Astron. Astrophys. Suppl. Ser. 134, 377-391
A.-L. Melchior1,2,3, C. Afonso4, R. Ansari5, É. Aubourg4, P. Baillon6, P. Bareyre4, F. Bauer4, J.-Ph. Beaulieu7, A. Bouquet2, S. Brehin4, F. Cavalier5, S. Char8, F. Couchot5, C. Coutures4, R. Ferlet7, J. Fernandez8, C. Gaucherel4, Y. Giraud-Héraud2, J.-F. Glicenstein4, B. Goldman4, P. Gondolo2,9, M. Gros4, J. Guibert10, D. Hardin4, J. Kaplan2, J. de Kat4, M. Lachièze-Rey4, B. Laurent4, É. Lesquoy4, Ch. Magneville4, B. Mansoux5, J.-B. Marquette7, E. Maurice11, A. Milsztajn4, M. Moniez5, O. Moreau10, L. Moscoso4, N. Palanque-Delabrouille4, O. Perdereau5, L. Prévôt11, C. Renault4, F. Queinnec4, J. Rich4, M. Spiro4, A. Vidal-Madjar7, L. Vigroux4, and S. Zylberajch4
Send offprint request: A.L.Melchior@qmw.ac.uk
1 - Astronomy Unit, Queen Mary and Westfield College, Mile End Road,
London E1 4NS, UK
2 - Laboratoire de Physique Corpusculaire et Cosmologie (UMR 7535),
Collège de France, 75231 Paris Cedex 05, France
3 - NASA/Fermilab Astrophysics Center, Fermi National Accelerator
Laboratory, Batavia, IL 60510-0500, U.S.A.
4 - CEA, DSM, DAPNIA, Centre d'Études de Saclay, 91191
Gif-sur-Yvette Cedex, France
5 - Laboratoire de l'Accélérateur Linéaire, IN2P3 CNRS,
Université Paris-Sud, 91405 Orsay Cedex, France
6 - CERN, 1211 Genève 23, Switzerland
7 - Institut d'Astrophysique de Paris, CNRS, 98 bis Boulevard Arago,
75014 Paris, France
8 - Universidad de la Serena, Faculdad de Ciencias, Departemento de
Fisica, Casilla 554, La Serena, Chile
9 - Max-Planck-Institut für Physik, Föhringer Ring 6, 80805
München, Germany
10 - Centre d'Analyse des Images de l'INSU, Observatoire de Paris, 61
avenue de l'Observatoire, 75014 Paris, France
11 - Observatoire de Marseille, 2 place Le Verrier, 13248 Marseille
Cedex 04, France
Received November 3, 1997; accepted August 5, 1998
Recent surveys monitoring millions of light curves of resolved stars
in the LMC have discovered several microlensing events. Unresolved
stars could however significantly contribute to the microlensing rate
towards the LMC. Monitoring pixels, as opposed to individual stars,
should be able to detect stellar variability as a variation of the
pixel flux. We present a first application of this new type of
analysis (Pixel Method) to the LMC Bar. We describe the complete
procedure applied to the EROS 91-92 data (one tenth of the existing
CCD data set) in order to monitor pixel fluxes. First, geometric and
photometric alignments are applied to each image. Averaging the
images of each night reduces significantly the noise level. Second,
one light curve for each of the 2.1 106 pixels is built and
pixels are lumped into 3.6 3.6
super-pixels,
one for each elementary pixel. An empirical correction is then applied
to account for seeing variations. We find that the final super-pixel
light curves fluctuate at a level of 1.8% of the flux in blue and
1.3% in red. We show that this noise level corresponds to about twice
the expected photon noise and confirms previous assumptions used for
the estimation of the contribution of unresolved stars. We also
demonstrate our ability to correct very efficiently for seeing
variations affecting each pixel flux. The technical results emphasised
here show the efficacy of the Pixel Method and allow us to study
luminosity variations due to possible microlensing events and variable
stars in two companion papers.
Key words: methods: data analysis -- techniques: photometric -- Galaxy: halo -- galaxies: Magellanic Clouds -- Cosmology: dark matter -- Cosmology: gravitational lensing
Copyright The European Southern Observatory (ESO)