Multiplicity among Young Brown Dwarfs and Very Low Mass Stars

Ahmic, Mirza; Jayawardhana, Ray; Brandeker, Alexis; Scholz, Alexander; Kerkwijk, M. H. van; Delgado-Donate, Eduardo; Froebrich, D.

doi:10.1086/522875

Cited by 47 publications

(64 citation statements)

References 49 publications

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“…DM91 found that G dwarfs tend to have lower mass companions (with a modal mass ratio of q ∼ 0.3), while surveys of M dwarfs by FM92 and RG97 found a flat distribution and several recent surveys of brown dwarfs (e.g., Close et al 2003;Burgasser et al 2003;Bouy et al 2003) found that their mass ratios are sharply peaked toward unity. By contrast, surveys of young associations have found that flat mass ratio distributions seem to dominate across a range of system masses, from ∼2 M to at least as low as 0.5 M (e.g., for Upper Sco), though a distribution biased toward unity seems to be universal among the lowest mass stars and brown dwarfs (Kraus et al 2006;Ahmic et al 2007).…”

Section: The Mass Ratio Distribution Of Wide Binariesmentioning

confidence: 86%

Unusually Wide Binaries: Are They Wide or Unusual?

Kraus

Hillenbrand

2009

ApJ

102

110

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We describe an astrometric and spectroscopic campaign to confirm the youth and association of a complete sample of candidate wide companions in Taurus and Upper Sco. Our survey found 15 new binary systems (three in Taurus and 12 in Upper Sco) with separations of 3 -30 (500-5000 AU) among all of the known members with masses of 2.5-0.012 M . The total sample of 49 wide systems in these two regions conforms to only some expectations from field multiplicity surveys. Higher mass stars have a higher frequency of wide binary companions, and there is a marked paucity of wide binary systems near the substellar regime. However, the separation distribution appears to be log-flat, rather than declining as in the field, and the mass ratio distribution is more biased toward similar-mass companions than the initial mass function or the field G-dwarf distribution. The maximum separation also shows no evidence of a limit at 5000 AU until the abrupt cessation of any wide binary formation at system masses of ∼0.3 M . We attribute this result to the post-natal dynamical sculpting that occurs for most field systems; our binary systems will escape to the field intact, but most field stars are formed in denser clusters and undergo significant dynamical evolution. In summary, only wide binary systems with total masses 0.3 M appear to be "unusually wide."

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Section: The Mass Ratio Distribution Of Wide Binariesmentioning

confidence: 86%

Unusually Wide Binaries: Are They Wide or Unusual?

Kraus

Hillenbrand

2009

ApJ

102

110

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“…Such small separation can have a strong impact on the disk (see e.g., Bitner et al 2010), and may explain why the disk is not detected at PACS wavelengths. However, out the of five M5 stars with known multiplicity, two of them are detected with the Herschel data even at small separation: objects #6 (28.9 separation, Kraus & Hillenbrand 2007) and #15 (0.13 separation Ahmic et al 2007;Lafrenière et al 2008). It does not seem (based on five sources) that binarity can solely explain the low detection rate of M5 stars in the Herschel map of Cha-I.…”

Section: Detection Statistics and Probabilitiesmentioning

confidence: 95%

“…Manoj et al (2011, and references therein) reported that five M5 stars in Cha I are in multiple systems, some of them having small separations. For instance 0.17 separates the primary and secondary of the Cha Ha2 system (Ahmic et al 2007;Lafrenière et al 2008) corresponding to about 28 AU at 165 pc. Such small separation can have a strong impact on the disk (see e.g., Bitner et al 2010), and may explain why the disk is not detected at PACS wavelengths.…”

