This week's PhD colloquia are highlighted.
| Date | Time | Title/Abstract | Speaker | Affil. |
|---|---|---|---|---|
| 05/02 Thursday DM1.15 | Dusty perspectives on the cradles of planets In this talk, I will present a brief overview of my PhD work, in which I used high-resolution radio observations from ALMA and VLA to investigate planet formation and disk substructures. The main goal was to understand how and when disk substructures form and how they relate to dust growth and planets. To address this, we studied two young systems, such as IRAS4A and HL Tau, as well as a population of disks in the nearby Lupus star-forming region. We asked whether substructures can be detected in optically thick environments and at optically thick wavelengths; whether the chemical structure of embedded young disks shows signatures of dust evolution, and, finally, whether substructures are only truly confined to large, massive disks or simply unresolved and hidden in compact disks. Together, the results of my PhD suggest that planet formation may begin very early in the disk lifetime, with important implications for how common planetary systems like our own may be. We also concluded that there is substantial value in studying small disks and optically thick regions with ALMA, beyond the brightest and largest disks, as these places provide equally important insights into disk structure and evolution. | Osmar Guerra-Alvarado | ||
| 16/02 Monday BW.0.31 | Modelling escaping atmospheres of highly irradiated exoplanets Due to observational biases in their detection techniques, many of the confirmed exoplanets orbit very close to their host stars. Consequently, their planetary atmospheres can be vulnerable to atmospheric escape. Observing such escaping atmospheres has become considerably more accessible thanks to the helium triplet feature at 1083 nm. This has enabled numerous transmission spectroscopy detections using ground-based rather than space-based telescopes. In this PhD colloquium talk, I will present a theoretical study of escaping exoplanetary atmospheres and their observable signatures. I will present the 1D, self-consistent theoretical model that we developed to numerically solve the hydrodynamic escape and the population of helium in the observationally important triplet state. I will show how atmospheric escape evolves over a planet’s lifetime and how related hydrogen and helium observational signatures are affected. Over shorter timescales, I will also highlight the influence that a stellar activity cycle can have on atmospheric escape. | Andrew Allan | ||
| 18/02 Wednesday BW0.17 | 14:00 | Probing the inner regions -A multi-wavelength view of accretion and outflow in protoplanetary disks The zoo of detected exoplanets reveals both the uniqueness of our own Solar System and the complexity of planetary system formation, sparking fundamental questions about how planetary systems form and evolve. Characterizing these processes is essential for understanding the origins of our own Solar System. In my thesis, we investigate planet formation from an observational point of view, focusing on the disks of gas and dust that surround young stars, known as protoplanetary disks. Using archival observations from the ALMA and VLA radio telescopes, we studied these disks across multiple wavelengths, focusing in particular on disk with large dust cavities, the so-called transition disks. We found that the compact emission close to stars in the cavity of most of these disks is dominated by free-free emission from ionized gas associated with jets and/or MHD winds. Moreover, we found a strong correlation between the ionized mass loss rate (as inferred form the free-free emission) and the accretion rate, suggesting that the outflow is strictly connected to the stellar accretion and that accretion in these disks is mainly driven by a jet and/or MHD wind. Consistent results are found in a larger sample of full protoplanetary disks (i.e., disks without large inner cavities). Among the studied transition disks, we found that the compact emission in AB Aur, one of the brightest transition disks in terms of compact free-free emission, reveals evidence for a precessing jet, possibly linked to the influenced of a companion object. Finally, we investigate the gas and dust structures in a sample of three transition disks around K and M stars. Contrary to expectation, no significant differences in the brightness temperature or in the gas-to-dust ratio are found between our disks and other transition disks around more luminous stars. This suggests that parameters other than luminosity play a role in setting the gas temperature structure. | Alessia Rota | |
| 23/02 Monday BW0.31 | 15:30 | A song of ice and gas: the formation and evolution of complex organic molecules (COMs). Probing chemical complexity in star-forming regions with ALMA and JWST Complex organic molecules (COMs), typically defined as carbon-bearing molecules with at least six atoms, have gained their popularity over the past several decades due to their importance in linking atoms and simple molecules with prebiotic species. COMs are suggested to be first formed in ice mantles of dust grains during the cold pre-stellar phase, and then sublimated into the gas phase when temperature goes up in the hot core phase. On one hand, gas-phase COMs can be observed in (sub)millimeter wavelengths using radio telescopes like ALMA, which have revealed a rich inventory of COMs in star-forming regions, particularly in protostars. On the other hand, the detection of solid-phase COMs (i.e., COM ices) was only confirmed for methanol (CH3OH), the simplest COM, but is now becoming promising for larger COMs using JWST and its Mid-InfraRed Instrument (MIRI). The absorption bands of COM ices mainly fall in the fingerprint region between 6.8 and 8.8 µm, which contains a series of vibrational modes of oxygen-bearing COMs (O-COMs). Tracing COMs in both gas and ice in young stellar objects (YSOs) can help us probe their formation history and shed light on how the chemistry evolves from simple to complex in the universe. In this talk, I will show the results from the latest ALMA and JWST observations (including both case and large-sample studies), with a nonexclusive focus on O-COMs, which are relatively abundant and therefore more detectable for both telescopes. In case studies of two chemically rich protostars, I made the first direct gas-to-ice comparisons in O-COM abundances, which suggest that both inheritance and reprocessing are playing a role in the evolution of COMs from ice to gas. Meanwhile, large-sample studies show strong evidence that O-COMs start forming in ices in very early stages of star formation. With the advent of JWST and the complement by ALMA, we are now entering a new era of exploring the complex chemistry in the universe. | Yuan Chen | |
| 26/03 Thursday | 14:00 | Willeke Mulder | STRW |
For questions and/or suggestions concerning the colloquium series. Please contact Andrew Sellek (e-mail ).