David's Astronomy Pages CCD Image Notes - Session 111 (2006-01-30) Notes (S110)   Notes (Main)   Home Page   Notes (S112)

Goto Images from 2006-01-30

Sky Condition Graph

Sky Conditions Chart (S111)

Notice  1)

See explanation of these graphs

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Frost Slugs & Ice Reflections (light anomalies)

Quality of images in the session was impacted by the development of icy deposits in the CCD camera (known as frost slugs for their dark 'slug-like' appearance).  This is an occasional occurrence in cooled CCD camera's caused by the dessicator in the camera become saturated.   (Previous problems with frost slugs or ice effects occurred on 2005-08-05 &  2004-11-13, 2003-11-21).  Recent damp, cold weather and the operation of the CCD camera at -30 deg C, 5 deg C cooler than normal operating temperature, may have contributed to the problem developing when it did.   Example of frost slug impact on images is shown in the CCD image below.  The dessicator was renewed by heating in an oven for 3 hours,  but given the next session was the following night (2006-01-31), the CCD camera was not fully clear of moisture and frost slugs also effected the next session as well (see Frost Slugs 2006-01-31)

Frost slugs
		Frost slugs are clearly visible in this image.  CCD Image 60s exposure, C Filter 2006-01-30  21:06h UT (#111011)
		Adjusting the black-white range removes the visual appearance of the frost slugs and give a workable image - in this case an image capturing the two minor planets16 Psyche & 11 Parthenope - but photometric analysis would be potentially compromised. Images of faint objects (like nebula/galaxies) are cosmetically degraded to the point that its only worth taking brighter objects (eg star clusters) when frost forms in the camera.
Ice Reflections
		During automap imaging at the start of the session, two galaxy-like objects happened to be caught on this 20s exposure,  in a position on either side of the mag +7.7 star SAO 21161.  (was this some freak gravitional lensing - no objects are recorded here on galaxy catalogs.    I spent two separate 10 minute periods re-acquirng the star and imaging it in order to try to confirm the objects, but nothing was seen around the star (see bottom image
		Adjusting the black-white range suggests the light anamolies are caused by reflections of the starlight off ice crystals on the CCD chip.
		The absence of any evidence of objects around the star in this later check image and the indication of a glare effect of a nearby mag +9.8 star suggest that the effects are cause by reflections of ice crystals associated with the frost slugs.

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