Close binary systems among very low‐mass stars and brown dwarfs

Jeffries, R. D.; Maxted, P. F. L.

doi:10.1002/asna.200510451

Cited by 14 publications

(24 citation statements)

References 21 publications

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“…The wider variation in a in the asymmetric Gaussian model allows the possibility of a significantly broader distribution to smaller separations. This would result in a large population of currently undetected spectroscopic binaries, as predicted in Jeffries & Maxted (2005).…”

Section: Model Parameter Resultsmentioning

confidence: 93%

“…This is similar to the separation distributions derived for higher mass primaries ( Duquennoy & Mayor 1991;Fischer & Marcy 1992). However, I will also consider an asymmetric Gaussian shape, as described in Jeffries & Maxted (2005). They use this shape to statistically examine the likelihood of spectroscopic binaries at separations less than 1Y2 AU, and introduce a sharp cutoff at 10Y20 AU to account for the lack of wide companions.…”

Section: Separation Distributionmentioning

confidence: 89%

“…The asymmetric Gaussian model of Jeffries & Maxted (2005) is constructed by multiplying equation (2) by a strong exponential cutoff beginning at 10 AU.…”

Section: Separation Distributionmentioning

confidence: 99%

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Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions

Allen¹

2007

ApJ

156

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I have undertaken a comprehensive statistical investigation of the ultracool dwarf companion distribution (spectral type M6 and later). Utilizing a Bayesian algorithm, I tested models of the companion distribution against data from an extensive set of space and ground-based imaging observations of nearby ultracool dwarfs. My main conclusions are fivefold: (1) confirm that the concentration of high mass ratio ultracool binary systems is a fundamental feature of the companion distribution, not an observational or selection bias; (2) determine that the wide (>$20 AU ) binary frequency can be no more than 1%Y2%; (3) show that the decreasing binary frequency with later spectral types is a real trend; (4) demonstrate that a large population of currently undetected low mass ratio systems are not consistent with the current data; and (5) find that the population of spectroscopic binaries must be at least 30% that of currently known ultracool binaries. The best-fit value for the overall M6 and later binary frequency is $20%Y22%, of which only $6% consists of currently undetected companions with separations less than 1 AU. If this is correct, then the upper limit of the ultracool binary population discovered to date is $75%. I find that the numerical simulation results of the ejection formation method are inconsistent with the outcome of this analysis. However, dynamics do seem to play an important role, as simulations of small-N clusters and triple system decays produce results similar to those of this work. The observational efforts required to improve these constraints are shown to be primarily large spectroscopic binary surveys and improved high-resolution imaging techniques.

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Section: Model Parameter Resultsmentioning

confidence: 93%

Section: Separation Distributionmentioning

confidence: 89%

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Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions

Allen¹

2007

ApJ

156

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“…This choice is motivated by the facts that first, in any galaxy, half of the massive stars are in binary systems, and second, that the fraction of massive stars in close binary systems (namely those which can give rise to SNe Ib/c) can be reasonably estimated at ∼30%, i.e. similar to the close binary frequency predicted for low mass systems (Jeffries & Maxted 2005). Therefore the estimated value for this parameter is given by:…”

Section: Snr Ib/c Modelsmentioning

confidence: 99%

The connection between gamma-ray bursts and supernovae Ib/c

Bissaldi¹,

Calura

Matteuccí

et al. 2007

A&A

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Context. It has been established that Gamma-Ray Bursts (GRBs) are connected to Supernovae (SNe) explosions of type Ib/c. Aims. We intend to test whether the hypothesis of type Ib/c SNe from different massive progenitors can reproduce the local GRB rate as well as the GRB rate as a function of redshift. We aim to predict the GRB rate at very high redshift under different assumptions about galaxy formation and star formation histories in galaxies. Methods. We assume different star formation histories in galaxies of different morphological types: ellipticals, spirals and irregulars, which have already been tested in self-consistent galaxy models reproducing both chemical and photometrical properties of galaxies. We explore different hypotheses concerning the progenitors of type Ib/c SNe: i) single massive stars (M > 25 M , Wolf-Rayet stars), ii) massive close binaries (12-20 M ), and iii) both Wolf-Rayet stars and massive binaries. We conclude that the mixed scenario (iii) is preferable to reproduce the local type Ib/c SN rates in galaxies and we adopt this scenario for comparison with the GRB rates. Results. We find an excellent agreement between the observed GRB local rate and the predicted type Ib/c SN rate in irregular galaxies, when a range for single Wolf-Rayet stars of 40-100 M is adopted. We also predict the cosmic type Ib/c SN rate by taking into account all the galaxy types in a unitary volume of the Universe and we compare it with the observed cosmic GRB rate as a function of redshift. By assuming the formation of spheroids at high redshift, we predict a cosmic type Ib/c SN rate, which is always higher than the GRB rate, suggesting that only a small fraction (0.1-1%) of type Ib/c SNe become GRBs. In particular, we find a ratio between the cosmic GRB rate and the cosmic type Ib/c rate in the range 10 −2 -10 −3 , in agreement with previous estimates. Finally, due to the high rate of star formation in spheroids at high redshift, which is our preferred scenario for galaxy formation, we predict more GRBs at high redshift than in the hierarchical scenario for galaxy formation, a prediction which remains to be proven by future observations.

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“…That fraction apparently drops further for late M dwarfs to 9 +4 −3 % beyond 3 AU (Siegler et al 2005), compared to 18±4% for early-M dwarfs over the same separation range. The total binary fraction of late-M dwarfs is however uncertain, because current observations have limited sensitivity to significantly closer binaries, which have been suggested to be fairly numerous (Jeffries & Maxted 2005). We are therefore observing with adaptive optics (AO) a well defined, nominally volume limited, sample of Based on observations obtained at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique of France, and the University of Hawaii; and observations made at the European Southern Observatory, Paranal, Chile through proposal 075.C-0733(A) and GTO NACO.…”

Section: Introductionmentioning

confidence: 98%

Five new very low mass binaries

Montagnier

Ségransan

Beuzit³

et al. 2006

A&A

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We report the discovery of companions to 5 nearby late M dwarfs (>M5), LHS1901, LHS4009, LHS6167, LP869-26 and WT460, and we confirm that the recently discovered mid-T brown dwarf companion to SCR1845-6357 is physically bound to that star. These discoveries result from our adaptive optics survey of all M dwarfs within 12 pc. The new companions have spectral types M5 to L1, and orbital separations between 1 and 10 AU. They add significantly to the number of late M dwarfs binaries in the immediate solar neighbourhood, and will improve the multiplicity statistics of late M dwarfs. The expected periods range from 3 to 130 years. Several pairs thus have good potential for accurate mass determination in this poorly sampled mass range.

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Close binary systems among very low‐mass stars and brown dwarfs

Cited by 14 publications

References 21 publications

Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions

Star Formation via the Little Guy: A Bayesian Study of Ultracool Dwarf Imaging Surveys for Companions

The connection between gamma-ray bursts and supernovae Ib/c

Five new very low mass binaries

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