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LDB.html
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<!DOCTYPE HTML>
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<title>LDB/BPMG: 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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<div class="title">The LDB age of Beta Pic</div>
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<p>Sometimes the best ideas really are the most simple ones! Such an example in acquiring very precise (within 10%), potentially very
accurate ages for stellar clusters is the lithium depletion boundary (LDB). Whilst stars heavier than 0.35 Solar-mass develop a radiative
core, which significantly complicates the rate at which lithium is burned, stars below this mass remain fully convective and the mixing
processes and lithium burning rate are extremely temperature sensitive, meaning once Li burning temperature is reached in a fully convective
star, the full Li supply is almost fully destroyed extremely rapidly (generally within 1-2 Myr). Since the physics of convective stars is
very well known (after all, it's just a hot ball of gas...) this provides a semi-fundamental way of estimating an age for a coeval cluster
of stars. Stars on the more luminous side of the LDB will be almost fully-depleted, whereas those on the less luminous side will be almost
fully-depleted. Locate this boundary and the age of the cluster can be very accurately measured. The level to which one can measure an
accurate LDB age is mainly dependent on the size of the LDB "gap".</p>
<p>Inspired by this technique I set out to spectroscopically observe candidate M-dwarf members of the Beta Pictoris moving group (BPMG) - a
nearby (d < 100 pc) association of stars with an isochronal age of ~12 Myr. Probably the best observing experience I will ever have is the
moment I saw the spectra for one of the Li-rich BPMG stars which I knew in the moment would set an LDB age of around 20 Myr, almost twice that
of the often-used isochronal value.</p>
<p>This age has a direct impact on our understanding of stellar, and sub-stellar evolution. For instance, by setting the age as double that
of the isochronal value would imply a 30% increase for planets observed in BPMG (e.g, Beta Pic b, AU Mic b), as well as having a new
empirical age benchmark to test stellar evolutionary models. One factor that may affect the LDB ages is the presence of dark magnetic star
spots, which reduce the overall luminosity of the stars, driving the LDB age upwards by ~1-3 Myr. Subsequent LDB age estimates for Beta Pic
vary between 20 and 26 Myr. One of my future goals is to develop a set of isochronal models which use LDB ages from clusters as empirical
age benchmarks.</p>
<div class="col-6 col-12-medium">
<section class="highlight">
<img src="images/LDB_BPMG.png" alt="" style="width:800px;height:800px;"/>
<h3>Identifying the LDB age of BPMG using 2 standard evolutionary models, and one that accounts for a strong surface magnetic field. Note
that the two standard models are in remarkable agreement and the non-standard model predicts a ~10% age increase.</h3>
</section>
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<img src="images/lightcurve_example.png" alt="" style="width:500px;height:400px;"/>
<h3>Testing how well evolutionary models simultaneous fit both the
CMD and Li-depletion </h3>
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<li><a href="CMD_Li.html" class="button style1">Learn More</a></li>
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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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<li><a href="Pisces.html" class="button style1">Learn More</a></li>
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<img src="images/LDB_BPMG.png" alt="" style="width:500px;height:400px;"/>
<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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<li><a href="LDB.html" class="button style1">Learn More</a></li>
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School of Chemical and Physical Sciences<br />
Lennard-Jones Building<br />
Keele University<br />
Staffordshire<bf />
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