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Abstract: I have undertaken a comprehensive statistical investigation of the ultracooldwarf companion distribution spectral type M6 and later. Utilizing a Bayesianalgorithm, I tested models of the companion distribution against data from anextensive set of space and ground-based imaging observations of nearbyultracool dwarfs. My main conclusions are fivefold: 1 Confirm that theconcentration of high mass ratio ultracool binary systems is a fundamentalfeature of the companion distribution, not an observational or selection bias;2 Determine that the wide >~20 AU binary frequency can be no more the 1-2%;3 Show that the decreasing binary frequency with later spectral types is areal trend; 4 Demonstrate that a large population of currently undetected lowmass ratio systems are not consistent with the current data; 5 Find that thepopulation of spectroscopic binaries must be be at least 30% that of currentlyknown ultracool binaries. The best fit value for the overall M6 and laterbinary frequency is ~20%-22%, of which only ~6% consists of currentlyundetected companions with separations less than 1 AU. If this is correct, thenthe upper limit of the ultracool binary population discovered to date is ~75%.I find that the numerical simulation results of the ejection formation methodare inconsistent with the outcome of this analysis. However, dynamics do seemto play an important role as simulations of small-N clusters and triple systemdecays produce results similar to those of this work. The observational effortsrequired to improve these constraints are shown to be primarily largespectroscopic binary surveys and improved high-resolution imaging techniques.



Autor: Peter R. Allen

Fuente: https://arxiv.org/







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