Locating Mass Loss

Numerical Modeling of Circumstellar Material in Binary Systems

Jennifer L. HoffmanUniversity of Wisconsin-Madison

Rice University

Binary evolution calculations oftenassume conservative mass transfer.

But mass loss from a binary system can have a large impact on itsfuture evolution.

How does mass loss occur inbinary systems?

Where does mass loss occurin binary systems?

LYRAE

Bright: V = 3.5 mag

Eclipsing: V = 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

Harmanec et al. 1996, A&A, 312, 879

We conducted optical spectropolarimetric observations of Lyr from 1992-1998.

Here is the polarized flux curve.

We’d like to understand itscharacteristics:

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.

Monte Carlo Radiative Transfer

Light is treated as an ensemble of virtual “photons,” each tracked individually.

A photon’s origin, direction, path length, and fate aredetermined by statistical probabilities.

Emit

Propagate

Scatter, update Stokes parameters(or absorb and forget photon)

Bin by exit angles

Repeat

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

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

There must be another source of DC polarization—the gainer.But it can’t contribute direct light, only polarized light.

We conclude that the 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.

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 affectedunless eq 10.

We found a good match for eq = 10, a = 0.3, and G = 1.5% of the total light.

Heavy curves represent observedflux and polarized flux;light and colored curves are themodel results.

The success of this disk modelmeans that we probably do not see evidence for mass loss atvisible wavelengths.

Future directions:

• What are the properties of 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 Lyr? FUSP, other polarimeters CHARA, other interferometers

• What does this model tell us about other binary-disk systems? Algols, W Sers YSO binaries

Monte Carlo polarization modeling can also be useful for studying

* disks and outflows in young stellar objects

* shape and structure of supernova envelopes

* and the geometry of luminous blue variables such as Car.