出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：12.9 million stars have been monitored by EROS during 7 seasons towards 4 directions in the
Galactic plane, away from the Galactic center. 27 microlensing event candidates have been found.
Estimates of the optical depths from the 22 best events are provided. A first order analysis shows
that our observations favour galactic models without a thick disk or a spiral structure. We find that
the average microlensing optical depth towards the complete EROS-catalogued stars of the spiral
arms is t = 0.50+.11
−.11, a number that is stable when moderately varying the selection criteria. As
EROS catalog is almost complete (unbiased) until IC = 18.5, the optical depth estimated for the
sub-sample of bright stars with IC < 18.5 (t = 0.39+.10
−.10) is easier to interpret.
A more precise interpretation requires either a better knowledge of the distance distribution of the
target stars, or a simulation based on a Galactic model. In this purpose, we discuss the concept of
optical depth for a given catalogue or for a limiting magnitude.
