Monitoring of the D doublet of neutral sodium during transits of two ‘evaporating’ planets

Gaidos, Eric; Hirano, Teruyuki; Ansdell, Megan

doi:10.1093/mnras/stz693

Cited by 9 publications

(10 citation statements)

References 65 publications

(84 reference statements)

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“…Our 5σ limit for Na of 9% is three times lower than the limit derived by Gaidos et al (2019) because we used shorter exposure times, which resulted in less Doppler smearing of the potential planet signal during our exposures. We also observed four transits while they observed two, increasing our total S/N.…”

Section: Resultscontrasting

confidence: 53%

“…We find ionization lifetimes of 1.8 × 10 3 s and 1.1 × 10 3 s for Na and Ca + , respectively. Our Na photoionization lifetime is a factor of 3.6 shorter than the value calculated by Gaidos et al (2019) of 3.930×10 3 s. They used the same MUSCLES SED, but a different Na ionization cross-section taken from Yeh & Lindau (1985) & Yeh (1993. Given the approximate nature of this estimate, the two photoionization lifetime values are sufficiently consistent.…”

Section: Dust and Gas Mass-loss Comparisonmentioning

confidence: 99%

“…While Gaidos et al (2019) have mainly attributed their nondetection of Na around K2-22 b to their instrument resolution being too low to resolve the narrow signal they expected from…”

Section: Stellar Radiation Pressurementioning

confidence: 99%

“…They also found that spectral lines over the range 3800Å -4025Å were shallower during transit. Gaidos et al (2019) searched for Na gas that was lost by the disintegrating rocky exoplanets Kepler-1520 b and K2-22 b with Subaru/HDS. They observed one transit of Kepler-1520 b on August 1, 2014 and two transits of K2-22 b on January 26 and 29, 2016.…”

Section: Introductionmentioning

confidence: 99%

“…Mura et al 2011). Our study involves a lower spectral resolution than that of Gaidos et al (2019), and our individual exposures are also shorter (213 s versus 900 s), resulting in significantly less smearing of potential planet signals because of the change in the radial component of the orbital velocity during exposures. This paper is structured as follows: Section 2 describes our observational data, Sections 3 and 4 describe our methods, Section 5 presents and discusses our results, and Section 6 concludes.…”

Section: Introductionmentioning

confidence: 99%

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Search for gas from the disintegrating rocky exoplanet K2-22b

Ridden-Harper

Snellen

Keller

et al. 2019

A&A

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Context. The red dwarf star K2-22 is transited every 9.14 hours by an object which is best explained by being a disintegrating rocky exoplanet featuring a variable comet-like dust tail. While the dust is thought to dominate the transit light curve, gas is also expected to be present, either from being directly evaporated off the planet or by being produced by the sublimation of dust particles in the tail. Aims. Both ionized calcium and sodium have large cross-sections, and although present at low abundance, exhibit the strongest atomic absorption features in comets. We therefore also identify these species as the most promising tracers of circumplanetary gas in evaporating rocky exoplanets and search for them in the tail of K2-22 b to constrain the gas-loss and sublimation processes in this enigmatic object. Methods. We observed four transits of K2-22 b with X-shooter on the Very Large Telescope operated by ESO to obtain time series of intermediate-resolution (R ∼ 11400) spectra. Our analysis focussed on the two sodium D lines (588.995 nm and 589.592 nm) and the Ca + triplet (849.802 nm, 854.209 nm, and 866.214 nm). The stellar calcium and sodium absorption was removed using the out-oftransit spectra. We searched for planet-related absorption in the velocity rest frame of the planet, which changes from approximately −66 to +66 km s −1 during the transit. Results. Since K2-22 b exhibits highly variable transit depths, we analysed the individual nights and their average. By injecting signals we reached 5σ upper limits on the individual nights that range from 11% -13% and 1.7% -2.0% for the sodium and ionized calcium absorption of the tail, respectively. Night 1 was contaminated by its companion star so we considered weighted averages with and without Night 1 and quote conservative 5σ limits without Night 1 of 9% and 1.4%, respectively. Assuming their mass fractions to be similar to those in the Earth's crust, these limits correspond to scenarios in which 0.04% and 35% of the transiting dust is sublimated and observed as absorbing gas. However, this assumes the gas to be co-moving with the planet. We show that for the high irradiation environment of K2-22 b, sodium and ionized calcium could be quickly accelerated to 100s of km s −1 owing to radiation pressure and entrainment by the stellar wind, making these species much more difficult to detect. No evidence for such possibly broad and blue-shifted signals are seen in our data. Conclusions. Future observations aimed at observing circumplanetary gas should take into account the possible broad and blue-shifted velocity field of atomic and ionized species.

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Section: Resultscontrasting

confidence: 53%

Section: Dust and Gas Mass-loss Comparisonmentioning

confidence: 99%

“…While Gaidos et al (2019) have mainly attributed their nondetection of Na around K2-22 b to their instrument resolution being too low to resolve the narrow signal they expected from…”

Section: Stellar Radiation Pressurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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