Section: Detection Statistics and Probabilitiesmentioning

confidence: 99%

TheHerschel/PACS view of disks around low-mass stars in Chamaleon-I

Olofsson¹,

Szücs²,

Henning³

et al. 2013

A&A

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Context. Circumstellar disks are expected to be planet birthplaces. The potential for forming one or more planets of various masses is essentially driven by the initial mass of the disks, a crucial parameter for any planet formation theory. Constraining the masses of disks is of great interest for low-mass stars, which are expected to harbor less massive disks.Aims. We present and analyze Herschel/PACS observations of disk-bearing M-type stars that belong to the young ∼2 Myr old Chamaleon-I star-forming region, to better constrain the properties of the circumstellar material and the stellar mass dependence of these parameters. Methods. We used the radiative transfer code RADMC to successfully model the spectral energy distributions (SEDs) of 17 M-type stars detected at PACS wavelengths. Our modeling strategy is carefully designed so that we search for the most probable disks parameters among a large grid of models, via Bayesian inference, which is an approach that has already proven successful. Results. Based on the modeling results, we first discuss the relatively low detection rates of M5 and later spectral type stars with respect to the PACS sensitivity, and argue that their disks masses, or flaring indices, are likely to be low (M disk ∼ 10 −5 M , γ ∼ 1.1). For M0 to M3 stars, we find a relatively broad range of disk masses (10 −4 -10 −3 M ), scale heights, and flaring indices. Via a parametrization of dust stratification, we can reproduce the peak fluxes of the 10 µm emission feature observed with Spitzer/IRS, and find that disks around M-type stars may display signs of dust sedimentation. We discuss a tentative correlation between the strength of the 10 µm emission feature and the parametrized stratification. Conclusions. The Herschel/PACS observations of low-mass stars in Cha-I provide new constraints on their disk properties, overall suggesting that disk parameters for early M-type stars are comparable to those for more massive stars (e.g., comparable scale height and flaring angles). However, regions of the disks emitting at about 100 µm may still be in the optically thick regime, preventing direct determination of disk masses. Thus the modeled disk masses should be considered as lower limits. Nevertheless, we are able to extend the wavelength coverage of SED models and start characterizing effects, such as dust sedimentation, an effort leading the way towards ALMA observations of these low-mass stars.

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“…(13) supposed by Neuhäuser et al (2002). (14) confirmed by Ahmic et al (2007), Lafrenière et al (2008) and Schmidt et al (2008b). (15) Schmidt et al (2008b).…”

Section: Introductionmentioning

confidence: 91%

“…(8) Neuhäuser et al (2002). (9) see also Ahmic et al (2007) and Lafrenière et al (2008). (10) Brandner (1992).…”

Section: Rx J11094-7627mentioning

confidence: 99%

Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions

Vogt

Schmidt

Neuhäuser

et al. 2012

A&A

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Context. The star-forming regions in Chamaeleon (Cha) are one of the nearest (distance ∼ 165 pc) and youngest (age ∼ 2 Myr) conglomerates of recently formed stars and the ideal target for population studies of star formation. Aims. We investigate a total of 16 Cha targets that have been suggested, but not confirmed, to be binaries or multiple systems in previous literature. Methods. We used the adaptive optics instrument Naos-Conica (NACO) at the Very Large Telescope Unit Telescope (UT) 4 / YEPUN of the Paranal Observatory, at 2-5 different epochs, in order to obtain relative and absolute astrometric measurements, as well as differential photometry in the J, H, and K band. On the basis of known proper motions and these observations, we analyse the astrometric results in our proper motion diagram (PMD: angular separation / position angle versus time), to eliminate possible (non-moving) background stars, establish co-moving binaries and multiples, and search for curvature as indications for orbital motion. Results. All previously suggested close components are co-moving and no background stars are found. The angular separations range between 0.07 and 9 arcsec, corresponding to projected distances between the components of 6-845 AU. Thirteen stars are at least binaries and the remaining three (RX J0919.4-7738, RX J0952.7-7933, VW Cha) are confirmed high-order multiple systems with up to four components. In 13 cases, we found significant slopes in the PMDs, which are compatible with orbital motion whose periods (estimated from the observed gradients in the position angles) range from 60 to 550 years. However, in only four cases there are indications of a curved orbit, the ultimate proof of a gravitational bond. Conclusions. A statistical study based on the 2MASS catalogue confirms the high probability of all 16 stellar systems being gravitationally bound. Most of the secondary components are well above the mass limit of hydrogen burning stars (0.08 M ), and have masses twice as high as this value or more. Massive primary components appear to avoid the simultaneous formation of equal-mass secondary components, while extremely low-mass secondary components are hard to find for both high and low mass primaries owing to the much higher dynamic range and the faintness of the secondaries.

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Multiplicity among Young Brown Dwarfs and Very Low Mass Stars

Cited by 47 publications

References 49 publications

Unusually Wide Binaries: Are They Wide or Unusual?

Unusually Wide Binaries: Are They Wide or Unusual?

TheHerschel/PACS view of disks around low-mass stars in Chamaleon-I

Astrometric confirmation of young low-mass binaries and multiple systems in the Chamaeleon star-forming regions

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