The Subaru Seminar is
usually held in Room 104 of the Hilo Base Facility, adjacent
to the main lobby. Everyone is welcome to attend. If you are
interested in giving a seminar, please contact Masayuki
Akiyama by email.
Monday 3 February at 11:00am
"Circumstellar Rings Around Young Vega-type Stars"
Taku Takeuchi (UC Santa Cruz)
Recent imaging of Vega-type stars has revealed structure in their
circumstellar disks that seem to be perturbed by unseen planets. For
example, Epsilon Eridani has a ~60 AU dusty ring, and a planet orbiting at
~40 AU is expected. While Epsilon Eridani is a relatively old (~1 Gyr)
main-sequence star, some of the other examples are young. HR4796A and
HD141569 are ~10 Myr old and their disks show ring structures with r~100AU.
If their rings are sculpted by planets, then the unseen planets must be
orbiting at around 100AU. However, according to the standard theory of
planet formation, it is difficult to form planets at such distant locations
from the central stars within their ages (~10Myr).
In this talk, I propose an alternative mechanism of making ring structure in
disks. As suggested by the 12CO observation of HD141569, there is probably a
small gas component in the disks (10-100 earth masses). In such gas disks,
the cooperative action of gas drag and stellar radiation pressure pushes
dust particles away from the central star and piles them up at the outer
edge of the gas disks. This dust migration makes the ring structure that
appears as if it were sculpted by planets. Therefore, ring images alone do
not clarify the presence of unseen planets. I will discuss observations that
can rule out or confirm our model, and thus yield evidence for the imaged
structures arising from planetary perturbations.
Seminars are also held at JAC,