Struve (Σ) 2470 HIP: 94043 SAO: 67870
RA: 19h 8.8m Dec: +34° 46′
Magnitudes: 7.03, 8.44
Position Angle: 267° (WDS 2013)
Spectral Type: B5
Distance: 1320 Light Years
Status: Not determined
Struve (Σ) 2474 HIP: 94076 SAO: 67879
RA: 19h 9.1m Dec: +34° 36′
Magnitudes AB: 6.78, 7.88 AC: 6.78, 11.42
Separation AB: 15.9″ AC: 96.80″
Position Angle AB: 263° (WDS 2013) AC: 123° (1998)
Spectral Type: “A” is G1, “B” is G5
Distance: 160 Light Years
Status: Physically related (WDS, codes U & Z); AC is WAL 105
(WDS data updated 10/6/2014)
This system of stars has earned a limited amount of fame as the “other” double-double in Lyra. Located to the south and east of Epsilon (ε) Lyrae, the better known system of that name, these four stars would very likely get more attention if they were located in a constellation with fewer objects to demand your attention — such as Ursa Minor ……………
……………. which is where I had planned to be on this night. But plans are never seriously made with intentions of following them, at least not when searching the sky for 60mm delights.
In a 60mm f16.7 with a 20mm Plössl, giving me 50x, I could see four stars immediately. But what really grabs your attention is the orientation of each of these pairs — they’re parallel to each other! And symmetrical as well! In my 60mm, each one of the pairs consists of a bright component with a fainter one hanging on for dear life at the edge.
Really an unusual sight, and much more deserving of attention than they get. (In case you’re wondering, the pairs of Epsilon (ε) Lyrae are oriented at roughly a ninety degree angle). To my eyes, all four of these are white in color, but Haas sees some yellow in Struve 2474.
There’s more than meets the eye, though, with this pair of stars. Σ 2470 is a spectroscopic binary, but it’s the other one Σ 2474, that’s really complicated. It’s primary consists of two stars lying one-tenth of an arc second apart. If you have a pressing urge to find them, the Washington Double Star Catalog (WDS) statistics for 2008 show the secondary (Ab) at a magnitude of 8.96 with a position angle of 258 degrees — but don’t get your hopes up too much unless you’re sitting at the eyepiece of a hundred inches or so of aperture! That pair of stars carries the designation CHR 84.
But hang on — there’s yet another star listed in the WDS, and this one lies within reach of most telescopes. Identified as WAL 105, it’s the “C” component of Σ 2474. It sits at a distance of 96.8″ with a position angle of 123 degrees, and a moderate magnitude of 11.4 — those figures were updated in the WDS in 1998 — and it’s labeled on the photo above. First identified in 1940, by 1998 it was determined that it’s not physically related to either Σ 2474 “A” or “B.”