Related papers: Pixel and Micro-lensing with NGST
Pixel lensing is gravitational microlensing of unresolved stars. The main target explored up to now has been the nearby galaxy of Andromeda, M31. The scientific issues of interest are the search for dark matter in form of compact halo…
We detail how microlensing internal to M31 could be used to test whether a large fraction of the matter in spiral galaxy haloes is composed of dark objects with masses comparable to those of stars, and in the process show how the…
M31 is a very tempting target for a microlensing search of compact objects in galactic haloes. It is the nearest large galaxy, it probably has its own dark halo, and its tilted position with respect to the line of sight provides an…
I discuss current and future applications of pixel lensing: the microlensing of unresolved stars. Pixel lensing is the tool of choice for studying the Macho dark matter content of external galaxies like Andromeda (M31), and is at the heart…
The Andromeda galaxy (M31) provides a new line of sight for Galactic MACHO studies and also a signature, near-far asymmetry, which may establish the existence of MACHOs in the M31 halo. We outline the principles behind the so-called…
It has been shown by Paczy\'nski that gravitational microlensing is potentially a useful method for detecting the dark constituents of the halo of our galaxy, if their mass lies in the approximate domain $10^{-6}<M/M_\odot<10^{-1}$.…
Microlensing is one of the most powerful tools for probing the nature of dark halo objects and the sources they lens. As our nearest massive galaxy, M31 provides a rich source population with many potential lenses in its halo crossing our…
Microlensing surveys search for the transient brightening of a background star that is the signature of gravitational lensing by a foreground compact object. This technique is an elegant way to search for astrophysical candidates that might…
We investigate $HST$/ACS and WFPC2 images at the positions of five candidate microlensing events from a large survey of variability in M31 (MEGA). Three closely match unresolved sources, and two produce only flux upper limits. All are…
I demonstrate that one can detect pixel gravitational microlensing events at the rate $\sim 180\ {\rm events}\ {\rm yr}^{-1}$ and that some fraction of events ($\sim 15$) will be good enough to measure time scales at the $20\%$ level if the…
We have obtained HST-NICMOS observations of five of M31's most metal rich globular clusters. These data allow photometry of individual stars in the clusters and their surrounding fields. However, to achieve our goals -- obtain accurate…
A new type of gravitational microlensing experiment toward a field where stars are not resolved is being developed observationally and theoretically: pixel lensing. When the experiment is carried out toward the M31 bulge area, events may be…
We report results from intensive monitoring of two fields on either side of M31,emphasizing microlensing involving stars and masses in M31. These results stem from the three-year VATT/Columbia survey of variability on 3d to 2m timescales.…
Microlensing is the tool of choice for the search and the analysis of compact halo objects ("MACHOs"), a still viable class of dark matter candidates at the galactic scale. Different analyses point towards an agreement in excluding dark…
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…
We consider the feasibility of directly observing gravitational microlensing in extra-galactic sources, whose stars are not generally resolved. This precludes use of the simple optical depth to microlensing formulation, which is applicable…
We present the first results of the analysis of data collected during the 1998-99 observational campaign at the 1.3 meter McGraw-Hill Telescope, towards the Andromeda galaxy (M31), aimed to the detection of gravitational microlensing…
Major progresses have been made this last year towards a better knowledge of the invisible mass. Michel Spiro will talk in details about the micro-lensing experiments and their promising results; the ROSAT satellite has provided extended…
Pixel lensing is the gravitational microlensing of light from unresolved stars contributing to the luminosity flux collected by a single pixel. A star must be sufficiently magnified, that is, the lens impact parameter must be less than a…
The developments summarized with the name ``weak gravitational lensing'' have led to exciting possibilities to study the (statistical properties of the) dark matter distribution in the Universe. Concentrating on those aspects which require…