Binary Formation Mechanisms: Constraints From the Companion Mass Ratio Distribution

Reggiani, Maddalena; Meyer, Michael

doi:10.1088/0004-637x/738/1/60

Cited by 105 publications

(86 citation statements)

References 50 publications

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“…However, Reggiani & Meyer (2011) found an uncertainty on this power-law slope of dN dq ∼ q −0.5±0.29 . This implies that the observed mass ratio distribution is still consistent with being flat at the two sigma level.…”

Section: Flat Mass Ratio Distributionmentioning

confidence: 95%

“…For the period distribution we use the log-normal distribution with a mean period of 5.03 and a dispersion of 2.28 in log 10 days, which was found by Raghavan et al (2010). For the secondary to primary mass ratio (q) we use the power-law from Reggiani & Meyer (2011) of dN dq ∼ q −0.5 for 0.1 < q < 1. By setting the maximum q to one we make the assumption that the observed (brightest) star in a binary will always be the most massive one.…”

Section: Binary Propertiesmentioning

confidence: 99%

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Characterizing a cluster’s dynamic state using a single epoch of radial velocities

Cottaar

Meyer

Parker

2012

A&A

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Context. Radial velocity measurements can be used to constrain the dynamical state of a stellar cluster. However, for clusters with velocity dispersions smaller than a few km s −1 the observed radial velocity distribution tends to be dominated by the orbital motions of binaries rather than the stellar motions through the potential well of the cluster. Aims. Our goal is to characterize the intrinsic velocity distribution of a cluster from a single epoch of radial velocity data even for a cluster with a velocity dispersion of a fraction of a km s −1 . Methods. We investigate a maximum likelihood procedure, which has been pioneered in the literature about ten years ago. Assuming a period, mass ratio, and eccentricity distribution for the binaries in the observed cluster this procedure fits a dynamical model describing the velocity distribution for the single stars and center of masses of the binaries, simultaneously with the radial velocities caused by binary orbital motions, using all the information available in the observed velocity distribution. We test the capability of this procedure to reproduce the velocity dispersion of an observed cluster, using radial velocity data of an open cluster and Monte Carlo simulations. Results. We find that the fits to the intrinsic velocity distribution depend only weakly on the binary properties assumed, so the uncertainty in the fitted parameters tends to be dominated by statistical uncertainties. Based on a large suite of Monte Carlo simulations we provide an estimate of how these statistical uncertainties vary with the velocity dispersion, binary fraction, and the number of observed stars, which can be used to estimate the sample size needed to reach a specific accuracy. Finally we test the method on the well-studied open cluster NGC 188, showing that it can successfully reproduce a velocity dispersion of only 0.5 km s −1 using a single epoch of the multi-epoch radial velocity data. Conclusions. If the binary period, mass ratio, and eccentricity distribution of the observed stars are roughly known, this procedure can be used to correct for the effect of binary orbital motions on an observed velocity distribution. This allows for the study of the dynamical state of a stellar cluster with a small velocity dispersion from a single epoch of radial velocity data.

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Section: Flat Mass Ratio Distributionmentioning

confidence: 95%

Section: Binary Propertiesmentioning

confidence: 99%

Characterizing a cluster’s dynamic state using a single epoch of radial velocities

Cottaar

Meyer

Parker

2012

A&A

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“…Concerning the mass-ratio distribution, we draw two masses randomly (in Model A) from the same single IMF in order to get the primary and the secondary masses; the approach adopted by Kroupa (1995a). For all other models (except Model D) we adopted a flat mass-ratio distribution (Reggiani & Meyer 2011), and the IMF used to obtain the mass for the primary had to adjusted (see Sect. 6.1) so that once the pairing is done we retrieve the single IMF from Chabrier (2005) presented above.…”

Section: Binary Propertiesmentioning

confidence: 99%

“…Nevertheless, recent studies of both the Galactic field (Raghavan et al 2010;Reggiani & Meyer 2011) and star forming regions (Kraus et al 2008(Kraus et al , 2011 indicate that, whereas there is no clear and unique best fit, a flat mass ratio distribution may be a better fit than a random pairing. Since this would result in a slightly smaller number of very low mass companions, we may expect the criterion on N 4 to be better fulfilled.…”

