Abstract:
With every new discovery of an extrasolar planet, the absence of planets in globular clusters
(
GCs
)
becomes more
and more conspicuous. Null detection of transiting hot Jupiters in GCs 47 Tuc,
ω
Cen, and NGC 6397 presents an
important puzzle, raising questions about the role played by cluster metallicity and environment on formation and
survival of planetary systems in densely populated stellar clusters. GCs were postulated to have many free-
fl
oating
planets, for which microlensing
(
ML
)
is an established tool for detection. Dense environments, well-constrained
distances and kinematics of lenses and sources, and photometry of thousands of stars simultaneously make GCs the
ideal targets to search for ML. We present
fi
rst results of a multisite, 69-night-long campaign to search for ML
signatures of low-mass objects in the GC M4, which was chosen because of its proximity, location, and the actual
existence of a planet. M4 was observed in
R
and
I
bands by two telescopes, 1
m T40 and 18-inch C18, of the
Wise
Observatory, Tel Aviv, Israel, from 2011 April to July. Observations on the 1
m telescope were carried out in
serice mode, gathering 12 to 48 20
s exposres per
night for a total of 69 nights. C18 observations were done for
about 4 hr a night for six
nights in 2011 May. We employ a semiautomated pipeline to calibrate and reduce the
images to the light curves that our group is developing for this purpose, which includes the differential photometry
package DIAPL, written by Wozniak and modi
fi
ed by W. Pych. Several different diagnostics are employed for
search of variability
/
transients. While no high-signi
fi
cance ML event was found in this observational run, we have
detected more than 20
new variables and variable candidates in the M4
fi
eld, which we present here.
