submenu
c Enter object plots submenu s Enter sky plots submenu
Model Fitting Submenu Keystroke Commands
\Y Enter submenu q Quit submenu
f Refit r Replot
p Print fit results m Print moments analysis
h Set ihwhmpsf to fitted value
Object Region Display Submenu Keystroke Commands
j Enter submenu q Quit submenu
i Display object o Overlay contours on object
a Overlay aperture on object m Overlay moments analysis on object
c Contour object s Mesh plot of object
g Replot
Sky Region Display Submenu Keystroke Commands
k Enter submenu q Quit submenu
i Display sky o Overlay contours on sky
a Overlay aperture on sky c Contour sky
s Mesh plot of object g Replot
Object Analysis Plots Submenu Keystroke Commands
c Enter submenu q Quit submenu
r Show major axis plot t Show position angle plot
c Show flux vs aperture plot e Show axis ratio vs aperture plot
p Show angle vs aperture plot w Show width estimate vs aperture plot
Sky Analysis Plots Submenu Keystroke Commands
s Enter submenu q Quit submenu
r Show major axis plot t Show position angle plot
h Show histogram plot
The following colon commands are supported.
File Management Colon Commands
:startdir Show the starting directory
:chdir Show / Set the current directory
:setdir Set the working directory to the current directory
:images [template] Show / Set a new image template
:objects [template] Show / Set a new objects file template
:results [template] Show / Set a new results file template
:robjects [template] Show / Set a new output objects file template
:imname [name] Show / Select the current image
:olname [name] Show / Select the current objects file
:rlname Show the current results file
:glname Show the current output objects file
:imnumber [number] Show / Select the current image number
:olnumber [number] Show / Select the current objects file number
:rlname Show the current results file number
:glname Show the current output objects file number
:logresults [yes/no] Log the results to the results file ?
Object List Management Commands
:oselect number Select the current object
:odelete number Delete the current object
:oundelete number Undelete the current object
:oadd geometry Add object to object list
:osave file Save current object list to objects file
Parameter Set Commands
:lpar pset List the pset parameters
:unlearn pset Unlearn the pset parameters
:epar pset Edit the pset parameters
Permitted values of pset are: "impars", "dispars", "findpars",
"omarkpars", "cenpars", "skypars", "photpars", "cplotpars",
and "splotpars".
Impars Parameter Colon Commands
:iscale [value] Show / Set the image scale
:ihwhmpsf [value] Show / Set the hwhm of the psf
:iemission [yes/no] Show / Set emission features switch
:iskysigma [value] Show / Set the sigma of the background
:imindata [value] Show / Set the minimum good data value
:imaxdata [value] Show / Set the maximum good data value
:inoisemodel [name] Show / Set the noise model
:ikgain [value] Show / Set the CCD gain keyword
:ikreadnoise [value] Show / Set the CCD readout noise keyword
:igain [value] Show / Set the CCD gain in e-/ADU
:ireadnoise [value] Show / Set the CCD readout noise in e-
:ikexptime [value] Show / Set the exposure time keyword
:ikairmass [value] Show / Set the airmass keyword
:ikfilter [value] Show / Set the ifilter id keyword
:ikobstime [value] Show / Set the time of observation keyword
:ietime [value] Show / Set the exposure time
:iairmass [value] Show / Set the airmass value
:ifilter [value] Show / Set the ifilter id
:iotime [value] Show / Set the time of observation
Permitted values of inoisemodel are: "poisson".
Dispars Parameter Colon Commands
:derase [yes/no] Show / Set the erase status
:dfill [yes/no] Show / Set the fill status
:dxviewport [value] Show / Set the x viewport
:dyviewport [value] Show / Set the y viewport
:dxmag [value] Show / Set the x magnification
:dymag [value] Show / Set the y magnification
:dztransform [name] Show / Set the intensity transform
:dzlimits [name] Show / Set the intensity limits algorithm
:dzcontrast [value] Show / Set the intensity contrast
:dznsample [value] Show / Set the number of sample lines
:dz1 [value] Show / Set the minimum intensity level
:dz2 [value] Show / Set the maximum intensity level
:dlutfile [value] Show / Set the user lookup table file
:drepeat [yes/no] Show / Set repeat status
Permitted values of dztransform are: "linear", "log", and "none".
