Rota1on!and!convec1on!in!cool!MS!stars! ! On!the!MS:! ! - - PowerPoint PPT Presentation
! What!do!numerical!simula1ons!tell!us! about!solar/stellar!dynamos?! ! ! Laurne!Jouve! IRAP>Toulouse>France! ! Cool$Stars$2016.Uppsala$ Rota1on!and!convec1on!in!cool!MS!stars! ! On!the!MS:! ! Fully!convec1ve!stars!below!M "
! On!the!MS:!
! Fully!convec1ve!stars!below!M"!<!0.35! ! Convec1ve!envelope!for!0.35!<!!M"!<!1.4!
! Rela1vely!fast!rota1on! !!!!!!but!large!spread! McQuillan!et!al.!(2014)! Reiners!(2008),!Siess!et!al.!(2000)! ZAMS!
Dona1!(2011)! Morin,!Dona1!et!al.!(2008>2010)!
! Mostly!mul1polar!for!M"!>!0.35! ! Mostly!dipolar!for!M"!<!0.35! ! Bistability!for!M"!<!0.2! ! Field!strength!increases!with!rota1on! ! More!and!more!toroidal!with!rota1on! Pe1t!et!al.!2008,!S.!Marsden’s!talk!
Dona1!et!al!2008,!Fares!et!al!2009,!Mengel!et!al!2016:!τ!boo:!2!years! Pe1t!et!al!2009,!Morgenthaler!et!al!2011:!HD!190771!(complex!variability)! Garcia!et!al!2010:!HD!49933:!120!days?!
Chromospheric!ac1vity!(Mount! Wilson!data,!Ca!II!HK!lines): Pcyc=(1/Ro)1.28+/>0.48!
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where!the!Rossby!number! Ro=Prot/τ! "
Noyes!et!al.!1984! Boro>Saika!et!al!2016:!HD!201091:!14!years!
Poloidal Toroidal Toroidal Poloidal
# Babcock-Leighton effect # α effect # Ω effect Dynamo mechanism: process through which motions of a conducting fluid can permanently regenerate and maintain a magnetic field against its ohmic dissipation
It consists of the regeneration of both poloidal and toroidal fields
Transport!of!magne1c!field!
# !Large>scale!flows!! (meridional!! circula1on)!! # !Downward!pumping!by!! penetra1ve!convec1on!! # !Transport!from!the!base!of!the!! convec1on!zone!to!the!surface! (magne1c!buoyancy)!!
Sources!of!magne1c!field!
1:!magne1c!field!genera1on,!self>induc1on! 2:!pumping!of!mag.!field!!
2’:!transport!by!meridional!flow! 3:!stretching!of!field!lines!through!Ω>effect!! ! 4:!Parker!instability! 5:!emergence+rota1on! 6:!recycling!through!α-effect!or! 7:!emergence!of!twisted!bipolar! structures!at!the!surface!
! Organize!field!at!large!scales!
Browning!et!al.!(2006)! Ghizaru!et!al.!(2010)! ! From these concentrations of toroidal field, buoyant loops can emerge" ! They do not rise to the surface to create well defined spots yet, this has to be modeled independently" Nelson!et!al.!(2014)!
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! Toroidal!flux!tube!introduced!at!the!base!of!the!convec1on!zone! ! Influence!of!the!Coriolis!force!and!! convec1on!introduce!asymetries!and!! modula1on!in!longitude! ! ! ! ! ! ! Bipolar!magne1c!regions!emerge,!with!proper1es!close!to!the!observed!ones!
Jouve!et!al.!2013!
Standard!model:!! single>celled!! meridional!! circula1on! Is!this!solar!model! applicable!for! rapidly>rota1ng! solar>like!stars?!
Cyclic!field! Bumerfly!diagram!close!to!observa1ons!
Scaling!of!MC!deduced!from! Brown!et!al.!2008:!Vp!α!Ω>0.9! Dikpa1!et!al.!2001!assumed!Vp!~Ω" Charbonneau!&!Saar!2001! assumed!Vp!α!Ω!or!log(Ω)! ΔΩ " increases!with!Ω!!
0.5!Ωsol! 5!Ωsol! Slower!cycle!when!! !!!!!Ω!increased! Pcyc!=!20!yr! Jouve,!Brown,!Brun!2010! !!!!Stronger!Btor! compared!to!Bpol! 1me! 1me!
!Mul1cell!! meridional! !!!!flow! 5!Ωsol,!Pcyc!=!5.2!yr,!bemer!agreement! Can!we!reconcile!this!model!with!stellar!! !!!!!!data!using!a!more!complex!MC?! 1me!
Jouve,!Brown,!Brun!2010!
! Weakly!stra1fied!(Dobler!2005)! ! More!strongly!stra1fied!(Browning!2008)! ! Systema1c!study!(Gas1ne!et!al.!2012)!
Aspect!ra1o,! density!contrast! and!influence!of! rota1on!(Rossby! number)!varied! !
Dipolar! Mul1polar! ! Most!recent!(Yadav!et!al.!2015)! Small!and!large!! !!scales!coexist!
! Change!in!Rossby! !!!!!(also!seen!in!planetary!dynamos)! !
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Ordering!role!of!Coriolis=dipolar!
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Iner1a!becomes!dominant=mul1polar! ! ! ! Two!regimes!for!low!Rossby!numbers! !!!!!(also!seen!in!planetary!dynamos)! !
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Strong!ini1al!field=no!shear! (no!role!of!shear!in!dynamo)!
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Weak!ini1al!field=shear! (shear!plays!a!role:!Parker!waves?)! ! ! ! Strong!stra1fica1on!leads!to!! !!!!!mul1polar!fields!
Christensen!&!Aubert!(2006)! Schrinner!et!al.!(2012)!
! Dipolarity!lost!for!Ro!>!0.1! ! Bistability!for!low!Ro! ! Variability!for!very!low!Ro:!! compa1ble!with!Parker!waves?! Gas1ne!et!al.!(2013)! Yadav!et!al.!(2015)! ! ZDI!reconstruc1on:!! > Field!geometry!recovered!(large>scale!only)! > Field!strength!underes1mated!
! Dynamo!models!of!solar>like!stars:! ! !>!Role!of!the!tachocline:!building!organised!field! !>!Is!a!tachocline!necessary!for!buoyant!loops!genera1on?! !>!What!is!missing!in!3D!models!to!actually!produce!spots?! !>!Models!commonly!applied!to!the!Sun!are!challenged!by!other!stars! ! ! ! ! Dynamo!models!of!fully!convec1ve!stars:! ! !>!Change!of!geometry!with!Rossby!number!(or!with!internal!structure?)! !>!Bistable!regime!for!late!M! !>!Temporal!variability!for!mul1polar!fields?! !>!Can!dipoles!(and!thus!bistability)!resist!strong!stra1fica1ons?!
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