NICMOS Kernel-Phase Interferometry II: Demographics of Nearby Brown Dwarfs

Abstract

Star formation theories have struggled to reproduce binary brown dwarf population demographics (frequency, separation, mass-ratio). Kernel-phase interferometry is sensitive to companions at separations inaccessible to classical imaging, enabling tests of formation at new physical scales below the hydrogen burning limit. We analyze the detections and sensitivity limits from our previous kernel-phase analysis of archival HST/NICMOS surveys of field brown dwarfs. After estimating physical properties of the 105 late M to T dwarfs using Gaia distances and evolutionary models, we use a Bayesian framework to compare these results to a model companion population defined by log-normal separation and power-law mass-ratio distributions. When correcting for Malmquist bias, we find a companion fraction of $F=0.11_{-0.03}^{+0.04}$ and a separation distribution centered at $\rho =2.2_{-1.0}^{+1.2}$ au, smaller and tighter than seen in previous studies. We also find a mass-ratio power-law index which strongly favors equal-mass systems: $\gamma =4.0_{-1.5}^{+1.7}-11_{-3}^{+4}$ depending on the assumed age of the field population ($0.9-3.1$ Gyr). We attribute the change in values to our use of kernel-phase interferometry which enables us to resolve the peak of the semimajor axis distribution with significant sensitivity to low-mass companions. We confirm the previously-seen trends of decreasing binary fraction with decreasing mass and a strong preference for tight and equal-mass systems in the field-age sub-stellar regime; only $0.9_{-0.6}^{+1.1}$ % of systems are wider than 20 au and $<1.0_{-0.6}^{+1.4}$% of systems have a mass-ratio $q<0.6$. We attribute this to turbulent fragmentation setting the initial conditions followed by a brief period of dynamical evolution, removing the widest and lowest-mass companions, before the birth cluster dissolves.

arXiv commentAccepted for publication in AJ, 20 pages, 9 figures (including 5 figure sets available at https://zenodo.org/record/7370349 and data behind the figure available at https://zenodo.org/record/7065651), 5 tables

