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Dim Dawes in Auriga

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#1 Asbytec


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Posted 10 December 2013 - 11:53 PM

It's interesting to see what happens when you go after dim Dawes pairs (fairly equal magnitude, and fainter with separations between 0.9" and 0.7" arc.) They do become very difficult as they get dimmer.

It's interesting because their separation is an indication of the actual angular measurement of the dimmer Airy discs. If they are separated by at least Dawes, the Airy discs cannot be physically smaller without having a huge black or dark space between them. And I suspect the ring structure would also shrink, if you can see it, would appear more like a classic figure 8 than an elongation. Of course there are obstruction and seeing effects, so a larger sample is needed. These are the first three on the Auriga list.

CatalogNumber=STT 112 (P.A. 50 SEP 0.9 MAG 7.92-8.21)
Comment=Tiny but beautiful easy split equal pair at 320x. Companion held NE. Well defined dark space. Both amber with faint ring. Seeing 9/10 NELM 4.

CatalogNumber=STF 799 (P.A. 162 SEP 0.8 MAG 7.3-8.26)
Comment=Fainter companion easily seen SSW at 320x. Dark space evident most times. Faint ring mostly around primary. Seeing 8/10. NELM 4.

CatalogNumber=HU 1233 (P.A. 28 SEP 0.7 MAG 9.44-9.67)
Comment=Very difficult. Elongation seen generally NS at 320x. Fainter companion suspected N. Dark space glimpsed once, maybe seeing effect. Seeing 8/10 NELM 4.

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Posted 11 December 2013 - 01:15 PM

Interesting report. RoT pA for HU1233 is 187mm so it should be very hard to impossible for 150mm, pA for STF799 is 150mm so "easily" hints for very good seeing and pA for STT112 is 131mm so it should really be easy with 150mm.

#3 Asbytec


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Posted 11 December 2013 - 01:27 PM

Wilfried, that sounds pretty accurate. If the Airy disc were smaller, HU 1233 should have been easier. Smaller Airy discs also involve energy per unit area. In other words, they would brighten, too. Not sure either is happening.

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