Permitted values of dzlimits are: "median", "image", and "user".
Findpars Parameter Colon commands
:fthreshold [value] Show / Set the detection threshold
:fradius [value] Show / Set the fitting radius
:fsepmin [value] Show / Set the minimum separation
:froundlo [value] Show / Set the lower ellipticity limit
:froundhi [value] Show / Set the upper ellipticity limit
:fsharplo [value] Show / Set the lower sharpness limit
:fsharphi [value] Show / Set the upper sharpness limit
Omarkpars Parameter Colon Commands
:objmark [yes/no] Show / Set the object marking switch
:otolerance [value] Show / Set the object matching tolerance
:ocharmark [value] Show / Set the object marking parameter
:onumber [yes/no] Show / Set the object numbering switch
:opcolormark [value] Show / Set the object mark color
:oscolormark [value] Show / Set the sky mark color
:osizemark [value] Show / Set the mark size
Permitted values of ocharmark are: "point", "box", "cross", "plus",
"circle", "diamond", and "shape".
Permitted values of opcolormark and oscolormark are: "red", "blue",
"green", and "yellow".
Cenpars Parameter Colon Commands
:calgorithm [value] Show / Set the centering algorithm
:cradius [value] Show / Set the centering radius
:cthreshold [value] Show / Set the centering threshold
:cminsnrati [value] Show / Set the minimum signal-to-noise ratio
:cmaxiter [value] Show / Set the maximum number of iterations
:cxyshift [value] Show / Set the maximum x or y coordinate shift
:ctrmark [yes/no] Show / Set the center marking switch
:ccharmark [value] Show / Set the center marking character
:ccolormark [value] Show / Set the center mark color
:csizemark [value] Show / Set the center mark size
Permitted values of calgorithm are: "none", "centroid1d", "gauss1d",
and "ofilter1d".
Permitted values of ccharmark are: "point", "box", "cross", "plus",
"circle", and "diamond".
Permitted values of ccolormark are: "red", "blue", "green" and
"yellow".
Skypars Parameter Colon Commands
:smode [value] Show / Set the sky fitting mode
:sgeometry [value] Show / Set the sky fitting geometry
:srannulus [value] Show / Set the inner radius of sky annulus
:saxratio [value] Show / Set the sky annulus axis ratio
:sposangle [value] Show / Set the sky annulus p.a. in degrees
:salgorithm [value] Show / Set the sky fitting algorithm
:sconstant [value] Show / Set the constant for constant sky fitting
:shwidth [value] Show / Set the half-width of histogram in sigma
:shbinsize [value] Show / Set the resolution of histogram in sigma
:shsmooth [yes/no] Show / Set the histogram smoothing switch
:smaxiter [value] Show / Set the max number of fitting iterations
:sloclip [value] Show / Set the lower clipping factor in %
:shiclip [value] Show / Set the upper clipping factor in %
:snreject [value] Show / Set the max number of rejection iterations
:sloreject [value] Show / Set the lower k-sigma rejection limit
:shireject [value] Show / Set the upper k-sigma rejection limit
:srgrow [value] Show / Set the region growing radius
:skymark [yes/no] Show / Set the sky marking switch
:scolormark [value] Show / Set the sky aperture mark color
Permitted values of smode are: "concentric" and "offset".
Permitted values of sgeometry are: "circle", "ellipse", "rectangle",
and "polygon".
Permitted values of salgorithm are: "zero", "constant", "mean",
"median", "mode32", "hcentroid", "hgauss", "hofilter", "hcrosscor".
Permitted values of scolormark are: "read", "blue", "green", and
"yellow".
