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<!DOCTYPE HTML>
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<title>KinHot: Alexander S. Binks</title>
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<h1><a href="index.html">Alexander S. Binks</a></h1>
<p>Astronomer, Stargazer and consumer of music</p>
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<li><a href="www.astro.keele.ac.uk">Keele Astrophysics</a></li>
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<p>Understanding the properties of young stars near the Sun is extremely important to facilitate a complete theory of star formation,
understand the local rate of star formation and identify the processes responsible in the dispersal of young star clusters. The locality of
such objects make them the prime targets for direct imaging studies for brown-dwarfs, disks and planetary systems, at a crucial evolutionary
stages where planetary systems are forming.</p>
<p>Thanks to large efforts and vast improvements in observational data, astronomers have identified several thousands of young (<100 Myr)
stars in the Solar neighbourhood (within ~100 pc), most of which have been identified as constituents of moving groups (MGs):
low-density, gravitationally-unbound, but kinematically coherent stellar ensembles that are approximately co-eval. MGs are thought to be the
link between dense star clusters and the sparse Galactic field, however, their dynamical origins remain largely unknown, with some evidence
suggesting some MG members may not have formed in the same star forming region.</p>
<p>Recent evidence is emerging that a considerable number of young, nearby stars are not kinematically linked with any of the approximately
dozen known MGs. Motivated by these findings I lead an investigation to quantify, for the first time, the fraction of young stars near the Sun
that do not belong to any known MGs. The method is to collect data from kinematically-unbiased all-sky surveys that identified young stars by
the prescence of their large amounts of surface lithium, a particularly reliable stellar youth indicator for Solar-type and low-mass stars.
A sample of 225 stars were compiled that are likely as young as 125 Myr, have at least one radial velocity measurement and have precise
astrometric data from Gaia DR2.</p>
<p>Galactic space velocities are calculated, revealing that at least half of the sample are not co-moving with any known MGs linked with any
known nearby MGs and 20% of this population are several 10s of km/s from their nearest MG in velocity space (see Figure, top). Intriguingly, an
investigation into the demographics of these objects shows that the kinematically-hot sample are systematically older than the MG sample
(see Figure, bottom).</p>
<p>Their origins are a mystery. Could they belong to very small kinematic groups, or larger kinematic entities yet to be identified? Are
they the dynamical ejectees of more distant SFRs from processes such as supernovae explosion or strong 3-body interactions? Or are they the
remnants of the high velocity tails in molecular clouds? The only way to really find this out is by tracing their Galactic orbits backwards
in time to their birth and locate the star forming region from which they were born. This requires extremely precise radial velocity
measurements, and I plan to acquire these in the near-future to understand the origins of these peculiar, kinematically-hot stars.</p>
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<img src="images/uvw.png" alt="" style="width:1200px;height:1000px;"/>
<h3>Grey boxes denote the 1-sigma velocity dispersions from the nearby, known MGs. Blue objects have kinematic links to at least 1 MG and red
objects have no kinematic links to any MG. A dozen or so objects have space velocities several 10s of km/s from the centroid of their MG and
represent some of the fastest stars in the Galactic plane.</h3>
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<h3>Top left: Li equivalent widths versus G-Ks. Top right: sky positions. Bottom left: absolute G versus G-Ks colour magnitude diagram.
Bottom right: ages and masses calculated from forward-modelling spectral energy distribution models. The red objects represent a systematically
older population with >99% statistical significance.</h3>
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<h3>Testing how well evolutionary models simultaneous fit both the
CMD and Li-depletion </h3>
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<h3>Half the young G/K stars within 100 pc are not kinematically
linked with any known moving groups</h3>
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<h3>Is there another kinematic "local association" of
young, nearby stars?</h3>
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<h3>What fraction of low-mass M-stars in young moving groups
have debris disks?</h3>
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<img src="images/Xray_VKs.png" alt="" style="width:500px;height:400px;"/>
<h3>Searching for new, nearby young stars in the Northern Hemisphere:
About 1/3 of fast rotating stars are genuinely young based on Li content.</h3>
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<h3>A Lithium Depletion Boundary age of 24+/-4 Myr for the Beta
Pictoris Moving Group: twice the age estimate from isochronal fitting.</h3>
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School of Chemical and Physical Sciences<br />
Lennard-Jones Building<br />
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Staffordshire<bf />
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