|
The Common Envelope (CE) interaction is an intricate problem. To-date, only individual aspects of
CE physical processes have been investigated analytically, suggesting what
physics cannot be overlooked, e.g., magnetic fields, or the internal energy of the gas.
Numerical simulations have taken a more comprehensive look at the problem with
promising yet sparse results. Today, there is an unprecedented opportunity to
use existing techniques to create a benchmark of results which will not only
unify past results, but will also provide a much needed quantitative description
of the CE phenomenon to be used in population syntheses and the interpretation
of stellar classes.
|
|
The 3D hydrodynamic, nested grid code, including self gravity of Burkert and Bodeheimer (1993),
was used by to investigated a prototypical AGB and red giant branch (RGB) common envelope
interaction (Terman & Taam 1996; Sandquist et al. 1998).
We have extended the
parameter space of AGB CE interactions to smaller
companions and more evolved AGB stars demonstrating the drastic dependence on initial
conditions.
The common envelope efficiency paramter, called alpha, is a single number used to express how much of the orbital energy of the companion is available to eject the envelope. From part simulations (and common sense), we know that alpha is not a constant but is dependent on paramters. The problem is that alpha might not be the best way to paramterize the common envelope problem. So, while continuing our work on hydrodynamics simulations, we are also studying the physics of the common envelope interaction in an analytical way. Thanks to the work of graduate student Jean-Claude Passy, this work has revealed that, as previously suspected by, e.g., Nelemans et al. (2001), alpha is a misleading paramter. The analytical paper is close to completion (De Marco, Passy, Moe & Mac Low, 2008).
The common envelope interaction is complex enough that anlytical work can at best reveal holes in our knowledge and guide the specific paramters sets that need a numerical investigation. The work with the nested grid code revealed that the use of a new, parallel and AMR code is needed.
After a conversation with a few Los Alamos coleagues (Falk Herwig, Chris Fryer and Brian O'Shea) we decided
to try and adapt of the cosmological simulation code Enzo to the stellar problem. Together with
Mordecai Mac Low (AMNH), Greg Bryan (Columbia) and Jeff Oishi (Berkeley) as well as the Los Alamos colleagues we are
working on the modifications. As expected this work is not for the faint hearted.
In the meantime Ron Taam has started simulating using the clode FLASH (Ricker & Taam 2007). We are in touch with them and forsee that the use of two codes on such a difficult problem cannot but be beneficial. We are also working with Chris Fryer's SPH code, SN-SPH, in order to have another paramter of comparison.
Finally, I am working with my ex-student Max Moe on the continuation of our population synthesis code to predict frequencies and characteristics of evolved binaries. Our "Papaer II" is close to completion.
Publicatons
Do Most Planetary Nebulae Derive from Binaries? I. Population Synthesis Model of the Galactic Planetary Nebula Population Produced by Single Stars and Binaries
Moe, M., & De Marco, O., 2006, ApJ 650, 916
Wolf-Rayet Central Stars and the Binary Evolution Channel
De Marco, O., Sandquist, E.L., Mac Low, M.-M., Herwig, F. & Taam, R.E.
2003, RMxAC, 18, 24
Offprint obtainable from the ADS.
Of Wolf-Rayet Central Stars and Common Envelopes
De Marco, O., Sandquist, E.L., Mac Low, M.-M., Herwig, F. & Taam, R.E.
2003, RMxAC, 15, 34
Offprint obtainable from the ADS.
|
