An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet

N. Nikolov; D. K. Sing; J. J. Fortney; J. M. Goyal; B. Drummond; T. M. Evans; N. P. Gibson; E. J.W. De Mooij; Z. Rustamkulov; H. R. Wakeford; B. Smalley; A. J. Burgasser; C. Hellier; Ch Helling; N. J. Mayne; N. Madhusudhan; T. Kataria; J. Baines; A. L. Carter; G. E. Ballester; J. K. Barstow; J. McCleery; J. J. Spake

doi:10.1038/s41586-018-0101-7

An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet

N. Nikolov, D. K. Sing, J. J. Fortney, J. M. Goyal, B. Drummond, T. M. Evans, N. P. Gibson, E. J.W. De Mooij, Z. Rustamkulov, H. R. Wakeford, B. Smalley, A. J. Burgasser, C. Hellier, Ch Helling, N. J. Mayne, N. Madhusudhan, T. Kataria, J. Baines, A. L. Carter, G. E. BallesterJ. K. Barstow, J. McCleery, J. J. Spake

Lunar and Planetary Lab

Research output: Contribution to journal › Article › peer-review

119 Scopus citations

Abstract

Broad absorption signatures from alkali metals, such as the sodium (Na i) and potassium (K i) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets^1-3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles^4-6. Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances^7-9. Here we report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. We are able to measure a precise, absolute sodium abundance of logϵ_Na = 6.9_-0.4 ^+0.6, and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Z_p/Z_o = 2.3_-1.7 ^+8.9). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets^10-12.

Original language	English (US)
Pages (from-to)	526-529
Number of pages	4
Journal	Nature
Volume	557
Issue number	7706
DOIs	https://doi.org/10.1038/s41586-018-0101-7
State	Published - May 24 2018

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Nikolov, N., Sing, D. K., Fortney, J. J., Goyal, J. M., Drummond, B., Evans, T. M., Gibson, N. P., De Mooij, E. J. W., Rustamkulov, Z., Wakeford, H. R., Smalley, B., Burgasser, A. J., Hellier, C., Helling, C., Mayne, N. J., Madhusudhan, N., Kataria, T., Baines, J., Carter, A. L., ... Spake, J. J. (2018). An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet. Nature, 557(7706), 526-529. https://doi.org/10.1038/s41586-018-0101-7

Nikolov, N, Sing, DK, Fortney, JJ, Goyal, JM, Drummond, B, Evans, TM, Gibson, NP, De Mooij, EJW, Rustamkulov, Z, Wakeford, HR, Smalley, B, Burgasser, AJ, Hellier, C, Helling, C, Mayne, NJ, Madhusudhan, N, Kataria, T, Baines, J, Carter, AL, Ballester, GE, Barstow, JK, McCleery, J & Spake, JJ 2018, 'An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet', Nature, vol. 557, no. 7706, pp. 526-529. https://doi.org/10.1038/s41586-018-0101-7

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title = "An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet",

abstract = "Broad absorption signatures from alkali metals, such as the sodium (Na i) and potassium (K i) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6. Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9. Here we report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. We are able to measure a precise, absolute sodium abundance of logϵNa = 6.9-0.4 +0.6, and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Zp/Zo = 2.3-1.7 +8.9). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets10-12.",

author = "N. Nikolov and Sing, {D. K.} and Fortney, {J. J.} and Goyal, {J. M.} and B. Drummond and Evans, {T. M.} and Gibson, {N. P.} and {De Mooij}, {E. J.W.} and Z. Rustamkulov and Wakeford, {H. R.} and B. Smalley and Burgasser, {A. J.} and C. Hellier and Ch Helling and Mayne, {N. J.} and N. Madhusudhan and T. Kataria and J. Baines and Carter, {A. L.} and Ballester, {G. E.} and Barstow, {J. K.} and J. McCleery and Spake, {J. J.}",

note = "Publisher Copyright: {\textcopyright} 2018 Macmillan Publishers Ltd., part of Springer Nature.",

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doi = "10.1038/s41586-018-0101-7",

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T1 - An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet

AU - Nikolov, N.

AU - Sing, D. K.

AU - Fortney, J. J.

AU - Goyal, J. M.

AU - Drummond, B.

AU - Evans, T. M.

AU - Gibson, N. P.

AU - De Mooij, E. J.W.

AU - Rustamkulov, Z.

AU - Wakeford, H. R.

AU - Smalley, B.

AU - Burgasser, A. J.

AU - Hellier, C.

AU - Helling, Ch

AU - Mayne, N. J.

AU - Madhusudhan, N.

AU - Kataria, T.

AU - Baines, J.

AU - Carter, A. L.

AU - Ballester, G. E.

AU - Barstow, J. K.

AU - McCleery, J.

AU - Spake, J. J.

PY - 2018/5/24

Y1 - 2018/5/24

N2 - Broad absorption signatures from alkali metals, such as the sodium (Na i) and potassium (K i) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6. Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9. Here we report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. We are able to measure a precise, absolute sodium abundance of logϵNa = 6.9-0.4 +0.6, and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Zp/Zo = 2.3-1.7 +8.9). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets10-12.

AB - Broad absorption signatures from alkali metals, such as the sodium (Na i) and potassium (K i) resonance doublets, have long been predicted in the optical atmospheric spectra of cloud-free irradiated gas giant exoplanets1-3. However, observations have revealed only the narrow cores of these features rather than the full pressure-broadened profiles4-6. Cloud and haze opacity at the day-night planetary terminator are considered to be responsible for obscuring the absorption-line wings, which hinders constraints on absolute atmospheric abundances7-9. Here we report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature. The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium. We are able to measure a precise, absolute sodium abundance of logϵNa = 6.9-0.4 +0.6, and use it as a proxy for the planet's atmospheric metallicity relative to the solar value (Zp/Zo = 2.3-1.7 +8.9). This result is consistent with the mass-metallicity trend observed for Solar System planets and exoplanets10-12.

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SP - 526

EP - 529

JO - Nature

JF - Nature

IS - 7706

ER -

An absolute sodium abundance for a cloud-free 'hot Saturn' exoplanet

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