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Overview

Theo Murphy meeting organised by Professor Sergey Yurchenko, Dr Matteo Brogi and Professor Jonathan Tennyson FRS.

The meeting aims to bring together exoplanetary astrophysicists working with novel high resolution spectroscopic techniques with providers of the high-resolution spectroscopic data both theoretical and experimental. There is a growing need for these communities to communicate their needs and capabilities. The spectroscopic community needs to learn about the molecules which are thought to be important for HR atmospheric studies. In turn, the astrophysical community (data users) needs to understand the limitations and capabilities of the HR laboratory data, both experimental and theoretical.

The schedule of talks and speaker biographies are available below. Speaker abstracts are also available below. 

Attending this event

This meeting is intended for researchers in relevant fields, and is a residential meeting.

  • Free to attend
  • Advance registration essential (please request an invitation)
  • This is an in-person meeting

Enquiries: contact the Scientific Programmes team

Organisers

Schedule


Chair

09:00-09:05
Introduction
09:05-09:45
Flash talk session
09:45-10:15
High resolution spectroscopy for the atmospheres of exoplanets

Abstract

High resolution spectroscopy (HRS) has proven to be a powerful technique for the characterisation of exoplanet atmospheres that has revolutionised our understanding of their compositions, structures, and dynamics. It does not require the planet to transit its host star, and can be combined with high contrast imaging to reach down to star-planet contrasts at the 10-6-10-7 level. It is our only avenue for the coming decade for the remote exploration of the atmospheres of the very nearest rocky exoplanets. In this talk Professor Birkby will outline the advances made in our understanding of exoplanet atmospheres via HRS. The HRS technique uses template-matching, typically via cross-correlation, to identify the unique chemical fingerprint species in the planet spectrum. The plethora of lines at high spectral resolution (R>20,000) make it difficult to mimic these species by random chance, making their detection robust, and delivering constraints on mixing ratios at the 0.1 dex level, and global wind speeds to 1 km/s, all with ground-based 4-8 m class telescopes. In its current form, HRS inherently relies on high accuracy and precision in the position and relative strength of each line in the theoretical spectrum. She will highlight what happens when this is not the case, and discuss areas where observational studies are driven by advances in laboratory and theoretical calculations of line lists.

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
Spectroscopic studies and libelists for (exo)planetary atmospheres

Abstract

The spectroscopy of small molecules (5 to 10 atoms) present in planetary atmospheres is paradoxically often both well and insufficiently characterised. On the one hand, many molecules (say water, methane, …) have been deeply studied for many decades. But, on the other hand, the recent needs for planetology have raised new needs: extreme conditions (for instance high temperature giant exoplanets) require the inclusion of a huge number of excited states, while new instrumental measurements require a higher precision. Line broadening parameters are also necessary to account for pressure effects also constitute an important research field. Recently, quantum chemistry calculations have strongly increased their capabilities leading to extensive models over wide spectral ranges with an excellent reliability on line intensities. Nevertheless, line-by-line intensities using effective models still have a role to play in order to provide a very good accuracy whenever line assignments are possible; in particular, this helps to refine ab initio molecular potentials. Professor Boudon presents here some recent results obtained in the Dijon group concerning some molecules with a high symmetry that are of interest for giant (ex)planets and the associated databases they have implemented.

Speakers

11:30-11:45
Discussion
11:45-12:15
Disentangling planet and stellar signatures at high spectral resolution

Abstract

Almost everything we know about exoplanets comes from light originating from their far more luminous host stars. As a consequence, signatures from stellar surface inhomogeneities can imprint themselves on exoplanet observations; this is especially prevalent at high spectral resolution where even subtle signatures can be decomposed. For Sun-like stars, such inhomogeneities are primarily driven by heat transport via convection at the surface interplaying with magnetic fields, giving rise to various phenomena from granulation and oscillations to faclue/plage, spots, and flares etc. In this talk, Dr Cegla will show how these phenomena alter the shape and position of the stellar absorption lines that we use to probe exoplanet characteristics. The impact is far-reaching, from exoplanet mass determination to our analysis of star-planet dynamical histories to teasing out the chemical makeup of exoplanet atmospheres. She will also discuss ongoing efforts to use high spectral resolution to unveil stellar variability fingerprints and disentangle underlying exoplanet signatures.

