Principles and Paradigms for ppne & PNe Engines: (More on CE, Accretion, B-fields)

Transcription

1 Principles and Paradigms for ppne & PNe Engines: (More on CE, Accretion, B-fields) Eric Blackman (U. Rochester) Primary Collaborator: Jason Nordhaus (U. Rochester)

2 On Theory and Modeling model vs. theory; Kepler vs. Newton exact vs. mean field (e.g. newspaper photograph, fluid mech) example: imposed jet vs. generation from first principles minimal set of unifying observations vs. details of each source simplified theory/paradigm which explains key observations and makes predictions vs. detailed model for 1 source sometimes helpful to separate theory from its specific application

3 Red Giant AGB AGB mostly spherical but maser jets in TP AGB: W43A, IRAS and IRAS , OH (e.g. Vlemmings et al. 06; Szymczak et al ) Pre-PNe TP- AGB Transition from spherical to aspherical Often (always?) explosive (O(100yr) in CO) (Alcolea 01;Bujarrabal, et al. 01) Binding energy: TP < AGB <RGB PNe Does explosive ppne phase also influence to PNe shape?

4 ppne fast winds require non-rad. force CO survey of proto-planetary nebula: (Bujarrabal et al. 2001) 32 objects: 28 have both fast outflow and expanding shell (slow outflow) ~ 80% of PPNe have fast outflow momenta, ( g cm/s) that supplied by radiation NOTE: total mechanical luminosity is often 37 as high as 10 erg/s ALL Accretion Models Give: L acc M Ṁ 5 v out 400 ( M R,11 R,11 ) 1/2 km/s radiative luminosity, but

5 Measured Magnetic Fields AGB stars: Maser emission in the OH shell of NML Cygni (Etoka & Diamond 2004) Central stars of PNe: Spectropolarimetric discovery of kg fields in the central stars. (e.g. Jordan et al. 2005; Sabin 07 (?)) Evolved AGB stars W43: precessing jet in a post-agb star; B-fields 85mG at ~500 AU; strong enough to collimate (Vlemmings et al. 06) Important: relation between observed fields and engine fields needs more work

6 Back to Common Envelope Engines Giant stars engulf companions (e.g. Paczynski 76; Iben Livio 93; Tamm 06; Webbink 07) Velocity difference between secondary and CE generates drag which drives in-spiral. α fraction ( ) of orbital energy released by secondary is available for mass ejection. α for given, tracking binding energy released provides final orbital separation Orbital Energy Deposition E bind = α E orb Might accretion disks from around primary?

7 Primary s Stellar Profile We consider initial 3 M star in phases: RGB, AGB, and interpulse AGB. Binding energy inside envelope: E bind (r) = MT M GM(r) dm(r) r AGB mass and density profile. Dotted line represents the core boundary. (model of Steve Kawaler)

8 L drag = ξπr 2 aρ (v v env ) 3 In-spiral Drag between companion and envelope induces in-spiral: Assume companion incurs approximate Keplerian circular motion at all radii. Orbit is supersonic at all r Cross section of secondary comes from its accretion radius: R a 2Gm 2 (v v env ) 2

9 In-spiral and Unbinding potential energy change of secondary: E orb (r) = GM T m 2 GMm 2 2r o 2r Combined with primary s binding energy and fraction of orbital energy available for mass ejection, final separation is determined. core Example: for interpulse AGB, a 0.02 brown dwarf with can eject envelope above ~ M α = cm. Solid line: Binding energy of envelope Dashed lines: energy deposited into CE from the change in orbital energy of the secondary

10 Tidal Shredding Tidal shredding radius estimated by equating differential gravitational force across the secondary to its self-gravity: (i) If (ii) If < critical radius to unbind envelope, companion survives > critical radius to unbind envelope, companion shreds Note: smallest companions (< phase. (Soker, Livio & Harpaz 1984) M ) may evaporate before completing CE

11 Companion: Survive or Shred? AGB star ITP-AGB star turnaround from BD Solid: binding energy equals change in orbital energy supplied by secondary Short-dashed: companion first fills Roche lobe, transfers mass Long-dashed: companion is tidally shredded

12 CE Ejection Scenarios a. CE Direct Ejection b. CE Envelope Driven Dynamo Ejection c. CE Disk Driven Ejection Ejected torus would precede jet; perhaps relevant to Huggins (2007)

13 Direct Envelope Ejection WD White Dwarf + Brown Dwarf Close Binary (a 0.6R ) In-spiral confined to pre-ce orbital plane. equatorial outflow expected M BD = 0.05M M W D = 0.4M Brown dwarf engulfed by RGB star, survived CE but ejected stellar envelope. (Maxted et al. 2006) Simulations suggest opening angle ~ deg. (Terman & Taam 1996; Sandquist et al. 1998; Edgar et al 2007)

14 Envelope Dynamo Ejection: NGC 7009: Saturn Nebula Differentially rotating interior derived from CE in-spiral Combination of a convective envelope with differential rotation may generate large-scale poloidal and toroidal fields via α Ω dynamo. Resulting Poynting flux may be large enough to unbind the envelope in a ~100 year outflow. ansae in PPNe and PNe: Upper limit on burst time is ~ 100 yr, consistent with transient dynamo + spin down.

