Another look at the dayside spectra of WASP-43b and HD 209458b: Are there scattering clouds?
Monthly Notices of the Royal Astronomical Society 526:2 (2023) 2133-2140
Abstract:The search for clouds on the dayside of hot Jupiters has been disadvantaged due to the limited number of high quality space-based observations of their dayside. To date, retrieval studies have found no evidence for grey clouds on the dayside, however none of these studies explored the impact of scattering clouds. In this study we reanalyse the dayside emission spectrum of the hot Jupiter WASP-43b considering the different Spitzer data in the literature. We find that, in 2 of the 4 data sets explored, retrieving with a model that contains a scattering cloud is favoured over a cloud free model by a confidence of 3.13-3.36 σ. The other 2 data sets finds no evidence for scattering clouds. We find that the retrieved H2O abundance is consistent regardless of the Spitzer data used and is consistent with literature values. We perform the same analysis for the hot Jupiter HD 209458b and find no evidence for dayside clouds, consistent with previous studies.
Latitudinal variations in methane abundance, aerosol opacity and aerosol scattering efficiency in Neptune's atmosphere determined from VLT/MUSE
ArXiv 2310.13525 (2023)
The Temporal Brightening of Uranus' Northern Polar Hood From HST/WFC3 and HST/STIS Observations
JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS American Geophysical Union (AGU) 128:10 (2023) ARTN e2023JE007904
Abstract:Hubble Space Telescope Wide-Field Camera 3 (HST/WFC3) observations spanning 2015 to 2021 confirm a brightening of Uranus' north polar hood feature with time. The vertical aerosol model of Irwin et al. (2023, https://doi.org/10.1038/s41550-023-02047-0) (IRW23), consisting of a deep haze layer based at ∼5 bar, a 1–2 bar haze layer, and an extended haze rising up from the 1–2 bar layer, was applied to retrievals on HST Space Telescope Imaging Spectrograph (STIS) (HST/STIS) observations (Sromovsky et al., 2014, 2019, https://doi.org/10.1016/j.icarus.2014.05.016, https://doi.org/10.1016/j.icarus.2018.06.026) revealing a reduction in cloud-top CH4 volume mixing ratio (VMR) (i.e., above the deep ∼5 bar haze) by an average of 0.0019 ± 0.0003 between 40–80◦N (∼10% average reduction) from 2012 to 2015. A combination of latitudinal retrievals on the HST/WFC3 and HST/STIS data sets, again employing the IRW23 model, reveal a temporal thickening of the 1–2 bar haze layer to be the main cause of the polar hood brightening, finding an average increase in integrated opacity of 1.09 ± 0.08 (∼33% increase) at 0.8 µm north of ∼45°N, concurrent with a decrease in the imaginary refractive index spectrum of the 1–2 bar haze layer north of ∼40°N and longwards of ∼0.7 µm. Small contributions to the brightening were found from a thickening of the deep aerosol layer, with an average increase in integrated opacity of 0.6 ± 0.1 (58% increase) north of 45°N between 2012 and 2015, and from the aforementioned decrease in CH4 VMR. Our results are consistent with the slowing of a stratospheric meridional circulation, exhibiting subsidence at the poles.
YARARA V2: Reaching sub-m s-1 precision over a decade using PCA on line-by-line radial velocities
Astronomy and Astrophysics 678 (2023)
Abstract:Context. The detection of Earth-like planets with the radial velocity (RV) method is extremely challenging today due to the presence of non-Doppler signatures such as stellar activity and instrumental signals that mimic and hide the signals of exoplanets. In a previous paper, we presented the YARARA pipeline, which implements corrections for telluric absorption, stellar activity, and instrumental systematics at the spectral level, and then it extracts line-by-line (LBL) RVs with a significantly better precision than standard pipelines. Aims. In this paper, we demonstrate that further gains in RV precision can be achieved by performing principal component analysis (PCA) decomposition on the LBL RVs. Methods. The mean-insensitive nature of PCA means that it is unaffected by true Doppler shifts, and thus can be used to isolate and correct nuisance signals other than planets. Results. We analysed the data of 20 intensively observed HARPS targets by applying our PCA approach on the LBL RVs obtained by YARARA. The first principal components show similarities across most of the stars and correspond to newly identified instrumental systematics for which we can now correct. For several targets, this results in an unprecedented RV root-mean-square of around 90 cm s-1 over the full lifetime of HARPS. We used the corrected RVs to confirm a previously published 120-day signal around 61 Vir, and to detect a super-Earth candidate (K ∼ 60 ± 6 cm s-1, m sin i = 6.6 ± 0.7 M·) around the G6V star HD 20794, which spends part of its 600-day orbit within the habitable zone of the host star. Conclusions. This study highlights the potential of LBL PCA to identify and correct hitherto unknown, long-term instrumental effects and thereby extend the sensitivity of existing and future instruments towards the Earth analogue regime.
Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer.
Space science reviews Springer Nature 219:7 (2023) 53