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"# Supporting a JWST Proposal with POSEIDON\n",
"\n",
"This tutorial will guide you through a typical workflow for examining the feasibility of a JWST proposal science case using POSEIDON.\n",
"\n",
"The steps we will cover are:\n",
"\n",
"1. Generating simulated JWST observations using [PandExo](https://github.com/natashabatalha/PandExo).\n",
"2. Scattering the simulated observations about a POSEIDON forward model.\n",
"3. Running an atmospheric retrieval on the synthetic JWST observations.\n",
"\n",
"The first portion of this tutorial assumes you have PandExo installed, which is not an official dependency of POSEIDON. Please see the [PandExo documentation](https://natashabatalha.github.io/PandExo/index.html) for installation instructions. "
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"### What is Your Science Case?\n",
"\n",
"The first part of any proposal is of course to come up with a good idea! \n",
"\n",
"For our purposes, let's imagine our science goal is to conclusively detect $\\rm{CH}_4$ in a hot Jupiter atmosphere — $\\rm{CH}_4$ has proven notoriously difficult to detect with Hubble (perhaps indicating it is destroyed by photodissociation), so detecting $\\rm{CH}_4$ and constraining its abundance is a rich science question.\n",
"\n",
"If we want to search for $\\rm{CH}_4$, let's first examine where this molecule has prominent absorption features. The plot below (from [MacDonald & Lewis, 2022](https://ui.adsabs.harvard.edu/abs/2022ApJ...929...20M/abstract)) shows the absorption cross sections for several important chemical species in hot Jupiter atmospheres.\n",
"\n",
"\n",
"
\n",
"\n",
"We see that $\\rm{CH}_4$ has a strong absorption band centred on 3.3 μm which doesn't coincide with many other molecules. So this feature is a good target for our $\\rm{CH}_4$ focused JWST proposal.\n"
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"### Choosing a Planet\n",
"\n",
"Choosing which exoplanet to focus your JWST proposal on involves many consideration. Some common factors include:\n",
"\n",
"- What have previous observations of this planet found?\n",
"- Stellar and planetary properties that make the system favourable.\n",
"- Theoretical predictions of novel physical or chemical processes in the target planet's atmosphere.\n",
"\n",
"You should ensure a clear justification of your planet, and it's wider significance, is provided in your proposal.\n",
"\n",
"For this tutorial, we are going to choose the hot Jupiter WASP-62b. Our reasoning is as follows:\n",
"\n",
"1. Observation of WASP-62b with the Hubble and Spitzer space telescopes indicate it has a clear atmosphere ([Alam et al., 2021](https://ui.adsabs.harvard.edu/abs/2021ApJ...906L..10A/abstract)), which increases the strength of absorption features and avoids composition-cloud degeneracies.\n",
"2. WASP-62b is the only known hot Jupiter in the continuous viewing zone of JWST, making it easy to schedule the observation.\n",
"3. Theoretical models predict the $\\rm{CH}_4$ abundance in WASP-62b's atmosphere should be at detectable levels."
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"### Selecting a JWST Instrument\n",
"\n",
"Now that we know our wavelength of interest, let's decide on an appropriate JWST instrument that covers the 3.3 μm $\\rm{CH}_4$ band.\n",
"\n",
"This graphic is one of my favourite go-to resources for summarising JWST's instrument capabilities (credit: [ExoCTK](https://exoctk.stsci.edu/)):\n",
"\n",
"
"
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"For maximum accuracy in retrieved abundances, generally we want the widest wavelength range possible. However, as shown on the right of the figure above, each instrument has a magnitude range limited by the brightness of the host star.\n",
"\n",
"Looking at [SIMBAD](http://simbad.u-strasbg.fr/simbad/sim-id?Ident=wasp-62) for WASP-62, we see that the host star J magnitude is 9.272. Therefore, the star is too bright to use the instrument mode with the widest wavelength range (NIRSpec PRISM). However, there is an ideal mode covering the 3.3 μm $\\rm{CH}_4$ band: NIRSpec G395H."
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"### Running PandExo\n",
"\n",
"Let's proceed to use PandExo to simulate JWST G395H transmission spectra performance for WASP-62b. \n",
"\n",
"