2,213 research outputs found

    Limits on the Gravity Wave Background From Microlensed Quasars

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    The paper previously submitted under this title is incorrect in that it drastically overestimates the cumulative deflection due to a gravitational wave (GW) background. Avi Loeb gives a simple argument that there can be no (Dω)1/2(D\omega)^{1/2} enhancement: since the problem is linear in hh, one can decompose the GWs into plane waves and for each of these there is no enhancement.Comment: This paper was incorrect in that it drastically overestimated the cumulative deflection due to a gravitational wave background. Withdraw

    Microlensing and the Stellar Mass Function

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    Traditional approaches to measuring the stellar mass function (MF) are fundamentally limited because objects are detected based on their luminosity, not their mass. These methods are thereby restricted to luminous and relatively nearby stellar populations. Gravitational microlensing promises to revolutionize our understanding of the MF. It is already technologically feasible to measure the MFs of the Galactic disk and Galactic bulge as functions of position, although the actual execution of this program requires aggressive ground-based observations including infrared interferometry, as well as the launching of a small satellite telescope. Rapid developments in microlensing, including the new technique of ``pixel lensing'' of unresolved stars, will allow one to probe the MF and luminosity function of nearby galaxies. Such observations of M31 are already underway, and pixel-lensing observations of M87 with the {\it Hubble Space Telescope} would permit detection of dark intra-cluster objects in Virgo. Microlensing techniques can also be applied to investigate the star-formation history of the universe and to search for planets with masses as small as the Earth's. Based on an invited talk at the January 1996 AAS meeting in San Antonio. PASP (June 1996) in press, (c) ASP, reproduced with permission.Comment: 31 pages with 7 embedded figures. PASP (June 1996) in press, (c) ASP, reproduced with permissio

    Self-Lensing By A Stellar Disk

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    I derive a general expression for the optical depth τ\tau for gravitational lensing of stars in a disk by Massive Compact Objects (Machos) in the same disk. For the more restricted case where the disk is self-gravitating and the stars and Machos have the same distribution function, I find \tau = 2\VEV{v^2}/c^2\sec^2 i where \VEV{v^2} is the mass-weighted vertical velocity dispersion, and ii is the angle of inclination. This result does not depend on any assumptions about the velocity distribution. As an example, if stars within the bar of the Large Magellanic Cloud (LMC) account for the observed optical depth τ8×108\tau\sim 8\times 10^{-8} as has recently been suggested, then v\gsim 60\,\kms. This is substantially larger than the measured dispersions of known LMC populations.Comment: 6 pages, no figures, phyzzx macro package, or request PostScript file to [email protected], OSU-TA-13/9