TESS reveals an improbable planet
2019 October 29

Using asteroseismic¹ data from NASA’s Transiting Exoplanet Survey Satellite (TESS), an international team², led by Instituto de Astrofísica e Ciências do Espaço (IA³) researcher Tiago Campante, studied the red-giant stars HD 212771 and HD 203949. These are the first detections of oscillations in previously known exoplanet-host stars by TESS. The result was published today in an article⁴ in The Astrophysical Journal.

Tiago Campante (IA & Faculdade de Ciências da Universidade do Porto - FCUP) explains that detecting these oscillations was only possible because: "TESS observations are precise enough to allow measuring the gentle pulsations at the surfaces of stars. These two fairly evolved stars also host planets, providing the ideal testbed for studies of the evolution of planetary systems."

Having determined the physical properties of both stars, such as their mass, size and age, through asteroseismology, the authors then focused their attention on the evolutionary state of HD 203949. Their aim was to understand how its planet could have avoided engulfment, since the envelope of the star would have expanded well beyond the current planetary orbit during the red-giant phase of evolution.

Co-author Vardan Adibekyan (IA & Universidade do Porto) comments: "This study is a perfect demonstration of how stellar and exoplanetary astrophysics are linked together. Stellar analysis seems to suggest that the star is too evolved to still host a planet at such a 'short' orbital distance, while from the exoplanet analysis we know that the planet is there!"

By performing extensive numerical simulations, the team thinks that star-planet tides might have brought the planet inward from its original, wider orbit, placing it where we see it today. Adibekyan adds: "The solution to this scientific dilemma is hidden in the 'simple fact' that stars and their planets not only form but also evolve together. In this particular case, the planet managed to avoid engulfment."

In the past decade, asteroseismology has had a significant impact on the study of solar-type and red-giant stars, which exhibit convection-driven, solar-like oscillations. These studies have advanced considerably with space-based observatories like CoRoT (CNES/ESA) and Kepler (NASA), and are set to continue in the next decade with TESS and PLATO (ESA).

Tiago Campante explains that: "IA's involvement in TESS is at the level of the scientific coordination within the TESS Asteroseismic Science Consortium (TASC). TASC is a large and unique scientific collaboration, bringing together all relevant research groups and individuals from around the world who are actively engaged in research in the field of asteroseismology. Following in the footsteps of its successful predecessor, the Kepler Asteroseismic Science Consortium (KASC), TASC is based on a collaborative and transparent working-group structure, aimed at facilitating open collaboration between scientists."


