Dr Jessica Chapman (ATNF)

Maser Observations of AGB and Post-AGB Stars - Dr Jessica Chapman Colloquium

ATNF Marsfield Lecture Theatre

Abstract

Radio observations of astrophysical masers have provided many insights
into mass loss from evolved stars. Observations of SiO, H2O and OH
masers allow us to probe the three-dimensional wind geometries,
kinematics and magnetic fields over a large range of radial distances
from the central stars. In this talk I will review maser observations
of three groups of sources: (i) the Mira variable and supergiant stars,
(ii) OH/IR stars and (iii) post-AGB stars. In general the outflows from
Miras and supergiants are axi-symmetric with enhanced densities towards
the equatorial plane. The winds from these stars are accelerated to some
tens of stellar radii. The magnetic fields of these stars may be
frozen in regions of enhanced density. The OH/IR stars have higher
mass-loss rates than Miras and appear to have far more uniform
envelopes with spherically symmetric outflows, weaker magnetic fields
and constant expansion velocities at large radii. The axi-symmetric
distributions seen in Miras and supergiant stars may provide a link to
understanding the bipolar outflows seen in some post-AGB stars. I will
discuss the identification of post-AGB stars and a simple two-wind
model for their outflows.