Photpars Parameter Colon Commands
:pgeometry [value] Show / Set the photometry aperture geometry
:papertures [value] Show / Set the photometry apertures
:paxratio [value] Show / Set the photometry aperture axis ratio
:pposangle [value] Show / Set the aperture position angle in degrees
:pzmag [value] Show / Set the photometry zero point
:photmark [yes/no] Show / Set the photometry aperture marking switch
:pcolormark [value] Show / Set the photometry aperture mark color
Permitted values of pgeometry are: "circle", "ellipse", "rectangle",
and "polygon".
Permitted values of pcolormark are: "red", "blue", "green", and
"yellow".
Eplotpars Parameter Colon Commands
:enx [value] Show / Set number of columns to be contoured
:eny [value] Show / Set number of lines to be contoured
:ez1 [value] Show / Set minimum greylevel to be contoured
:ez2 [value] Show / Set maximum greylevel to be contoured
:ez0 [value] Show / Set the greylevel of the zero contour
:encontours [value] Show / Set the number of contours to be plotted
:edz [value] Show / Set the contour greylevel interval
:ehilomark [value] Show / Set the high / low contour marking option
:edashpat [value] Show / Set the bit pattern for drawing lines
:elabel [yes/no] Show / Set the major contours labeling switch
:ebox [yes/no] Show / Set the box drawing switch
:eticklabel [yes/no] Show / Set the tick mark labeling switch
:exmajor [value] Show / Set the number of major x axis divisions
:exminor [value] Show / Set the number of minor x axis divisions
:eymajor [value] Show / Set the number of major y axis divisions
:eyminor [value] Show / Set the numver of minor y axis divisions
:eround [yes/no] Show / Set the axis rounding switch
:efill [yes/no] Show / Set viewport filling switch
Permitted values of ehilomark: "none", "hilo", and "pixel".
Aplotpars Parameter Colon Commands
:anx [value] Show / Set number of columns to be plotted
:any [value] Show / Set number of lines to be plotted
:az1 [value] Show / Set minimum greylevel to be plotted
:az2 [value] Show / Set maximum greylevel to be plotted
:alabel [yes/no] Show / Set the axes drawing switch
:angv [value] Show / Set the vertical viewing angle
:angh [value] Show / Set the horizontal viewing angle
Xgphot can be run non-interactively by setting the interactive parameter to "no". In this mode xgphot will either measure the objects specified in the input objects files objects or create and measure an object list automatically using the current values of the impars and findpars parameters. If default object and sky aperture geometry will be taken from the objects file; or if not defined there from the skypars and photpars parameter sets. All the measurements are written to the results files regardless of the value of logresults . If verbose is "yes" a short summary of each object measurement will also be printed on the standard output.
The input objects file consists of a list of object descriptions. Each object description consists of an object region description and an optional sky region description. If the sky description is present it must be separated from the object description by the string " ; " as shown below.
Syntax object region definition [; [sky region definition]] Example 256.23 258.31 circle 25.0 256.23 258.31 circle 25.0 ; 256.23 258.31 circle 25.0 ; circle 30.0 40.0
Object regions may be points, circles, ellipses, rectangles, polygons, or undefined. Each geometry has its own syntax as shown below.
Syntax
point: x y
circle: x y circle radii
ellipse: x y ellipse radii [axratio [pa]]
rectangle: x y rectangle radii [axratio [pa]]
polygon: x y polygon [[radii] {
xver1 yver1
xver2 yver2
... ...
xverN yverN
}]
undefined: x y INDEF [INDEF [axratio [pa]]
Example
256.23 258.31
256.23 258.31 circle 25.0
256.23 258.31 ellipse 25.0 0.75 33.0
256.23 258.31 rectangle 25.0 0.75 33.0
256.23 258.31 polygon 5,10,15 {
100.0 100.0
200.0 100.0
200.0 200.0
100.0 200.0
}
356.23 358.31 polygon 5,10,15
256.23 258.31 INDEF INDEF
The x and y coordinates are required in all cases. The radii field may define a single radius, e.g. "10.0", a list of radii, e.g. "3,6,9,12,15,18", or a range of radii, e.g. "1:20.0:2.0". If the polygon radii field is present it is treated as a width, and the polygonal object aperture is extended outward by the size of the radii. Objects with missing or INDEF valued required radii fields will automatically have their geometries set to INDEF. All radii measurements are assumed to be in units of the impars.iscale parameter. Missing axis ratio and position angle fields default to the values of 1.0 and 0.0 respectively. If the vertices field of a polygonal object is ommitted, the vertices of the last defined object polygon are used. If no object polygon has been defined by the time the first polygonal object appears in the list, the object geometry is set to INDEF.
