Subject: m. shara's abstract

From: Mike Shara <[email-masked]>
Date: Thu, 20 Apr 95 19:36:34 EDT

Searches for Variables in Globular Cluster Cores

Close binaries are widely believed to exist in large numbers in the cores
of globular clusters. If present, these binaries are critical sources and sinks of energy that drive the dynamical evolution of their host clusters.

I report on groundbased and HST searches for binaries (based on variability)
in the outskirts and cores of several globular clusters; dwarf nove
and contact binaries should be particularly easy to find. Dense and
loose clusters have been thoroughly searched on timescales 
ranging from minutes to years.

Detailed simulations demonstrate that virtually all binaries with M < 8,
amplitudes > 0.1 mag and periods of 2-20 hours should have been found. This
includes virtually all known contact binaries.

At least 1/3 of all dwarf novae present in several globulars should also have
been seen (very easily!) in eruption at M=4-6 .

Simple tidal capture theory predicts that dozens of interacting binaries should
have been found in our searches; the observed number is typically one
or two objects per cluster. Unless tidal capture binaries are rapidly
destroyed, ejected, or much fainter than their Galactic counterparts, 
we must conclude that very close binaries in globular cores are rare,
and that their total influence on cluster dynamical evolution is less
than currently claimed.