Dynamical biasing in binary star formation: implications for brown dwarfs in binaries

McDonald, J. M.; Clarke, C. J.

doi:10.1093/mnras/262.3.800

Cited by 60 publications

(40 citation statements)

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“…These aggregates experience rapid dynamical decay and eventually leave a bound binary system, while other fragments are dynamically ejected mostly as single remnants (e.g., McDonald & Clarke 1993, 1995Sterzik & Durisen 1998). Since few-body interactions occur on a small scale within protostellar aggregates (r ∼ a few 100 AU) and on a very short time scale (∼10 4 yr), the resulting primordial binary fraction is not expected to depend strongly upon the global properties of the star forming region.…”

Section: A Universal Mechanism For Binary Formation?mentioning

confidence: 99%

The formation and evolution of binary systems

Bouvier

Duchêne

Mermilliod

et al. 2001

A&A

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Abstract. With the aim of investigating the binary population of the 700 Myr old Praesepe cluster, we have observed 149 G and K-type cluster members using adaptive optics. We detected 26 binary systems with an angular separation ranging from less than 0.08 to 3.3 arcsec (15-600 AU). After correcting for detection biases, we derive a binary frequency (BF) in the log P (days) range from 4.4 to 6.9 of 25.3 ± 5.4%, which is similar to that of field G-type dwarfs ( We compare the distribution of cluster binaries to the binary populations of star forming regions, most notably Orion and Taurus, to critically review current ideas regarding the binary formation process. We conclude that it is still unclear whether the lower binary fraction observed in young clusters compared to T associations is purely the result of the early dynamical disruption of primordial binaries in dense clusters or whether it reflects intrinsically different modes of star formation in clusters and associations. We also note that if Taurus binaries result from the dynamical decay of small-N protostellar aggregates, one would predict the existence of a yet to be found dispersed population of mostly single substellar objects in the Taurus cloud.

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Section: A Universal Mechanism For Binary Formation?mentioning

confidence: 99%

The formation and evolution of binary systems

Bouvier

Duchêne

Mermilliod

et al. 2001

A&A

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“…McDonald & Clarke (1993) investigated binary formation by dynamical capture within a small cluster and suggested that the binary frequency decreases with decreasing primary mass. The fact that the binary frequency has no correlation with the primary mass in the Taurus YSOs rejects such a dynamical capture process as the binary formation mechanism.…”

Section: Binary Frequencymentioning

confidence: 99%

A Near-Infrared Search for Companions around Very Low Luminosity Young Stellar Objects in Taurus

Itoh

Tamura

Nakajima

1999

The Astronomical Journal

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We have carried out a near-infrared search for companions around 23 very low luminosity young stellar objects (YSOs) in the Taurus molecular cloud. After sophisticated photometry and analysis, Ðve extremely low luminosity YSO (ELL-YSO) candidate companions were identiÐed by both their nearinfrared colors and proximity to the primary (separation less than 6A). They show infrared excess, as do ordinary YSOs. Their absolute J-band magnitudes range from 9 to 12 mag. The masses of these companions are estimated from their J-band luminosities, which use recent evolutionary tracks for very low mass objects. It is found that all are young brown dwarf candidates. The Ks-band magnitude di †erence between the ELL-YSO candidate companions and their primaries ranges from 2 to 6 mag, signiÐcantly larger than observed in T Tauri binaries. It is suggested that the companions are formed by the fragmentation of a disk around the primary. The binary frequency is for systems with a period ranging 22~1 0 9 % between 107È108 days. This frequency is consistent with that of T Tauri stars, but it is signiÐcantly higher than that of low-mass main-sequence stars.

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“…Traditionally, these classes of models have been divided into capture and fragmentation scenarios. Capture refers to the tidal capture of two unbound objects on a timescale that is long compared to the collapse time of each component (e.g., McDonald & Clarke 1993). For each primary star the mass of the secondary is chosen randomly from the single star mass function and the secondary mass distribution would reflect the IMF.…”

Section: Introductionmentioning

confidence: 99%

Binary Formation Mechanisms: Constraints From the Companion Mass Ratio Distribution

Reggiani

Meyer

2011

ApJ

104

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We present a statistical comparison of the mass ratio distribution of companions, as observed in different multiplicity surveys, to the most recent estimate of the single-object mass function. The main goal of our analysis is to test whether or not the observed companion mass ratio distribution (CMRD) as a function of primary star mass and star formation environment is consistent with having been drawn from the field star initial mass function (IMF). We consider samples of companions for M dwarfs, solar-type stars, and intermediate-mass stars, both in the field as well as clusters or associations, and compare them with populations of binaries generated by random pairing from the assumed IMF for a fixed primary mass. With regard to the field we can reject the hypothesis that the CMRD was drawn from the IMF for different primary mass ranges: the observed CMRDs show a larger number of equal-mass systems than predicted by the IMF. This is in agreement with fragmentation theories of binary formation. For the open clusters α Persei and the Pleiades we also reject the IMF random-pairing hypothesis. Concerning young star-forming regions, currently we can rule out a connection between the CMRD and the field IMF in Taurus but not in Chamaeleon I. Larger and different samples are needed to better constrain the result as a function of the environment. We also consider other companion mass functions and we compare them with observations. Moreover the CMRD both in the field and clusters or associations appears to be independent of separation in the range covered by the observations. Combining therefore the CMRDs of M (1-2400 AU) and G (28-1590 AU) primaries in the field and intermediate-mass primary binaries in Sco OB2 (29-1612 AU) for mass ratios, q = M 2 /M 1 , from 0.2 to 1, we find that the best chi-square fit follows a power law dN/dq ∝ q β , with β = −0.50 ± 0.29, consistent with previous results. Finally, we note that the Kolmogorov-Smirnov test gives a ∼1% probability of the observed CMRD in the Pleiades and Taurus being consistent with that observed for solar-type primaries in the field over comparable primary mass range. This highlights the value of using CMRDs to understand which star formation events contribute most to the field.

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Dynamical biasing in binary star formation: implications for brown dwarfs in binaries

Cited by 60 publications

References 0 publications

The formation and evolution of binary systems

The formation and evolution of binary systems

A Near-Infrared Search for Companions around Very Low Luminosity Young Stellar Objects in Taurus

Binary Formation Mechanisms: Constraints From the Companion Mass Ratio Distribution

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