486 research outputs found
How to De-Rotate the Cosmic Microwave Background Polarization
If the linear polarization of the cosmic microwave background (CMB) is
rotated in a frequency-independent manner as it propagates from the surface of
last scatter, it may introduce a B-mode polarization. Here I show that
measurement of higher-order TE, EE, EB, and TB correlations induced by this
rotation can be used to reconstruct the rotation angle as a function of
position on the sky. This technique can be used to distinguish primordial B
modes from those induced by rotation. The effects of rotation can be
distinguished geometrically from similar effects due to cosmic shear.Comment: 4 pages, this version to appear in PR
Microlensing by Stars
If stars at the lower end of the main sequence are responsible for the
microlensing events observed in the Galactic bulge, then light from the lensing
star contributes to the observed brightness. The background and lensing stars
generally have different colors, and the relative brightness changes during the
microlensing event. Therefore, microlensing light curves are not perfectly
achromatic if hydrogen-burning stars are the lenses. In most cases, the color
shift will be too small to be observable, but we argue that given the current
microlensing rates, it is plausible that a few color-shifted microlensing
events could be observed in the near future, especially if strategies are
optimized to search for them. Although rare, such an event could potentially
provide a wealth of information: Light curves in two bands can be used to
determine the masses and distances of the two stars as well as the transverse
speed of the lensing star. Light curves in additional wavebands could make the
determination more precise.Comment: 11 pages, uuencoded, compressed Postscrip
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