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# PLATYPOS - PLAneTarY PhOtoevaporation Simulator
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Tool to estimate the atmospheric mass loss of planets induced by the stellar X-ray and extreme UV irradiance. 
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![](./supplementary_files/V1298Tau_press_release.png)
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## Our Model Assumptions
We do not make use of full-blown hydrodynamical simulations, but instead couple existing parametrizations of planetary mass-radius relations with an energy-limited hydrodynamic escape model to estimate the mass-loss rate over time.
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### Mass-loss description: <br> 
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;\dot{M}&space;=&space;\epsilon&space;\frac{(\pi&space;R_{XUV}^2)&space;F_{\mathrm{XUV}}}{K&space;G&space;M_{pl}/R_{pl}&space;}&space;=&space;\epsilon&space;\frac{3&space;\beta^2&space;F_{\mathrm{XUV}}}{4&space;G&space;K&space;\rho_{pl}}\,," target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;\dot{M}&space;=&space;\epsilon&space;\frac{(\pi&space;R_{XUV}^2)&space;F_{\mathrm{XUV}}}{K&space;G&space;M_{pl}/R_{pl}&space;}&space;=&space;\epsilon&space;\frac{3&space;\beta^2&space;F_{\mathrm{XUV}}}{4&space;G&space;K&space;\rho_{pl}}\,," title="\small \dot{M} = \epsilon \frac{(\pi R_{XUV}^2) F_{\mathrm{XUV}}}{K G M_{pl}/R_{pl} } = \epsilon \frac{3 \beta^2 F_{\mathrm{XUV}}}{4 G K \rho_{pl}}\,," /></a>
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where 
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;F_{\mathrm{XUV}}" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;F_{\mathrm{XUV}}" title="\small F_{\mathrm{XUV}}" /></a>
is the flux impinging on the planet, 
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;R_{pl}" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;R_{pl}" title="\small R_{pl}" /></a>
and 
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;R_{XUV}" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;R_{XUV}" title="\small R_{XUV}" /></a>
are the planetary radii at optical and XUV wavelengths, respectively (
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;\beta&space;=&space;R_{XUV}/R_{pl}" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;\beta&space;=&space;R_{XUV}/R_{pl}" title="\small \beta = R_{XUV}/R_{pl}" /></a>).
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;M_{pl}" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;M_{pl}" title="\small M_{pl}" /></a>
is the mass and 
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;\rho_{pl}" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;\rho_{pl}" title="\small \rho_{pl}" /></a>
the density of the planet, 
<a href="https://www.codecogs.com/eqnedit.php?latex=\small&space;\epsilon" target="_blank"><img src="https://latex.codecogs.com/gif.latex?\small&space;\epsilon" title="\small \epsilon" /></a>
is the efficiency of the atmospheric escape with a value between 0 and 1, and K is a factor representing the impact of Roche lobe overflow (Erkaev et al., 2007), which can take on values of 1 for no Roche lobe influence and <1 for planets filling significant fractions of their Roche lobes.
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### Planet Model description: <br>
At the moment, the user can choose between two planet models.

1. *Planet with a rocky core and H/He envelope atop* <br>
We use the tabulated models of Lopez & Fortney (2014), who calculate radii for low-mass planets with hydrogen-helium envelopes on top of Earth-like rocky cores, taking into account the cooling and thermal contraction of the atmospheres of such planets over time. Their simulations extend to young planetary ages, at which planets are expected to still be warm and possibly inflated. Simple analytical fits to their simulation results are provided, which we use to trace the thermal and photoevaporative evolution of the planetary radius over time.

1. *Planet which follows the empirical mass-radius relationships observed for planets around older stars* <br> 
(see Otegi et al. (2020), also Chen & Kipping (2017)) <br> 
These "mature" relationships show two regimes, one for small rocky planets up to radii of about 2 Earth radii and one for larger planets with volatile-rich envelopes. The scatter is low in the rocky planet regime and larger in the gaseous planet regime: as core vs. envelope fractions may vary, there is a broader range of observed masses at a given planetary radius for those larger planets. 

1. *Giant planets with mass-radius relations computed using MESA* <br>
To be implemented...


## Repository Structure:

* **platypos_package**: contains the planet classes & all the necessary funtions to construct a planet and make it evolve 
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                        (LoF014 planet with rocky core & gaseous envelope OR planet based on mass-radius relation for mature planets (Ot20))
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* **supplementary_files**: contains some extra files for plotting 
                         (Tu et al., 2015 model tracks for the X-ray luminosity evolution, 
                         Jackson et al., 2012 sample of X-ray measurements in young clusters)

* **example_V1298Tau**: evolve the four young V1298 Tau planets as shown in "X-ray irradiation and evaporation of the four young planets around V1298 Tau" (Poppenhaeger, Ketzer, Mallon 2020)
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                        [Link to our paper: ](https://arxiv.org/abs/2005.10240)
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* **population_evolution**: evolve a whole population of planets (to be fully implemented in the future)