Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946

L. Palethorpe; A. Anna John; A. Mortier; J. Davoult; T. G. Wilson; K. Rice; A. C. Cameron; Y. Alibert; L. A. Buchhave; L. Malavolta; J. Cadman; M. López-Morales; X. Dumusque; A. M. Silva; S. N. Quinn; V. Van Eylen; S. Vissapragada; L. Affer; D. Charbonneau; R. Cosentino; A. Ghedina; R. D. Haywood; D. Latham; F. Lienhard; A. F. Martínez Fiorenzano; M. Pedani; F. Pepe; M. Pinamonti; A. Sozzetti; M. Stalport; S. Udry; A. Vanderburg

doi:10.1093/mnras/stae707

Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946

L. Palethorpe^*, A. Anna John, A. Mortier, J. Davoult, T. G. Wilson, K. Rice, A. C. Cameron, Y. Alibert, L. A. Buchhave, L. Malavolta, J. Cadman, M. López-Morales, X. Dumusque, A. M. Silva, S. N. Quinn, V. Van Eylen, S. Vissapragada, L. Affer, D. Charbonneau, R. CosentinoA. Ghedina, R. D. Haywood, D. Latham, F. Lienhard, A. F. Martínez Fiorenzano, M. Pedani, F. Pepe, M. Pinamonti, A. Sozzetti, M. Stalport, S. Udry, A. Vanderburg

^*Corresponding author for this work

Physics and Astronomy

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Abstract

We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ($M_*$ = 1.17 M$_{\odot}$, $R_*$ = 1.31 R$_{\odot}$) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period $P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of $M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a $\sim$1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq} = 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.

Original language	English
Article number	stae707
Journal	Monthly Notices of the Royal Astronomical Society
Early online date	5 Mar 2024
DOIs	https://doi.org/10.1093/mnras/stae707
Publication status	E-pub ahead of print - 5 Mar 2024

Bibliographical note

19 pages, 13 figures, 5 tables. Accepted for publication in MNRAS

ACKNOWLEDGEMENTS The HARPS-N project was funded by the Prodex Program of the Swiss Space Office(SSO), the Harvard University Origin of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), University of St. Andrews, Queen’s University Belfast, and University of Edinburgh. Wethank Suzanne Aigrain for her work in obtaining observations. MPi acknowledges the financial support from the ASI-INAF Addendum n.2018-24-HH.1-2022 “Partecipazione italiana al Gaia DPAC- Operazioni e attività di analisi dati”. ACC and TW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. KR acknowledges support from STFC Consolidated grant number ST/V000594/1. AAJ acknowledges support from a World-Leading St Andrews Doctoral Scholarship. This work has been carried out within the framework of the NCCR Planet S supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC)’s Ernest Rutherford Fellowship (grant number ST/V004735/1).
FPE would like to acknowledge the Swiss National Science Foundation (SNSF) for supporting research with HARPS-N through the SNSF grants nr. 140649, 152721, 166227 and 184618. The HARPSN Instrument Project was partially funded through the Swiss ESAPRODEX Programme. This work has been carried out within the framework of the NCCR Planet S supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon2020 research and innovation programme (grant agreement SCORE No 851555).

Keywords

astro-ph.EP

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Palethorpe, L., John, A. A., Mortier, A., Davoult, J., Wilson, T. G., Rice, K., Cameron, A. C., Alibert, Y., Buchhave, L. A., Malavolta, L., Cadman, J., López-Morales, M., Dumusque, X., Silva, A. M., Quinn, S. N., Eylen, V. V., Vissapragada, S., Affer, L., Charbonneau, D., ... Vanderburg, A. (2024). Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946. Monthly Notices of the Royal Astronomical Society, Article stae707. Advance online publication. https://doi.org/10.1093/mnras/stae707

