main ▁sequence ▁stars . ▁As ▁to ▁their ▁X - ray ▁emission ▁properties , ▁some ▁are ▁ ▁rem in is cent ▁of ▁hot ▁stars , ▁ ▁others ▁point ▁to ▁cor onal ▁activity ▁as ▁in ▁cool ▁stars , ▁in ▁particular ▁the ▁presence ▁of ▁fl ares ▁and ▁very ▁high ▁temper atures . ▁ ▁The ▁nature ▁of ▁these ▁strong ▁em issions ▁has ▁remained ▁controvers ial ▁with ▁models ▁including ▁ ▁un stable ▁stell ar ▁wind s , ▁ ▁coll iding ▁wind s , ▁ ▁magnetic ▁cor ona e , ▁ ▁disk ▁cor ona e , ▁ ▁wind - f ed ▁magnet os pher es , ▁ ▁acc ret ion ▁shock s , ▁ ▁the ▁operation ▁of ▁a ▁she ar ▁dynam o , ▁ ▁the ▁presence ▁of ▁unknown ▁late - type ▁compan ions . ▁ ▁K ▁gi ants ▁The ▁FK ▁Com ▁stars ▁are ▁gi ants ▁of ▁spectral ▁type ▁K ▁with ▁an ▁unus ually ▁rapid ▁rotation ▁and ▁signs ▁of ▁extreme ▁activity . ▁Their ▁X - ray ▁cor ona e ▁are ▁among ▁the ▁most ▁l umin ous ▁( L X ▁ ≥ ▁ 1 0 3 2 ▁erg · s − 1 ▁or ▁ 1 0 2 5 ▁W ) ▁and ▁the ▁h ott est ▁known ▁with ▁dominant ▁temper atures ▁up ▁to ▁ 4 0 ▁M K . ▁However , ▁the ▁current ▁popular ▁hypothesis ▁involves ▁a ▁mer ger ▁of ▁a ▁close ▁binary ▁system ▁in ▁which ▁the ▁orb ital ▁angular ▁momentum ▁of ▁the ▁companion ▁is ▁transferred ▁to ▁the ▁primary . ▁ ▁Pol l ux ▁is ▁the ▁bright est ▁star ▁in ▁the ▁const