2025A&A...701A.276B

Query : 2025A&A...701A.276B

2025A&A...701A.276B - Astronomy and Astrophysics, volume 701A276 (2025/9-1)

Quantifying thermal water dissociation in the dayside photosphere of WASP-121 b using NIRPS.

BAZINET L., ALLART R., BENNEKE B., PELLETIER S., WARDENIER J.P., COOK N.J., FORVEILLE T., NIELSEN L.D., AL MOULLA K., ARTIGAU E., BARON F., BARROS S.C.C., BONFILS X., BOUCHY F., BRYAN M., CANTO MARTINS B.L., CLOUTIER R., COWAN N.B., DE FREITAS D.B., DE MEDEIROS J.R., DELFOSSE X., DOYON R., DUMUSQUE X., EHRENREICH D., GONZALEZ HERNANDEZ J.I., LAFRENIERE D., DE CASTRO LEAO I., LOVIS C., MALO L., MELO C., MIGNON L., MORDASINI C., PEPE F., REBOLO R., ROWE J., SANTOS N.C., SEGRANSAN D., SUAREZ MASCARENO A., UDRY S., VALENCIA D., WADE G., ABREU M., AGUIAR J.L.A., ALLAIN G., ARIAL T., AUGER H., BLIND N., BOHLENDER D., BOUCHER A., BOURRIER V., BOVAY S., BROEG C., BROUSSEAU D., CABRAL A., CADIEUX C., CARMONA A., CHALLITA Z., CHAZELAS B., COELHO J., COINTEPAS M., COSTA SILVA A.R., COULOMBE L.-P., CRISTO E., DARVEAU-BERNIER A., DAUPLAISE L., DE LIMA GOMES R., FONTINELE D.O., FRENSCH Y.G.C., GENEST F., GENOLET L., GRACIA TEMICH F., HERNANDEZ O., HOEIJMAKERS H.J., HUBIN N., JAYAWARDHANA R., KAUFL H.-U., KERLEY D., KOLB J., KRISHNAMURTHY V., KUNG B., LAMONTAGNE P., LIM O., LO CURTO G., LUIS RASILLA J., MARTINS A.M., MATTHEWS J., MAYER J.-S., MESSIAS Y.S., METCHEV S., MOUNZER D., NARI N., OSBORN A., OUELLET M., PARC L., PASQUINI L., PEROUX C., PIAULET-GHORAYEB C., POMPEI E., POULIN-GIRARD A.-S., RESHETOV V., SAINT-ANTOINE J., SARAJLIC M., SCHNELL R., SEGOVIA A., SEIDEL J., SILBER A., SINCLAIR P., SORDET M., SOSNOWSKA D., SRIVASTAVA A., STEFANOV A.K., TEIXEIRA M.A., THIBAULT S., VALLEE P., VANDAL T., VAULATO V., WEHBE B., WEISSERMAN D., WEVERS I., WILDI F., YARIV V. and ZINS G.

Abstract (from CDS):

The intense stellar irradiation of ultra-hot Jupiters results in some of the most extreme atmospheric environments in the planetary regime. On their daysides, temperatures can be sufficiently high for key atmospheric constituents to thermally dissociate into simpler molecular species and atoms. This dissociation drastically changes the atmospheric opacities and, in turn, critically alters the temperature structure, atmospheric dynamics, and day-night heat transport. To date, however, simultaneous detections of the dissociating species and their thermally dissociation products in exoplanet atmospheres have remained rare. In this work we present the simultaneous detections of H2O and its thermally dissociation product OH on the dayside of the ultra-hot Jupiter WASP-121 b based on high-resolution emission spectroscopy with the recently commissioned Near InfraRed Planet Searcher (NIRPS). We retrieved a photospheric abundance ratio of log10(OH/H2O) = -0.15 ± 0.20, indicating that there is about as much OH as H2O at photospheric pressures, which confirms predictions from chemical equilibrium models. We compared the dissociation on WASP-121 b with other ultra-hot Jupiters and show that a trend in agreement with equilibrium models arises. We also discuss an apparent velocity shift of 4.79–0.97+0.93 km s–1 in the H2O signal, which is not reproduced by current global circulation models. Finally, in addition to H2O and OH, the NIRPS data reveal evidence of Fe and Mg, from which we inferred a Fe/Mg ratio consistent with the solar and host star ratios. Our results demonstrate that NIRPS can be an excellent instrument to obtain simultaneous measurements of refractory and volatile molecular species, thus paving the way for many future studies on the atmospheric composition, chemistry, and the formation history of close-in exoplanets.

Abstract Copyright: © The Authors 2025

Journal keyword(s): atmospheric effects - instrumentation: spectrographs - techniques: spectroscopic - planets and satellites: atmospheres - planets and satellites: gaseous planets

Simbad objects: 8

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Number of rows : 8
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 HD 10069b Pl 01 37 25.0332798696 -45 40 40.374717456           ~ 444 1
2 BD+01 316b Pl 01 46 31.8575937456 +02 42 02.030065560           ~ 302 0
3 HD 15082b Pl 02 26 51.0582618096 +37 33 01.736482032           ~ 403 1
4 CD-38 3220 * 07 10 24.0604565856 -39 05 50.571250476   11.00 10.51     F6V 145 0
5 CD-38 3220b Pl 07 10 24.0604565856 -39 05 50.571250476           ~ 421 0
6 BD-03 2978b Pl 10 42 14.0836906368 -03 50 06.260144388           ~ 150 0
7 HD 133112b Pl 15 02 44.8678907928 -03 01 52.986571896           ~ 144 0
8 BD-05 5432b Pl 21 00 06.1968214728 -05 05 40.034944176           ~ 219 1

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