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Sirius B Observing Challenge - Results

Challenge results

 

Alan Whitman (RASC Okanagan Centre), has recently published "October's dawn window for Sirius B", Sky & Telescope 126, 4 (Oct. 2013), 30-31.


Dr. Roger Ceragioli (Vancouver Centre, and University of Arizona's Steward Observatory Mirror Lab), on 2013 October 20, writes:

I wanted to report a positive sighting of Sirius B with a 145 mm refractor tonight.
 
You see, I have long been extremely skeptical of amateur reports of seeing Sirius B through small telescopes -- that is, less than about 400 mm.  I tried many, many times over the past 10 years using 200 mm refractors, but saw nothing.  And now I know the reason why.  I have previously seen Sirius B in a 600 mm and 400 mm reflector from the Florida Keys during the Winter Star Party in 2009.
 
After much fruitful discussion with Alan Agrawal, a skilled amateur observer, who alerted me to the value of using simple polished glass balls as eyepieces, I renewed the assault on Sirius B recently.  And tonight with success!
 
I used a 145 mm f/8 semi-apochromat of my own construction.  It has the secondary spectrum of a 150 mm f/15 achromat, but in a much more compact package.  Essential to my success tonight was the use of an aperture mask with a hexagonal opening.  This device has long been recommended by double-star observers such as W.R. Dawes.  It alters the diffraction pattern of stars from the normal bull's-eye pattern to one in which a bright star shows the Airy disk, but with the diffraction rings mostly suppressed.  Instead of rings, one gets 6 rather dim diffraction spikes around a star.  The important point is that most of the light normally seen in the immediate vicinity of a bright star is removed, and channeled into the spikes.  Faint companions near bright primary stars in close double stars are more easily seen.
 
But the benefits of the hexagonal mask go beyond this.  The spikes essentially disappear around fainter stars (say 3rd mag. in moderately light-polluted skies, like mine in the middle of Tucson under a full moon).  It's as if the mask contracts the images of these stars and makes them appear as simple tiny disks.  Even around a planet like Jupiter, where the spikes can be seen, the halo of scatter light that usually accompanies the image of Jupiter is significantly diminished.
 
So I highly recommend the use of a hexagonal mask for all double-star and lunar/planetary observing.  It really helps, even on extended objects, I think.
 
The second essential device for seeing Sirius B tonight was an occulting bar.  I took an old Kellner eyepiece and fitted a narrow strip of aluminum foil onto the field lens.  Kellners are helpful in this regard since the internal eyepiece focus is normally very close to the exterior surface of the field lens: this makes attaching an aluminum strip (occulting bar) easy.  Glue it onto the lens surface!  I have an old 12 mm Kellner with such a bar.
 
Tonight [2013 October 20] at 4 am MST, we had very tranquil skies in Tucson and the air was not cold (ca. +50F/10C).  Sirius was high in our sky and not twinkling.  It formed a good diffraction pattern in the telescope.  Sirius B has a position angle of roughly 90 degrees or so with respect to A.  So I rotated the mask such that the spikes straddled east and did not run in that direction.  Using a 2x Barlow in my telescope gives about 190x with the 12 mm Kellner.  Next, I positioned the bar so as to run N-S, with Sirius A behind the bar and blocked, but near its edge.  The periodic drive error of my Losmandy G-11 is helpful in that Sirius A could be made alternately to approach and recede from the edge of the foil all the while staying behind it.  The 6 diffraction spikes continued to be visible where they were not blocked by the occulting bar.
 
With this arrangement most of the interfering light from Sirius A was blocked, except for a little secondary spectrum which announced the approach of A to the edge of the foil bar.  Within a few moments of obtaining sharp focus and setting A behind the bar, on the east side of A in the expected position I saw a very faint, but quite definite little star: Sirius B.  It appeared within the circle of secondary spectrum caused by A.  Then I rotated the mask several times in succession and examined the image.  The spikes clearly rotated with the mask.  But the faint star did not so move: the spikes shifted with respect to it.  So for the first time I feel quite sure that I have seen Sirius B in one of my own telescopes, and that a 145 mm.
 
If I brought Sirius A out from behind the bar, Sirius B instantly vanished in the glare of A.  Even using the bar but not the hexagonal mask rendered B invisible, since the non-use of the mask greatly increased the halo of light around A.  Only the simultaneous combination of mask/bar so reduced the stray light that B showed itself, and very clearly.
 
So now for the first time I'm willing to credit the idea that Sirius B can be seen even in a 100 mm telescope (using the mask and bar), as the French doublestar observer, Paul Couteau says was done at Nice 50 years ago.
 

Cheers and all the best.

and, from 2013 October 31:

I just came in from observing.  The seeing was again very good tonight, after some days of turbulence from a storm that passed to the north of us.
 
I looked for Sirius B using my 145 mm f/8 semi-apo refractor, which gives excellent images.  With the hexagonal aperture mask in place and by using an occulting bar, it is quite easy to see B.  There is no doubt whatever of its visibility, and no delusion.  I could also see it even without the occulting bar to block A, but only because I knew exactly where B was.  I could not see B without the use of the aperture mask and/or occulting bar.
 
Recently, I also made a hexagonal mask with a greatest dimension of 100 mm (actually 4 inches).  That I tried as well tonight.  Yes, it is possible to see B with only 4" of aperture -- using the mask and the occulting bar.  Probably the same could be done for 3" of aperture, although then certainly one would be near the limits of visibility for sure and the sighting might be in question.  But it was still clear at 4", although much less plain than at 145 mm.
 
I used an old Celestron 12 mm Kellner eyepiece and a 2x Ultima Barlow, which give about 190x in my refractor.  The seeing must be very good, or the observation will fail.
 
Roger
 

Dr. Ceragioli's doctoral thesis in classics was on Sirius in Antiquity (Feruidus ille canis: the Lore and Poetry of the Dog Star in Antiquity, Harvard 1992), and he has contributed articles on the fascinating observational history of this star in the Journal for the History of Astronomy (see this, and its conclusion), Sky &Telescope, and other publications.