EROS II Galactic Spiral Arms project
Following the suggestion of Paczynski the EROS project has begun few years ago a systematic survey
of the Magellanic Clouds to look for microlensing events due to
MACHOs.
Seven candidates have already been published, based on
three years (1996-98) of observations:
The few hundred events observed towards the Galactic Centre
have strengthened the hypothesis of a barred structure.
The early suggestion of de Vaucouleurs (1964)
that the Galaxy is barred is now supported by many other observations
including photometric measurements, studies of gas, stellar kinematics
and star counts.
Nevertheless, the bar parameters (shape, size, mass ...)
are not yet precisely known.
The estimate of the disc contribution to the optical depth
can be refined by investigating lines
of sight that do not go through the hypothetic ellipsoidal structure
in the Galactic Centre.
Therefore the EROS II team has chosen to search for microlensing in
four regions of the Galactic plane, located at a large angle from the
Galactic Centre (the so-called Spiral Arms),
corresponding to a total of 29 fields, refered as
beta & gamma Sct, gamma Nor and theta Mus.
The distance estimate of the source stars used in these papers
is 7 kpc, in rough agreement with the distance to the
spiral arms,
but its uncertainty is limiting further interpretation of our microlensing
optical depth estimates.
Until now, very few distant cepheids have been found in
the Galactic plane.
A dedicated variable star search was performed
between April and June 1998, mainly to detect pulsating stars
that can be used to better constrain the distance of the monitored
star population.
This search has been performed on a subset of our galactic plane fields
and the analysis was restricted to the brightest stars.
The preprint of Observation of periodic variable stars towards the spiral arms by EROS accepted by A&A (astro-ph/0204246) can be found in various formats:
Abstract,
Psfile (0.4Mb), Source (1.7Mb), see also EROS II GSA Variable stars Web page
Frederic Derue
Last modified: Tue Oct 2 18:27:19 CEST 2001