Another red giant and another exoplanet, but until we know more, they all look more or less the same.
Illustration: ESA.
Using asteroseismology, a team led by an Instituto de Astrofísica e
Ciências do Espaço (IA) researcher, studied two red-giant stars known to
host exoplanets, and for one of them found a seemingly improbable
planet. Several researchers connected to SAC are co-authors.
Surprise: An exoplanet shouldn't have survived the expansion of it's red giant star, but still it is there.
Using asteroseismic data from NASA’s Transiting Exoplanet Survey Satellite (TESS), an international team, led by Instituto de Astrofísica e Ciências do Espaço (IA) 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 29 October 2019 in an article 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.
Exoplanethunter TESS - now through half of it's nominal mission.
Illustration: NASA.
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.”