@article{dfac2926936c4c8aab3c6600355e6bf7,

title = "Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946",

abstract = "We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ($M_*$ = 1.17 M$_{\odot}$, $R_*$ = 1.31 R$_{\odot}$) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period $P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of $M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a $\sim$1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq} = 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets. ",

keywords = "astro-ph.EP",

author = "L. Palethorpe and John, {A. Anna} and A. Mortier and J. Davoult and Wilson, {T. G.} and K. Rice and Cameron, {A. C.} and Y. Alibert and Buchhave, {L. A.} and L. Malavolta and J. Cadman and M. L{\'o}pez-Morales and X. Dumusque and Silva, {A. M.} and Quinn, {S. N.} and Eylen, {V. Van} and S. Vissapragada and L. Affer and D. Charbonneau and R. Cosentino and A. Ghedina and Haywood, {R. D.} and D. Latham and F. Lienhard and Fiorenzano, {A. F. Mart{\'i}nez} and M. Pedani and F. Pepe and M. Pinamonti and A. Sozzetti and M. Stalport and S. Udry and A. Vanderburg",

note = "19 pages, 13 figures, 5 tables. Accepted for publication in MNRAS ACKNOWLEDGEMENTS The HARPS-N project was funded by the Prodex Program of the Swiss Space Office(SSO), the Harvard University Origin of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), University of St. Andrews, Queen{\textquoteright}s University Belfast, and University of Edinburgh. Wethank Suzanne Aigrain for her work in obtaining observations. MPi acknowledges the financial support from the ASI-INAF Addendum n.2018-24-HH.1-2022 “Partecipazione italiana al Gaia DPAC- Operazioni e attivit{\`a} di analisi dati”. ACC and TW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. KR acknowledges support from STFC Consolidated grant number ST/V000594/1. AAJ acknowledges support from a World-Leading St Andrews Doctoral Scholarship. This work has been carried out within the framework of the NCCR Planet S supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC){\textquoteright}s Ernest Rutherford Fellowship (grant number ST/V004735/1). FPE would like to acknowledge the Swiss National Science Foundation (SNSF) for supporting research with HARPS-N through the SNSF grants nr. 140649, 152721, 166227 and 184618. The HARPSN Instrument Project was partially funded through the Swiss ESAPRODEX Programme. This work has been carried out within the framework of the NCCR Planet S supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. This project has received funding from the European Research Council (ERC) under the European Union{\textquoteright}s Horizon2020 research and innovation programme (grant agreement SCORE No 851555).",

year = "2024",

month = mar,

day = "5",

doi = "10.1093/mnras/stae707",

language = "English",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

publisher = "SIPRI/Oxford University Press",

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Palethorpe, L, John, AA, Mortier, A, Davoult, J, Wilson, TG, Rice, K, Cameron, AC, Alibert, Y, Buchhave, LA, Malavolta, L, Cadman, J, López-Morales, M, Dumusque, X, Silva, AM, Quinn, SN, Eylen, VV, Vissapragada, S, Affer, L, Charbonneau, D, Cosentino, R, Ghedina, A, Haywood, RD, Latham, D, Lienhard, F, Fiorenzano, AFM, Pedani, M, Pepe, F, Pinamonti, M, Sozzetti, A, Stalport, M, Udry, S & Vanderburg, A 2024, 'Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946', Monthly Notices of the Royal Astronomical Society. https://doi.org/10.1093/mnras/stae707

TY - JOUR

T1 - Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946

AU - Palethorpe, L.

AU - John, A. Anna

AU - Mortier, A.

AU - Davoult, J.

AU - Wilson, T. G.

AU - Rice, K.

AU - Cameron, A. C.

AU - Alibert, Y.

AU - Buchhave, L. A.

AU - Malavolta, L.

AU - Cadman, J.

AU - López-Morales, M.

AU - Dumusque, X.

AU - Silva, A. M.

AU - Quinn, S. N.

AU - Eylen, V. Van

AU - Vissapragada, S.

AU - Affer, L.

AU - Charbonneau, D.

AU - Cosentino, R.

AU - Ghedina, A.

AU - Haywood, R. D.

AU - Latham, D.

AU - Lienhard, F.

AU - Fiorenzano, A. F. Martínez

AU - Pedani, M.

AU - Pepe, F.

AU - Pinamonti, M.

AU - Sozzetti, A.

AU - Stalport, M.

AU - Udry, S.

AU - Vanderburg, A.