Speakers

12:15-12:30
Discussion

Chair

13:30-14:00
Dynamics of exoplanet atmospheres revealed with near infrared spectroscopy

Abstract

Investigating the spectral signatures of exoplanets allows us to constrain their physical and chemical properties and shed light on their formation histories. Particularly, studies at high-resolution offer opportunities to probe the atmospheres of cloudy exoplanets whose features remain obscured at lower resolution. Moreover, dynamics within the atmospheres can be investigated by resolving the Doppler shifts and line profiles of the absorbing and emitting material. Measuring these features independently for each atmospheric species and at different phases of the orbit can reveal the planets' 3D structures in the form of wind patterns, hot spots, and day-to-night side contrasts. The signatures of highly volatile species such as hydrogen and helium, further, can yield insights into atmospheric escape and the interaction of the escaping material with the stellar wind. In this talk Dr Nortmann delves into some of the dynamic processes occurring in exoplanet atmospheres that can be studied though near infrared observations with state-of-the art spectrographs.

Speakers

14:00-14:15
Discussion
14:15-14:45
On the magnetic response of chromium hydride near 860 nm, and consequences for telescope polarimetic studies

Abstract

Dr Ross will describe laser-induced fluorescence experiments performed to investigate the magnetic response of some first-row transition metal monohydrides observed in the spectra of cool stars, and in particular the pathological A 6Σ+ -X  6Σ+ system of CrH. The spectra, and the subsequent fitting and modelling, illustrate the consequences that even modest magnetic fields may have on spectral features. The MH radicals are produced at around 450 K, sputtering metal from a cathode of chromium-iron alloy with a flow of 10% H2 in argon. These temperatures are far below the 3000 K associated with cool stars, but have the advantage of  giving at least partially-resolved spectra even in Doppler-limited conditions. The group has recorded laser excitation spectra using linear or circularly polarized light, in static magnetic fields up to 0.5 Tesla, and compare their observations with standard Hamiltonian model taken from C Western's Pgopher program, and with spectra recorded at the Canada France Hawaii telescope on the visible (ESPaDoNs) and infrared (SPIRou) spectropolarimeters, considering a small selection of cool (dwarf) stars exhibiting known degrees of magnetism. The talk will illustrate what can – and what cannot – be extracted from molecular data in this context, and describe some of the challenges faced when trying to incorporate effective Landé factors in spectral simulations for stellar objects.

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Synergy space and ground: an asset for exoplanet spectroscopy

Abstract

Thousands of planets orbiting stars other than our own are being discovered. Since their discovery in the 1990s this field of astronomy and planetary science has exploded, being today one of the most exciting and dynamic. Even within the limits of our current observational capabilities, studies of extrasolar planets have provided a unique contribution to improving our view of the place that the Solar System and the Earth occupy in the galactic context.

The arrival of more performing and dedicated facilities from space and the ground in the coming decade, will provide an unprecedented opportunity to study these worlds. In this talk, Professor Tinetti will focus on the complementarity of space and ground, and review highlights and pitfalls of currently available techniques to sound exoplanet atmospheres. Most importantly, they will highlight the need to use said facilities and techniques synergistically to advance in this field of research in the coming decade and beyond.

Speakers

16:00-16:15
Discussion
16:15-17:00
Poster flash talks
17:00-18:15
Poster session

Chair

09:00-09:30
MAESTRO: building access and community standards for opacity data at the onset of next-generation exoplanet atmosphere observations