Sky regions may be points, circles, ellipses, rectangles, polygons, objects, or undefined. The object option means "use the same geometry as the object region". Each geometry has its own syntax as shown below.
Syntax
point: [x y INDEF]
circle: [x y] circle srin srout
ellipse: [x y] ellipse srin srout [axratio [pa]]
rectangle: [x y] rectangle srin srout [axratio [pa]]
polygon: [x y] polygon [[srin srout] {
xver1 yver1
xver2 yver2
... ...
xverN yverN
}]
object: [x y] object srin srout
undefined:
Example
256.23 258.31 ; 356.23 358.31
256.23 258.31 ; circle 30. 40.
256.23 258.31 ; 356.23 358.31 circle 30. 40.
256.23 258.31 ; ellipse 30. 40.
256.23 258.31 ; 356.23 358.31 ellipse 30. 40.
256.23 258.31 ; 356.23 358.31 ellipse 30. 40. 0.75 48.2
256.23 258.31 ; rectangle 30. 40.
256.23 258.31 ; 356.23 358.31 rectangle 30. 40.
256.23 258.31 ; 356.23 358.31 rectangle 30. 40. 0.75 48.2
256.23 258.31 ; 356.23 358.31 object
256.23 258.31 ; polygon 10 15 {
100.0 100.0
200.0 100.0
200.0 200.0
100.0 200.0
}
256.23 258.31 ; 356.23 358.31 polygon 10 15 {
100.0 100.0
200.0 100.0
200.0 200.0
100.0 200.0
}
Sky regions may be concentric with the object region, i.e. no x and y sky region coordinates are defined, or offset, i.e. the x and y coordinates are defined. If the sky geometry is "object", then the sky region inherits the geometry, axis ratio, and position angle of the object region. The inner and out sky annulus radii must be defined for all geometries except polygonal. Missing or undefined axis ratio and position fields default to values of 1.0 and 0.0 respectively.
A brief description of the object finding algorithms, the centering algorithms, the sky fitting algorithms and the photometry algorithms can be found in the online help pages for the findpars , centerpars , fitskypars, and photpars tasks.
The image data dependent parameters, the image display parameters, and the object list marking parameters are described in the help for the impars , dispars , and omarkpars parameter sets. The object and sky region contour and surface plotting parameters are described in the help for the cplotpars and splotpars tasks.
If interactive = "no" and verbose = "yes", or interactive = "yes" and guifile = "", then the following quantities are printed on the standard output as each object is measured.
image xcenter ycenter msky hw[N] ax[N] pa[N] flux[N] mag[N] merr[N]
pier[N] logresults
where N is the index of the largest aperture. Image, xcenter, ycenter, and sky are the image name, x and y coordinates of the object center, and the modal sky value respectively. Hw, ax, and pa are the half-width at half-max, axial ratio, and position angle of the object derived from a second order moment analysis through the largest aperture. Flux, mag, and magerr are the flux, magnitude, and magnitude error computed through the largest aperture. Pier is the photometry error code described below. Logresults is log+ or log- depending on whether or not results logging is turned on or off. If interactive = "yes" and the guifile is defined, then the above quantities minus the image name are written to the status line in the image display window.
In both interactive mode full output is written to the output text file results if logresults is "yes". In batch mode full output is always written to the results file if one is defined. At the beginning of each results file is a header listing the values of all the algorithm parameters at the time the first object record is written. From that point on a new parameter record is written to the results file every time the parameter value is altered.
For each object measured the following quantities are written to the results file.
xinit yinit id objects lid
xcenter ycenter xshift yshift xerr yerr cier cerror
xsky ysky msky stdev nsky nrej sier serror
rapert sum area flux mag merr pier perror
hwidth sharpness axratio ell theta
Objects is the name of the input objects file.
