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Astronomical Applications Department, U.S. Naval Observatory - Scifull (Page 15)

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Astronomical Applications Department, U.S. Naval Observatory - Scifull
could have a significant impact. Much of this is abstracted from the Appendix, written by K.
Cudworth of Yerkes Observatory.
G. Stellar Masses
Stellar masses have been determined mainly for detached main-sequence eclipsing binaries with
well-separated spectral lines of the two components, and for nearby visual binaries of known
Less than 5% of visual binaries (most of which are less than 20
pc distant) have good
mass determinations.
POINTS, with its 3-4 orders of magnitude parallax measurement
improvement, would greatly increase the number of accurate mass determinations. Further, since
POINTS measurements would give the motions of each component in an inertial frame, the indi
vidual masses of both components could be determined, rather than the usual sum of masses.
An intriguing possibility for determining masses for isolated foreground stars is the deflection of
light from background stars. The changing impact parameter produced by the relative motion of
the stars will lead to an apparent variation in the position of the background star. Lens candi
dates might be found in catalogs of high-proper-motion stars.
Masses for the most massive stars ­ O, B, and
Wolf-Rayet (WR) stars ­ would constrain high-
mass stellar evolution models, especially the later stages of evolution.
POINTS could observe
binaries containing high-mass components
and determine their masses, as well as calibrate the
absolute luminosities of these stars.
H. Stellar Luminosities
One of the most fundamental relations in stellar astrophysics is that among mass, luminosity,
chemical composition, effective temperature, and age. Only relatively nearby stars are
rically available for determining all of these parameters, so current knowledge spans just a few
spectral types. POINTS's distance measurements would increase the useful observing volume a
POINTS Science
16:29 Wednesday, January 03, 1996
page 15 of 20
Currently, O star and WR star absolute luminosity calibrations rely mainly on distance determinations to galactic
clusters containing these objects (Lundstrom, I., and Stenholm, B., 1984, Astron & Astrophys Supp 58, 163).
POINTS, by making direct distance measurements to fields stars as well as cluster members, could greatly
improve these calibrations. O stars are brighter than m = 15, and most galactic
WR stars (129 out of 158) are
brighter than m = 14.0.
The binary frequency among O stars and WR stars is ~40-45% (Garmany, C.D., Conti, P.S., and Massey, P.,
1980, Astrophys J 242, 1063; Moffat, A.F.J., Lamontagne, R., Shara, M.M., and McAlister, H.A., 1986, Astron J
91, 1392)
Abbott, D.C., and Conti, P.S., 1987, Ann Rev Astron Astrophys 25, 113, "Wolf-Rayet Stars"
e.g. Gliese, W., 1969, Veroff. Astron. Rechen-Inst. Heidelberg No. 22;
Gliese, W., and Jahreiss, H., 1979, Astron & Astrophys Supp 38, 423
Heintz, W.D., 1985, in Calibration of Fundamental Stellar Quantities,
IAU Symp. 111, eds. Hayes et al., Reidel, p.
Popper, D.M., 1980, Ann Rev Astron Astrophys 18, 115

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