Rho (ρ) Ophiuchi (H II 19) HIP: 80473 SAO: 184381
RA: 16h 25.6m Dec: -23° 27′
Magnitudes: 5.1, 5.7
Position Angle: 338° (WDS 2012)
Distance: 394 Light Years
Spectral Type: B2, B2
Status: Gravitationally linked, orbit chart can be seen here.
You’ll find Rho (ρ) located a bit north of Antares in Scorpius, and just across the border into Ophiuchus. And, the first thing you’ll notice in your eyepiece is a pleasing asterism shaped like a reversed open “L,” with Rho (ρ) at the center of it — or, depending on how the asterism is oriented in your eyepiece, you might see a triangle instead.
But however you see it, you’ll find this is a fine, yellow-tinged double that requires a bit of magnification in a 60mm scope in order to split it. Using a sixty millimeter f/16.7 (focal length of 1000mm) and a 25mm Plössl (40x), the primary and secondary were just touching. Doubling the magnification to 80x with a 12.5mm Ortho, I had no problem separating them provided the seeing was relatively steady —- which it wasn’t on the first night out, but was much improved a couple of nights later. In an 80mm f/15, I was able to get a clean split at 48x with the 25mm Plössl.
According to the information on Jim Kaler’s web site , these are LARGE stars! The 5.1 magnitude primary has nine times the mass of our sun and is 4900 times more luminous. The slightly dimmer secondary is not very far behind it with a mass eight times greater than the sun and is 2100 times more luminous. Rho (ρ) is surrounded by dark clouds of dust which makes it appear two magnitudes fainter to us than what it would otherwise, and also lies in a reflection nebula illuminated by surrounding stars – none of which, unfortunately, is visible in a small refractor.
Observations made on June 5th and June 11th with a 60mm and 80mm refractor.