hydef07, september 19, 2007 common envelope evolution - steven diehl, t-6 (lanl) - the formation of...
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HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
The Formation of The Formation of Hydrogen Deficient Hydrogen Deficient
Stars Through Common Stars Through Common Envelope EvolutionEnvelope Evolution
By Steven DiehlTheoretical Astrophysics Group (T-6)
Los Alamos National Laboratory
Main Collaborators: Chris FryerFalk HerwigOrsola De Marco
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
OverviewOverview
• The SPH technique: a brief introduction
• Common Envelope Evolution– Conceptual Picture– Why do we care?– Preliminary SPH simulations– Some Results
• [Double Degenerate Mergers -> Chris Fryer’s talk on Friday]
• Summary and Outlook
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
Smooth Particle Smooth Particle HydrodynamicsHydrodynamics
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
SPH - The Concept SPH - The Concept • SPH = Smooth Particle Hydrodynamics• Lagrangian Techique:
– Fluid/Gas properties are carried by SPH particles: Temperature, mass, density, composition, velocity, …
– Intrinsically adaptive, particles follow fluid flow
– Every particle represents a gas “blob”
• Each point in the gas flow is the result of a superposition of many SPH particles (usually around 64-128)
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
SPH vs. Grid CodesSPH vs. Grid Codes
SPH Grid
Angular Momentum Conservation
++ -
Shock resolving -- ++
Ease of implementing complex physics
+ -
Ease of setup + -
Computational Speed ++ --
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
Common Envelope Common Envelope Evolution (CE)Evolution (CE)
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Conceptual PictureCE - Conceptual Picture• Low-mass companion enters the atmosphere of a red giant or asymptotic giant branch star
• Companion spirals in and transfers orbital energy and angular momentum into the envelope
• Parts or all of the envelope is removed
• The companion either stops in a tight orbit or even merges into the core
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE: When does it start?CE: When does it start?• Thermal Pulses trigger radius peaks
• Companion get engulfed by the envelope
• CE evolution starts
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De Marco et al. (2003)
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE and H-Deficient StarsCE and H-Deficient Stars• After CE: only little mass from the H-envelope may be left
• a dredge-up event dilutes the remaining mass
-> Hydrogen-deficiency
QuickTime™ and aTIFF (Uncompressed) decompressor
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Herwig 1999
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Previous WorkCE - Previous Work• SPH simulations by Rasio et al (1995)
– Only one simulations available, between a 4M red giant and a 0.7M main sequence companion
– Low resolution (50k particles), a factor of 2 lower than even our smallest test runs
• Nested grids by De Marco et al (2003)– Technique limited, unable to cover the huge dynamical ranges
– They are now improving with AMR codes (Enzo)
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Number of time CE - Number of time stepssteps
• Time stepping: dt~h/cs• Core size: <0.1 solar radii• BD of 0.05 should spiral to around .6 solar radii, Number of particles required: >10000 within the last radius. -> required h of at least 0.01 Rsun
• Cs around the core is about 100Rsun/day
• -> dt is about 0.01/100=1/10000 day• Need a few hundred days or years to complete -> Millions of time steps
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Worst case: Planets/Brown CE - Worst case: Planets/Brown DwarfsDwarfs
• The lower the mass of the companion, the further it is expected to spiral inwards
• More resolution required inside a smaller Volume
• Numerically more challenging, as the sound speed rises fast close to the center
• Dynamical range: 0.01 - 100 solar radii for RG, for AGB stars it gets even worse
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - ScalingCE - Scaling• Let’s assume we increase the resolution by a factor of q: h’=h/q
• if h’=h/q then cs’=qcs and dt’h’/cs’dt/q2
-> number of time-steps: Ndt’=q2Ndt
• Number of particles (3d-Volume): h’=h/q -> N’=q3N
• Computing speed per timestep: µ’N’logN’ µ (if all particles updated all the time)
• Total computing time: µ’tot=µ’*Ndt’q5 logq3µtot
• q=2 -> µ’tot=66µtot, q=10 -> µ’tot=690775µtot
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Avoiding the worst CE - Avoiding the worst casecase
• Individual time-stepping of particles absolutely crucial, this avoids the NlogN scaling of the time step, only the system time step (all particles advanced) scales this way.
