Whitepeak Observatory, Tacoma, WA

Test your Scope on 52 Orionis

52 Orionis, also known as Struve 795 after it's discoverer, F.G.W. Struve, is a somewhat rare double, being a pairing of virtually equal 6th magnitude stars and lies in a fine location, just south of a line drawn from the sholder stars, Betelgeuse to Bellatrix. Here is a finder chart of the immediate area to help locate this special equal brightness "Dawes" double.

Both components belong to a spectral class of A5V which is a hot and white main sequence dwarf-type star like our cooler, yellowish G-type Sun. 52 Orionis, both components A and B, burn quite hot at 10,000 kelvin or so--about twice the temperature of our Sun-- and this accounts for their "hotter" color--white. The hotter the star the more it's spectrum moves into the left, bluer end of the spectrum; the cooler, the more towards red it's color goes.

This is a challenging pair in a smaller telescope, but represent almost the ideal test pair for a 4- 5" scope as they are exactly what Dawes used as his standard--an equal pair of 6th magnitude. Looking through the literature I found numerous separations listed for this pair ranging from 1.4 to 1.0"arc. In an effort to refine this figure a bit I sent off for some additional information from the Washingtioon Double star Catalogue folks.

I plotted over 100 observations of 52 Ori from 1824 through 2003 from data I received from the US Naval Observatory to try and get an idea of what this binary is doing and what it's present seapration actually is. Here is the plot:

From the plot it's obvious that this binary is closing up and it's also obvious that there is a rather significant error range in the observations generally; and this error range seems pretty consistant in scope throughout the period observations were gathered (accuracy-wise, the old timers did as well as the late 20th century folks in other words).

Of the eight measurements recorded for this pair in the last 10 years, there were three speckle measurements and one AO measurement (all professional, three made with over 100" aperture); the most recent was the AO measurement at 1.08" and the average of all four professional measurements is 1.10" at 216.5 degrees. Tofol Tobal of Garraf Astronomical Observatory in Spain and coordinator of the OAG general Catalog of Double Stars, measured this double with a 4" refractor (!) and micrometer in 2000; his results were 1.18" 215.8 degrees.

My observations of this pair in my 5" achromat were very challenging both times. The first observation was done under rather poor seeeing (>2"nominal) and all I could get was a definate elongation. The second attempt was made under much better seeing (~1.5"nominal) and a "Dawes" type separation was made--a distinct separation but lacking a distinct black line between the pair. Better seeing would accomplish the latter criteria I feel. This double is right on the Rayleigh limit for a 5" (1.1"arc) and so makes a textbook star splitting test for a 4-6" scope.


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