Halo structure, masses of dark objects and parallax microlensing

Details Halo structure, masses of dark objects and parallax microlensing Halo structure, masses of dark objects and parallax microlensing

1997-08-11

arxiv.org/abs/astro-ph/9708100v1

Astronomy and Astrophysics

Astrophysics

MNRAS LaTeX style, 14 pages, 13 multi-part figures embeded. Also available from http://www.tac.dk/~draza/papers/macho1.ps.Z

Scientific paper

We study the use of parallax microlensing to separate the effects of the mass function of dark massive halo objects (MHOs or `machos') on the one hand and their spatial distribution and kinematics on the other. This disentanglement is supposed to allow a much better determination of the two than could be achieved entirely on the basis of the durations of events. We restrict our treatment to the same class of power-law spherical models for the halo of MHOs studied in a previous paper (astro-ph/9609187). Whereas the duration-based error in the average MHO mass, \mu exceeds (at N=100 events) \mu by a factor of 2 or more, parallax microlensing remarkably brings it down to 15-20% of \mu, regardless of the shape of the mass function. In addition, the slope \alpha of the mass function, dn/d\mu\propto\mu^{\alpha}, can be inferred relatively accurately (\sigma_{\alpha} < 0.4) for a broader range, -3 <\alpha < 0. The improvement in the inference of the halo structure is also significant: the index \gamma of the density profile (\rho\sim R^{-\gamma}) can be obtained with the error \sigma_{\gamma} <0.4. While in a typical situation the errors for the parameters specifying the velocity dispersion profile are of about the same magnitude as the parameters themselves, virtually all the uncertainty is `concentrated' in linear combinations of the parameters that may have little influence on the profile and thus allow its reasonably accurate inference.

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