4 research outputs found
High precision microlensing maps of the Galactic bulge
We present detailed maps of the microlensing optical depth and event density
over an area of 195 sq. deg towards the Galactic bulge. The maps are computed
from synthetic stellar catalogues generated from the Besancon Galaxy Model,
which comprises four stellar populations and a three-dimensional extinction map
calibrated against the Two-Micron All-Sky Survey. The optical depth maps have a
resolution of 15 arcminutes, corresponding to the angular resolution of the
extinction map. We compute optical depth and event density maps for all
resolved sources above I=19, for unresolved (difference image) sources
magnified above this limit, and for bright standard candle sources in the
bulge. We show that the resulting optical depth contours are dominated by
extinction effects, exhibiting fine structure in stark contrast to previous
theoretical optical depth maps. Optical depth comparisons between Galactic
models and optical microlensing survey measurements cannot safely ignore
extinction or assume it to be smooth. We show how the event distribution for
hypothetical J and K-band microlensing surveys, using existing ground-based
facilities such as VISTA, UKIRT or CFHT, would be much less affected by
extinction, especially in the K band. The near infrared provides a substantial
sensitivity increase over current I-band surveys and a more faithful tracer of
the underlying stellar distribution, something which upcoming variability
surveys such as VVV will be able to exploit. Synthetic population models offer
a promising way forward to fully exploit large microlensing datasets for
Galactic structure studies.Comment: 8 pages, submitted to MNRA
Gaia Universe Model Snapshot : A statistical analysis of the expected contents of the Gaia catalogue
Context. This study has been developed in the framework of the computational
simulations executed for the preparation of the ESA Gaia astrometric mission.
Aims. We focus on describing the objects and characteristics that Gaia will
potentially observe without taking into consideration instrumental effects
(detection efficiency, observing errors). Methods. The theoretical Universe
Model prepared for the Gaia simulation has been statistically analyzed at a
given time. Ingredients of the model are described, giving most attention to
the stellar content, the double and multiple stars, and variability. Results.
In this simulation the errors have not been included yet. Hence we estimate the
number of objects and their theoretical photometric, astrometric and
spectroscopic characteristics in the case that they are perfectly detected. We
show that Gaia will be able to potentially observe 1.1 billion of stars (single
or part of multiple star systems) of which about 2% are variable stars, 3% have
one or two exoplanets. At the extragalactic level, observations will be
potentially composed by several millions of galaxies, half million to 1 million
of quasars and about 50,000 supernovas that will occur during the 5 years of
mission. The simulated catalogue will be made publicly available by the DPAC on
the Gaia portal of the ESA web site http://www.rssd.esa.int/gaia/.Comment: 21 pages, 21 figures, accepted for publication in Astronomy and
Astrophysics, typos corrected in author name