15 Disk Dynamo Ejection: here companion is shredded into a disk around proto-wd. HD 44179: Red Rectangle Accretion disk rotational energy may be extracted via a disk-driven/dynamo outflow (Blackman, Frank, & Welch 2001). For a 0.03 M brown dwarf with ~10% of its mass forming a disk, accretion rate (Reyes-Ruiz & Lopez 1999) Ṁ 10 4 (t/10yr) 5/4 M yr 1 Carbon-rich outflows with oxygen-rich contamination. (NASA, ESA, Van Winckel Cohen) L acc (t/10yr) 5/4 R i,10 1 erg/s (Blackman, Frank, \& Welch 2001)

16 Astrophysical Dynamos non-helical dynamos: do not make large scale fields helical dynamos (HD): make large scale fields Flow dominated HD inside astrophysical rotators Magnetically Dominated HD in coronae large scale field growth in astrophysical rotators is a coupling between the FDHD + MDHD coronal relaxation is part of the MDHD process, and jets can result Saturation of HD recently understood in terms of magnetic helicity evolution Observations mostly probe coronae and above MRI can drive both Non-helical and Helical Dynamos

17

18

19

20 α Ω Helical Dynamos Differential Rotation + Helical Turbulence Toroidal from Poloidal ( - effect) Differential rotation shears poloidal field, adding toroidal field. α Ω Toroidal to Poloidal ( - effect) As convective eddies (blobs) rise into less dense regions, they expand and twist Field Reversals Loop expansion and and footpoint diffusion lead to field reversals, and cycle period

21

22 Dynamo Scenarios: Isolated AGB (Pascoli 97, Blackman et al. 01; Soker & Zoabi 2002 ;Nordhaus, Blackman, Frank 07) (1) Transient Dynamo: No re-seeding of differential rotation -Initial rotation profile is only source of differential rotation energy. -resulting transient dynamo is insufficient (2) Quasi Steady Dynamo: -Re-seeding of differential rotation via convection + rotation -Posssibly sufficient if Poynting flux is trapped Common envelope (Nordhaus, Blackman, Frank 07) (3) In-spiral of the secondary spins up envelope -Transient Dynamos, but sufficient to unbind envelope, produce ansae, cycle periods Accretion Disk (e.g. Blackman, Frank, Welch, 01; Nordhaus & Blackman 07) (4) accretion provides turbulence needed for helical dynamo -sufficient to power long term outflows (PNe, PN) of decaying power

23 Progenitor Geometry Meridional Slice of Dynamo Geometry Convective Zone Core Shear Zone r = r + L c 1 r = r c α - layer z^ x^ Convection Zone Ω - layer y^ r = r - L c (Nordhaus, Blackman, Frank 2006) Convection + Differential rotation induced by the in-spiraling secondary can power a dynamo.

24 Poloidal Field Envelope Dynamo Equations Toroidal Field Velocity Shear Poynting Flux (Velocity evolution)

25 Common Envelope Dynamo: Results I 0.02M Brown Dwarf Companion Thermally Dominated Model!! T M The insets represent the time evolution from 0 to 0.2 yrs. Heat resulting from turbulent dissipation is responsible for unbinding the envelope after ~ 20 yrs. The resulting outflow is expected to be spherical or quasi-spherical.

26 Common Envelope Dynamo: Results II Magnetically Dominated Model 0.05M Brown Dwarf Companion Insets represent time evolution from 0 to 0.2 yrs. Poynting flux is responsible for unbinding the envelope within ~ 50 yrs.!! M Resultant poloidal outflow is expected, with weaker equatorial outflow (e.g. Matt et al. 2006)

27 Summary of Envelope-Dynamo-Driven Outflow

28 2006 Simulation of Magnetic Explosion

29 Summary of CE induced Disk-Dynamo Outflow (Reyes-Ruiz & Lopez 1999)

30 From Disk From Star (requires reseeding)

31 Conclusions... -Magnetic fields and binaries: co-conspirators in producing asymmetric ppne and PNe. -Jets come from B-fields, which come from dynamos, which in turn benefit from binaries supplying the necessary differential rotation and/or accretion power. -Common envelope evolution, from low mass companions can seemingly produce both dust tori and bipolar outflows. -Variety of possible outcomes of CE evolution require more study -ppne/pne: timely application of dynamo, accretion, and jet theory -Accretion onto primary provides needed power for ppne -obstacles for isolated AGB stars to make sustained bipolar PNe from MHD dynamos

32 Laundry list for Linking Theory. + Obs. (1) absence or presence of Carbon rich p/pne? (could imply CE; but e.g Ant) contamination of abundances by companion/ouflow? (...improve mixing theory) relation between dust tori and poloidal outflows? Do all p/pne go through asymmetric phase? Are maser jets in post-agbs precursors to the PNe jets via same mechanism? Evidence for steady vs. bursty/multiple outflows and the time scales are time scales of precession: consistent with observed binaries or consistent with rocket effect? maximum & distribution of outflow speeds (constrains accretion engine)

33 Linking Theory. + Obs. (2) disk predictions: variability, double peaked line profiles? ambiguities in geometry and orientation? characterizing time evolution of non-axisymmetry point X-rays; (issue of obscuration and youth); novae, B-fields, variability compare shaping from: magnetic, non-mag but binary companion; supersonic launch, single star