Pre-main-sequence isochrones – II. Revising star and planet formation time-scales

Bell, Cameron P. M.; Naylor, T.; Mayne, Nathan J.; Jeffries, R. D.; Littlefair, S. P.

doi:10.1093/mnras/stt1075

Cited by 255 publications

(260 citation statements)

References 128 publications

(200 reference statements)

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“…A full investigation of the Li depletion pattern and comparison with models is deferred to a subsequent GES paper (Franciosini et al, in prep.). An empirical comparison is also possible; for instance Dahm (2005) shows that stars with V − I ∼ 2.7 in NGC 2362 (age 12 Myr; Bell et al 2013) show no evidence for significant Li depletion, whereas the β Pic association (age 21 ± 4 Myr; Binks & Jeffries 2014) has many M-dwarfs where Li cannot be detected (Mentuch et al 2008). Hence this comparison also suggests that population A is older than 10 Myr (but younger than 20 Myr).…”

Section: Age Puzzlementioning

confidence: 93%

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

Jeffries

Jackson

Cottaar

et al. 2014

A&A

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Context. A key science goal of the Gaia-ESO survey (GES) at the VLT is to use the kinematics of low-mass stars in young clusters and star forming regions to probe their dynamical histories and how they populate the field as they become unbound. The clustering of low-mass stars around the massive Wolf-Rayet binary system γ 2 Velorum was one of the first GES targets. Aims. We empirically determine the radial velocity precision of GES data, construct a kinematically unbiased sample of cluster members and characterise their dynamical state. Methods. Targets were selected from colour-magnitude diagrams and intermediate resolution spectroscopy was used to derive radial velocities and assess membership from the strength of the Li i 6708 Å line. The radial velocity distribution was analysed using a maximum likelihood technique that accounts for unresolved binaries. Results. The GES radial velocity precision is about 0.25 km s −1 and sufficient to resolve velocity structure in the low-mass population around γ 2 Vel. The structure is well fitted by two kinematic components with roughly equal numbers of stars; the first has an intrinsic dispersion of 0.34 ± 0.16 km s −1 , consistent with virial equilibrium. The second has a broader dispersion of 1.60 ± 0.37 km s −1 and is offset from the first by 2 km s −1 . The first population is older by 1-2 Myr based on a greater level of Li depletion seen among its M-type stars and is probably more centrally concentrated around γ 2 Vel. Conclusions. We consider several formation scenarios, concluding that the two kinematic components are a bound remnant of the original, denser cluster that formed γ 2 Vel, and a dispersed population from the wider Vela OB2 association, of which γ 2 Vel is the most massive member. The apparent youth of γ 2 Vel compared to the older (≥10 Myr) low-mass population surrounding it suggests a scenario in which the massive binary formed in a clustered environment after the formation of the bulk of the low-mass stars.

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Section: Age Puzzlementioning

confidence: 93%

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

Jeffries

Jackson

Cottaar

et al. 2014

A&A

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128

256

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“…Thus, for very young clusters with an age less than about 5−10 Myr, age uncertainties may be approximately the actual age estimate (Bell et al 2013). Fortunately, the change in rotation rates at these very young ages are relatively mild, so that the modelling does not suffer much from these uncertainties (i.e.…”

Section: Observational Constraints On the Rotational Evolution Of Lowmentioning

confidence: 95%

Improved angular momentum evolution model for solar-like stars

Gallet

Bouvier

2015

A&A

229

290

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Context. Understanding the physical processes that dictate the angular momentum evolution of solar-type stars from birth to maturity remains a challenge for stellar physics. Aims. We aim to account for the observed rotational evolution of low-mass stars over the age range from 1 Myr to 10 Gyr. Methods. We developed angular momentum evolution models for 0.5 and 0.8 M stars. The parametric models include a new wind braking law based on recent numerical simulations of magnetised stellar winds, specific dynamo and mass-loss rate prescriptions, as well as core-envelope decoupling. We compare model predictions to the distributions of rotational periods measured for low-mass stars belonging to star-forming regions and young open clusters. Furthermore, we explore the mass dependence of model parameters by comparing these new models to the solar-mass models we developed earlier.Results. Rotational evolution models are computed for slow, median, and fast rotators at each stellar mass. The models reproduce reasonably well the rotational behaviour of low-mass stars between 1 Myr and 8−10 Gyr, including pre-main sequence to zero-age main sequence spin up, prompt zero-age main sequence spin down, and early-main sequence convergence of the surface rotation rates. Fast rotators are found to have systematically shorter disk lifetimes than moderate and slow rotators, thus enabling dramatic pre-main sequence spin up. They also have shorter core-envelope coupling timescales, i.e., more uniform internal rotation. As for the mass dependence, lower mass stars require significantly longer core-envelope coupling timescales than solar-type stars, which results in strong differential rotation developing in the stellar interior on the early main sequence. Lower mass stars also require a weaker braking torque to account for their longer spin-down timescale on the early main sequence, while they ultimately converge towards lower rotational velocities than solar-type stars in the longer term because of their reduced moment of inertia. We also find evidence that the mass dependence of the wind braking efficiency may be related to a change in the magnetic topology in lower mass stars. Conclusions. We have included in parametric models the main physical processes that dictate the angular momentum evolution of low-mass stars. The models suggest that these processes are quite sensitive to both mass and instantaneous rotation rate. We have worked out and reported here the main trends of these mass and rotation dependencies, whose origin still have to be addressed through a detailed modelling of magnetised stellar winds, internal angular momentum transport processes, and protoplanetary disk dissipation mechanisms.

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“…In other words, there is a degeneracy between the time-span since star formation onset (t) and the star formation efficiency per free-fall time ( ff ). Should the lifetime of Class II objects be significantly longer than 2 Myr, as suggested by Bell et al (2013), t may be substantially larger than 2 Myr in the regions mapped by Gutermuth et al (2011). The derived star formation efficiency per free-fall time would accordingly be shorter.…”

Section: The Local Star-formation Relationmentioning

confidence: 96%

Local‐density driven clustered star formation: Model and (some) implications

Parmentier

2014

Astron Nachr

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A positive power-law trend between the local surface densities of molecular gas, Σgas, and young stellar objects, Σstars, in molecular clouds of the solar neighbourhood has recently been identified. How it relates to the properties of embedded clusters has so far not been investigated. To that purpose, we model the development of the stellar component of molecular clumps as a function of time and local volume density. Specifically, we associate the observed volume density gradient of molecular clumps to the density-dependent free-fall time and we obtain the molecular clump star formation history by applying a constant star formation efficiency per free-fall time, ff . The model reproduces naturally the observed (Σgas, Σstars) relation quoted above. The consequences of our model in terms of cluster survivability after residual star-forming gas expulsion and in terms of star age distribution in young gas-free clusters are discussed.

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Pre-main-sequence isochrones – II. Revising star and planet formation time-scales

Cited by 255 publications

References 128 publications

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

TheGaia-ESO Survey: Kinematic structure in the Gamma Velorum cluster

Improved angular momentum evolution model for solar-like stars

Local‐density driven clustered star formation: Model and (some) implications

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