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diff --git a/noao/digiphot/daophot/doc/datapars.hlp b/noao/digiphot/daophot/doc/datapars.hlp new file mode 100644 index 00000000..3e4345a1 --- /dev/null +++ b/noao/digiphot/daophot/doc/datapars.hlp @@ -0,0 +1,289 @@ +.help datapars May00 noao.digiphot.daophot +.ih +NAME +datapars -- edit the data dependent parameters +.ih +USAGE +datapars +.ih +PARAMETERS +.ls scale = 1.0 +The scale of the image in user units, e.g. arcseconds per pixel. All DAOPHOT +distance dependent parameters are assumed to be in units of scale. If +\fIscale\fR = 1.0 these parameters are assumed to be in units of pixels. Most +DAOPHOT users should leave \fIscale\fR set to 1.0 unless they intend to compare +their aperture photometry results directly with data in the literature. +.le +.ls fwhmpsf = 2.5 (scale units) +The full-width half-maximum of the point spread function in scale units. +The DAOFIND task and the PHOT task "gauss" and "ofilter" centering algorithms +depend on the value of fwhmpsf. DAOPHOT users can either determine a value +for fwhmpsf using an external task such as IMEXAMINE, or make use of the +interactive capabilities of the DAOPHOT tasks to set and store it. +.le +.ls emission = yes +The features to be measured are above sky. By default the DAOPHOT package +considers all features to be emission features. DAOPHOT users should +leave this parameter set to "yes". +.le +.ls sigma = 0.0 +The standard deviation of the sky pixels. The DAOFIND task and the PHOT task +"constant" sky fitting algorithm error estimate depend on the value of sigma. +DAOPHOT users should set sigma to a value representative of the noise in +the sky background. +.le +.ls datamin = INDEF +The minimum good pixel value. Datamin defaults to -MAX_REAL the minimum +floating point number supported by the host computer. Datamin is used +to detect and remove bad data from the sky aperture, detect and flag +bad data in the aperture photometry aperture, and detect and remove bad +data from the PSF fitting aperture. DAOPHOT users should either leave +datamin set to INDEF or set it to a number between 5-7 sigma below the +sky background value. +.le +.ls datamax = INDEF +The maximum good pixel value. Datamax defaults to MAX_REAL the maximum +floating point number supported by the host computer. Datamax is used +to detect and remove bad data from the sky aperture, detect and flag +bad data in the aperture photometry aperture, and detect and remove bad +data from the PSF fitting aperture. DAOPHOT users should either leave +datamax set to INDEF or set it to the linearity or saturation +limit of the detector. +.le +.ls noise = "poisson" +The noise model used to estimate the uncertainties in the computed +magnitudes. DAOPHOT users must leave noise set to "poisson". +.le +.ls ccdread = "" +The image header keyword defining the readout noise parameter whose units +are assumed to be electrons. +.le +.ls gain = "" +The image header keyword defining the gain parameter whose units are assumed to +be electrons per adu. +.le +.ls readnoise = 0.0 +The readout noise of the detector in electrons. DAOPHOT users should set +readnoise or ccdread to its correct value before running any of the DAOPHOT +package tasks in order to ensure that the PSF fitting weights, magnitude +error estimates, and chi values are correct. +.le +.ls epadu = 1.0 +The gain of the detector in electrons per adu. DAOPHOT users should set this +epadu or gain to its correct value before running any of the DAOPHOT package +tasks in order to ensure that the PSF fitting weights, magnitude error +estimates, and chi values are correct. +.le +.ls exposure = "" +The image header exposure time keyword. The time units are arbitrary but +must be consistent for any list of images whose magnitudes are to be compared. +The computed magnitudes are normalized to one timeunit by the PHOT task. +As the magnitude scale of the DAOPHOT package is set by the PHOT task, +setting exposure can save DAOPHOT users a lot of unnecessary zero point +corrections in future analysis and calibration steps. +.le +.ls airmass = "" +The image header airmass keyword. The airmass parameter is not used +directly by DAOPHOT but the airmass value is stored in the output file +and its presence there will simplify future calibration steps. +.le +.ls filter = "" +The image header filter id keyword. The filter parameter is not used +directly by DAOPHOT but the filter id is stored in the output file +and its presence