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
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, AA, 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. Wed like to
understand its characteristics secondary
eclipse but no primary, flat polarization level
out of eclipse, bumps at intermediate
phases. Its 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 photons 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.
7
(No Transcript)
8
(No Transcript)
9
Problem! Large optical depths dont give enough
QDC. But small optical depths dont match the
light curve.
10

• There must be another source of DC
  polarizationthe gainer.
• But it cant 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 Lyrs
  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.