Königstuhl Kolloquium

Brown dwarfs are often described as failed stars, however the flip side of this description is that they can also be described as over-ambitious planets. With masses between 13-70 Jupiter masses they have cool atmospheres dominated by cloud features, molecules and show features due to weather.  These atmospheres have a lot of similarities with atmospheres we see in planets in our solar system, and also directly imaged exoplanets.  The question then is: How like hot Jupiters are irradiated brown dwarfs? 

In this seminar I will describe the known irradiated brown dwarfs and how they evolve into post-common envelope systems containing a white dwarf. These rare binaries have very short periods (~hrs) and the brown dwarf is irradiated by the white dwarf companion, often with large amounts of UV radiation. I will discuss the atmospheres of these highly irradiated brown dwarfs and their similarities with irradiated exoplanets.

All planetary atmospheres are 3D in nature. This is particularly true for the majority of exoplanets we observe today : tidally-locked, close in, giant planets. Atmospheric flow from the dayside to nightside of these worlds shape the 3D thermal, chemical and cloud structure. Understanding this 3D structure is crucial to properly interpret current and future observations.

I will show how recent breakthrough in telescopes and instrumentations allow us directly measure dynamical quantities and map the 3D structure of exoplanets. I will particularly highlight how wind speeds can be directly measured from ground-based high-spectral resolution observations and how temperature, chemical and cloud maps can be obtained through JWST observations, including the recently observed NIRspec/PRISM phase curve of the hot Jupiter NGTS-10b.

Signature Speaker

All planetary atmospheres are 3D in nature. This is particularly true for the majority of exoplanets we observe today : tidally-locked, close in, giant planets. Atmospheric flow from the dayside to nightside of these worlds shape the 3D thermal, chemical and cloud structure. Understanding this 3D structure is crucial to properly interpret current and future observations.

I will show how recent breakthrough in telescopes and instrumentations allow us directly measure dynamical quantities and map the 3D structure of exoplanets. I will particularly highlight how wind speeds can be directly measured from ground-based high-spectral resolution observations and how temperature, chemical and cloud maps can be obtained through JWST observations, including the recently observed NIRspec/PRISM phase curve of the hot Jupiter NGTS-10b.

Signature Speaker

As the fuel for star formation, molecular gas plays a crucial role in the evolution of galaxies. Advanced millimeter-wave facilities now make it possible to study the gas properties of large samples of nearby galaxies and to peer into the cold ISM of “typical” star forming galaxies throughout cosmic time. However, many details of the interplay between gas and star formation that drives galaxy evolution remain unsettled. In this talk, I will present my work refining our tools for measuring and interpreting the observational signatures of molecular gas. I will begin by reviewing recent efforts to measure the cosmic abundance of molecular gas, and its evolution over time. Pioneering studies with ALMA, NOEMA, and the VLA have now constrained the global history of molecular gas to cosmic noon and beyond. Achieving precision measurements of this history will require extensive surveys which push the limits of current facilities. I have developed mocks for current and future surveys to help guide the design of the next generation of molecular gas deep fields. Precision measurements of the cosmic molecular gas history require surveys over significantly larger volumes than have been achieved to date, and I will discuss possible avenues for accomplishing such a survey. The novel technique of “line intensity mapping” (LIM), which can constrain the agreagate gas content of galaxies too faint to be individually detected, provides one path forward using existing facilities. I will provide an overview of the LIM technique, highlight a few upcoming line intensity mapping projects, and present upper limits on the CO-galaxy cross-power spectrum at redshift 2 derived from the exploratory CO Power Spectrum Survey, which serve as a proof of concept for future projects.

While much of our understanding of molecular gas comes from studies using the CO(1-0) line, other tracers gas tracers such as the higher energy CO lines, are increasingly popular. In the second half of my talk I will introduce the Arizona Molecular ISM Survey with the SMT (AMISS), a multi-line study of 177 nearby galaxies designed cross-calibrate the CO(1-0), CO(2-1), and CO(3-2) lines as tracers of molecular gas. The large sample and careful calibration of AMISS make it possible to robustly measure correlations between the excitation of CO emitting gas and host galaxy properties on a galaxy integrated scale. The three lines are not perfectly interchangeable tracers and the luminosity ratios between them vary systematically over the galaxy population. Using the AMISS sample, I characterize these trends, providing an empirical prescription for translating between gas measurements made with different CO lines, and then explore the utility of CO line ratios as diagnostics of conditions in the interstellar media of galaxies.

