If this option is present, then when the application extracts the list of objects from the CCD, it will try to remove CCD blemishes. The algorithm is currently rather crude, and will likely change in future.
Some of the `objects' detected by EXTRACTOR are in fact CCD defects, or readout errors, or the like. These are very bright, so they can confuse a matching program which examines only or preferentially the brightest objects.
By default, autoastrom will warn of the existence of
anything it thinks is a defect, based on a plausible
heuristic, and you can control this using this option.
The options takes a list of keywords, which it processes
as shown in Table 2.
| Keyword | Description |
|---|---|
| ignore | Completely ignore defects. |
| warn | Warn about possible defects, but do nothing further. This is the default. |
| remove | Remove any suspected defects from the catalogue of CCD objects. |
| badness | Provide the threshold for defect removal and warnings. Any objects with a badness greater than the value specified here are noted or removed. The default threshold is 1. |
Keywords for
--defectsoption
The heuristic works by assigning a `badness' to each
object on the CCD. Objects with a position variance,
or
,
smaller than one pixel, and objects whose flux density
(counts/pixel) is significantly higher than the average,
are given high scores. One can observe that line and
point defects score high with this, with a badness greater
than 1, but this is not completely reliable.
We can afford a few uncaught defects, and we can afford to discard a few real, but very small, sources, since the match algorithms will generally simply ignore these. What we need to avoid is a CCD catalogue which is dominated by bright sources which have no counterpart on the sky.
We emphasise that this defect-removal algorithm is not particularly sophisticated -- if the object-extraction is producing spurious objects, you may need to mask the defects out by hand, using GAIA or similar.
If you have any observations on the reliability, or indeed usefulness, of this option, the author would be interested to receive them.
This option is not always necessary when used with the default FINDOFF matching algorithm, but it is vital when used with the `match' matching algorithm (see Section 2.4.8), since that algorithm uses only the brightest objects detected.
Type: string; default: --defects=warn