Ecology of Blue Stragglers: Closing Thoughts and Discussion

“Two Perspectives are Better than One” MicroEconomics MicroAstronomics MacroEconomics MacroAstronomics Bimodal radial distributions Dual CMD sequences Kudos to Ferraro et al. for making data available! Lanzoni Dalessandro

MicroAstronomics MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence of F BSS on f bin, photo Knigge Santana

MicroAstronomics MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling Perets Chen Kudos to Davies! McMillan Kudos to Ahumada for catalogs

MicroAstronomics Binary frequencies Binary period distributions Binary secondary stars MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling  Geller

All of the preceding: High binary fraction Deficit of short (and very long) periods Low orbital eccentricities Small mass functions No visible secondaries tell us that FBS are a species sui generis Hard binary frequency 76% Hard binary frequency 76% Typical orbital period ≈ 1000 days Typical orbital period ≈ 1000 days Typical secondary mass 0.5 M o Typical secondary mass 0.5 M o Lower orbital eccentricities Lower orbital eccentricities All SB1 All SB1 Preston(Field) Mathieu (NGC 188)

MicroAstronomics Binary frequencies Binary period distributions Binary secondary stars Modestly rapidly rotating MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling Lovisi

MicroAstronomics Binary frequencies Binary period distributions Binary secondary stars Modestly rapidly rotating Early chemical abundances Early mass measurements MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling Mucciarelli 1.58 M o 2.52 M o 1.07 d S1082

MicroAstronomics Binary frequencies Binary period distributions Binary secondary stars Modestly rapidly rotating Early chemical abundances Early mass measurements Evolutionary tracks MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling Mass transfer modeling Sills Ivanova

MicroAstronomics Binary frequencies Binary period distributions Binary secondary stars Modestly rapidly rotating Early chemical abundances Early mass measurements Evolutionary tracks MacroAstronomics Bimodal radial distributions Dual CMD sequences No dependence on collision rate Dependence on environment (N vs  ) Dependence on M core, f bin Population synthesis Cluster dynamical modeling Mass transfer modeling “Two Perspectives are Better than One”

Outstanding Questions In light of this workshop, what should be the definition of a blue straggler? ( but only if you are “under 40”! ) ( or over 70 – George Preston gets last word! )

What is the CMD telling us? Do we understand CMD locations of BS? Do we understand CMD locations of BS? Should we believe anything from (standard) evolution theory? Should we believe anything from (standard) evolution theory? Alison – “I don’t understand how to get such low luminosities.” Natasha – “I don’t understand how to get those masses.” x Photometric Dynamical 1.5 M o Outstanding Questions

What is the CMD telling us? Do we understand CMD locations of BS? Do we understand CMD locations of BS? Should we believe anything from (standard) evolution theory? Should we believe anything from (standard) evolution theory? Should we believe anything from population synthesis? And Should we believe anything from population synthesis? And therefore “kitchen sink” models? therefore “kitchen sink” models? Outstanding Questions

Do stellar collisions occur? What is the CMD telling us? Leigh, Knigge, Sills, Perets, Sarajedini & Glebbeek (2012)

Outstanding Questions Do stellar collisions occur? What are the products? Where are the products? What is the CMD telling us? Superb work has been done at the macro level - Now the work needs to be done at the micro level, both observation and theory. both observation and theory. In both globular clusters and open clusters … Abundances, rotation, masses, binarity, companions Leigh & Sills 2011

Outstanding Questions Do stellar collisions occur? What is the CMD telling us? What can we learn from angular momentum? What are we missing by not considering magnetic fields? magnetic fields? 7 Gyr 2.5 Gyr

Outstanding Questions Do stellar collisions occur? What is the CMD telling us? What can we learn from chemical abundances? Is there hope of microastronomic diagnostics of formation? Is there hope of microastronomic diagnostics of formation? What can we learn from angular momentum? What are we missing by not considering magnetic fields? Need to learn more from George P. about s-process abundances!

Outstanding Questions Do stellar collisions occur? What is the CMD telling us? What can we learned from evolved populations? Possible indirect handle on masses What can we learn from chemical abundances? What can we learn from angular momentum? What are we missing by not considering magnetic fields?

Outstanding Questions Do stellar collisions occur? What is the CMD telling us? What can we learned from evolved populations? Possible indirect handle on masses What can we learn from chemical abundances? What can we learn from angular momentum? What are we missing by not considering magnetic fields? Are there circumstellar diagnostics for any of these processes? Has anyone looked? Has anyone looked?

How Shall We Move Forward?WisconsinBadger

“Clean Up (Y)our Language!”“Binary” as in “Binary Frequency” as in “Close Binary” Mathieu Davies Chen binary as in “Consistent with binary formation channel”

“Clean Up (Y)our Language!” Mass Transfer As in “Consistent with mass transfer origin” Roche Lobe Overflow Case A Case B Case C Wind Wind Roche Lobe Overflow Common Envelope MergerAMLKozai W UMa Unstable

“Clean Up (Y)our Language!”“Collision” as in “Single Star – Single Star” as in “Resonant Encounter” as in “Collisional Encounter” as in “Collisional Dynamics”

“Need to Think Out of the Box”

Blue Stragglers Sub-Subgiants Yellow Giants Blue stragglers are one part of a larger evolutionary system

Corollary 1: “Not Strange, Just Different” “Need to Think Out of the Box” Blue stragglers and friends are not “anomalous” They are a major stellar evolution channel

We need to be prepared to accept that… blue stragglers broadly may not be fundamentally special, Corollary 2: “Its an Interacting Binary!” “Need to Think Out of the Box” and may belong more to the field of interacting binaries than to stellar dynamics. The good news is that is a very rich field to learn from! (e.g, Boffin)

“Competitive Advantage” In star clusters … Blue stragglers trace the interface of two classic fields Stellar Dynamics Binary Evolution To move forward in the Ecology of Blue Stragglers, I urge that we keep our focus on star clusters while being deeply cognizant of interacting binaries.

“Scientific Method” Especially in observations, we need more overlap and diversity of experimenters

Thank You All!

Discussion In light of this workshop, what should be the definition of a blue straggler?

Thank You to the LOC! Maria Eugenia Gomez Paulina Jiron Dave Jones Andrea Mehner Amy Tyndall