The Coronae of γ Draconis

The Chandra X-Ray Observatory has detected coronal ( T ≳ 10 6 K) emission from the red giant γ Draconis (HD 164058: K5 III; d = 45 pc), now fully resolved from a stronger source 21'' to the SE that had confused earlier measurements by Röntgensatellit ( ROSAT ). The second source is coincident with the 13th magnitude visual component ADS 10923B (γ Dra B), possibly a dM star in a wide orbit around the red giant. The 0.2-2 keV luminosity of γ Dra is L X ~ 1.2 × 10 27 ergs s -1 (1 σ confidence interval), assuming log( T cor ) ≳ 6.5 K, while that of the faint optical companion is 3.2 × 10 27 ergs s -1 , assuming the same distance. Both sources have an intermediate spectral hardness within the range displayed by coronal stars. γ Dra has L X / L bol an order of magnitude brighter than the other red giants previously imaged by Chandra , Arcturus (α Boo: K1.5 III) and Aldebaran (α Tau: K5 III), despite having an only 2 × elevated L C iv / L bol ( T ~ 10 5 K).