Failed Stars and Super Planets A Report Based on the January 1998 Workshop on Substellar-Mass Objects (1998) / Chapter Skim
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5 Statistical Detections, Galactic Structure, and the Mass Content of the Universe
5 Statistical Detections, Galactic Structure, and the Mass Content of the Universe
Pages 44-52
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From page 44... ...
and the brown dwarf MF. Candidates for the baryonic dark matter include dwarf stars and diffuse gas, and the leading candidate for the nonbaryonic matter is long-lived elementary particles left over from the earliest moments of creation.
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From page 45... ...
Because of small-number statistics, no attempt has yet been made to estimate the local brown dwarf MF, although this should be possible in the relatively near future. About 10 globular cluster EFs have now been measured down to (or in some cases nearly to)
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From page 46... ...
Gravitational microlensing provides a complementary window on the brown dwarf MF, as well as on the composition of the dark halo and other components of the galaxy (see presentation by A Gould)
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From page 47... ...
Indeed, some researchers claim that the observed tensing rate toward the bulge is two standard deviations larger than expected even with a 28 billion solar mass bar and a full disk.5 However, as discussed above, the bulge MF is now measured: it is not rising steeply, but rather is flat. The total mass in bulge stars is only about 14 billion solar masses.
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From page 48... ...
Reduction of part of these data has yielded databases containing light curves in two colors for more than 20 million stars. Careful analysis has revealed ~200 microlensing events, out of which ~14 are toward the primary target, the Large MagelIanic Cloud.
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From page 49... ...
Two worldwide follow-up groups the Probing Lensing Anomalies Network (PLANET) and the Global Microlensing Alert Network (OMAN - are already established and are gaining access to substantial amounts of telescope time.
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From page 50... ...
The simplest interpretation of the microlensing events seen thus far is that onetI~ird of the halo is dark stars of half solar mass; two-thirds is unexplained (and consistent with being cold dark-matter particles) , and the baryonic dark matter is dark stars.
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From page 51... ...
Optical depth to a particular source location depends only on the mass density of the lenses, but the actual probability that a source is within Rot of a lens depends on the distribution of lenses and sources along the line sight. The distribution of frequencies of particular time scales for events, however, depends on the velocity dispersions of lenses and sources, the mass function of the lenses, as well as the distribution of lenses and 6A.
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From page 52... ...
As about 3% of nearby stars have giant planets orbiting within 0.2 AU, possibly migrating there from further away, the most important contribution of an intensive microlensing search for planets may be the verification that many Jupiters are located where they are likely to have formed, thereby preserving the space closer to the stars for terrestrial planets.
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