▁counter parts ▁to ▁stars ▁can ▁be ▁identified ▁by ▁calculating ▁the ▁angular ▁separation ▁between ▁source ▁cent roid s ▁and ▁the ▁position ▁of ▁the ▁star . ▁The ▁maximum ▁allow able ▁separation ▁is ▁a ▁comprom ise ▁between ▁a ▁larger ▁value ▁to ▁identify ▁as ▁many ▁real ▁matches ▁as ▁possible ▁and ▁a ▁smaller ▁value ▁to ▁minim ize ▁the ▁probability ▁of ▁sp ur ious ▁matches . ▁" An ▁adopted ▁matching ▁criter ion ▁of ▁ 4 0 " ▁finds ▁nearly ▁all ▁possible ▁X ‐ ray ▁source ▁matches ▁while ▁keeping ▁the ▁probability ▁of ▁any ▁sp ur ious ▁matches ▁in ▁the ▁sample ▁to ▁ 3 % ." ▁ ▁Sol ar ▁X - ray ▁astronom y ▁ ▁All ▁of ▁the ▁detected ▁X - ray ▁sources ▁at , ▁around , ▁or ▁near ▁the ▁Sun ▁appear ▁to ▁be ▁associated ▁with ▁processes ▁in ▁the ▁cor ona , ▁which ▁is ▁its ▁outer ▁atmosphere . ▁ ▁Cor onal ▁he ating ▁problem ▁In ▁the ▁area ▁of ▁solar ▁X - ray ▁astronom y , ▁there ▁is ▁the ▁cor onal ▁he ating ▁problem . ▁The ▁photos phere ▁of ▁the ▁Sun ▁has ▁an ▁effective ▁temperature ▁of ▁ 5 , 5 7 0 ▁K ▁yet ▁its ▁cor ona ▁has ▁an ▁average ▁temperature ▁of ▁ 1 – 2 ▁× ▁ 1 0 6 ▁K . ▁However , ▁the ▁h ott est ▁regions ▁are ▁ 8 – 2 0 ▁× ▁ 1 0 6 ▁K . ▁The ▁high ▁temperature ▁of ▁the ▁cor ona ▁shows ▁that ▁it ▁is ▁he ated ▁by ▁something ▁other ▁than ▁direct ▁heat ▁condu ction ▁from ▁the ▁photos phere . ▁ ▁It ▁is