As the fuel for star formation, molecular gas plays a crucial role in the evolution of galaxies. Advanced millimeter-wave facilities now make it possible to study the gas properties of large samples of nearby galaxies and to peer into the cold ISM of “typical” star forming galaxies throughout cosmic time. However, many details of the interplay between gas and star formation that drives galaxy evolution remain unsettled. In this talk, I will present my work refining our tools for measuring and interpreting the observational signatures of molecular gas. I will begin by reviewing recent efforts to measure the cosmic abundance of molecular gas, and its evolution over time. Pioneering studies with ALMA, NOEMA, and the VLA have now constrained the global history of molecular gas to cosmic noon and beyond. Achieving precision measurements of this history will require extensive surveys which push the limits of current facilities. I have developed mocks for current and future surveys to help guide the design of the next generation of molecular gas deep fields. Precision measurements of the cosmic molecular gas history require surveys over significantly larger volumes than have been achieved to date, and I will discuss possible avenues for accomplishing such a survey. The novel technique of “line intensity mapping” (LIM), which can constrain the agreagate gas content of galaxies too faint to be individually detected, provides one path forward using existing facilities. I will provide an overview of the LIM technique, highlight a few upcoming line intensity mapping projects, and present upper limits on the CO-galaxy cross-power spectrum at redshift 2 derived from the exploratory CO Power Spectrum Survey, which serve as a proof of concept for future projects.

While much of our understanding of molecular gas comes from studies using the CO(1-0) line, other tracers gas tracers such as the higher energy CO lines, are increasingly popular. In the second half of my talk I will introduce the Arizona Molecular ISM Survey with the SMT (AMISS), a multi-line study of 177 nearby galaxies designed cross-calibrate the CO(1-0), CO(2-1), and CO(3-2) lines as tracers of molecular gas. The large sample and careful calibration of AMISS make it possible to robustly measure correlations between the excitation of CO emitting gas and host galaxy properties on a galaxy integrated scale. The three lines are not perfectly interchangeable tracers and the luminosity ratios between them vary systematically over the galaxy population. Using the AMISS sample, I characterize these trends, providing an empirical prescription for translating between gas measurements made with different CO lines, and then explore the utility of CO line ratios as diagnostics of conditions in the interstellar media of galaxies.

The Galactic center region has a mass of ~10^9 M_sun. It consists of the nuclear stellar disk (NSD), a flat, rotating stellar structure, and the nuclear star cluster (NSC), the densest concentration of stars in the Galaxy. 

The NSC and NSD are distinct structures of the Milky Way, but also connected to the larger Milky Way structures, e.g. via the inflow and outflow of gas, and the infall of star clusters. Our knowledge of the larger Milky Way structures, Galactic disc, bulge and halo, has expanded in recent years through surveys and dedicated missions. Hidden behind large amounts of interstellar dust, the Galactic centre structures, NSC and NSD, are inaccessible for these surveys, and they miss an important piece for our understanding of the Milky Way's formation and evolution. 

In this talk I will present spectroscopic observations of the Galactic centre, resulting in >\;2,500 stellar spectra. I will show the spatial distribution of young (few Myr old) stars, the metallicity distribution of the older (several Gyr) red giant stars, and spatial variations of the metallicity distribution. 

The Galactic center region has a mass of ~10^9 M_sun. It consists of the nuclear stellar disk (NSD), a flat, rotating stellar structure, and the nuclear star cluster (NSC), the densest concentration of stars in the Galaxy. 

The NSC and NSD are distinct structures of the Milky Way, but also connected to the larger Milky Way structures, e.g. via the inflow and outflow of gas, and the infall of star clusters. Our knowledge of the larger Milky Way structures, Galactic disc, bulge and halo, has expanded in recent years through surveys and dedicated missions. Hidden behind large amounts of interstellar dust, the Galactic centre structures, NSC and NSD, are inaccessible for these surveys, and they miss an important piece for our understanding of the Milky Way's formation and evolution. 

