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The test runs of new version of `swift_rmvsy` program, which
includes also **seasonal variant** of Yarkovsky thermal effect, are
presented. The main aim is to reproduce results from
Farinella *et al.* (1998).
Analytical calculations lead to following drift rates in semimajor axis
for three basic types of asteroid fragments.

The following graphs was inspired by paper
Bottke, W. *et al.*:
**Dynamical Evolution of main Belt Meteoroids: Numerical Simulations
Incorporating Planetary Perturbations and Yarkovsky Thermal Forces.**
Draft of paper for Icarus Feb 19th 1999.

Dependence of z - component of thermal acceleration *a*_{th}(z)
on x or y coordinates for one orbital revolution of **10 m** asteroid
fragment. The vectors of *a*_{th} are marked with bright vertical
lines. The time step was **36.525 day**, spin axis orientation was
(1,0,0).
The value of thermal lag angle could be observed as a ratio of orange ellipses
major axes. Smaller lag angle leads to narrower ellipse on the left side
picture.

The same two pictures are reproduced for a smaller asteroid fragment
with radius *R* = 1 m. Notice that thermal accelerations are approximately
5 times larger than in previous case, while thermal lag angle is much smaller.

These are linear drift rates calculated from outputs of `swift_rmvsy`
program. The integration time was 0.1 Myr. Startup semimajor axes were
taken 2 AU for iron rich and regolith covered fragments and 1 AU, 2 AU, 3 AU
for bare basalt bodies. All startup values of other orbital elements were
zeroes. Spin axes of all fragments lie in orbital plane (ie. maximal
seasonal drift rate, due to cos^{2}(*obliquity*) dependence).
However, the time of integration was not long enough to calculate drift
rates for small iron rich fragments, this could be seen in graphs as
a termination of blue line near *R* = 5 m.

Miroslav Broz: miroslav.broz@usa.net, last updated Mar 15th 1999