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White Dwarf Companions of Blue Stragglers as Evidence of Recent Mass Transfer

Event Details

Event Dates: 

Friday, October 3, 2014 - 12:00pm

Seminar Location: 

  • CASA Conference Room C324

Speaker Name(s): 

Natalie Gosnell

Speaker Affiliation(s): 

UT Austin
Seminar Type/Subject

Scientific Seminar Type: 

  • Astrophysics Lunch Seminar

Event Details & Abstract: 

The formation mechanism of blue straggler stars, defined to be brighter and bluer than the main sequence turnoff in a star cluster, has been a question for almost six decades. Hubble Space Telescope (HST) far-ultraviolet (far-UV) observations directly reveal, for the first time, the formation histories for blue straggler stars in the old (7 Gyr) open cluster NGC 188. In comparison to the blue straggler populations in younger open clusters and in globular clusters, the cooler temperatures (6,000 to 6,750 K) and close proximity (2.5 kpc) of the blue stragglers in NGC 188 allow for in-depth high-resolution spectroscopic investigation. Long-term radial velocity studies revealed that over 75% of the NGC 188 blue stragglers exist in binaries with a prevalence of 1000-day periods and a statistical secondary mass distribution that peaks at 0.5 Msolar, suggestive of Carbon/Oxygen white dwarf companions. Using HST/ACS/SBC far-UV photometry I will present direct observational detections of young (<300 Myr), hot white dwarf companions to three blue stragglers. Given the age distribution predicted in full N-body models, which translates into a white dwarf temperature distribution, three detections are consistent with all blue stragglers in long-period binaries being formed through mass transfer. The existence of these binaries in a well-studied cluster environment provides an unprecedented opportunity to observationally constrain mass transfer models, including constraints on the progenitor binary system.