A weak spectral signature of water vapour in the atmosphere of HD 179949 b at high spectral resolution in the L band

Abstract

High resolution spectroscopy (R 20, 000) is currently the only known method to constrain the orbital solution and atmospheric properties of non-transiting hot Jupiters. It does so by resolving the spectral features of the planet into a forest of spectral lines and directly observing its Doppler shift while orbiting the host star. In this study, we analyse VLT/CRIRES (R = 100, 000) L-band observations of the non-transiting giant planet HD 179949 b centred around 3.5 µm. We observe a weak (3.0 σ, or S/N = 4.8) spectral signature of H 2 O in absorption contained within the radial velocity of the planet at superior-conjunction, with a mild dependence on the choice of line list used for the modelling. Combining this data with previous observations in the K -band, we measure a detection significance of 8.4 σ for an atmosphere that is most consistent with a shallow lapse-rate, solar C/O ratio, and with CO and H 2 O being the only major sources of opacity in this wavelength range. As the two sets of data were taken three years apart, this points to the absence of strong radial-velocity anomalies due, e.g., to variability in atmospheric circulation. We measure a projected orbital velocity for the planet of K P = (145.2 ± 2.0) km s −1 (1 σ) and improve the error bars on this parameter by ∼70%. However, we only marginally tighten constraints on orbital inclination (66.2 +3.7 −3.1 degrees) and planet mass (0.963 +0.036 −0.031 Jupiter masses), due to the dominant uncertainties of stellar mass and semi-major axis. Follow ups of radial-velocity planets are thus crucial to fully enable their accurate characterisation via high resolution spectroscopy.

Five carbon- and nitrogen-bearing species in a hot giant planet’s atmosphere

“…We confirm our detections with alternative high-resolution line lists for a number of species, as detailed in Extended Data Table 3. Such tests are crucial for robust detections as recent work has shown that high-resolution detections can be affected by the choice of line list 23,55 . We detect H 2 O with both the HITEMP and POKAZATEL line lists at similar significance, but our CH 4 and NH 3 detections are weaker with the HITRAN line list.…”

The ExoMolOP database: Cross sections andk-tables for molecules of interest in high-temperature exoplanet atmospheres

“…It is stressed that this database is not intended for highresolution applications. It would be beneficial to compute a series of very high-resolution cross sections, but restricted only to wavelength regions necessary to match available observational data for cross-correlation studies; see, for example, de Kok et al (2014), Hawker et al (2018, Mollière & Snellen (2019), Webb et al (2020). Currently, only a small sample of the line lists which are detailed in Tables 7 -14 of Section 5 are suitable for use in high-resolution applications, with cross sections typically required to be sampled to a resolution of at least R = λ ∆λ = 100,000.…”

Aerosols in Exoplanet Atmospheres

“…Thermal emission has been detected from two distinct populations of exoplanets: directly imaged young giant exoplanets in wide orbits about their host stars and transiting worlds on tight orbits ranging from hot Jupiters to rocky planets. Emission from a handful of non-transiting exoplanets have also been detected (Birkby et al, 2017;Brogi et al, 2012;Crossfield et al, 2010;Harrington et al, 2006;Lockwood et al, 2014;Piskorz et al, 2016Piskorz et al, , 2017Webb et al, 2020), but these observations have not yet been used to infer aerosol properties. The nadir geometry of emission observations allows us to probe deeper into the atmosphere than transmission, with the emitted flux being a sensitive function of atmospheric thermal structure in addition to chemical composition and aerosol distribution.…”