• Be smart on where to put the extra resolution, only add particles at center
• Even then, we probably have to regrid the center of the simulation at one point for very low-mass companions
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - DISCLAIMERCE - DISCLAIMER• All the results you will see are to be considered VERY PRELIMINARY
• We have significantly modified the code and improved its performance. These are test runs and we are still in the debugging phase
• Do NOT take these results quantitatively literally, but rather use them to get an intuition on how the dynamics work out
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Test Run: 0.9RG, CE - Test Run: 0.9RG, 0.25WD0.25WD
• 0.9 solar mass Red Giant (RG) and 0.25 solar mass White Dwarf (WD) companion
QuickTime™ and aMotion JPEG OpenDML decompressor
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HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Test Run: 0.9RG, CE - Test Run: 0.9RG, 0.05BD0.05BD
• Dynamics are always similar: Bow-shock structure around the companion, spirals in, spiral density wave transports angular momentum and mass outward
QuickTime™ and aMotion JPEG OpenDML decompressor
are needed to see this picture.
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Comparison R vs. TCE - Comparison R vs. T• Heavy companion spirals in faster, but then stalls
• Low-mass companion still keeps on going at the end of the simulation (as far as we have run it)
• Low-mass comp. are more likely to produce tight binaries or merge into the core
0.25M
0.05M
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Comparison E vs TCE - Comparison E vs T• Red: total thermal energy of the envelope
• Green: negative value of orbital energy
• Blue: orbital energy transferred into the envelope
• Energy is still transferred from low-mas companion, high-mass essentially stopped
0.25M
0.05M
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - When Does it Stop?CE - When Does it Stop?• The evolution seems to seize when the energy released due to a decrease in orbit dR is larger than the energy to shed the envelope between R and R-dR
-> I.e. you shed faster than you spiral in
-> there is no more material to plow through
-> you can’t transfer the energy into the envelope anymore
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Comparison R vs RdMCE - Comparison R vs RdM• Plot is logR vs R*dM, I.e. area under the curve is proportional to the mass at that radius
• Colors: different times (dark=early)
• 0.25M: order of magnitude further out
0.25M
0.05M
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Open Questions for CE - Open Questions for RGRG
• Does the evolution really stop at the end? Or does the RG recuperate and increase in size again? -> map the remnant into a stellar evolution code
• Is the remaining envelope mass below the critical mass to support the Giant solution?
• If it is, will the envelope expand again and start “born-again CE”?
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Open Questions for CE - Open Questions for CompanionsCompanions
• Which companions merge into the core? What are the consequences for the composition of the envelope and nuclear burning?
• Do the companions accrete mass?• Or do they rather lose mass?• Can the companions survive at all?-> we will use different spots in the CE companion trajectory and do zoom-in study on the companion
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
CE - Open Questions for CE - Open Questions for EjectaEjecta
• Does all of the ejected envelope stay/become unbound? Does some of it fall back?
• When do the ejecta form dust, and would they be observable?
• Could this process explain some of the dust composition and morphology seen in some planetary nebula?
• Can the ejecta be crucial for forming a planetary nebula when for example a wind plows into it later on?
HYDEF07, September 19,
2007
Common Envelope Evolution- Steven Diehl, T-6 (LANL) -
SUMMARY AND OUTLOOKSUMMARY AND OUTLOOK• We now have a tool to successfully model common envelope evolution with SPH
• The code is fast, robust and versatile
• CE simulations will provide valuable input for PN formation, stellar population synthesis models, dust formation, hydrogen deficient stars, etc.