Are there brown dwarfs in globular clusters?

Abstract

We present an analytical method for constraining the substellar initial mass function in globular clusters, based on the observed frequency of transit events. Globular clusters typically have very high stellar densities where close encounters are relatively common, and thus tidal capture can occur to form close binary systems. Encounters between main sequence stars and lower-mass objects can result in tidal capture if the mass ratio is > 0.01. If brown dwarfs exist in significant numbers, they too will be found in close binaries, and some fraction of their number should be revealed as they transit their stellar companions. We calculate the rate of tidal capture of brown dwarfs in both segregated and unsegregated clusters, and find that the tidal capture is more likely to occur over an initial relaxation time before equipartition occurs. The lack of any such transits in recent HST monitoring of 47 Tuc implies an upper limit on the frequency of brown dwarfs (< 15 % relative to stars) which is significantly below that measured in the galactic field and young clusters.

MNRAS in press

References in corpus (3)

• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• A Study of the Luminosity and Mass Functions of the Young IC 348 Cluster using FLAMINGOS Wide-Field Near-Infrared Images
• A Substellar Mass Function for Alpha Per

Cited by in corpus (6)

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• Mergerburst Transients of Brown Dwarfs with Exoplanets
• Accretion of sub-stellar companions as the origin of chemical abundance inhomogeneities in globular clusters
• An upper limit for the growth of inner planets?
• Forming short period sub-stellar companions in 47 Tuc: I. Dynamical model and brown dwarf tidal capture rates
• Uncovering the Rapidly Evolving Orbits of the Dynamic TOI-201 System