OR Delphini (STF 2725): A Binary Star That Makes an Attractive Double-Double in Delphinus

OR Delphini, also known as Struve 2725, is a binary star in the constellation Delpinus. It’s best viewed in summer and autumn. This close pair is not far from the attractive Gamma Delphini pair of stars. In fact, with a wider field eyepiece, one can see both doubles in the same view—making this an alluring double-double in the Delpinus not to be missed!

OR Delphini’s primary star appears as an orange-yellow star shining at a magnitude of 7.5. It’s classified as a K0 star. Its secondary dimmer companion lies close at 6.2 arcseconds away, orbiting slowly away from the primary until the 25th century when its orbital path will return it closer to the primary star. You can see a map of the orbit here.

The two stars lie roughly 226 Astronomical Units away from each other and make their home 118.9 light-years from Earth.

My Observations

This is a lovely binary star. The primary star appears to be a vibrant buttery yellow against the black sky. My 10mm eyepiece splits the pair well. I can’t quite tell the color of this secondary, though it appears slightly yellow. With my wider-field 32mm eyepiece, I can include OR Delphini and Gamma Delphini in one view. Gamma Delphini is a slightly brighter pair than the dimmer OR Delphini.

Key Stats

Constellation	Delphinus
Best Viewing	Autumn
Visual Magnitude	+7.5 | +8.2
Absolute Visual Magnitude	+4.7
Distance from Earth	118.9 ly
Separation	6.2″ | 226 AU
Position Angle	11.6°
Orbital Period	2945 years
Milky Way Location	Orion Spur
My Viewing Grade	A-
Designations	STF 2725, SAO 106466, HD 197913, HIP 102490, OR Del

Sources

Banner shared under the Creative Commons Attribution-Share Alike 4.0 International license. Photo by David Ritter. Details here.

Sketch by Wayne McGraw