About me

I’m a PhD student at the Laboratoire d’Astrophysique de Marseille (LAM) and Aix-Marseille University, France, since October 2019. I obtained my M.Sc in Astrophysics in June 2019 at Lund University, in Sweden, and my B.Sc in Physics at Complutense University of Madrid, Spain. My research studies focus on the internal structure of exoplanets, their atmosphere and how their host star can influence their bulk composition.

Planetary and stellar composition

Determining the internal structure of exoplanets is essential to obtain its composition and its surface conditions, which enable us to know if the planet is habitable. Water is one of the most abundant volatiles that can be found in planetary bodies. Depending on the surface conditions of the planet, water can be in a liquid, ice, or vapour phases, which present very different densities. Thus, it is required to take into account these different phases with equations of state and pressure-temperature profiles that are valid under planetary interior conditions. In addition, it is necessary to treat data from mass, radius and stellar chemical composition with a Bayesian approach to infer the most likely ratios of volatiles and silicates that form an exoplanet. These are the two topics I’m currently working on in my PhD, whose latest results can be seen in Acuña et al. 2021.

The chemical composition of the host star, particularly the Fe and Si abundances, can be used to constrain the bulk composition of its exoplanet. Furthermore, planet formation might also affect the composition on the host star. Meléndez et al. 2009 proposed that stars harbouring rocky planets could present less refractory elements in their photospheres than stars without planets. This difference in chemical composition was very subtle, and required a detailed and precise chemical analysis of different rocky planet hosts. This was the motivation of my master thesis, in which I conducted a line-by-line, differential chemical analysis of a sample of planet hosts. My results confirmed that the Sun is depleted in refractory elements compared to solar twins without exoplanets. However, the other planet hosts in my sample were very diverse in chemical composition. This diversity has been later confirmed with a greater sample of stars by Liu et al. 2020.

Exoplanet atmospheres

Exoplanets with extended atmospheres are favourable targets for transmission spectroscopy. With this technique, we can detect spectral features from the exoplanet’s atmosphere, such as a slope at short visible wavelengths caused by Rayleigh scattering. However, if clouds form in the atmosphere, they will absorb most of the radiation coming from the star and the transmission spectrum will be flat with no spectral features. During my internship in the European Space Agency (ESA), I worked on a pipeline to reduce and analyse observational data from transmission spectroscopy of a sample of hot Jupiters. As a result, I obtained the transmission spectrum of one hot Jupiter, WASP-74 b, that presents a Rayleigh slope at short wavelengths, concluding that its atmosphere is at least partially clear. This was presented in a poster session at the ARIEL 2020 conference.

Publications

TOI-220 b: a warm sub-Neptune discovered by TESS. S. Hoyer, D. Gandolfi, D. J. Armstrong, M. Deleuil, L. Acuña et al. 2021.

Characterisation of the hydrospheres of TRAPPIST-1 planets. L. Acuña, M. Deleuil, O. Mousis et al. 2021.

Planetary system LHS 1140 revisited with ESPRESSO and TESS. J. Lillo-Box, P. Figueira, A. Leleu, L. Acuña et al. 2020.

Masses for the seven planets in K2-32 and K2-233. Four diverse planets in resonant chain and the first young rocky worlds. J. Lillo-Box, T. A. Lopez, A. Santerne, L. D. Nielsen, S.C.C. Barros, M. Deleuil, L. Acuña et al. 2020.

Detailed chemical compositions of planet hosting stars: I. Exploration of possible planet signatures. F. Liu, D. Yong, M. Asplund, H. S. Wang, L. Spina, L. Acuña et al. 2020.

Irradiated ocean planets bridge super-Earth and sub-Neptune populations. O. Mousis, M. Deleuil, A. Aguichine, E. Marcq, J. Naar, L. Acuña Aguirre et al. 2020.

Master thesis: Detailed analysis of the chemical composition of stars harboring Earth-like planets. Lorena Acuña, supervised by Fan Liu. 2019.

Contact

Address:

LAM - Laboratoire d’Astrophysique de Marseille.

Pôle de l’Étoile Site de Château-Gombert. 38, rue Frédéric Joliot-Curie 13388 Marseille cedex 13 FRANCE

Email:

lorena.acuna@lam.fr/