In this talk I will present spectroscopic observations of the Galactic centre, resulting in >\;2,500 stellar spectra. I will show the spatial distribution of young (few Myr old) stars, the metallicity distribution of the older (several Gyr) red giant stars, and spatial variations of the metallicity distribution. 

Blazars are those kinds of active galactic nuclei, where the relativistic jet points towards Earth. Due to relativistic beaming, the processes inside the jet can be studied in great detail. Kinetic radiation codes provide an excellent opportunity to obtain the particle distributions and to describe interaction processes within the jet, as well as to model the radiative output of the jet. Here, I will present the code "ExHaLe-jet" that describes extended jets considering both leptonic and hadronic processes. I will highlight the influence of thermal photon sources external to the jet, which are prime targets for particle-photon interactions inside the jet.
In a second part of the talk, I will discuss a recent observational result, where a blazar jet seems to suddenly, partially switch off. 

Blazars are those kinds of active galactic nuclei, where the relativistic jet points towards Earth. Due to relativistic beaming, the processes inside the jet can be studied in great detail. Kinetic radiation codes provide an excellent opportunity to obtain the particle distributions and to describe interaction processes within the jet, as well as to model the radiative output of the jet. Here, I will present the code "ExHaLe-jet" that describes extended jets considering both leptonic and hadronic processes. I will highlight the influence of thermal photon sources external to the jet, which are prime targets for particle-photon interactions inside the jet.
In a second part of the talk, I will discuss a recent observational result, where a blazar jet seems to suddenly, partially switch off. 

With a new-generation of great observatories coming online this decade, unprecedented insights into exoplanets will soon be within reach. Observatories such as the James Webb Space Telescope (JWST) notably enable the study of atmospheres around terrestrial exoplanets and can reveal tri-dimensional structures in the atmospheres of their larger counterparts. Robustly leveraging new observations to reach such achievements will however require extra care as the models currently used may not be up to par with their precision. 

During this presentation, I will introduce work done by MIT's Disruptive Planets group and collaborators towards supporting the robust in-depth characterization of exoplanets. I will specifically discuss how not accounting for the true shape of a planet can lead to a misinterpretation of its interior properties as well as atmospheric structure\; how the current state of our understanding of light-matter interactions can similarly affect our interpretation of planetary spectra and thus inferences regarding their atmospheric properties\; and how the current state of emission spectrum models for stars may even prevent from disentangling between the contribution of a planet and its host star, to start with.  I will also present possible ways to address these challenges. I will end with a step-by-step roadmap to the robust characterization of temperate terrestrial planets with JWST, which includes habitability assessment

With a new-generation of great observatories coming online this decade, unprecedented insights into exoplanets will soon be within reach. Observatories such as the James Webb Space Telescope (JWST) notably enable the study of atmospheres around terrestrial exoplanets and can reveal tri-dimensional structures in the atmospheres of their larger counterparts. Robustly leveraging new observations to reach such achievements will however require extra care as the models currently used may not be up to par with their precision. 

During this presentation, I will introduce work done by MIT's Disruptive Planets group and collaborators towards supporting the robust in-depth characterization of exoplanets. I will specifically discuss how not accounting for the true shape of a planet can lead to a misinterpretation of its interior properties as well as atmospheric structure\; how the current state of our understanding of light-matter interactions can similarly affect our interpretation of planetary spectra and thus inferences regarding their atmospheric properties\; and how the current state of emission spectrum models for stars may even prevent from disentangling between the contribution of a planet and its host star, to start with.  I will also present possible ways to address these challenges. I will end with a step-by-step roadmap to the robust characterization of temperate terrestrial planets with JWST, which includes habitability assessment

