Estimation of the XUV radiation onto close planets and their evaporation

By J. Sanz-Forcada, G. Micela, I. Ribas, A. Pollock, C. Eiroa, Á. Velasco, E. Solano, D. García-Álvarez. 2011

307 citations recorded by the source corpus.

Context. The current distribution of planet mass vs. incident stellar X-ray flux supports the idea that photoevaporation of the atmosphere may take place in close-in planets. Integrated effects have to be accounted for. A proper calculation of the mass loss rate through photoevaporation requires the estimation of the total irradiation from the whole XUV (X-rays and extreme ultraviolet, EUV) range. Aims. The purpose of this paper is to extend the analysis of the photoevaporation in planetary atmospheres from the accessible X-rays to the mostly unobserved EUV range by using the coronal models of stars to calculate the EUV contribution to the stellar spectra. The mass evolution of planets can be traced assuming that thermal losses dominate the mass loss of their atmospheres. Methods. We determine coronal models for 82 stars with exoplanets that have X-ray observations available. Then a synthetic spectrum is produced for the whole XUV range (∼1−912 A). The determination of the EUV stellar flux, calibrated with real EUV data, allows us to calculate the accumulated effects of the XUV irradiation on the planet atmosphere with time, as well as the mass evolution for planets with known density. Results. We calibrate for the first time a relation of the EUV luminosity with stellar age valid for late-type stars. In a sample of 109 exoplanets, few planets with masses larger than ∼1.5 MJ receive high XUV flux, suggesting that intense photoevaporation takes place in a short period of time, as previously found in X-rays. The scenario is also consistent with the observed distribution of planet masses with density. The accumulated effects of photoevaporation over time indicate that HD 209458b may have lost 0.2 MJ since an age of 20 Myr. Conclusions. Coronal radiation produces rapid photoevaporation of the atmospheres of planets close to young late-type stars. More complex models are needed to explain the observations fully. Spectral energy distributions in the XUV range are made available for stars in the sample through the Virtual Observatory for the use in future planet atmospheric models.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/156c48412d196536d007522c1b7219f06d97b8cf

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Citations in the corpus

THE ULTRAVIOLET RADIATION ENVIRONMENT AROUND M DWARF EXOPLANET HOST STARS (2012, background): “…University, Princeton, NJ 08544 diation can heat the atmosphere to ∼ 104 K (Yelle 2004; Murray-Clay et al. 2009), resulting in atmospheric mass-loss (Sanz-Forcada et al. 2011) and the inflated exospheres observed in H I Lyα (Vidal-Madjar et al. 2003; Lecavelier des Etangs et al. 2012) and metal…”
Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b (2012, background): “Assuming a realistic emission measure distribution (Sanz-Forcada et al. 2011), we can estimate the total luminosity across the X-ray/EUV band at the time of our observation to be 7.1×1028erg s−1, corresponding to an energy-limited evaporation rate of 4.4×1011g s−1.”
The coronal X-ray - age relation and its implications for the evaporation of exoplanets (2011, background): “Sanz-Forcada et al. (2011) attempt to circumvent this problem using coronal modelling to extrapolate the EUV flux from the X-ray flux of planet hosting stars that have been observed in the X-ray.”
HAZMAT. I. THE EVOLUTION OF FAR-UV AND NEAR-UV EMISSION FROM EARLY M STARS (2014, methodology): “Lecavelier Des Etangs (2007) and Sanz-Forcada et al. (2011) estimate EUV fluxes in known, old, solar-type planet hosts using coronal models fits to X-ray spectra.”
Planetary evaporation by UV and X‐ray radiation: basic hydrodynamics (2012, background): “…the T-Tauri phase (Alexander et al. 2004) and at late times (Ribas et al. 2005), perhaps - indicates fall off with time is similar, if not identical, (see also Sanz-Forcada et al. 2011), we make a simple assumption and couple the X-ray and EUV luminosity to have identical values at all times.”
A chemical model for the atmosphere of hot Jupiters (2012, background): “Between 0.5 and 90 nm, it is based on data from the X-exoplanets Archive at the CAB (Sanz-Forcada et al. 2011).”
The Extreme Ultraviolet and X-Ray Sun in Time: High-Energy Evolutionary Tracks of a Solar-Like Star (2015, background): “Sanz-Forcada et al. (2011) derived a power law to convertLX (5-100Å) into EUV luminosity,LEUV (100-920Å), of logLEUV = 4.8+ 0.86 logLX , whereLX andLEUV are in erg s−1.”
The SRG/eROSITA all-sky survey (2024, unknown): “…et al. 2011), which plays an important role in the determination of the physical characteristics of the orbiting planets’ atmospheres, with implications for the potential habitability of such planets (Lammer et al. 2003; Sanz-Forcada et al. 2011; Poppenhaeger et al. 2021; Foster et al. 2022).”
A STUDY OF THE SHORTEST-PERIOD PLANETS FOUND WITH KEPLER (2014, background): “…have lost most of their gaseous envelopes to photoevaporation (Watson et al. 1981; Lammer et al. 2003; Baraffe et al. 2004; Murray-Clay et al. 2009; Valencia et al. 2009; Sanz-Forcada et al. 2011; Lopez, Fortney, & Miller 2012; Lopez & Fortney 2013a; Owen & Wu 2013; Kurokawa & Kaltenegger 2013).”
THE MUSCLES TREASURY SURVEY. I. MOTIVATION AND OVERVIEW (2016, methodology): “It is estimated to have an age between 0.56 - 3.62 Gyr (Kiraga & Stepien 2007; Sanz-Forcada et al. 2011) and a solar metallicity, [Fe/H] = −0.01 (Neves et al. 2014).”