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'Alpha Coronae Borealis' (α CrB / α Coronae Borealis) is a binary star in the constellation Corona Borealis. It also has the traditional names 'Gemma' or 'Alphekka' or 'Alphecca'.
α CrB is an eclipsing binary system similar to Algol (β Per). Its period is 17.36 days, with magnitude varying from +2.21 to +2.32, which is hardly noticeable to the unaided eye.
α CrB is believed to be a stream star member of the Ursa Major Moving Group.
A large disc of dust and material has been shown to exist around Alphecca, prompting speculation of a similar planetary/proto-planetary system to that currently assumed around Vega. How the binary-star dynamic would affect such a system is the subject of intense debate.
The name ''Gemma'' is Latin for "jewel". The other traditional name comes from Arabic ''al-fakkah'', "the broken" (ring of stars), from 'فكّ' ''fakk'' "unsealed"). In astrology it is one of the Behenian fixed stars and has the symbol .

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★ Tomkin, J.; Popper, D. M., 1986, "Rediscussion of eclipsing binaries. XV - Alpha Coronae Borealis, a main-sequence system with components of types A and G", ''Astronomical Journal'', vol. 91, June 1986.