The Bimodal Distribution in Exoplanet Radii: Considering Varying Core Compositions and $rm H_{2}$ Envelop Sizes. (arXiv:2002.02166v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Modirrousta_Galian_D/0/1/0/all/0/1">Darius Modirrousta-Galian</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Locci_D/0/1/0/all/0/1">Daniele Locci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Micela_G/0/1/0/all/0/1">Giuseppina Micela</a>
Several models have been introduced in order to explain the radius
distribution in exoplanet radii observed by Fulton et al. (2017) with one peak
at $rm sim 1.3 R_{oplus} $ the other at $rm sim 2.4 R_{oplus} $ and the
minimum at $rm sim 1.75R_{oplus} $. In this paper we focus on the hypothesis
that the exoplanet size distribution is caused by stellar XUV-induced
atmospheric loss. We evolve $10^{6}$ synthetic exoplanets by exposing them to
XUV irradiation from synthetic ZAMS stars. For each planet we set a different
interior composition which ranged from $rm 100 : wt%$ Fe (very dense)
through $rm 100 : wt%$ $rm MgSiO_{3}$ (average density) and to $rm 100 :
wt%$ $rm H_{2}O$ ice (low density) with varying hydrogen envelop sizes which
varied from $rm 0 : wt%$ (a negligible envelop) to $rm 100 : wt%$ (a
negligible core). Our simulations were able to replicate the bimodal
distribution in exoplanet radii. We argue that in order to reproduce the
distribution by Fulton et al. (2017) it is mandatory for there to be a paucity
of exoplanets with masses above $rm sim 8M_{oplus}$. Furthermore, our
best-fit result predicts an initial flat distribution in exoplanet occurrence
for $rm M_{P} lesssim 8M_{oplus}$ with a strong deficiency for planets with
$rm lesssim 3M_{oplus}$. Our results are consistent with the $rm sim
1.3R_{oplus}$ radius peak mostly encompassing denuded exoplanets whilst the
$rm sim 2.4R_{oplus}$ radius peak mainly comprising exoplanets with large
hydrogen envelops
Several models have been introduced in order to explain the radius
distribution in exoplanet radii observed by Fulton et al. (2017) with one peak
at $rm sim 1.3 R_{oplus} $ the other at $rm sim 2.4 R_{oplus} $ and the
minimum at $rm sim 1.75R_{oplus} $. In this paper we focus on the hypothesis
that the exoplanet size distribution is caused by stellar XUV-induced
atmospheric loss. We evolve $10^{6}$ synthetic exoplanets by exposing them to
XUV irradiation from synthetic ZAMS stars. For each planet we set a different
interior composition which ranged from $rm 100 : wt%$ Fe (very dense)
through $rm 100 : wt%$ $rm MgSiO_{3}$ (average density) and to $rm 100 :
wt%$ $rm H_{2}O$ ice (low density) with varying hydrogen envelop sizes which
varied from $rm 0 : wt%$ (a negligible envelop) to $rm 100 : wt%$ (a
negligible core). Our simulations were able to replicate the bimodal
distribution in exoplanet radii. We argue that in order to reproduce the
distribution by Fulton et al. (2017) it is mandatory for there to be a paucity
of exoplanets with masses above $rm sim 8M_{oplus}$. Furthermore, our
best-fit result predicts an initial flat distribution in exoplanet occurrence
for $rm M_{P} lesssim 8M_{oplus}$ with a strong deficiency for planets with
$rm lesssim 3M_{oplus}$. Our results are consistent with the $rm sim
1.3R_{oplus}$ radius peak mostly encompassing denuded exoplanets whilst the
$rm sim 2.4R_{oplus}$ radius peak mainly comprising exoplanets with large
hydrogen envelops
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