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Rho (ρ) Herculis and STT 329 (OΣ 329)

Rho (ρ) Herculis  (Σ 2161)  (H II 3 — AB only)          HIP: 85112    SAO: 66000
RA: 17h 23.7m   Dec: +37° 09′
Magnitudes   AB: 4.5, 5.4     AC: 4.50, 13.53
Separation    AB: 4.0″           AC: 117.7″
Position Angle   AB: 321°  (WDS 2015)    AC: 222°  (WDS 2002)
Distance: 393 Light Years  (Simbad)
Stellar Classification: B9, A0

You’ll find Rho (ρ) Herculis located just to the east and slightly north of Pi (π) Herculis, which marks Hercules’ left (east) shoulder.  (Stellarium screen image with labels added – click on the chart for a larger view).

In my 76mm f/15.7 Tasco Rho (ρ) Herculis is a pair of of glowing white stars that leap out of the eyepiece at you.  At a mere 48x they are distinct, individual, gleaming globes, even though they seem to be barely touching one another.  With a change to a 9mm Meade Plössl (133x), I found two distinctly separate white globes of light, with the smaller and fainter of the pair still parked close to the primary.   I also had a good view of them in a 102mm refractor at 55x, which showed a very tight but distinctly split pair of white stars,  and a 127mm refractor provided a similar, but brighter, view at 59x.

This is a sketch done by Steve McGaughey with a four inch refractor. East and west are reversed in this view, with north just left of the top, west just below the middle left of the image, and east just above the middle right of the image. Rho Herculis is at the left edge of the view, OΣ 329 is near the bottom right edge.  Click for a larger view.

(For another version of the sketch above with all of the field stars labeled, click here).

There’s a thirteenth magnitude companion — out of reach the night I was looking for it — lying two arc minutes in the distance, and there may be another one, Aa, but no definite information exists at this time on it.   There’s a small treasure trove of information to be found on Jim Kaler’s web site for this dazzling white duo.

STT 329   (OΣ 329)
HIP: 85181 
SAO: 66014
RA: 17h 24.5m
Dec: +36° 57′
Magnitudes: 6.35, 9.88
Separation:  33.5″
Position Angle: 12°  (WDS 2012)
Distance:  758 LY  (Simbad)
Stellar Classification: G5, F0

If you haven’t noticed it yet, just to the east of Rho (ρ) at a distance of about fifteen arc minutes is STT 329 (OΣ 329).  If you move Rho to the northwest corner of your eyepiece, you should see both pairs of stars in the same field, as shown in the sketch.  The 6.35 magnitude primary is shadowed to the north by a much fainter 9.9 magnitude star.  Both were easily visible in the 102mm and 127mm refractors at 55x and 59x, respectively.  Using a 20mm eyepiece for 60x in the 76mm refractor, I was able to see the fainter companion easily with averted vision.  I saw the primary as white in all three scopes.

The best view here is with a low power eyepiece — you want to get both pairs of stars comfortably situated in the field of view in order to feel the full impact of the view.


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