43,549 research outputs found
Methanol Masers as Tracers of Circumstellar Disks
We show that in many methanol maser sources the masers are located in lines,
with a velocity gradient along them which suggests that the masers are situated
in edge-on circumstellar, or protoplanetary, disks. We present VLBI
observations of the methanol maser source G309.92+0.48, in the 12.2 GHz
transition, which confirm previous observations that the masers in this source
lie along a line. We show that such sources are not only linear in space but,
in many cases, also have a linear velocity gradient. We then model these and
other data in both the 6.7 GHz and the 12.2 GHz transition from a number of
star formation regions, and show that the observed spatial and velocity
distribution of methanol masers, and the derived Keplerian masses, are
consistent with a circumstellar disk rotating around an OB star. We consider
this and other hypotheses, and conclude that about half of these methanol
masers are probably located in edge-on circumstellar disks around young stars.
This is of particular significance for studies of circumstellar disks because
of the detailed velocity information available from the masers.Comment: 38 pages, 13 figures accepted by Ap
Properties of magnetic nanodots with perpendicular anisotropy
Nanodots with magnetic vortices have many potential applications, such as
magnetic memories (VRAMs) and spin transfer nano-oscillators (STNOs). Adding a
perpendicular anisotropy term to the magnetic energy of the nanodot it becomes
possible to tune the vortex core properties. This can be obtained, e.g., in Co
nanodots by varying the thickness of the Co layer in a Co/Pt stack. Here we
discuss the spin configuration of circular and elliptical nanodots for
different perpendicular anisotropies; we show for nanodisks that micromagnetic
simulations and analytical results agree. Increasing the perpendicular
anisotropy, the vortex core radii increase, the phase diagrams are modified and
new configurations appear; the knowledge of these phase diagrams is relevant
for the choice of optimum nanodot dimensions for applications. MFM measurements
on Co/Pt multilayers confirm the trend of the vortex core diameters with
varying Co layer thicknesses.Comment: 7 pages, 8 figure
- …