Section: Binary Pairing (Model B)mentioning

confidence: 99%

Reverse dynamical evolution ofηChamaeleontis

Becker

Moraux

Duchêne

et al. 2013

A&A

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Context. In the scope of the star formation process, it is unclear how the environment shapes the initial mass function (IMF). While observations of open clusters propose a universal picture for the IMF from the substellar domain up to a few solar masses, the young association η Chamaeleontis presents an apparent lack of low mass objects (m < 0.1 M ). Another unusual feature of this cluster is the absence of wide binaries with a separation >50 AU. Aims. We aim to test whether dynamical evolution alone can reproduce the peculiar properties of the association under the assumption of a universal IMF. Methods. We use a pure N-body code to simulate the dynamical evolution of the cluster for 10 Myr, and compare the results with observations. A wide range of values for the initial parameters are tested (number of systems, typical radius of the density distribution and virial ratio) in order to identify the initial state that would most likely lead to observations. In this context we also investigate the influence of the initial binary population on the dynamics and the possibility of having a discontinuous single IMF near the transition to the brown dwarf regime. We consider as an extreme case an IMF with no low mass systems (m < 0.1 M ). Results. The initial configurations cover a wide range of initial density, from 10 2 to 10 8 stars/pc 3 , in virialized, hot and cold dynamical state. We do not find any initial state that would evolve from a universal single IMF to fit the observations. Only when starting with a truncated IMF without any very low mass systems and no wide binaries, can we reproduce the cluster core properties with a success rate of 10% at best. Conclusions. Pure dynamical evolution alone cannot explain the observed properties of η Chamaeleontis from universal initial conditions. The lack of brown dwarfs and very low mass stars, and the peculiar binary properties (low binary fraction and lack of wide binaries), are probably the result of the star formation process in this association.

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“…Several surveys in the past decades focused on the detection of stellar binaries with the purpose of characterizing the occurrence of companions and their mass distribution both in the field (e.g., Raghavan et al 2010;Janson et al 2012) and in star-forming regions (e.g., Patience et al 2002). Reggiani & Meyer (2013), in an update of Reggiani & Meyer (2011), have shown that in the field the CMRD is consistent with being universal, independent of primary mass and separation in the range covered by the observations, and can be fit by a single power-law slope dN/dq ∝ q β , with β = 0.25 ± 0.29. In addition, N-body simulations suggest that the CMRD is only modestly affected by dynamics, even in dense clusters, as opposed to the semimajor axis (SMA) distribution (Parker & Reggiani 2013).…”

Section: Introductionmentioning

confidence: 99%

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

Reggiani

Meyer

Chauvin

et al. 2016

A&A

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Context. In recent years there have been many attempts to characterize the occurrence and distribution of stellar, brown dwarf (BD), and planetary-mass companions to solar-type stars with the aim of constraining formation mechanisms. From radial velocity observations a dearth of companions with masses between 10-40 M Jupiter has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. Aims. We present a model for the substellar companion mass function (CMF). This model consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the radial velocity measured CMF for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program (NaCo-LP) and the complementary archive datasets, which probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. Methods. We developed a Monte Carlo simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions (mass, semimajor axis, eccentricity, and inclination). Comparing the predictions with the results of the observations, we calculate the likelihood of different models and which models can be ruled out. Results. Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius ( 100 AU) is introduced for the planet separation distribution. Some regions of parameter space can be excluded by the observations. Conclusions. We conclude that the results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 M Jupiter , in agreement with radial velocity measurements. In this picture the dearth of objects in this mass range would naturally arise from the shape of the mass distribution, without the introduction of any distinct formation mechanism for BDs. This kind of model for the CMF allows us to determine the probability for a substellar companion as a function of mass to have formed in a disk or from protostellar core fragmentation, as such mechanisms overlap in this mass range.

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Binary Formation Mechanisms: Constraints From the Companion Mass Ratio Distribution

Cited by 105 publications

References 50 publications

Characterizing a cluster’s dynamic state using a single epoch of radial velocities

Characterizing a cluster’s dynamic state using a single epoch of radial velocities

Reverse dynamical evolution ofηChamaeleontis

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits

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