Seminar: Companion wind shaping in binaries involving an AGB star

  • Date: –15:00
  • Location: Ångströmlaboratoriet, Lägerhyddsvägen 1 Hjorter's room (Å73101)
  • Lecturer: Lam Doan
  • Contact person: Sofia Ramstedt
  • Seminarium

The asymptotic giant branch (AGB) stars are characterized by low-velocity and massive winds. These stellar winds blow away dust and gas from the central stars and create extended circumstellar envelopes (CSEs). Because of the isotropic radiation field from the central star, the envelope is expected to be spherical to the first approximation from stellar wind theory.

There is growing observational evidence for aspherical features, e.g., torii, jets, and bipolar outflows, in a number of AGB CSEs. Moreover, proto-planetary nebulae (proto-PNe) and PNe, the next evolutionary phases after the AGB, show a wide range of asymmetric morphologies. In many cases, an embedded binary system has been detected in the gas envelopes. This is pointing to the gravitational effect of the companion as a potentially important envelope-shaping mechanism.

The thesis studies two interesting examples of (post) AGB stars that have striking morphologies of the CSEs. The S-star π1 Gruis shows a CSE structure consisting of a low-velocity expanding spiral and a fast bipolar outflow. The circumstellar environment of the post-AGB (or post-RGB) star HD 101584 shows an equatorial density enhancement disk and a high-velocity bipolar outflow. The same conclusion can be drawn for both sources, i.e., that the radiation pressure on the dust/gas is not sufficient to explain the observed energetic outflows. Instead, interaction with the companions is proposed to shape the envelopes and to some extent be responsible for accelerating the gas.