Formation of Low-Mass Stars and Brown Dwarfs

Hennebelle, P.

doi:10.1051/eas/1257003

Cited by 4 publications

(3 citation statements)

References 140 publications

(218 reference statements)

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“…recently summarised, for example, by Bastian et al (2010), Kroupa et al (2011), andJeffries (2012). In the substellar regime, the characterization of the mass spectrum of a cluster gains another importance, since it could help distinguish among different formation scenarios for brown dwarfs (e.g., Hennebelle 2012). This is the goal of a large programme (P.I.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses

Oliveira

Moraux

Bouvier

et al. 2013

A&A

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Context. Brown dwarfs represent a sizable fraction of the stellar content of our Galaxy and populate the transition between the stellar and planetary mass regime. There is, however, no agreement on the processes responsible for their formation. Aims. We have conducted a large survey of the young, nearby cluster IC 348, to uncover its low-mass brown dwarf population and have studied the cluster properties in the substellar regime. Methods. Deep optical and near-IR images taken with MegaCam and WIRCam at the Canada-France-Hawaii Telescope (CFHT) were used to select photometric candidate members. A spectroscopic follow-up of a large fraction of the candidates was conducted to assess their youth and membership. Results. We confirmed spectroscopically 16 new members of the IC 348 cluster, including 13 brown dwarfs, contributing significantly to the substellar census of the cluster, where only 30 brown dwarfs were previously known. Five of the new members have a L0 spectral type, the latest-type objects found to date in this cluster. At 3 Myr, evolutionary models estimate these brown dwarfs to have a mass of ∼13 M Jup . Combining the new members with previous census of the cluster, we constructed the initial mass function (IMF) complete down to 13 M Jup . Conclusions. The IMF of IC 348 is well fitted by a log-normal function and we do not see evidence for variations of the mass function down to planetary masses when compared to other young clusters.

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Section: Introductionmentioning

confidence: 99%

Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses

Oliveira

Moraux

Bouvier

et al. 2013

A&A

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“…We have addressed the question of whether the fields threading the gas are swept along by it by estimating the timescale for ambipolar diffusion of the field out of the gas, following Eq. (2.18) of Hennebelle (2012), which shows that the diffusion time varies as n · n i (L/B) 2 where n and n i are the number densities of atoms and of ions, respectively, L is a characteristic length scale and B is the field strength. For our extended and thin flows (L ∼ 1000 AU, n ∼ 0.3×10 3 cm −3 and for characteristic numbers of the ionization fractions in the cold gas and with B set to a few microGauss (Padoan 2018), diffusion timescales are at least one order of magnitude greater than 10 6 years.…”

Section: The Turbulent Casementioning

confidence: 96%

Dust cleansing of star-forming gas

Gustafsson

2018

A&A

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Aims. The possibility that the chemical composition of the solar atmosphere has been affected by radiative dust cleansing of late and weak accretion flows by the proto-sun itself is explored. Methods. Estimates, using semi-analytical methods and numerical simulations of the motion of dust grains in a collapsing nonmagnetic and non-rotating gas sphere with a central light source are made in order to model possible dust-cleansing effects.Results. Our calculations indicate that the amount of cleansed material may well be consistent with the abundance differences observed for the Sun when compared with solar-like stars and with the relations found between these differences and the condensation temperature of the element. Conclusions. It seems quite possible that the proposed mechanism produced the significant abundance effects observed for the Sun, provided that late and relatively weak accretion did occur. The effects of cleansing may, however, be affected by outflows from the Sun, the existence and dynamics of magnetic fields and of the accretion disk, and the possible presence and location of the early Sun in a rich stellar cluster.

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“…Brown dwarfs are substellar objects whose masses are intermediate between the latest M-type stars and the most massive planets (Hayashi & Nakano 1963;Shu 1977;Becklin & Zuckerman 1988;Rebolo et al 1995;Oppenheimer et al 1995;Saumon et al 2006). Similar to stars, brown dwarfs form from interstellar molecular gas cloud core collapse (Uehara & Inutsuka 2000; Bate et al 2002;Krumholz et al 2005;Whitworth & Stamatellos 2006;Chabrier et al 2007; Corresponding author: Joe Zalesky jazalesk@asu.edu Whitworth et al 2007;Hennebelle 2012), but do not achieve masses high enough to sustain core H-fusion over their lifetime (Burrows et al 2001). As the effective temperatures of brown dwarfs are much cooler than those of stars (< 2500K), molecules and condensates form in their photospheres and dominate the spectral energy distribution.…”

Section: Introductionmentioning

confidence: 99%

A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late-T Dwarfs

Zalesky,

Saboi,

Line

et al. 2022

Preprint

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The spectra of brown dwarfs are key to exploring the chemistry and physics that take place in their atmospheres. Late-T dwarf spectra are particularly diagnostic due to their relatively cloud-free atmospheres and deep molecular bands. With the use of powerful atmospheric retrieval tools applied to the spectra of these objects, direct constraints on molecular/atomic abundances, gravity, and vertical thermal profiles can be obtained enabling a broad exploration of the chemical/physical mechanisms operating in their atmospheres. We present a uniform retrieval analysis on low-resolution IRTF SpeX near-IR spectra of a sample of 50 T dwarfs, including new observations as part of a recent volume-limited survey. This analysis more than quadruples the sample of T dwarfs with retrieved temperature profiles and abundances (H 2 O, CH 4 , NH 3 , K and subsequent C/O and metallicities). We are generally able to constrain effective temperatures to within 50K, volume mixing ratios for major species to within 0.25dex, atmospheric metallicities [M/H] to within 0.2, and C/O ratios to within 0.2. We compare our retrieved constraints on the thermal structure, chemistry, and gravities of these objects with predictions from self-consistent radiative-convective equilibrium models and find, in general though with substantial scatter, consistency with solar composition chemistry and thermal profiles of the neighboring stellar FGK population. Objects with notable discrepancies between the two modeling techniques and potential mechanisms for their differences, be they related to modeling approach or physically motivated, are discussed more thoroughly in the text.

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Formation of Low-Mass Stars and Brown Dwarfs

Cited by 4 publications

References 140 publications

Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses

Spectroscopy of brown dwarf candidates in IC 348 and the determination of its substellar IMF down to planetary masses

Dust cleansing of star-forming gas

A Uniform Retrieval Analysis of Ultra-cool Dwarfs. IV. A Statistical Census from 50 Late-T Dwarfs

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