▁stell ar ▁environments . ▁Some ▁stars , ▁for ▁example , ▁seem ▁to ▁have ▁magnetic ▁fields , ▁foss il ▁stell ar ▁magnetic ▁fields ▁left ▁over ▁from ▁their ▁period ▁of ▁formation , ▁while ▁others ▁seem ▁to ▁generate ▁the ▁field ▁an ew ▁frequently . ▁ ▁Ext ras olar ▁X - ray ▁source ▁ast rom etry ▁ ▁With ▁the ▁initial ▁detection ▁of ▁an ▁ex tras olar ▁X - ray ▁source , ▁the ▁first ▁question ▁usually ▁asked ▁is ▁" What ▁is ▁the ▁source ?" ▁An ▁extensive ▁search ▁is ▁often ▁made ▁in ▁other ▁w avel ength s ▁such ▁as ▁visible ▁or ▁radio ▁for ▁possible ▁coinc ident ▁objects . ▁Many ▁of ▁the ▁verified ▁X - ray ▁locations ▁still ▁do ▁not ▁have ▁readily ▁disc ern ible ▁sources . ▁X - ray ▁ast rom etry ▁becomes ▁a ▁serious ▁concern ▁that ▁results ▁in ▁ever ▁greater ▁dem ands ▁for ▁fin er ▁angular ▁resolution ▁and ▁spectral ▁rad iance . ▁ ▁There ▁are ▁inher ent ▁difficulties ▁in ▁making ▁X - ray / opt ical , ▁X - ray / radio , ▁and ▁X - ray / X - ray ▁ident ifications ▁based ▁sole ly ▁on ▁position al ▁coinc idents , ▁especially ▁with ▁hand ic aps ▁in ▁making ▁ident ifications , ▁such ▁as ▁the ▁large ▁un cert aint ies ▁in ▁position al ▁determin ants ▁made ▁from ▁bal lo ons ▁and ▁rock ets , ▁poor ▁source ▁separation ▁in ▁the ▁crow ded ▁region ▁toward ▁the ▁gal actic ▁center , ▁source ▁vari ability , ▁and ▁the ▁multip licity ▁of ▁source ▁nom en cl ature . ▁ ▁X ‐ ray ▁source