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Astronomical Applications Department, U.S. Naval Observatory - Scifull (Page 16)

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Astronomical Applications Department, U.S. Naval Observatory - Scifull
billion-fold and would permit coverage of all spectral types. By concentrating on binary systems
within clusters, we could empirically add age to the mass-luminosity relation and more fully test
stellar evolution models.
Among the most luminous stars in our Galaxy are the O stars, the faintest of which is m
V
= 15.2.
[58]
As with the Cepheids, none is close enough for ground-based trigonometric parallax meas
-
urements. The same problem exists for all early spectral types, from O to A. Hence, the only
methods currently available for absolute magnitude calibration of these stars are color-magnitude
(CM) diagram fitting and secular and statistical parallaxes. POINTS would measure trigonomet
-
ric parallaxes for early stars, thereby finally putting their absolute magnitude calibrations on a
firm footing.
I. Evolution of Interacting Binary Systems
The evolutionary history of interacting binary systems is a major unsolved problem in astrophys
-
ics. These interesting systems include novae, nova-like variables,
[59]
Be star x-ray binary
systems,
[60]
Wolf-Rayet stars,
[61]
low-mass x-ray binaries (LMXRBs), Type I supernovae, and
galactic black hole candidates (BHCs).
[62]
The origins of these systems are intimately associated
with the complex behavior of compact binaries with mass transfer and mass loss. Questions
involving interacting binaries are closely related to stellar mass determination. It is impossible to
place any particular system in its evolutionary context without accurate knowledge of the masses
and orbital separation. By measuring the motion of the center of light in compact binaries (for
which we have radial velocity information for the secondary), POINTS can provide measure
-
ments of the orbital inclination and separation. The scarcity of definitive mass and orbit determi
-
nations suggests that even a modest number of POINTS measurements will represent a
breakthrough.
Specific questions that will be addressed by accurate mass and orbit determinations include:
What are the precursors to LMXRBs? Are they formed by accretion-induced collapse of white
dwarfs? How many are in hierarchical triples? How does the mass distribution of neutron stars
compare with that of high-mass x-ray binaries? What is the origin of Type I supernovae? Are
there enough white dwarf binary systems with masses near
Chandrasekhar limit to account for
SN I numbers? If accretion onto white dwarfs past the
Chandrasekhar limit leads to Type I
d:\points\proposal\sz1\scifull.lwp
POINTS Science
16:29 Wednesday, January 03, 1996
page 16 of 20
[62]
Cowley, A.P., 1992, Ann Rev Astron Astrophys 30, 287, "Evidence for Black Holes in Stellar Binary Systems"
[61]
Massey, P., 1981, Astrophys J 246, 153;
Moffat, A.F.J., Lamontagne, R., Shara, M.M., and McAlister, H.A., 1986, Astron J 91, 1392;
Vanbeveren, D., and Conti, P.S., 1980, Astron & Astrophys 88, 239
[60]
These consist of a recently-formed neutron star and a Be star companion in an eccentric orbit.
[59]
Nova-like variables include cataclysmic variables,
UX UMa variables, dwarf novae, AM Her stars, symbiotic
stars.
[58]
Catalogue of galactic O Stars, Cruz-Gonzalez, C., et al. 1974, Rev. Mex. Astron. Astrof. 1, 211

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