| dc.description.abstract |
Newly formed stars accrete material from their parent cloud, which, due to conservation of angular
momentum, collapses into a disk-like structure around the young star. After approximately one
million years, the envelope around the star has completely dissipated and the system becomes
observable at optical wavelengths, making it possible to study the interaction between the star and
the disk.
Low-mass stars at this stage, known as Classical T Tauri Stars (CTTSs), have strong magnetic
fields that disrupt the accretion disk at a distance of a few stellar radii from the star. Gas flows from
the disk to the star along the magnetic field lines in a process called magnetospheric accretion,
ending in a shock at the stellar surface, which heats the photosphere and creates a hot spot.
Magnetospheric accretion is a complex process involving the exchange of matter, angular
momentum, and energy between the disk and the star. This process is accompanied by mass loss
via stellar and disk winds, which are driven by open magnetic field lines. These outflows play a
critical role in angular momentum extraction, preventing the star from spinning up.
In this PhD dissertation, I will discuss the main results of my research, which is based on high-
resolution spectroscopic data from the Echelle SPectrograph for Rocky Exoplanet and Stable
Spectroscopic Observations (ESPRESSO), the latest-generation echelle spectrograph at the
European Southern Observatory's Very Large Telescope (VLT), and photometric data from the
Transiting Exoplanet Survey Satellite (TESS).
High-resolution spectroscopy can be used to study the star-disk interaction and investigate the
structure of the magnetosphere and its temperature stratification, as well as the kinematics of CTTS
outflows and their complex, layered structure.
High-cadence photometric data from TESS allow to test magnetohydrodynamic simulations by
analyzing the rotational modulation of the hot spot. The analysis of the frequency spectrum of
CTTSs light curves enables the determination of the radius at which the disk is truncated by the
stellar magnetic field.
When combined together, these two techniques permit the determination of the amount of angular
momentum per unit time transferred from the star to the disk, allowing to constrain the mechanisms
that prevent the stellar spin-up in CTTSs. |
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