Abstract

The characterisation of a diverse set of exoplanet atmosphere observations, ranging from hot gas giants to small temperate rocky worlds, will be one of the legacies of exoplanet science in the coming decade. Our understanding and interpretation of such observations will hinge on our ability to link observations with atmospheric theoretical studies that critically rely on fundamental molecular and atomic opacities. Computing such opacities is a highly inaccessible process which requires several terabytes of available disk space, hours of CPU time per pressure-temperature combination, and requires users to carefully aggregate line lists data from various sources. Ultimately, this limits access to data and model intercomparison studies within the exoplanet community. To interpret next generation exoplanet observations successfully and robustly, the community needs access to validated and up-to-date opacities. This was the motivation for the MAESTRO (Molecules and Atoms in Exoplanet Science: Tools and Resources for Opacities) database, a new NASA-supported opacity service that can be accessed by the community via a web interface. Professor Lewis will present MAESTRO and discuss the outcome of a multi-year collaboration to develop community standards in computing opacities. This is timely because subtle choices in opacities lead to model inconsistencies in the analysis of both high-resolution (R>10,000) and low resolution (JWST-like) observations. The MAESTRO team reflects a diversity in expertise: the maintainers of ExoMol, HITRAN/HITEMP, and various exoplanet and stellar atmosphere models. With its recent release, MAESTRO will prove to be an invaluable community resource in the era of JWST and beyond. 

Speakers

09:30-09:45
Discussion
09:45-10:15
Modelling exoplanet atmospheres at high resolution

Abstract

In recent years ground-based high-resolution spectroscopy has revolutionised how we detect and constrain constituent chemical species in the atmospheres of exoplanets. In the last five years alone a range of new spectrographs have come online, capable of higher sensitivity and spectral coverage. These facilities allow for very high spectral resolution observations (R>20,000) to detect many thousands of individual line features from spectrally active species in the atmosphere. A wide array of molecular, atomic and ionic species have been clearly observed in numerous transiting exoplanets, ranging from the optical to infrared, most notably for ultra-hot Jupiters with temperatures in excess of 2000K. From recent work on retrievals we have also been able to determine chemical abundances and explore a wide range of parameter space through robust statistical frameworks. These frameworks are essential for accurate characterisation, determining formation and migration of exoplanets as well as contextualising our own Solar System. In addition, with the spectral power and sensitivity of high-resolution spectroscopy we have been able to explore atmospheric dynamics in exoplanets for the first time. This due to atmospheric winds which result in Doppler shifts and broadening of signals of exoplanetary spectra. Dr Gandhi will discuss the latest developments in theoretical modelling of exoplanets at high resolution as well as the constraints and trends that we observe in the chemistry and dynamics from observations. They will also discuss the next generation of large ground-based facilities, which will enable us to explore the atmospheres of much cooler, rocky planets for the first time when they come online at the end of the decade.

Speakers

10:15-10:30
Discussion
10:30-11:00
Break
11:00-11:30
HITRAN and HITEMP data for high resolution exoplanet spectroscopy

Abstract

Studies of exoplanets have accelerated in recent years thanks to improved observation and analysis techniques. Exoplanet atmospheres have been shown to be diverse, not just in temperature, but also composition, and the latest analyses from JWST spectra are already revealing tantalising discoveries. Characterising these atmospheres is dependent on the unique molecular signatures that are present in their spectra. Therefore it is vital that the spectroscopic parameters used for interpreting atmospheric models are accurate and appropriate for these new worlds. The HITRAN and HITEMP databases provide line-by-line parameters for 55 molecules, experimental cross-sections for over 300 molecules for which no reliable quantum mechanical models exist, as well as collisional induced absorption data. This presentation will highlight the state-of-the-art data available in HITRAN and HITEMP with a particular focus on recent line list improvements and the addition of line-broadening parameters for planetary atmospheres (such as those dominated by H2/He, or CO2). This presentation will also contemplate the limitations of current spectroscopic data for the interpretation of planetary spectra.

Speakers

11:30-11:45
Discussion
11:45-12:15
Use of the ExoMol database of high accuracy spectroscopy of exoplanets

Abstract

The use of high resolution spectroscopy using cross correlation techniques to study the spectra of molecules in the atmospheres of exoplanets places significant demands on the accuracy of the laboratory data used to analyse these spectra. The ExoMol project provides molecular line lists for exoplanetary and other atmospheres which are computed using first principles quantum mechanical methods informed by available experimental data. The original ExoMol line lists focused heavily on providing completeness at higher temperatures allowing opacities to be generated and the construction of appropriate spectral models for analysing transit spectra. The much higher resolution needed for cross correlation spectroscopy means that these line lists need to be refactored. To do this we use available laboratory measurements which are used to provide high accuracy energy levels which in turn are used generate key portions of the molecular spectrum with required accuracy. The talk will describe the MARVEL (measured active rotation vibration energy levels) procedure used for this process and the development of appropriate high accuracy models for challenging molecules such as VO, as well as how this method can be used to provide accurate spectra of isotopically substituted molecules.

