Three-dimensional Distribution of Interstellar Clouds
Bright background starlight passing through intervening interstellar clouds contains interstellar
absorption lines. POINTS could determine accurate distances to many of these stars, allowing us
to map out more fully and to greater distances the distribution of the cold, warm and hot
ISM
components.
[43]
The Galactic Thick Disk
Modern star counts provide evidence for a galactic "thick disk", composed of metal-poor stars
with a vertical scale height on the order ~1-1.5
kpc.
[44]
POINTS could prove vital in determining
the kinematics of the thick-disk population and thus discriminating between the many thick-disk
formation models. Measurements would be made of stars
2 kpc above the plane, where the
thick disk dominates.
The Galactic Warp
The nearest edge-on spiral disk is the Milky Way. Early 21 cm radio observations showed that
our galactic disk is warped beyond the solar circle.
[45]
At R~16 kpc in the north, the H I disk
curls up to over 3 kpc above the plane, while in the south the disk extends ~1
kpc below the
plane at R~15 kpc and turns back up, reaching the plane again at R~20
kpc.
[46]
The warp can also
be characterized by studies of the distances and proper motions of
OB stars in the outer disk.
[47]
Current optical studies are hampered by uncertainties in the optical reference frame, and it is dif
-
ficult to explain the warp with existing dynamical models.
[48]
POINTS observations of the galac-
tic warp would help constrain the models and provide valuable information about the halo mass
distribution and the later stages of galaxy formation.
E. Globular Clusters
The globular clusters provide an ideal laboratory for studying stellar evolution and long-term
stellar dynamical effects. The relaxation time in the core is ~10
8
yr, while in the outer parts it is
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[48]
Binney, J., 1992, Ann Rev Astron Astrophys 30, 51, "Warps"
[47]
Miyamoto, M., Yoshizawa, M., and Suzuki, S., 1991, Astrophys. Space Sci. 177, 399, "The galactic Warp and
Rotations of the Fundamental System";
Miyamoto, M., Yoshizawa, M., and Suzuki, S., 1988, Astron & Astrophys 194, 107, "An Optical Warp of the Gal-
axy"
[46]
Henderson, A.P., Jackson, P.D., and Kerr, F.J., 1982, Astrophys J 263, 116
[45]
Burke, B.F., 1957, Astron J 62, 90;
Kerr, F.J., 1957, Astron J 62, 93
[44]
e.g. Gilmore, G., Wyse, R.F.G., and Kuijken, K., 1989, Ann Rev Astron Astrophys 27, 555, "Kinematics, Chemis-
try, and Structure of the Galaxy"
[43]
See e.g. Frisch, P.C., and York, D.G., 1984, IAU Symp. 81, p. 113, The Local Interstellar Medium, eds. Kondo et
al.
