Phd Projects at CAS

PhD Project in Theory

Regions of the interstellar medium filled with atomic and molecular gas are the environments where the first stages of star formation occur. The nested hierarchical structure of molecular gas distribution, from diffuse giant clouds of up to hundreds of pc, through denser ~10 pc clouds and pc-sized clumps, down to very dense sub-pc cores, has a complex filamentary shape. Impressive recent progress in observing molecular gas and dust at different spatial scales has greatly improved our understanding of the density distribution in such environments. Combining these observations with sophisticated models of radiative transfer and applying recent advances in the theory of cosmic ray (CR) propagation in molecular gas makes it possible to self-consistently compute detailed physical and chemical structure of molecular clouds.

CRs are the main source of ionization of molecular gas. Interaction of the ionized hydrogen with neutral hydrogen molecules quickly leads to the formation of H3+ ions. These ions, in turn, trigger a chain of chemical reactions between charged and neutral gas species, producing several other key molecules. The ongoing activity of the CAS Theory Group in studying the CR transport and applying these models to nearby diffuse molecular clouds has delivered all essential ingredients necessary to start exploring the first stages of gas-phase chemistry in these objects.

We offer a Ph.D. position with the topic of CR-driven chemistry in diffuse molecular clouds. The work will be carried out at the interface between the CR theory and astrochemistry. It will be focused on analyzing observationally constrained ionization in nearby molecular clouds, applying and developing available chemical models to compute the formation of key molecular species in these regions, and providing predictions for future dedicated observations. The Ph.D. candidate will work in close collaboration with the members of CAS-Theory group, and will obtain necessary support and complementary advice from experts in astrochemistry and observations.

Supervisor: Dr.  Alexei Ivlev


PhD Project in Laboratory

In preparation for the upcoming observing facilities that will observe exoplanets, such as the ELT, ARIEL, and VLTI/ GRAVITY+ and the recently launched JWST, laboratory work is necessary. These facilities will provide an unprecedented sample of spectra of exoplanetary atmospheres and will, therefore, build a 'standard model' of how a planet's chemistry depends on its star and the condition of its birth. Laboratory data on stable molecules that compose exoplanetary atmospheres, however, are far from complete, especially at high temperatures. The impact of dominant gases on the trace species is also rather unknown, thereby making the determination of molecular abundances difficult. Infrared laboratory spectra will therefore be critical to interpret the upcoming data on exoplanetary atmospheres. This PhD project will be focused on high-resolution laboratory infrared spectroscopy to determine the effect of broadening induced by temperature and pressure with a set of different broadeners, to account for the different chemical environments. Supervisor: Dr. S. Spezzano


The Environment and Disk connection

The classical picture of star-formation involves a process dominated by the material in the parental dense core, and it is the underlying assumption for simulating the star- and disk-formation process in an isolated box, which has been widely used to learn about the star-formation process. The way in which the material is delivered down to the disk-forming scales plays a critical role, with important implications for planet formation. It controls the amount of angular momentum that is deposited in the central region, which affects the disk size and its chemical composition. Further, there is mounting observational evidence that the planet formation process starts earlier than previously thought, when material is still being deposited onto the disk from the surrounding environment. It is, therefore, crucial to understand the disk build-up phase, since this determines the initial conditions for planet formation.

Recent observations at different evolutionary stages, from the embedded Class 0 up to the late Class II, have revealed the presence of accretion streamers reaching disk scales. The different observational techniques highlight the complementary nature of the various observatories, building a more complete understanding of the accretion process onto the disk. These accretion flows could provide a mechanism to trigger accretion outbursts or modify the chemical abundances of the central region. At the same time, new numerical simulations of the disk and star-formation process have explored the role of non-spherical accretion onto the disk formation scales. However, the role of this previously unaccounted mass delivery mechanism on the early planet formation process is not well explored.

The PhD project will focus on study the interplay between disks and the environment. The data for the project is mostly based on an ongoing NOEMA large program, which is surveying 32 embedded young stellar objects in the Perseus molecular with many molecular lines (data have been obtained for 3/4 of the sample, and to be finished at the end of the year). Complementary ALMA observations are expected, thanks to different already approved ALMA projects. Some analysis techniques are already available, although opportunities for improving them are available and welcomed. In summary, this project will work very close with interferometric observations of molecular lines, and with a particular interest in constraining the disk and streamer interaction and their role in the disk and planet formation.

Related articles:

Pineda et al. (2020) link
Hsieh et al. (2023) link
Valdivia-Mena et al. (2022) link
Pineda et al. (2022) link

NOEMA large program: link

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