Figure: Dust continuum ALMA observation (left) vs simulated observation (right) of the protoplanetary disk around HD 100546.

We present the self-calibrated 0.9mm deep ALMA observations of the protoplanetary disk around HD 100546. By analyzing them, we confirm the existence of two dust rings as suggested by recent literature, and find that the outer ring is much fainter than the inner one.

Assuming that the two dust rings are caused by two embedded planets, we managed to generate a simulated observation which closely reproduces the ALMA image and match the radial intensity profile. To do so, we ran multi-fluid simulations (gas and multiple dust species) employing the planet-disk interaction code FARGO3D (Benítez-Llambay & Masset 2016), and used its outputs for the gas and dust distribution to perform radiative transfer calculations with the code RADMC-3D. Animation of one of the gas numerical simulations at this URL (credit: Max Ackermann Pyerin).

We find that an inner planet located at 13au with eight Jupiter masses as well as an outer planet located at 143au with three Jupiter masses lead to the best agreement between the ALMA and simulated observation. To explain the very low brightness of the outer ring relative to the inner one, we demonstrate that the outer planet needs to form much later than the inner one, and that the initial disk gas surface density needs to follow an exponentially tapered power law.

• Publication: Pyerin, Delage et al. (2021).

• My contribution: Max Ackermann Pyerin was a bachelor student from the University of Heidelberg working in our research group in the context of his bachelor thesis. I supervised him for the theoretical/numerical modelling part of the publication (FARGO3D & RADMC-3D), leading to the simulated observations presented in the paper.

Figure: Probability distribution of the gap size (measured with its outer edge) and accretion rate (measure at 1.5au) for a population synthesis model of protoplanetary disks dispersing through X-ray photoevaporation, with the presence of a dead zone (top) or without (bottom).

Observations of young stars hosting transition disks show that several of them have high accretion rates, despite their disks presenting extending cavities in their dust continuum emission. This represents a challenge for theoretical models, which struggle to reproduce both features simultaneously. 

We demonstrate that a disk evolution model (gas and dust dynamics with grain growth included, using the code DustPy), including X-ray photoevaporative dispersal and a dead zone prescription, successfully explains such observable properties of transition disks. This is due to the differential evolution of the inner and outer disk: the higher turbulence in the outer disk leads its accretion rate to decrease faster and enter into the photoevaporative dispersal regime earlier, compared to the inner disk that hosts a dead zone with much lower turbulence. 

To do so, we performed a population synthesis study of the gas component, and obtained simulated observations as well as SEDs of the dust component through radiative transfer calculations with the code RADMC-3D. For a dead zone of turbulence level 1e-4 and an extent of 10au, we predict that 63% of transition disks should still be accreting and find that half of them display high accretion rates. From our dust evolution simulations, we show that the inner disk retains millimiter-to-centimeter dust particles, while the dust in the outer disk forms a ring at the edge of the photoevaporative gap with grain sizes ranging from micrometer to a few millimeters.

• Publication: Gárate, Delage et al. (2021). MPIA press release at this URL.

• My contribution: In the study, we show that the fraction of accreting transition disks is crucially controlled by the turbulence level in the dead zone and its extent. I thus performed a validation test for the dead zone prescriptions used in the publication by using the 1+1D MRI-driven disk accretion model presented in Delage et al. (2022).

The Project EDEN is a collaborative project led by Prof. Daniel Apai between the Steward Observatory of the University of Arizona, MPIA, the Vatican observatory, and the NCU Institute for Astrophysics. It exploits state-of-the-art knowledge and methods in astrophysics, planetary science, and astrobiology in order to search for and characterize nearby planets around late M-dwarf stars. The main goal is to search for life in the solar neighborhood, leading to the discovery of the closest habitable planets to us where humankind could potentially send probes.

Here, we present the yet most powerful photometric monitoring campaign of 22 nearby late M-dwarfs, utilizing data from over 1000 nights on 6 medium-diameter telescope (including the Calar Alto 123m). Our survey samples all known, northern late M-dwarfs within 15pc, with additional targets between 15pc and 19pc.

• Publication: Dietrich et al., incl. Delage (2023).

• My contribution: I am part of the observing team. I have been fully controlling the Calar Alto 123m telescope, and have remotely led over 30 nights so far (from taking the dark and flats to observing the science objects).

Figure: Physical mechanism behind the run-away disintegration of the ultra-short period rocky planets.

Among the incredible diversity of observed extra-solar planets, there is a class of planets called ultra-short period (USP) planets, which are planets revolving their host star in less than a day. The USP planet KIC 12557548b is of particular interest because its transit profile is very unusual: it is is time-dependent, wavelength-dependent, and has an asymmetric shape. The leading interpretation is an elongated dusty comet-like tail, gravitationally bound to the solid-body planet. KIC 12557548b is in such a close-in orbit that its rocky crust is disintegrating over time through sublimation/evaporation. The run-away disintegration process is a thermal hydrodynamic atmospheric escape made of dust and gas occurring in the form of a Parker-type outflow, and called "Catastrophic Evaporation" phase.

To describe the outflow properties when the planet undergoes the Catastrophic Evaporation phase, we built a time-dependent 1D radiative-hydrodynamic model accounting for dust-gas interactions. Such a model is a direct follow-up of the work done by Perez-Becker & Chiang (2013), which hypothesized that the time-variability of that phase comes from the time-dependent coupling between the gas density at the base of the outflow and the dust optical depth.

We find that that this idea does not explain the time-variability of the Catastrophic Evaporation phase. Instead, we propose two new ideas worth exploring for future works: it might come from (1) the time-dependent condensation process of dust particles within the gaseous outflow; or (2) the time-dependent rain-out process of dust particles from the gaseous outflow.

• Publication: MSc thesis (not public).