Radiative Forces in Interacting Binaries Stan Owocki Bartol Research Institute University of Delaware collaborators: Ken Gayley - U. Iowa Rich Townsend - Bartol/UDel Steve Cranmer - HS-CfA

Aug 17, Light transports energy (& information) But it also has momentum, p=E/c Often negligible, because c is so high But becomes significant for very bright objects, e.g. Lasers, Hot stars, QSO/AGN’s Key question: how big is force vs. gravity?? Light’s Momentum

Aug 17, Radiative force e.g., for internal radiation source from a star, compare electron scattering force vs. gravity  g el g grav   e L 4  GMGMc r  L 4  r 2 c Th  e GM 2   ~ For sun,  O ~ 2 x But for hot-stars with L~ 10 6 L O ; M=10-50 M O... if  gray => g eff ~M eff ~(1-  )M

Aug 17, Could radiation alter a companion’s tidal distortion?  =g rad /g grav  (r)=(1-  )GM/r Internal vs. External Radiation source Drechsel et al. 1995

Aug 17, Trapping of internal radiation source

Aug 17, External radiation source I + ~I * I + ~I * /(1+  ) g rad ~I * /(1+  )=const.  0 as  

Aug 17, Radiation can not alter a companion’s tidal distortion  =g rad /g grav  (r)=(1-  )GM/r because radiation source is external

Aug 17, Saturation of Line-Driving For strong, optically thick lines: g rad ~g grav sets characteristic density for radiative forces to be important

Aug 17, (non)-Effect of Radiation on RLOF Dessart, Langer & Petrovich 2003 prim>sec Mdot: prim~secprim<sec

Aug 17, Radiative Braking  wr =  o  wr =5  o prevents wind accretion onto companion

Aug 17, Radiatively driven surface shear Could explain Struve-Sahade effect - see Ken Gayley’s talk

Aug 17, Summary Radiative forces very important for winds  Desaturation of lines by velocity gradient, g lines ~ dv/dr  But also ~1/  => only effective for moderate density  Radiative braking can prevent wind-star accretion Radiative forces NOT important in tidal distortion, RLOF  Reflection of external radiation gives limited g rad ~ I * /(1+  )  Cannot reshape star  Cannot stop RLOF (momentum density too high) But can drive surface shear flow  Flux and flow parallel to surface  May explain Struve-Sahade, cf. Ken Gayley’s talk