Notes

1. Asteroseismology is the study of stellar interiors, by measuring seismic oscillations at the star’s surface. In seismology, the different vibration modes from an Earthquake can be used to study the Earth’s interior, in order to get data from the composition and depth of its different layers. In a similar fashion, oscillations at the star’s surface can be used to infer the internal structure and composition of a star.
2. The team is: Tiago L. Campante (Instituto de Astrofísica e Ciências do Espaço, Dep. Física e Astronomia Faculdade de Ciências da Universidade do Porto & Kavli Institute for Theoretical Physics, U. California), Enrico Corsaro (INAF | Osservatorio Astrosico di Catania), Mikkel N. Lund (Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Kavli Institute for Theoretical Physics, U. California) Benoît Mosser (LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, U. Paris), Aldo Serenelli (Institute of Space Sciences (ICE, CSIC) Campus UAB, Institut d'Estudis Espacials de Catalunya (IEEC) & Kavli Institute for Theoretical Physics, U. California), Dimitri Veras (Centre for Exoplanets and Habitability, Dep. of Physics, U. Warwick & Kavli Institute for Theoretical Physics, U. California), Vardan Adibekyan (Instituto de Astrofísica e Ciências do Espaço), H. M. Antia (Tata Institute of Fundamental Research), Warrick Ball (School of Physics and Astronomy, U. Birmingham & Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U.), Sarbani Basu (Dep.of Astronomy, Yale U.), Timothy R. Bedding (Sydney Institute for Astronomy (SIfA), School of Physics, U. Sydney, Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Kavli Institute for Theoretical Physics, U. California) Diego Bossini (Instituto de Astrofísica e Ciências do Espaço), Guy R. Davies (School of Physics and Astronomy, U. Birmingham, Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U.), Elisa Delgado Mena (Instituto de Astrofísica e Ciências do Espaço), Rafael A. García (IRFU, CEA & AIM, CEA, CNRS, U. Paris-Saclay), Rasmus Handberg (School of Physics and Astronomy, U. Birmingham, Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U.) Marc Hon (School of Physics, U. New South Wales), Stephen R. Kane (Dep. Earth and Planetary Sciences, U. California) Steven D. Kawaler (Dep. of Physics and Astronomy, Iowa State U. & Kavli Institute for Theoretical Physics, U. California), James S. Kuszlewicz (Max-Planck-Institut für Sonnensystemforschung & Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U.), Miles Lucas (Dep. of Physics and Astronomy, Iowa State U.) Savita Mathur (Instituto de Astrofsica de Canarias (IAC) & U. La Laguna (ULL), Dep. de Astrofsica), Nicolas Nardetto (U.Côte d'Azur, Observatoire de la Côte d'Azur, CNRS, Laboratoire Lagrange) Martin B. Nielsen (School of Physics and Astronomy, U. Birmingham), Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Center for Space Science, NYUAD Institute, New York U. Abu Dhabi), Marc H. Pinsonneault, Dep. of Astronomy, Ohio State U., & Kavli Institute for Theoretical Physics, U. California), Sabine Reffert & Landessternwarte, Zentrum für Astronomie der U. Heidelberg), Víctor Silva Aguirre (Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U.) Keivan G. Stassun (Vanderbilt U., Dep. of Physics and Astronomy, Vanderbilt Initiative in Data-intensive Astrophysics (VIDA)), Dennis Stello (School of Physics, U. New South Wales, Sydney Institute for Astronomy (SIfA), School of Physics, U. Sydney, Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Kavli Institute for Theoretical Physics, U. California)), Stephan Stock (Landessternwarte, Zentrum für Astronomie der U. Heidelberg), Mathieu Vrard (Instituto de Astrofísica e Ciências do Espaço) Mutlu Yildiz (Dep. of Astronomy and Space Sciences, Science Faculty, Ege U.), William J. Chaplin (School of Physics and Astronomy, U. Birmingham, Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Kavli Institute for Theoretical Physics, U. California), Daniel Huber (Institute for Astronomy, U. Hawai’i & Kavli Institute for Theoretical Physics, U. California), Jacob L. Bean (Dep. of Astronomy and Astrophysics, U. Chicago), Zeynep Çelik Orhan (Dep. of Astronomy and Space Sciences, Science Faculty, Ege U.), Margarida S. Cunha (Instituto de Astrofísica e Ciências do Espaço, Dep. Física e Astronomia Faculdade de Ciências da Universidade do Porto) Jørgen Christensen-Dalsgaard (Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Kavli Institute for Theoretical Physics, U. California), Hans Kjeldsen (Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U. & Institute of Theoretical Physics and Astronomy, Vilnius U.), Travis S. Metcalfe (Space Science Institute, Max-Planck-Institut für Sonnensystemforschung), Andrea Miglio (School of Physics and Astronomy, U. Birmingham & Stellar Astrophysics Centre (SAC), Dep. of Physics and Astronomy, Aarhus U.), Mário J. P. F. G. Monteiro (Instituto de Astrofísica e Ciências do Espaço, Dep. Física e Astronomia Faculdade de Ciências da Universidade do Porto), Benard Nsamba (Instituto de Astrofísica e Ciências do Espaço), Sibel Ortel (Dep. of Astronomy and Space Sciences, Science Faculty, Ege U.), Filipe Pereira (Instituto de Astrofísica e Ciências do Espaço), Sérgio G. Sousa (Instituto de Astrofísica e Ciências do Espaço, Dep. Física e Astronomia Faculdade de Ciências da Universidade do Porto), Maria Tsantaki (Instituto de Astrofísica e Ciências do Espaço) and Margaret C. Turnbull (SETI Institute, Carl Sagan Center for the Study of Life in the Universe)
3. The Instituto de Astrofísica e Ciências do Espaço (Institute of Astrophysics and Space Sciences – IA) is the reference Portuguese research unit in this field, integrating researchers from the University of Lisbon and the University of Porto, and encompasses most of the field’s national scientific output. It was evaluated as "Excellent" in the last evaluation of research and development units undertaken by Fundação para a Ciência e Tecnologia (FCT). IA's activity is funded by national and international funds, including FCT/MCES (UID/FIS/04434/2019).
4. The article “TESS Asteroseismology of the known red-giant host stars HD 212771 and 203949” was published in the The Astrophysical Journal (DOI: 10.3847/1538-4357/ab44a8)

Contacts
Tiago Campante

Science Communication Group
Ricardo Cardoso Reis
Sérgio Pereira
Daniel Folha (Coordination, Porto)
João Retrê (Coordination, Lisboa)