▁that ▁age ▁have ▁already ▁left ▁the ▁main ▁sequence . ▁ ▁In ▁fact , ▁when ▁the ▁stars ▁of ▁the ▁cluster ▁are ▁pl otted ▁on ▁the ▁H ert z spr ung - Russ ell ▁diagram , ▁there ▁is ▁a ▁distinct ▁" turn - off " ▁representing ▁the ▁stars ▁which ▁have ▁terminated ▁hydro gen ▁fusion ▁in ▁the ▁core ▁and ▁are ▁dest ined ▁to ▁become ▁red ▁gi ants . ▁ ▁As ▁the ▁cluster ▁ages , ▁the ▁turn - off ▁moves ▁progress ively ▁down ▁the ▁main ▁sequence . ▁ ▁It ▁appears ▁that ▁M 6 7 ▁does ▁not ▁contain ▁an ▁un bi ased ▁sample ▁of ▁stars . ▁One ▁cause ▁of ▁this ▁is ▁mass ▁seg reg ation , ▁the ▁process ▁by ▁which ▁l ighter ▁stars ▁gain ▁speed ▁at ▁the ▁exp ense ▁of ▁more ▁massive ▁stars ▁during ▁close ▁enc oun ters , ▁which ▁causes ▁the ▁l ighter ▁stars ▁to ▁be ▁at ▁a ▁greater ▁average ▁distance ▁from ▁the ▁center ▁of ▁the ▁cluster ▁or ▁to ▁escape ▁altogether ▁ ▁A ▁March ▁ 2 0 1 6 ▁joint ▁A IP / J H U ▁study ▁by ▁Bar nes ▁at ▁al . ▁on ▁rot ational ▁periods ▁of ▁ 2 0 ▁Sun - like ▁stars , ▁measured ▁by ▁the ▁effects ▁of ▁moving ▁star sp ots ▁on ▁light ▁curves , ▁suggests ▁that ▁these ▁approximately ▁ 4 ▁G yr ▁old ▁stars ▁spin ▁for ▁about ▁ 2 6 ▁days ▁- ▁much ▁like ▁our ▁Sun , ▁which ▁has ▁a ▁period ▁at ▁the ▁equ ator ▁of ▁ 2 5 . 3 8 ▁days . ▁Me asure ments ▁were ▁carried ▁out ▁as ▁part