Fellows :: Stars

Here you may find information on the fellows of the PhD::SPACE Program that have selected a topic on the thematic line on Towards a comprehensive study of stars.

2019/B025 Fellow: Thibault Boulet (ongoing)

Fellowship: PD/00040/2012 – PD/BD/150426/2019 - FCT

Advisors: Tiago Campante (IA-U.Porto), Vardan Adibekyan (IA-U.Porto), Aldo Serenelli (ICE-CSIC and IEEC, Bellaterra, Spain)

PhD Topic (2019/224): Galactic archaeology of solar-type stars with the NASA TESS mission

The Transiting Exoplanet Survey Satellite (TESS) is a NASA space mission, launched in April 2018, that will perform an all-sky survey for planets transiting bright nearby stars. Furthermore, TESS’s excellent photometric precision will enable asteroseismology, the study of stars by the observation of their natural, resonant oscillations. Asteroseismology is proving to be particularly relevant for the study of solar-type stars (i.e., low-mass, main-sequence stars and cool subgiants), in great part due to the exquisite photometric data previously made available by NASA’s Kepler space telescope and, more recently, by the repurposed K2 mission. In extending the legacy of Kepler/K2, one will perform an ensemble asteroseismic study of bright solar-type stars that reside in the solar neighborhood, making use of data collected by TESS. The proposed research will provide a well-characterized sample of benchmark solar-type stars to be used in studies of the chemical evolution of the solar neighborhood, which in turn will impact on Galactic archaeology studies. Specifically, one will aim at constraining the relation between age and elemental abundances for nearby field stars. Calibration of this relation with the accuracy and precision offered by asteroseismology is crucial for a better understanding of the chemical history of the Galaxy, and offers clues to the degree to which different stellar populations in the disk have mixed. This relation can then be used to estimate the ages of stars with no asteroseismic measurements but with precise abundance determinations (e.g., using the high-resolution ESPRESSO spectrograph at the VLT), thus allowing to significantly expand the above sample beyond the solar neighborhood.

University: Porto

Start date: 2019/10/01

2016/B012 Fellow: Pedro I. T. K. Sarmento (completed)

Fellowship: PD/00040/2012 – PD/BD/128050/2016 - FCT

Advisors: Barbara Rojas-Ayala (Universidad Andrés Bello, Chile), Elisa Delgado Mena (IA-U.Porto)

PhD Topic (2016/220c): Towards a Comprehensive Understanding of the tiny Stars at NIR Wavelengths

The project consists in a comprehensive study of the NIR spectroscopic properties of M dwarf stars by studying a large number of binary systems composed of a solar type star and an M dwarf secondary. It involves the development and test of techniques to derive accurate and reliable effective temperatures, surface gravities and metallicities from APOGEE near infrared spectra. The goal of the project is to provide not only reliable measurements of the fundamental parameters for the tiny stars, but also provide consistency and estimate the real precision of the different methods involving photometry, spectroscopy and evolutionary models. This comprehensive study is fundamental for the proper and accurate characterization of the larger stellar component of the Galaxy, which will improve our knowledge of their nature and the chemical and dynamical evolution of the Milky Way.

University: Porto

Start date: 2016/10/01

2015/B008 Fellow: Benard Nsamba (completed)

Fellowship: PD/00040/2012 – PD/BD/113744/2015 - FCT

Advisors: Mário J. P. F. G. Monteiro (IA-U.Porto & FCUP), Tiago L. Campante (University of Birmingham)

PhD Topic (2015/212): Asteroseismic characterization of exoplanet-host stars in preparation for NASA’s TESS and ESA’s PLATO space missions

New insights on stellar evolution and stellar interiors physics are being made possible by asteroseismology, the study of stars by the observation of their natural, resonant oscillations. Asteroseismology is proving to be particularly significant for the study of solar-type stars, in great part due to the exquisite data that have been made available by NASA’s Kepler space telescope. The future looks even brighter, with NASA’s TESS and ESA’s PLATO space missions promising to revolutionize the field and increase the number of stars with detected oscillations by several orders of magnitude. The information contained in stellar oscillations allows the internal stellar structure to be constrained to unprecedented levels, while also allowing fundamental stellar properties (e.g., mass, radius, and age) to be precisely determined. In anticipation of the flood of observations from future space missions, the main goal of this project is to develop and test state-of-the-art asteroseismic techniques for the estimation of fundamental stellar properties. Particular attention will be focused on calibrating the determination of age, due to the strong dependence this quantity has on stellar physics. The goal is to address the critical requirement to obtain precise estimates of age for stars at different phases of evolution and/or with planetary systems where signatures of life are to be observed. A very important component of this project will be to understand the systematics on the derived properties that arise from changes in the input physics and the effects introduced by different evolutionary and pulsation codes. The implications of this project will be far-reaching. Not only should it provide important contributions to theories of stellar structure, stellar dynamics and evolution, but it will also play an important role in the characterization of planet-candidate host stars and their planetary systems.

University: Porto

Notes: This topic is a mixed fellowship (up to 12 months  in Birmingham/UK).

2015/B006 Fellow: Raquel M. G. de Albuquerque (completed)

Fellowship: PD/00040/2012 – PD/BD/113745/2015 - FCT

Advisors: João Lima (IA-U.Porto & FCUP), Jorge Filipe Gameiro (IA-U.Porto & FCUP), Christophe Sauty (Observatoire de Paris)

PhD Topic (2015/214c): Accretion versus outflow regions around Young Stellar Objects

The evolution of young stellar objects (YSO’s) is critically dependent on the balance between the accretion of matter coming from their surrounding disks and the collimated jets outflowing around their poles. The magnetic field plays a crucial role in both channelling these flows of plasma and controlling their dynamics and energetics.

Modelling the overall stellar formation on all scales from the global collapse and jet feedback down to the inner disk star interaction is presently out of reach. Thus, we concentrate on the central magnetospheric accretion connected to the stellar outflow in class II objects like classical T Tauri stars.

T Tauri stars are well observed objects. In such evolved protostars, observational evidences suggest that jets originate in the inner regions of the accretion disk or even closer in the magnetosphere of the central source.

Thus it is crucial to understand the connection between these two regions, one controlling accretion and the other responsible for the jet.

In this project we aim firstly, at modelling the structure of the magnetosphere of the YSO in which accretion takes place using existing numerical codes like PLUTO. This approach will enable a blending between accretion and outflow regions around YSO’s. The advantage of such numerical approach is to enable the study of time dependent solutions. Secondly, the solutions found will be used in a separate radiative transfer model to compute line profiles and test the consistency of the MHD solutions with observations.

University: Porto