Search

This paper presents a collective analytic work on the document in its transition to digital form carried out within a network of researchers of the CNRS Information and Communication Science and Technology (STIC) Department. The collective drafting of a text, carried out with a device of annotations, built an analytical inventory of research in progress. It stressed three topics: the form, the text and the medium which reflect the radical transformations that are taking place and the issues still going on. In particular, the more and more dynamic construction of documents actually transforms their traditional stability. The advance of the collective thought could lead to the development of a theory of the document.

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 unmistakable signature of microlensing. However most stars of M31 are not resolved and one has to use the ``pixel method'': monitor the pixels of the image rather than the stars. AGAPE is the implementation of this idea. Data have been collected and treated during two autumns of observation at the 2 metre telescope of Pic du Midi. The process of geometric and photometric alignment, which must be performed before constructing pixel light curves, is described. Seeing variations are minimised by working with large super-pixels (2.1) compared with the average seeing. A high level of stability of pixel fluxes, crucial to the approach, is reached. Fluctuations of super-pixels do not exceed 1.7 times the photon noise which is 0.1% of the intensity for the brightest ones. With such stable data, 10 microlensing events are expected for a full ``standard halo''. With a larger field, a regular and short time sampling and a long lever arm in time, the pixel method will be a very efficient tool to explore the halo of M31., Comment: 15 pages, 15 figures. Text and figures with better definition will also be available at http://cdfinfo.in2p3.fr/Experiences/AGAPE/publis.html Modified according to the requirement of the referee. To appear in A&A

AGAPE is an observational search of massive compact halo objects (MACHOs) in the direction of M31 by means of a novel method: the gravitational microlensing of unresolved stars. The search consists in examining CCD pixel light curves for microlensing features. The high level of temporal stability necessary to detect microlensing events has been achieved, with quiet pixels stable within a factor of two of the photon noise (the brightest ones down to a level of 0.001 mag). The data analysis is still in progress, but hundreds of variable objects (cepheids, novae, ...) have already been found. Among them there are several lightcurves that resemble microlensing events., Comment: presented at the International Conference on "Dark and Visible Matter in Galaxies" (Sesto Pusteria, Italy, 2-5 July 1996), 8 pages, 7 figures, uses paspconf.sty, psfig.sty

A status report of the microlensing search by the pixel method in the direction of M31, on the 2 meter telescope at Pic du Midi is given. Pixels are stable to a level better than 0.5%. Pixel variations as small as 0.02 magnitude can clearly be detected., 5 pages, Latex2e, includes 5 figures, uuencoded gziped tar file. Proceedings of the workshop ``The dark side of the Universe : experimental efforts and theoretical framework'' Roma 13-14 November 1995

The galaxy M31 is a very good potential target for microlensing searches. However, only few stars are resolved, and a different method is therefore needed : monitor pixels and not stars. This method and the present status of the study of its feasibility are presented here.

We apply the pixel method of analysis (sometimes called ``pixel lensing'') to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Mo Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method should detect 10 to 20 times more microlensing events for M>0.05 Mo Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1 -- 0.5 Mo, a pixel analysis of the three-year EROS-1 data set covering 0.39 deg^2 would yield 4 events. We apply the pixel method of analysis (sometimes called ''pixel lensing'') to a small subset of the EROS-1 microlensing observations of the bar of the Large Magellanic Cloud (LMC). The pixel method is designed to find microlensing events of unresolved source stars and had heretofore been applied only to M31 where essentially all sources are unresolved. With our analysis optimised for the detection of long-duration microlensing events due to 0.01-1 Mo Machos, we detect no microlensing events and compute the corresponding detection efficiencies. We show that the pixel method, applied to crowded fields, should detect 10 to 20 times more microlensing events for M>0.05 Mo Machos compared to a classical analysis of the same data which latter monitors only resolved stars. In particular, we show that for a full halo of Machos in the mass range 0.1-0.5 M $\bigodot$, a pixel analysis of the three-year EROS-1 data set covering $0.39deg^{2}$ would yield $\simeq 4$ events.