Id and lid are the object sequence numbers in the output results and input
objects files respectively. Cier and cerror are the centering algorithm
error code and associated
error message respectively. Xinit, yinit, xcenter, ycenter, xshift, yshift,
xerr, and yerr are self explanatory and output in pixel units. The sense of
the xshift and yshift definitions is as follows.
xshift = xcenter - xinit
yshift = ycenter - yinit
Sier and serror are the sky fitting error code and associated error message respectively. Xsky and ysky define the center of the sky region. Xsky and ysky should be the same as xcenter and ycenter if the sky fitting mode is "concentric", otherwise they may be different. Msky and stdev are the estimate of the sky value per pixel and the standard deviation of the sample of sky pixels used to compute flux, mag, and merr. Nsky and nsrej are the number of sky pixels used to compute the sky value and the number of sky pixels rejected from the sky fit respectively.
Rapert, sum, area, and flux are the radius of the photometry aperture in scale units, the total number of counts including sky in the aperture, the area of the aperture in square pixels, and the total number of counts excluding sky in the aperture. Mag and merr are the magnitude and error in the magnitude in the aperture as computed below.
flux[N] = sum[N] - area[N] * msky
mag[N] = zmag - 2.5 * log10 (flux[N]) + 2.5 * log10 (itime)
merr[N] = 1.0857 * error[N] / flux[N]
error[N] = sqrt (flux[N] / epadu + area[N] * stdev**2 +
area[N]**2 * stdev**2 / nsky)
Pier and perror are photometry error code and accompanying error message.
Hwidth, sharpness, axratio, ell, and theta are the estimates of the half-width at half-maximum, the sharpness statistic, the axis ratio, the ellipticity, and the position angle of the object, derived from a second order moment analysis as shown below.
dx = x - xcenter
dy = y - ycenter
di = i - msky
Mxx[N] = sum (di * dx * dx) / flux[N]
Mxy[N] = sum (di * dx * dy) / flux[N]
Myy[N] = sum (di * dy * dy) / flux[N]
hwidth[N] = sqrt (log (2) * (Mxx[N] + Myy[N]))
sharpness[N] = hwidth[N] / fwhmpsf
ell[N] = sqrt ((Mxx[N] - Myy[N]) ** 2 + 4 * Mxy[N] ** 2) /
(Mxx[N] + Myy[N])
axratio[N] = 1.0 - ell[N]
theta[N] = 0.5 * atan (2 * Mxy[N] / (Mxx[N] - Myy[N]))
The exposure time, airmass, filter id, and time of observation are stored in the header keywords, ietime, iairmass, ifilter, and iotime and updated to the appropriate values when the image being analyzed is changed.
If the object centering was error free then the field cier will be zero. Non-zero values of cier flag the following error conditions.
0 # No error
301 # The input image is undefined
302 # The centering aperture is off the image
303 # The centering aperture is partially off the image
304 # The centering aperture is too small
305 # There is bad data in the centering aperture
306 # The S/N ratio in the centering aperture is too low
307 # The x or y center fit is singular
308 # The x or y center fit did not converge
309 # The x or y center shift is greater than maxshift
If all goes well during the sky fitting process then the error code sier will be 0. Non-zero values of sier flag the following error conditions.
0 # No error
401 # The input image is undefined
402 # The sky aperture is undefined
403 # The sky aperture is partially off the image (not used)
404 # The sky pixel histogram is undefined
405 # The sky pixel histogram is flat or concave
406 # There are too few points for a good sky fit
407 # The sky fit is singular
408 # The sky fit did not converge
409 # The graphics stream is undefined (not used)
410 # The file of sky values is undefined (not used)
411 # The sky file is at EOF (not used)
412 # Cannot read the sky file values correctly (not used)
413 # The best fit parameters are non-physical
If no error occursor during the measurement of the magnitudes then pier is 0. Non-zero values of pier flag the following error conditions.
