in suitable units, where r is the distance to a
nearby star, v
r
is the star's radial velocity,
is
its galactic longitude, and
µ
is its proper
motion (i.e., transverse velocity). POINTS
can accurately measure r and
µ
to many nearby
stars of all spectral types. Thus, when com
-
bined with existing radial velocity data, A and
B can be accurately determined. This in turn
places constraints on
0
, R
0
, and the local
slope of the rotation speed
via the
[dQ/dR]
R
0
definitions of A and B,
(2)
A h
1
2
Q
R
-
dQ
dR
R
0
B h
-
1
2
Q
R
+
dQ
dR
R
0
and hence sets the distance scale for the Gal
-
axy. (The next section discusses other meth-
ods for determining R
0
.)
The rotation curve,
(R), measures the mass
distribution. The most reliable method for
determining
(R) has been H I velocity meas-
urements, the so-called tangent method.
Inside the solar circle, the maximum radial
velocity of any material in the disk is
(3)
v
max
=
Q(R
0
sin k)
-
Q
0
sin k
Unfortunately, this method fails outside the
solar circle. Indirect methods must be used.
Current data suggest that the curve is consis
-
tent with being flat, or perhaps rising slightly,
out to ~18 kpc.
[11]
However, the errors in
velocity and distance are large (>10%), and,
more importantly, the shape of the rotation
curve from these methods is sensitive to the
values assumed for
0
and R
0
.
[12]
POINTS
d:\points\proposal\sz1\scifull.lwp
POINTS Science
16:29 Wednesday, January 03, 1996
page 5 of 20
[2]
Numbers for globulars reflect V magnitudes of the
horizontal branch brighter than or equal to 16.0 and
20.0.
[1]
at minimum light
14
4
Satellites
2,914
464
Asteroids
Solar System
98
7
BL Lac objects
1,959
13
Quasars
AGN
Magellanic Clouds
3
0
Dwarf Spheroidals
125
38
Globular Clusters
[2]
1,155
1,003
Open Clusters
~10
~6
Black Hole Candidates
13
1
LMXRBs
Globular Cluster Binaries
158
131
WR Stars
61
61
Be Star Binaries
42
21
Symbiotic Stars
9
0
AM Her Stars
233
9
Dwarf Novae
10
4
UX UMa
4
0
Cataclysmics
450
59
Nova-like Variables
133
22
Novae
Interacting Binaries
[1]
180
180
Radio Stars
>3066
>2263
Carbon Stars
>106
27
Halo K Giants
247
56
Planetary Nebulae
>80,000
>80,000
F - K Stars
664
656
O Stars
>878
>878
Subdwarfs
6,047
738
RR Lyrae Variables
172
81
W Virginis Variables
459
369
Cepheid Variables
Field Stars
m
18.0
m
14.0
Target Category
Table 3
Number of Objects Brighter than 14
th
and 18
th
Magnitude
[12]
Fich and Tremaine 1991;
Fich, M., Blitz, L., and Stark, A.A., 1989, Astrophys J 342, 272
[11]
Fich, M. and Tremaine, S., 1991, Ann Rev Astron Astrophys 29, 409, "The Mass of the Galaxy"
