Defense
Student: Pâmela Reis Querido
Program: Astronomy
Title: “Mass loss in Be stars: a spectroscopic and polarimetric approach"
Advisor: Prof. Dr. Alex Cavaliéri Carciofi - IAG/USP
Judging comitee:
- Prof. Dr. Alex Cavaliéri Carciofi – Presidente e Orientador – IAG/USP
- Prof. Dr. Marcos Perez Diaz – IAG/USP
- Dr. Felipe Donizeti Teston Navarete - LNA/MCTI
- Prof. Dr. Rodrigo Georgetti Vieira – UFS (por videoconferência)
Abstract:
Be stars are objects of great interest in stellar astrophysics, as they lie near the critical
rotation limit for massive main-sequence stars. In combination with non-radial pulsations,
their rapid rotation leads to mass loss events, resulting in the formation of viscous
decretion disks. Understanding the mechanisms responsible for the ejection of material
and the formation of circumstellar disks around these stars is essential not only for
elucidating stellar physics under extreme conditions but also for understanding the
evolution of massive stars. This master's project aims to develop a robust and general
methodology to investigate mass-loss events in Be stars, accounting for the diversity of
observables used in their study. The analysis was based on data from the FRISBeEE
project (Following Really Intensively with Spectroscopy: Be Emission Events), which
conducts systematic monitoring of Be stars using the LCO's (\textit{Las Cumbres}
Observatory), NRES (Network of Robotic Echelle Spectrographs) and amateur
spectroscopy. Additionally, observational campaigns were carried out at the \textit{Pico
dos Dias} Observatory (OPD), focusing on high-precision polarimetric data to capture
microvariations in polarization associated with mass ejection events. The sample includes
representative cases with different morphological complexities of the circumstellar disks,
such as stars with well-developed disks, stars without pre-existing disks, and binary
systems. The methodology involved the development of a manual spectral analysis code
capable of extracting key parameters such as equivalent width, peak separation, line
center velocity, and other classical metrics related to disk asymmetries. However, defining
certain parameters proved to be one of the major challenges of this work, due to the
complexity of the analyzed line profiles. In this context, several strategies were tested and
compared, and a new approach was proposed for handling some spectral quantities. For
polarimetry, time evolution of linear polarization and polarization angle, as well as $QU$
diagrams, were produced, allowing the identification of variations associated with dynamic
events in the disk. In cases such as f\,Car, $\pi$\,Aqr, and 12\,Vul, spectroscopic and
polarimetric signatures allowed us to track the formation/dissipation and homogenization
of the disk over time. In contrast, for V658\,Car, the data confirm the complexity
introduced by binary interactions, which result in complex line profiles. This work
highlights the importance of multifaceted observational approaches -- combining high-
precision spectroscopy and polarimetry -- for studying mass-loss mechanisms in Be stars.
The results presented here contribute to advancing our understanding of the physical
processes governing mass loss and disk evolution in these stars and provide valuable input
for future hydrodynamic models. Furthermore, the developed methodology can be applied
to future studies, expanding our understanding of other stars.
Palavras- chave: Be stars, Mass loss, Circumstellar disk, Spectroscopy, Polarimetry