Locating Mass Loss

1. Locating Mass Loss Numerical Modeling of Circumstellar Material in Binary Systems Jennifer L. Hoffman University of Wisconsin-Madison Rice University

2. Where does mass loss occur in binary systems? Binary evolution calculations often assume conservative mass transfer. But mass loss from a binary system can have a large impact on its future evolution. How does mass loss occur in binary systems?

3. b LYRAE Harmanec et al. 1996, A&A, 312, 879 Bright: V = 3.5 mag Eclipsing: DV = 0.86 mag Interacting: P = 12.9+ d Reversed: Mg/Ml 5 Gainer hidden by disk Evidence for a jet Dave McCarty, Coca-Cola Space Science Center

4. We conducted optical spectropolarimetric observations of b Lyr from 1992-1998. Here is the polarized flux curve. We’d like to understand its characteristics: secondary eclipse but no primary, flat polarization level out of eclipse, “bumps” at intermediate phases. It’s a complex problem, so we need a sophisticated analysis tool.

5. Monte Carlo Radiative Transfer Light is treated as an ensemble of virtual “photons,” each tracked individually. Bin by exit angles Emit Propagate Repeat Scatter, update Stokes parameters (or absorb and forget photon) A photon’s origin, direction, path length, and fate are determined by statistical probabilities.

6. We modeled b Lyr with a uniform ellipsoidal star and an electron- scattering disk of uniform density shaped like a spherical wedge.

9. Problem!Large optical depths don’t give enough QDC. But small optical depths don’t match the light curve.

10. There must be another source of DC polarization—the gainer. • But it can’t contribute direct light, only polarized light. • We conclude that the b Lyr disk is • geometrically thick, • low in albedo, and • optically thick at the midplane • to hide the gainer, but optically thin at the • edges to let scattered light through.

11. Next simplest disk model: ne e-z/C. Here, C = 1. We let gainer emit light, so that L + D + G = 1, but kept G small (few % of total light). Even for very low G contributions, the light curve is affected unless teq 10.

12. We found a good match for teq = 10, a = 0.3, and G = 1.5% of the total light. Heavy curves represent observed flux and polarized flux; light and colored curves are the model results. The success of this disk model means that we probably do not see evidence for mass loss at visible wavelengths.

13. Future directions: • What are the properties of b Lyr’s circumstellar material at other • wavelengths? • disk albedo, optical depth spectra, composition •  relative temperatures of components •  characteristics, location of the jet •  characteristics, location of other mass concentrations • What does this model predict for future observations of b Lyr? •  FUSP, other polarimeters •  CHARA, other interferometers • What does this model tell us about other binary-disk systems? •  Algols, W Sers •  YSO binaries

14. Monte Carlo polarization modeling can also be useful for studying • disks and outflows in young stellar objects • shape and structure of supernova envelopes

15. and the geometry of luminous blue variables such as h Car.