The Coronae of γ Draconis

The Chandra X-Ray Observatory has detected coronal (T 106 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 Rontgensatellit (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 LX ~ 1.2 × 1027 ergs s-1 (1 σ confidence interval), assuming log(Tcor) 6.5 K, while that of the faint optical companion is 3.2 × 1027 ergs s-1, assuming the same distance. Both sources have an intermediate spectral hardness within the range displayed by coronal stars. γ Dra has LX/Lbol 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 LC iv/Lbol (T ~ 105 K).