WIYN Open Cluster Study. LXXXVII. HST Ultraviolet Detection of Hot White Dwarf Companions to Blue Lurkers in M67

Abstract

We present the results of our Hubble Space Telescope far-ultraviolet survey of the blue lurkers (BLs) in M67. We find evidence for two white dwarf companions among the BLs that are indicative of mass transfer from an evolved companion, one in WOCS 14020 and the other in WOCS 3001. The cooling ages of the white dwarfs suggest that mass transfer in these systems occurred $\sim$300--540 Myr and $\sim$600--900 Myr ago, respectively. The rotation periods and cooling ages of the BLs are consistent with spin-up and subsequent single-star spin-down models, and binary evolution models yield plausible evolutionary pathways to both BLs via highly non-conservative mass transfer. We conclude that the BLs are lower-luminosity analogues to the classical blue stragglers.