Gravitational microlensing of stars of nonzero angular size

Details Gravitational microlensing of stars of nonzero angular size Gravitational microlensing of stars of nonzero angular size

Dec 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995azh....72..873b&link_type=abstract

Astronomicheskij Zhurnal, vol. 72, p. 873

Astronomy and Astrophysics

Astronomy

6

Gravitational Lenses, Angular Resolution, Stellar Magnitude, Light Curve, Limb Darkening, Nonlinear Equations, Least Squares Method, Stellar Color

Scientific paper

The possibility of employing gravitational-microlensing observations for high angular resolution studies of stars is explored. The decrease in the amplification factor of a gravitational lens with increasing angular distance from its optical axis and the finite angular diameter of a stellar disk result in a divergence of the microlensing light curve from the curve corresponding to a point source. The effects of finite stellar angular sizes and limb darkening on the observed microlensing curve are examined. It is shown that the angular radius of a star, measured in fractions of the Einstein-cone radius, can be determined using a nonlinear least-squares fitting procedure. The currently available methods of solving this problem, which allow point estimates and confidence intervals to be obtained for the parameters, are discussed. The wavelength dependence of limb darkening results in a chromatic effect during microlensing observations of stars, generally seen as reddening. Color variations in the standard broad-band UBV system are estimated for various microlensing conditions. The effect is rather small, with color variations no larger than 0.015 m. However, it can be enhanced by a special choice of the detector passbands that ensure a maximum limb-darkening difference. An important feature of the effect is its dependence only on the ratio of the angle between the lens and the true direction toward the star to the stellar angular radius.

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