The observation by the Swift X-ray Telescope of the Fe K \alpha _ { 1 } , \alpha _ { 2 } doublet during a large flare on the RS CVn binary system II Peg represents one of only two firm detections to date of photospheric Fe K \alpha from a star other than our Sun .
We present models of the Fe K \alpha equivalent widths reported in the literature for the II Peg observations and show that they are most probably due to fluorescence following inner shell photoionisation of quasi-neutral Fe by the flare X-rays .
Our models constrain the maximum height of flare the to 0.15 R _ { * } assuming solar abundances for the photospheric material , and 0.1 R _ { * } and 0.06 R _ { * } assuming depleted photospheric abundances ( [ M/H ] = -0.2 and [ M/H ] = -0.4 , respectively ) .
Accounting for an extended loop geometry has the effect of increasing the estimated flare heights by a factor of \sim 3 .
These predictions are consistent with those derived using results of flaring loop models , which are also used to estimate the flaring loop properties and energetics .
From loop models we estimate a flare loop height of 0.13 R _ { * } , plasma density of \sim 4 \times 10 ^ { 12 } cm ^ { -3 } and emitting volume of \sim 6 \times 10 ^ { 30 } cm ^ { 3 } .
Our estimates for the flare dimensions and density allow us to estimate the conductive energy losses to E _ { cond } \leq 2 \times 10 ^ { 36 } erg , consistent with upper limits previously obtained in the literature .
Finally , we estimate the average energy output of this large flare to be \sim 10 ^ { 33 } erg sec ^ { -1 } , or 1/10th of the stellar bolometric luminosity .