there will simplify future calibration steps. +.le +.ls obstime = "" +The image header time of observation keyword. The obstime parameter is not used +directly by DAOPHOT but the obstime value is stored in the output file +and its presence there will simplify future calibration steps. +.le +.ls itime = 1.0 +The exposure time for the image in arbitrary units. The DAOPHOT magnitudes are +normalized to 1 timeunit by the PHOT task using the value of exposure in the +image header if exposure is defined or the value of itime. +.le +.ls xairmass = INDEF +The airmass value. The airmass is read from the image header if airmass +is defined or from xairmass. The airmass value is stored in the DAOPHOT +output files. +.le +.ls ifilter = "INDEF" +The filter id string. The filter id is read from the image header if filter +is defined otherwise from ifilter. The filter id is stored in the DAOPHOT +output files. +.le +.ls otime = "INDEF" +The value of the time of observation. The time of observation is read from +the image header if obstime is defined otherwise from otime. The time of +observation is stored in the DAOPHOT output files. +.le + +.ih +DESCRIPTION + +\fIDatapars\fR sets the image data dependent parameters. These parameters are +functions, of the instrument optics, the noise characteristics and range of +linearity of the detector, and the observing conditions. Many of the +centering, sky fitting, and photometry algorithm parameters in the CENTERPARS, +FITSKYPARS, PHOTPARS, and DAOPARS parameter sets scale with the data dependent +parameters. + +The parameter \fIscale\fR sets the scale of the apertures used by the +centering, sky fitting, aperture photometry, and psf fitting algorithms. +Scale converts radial distance measurements in pixels to radial distance +measurements in scale units. The DAOPHOT parameters cbox, maxshift, rclean +and rclip in the CENTERPARS parameter set; annulus, dannulus, and rgrow in +FITSKYPARS parameter set; apertures in the PHOTPARS parameter set; and psfrad, +fitrad, sannulus, wsannulus, and matchrad in the DAOPARS parameter set are +expressed in units of the scale. The scale parameter is useful in cases where +the observations are to be compared to published aperture photometry +measurements in the literature. + +The parameter \fIfwhmpsf\fR defines the full-width at half-maximum of the +stellar point spread function. The DAOFIND task, the PHOT task centering +algorithms "gauss" and "ofilt", and the PSF modeling task PSF all require +an accurate estimate for this parameter. + +By setting the \fIscale\fR and \fIfwhmpsf\fR appropriately the aperture +sizes and radial distances may be expressed in terms of the half-width +at half-maximum of the stellar point spread function. The way to do this +is to define the scale parameter in units of the number of half-width at +half-maximum per pixel, set the fwhmpsf parameter to 2.0, and then +set the remaining scale dependent centering, sky fitting, aperture photometry, +and psf fitting algorithm parameters in CENTERPARS, FITSKYPARS, PHOTPARS, +and DAOPARS to appropriate values in units of the half-width at half-maximum +of the point-spread function. Once an optimum set of algorithm parameters is +chosen, the user need only alter the DATAPARS scale parameter before +executing a DAOPHOT task on a new image. + +If \fIemission\fR is "yes", the features to be measured are assumed to +be above sky. By default the DAOPHOT package considers all features to be +emission features. DAOPHOT users should leave this parameter set to "yes". +Although the DAOFIND and PHOT tasks can detect and measure absorption features +the PSF fitting tasks currently cannot. + +The parameter \fIsigma\fR estimates the standard deviation of the sky +background pixels. The star finding algorithm in DAOFIND uses sigma +and the \fIfindpars.threshold\fR parameter to define the stellar +detection threshold in adu. The PHOT task centering algorithms use sigma, +1) with the \fIcenterpars.kclean\fR parameter to define deviant pixels +if \fIcenterpars.clean\fR is enabled; 2) to estimate the signal to +noise ratio in the centering box; 3) and with the \fIcenterpars.cthreshold\fR +parameter to define a lower intensity limit for the pixels to be used +for centering. If sigma is undefined or <= 0.0 1) no cleaning is performed +regardless of the value of centerpars.clean; 2) the background noise in the +centering box is assumed to be 0.0; and 3) default cutoff intensity is used +for centering. + +The \fIdatamin\fR and \fIdatamax\fR parameters define the good data range. +If datamin or datamax are defined bad data is removed from the sky pixel +distribution before the sky is fit, data containing bad pixels in the +photometry apertures is flagged and the corresponding aperture photometry +magnitudes are set to INDEF, and bad data removed from the PSF fitting +aperture. DAOPHOT users should set datamin and datamax to appropriate values +before running the DAOPHOT tasks. + +DAOPHOT users must leave \fInoise\fR set to "poisson". This model includes +Poisson noise from the object and both Poisson and readout noise in the sky +background. + +The parameters \fIgain\fR and \fIepadu\fR define the image gain. +The gain parameter specifies which keyword in the image header contains +the gain value. If gain is undefined or not present in the image header +the value of epadu is used. Epadu must be in units of electrons per adu. +DAOPHOT users should set either gain or epadu to a correct value before +running any of the DAOPHOT package tasks to ensure that the aperture +photometry magnitude error estimates, and the PSF fitting weights, chis, and +magnitude error estimates are computed correctly. + +The two parameters \fIccdread\fR and \fIreadnoise\fR define the image +readout noise. The ccdread parameter specifies which keyword in the +image header contains the readout noise value. If ccdread is undefined or +not present in the image header the value of readnoise is used. +Readnoise is assumed to be in units of electrons. +DAOPHOT users should set either ccdread or readnoise before running any +DAOPHOT tasks to insure that the PSF fitting weights, chis, and magnitude +error estimates are computed correctly. + +The magnitudes computed by PHOT are normalized to an exposure time of 1 +timeunit using the value of the exposure time in the image header parameter +\fIexposure\fR or \fIitime\fR. If exposure is undefined or not present +in the image header a warning message is issued and the value of itime +is used. The itime units are arbitrary but must be consistent for images +analyzed together. As the magnitude scale in DAOPHOT is determined by the +PHOT task setting either exposure or itime can save DAOPHOT users a lot +of unnecessary zero point corrections in future analysis and calibration +steps. + +The parameters \fIairmass\fR and \fIxairmass\fR define the airmass +of the observation. The airmass parameter specifies which keyword in the +image header contains the airmass value. If airmass is undefined or +not present in the image header the value of xairmass is used. +The airmass values are not used in any DAOPHOT computations, however their +presence in the DAOPHOT output files will simplify future reduction steps. + +The parameters \fIfilter\fR and \fIifilter\fR define the filter +of the observation. The filter parameter specifies which keyword in the +image header contains the filter id. If filter is undefined or not present +in the image header the value of ifilter is used. The filter id values are +not used in any DAOPHOT computations, however their presence in the DAOPHOT +output files can will simplify future reduction steps. + +The parameters \fIobstime\fR and \fIotime\fR define the time +of the observation (e.g. UT). The obstime parameter specifies which keyword +in the image header contains the time stamp of the observation. If obstime is +undefined or not present in the image header the value of otime is used. +The time of observations values are not used in any DAOPHOT +computations, however their presence in the DAOPHOT output files can +greatly simplify future reduction steps. + + +.ih +EXAMPLES + +1. List the data dependent parameters. + +.nf + da> lpar datapars +.fi + +2. Edit the data dependent parameters. + +.nf + da> datapars +.fi + +3. Edit the data dependent parameters from within the PSF task. + +.nf + da> epar psf + + ... edit a few parameters + + ... move to the datapars parameter and type :e + + ... edit the datapars parameters and type :wq + + ... finish editing the psf parameter and type :wq +.fi + +4. Save the current DATAPARS parameter set in a text file datnite1.par. +This can also be done from inside a higher level task as in the previous +example. + +.nf + da> epar datapars + + ... edit a few parameters + + ... type ":w datnite1.par" from within epar +.fi +.ih +TIME REQUIREMENTS +.ih +BUGS + +.ih +SEE ALSO +epar,lpar,daofind,phot,pstselect,psf,group,peak,nstar,allstar,substar,addstar +.endhelp |