Friday, July 18, 2008

-Ran the other detection methods on the dataset:
vtpdetect found many spurious sources and was defining large areas as sources, which could be expected as it is geared for very faint and extended sources
-wavdetect- takes much longer and creates larger files, so it's easier to crop field and choose a chip to centralize the cluster core, which- counts found are much lower than the same source's counterpart using the other detection methods; also not ideal because it requires the input of parameters like wavelet length and false source detection rates, the best values for which I am not sure of.... also geared towards closely spaced and extended sources, which ours aren't for the most part.

Went back to try to make celldetect work, and I realized that the sources that I believed to be spurious were in fact valid, for the most part. Viewing in Ds9 was cropping the field and centralizing on one ccd chip, creating white space at the edges though the field continued.
Readjusting binning and resolution parameters allows for the entire array to be viewed.

This is good news for me because it seems to be the best suited detection method. However, using the other methods, I've noticed a pretty severe discrepancy in net counts for corresponding sources, which worries me about the validity of the counts. Also the count rate, NET_RATE, and exposure time, EXP_TIME data model outputs are not yet implemented in the celldetect version and are just arrays of zeros.
To find count rate, I went back and manually (using dmextract) extracted the net counts and exposure times to find the count rate. As the net counts found with dmextract and celldetect were different enough, I think this may be a pretty inaccurate way to do this. (for the possible matching source, net counts found manually were 62.5, whereas with celldetect 48.5). The exposure time with this method was 5102.559, and thus the count rate was 1.23*10^-2.

Because of this, finding the minimum count rate that we could expect to detect (to know if perhaps the source is present, with a flux too low to be detected) is proving variable based on detection method. For celldetect with a 3 sigma, the default seemingly the best value, the lowest rate is around 5.037e-3. Our two sources should theoretically be detectable, as their count rates are: 0931+3622 (1.5-2.5 *10^-2) and 1532+4727 (.9-1.9*10^-2). I computed this value using the full energy range (.5-8KeV) I am working on the minimum count rate for a much softer range (.1-1 Kev)
(should I be looking as low as .06-.1 KeV?- was the energy range given in "The Coolest X-Ray Emitting WD's" This seems very soft...?)
For our two sources, it still looks as though only 153225.49+472700.9 could match a source anywhere near it's supposed position- I haven't yet computed it's theoretical xray count rate.. will do that in the morning.....

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