Bertrand Goldman



Universidad de Chile, Santiago
DAPNIA/SPP, Saclay, France
ESO, Santiago

Estimated local Dark Matter
10^-2 M_o/pc³.
If baryonic,
white dwarfs are a possible candidate.
Other cool objects of interest:
disk WDs (age)
brown dwarfs
Study of the Galactic dynamic.

Use the EROS II two-color Wide-Field Imager
to survey a large volume of sky
looking for white and brown dwarfs
by proper motion

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a one square degree field of view
in two bands centered on V and I
two cameras of eight 2k x2k CCDs each
(twice 8k x4k, 128Mo total)
beyond a dichroic beam splitter
0”.6 pixel size
average limiting magnitude: ~20.5^mag in I
~21.5^mag in V with 5 to 10min exposures
280°² surveyed each year,
180 Go since ’96
2 images/field/epoch in average
a 4—6 year search project (1996—2001)
observing time: ~12 dark nights/yr

Sensitivity
Astrometric reduction:
Mean residual = 20 mas
Precision for high fluxes = 25 mas
(1s, total errors, per frame),
which is 50km/s (3s) at 150pc
with a one year baseline
Errors dominated by photon noise
for most expected candidates
(with low signal-to-noise ratio)

Astrometric reduction:
Using a preliminary Monte-Carlo
Approximative efficiency of 80%
low dependancy with flux
down to 5s above background

Multiple images used when available
Detection in both colours
possible for V-I~1 cool WDs

Expected candidates:

Spherical halo full of… total present day
reduction*
…white dwarfs of VJ=17^mag 100 WDs 5 WDs
…brown dwarfs of IC=17^mag 200 BDs 5 BDs

* high cut-offs to be lowered
when more epochs become available

no fast white dwarf,
using both colours, with 4 expected
imposing both colour selection yields
one serious candidate,
confirmed using third epoch image
MI=16.9, I-K = 5.7, I-J=3.7 (DENIS)
serious brown dwarf candidate
many uncertain candidates,
found using one colour and low cuts
to be easily confirmed/rejected
with a third epoch (coming)
many very red objects
selected by their colour only
VJ-IC > 4
interesting BD candidates
to be confirmed by DENIS

Conclusion
A high proper motion survey
competitive with Whole Sky Surveys
and HST pencil beams
in the domain of fast moving faint objects

Prelimary analysis helds
no halo white dwarfs
where a few expected

One interesting brown dwarf candidate

Depending of follow-up observing time availability:
study of disk white dwarfs, subdwarfs

Shared observing time
with extragalactic programs:
prefiguration of programs
to be developed on larger telescopes
smaller pixel size, larger mosaics