Abstract: In the cold dark matter model, we think the Milky Way \;hosts many dark matter subhalos - some of them host luminous dwarf galaxies, others devoid of stars. \;In this talk, I'll discuss how cold dark matter substructures get trimmed down due to the Milky Way tidal field and how this affects embedded dwarf galaxies. \;In particular, I'll show that if dark matter subhalos have centrally-divergent density cusps, they are very resilient to tidal effects, and the sizes and velocity dispersions of heavily-stripped Milky Way satellite galaxies are set by the properties of their underlying dark matter subhalos. \;The results raise challenging questions about the nature of dark matter on galactic scales, as the existence of extended and dynamically cold Milky Way satellite galaxies, like the Crater 2 and Antlia 2 dwarfs, appears in conflict with simple predictions from cold dark matter models. \;

Linear fitting is often used for interpolation of data, for example when you have calibration data and you want to fit a smooth, flexible function. Or you want to de-trend a time series or normalize a spectrum. I will discuss how this fitting is done, with ordinary least squares and extensions thereof. Extremely surprisingly, it is often valuable to choose far more parameters than data points, despite folk rules to the contrary\; over-fitting is not (mainly) a problem of having too many parameters. It is even possible to take the limit of infinite parameters, at which a regularized least-squares fit can become the mean of a Gaussian process, which is a very useful model. I recommend cross-validation as a practical method for model selection, and jackknife resampling as a practical method for estimating the uncertainties of the predictions made by the model. (work with Soledad Villar)

Recent observing campaigns have revealed a great diversity in exoplanetary systems whose origin is yet to be understood. How and when planets form, and how they evolve and interact with their birth environment, the protoplanetary disks, are major open questions. Protoplanetary disks evolve and dissipate rapidly while planets are forming, implying a direct feedback between the processes of planet formation and disk evolution. These mechanisms leave clear imprints on the disk structure that can be directly observed. In the past few years, high-resolution observations of protoplanetary disks obtained in the infrared and in the millimeter regime have led to exquisite images and shown that small scale structures are ubiquitous in protoplanetary disks. I will present recent observational results on protoplanetary disks obtained with VLTI, VLT/SPHERE and ALMA, that allow to probe the disk structure and the dynamics of solids, and in particular, in the so far unique system that hosts two directly imaged protoplanets.

Recent observing campaigns have revealed a great diversity in exoplanetary systems whose origin is yet to be understood. How and when planets form, and how they evolve and interact with their birth environment, the protoplanetary disks, are major open questions. Protoplanetary disks evolve and dissipate rapidly while planets are forming, implying a direct feedback between the processes of planet formation and disk evolution. These mechanisms leave clear imprints on the disk structure that can be directly observed. In the past few years, high-resolution observations of protoplanetary disks obtained in the infrared and in the millimeter regime have led to exquisite images and shown that small scale structures are ubiquitous in protoplanetary disks. I will present recent observational results on protoplanetary disks obtained with VLTI, VLT/SPHERE and ALMA, that allow to probe the disk structure and the dynamics of solids, and in particular, in the so far unique system that hosts two directly imaged protoplanets.

Recent observing campaigns have revealed a great diversity in exoplanetary systems whose origin is yet to be understood. How and when planets form, and how they evolve and interact with their birth environment, the protoplanetary disks, are major open questions. Protoplanetary disks evolve and dissipate rapidly while planets are forming, implying a direct feedback between the processes of planet formation and disk evolution. These mechanisms leave clear imprints on the disk structure that can be directly observed. In the past few years, high-resolution observations of protoplanetary disks obtained in the infrared and in the millimeter regime have led to exquisite images and shown that small scale structures are ubiquitous in protoplanetary disks. I will present recent observational results on protoplanetary disks obtained with VLTI, VLT/SPHERE and ALMA, that allow to probe the disk structure and the dynamics of solids, and in particular, in the so far unique system that hosts two directly imaged protoplanets.

