We continue after the break with a talk by Vincent Boudon about „Spectroscopic studies and linelists for (exo)planetary atmospheres“.

Two approaches:

1) Global modelling from direct quantum computations allows for very good line intensities, but lower accuracy for line positions because of high computational costs.

2) Line-by-line analysis where we reach high accuracy but at limited spectral range.

So in summary, the trade-off is between accuracy and spectral coverage! ☺️

#SEHR2023

How do we apply this to planetology? The example of methane!

Methane has a quite complex level structure 😮‍💨 The way I understand this (and I don’t), everything has to be taken into account when calculating the line lists. A crazy difficult task. 😭 #SEHR2023

So why are these line lists important for me? 🥺

Broadly speaking I am using them to figure out what fingerprint a given #atom or #molecule would imprint on the spectrum of the #planet. For some atoms the line lists are very accurate, and allow us to confidently detect these in atmospheres by comparing the spectrum to the predictions. For others, the lists are less accurate and more difficult to calculate. Mostly for molecules. This means it is VERY hard to match the fingerprints. #SEHR2023

Next up, we have Heather Cegla with a talk about „Disentangling planet and stellar signatures at high spectral resolution“ ⭐️<—>🪐

So let’s focus on the star!! 🤓 Similarly to exoplanet atmospheres, we compare the observed spectrum with the theoretical prediction.

To be able to detect exoplanets similar to Earth, the precision needs to be extreeemly high. Otherwise, we cannot see the velocity shifts in the star spectrum.

#SEHR2023

Sadly, #stars are not really this static discs in the sky, but actually way more complex. Just take the #Sun as an example!

So imagine, if we already struggle with the Sun, how do we deal with stars many light years away? What are their influences we have to be aware of in our exoplanet observations? 🥺

There is a lot to be aware of! Here as an example for centre-to-limb variations.

Granulation on the stellar surface will affect the shape of the stellar line. #SEHR2023

Would be too convenient if all stars behaved the same, right? 😂😭

Take home here: Convection/granulations induces asymmetries, a net blue-shift and temporal velocity shifts!

To make this even harder: Suppression of convection by magnetic fields on different scales (complete, but also partial by faculae/plage). These dark patches cause asymmetries that are possibly falsely interpreted as a detection of planets 🫠🙄

#SEHR2023

So, to summarise this for my brain: Granulation/convection and migration have an effect on what we observe. At orders that are important for detecting small planets and over a wide wavelength range…

Heather’s group is studying these effects using magneto-hydrodynamic simulations.

Where comes high res in? Resolution matters. Low res eats up the asymmetries and we cannot see it anymore. So high res is needed to resolve these asymmetries!

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Rotating stars? Yep, also rotation matters! I don’t really see the trend 😥

Heather points out that we need to know the star to know the planet, but we can also use the planet to isolate parts of the stellar surface. This allows us to study small parts of the stellar surface, and also the geometry of the system. #SEHR2023

Continue we shall! The first talk of Session 2 at #SEHR2023 is given by Lisa Nortmann about “Dynamics of exoplanet atmospheres revealed by near infrared spectroscopy”.

#ExoplanetsAre3D too! There are different ways on how we see this in observations? This might be seen in line broadening (due to rotation of the planet), velocity blueshifts (due to wind day- to nightside), super-rotational winds, and time-variability.

Hihi, I even spotted my name on these slides 😇😇🥰

Okay, this is so cool. Let’s look at this for a second!

If you start increasing the velocity of the planetary rotation, the line shape changes quite drastically. The upper panel shows the true shape, while the lower shows what you observe at R~100,000 (Fig 1.) You start seeing the effects also very strongly if we add a jet. This is SO COOL 🤩 #SEHR2023

Next up, we have Amanda Ross with “On the magnetic response of chromium hydride near 860 nm, and consequences for telescope polarimetric studies”.

Amanda promised no exoplanets in this talk, but more of a link between laboratory work & stars. So let’s see how much I can understand.

So if we look at cool stars, it seems CrH and FeH survive. They are small, but oh boy, not simple because of the electrons.

FeH shows a redshift in the spectrum. It is not constant though.

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So why is that? The star is magnetically active 🧲 Okay, my nightmare is complete. Magnetic fields scare me 😳

(And to my understanding this is where the electrons become important???? 🫠). Wow, my Physics III is a bit rusty 😭

So apparently CrH is the better test bed for this (due to being more sensitive to magnetic activity???). Help me out here, friends!

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Last talk of the day is by Giovanna Tinetti about “Synergy space & ground: An asset for exoplanet spectroscopy”

Giovanna said it very nicely: the different techniques to study exoplanets are not competing. They are very much complementary.

With existing and upcoming space- and ground-based telescopes, there are plenty of synergies. High and low resolution are highly complementary ✨

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Different instruments cover different wavelengths and have thus a different research focus. So using their capabilities together allows/will allow to study planets on a population level over a wide range of parameters. From the ground. From space. In the optical, infrared, etc. At high and low resolution. You name it. Dream big.

