The coronal X-ray - age relation and its implications for the evaporation of exoplanets

By Alan P. Jackson, T. Davis, P. Wheatley. 2011

173 citations recorded by the source corpus.

We study the relationship between coronal X-ray emission and stellar age for late-type stars, and the variation of this relationship with spectral type. We select 717 stars from 13 open clusters and find that the ratio of X-ray to bolometric luminosity during the saturated phase of coronal emission decreases from 10−3.1 for late K dwarfs to 10−4.3 for early-F-type stars [across the range 0.29 ≤ (B−V)0 < 1.41]. Our determined saturation time-scales vary between 107.8 and 108.3 yr, though with no clear trend across the whole FGK range. We apply our X-ray emission–age relations to the investigation of the evaporation history of 121 known transiting exoplanets using a simple energy-limited model of evaporation and taking into consideration Roche lobe effects and different heating/evaporation efficiencies. We confirm that a linear cut-off of the planet distribution in the M2/R3 versus a−2 plane is an expected result of population modification by evaporation and show that the known transiting exoplanets display such a cut-off. We find that for an evaporation efficiency of 25 per cent we expect around one in ten of the known transiting exoplanets to have lost ≥5 per cent of their mass since formation. In addition we provide estimates of the minimum formation mass for which a planet could be expected to survive for 4 Gyr for a range of stellar and planetary parameters. We emphasize the importance of the earliest periods of a planet’s life for its evaporation history with 75 per cent expected to occur within the first Gyr. This raises the possibility of using evaporation histories to distinguish between different migration mechanisms. For planets with spin-orbit angles available from measurements of the Rossiter–McLaughlin effect, no difference is found between the distributions of planets with misaligned orbits and those with aligned orbits. This suggests that dynamical effects accounting for misalignment occur early in the life of the planetary system, although additional data are required to test this.

Subfields: Astronomy and Astrophysics, Education, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4a9e624741816cb849b40bd7f4a90ed6d49ed2d0

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Education

In Instrumentation

Citations in the corpus

Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation (2017, methodology): “To describe this regime we use the energy-limited escape rate given by Jackson et al. (2012) with the X-ray flux from 1 to 20 Å taken from Ribas et al. (2005).”
The California-Kepler Survey. VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap (2018, background): “This quantity is a strong function of stellar mass since L L dt MX bol 3 ò µ -( ) (Jackson et al. 2012).”
SUPER-EARTH ATMOSPHERES: SELF-CONSISTENT GAS ACCRETION AND RETENTION (2015, background): “…Wu 2013) and the small fraction of ionizing radiation out of the total bolometric stellar flux, which is taken to be a constant ∼ 10−3 for the first tUV ∼ 100 Myr, and then decreases with time as t−1.25 (see, e.g. Jackson et al. 2012; Lopez et al. 2012; Owen & Jackson 2012, and references within).”
Atmospheric Escape and the Evolution of Close-In Exoplanets (2018, methodology): “Equation 6 exists in the literature with many different pre-factors (e.g. Lecavelier Des Etangs 2007; Erkaev et al. 2007; Jackson et al. 2012; Lopez et al. 2012; Kurokawa & Nakamoto 2014; Chen & Rogers 2016).”
Origin and loss of nebula-captured hydrogen envelopes from ‘sub’- to ‘super-Earths’ in the habitable zone of Sun-like stars (2014, background): “During the saturation phase of a solar-like G-type star (6 0.1 Gyr), the stellar X-ray luminosity is saturated at a level of about 0.1% of the bolometric luminosity (Pizzolato et al. 2003; Jackson et al. 2012).”
HOW THERMAL EVOLUTION AND MASS-LOSS SCULPT POPULATIONS OF SUPER-EARTHS AND SUB-NEPTUNES: APPLICATION TO THE KEPLER-11 SYSTEM AND BEYOND (2012, methodology): “Following the X-ray observations of Jackson et al. (2012), we assume that at ages younger than 100 Myr the stellar XUV flux saturates and is constant at the 100 Myr value.”
Photoevaporation and high-eccentricity migration created the sub-Jovian desert (2018, background): “Additionally, Jackson et al. (2012) and Kurokawa & Nakamoto (2014) suggested photoevaporation was important in sculpting the mass distribution of close-in giant planets.”
KEPLER PLANETS: A TALE OF EVAPORATION (2013, methodology): “Let the efficiency of converting received energy to PdV work be η, so the mass-loss rate is simply: Ṁ = η LHER 3 p 4GMpa2 (1) where LHE is the high energy luminosity (X-rays or EUV), Mp is the planet mass, Rp is the planet radius and a is the separation from the parent star.”
HAZMAT. I. THE EVOLUTION OF FAR-UV AND NEAR-UV EMISSION FROM EARLY M STARS (2014, background): “…spectral types, Hα equivalent widths, and ages at the value of log(LX/Lbol) ∼ −3, with the bulk of the dispersion in both field and cluster samples between log(LX/Lbol) of –2 and –4, primarily due to variations in stellar rotation (Stauffer et al. 1997; Delfosse et al. 1998; Jackson et al. 2012).”
PLANETARY POPULATION SYNTHESIS COUPLED WITH ATMOSPHERIC ESCAPE: A STATISTICAL VIEW OF EVAPORATION (2014, methodology): “…calculated using an an energy-limited model and by assuming that part of the heating energy is converted to PdV work with the efficiency factor ǫ (Jackson et al. 2012): ṁ = ǫ 16πFR3p 3GMpK(ξ) (1) whereMp is the planetary mass, Rp is the planet’s radius at the optical depth τ = 2/3 in the…”
Planetary evaporation by UV and X‐ray radiation: basic hydrodynamics (2012, methodology): “…MNRAS 000, 1–18 Lammer et al. (2009) use the ‘energy-limited’ formalism for pure EUV evaporation, Penz et al. (2008) use fixed heating efficiency models that include X-ray and EUV luminosity and Jackson et al. (2012) use the ‘energy-limited’ formalism to assess the role of pure X-ray evaporation.”
The Evaporation Valley in the Kepler Planets (2017, methodology): “(22) We further choose a0 = 0.5 and tsat = 100 Myrs, and Lsat ≈ 10−3.5L (M∗/M ), motivated by the body of observational and modelling works (e.g. Güdel et al. 1997; Ribas et al. 2005; Jackson et al. 2012; Tu et al. 2015).”