Recent observing campaigns have revealed a great diversity in exoplanetary systems whose origin is yet to be understood. How and when planets form, and how they evolve and interact with their birth environment, the protoplanetary disks, are major open questions. Protoplanetary disks evolve and dissipate rapidly while planets are forming, implying a direct feedback between the processes of planet formation and disk evolution. These mechanisms leave clear imprints on the disk structure that can be directly observed. In the past few years, high-resolution observations of protoplanetary disks obtained in the infrared and in the millimeter regime have led to exquisite images and shown that small scale structures are ubiquitous in protoplanetary disks. I will present recent observational results on protoplanetary disks obtained with VLTI, VLT/SPHERE and ALMA, that allow to probe the disk structure and the dynamics of solids, and in particular, in the so far unique system that hosts two directly imaged protoplanets.

Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition\; they provide the most stringent tests of general relativity, they make possible the study of faint and rare objects such as black holes and neutron stars, and they are the progenitors of gravitational wave sources. The components of binaries often interact, dramatically changing their evolution and giving rise to a spectacular zoo of astrophysical phenomenology. To understand stars -- particularly massive stars -- it is necessary to understand binaries. Large-scale stellar surveys such as Gaia, TESS, and SDSS-V are transforming the binary field, making possible both comprehensive population demographics and the discovery of rare objects. I will discuss new insights gleaned from surveys in recent years, including the creation of stripped-envelope stars following binary mass transfer, the formation of equal-mass "twin" binaries in circumbinary disks, the metallicity-dependence of the binary fraction, and the discovery of planets in binaries. I will focus in particular on the search for dormant stellar-mass black holes in binaries, discussing recent candidates and the path forward to characterizing the detached black hole population.

Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition\; they provide the most stringent tests of general relativity, they make possible the study of faint and rare objects such as black holes and neutron stars, and they are the progenitors of gravitational wave sources. The components of binaries often interact, dramatically changing their evolution and giving rise to a spectacular zoo of astrophysical phenomenology. To understand stars -- particularly massive stars -- it is necessary to understand binaries. Large-scale stellar surveys such as Gaia, TESS, and SDSS-V are transforming the binary field, making possible both comprehensive population demographics and the discovery of rare objects. I will discuss new insights gleaned from surveys in recent years, including the creation of stripped-envelope stars following binary mass transfer, the formation of equal-mass "twin" binaries in circumbinary disks, the metallicity-dependence of the binary fraction, and the discovery of planets in binaries. I will focus in particular on the search for dormant stellar-mass black holes in binaries, discussing recent candidates and the path forward to characterizing the detached black hole population.

Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition\; they provide the most stringent tests of general relativity, they make possible the study of faint and rare objects such as black holes and neutron stars, and they are the progenitors of gravitational wave sources. The components of binaries often interact, dramatically changing their evolution and giving rise to a spectacular zoo of astrophysical phenomenology. To understand stars -- particularly massive stars -- it is necessary to understand binaries. Large-scale stellar surveys such as Gaia, TESS, and SDSS-V are transforming the binary field, making possible both comprehensive population demographics and the discovery of rare objects. I will discuss new insights gleaned from surveys in recent years, including the creation of stripped-envelope stars following binary mass transfer, the formation of equal-mass "twin" binaries in circumbinary disks, the metallicity-dependence of the binary fraction, and the discovery of planets in binaries. I will focus in particular on the search for dormant stellar-mass black holes in binaries, discussing recent candidates and the path forward to characterizing the detached black hole population.

Binary stars are foundational to modern astrophysics. They underpin precision measurements of stellar structure, age, and composition\; they provide the most stringent tests of general relativity, they make possible the study of faint and rare objects such as black holes and neutron stars, and they are the progenitors of gravitational wave sources. The components of binaries often interact, dramatically changing their evolution and giving rise to a spectacular zoo of astrophysical phenomenology. To understand stars -- particularly massive stars -- it is necessary to understand binaries. Large-scale stellar surveys such as Gaia, TESS, and SDSS-V are transforming the binary field, making possible both comprehensive population demographics and the discovery of rare objects. I will discuss new insights gleaned from surveys in recent years, including the creation of stripped-envelope stars following binary mass transfer, the formation of equal-mass "twin" binaries in circumbinary disks, the metallicity-dependence of the binary fraction, and the discovery of planets in binaries. I will focus in particular on the search for dormant stellar-mass black holes in binaries, discussing recent candidates and the path forward to characterizing the detached black hole population.