Point Source Extraction

The PHT Interactive Analysis (PIA) version 7.3 was used with the default settings to reduce the edited raw data to the AAP(Astronomical Analysis Processing) products. At this level of image-processing, the astronomical signals especially at 95 jm are buried under the predominant noise that is caused by drift in the responsivity of the detectors. The responsivity drift was successfully corrected by using the MEDIAN filter routine developed by Kawara et al. (1998) [1]. The drift corrected maps of the four sub-fields are rebinned into 2.3''/pixel at 95jm or 4.6''/pixel at 175jm, and then mosaiced into the 44' x 44' maps of LHEX and LHNW. Finally, the IRAF gauss routine was applied with sigma = 6 for smoothing the images.

Fig. 1. Sources extracted by DAOPHOT are plotted on the LHEX 95^m map on the left and the 175^m map on the right. The brightest source is F10507+5723 which is the only IRAS source in the survey fields.

IRAF DAOPHOT is likely to be the unique tool to extract source in the maps by the following reasons; (1) as shown in Fig. 1, the maps are very crowded and (2) FWHM measurements of profiles of bright sources indicate all of them are not significantly extended and are point sources. DAOPHOT has indeed been developed to perform stellar photometry in crowded fields [4]. The point spread function to be fed to DAOPHOT was created by using several brightest sources in LHEX.

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