Speakers

12:15-12:30
Discussion

Chair

13:30-14:00
Using a variety of molecules in exoplanet atmosphere studies

Abstract

Exoplanet atmospheres are thought to host a rich variety of molecular species, and so having appropriate line list data (molecular energy levels and transitions) and opacities (as a function of pressure and temperature) is important for proper atmospheric characterisation. The requirements for molecular data differ depending on whether they are to be used for low- or high-resolution studies. Dr Chubb will talk about methods which use laboratory data to bring theoretically computed line lists towards spectroscopic accuracy, in order that they can be used in high-resolution cross-correlation studies. They have led such projects as part of the ORBYTS (Original Research For Young Twinkle Students) initiative, where groups of 16–18 year olds are involved in conducting and publishing real research. The ExoMolOP database, on the other hand, is primarily for retrieval codes which make use of low-resolution spectra, requiring the line lists to be complete up to high-temperatures (typically 1000-2000K). Dr Chubb will talk a bit about these data and how they have been used to search for molecules in exoplanet atmospheres. They will also talk a little on how high-resolution molecular data can be used in the modelling of polarised reflection spectra to determine cloud properties in exoplanet atmospheres.

Speakers

14:00-14:15
Discussion
14:15-14:45
Metals and more: high-resolution spectroscopy of ultra-hot Jupiters

Abstract

Ultra-hot Jupiters tend to orbit hot early type stars in short periods and are heated to extreme temperatures far over 2,000 K on their day-sides. All but the most strongly bound molecules are dissociated and many atoms may be significantly thermally ionised. The dominant sources of line opacity are due to metals and some molecules including metal oxides. Much of these absorb efficiently at short wavelengths, causing strong thermal inversions. These inversions affect the atmospheric structure, chemistry, as well as global circulation of gas and heat. Excitingly, these thermal inversions can be observed very effectively using high-resolution spectroscopy of the day-side, where a multitude of metals exhibit line emission. Together with transmission spectroscopy that senses the day-to-night terminator, we can use these observations to constrain the chemical and thermal structure of the atmosphere in three dimensions. The group has analysed observations of a collection of ultra-hot Jupiters, and find tantalising commonalities and differences between them.

Speakers

14:45-15:00
Discussion
15:00-15:30
Break
15:30-16:00
Recent theoretical approaches to high-resolution pressure-broadening parameters for remote sensing of exoplanetary atmospheres

Abstract

Spectroscopic studies of exoplanetary atmospheres by the next-generation space missions, such as the James Webb Space Telescope (JWST) and Atmospheric Remote-sensing Exoplanet Large-survey (ARIEL), will rely on spectroscopic data available at mid-infrared and visible/infrared wavelengths for the bulk of already detected or expected molecules. Due to the specific conditions of hot atmospheres and chemical reactions which lead to the formation of spectroscopically active species ('exotic' molecules and molecular ions), laboratory studies are extremely scarce in both infrared/microwave and visible/ultraviolet regions. Therefore, there is a huge demand for robust theoretical approaches and estimates that could provide line-shape parameters for wide ranges of temperatures and pressures and large variety of perturbers.

For the UV region, where the lack of the line shape data is especially critical, theoretical modelling, motivated by the known effect of the strongly dominating adiabatic collisions, is introduced based on the Fourier-integral/phase-shift theory and ab initio interaction potentials. For the IR/MW region, where many classical, quantum-mechanical, and semi-classical theoretical approaches to collisional line-broadening and shifting are available but require pre-computed reliable potential-energy surfaces and CPU-costly calculations for each collisional pair, Professor Buldyreva suggests a simple theoretical expression requiring a minimal set of input parameters (kinetic molecular properties and the character of the leading term in the intermolecular interaction potential). Examples for active molecules from the ExoMol database are given.

Speakers

16:00-16:15
Discussion
16:15-17:00
Panel session