N1 - 19 pages, 13 figures, 5 tables. Accepted for publication in MNRAS ACKNOWLEDGEMENTS The HARPS-N project was funded by the Prodex Program of the Swiss Space Office(SSO), the Harvard University Origin of Life Initiative (HUOLI), the Scottish Universities Physics Alliance (SUPA), the University of Geneva, the Smithsonian Astrophysical Observatory (SAO), the Italian National Astrophysical Institute (INAF), University of St. Andrews, Queen’s University Belfast, and University of Edinburgh. Wethank Suzanne Aigrain for her work in obtaining observations. MPi acknowledges the financial support from the ASI-INAF Addendum n.2018-24-HH.1-2022 “Partecipazione italiana al Gaia DPAC- Operazioni e attività di analisi dati”. ACC and TW acknowledge support from STFC consolidated grant numbers ST/R000824/1 and ST/V000861/1, and UKSA grant number ST/R003203/1. KR acknowledges support from STFC Consolidated grant number ST/V000594/1. AAJ acknowledges support from a World-Leading St Andrews Doctoral Scholarship. This work has been carried out within the framework of the NCCR Planet S supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. R.D.H. is funded by the UK Science and Technology Facilities Council (STFC)’s Ernest Rutherford Fellowship (grant number ST/V004735/1). FPE would like to acknowledge the Swiss National Science Foundation (SNSF) for supporting research with HARPS-N through the SNSF grants nr. 140649, 152721, 166227 and 184618. The HARPSN Instrument Project was partially funded through the Swiss ESAPRODEX Programme. This work has been carried out within the framework of the NCCR Planet S supported by the Swiss National Science Foundation under grants 51NF40_182901 and 51NF40_205606. This project has received funding from the European Research Council (ERC) under the European Union’s Horizon2020 research and innovation programme (grant agreement SCORE No 851555).

PY - 2024/3/5

Y1 - 2024/3/5

N2 - We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ($M_*$ = 1.17 M$_{\odot}$, $R_*$ = 1.31 R$_{\odot}$) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period $P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of $M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a $\sim$1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq} = 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.

AB - We report on the detailed characterization of the HD 77946 planetary system. HD 77946 is an F5 ($M_*$ = 1.17 M$_{\odot}$, $R_*$ = 1.31 R$_{\odot}$) star, which hosts a transiting planet recently discovered by NASA's Transiting Exoplanet Survey Satellite (TESS), classified as TOI-1778 b. Using TESS photometry, high-resolution spectroscopic data from HARPS-N, and photometry from CHEOPS, we measure the radius and mass from the transit and RV observations, and find that the planet, HD 77946 b, orbits with period $P_{\rm b}$ = $6.527282_{-0.000020}^{+0.000015}$ d, has a mass of $M_{\rm b} = 8.38\pm{1.32}$M$_\oplus$, and a radius of $R_{\rm b} = 2.705_{-0.081}^{+0.086}$R$_\oplus$. From the combination of mass and radius measurements, and the stellar chemical composition, the planet properties suggest that HD 77946 b is a sub-Neptune with a $\sim$1\% H/He atmosphere. However, a degeneracy still exists between water-world and silicate/iron-hydrogen models, and even though interior structure modelling of this planet favours a sub-Neptune with a H/He layer that makes up a significant fraction of its radius, a water-world composition cannot be ruled out, as with $T_{\rm eq} = 1248^{+40}_{-38}~$K, water may be in a supercritical state. The characterisation of HD 77946 b, adding to the small sample of well-characterised sub-Neptunes, is an important step forwards on our journey to understanding planetary formation and evolution pathways. Furthermore, HD 77946 b has one of the highest transmission spectroscopic metrics for small planets orbiting hot stars, thus transmission spectroscopy of this key planet could prove vital for constraining the compositional confusion that currently surrounds small exoplanets.

KW - astro-ph.EP

U2 - 10.1093/mnras/stae707

DO - 10.1093/mnras/stae707

M3 - Article

SN - 0035-8711

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

M1 - stae707

ER -

Confronting compositional confusion through the characterisation of the sub-Neptune orbiting HD 77946

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