The homogeneous characterisation of Ariel host stars

Abstract

The Ariel mission will characterise the chemical and thermal properties of the atmospheres of about a thousand exoplanets transiting their host star(s). The observation of such a large sample of planets will allow to deepen our understanding of planetary and atmospheric formation at the early stages, providing a truly representative picture of the chemical nature of exoplanets, and relating this directly to the type and chemical environment of the host star. Hence, the accurate and precise determination of the host star fundamental properties is essential to Ariel for drawing a comprehensive picture of the underlying essence of these planetary systems. We present here a structured approach for the characterisation of Ariel stars that accounts for the concepts of homogeneity and coherence among a large set of stellar parameters. We present here the studies and benchmark analyses we have been performing to determine robust stellar fundamental parameters, elemental abundances, activity indices, and stellar ages. In particular, we present results for the homogeneous estimation of the activity indices S and log(R HK ), and preliminary results for elemental abundances of Na, Al, Mg, Si, C, N. In addition, we analyse the variation of a planetary spectrum, obtained with Ariel, as a function of the uncertainty on the stellar effective temperature. Finally, we present our observational campaign for precisely and homogeneously characterising all Ariel stars in order to perform a meaningful choice of final targets before the mission launch.

Zeta-Payne: A Fully Automated Spectrum Analysis Algorithm for the Milky Way Mapper Program of the SDSS-V Survey

“…Though space-based (photometric) missions deliver highquality, high-duty cycle, and nearly uninterrupted time-series of data full of information, a considerable amount of stellar astrophysics applications, both at the level of individual objects and their ensembles, require precise atmospheric parameters and chemical compositions of stars, as well as estimates of their surface rotation and radial velocities. For example, (transiting) exoplanet studies often rely on ground-based spectroscopic measurements for the inference of planetary masses and properties of their host stars (e.g., Danielski et al 2021). The study of planetary atmospheres through the method of transmission spectroscopy is another application (e.g., Kreidberg 2017;Limbach et al 2020).…”

Determination of stellar parameters for Ariel targets: a comparison analysis between different spectroscopic methods

“…For a global approach to characterize the stars of Ariel Reference Sample see also [15], where an overview on the methods used to determine stellar fundamental parameters, elemental abundances, activity indices, and stellar ages for the Ariel Reference Sample is given and in particular, results for the homogeneous estimation of elemental abundances of Al, Mg, Si, C, N, and the activity indices S and log(R' HK) are presented.…”

The GAPS Programme with HARPS-N at TNG. XXXV. Fundamental properties of transiting exoplanet host stars

“…Therefore, our analysis based on a careful method leads to log g results that are very close to the values derived in accurate ways (through transit light curves or Gaia parallaxes), even if we are aware that the kind of analysis performed in this work is strongly time-consuming and cannot be easily applied to surveys of hundreds-thousand targets. Similar method to derive trigonometric log g was already applied by Brucalassi et al (2021) for ∼ 150 targets within the Ariel reference sample (see also Tinetti et al 2021;Danielski et al 2021;Magrini et al 2022). Due to the high quality of the Gaia parallax, the authors suggest to adopt trigonometric log g as a viable possibility for big stellar samples for which some spectroscopic methods based on automatic tools tend to under/over-estimate the surface gravity at low and high temperatures.…”