April 22, 2019

Astro-Challenge: The Colorful Hues of Struve 3053.

Finding Struve 3053. (Created by Author Using Starry Night).

Didn’t get what you wanted for Christmas? Neither did we, at least in terms of an automated backyard observatory and a private mountain top to perch it on… but such is the game of astronomy. We continue on, telling ourselves you don’t really need money to enjoy this hobby, that the night skies are free to all who dare trudge out into the cold winter northern hemisphere evenings…

OK, I’ll give you one more target for 2011 that makes wintertime astronomy worth-while; Struve 3053 in the constellation Cassiopeia. Another star that vies for the title of the “Winter Albireo”, this colorful double would probably also be a star party favorite if it were just a pinch above naked eye visibility. Located on the Cepheus-Cassiopeia border, this pair almost always illicits “ohs” and “ahs” as the uninitiated sweep the rich star fields along the galactic plane. Struve (sometimes annotated as “?”) 3053 consists of a pair of stars at a visual magnitude of +6.0 and +7.2 respectively with an apparent angular separation of 15” arc seconds and a position angle of 71° degrees, an easy split for a small telescope. Color contrasts vary from an orange tinged-white primary to a pearly-blue secondary; it’s always a fun and useful study to ask new observers of any colored double star what colors they see. Both share a common proper motion to suggest that they are indeed a true binary pair. The pair consists of a G8III class star weighing in at 1.1 solar masses & a surface temperature of 4800 K (HIP 207, the 6th magnitude star) and a A2V star of 2.4 solar masses at a temperature of 9000 K. The orbital period of the pair isn’t precisely known, but at a distance of 2,000+ light years, the spread of the pair must be considerable, in the order of thousands (about 9,482 A.U.s, or 0.15 light-years, to be precise!) of astronomical units apart.

The setting circle positions for the pair are as follows;

Declination: +66° North 06’

Right Ascension: 00 Hours 02.6’

The pair rides high in the post-dusk skies for northern latitude observers for the remainder of the winter season.

The Struve catalog of double stars owes its existence to 19th century astronomer Friedrich Georg Wilhelm von Struve, himself a member of the famous Struve dynasty of Danish-German astronomers. F.G.W. Struve pioneered study of multiple stars and published his 1st edition of his famous catalog of the same in 1827. This was done while he was the director at the Dorpat Observatory in what is now Tartu, Estonia. The Dorpat observatory sported a 9.5” aperture, 14-foot long telescope known as the “Great Dorpat Refractor” which was the largest refracting telescope of its day. It also utilized a new innovation known as a German Equatorial Mount, which was gravity-driven by counter-weights and a clock-shaft, allowing the observer to track the sky. This now familiar design became more prevalent in the later 19th century with the advent of astrophotography. Occasionally, you see a Struve designation marked “O?” for his son Otto, who was born in 1819 and who would himself become an astronomer of note. It’s fun to think of young Otto playing around the Dorpat refractor as a child, or perhaps re-lighting the lantern or cranking up the counter-weights as his father made observations. F.G.W. Struve used a micrometer incorporating a spider web filament that was illuminated by use of mirrors and a candle flame. He conducted accurate measurements of 2714 double stars from 1824 to 1837, noting the separation, position angle, and precise timing of each as they crossed the thin line of the micrometer. This technique also enabled Struve to measure our friend, the annual aberration of starlight as well the parallax of Vega, 25 light years distant. He also noted the effects of the interstellar extinction of starlight about a century before it was adequately explained by scattering caused by interstellar dust. Incredibly, he even measured this effect of interstellar reddening or dimming to be on the order of 1.0 magnitudes per kilo parsec, on par with the modern estimated value of 0.7-1.0! Remember, our featured star ?3053 is about 2,000 light years = 613 parsecs distant, for a loss of about 0.6 magnitudes in visual brightness. Quite impressive work, with little more than a candle flame, a strand of spider’s silk, and a good set of eyes… F.G.W Struve gave his descendants an astronomical name to live up to!


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