Last night was calm and the air was steady, so it was a good opportunity to look at a couple close double stars: Izar (Epsilon Boötis) and Porrima (Gamma VIrginis). I was briefly joined by the neighborhood raccoon, which paused to watch while on its nightly patrol.
Izar is a challenge for small telescopes, with a separation of 2.9 arcsec. The pair consists of a magnitude-2.6 primary (spectral type K0, orange) and a magnitude-4.8 secondary (spectral type A2, blue). Using the Celestron C6 (FL ≅ 1600mm) and a Criterion A.R. 7-mm eyepiece (magnification = 228x) I had no trouble visually separating this golden and blue pair.
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| Izar. C6 + 2.5x Powermate + E-M5iii. ISO 400, 1/5 s, stack of six images. |
Porrima consists of two nearly identical F0 (blue) stars with individual magnitudes of 3.6. They orbit each other with an eccentric orbit with a period of 169 y. At their closest approach, which occurred in 2006, the separation was about 0.4 arcsec. They are currently separated by 3.5 arcsec. This separation will more than double when they are at maximum separation in 2107.
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| Porrima. C6 + 2.5x Powermate + E-M5iii. ISO 400, 1/5 s, stack of seven images. |
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| finder chart for Izar. credit SkySafariAstronomy.com |
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| finder chart for Porrima. credit: SkySafariAstronomy.com |
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