References in corpus (78)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Embedded Clusters in Molecular Clouds
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• A Survey of Stellar Families: Multiplicity of Solar-Type Stars
• A Non-Gray Theory of Extrasolar Giant Planets and Brown Dwarfs
• Stellar Multiplicity
• Evolutionary models for very-low-mass stars and brown dwarfs with dusty atmospheres
• The Theory of Brown Dwarfs and Extrasolar Giant Planets
• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• A Giant Planet Candidate near a Young Brown Dwarf
• The Formation of Brown Dwarfs as Ejected Stellar Embryos
• The Hawaii Infrared Parallax Program. I. Ultracool Binaries and the L/T Transition
• Stellar, brown dwarf and multiple star properties from a radiation hydrodynamical simulation of star cluster formation
• The Formation of a Bound Star Cluster: From the Orion Nebula Cluster to the Pleiades
• Stellar, Brown Dwarf, and Multiple Star Properties from Hydrodynamical Simulations of Star Cluster Formation
• Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with the Hubble Space Telescope WPFC2
• The Formation Mechanism of Brown Dwarfs
• The properties of brown dwarfs and low-mass hydrogen-burning stars formed by disc fragmentation
• Fundamental Parameters and Spectral Energy Distributions of Young and Field Age Objects with Masses Spanning the Stellar to Planetary Regime
• The VAST Survey - III. The multiplicity of A-type stars within 75 pc
• Detection of Nine M8.0-L0.5 Binaries: The Very Low Mass Binary Population and its Implications for Brown Dwarf and VLM Star Formation
• A new set of atmosphere and evolution models for cool T-Y brown dwarfs and giant exoplanets
• The Effects of Radiative Transfer on Low-Mass Star Formation
• Multiplicity of Nearby Free-floating Ultra-cool Dwarfs: a HST-WFPC2 search for companions
• Mapping the Shores of the Brown Dwarf Desert II: Multiple Star Formation in Taurus-Auriga
• The Formation of Low-Mass Binary Star Systems Via Turbulent Fragmentation
• The Hawaii Infrared Parallax Program. II. Young Ultracool Field Dwarfs
• The Formation and Early Evolution of Low-mass Stars and Brown Dwarfs
• Distances, Luminosities, and Temperatures of the Coldest Known Substellar Objects
• A search for L dwarf binary systems
• Hubble Space Telescope NICMOS Observations of T Dwarfs: Brown Dwarf Multiplicity and New Probes of the L/T Transition
• The NIRSPEC Ultracool Dwarf Radial Velocity Survey
• Hubble Space Telescope Observations of Binary Very-Low-Mass Stars and Brown Dwarfs
• The Solar Neighborhood XLV. The Stellar Multiplicity Rate of M Dwarfs Within 25 pc
• Individual Dynamical Masses of Ultracool Dwarfs
• Gravitational fragmentation and the formation of brown dwarfs in stellar clusters
• A search for binary systems among the nearest L dwarfs
• The dynamics and outcome of star formation with jets, radiation, winds, and supernovae in concert
• The Wide Brown Dwarf Binary Oph 1622-2405 and Discovery of A Wide, Low Mass Binary in Ophiuchus (Oph 1623-2402): A New Class of Young Evaporating Wide Binaries?
• Preliminary Trigonometric Parallaxes of 184 Late-T and Y Dwarfs and an Analysis of the Field Substellar Mass Function into the "Planetary" Mass Regime
• Photometry and Proper Motions of M, L, and T Dwarfs from the Pan-STARRS1 3$\pi$ Survey
• A Survey for Spectroscopic Binaries Among Very Low-Mass Stars
• Discovery of a Planetary-mass Companion to a Brown Dwarf in Taurus
• The First Discovery of a Wide Binary Brown Dwarf
• On the Distribution of Orbital Eccentricities for Very Low-Mass Binaries
• A Volume-Limited Sample of Ultracool Dwarfs. I. Construction, Space Density, and a Gap in the L/T Transition
• Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association
• Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions
• Discovery of a Wide Binary Brown Dwarf Born in Isolation
• On the origin of the distribution of binary-star periods
• Constraining the multiplicity statistics of the coolest brown dwarfs: binary fraction continues to decrease with spectral type
• An Adaptive Optics Survey of M8-M9 Stars: Discovery of 4 Very Low mass Binaries With at Least One System Containing a Brown Dwarf Companion
• Multiplicity and Optical Excess Across the Substellar Boundary in Taurus
• Multiple Star Formation to the Bottom of the IMF
• The Hawaii Infrared Parallax Program. IV. A Comprehensive Parallax Survey of L0-T8 dwarfs with UKIRT
• On the universal outcome of star-formation: Is there a link between stars and brown-dwarfs?
• Binary frequency of very young brown dwarfs at separations smaller than 3 AU
• The Decay of Accreting Triple Systems as Brown Dwarf Formation Scenario
• Multiplicity at the Stellar/Substellar Boundary in Upper Scorpius
• Dancing in the Dark: New Brown Dwarf Binaries from Kernel Phase Interferometry
• Discovery of the Widest Very Low Mass Field Binary
• Protostellar Feedback in Turbulent Fragmentation: Consequences for Stellar Clustering and Multiplicity
• Brown Dwarf Binaries from Disintegrating Triple Systems
• Undetected Binary Stars Cause an Observed Mass Dependent Age Gradient in Upper Scorpius
• WISE2150-7520AB: A very low mass, wide co-moving brown dwarf system discovered through the citizen science project Backyard Worlds: Planet 9
• Binary stars in Upper Scorpius
• Constraints on the binary Properties of mid to late T dwarfs from Hubble Space Telescope WFC3 Observations
• The dynamical evolution of very-low mass binaries in open clusters
• A wide planetary-mass companion to a young low-mass brown dwarf in Ophiuchus
• Binary Formation in the Orion Nebula Cluster: Exploring the Sub-stellar Limit
• Beyond the Local Volume. II. Population Scaleheights and Ages of Ultracool Dwarfs in Deep HST/WFC3 Parallel Fields
• Demographics of the M-star Multiple Population in the Orion Nebula Cluster
• NICMOS Kernel-Phase Interferometry I: Catalogue of Brown Dwarfs Observed in F110W and F170M

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