The adventure has just begun ❤️✨

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We are doing “quite well” for H-rich planets in terms of available line lists. But what about smaller, more chemically complex planets? Is there still H2? Is there a secondary atmosphere?

The information about super-Earths and sub-Neptunes is not very extensive. One of the examples: K2-18 b.

But there is a lot left to do, and luckily, #JWST will have a look at it as well.

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Future missions, such as #Ariel, will contribute in the quest of characterising these colder/smaller planets.

One of the key questions: Are there chemical trends? How does this link to planet formation?

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Our second day is opened by Nikole Lewis about ”MAESTRO: building access and community standards for opacity data at the onset of next-gen exoplanet atmosphere observations”

Nikole calls us ”consumers of line lists” and asks: Do you know what’s in your #opacities? I am honest: No I don’t 🤓

This is the goal of MAESTRO: making sure we are better educated consumers. So stop eating junk food 🫠 #SEHR2023

In light of the time that has been asked/awarded for #JWST in the field of exoplanet #atmospheres, a question arises: What opacities does the community need in terms of #composition, #temperature and #pressure?

So in comparison to the H/He dominated atmospheres of ultra-hot Jupiters that “we are used to”, we need to start accounting for way more complex molecules when pushing towards colder temperatures.

But this is not only true for #space, but also for ground-based facilities! #SEHR2023

So what’s the hurdle? There’s not only one 😅

1) Knowing which line list database to use: because it matters! ✨

2) Knowing what to do if the data doesn’t exist 🥹

3) Knowing how to store Tb’s of data (and also how to “transfer” the data) ✉️❌

4) Remembering what line list you used for paper X, and why 🤔

#SEHR2023

This is where MAESTRO comes in! It is a community tool for computing, visualising, and manipulating molecular and atomic opacities.

I LOVE THE ACRONYM: It makes sense 🥹🥹🥹

The goal: set data standards and improve standards.

Note to self: Need to check out #MAESTRO ✨

Next up, we have Sid Gandhi about “Modelling exoplanet atmospheres at high resolution”

One way to detect species is to use the cross-correlation technique.

Sid draws up a nice comparison/pro-&con-list of high- vs low-res observations, and walks us through how we go from line list to cross-sections. I think I will try this calculation myself when back at home to completely understand the magic behind it ✨

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In recent years, we have come a far way though. The agreement for water, CO and CO2 between different line lists agree pretty well . I wonder how this looks for atoms? 🤔

One thing is for sure: I will go home from this conference with a bit more of awareness what is actually behind the term “line list”. It’s a lot. I don’t understand the majority of it. But I am starting to learn.

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For the second part of the talk, Sid shifts focus to multi-dimensional effects. #PlanetsAre3D

Our observations show a lot of structures that we need to investigate and we can do that using 2D retrievals: cutting the atmosphere in leading/trailing terminator to disentangle the signals. We can also look at this temporally resolved where at different times on the orbit, we probe different parts of the #atmosphere.

Thanks to high-res we can break degeneracies between Fe and clouds.

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Next up we have Robert Hargreaves about “HITRAN and HITEMP data for high resolution exoplanet spectroscopy”

Both HITRAN and HITEMP are databases for molecular spectroscopic parameters. The latest release is called HITRAN2020 and contains a lot of useful info, and also increased accuracy, new additions and expanded spectral coverage.

#SEHR2023

Line lists seem to be linked to food… what is the line shape “diet”? 😂

The latest addition is the molecule CH3CN. So you see, the molecules get more and more complex.

For Ozone, the latest update resulted in improved consistency between different wavelength regions.

HITRAN offers broadening parameters for key planetary molecules in HITRAN2020. #SEHR2023

There are plenty of more updates that I won’t mention here. Go check out www.hitran.org if you’re interested. ✨

We move on to HITEMP (basically a part of HITRAN, but with many more lines because this is needed for hot planets). There are 8 molecules in HITEMP.

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Next up, we have Jonathan Tennyson on the “Use of the #ExoMol database of high accuracy spectroscopy of exoplanets”

To my understanding, one of the major differences between ExoMol and HITRAN/HITEMP is that ExoMol is purely computational, while HITRAN/HITEMP is empirical. Correct me if I am wrong, please 😅

This means that there is no right or wrong on what to use. Right?

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Okay, so I need to out down my thoughts here:

I feel like I have no chance of choosing “the right line list” as a consumer. So I am wondering: How do I decide? What is right? What is wrong? How right/wrong am I? Help? 😭

#ExoMolHD includes an uncertainty column that tells you which lines to use, and which we shouldn’t. This means we should regenerate our templates we use to do cross-correlations with. Noted.

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Next up we have Katy Chubb about “using a variety of molecules in exoplanet atmosphere studies” ✨

1) How do we know what the spectra of molecules look like?

We can measure their spectra in the lab, or we can calculate the spectra from quantum methods. This way we get line lists so we can calculate the cross-sections (sooooo I wish this talk would’ve been one of the first ones…)

#SEHR2023