Mu Bootis (Struve 28 / 1938)

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Observation Notes:

I wasn’t prepared for what a pleasant surprise this ‘double’ star was at high magnification when the B star turned out to be a close double itself. The yellow primary appeared to be separated from the BC combo by about 120 arcseconds. The actual value is 108.4. I estimated the main PA at about 164°, with an actual value of 171°.

The BC combo appeared purplish-blue, and were close enough that their first diffraction rings intersected each other, but did not intersect the diffraction discs. This works out to a separation of about 2.2 arcseconds. Their PA appeared to be from 0 to 10°. When I first checked the WDS Catalog, I was momentarily frustrated to see 1.3 arcseconds and 327 degrees. But then I realized that was a measurement from 1826 on a very close pair. It turns out their orbital period is 246 years. The actual 2007.3 values calculated from Brian Workman’s calculator are 2.25 arcseconds and 6.2°.

Subject Mu Boötis (A-BC: STF 28 / BC: STF 1938)
Classification Multiple Star
Position (J2000) Boötes [RA: 15:24:29.3 / Dec: +37:22:38]*
Position Angle* A-BC: 171° (1834); BC: 6.2° (2007.3)
Separation* A-BC: 108.4″ (1834); BC: 2.25″ (2007.3)
Magnitudes* A: 4.3 / B: 7.2 / C: 7.8 / BC: 6.5
Spectral Types* A: F0V / BC: G0V
Date/Time APR 29, 2007 – 12:40 AM MST (APR 29, 2007 – 07:40 UT)
Observing Loc. Flagstaff, AZ (Home)
Instrument Orion SVP 6LT Reflector (150 mm dia./1200 mm F/L)
Eyepieces/Mag. 10 mm + 2X Barlow (240X)
Conditions Mostly clear, slightly breezy, nearly full moon
Seeing 5-6/10 Pickering
Transparency NELM Mag ~5.0
References The Washington Visual Double Star Catalog, 1996.0 (Worley+, 1996); Catalogue of Stellar Spectral Classifications (Skiff, 2005)

*Based on published data.