0 # No error
501 # The photometry aperture is off the image
502 # The photometry aperture is partially off the image
503 # The sky value is undefined
504 # The object is too faint
505 # There is bad data in the photometry aperture
1. Interactively measure a few stars in the IRAF test image dev$wpix without using the gui and without updating the algorithm parameters.
xa> xgphot dev$wpix "" default guifile=""
... type :epar impars to edit the images parameter set
(set ihwhmpsf to 1.2, ikgain to "", ikreadnoise to "",
igain to 11.0, ireadnoise to 75.0, ikexptime to ITIME,
and ikfilter to "", leaving the other parameters at their
default values)
... type :wq to save the new impars parameters
... type :epar skypars to edit the sky fitting parameter set
(set srannulus to 20.0 and swannulus to 5.0 and leave the
other parameters set to their default values)
... type :wq to save the new skypars parameters
... type :epar photpars to edit the photometry parameter set
(set papertures to 15.0 and leave the other parameters at
their default values)
... type :wq to save the new photpars parameters
... move to star near x,y = 441,410 and type spacebar to measure
... type Z twice to zoom in on the star
... type j to enter the object region display menu, followed by
a to display the object region and object aperture, s to
display a mesh plot of the object region, c to display a
contour plot of the object region, and q to quit
... type k to enter the sky region display menu, followed by
a to display the sky region and sky aperture, s to display a
mesh plot of the sky region, c to display a contour plot of
the sky region, and q to quit
... type c to enter the the object results display menu, r to
display the semi-major axis profile, t to display the position
angle profile, and q to quit
... type s to enter the sky results display menu, r to display
the semi-major axis profile, t to display the position angle
profile, and q to quit
... type i to redisplay the image
... measure a few other objects and use the plots and epar to
refine the algorithm parameter settings
... type :logresults yes to enable results logging
... move to stars to be measured and type spacebar to measure
... type Q to quit
2. Fit an elliptical gaussian to several objects in the IRAF test image dev$wpix interactively but without using the default gui.
xa> xgphot dev$wpix "" default guifile=""
... move the cursor to the objects of interest and type x
(Hw: is the the fitted half-width at half-max, Ax: is the
fitted axis ratio, and Pa is the fitted position angle in
degrees cw from the +x axis)
... to see a plot of the same object type \X
... type i to redisplay the image
... move to another object and type y to compute and fit
the model
... type Q to quit
.fi.
3. Automatically detect and measure stellar objects in the IRAF test image
dev$wpix using, a hwhmpsf of 1.2 pixels, a detection threshold of 300
counts, the x and y coordinates computed by the automatic star finding
routine (recentering is turned off), a circular annular sky aperture of
inner radius 15 pixels and width 10 pixels, and a circular photometry
aperture of radius 10 pixels.
.nf
xa> xgphot dev$wpix "" default ihwhmpsf=1.2 fthreshold=300 \
calgorithm=none srannulus=15 swannulus=10 papertures=10 \
interactive-
4. Measure the brightness of a single object observed in 25 consecutive frames and write the results to a single output file called results.25. The object is at approximately the same position in all the frames so a single object file should be sufficient for all the frames. Use a centering radius of 4.5 pixels, a circular sky annulus of inner radius 25 pixels and width 5 pixels and a circular photometry aperture of radius 20. Write all the results to a single file.
xa> type imlist
dev$wpix
dev$wpix
dev$wpix
...
dev$wpix
xa> type objects
258. 258.
xa> xgphot @imlist objects results.25 cradius=4.5 srannulus=25 \
swannulus=5 papertures=20.0 interactive-
5. Measure the brightness inside the ellipse specified in the following objects file. Note that 0.7 is the ratio of the minor to major axes not the ellipticity. Turn off recentering and set the background value to 42.0 counts.
xa> type objects
257.87 258.89 ellipse 50 0.75 33.0
xa> xgphot dev$wpix objects wpix.ell calgorithm=none \
salgorithm=constant skyvalue=42.0 interactive-
xa>
xguiphot,impars,dispars,findpars,omarkpars,cenpars,skypars,photpars