Pixel values should be reasonable numbers. WAVDETECT probability distributions have been derived assuming Poisson statistics. WAVDETECT simply will not work with fluxed images. The calculated correlation values are so small that no detections occur.

If auto-naming (outfile=.) is used, the output file will have the suffix "_src"

If auto-naming is used (scellfile=.), the output file will have the suffix "_scell"

If auto-naming is used (imagefile=.), the output file will have the suffix "_image"

During its second stage, wavdetect makes one normalized background estimate from the stack of per-scale normalized backgrounds produced during the first stage. It writes this computed background to this file. If auto-naming is used (defnbkgfile=.), the output file will have the suffix "_nbkg"

If auto-naming is used (regfile=.), the output file will have the suffix "_reg". NB: autonaming for regfile is not currently operational.

The datamodel will support more than one output format (eg: "fits", "iraf"). This parameter selects among them. Use "default" to set the output kernel to be the same as that for the input file.

ellsigma is a multiplicative factor applied to sigma, the standard deviation of the distribution, to scale the major and minor axes of the ellipses for each source. ellsigma affects both the outfile and the ASCII region file (regfile). This feature is included so that the graphics overlay will be more visible and under the user's control. Often a value greater than 3 is helpful.

Use a previously computed background in the specified file in place of constructing a new default normalized background. When using bkginput, enter "none" for the default normalized background file.

*After* the final background estimate B is made, the threshold correlation is recomputed by solving for C_o:

sigthresh = integral(C_o dC) PSD(C(B))

Here, C = avg[W*D], where D are the *raw* data. (The iterations are simply to compute background. Once we have that, we go back to the beginning.)

If C is less than or equal to C_o in a pixel, then that pixel is considered to be associated with a source. If the pixel is also the location of a local maximum in C-space, the location of that maximum is output to a FITS table.

sigthresh should not be significantly larger than one over the number of pixels in the image; for a 1024x1024 image, that means sigthresh ~ 1.e-6. If, in this case, sigthresh = 1.e-5, there will be approximately 10 strong background fluctuations detected as sources.

sigthresh should not be smaller than *roughly* 1.e-9 - 1.e-10; even at this point, the accuracy of the computed detection thresholds is unknown (though probably fine for most applications).

Significance threshold for cleansing data during iterations. In each pixel, during each iteration, the background, and correlation of the wavelet function and the current data (C' = avg[W*D']), are estimated. The background estimate B' implies a probability sampling distribution (PSD) for C', i.e. the distribution that C' would have if there was locally no source in the image and D' were sampled from background. A threshold C_o' is calculated from this PSD, using the supplied value of bkgsigthresh (e.g. 10**-2) by solving the following for C_o':

bkgsigthresh = integral(C_o' dC') PSD(C'(B'))

If C' is greater than or equal to C_o', the data in the pixel is replaced with the background estimate. In this way, putative sources are eliminated from the data image, along with weak (but otherwise undetectable) sources and background fluctuations, so that a better background estimate can be made.

This value should be no larger than 0.05 (the usual 5 per cent, or 95 per cent, statistical criterion for rejecting the null hypothesis, which is that the pixel in question has data sampled solely from the background); it should not be smaller than sigthresh.

If set to zero and no exposure file is used, the program sets the exposure time to 1.0 when estimating sorce rates.

If set to a non-zero value and no exposure file is used, the program uses the input value when estimating source rates.

If set to zero and an exposure file is used, the program uses the value from the exposure file when estimating source rates.

If set to a non-zero value and an exposure file is used, the program uses the quantity exptime*(expfile value at source/max expfile value) when estimating source rates.

For each pixel, a relative exposure is calculated (pixel exposure value over maximum value of exposure in map). If this relative exposure is less than the parameter expthresh, then the pixel in question is not analyzed: the background, correlation, et al., are set to zero.

expthresh should not be less than 0.1 (or else the accuracy of normalization will be too low); if set close to 1, only very limited regions of the FOV will be considered when source correlation maxima are listed. Typical values would be 0.1-0.2.

Livetime of predetermined background. This parameter should only be used *if* the user has provided a normalized background image (rather than having wavdetect calculate it). A value of 0 will make the exposure time used for background time. If bkgtime is non-zero and no background map is supplied, the source parameters will be adversely affected (i.e. wrong).

Wtransform produces a complete set of outputs for each scale. Small scales tend to detect small features, and larger scales larger features.

Values are typically 2**n, where n is an integer, and n_lo and n_hi are chosen with respect to instrumental PSF sizes. For the ROSAT PSPC, for instance, this could mean n_lo = 1 pixel, n_hi = 16 pixels. Note that larger scales might need to be used to characterize (i.e. derive good source property estimates for) extended sources.

2**n should not be larger than the size of the image (in pixels) divided by 5 (in which case the extent of the wavelet function is larger than the image itself, which could lead to strange results).

The user specifies how many iterations the program should go through to calculate the background. However, the background is for all intents and purposes calculated if there are very few new pixels being cleansed (see bkgsigthresh). If the ratio of *newly* cleansed pixels to the overall number of pixels in the dataset is less than the parameter iterstop, the program quits iterating and uses the current background estimate as the final background estimate.

A typical value is 0.001: stop iterating when only one of every thousand pixels is being cleansed. This parameter should not be larger than 1, nor smaller than one over the number of pixels in the dataset.

By default (when both offsets are set to INDEF), wavdetect calculates the off-axis angle using the nominal pointing of the data file as the origin. Users may change this behavior by specifying offsets to any numerical values; the offsets provide the location of the optical axis with respect to the center of the data file.

A typical scenario in which the users may select to use offsets is when their data file is a sum of two or more observations, with different pointings. The nominal pointing in such data file is usually poorly defined and the off-axis angle could be calculated from an undesired origin, leading to suboptimal selection of the detect cell size. The ability to set the origin explicitly with x/yoffset solves this problem.

For ROSAT PSPCB, eband and eenergy parameters are ignored. The values 1 keV and .393 are used.

Percentage of encircled energy, expressed as a fraction of 1.0, which the PSF size (see "eband") should contain. Suggested values: .393 (one-sigma percentage threshold for a two-dimensional Gaussian), or 0.500. The efficiency of the algorithm is reduced if this fraction is made too high (say, 0.900) or too low.

The encircled energy fraction of the PSF is used to estimate the PSF size, in pixels, at the location of each detected source. The default value (0.393) is the one-sigma integrated volume of a normalized two- dimensional Gaussian, thus the estimated PSF size should be approximately one sigma. The PSF size is used only to select a flux image; a source cell is computed using this image, and source properties are estimated using the data within the computed cell. NB: Unlike celldetect, the PSF library and eenergy have no effect on the detection process in wavdetect.

If the value of eenergy is set too high, there is the risk that the computed source cell will contain more than one source, rendering source property estimates moot. On the other hand, if the value is set too low, then the computed cell may be too small and contain only a fraction of the source counts.

For ROSAT PSPCB, eband and eenergy parameters are ignored. The values 1 keV and .393 are used.

FITS file of PSF information. A file for Chandra is included with the release. The user may not specify "CALDB" for this parameter.