2008-02-14

Rojetín - preliminary 21 mag/"

Today, I processed zenith's images of night sky taken during Saturday's trip to Rojetín. Original RAWs has been converted to FITSes by rawtran.

Dark frames has been processed by mdark utility from Munipack. My fast statistical analysis of a noise of the dark images shows pretty Gaussian histogram with center on level 380 and thickness about 7-8. The noise looks little bit greater then noise of our CCD camera at the same temperature (approx. 0°C). The dark frame reveals a smooth electro-luminescence at a corner probably due to a fast transfer of electrons to an A/D converter.

The converted light images has been corrected by the darks. The application claimed a small modification of rawtran because our camera detects a gravity direction and it automatically rotates images to a portrait orientation and rawtran needs rotate it back (if not, the size of lights and darks are different).

A combination of our Canon 30D camera and our 17mm Canon's fish-eye gives us a scale about 21 pix/°, eg. 2.9' per pixel near center of projection. I determined the value by use of two stars (therefore it is preliminary only!). A precise analysis will need construction of a model of the projection.

All light images has been processed by muniphot by a standard way (determination of a mean background, finding of stars and an aperture photometry). To my surprise, it works without any troubles. The number of found stars for 3-σ is almost 13 000 and for 1-σ over 50 thousands (!). The limiting magnitude of stars (1-σ) has been determined approximately on 10 magnitudes for 30sec in wide-band of sensitivity of our camera. The photometrical calibration (determination of a zero level for instrumental magnitudes by using of known stars) shows a relative great scatter for stars in the interval 2-7 mag. The position on the chip (near center or border) along with position in Milky way doesn't matter. Opposite with this, the color of stars is important and red stars are unusable for it. It may be due to a mist (or another reason).

My determination of sky brightness on place non-confused by Milky way but near of zenith gives value of 21.0 magnitude per square arcsecond with uncertainlity not better than 0.5. So the place satisfy of hard requirements for our observations.
Post a Comment