Exoplanets & Exomoons

Constraints On Atmospheric Water Abundance and Cloud Deck Pressure in the Warm Neptune GJ 3470 b via CARMENES Transmission Spectroscopy

By Keith Cowing
Status Report
April 11, 2024
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Constraints On Atmospheric Water Abundance and Cloud Deck Pressure in the Warm Neptune GJ 3470 b via CARMENES Transmission Spectroscopy
SVD/PCA based detrending process and the effect of model reprocessing for order number 11 of Night 1 of CARMENES observation. (a) Data after calibration through CARACAL, (b) After SVD/PCA based detrending and strong residual masking – the orange line shows the cross-section along which the spectra for (e) is drawn, (c) Nominal exoplanet model signal that is to be injected into noiseless data matrix before reprocessing – the black line represents the cross-section for drawing the spectrum in (f), (d) Reprocessed model signal showing the model signal + artefacts in the out-of-transit phases – blue is the cross-section for drawing (g) and reddish brown for (h), (e) Cross-section at mid-transit time (Phase = 0) for the processed and normalised data in (b) showing variations around 1.0, (f) Same as (e) but for the nominal model signal in (c), (g) Same as (e) but for the reprocessed model signal in (d). The differences between (f) and (g) notably in the line depths and wing shapes illustrate the effect of the SVD/PCA based detrending procedure on the the model signal and by definition any actual signal that would be present in the data, (h) Cross-section at an out-of-transit time (Phase ≈ 0.02) showcasing the nature of the artefacts caused due to model reprocessing with a similar scale as in (g). — astro-ph.EP

Observations of cooler atmospheres of super-Earths and Neptune sized objects often show flat transmission spectra.

The most likely cause of this trend is the presence of aerosols (i.e. clouds and hazes) in the atmospheres of such objects.

High-resolution spectroscopy provides an opportunity to test this hypothesis by targeting molecular species whose spectral line cores extend above the level of such opaque decks. In this work, we analyse high-resolution infrared observations of the warm Neptune GJ 3470 b taken over two transits using CARMENES (R ∼ 80,000) and look for signatures of H2O (previously detected using HST WFC3+Spitzer observations) in these transits with a custom pipeline fully accounting for the effects of data cleaning on any potential exoplanet signal.

We find that our data are potentially able to weakly detect (∼3σ) an injected signal equivalent to the best-fit model from previous HST WFC3+Spitzer observations. However, we do not make a significant detection using the actual observations. Using a Bayesian framework to simultaneously constrain the H2O Volume Mixing Ratio (VMR) and the cloud top pressure level, we select a family of models compatible with the non detection.

These are either very high VMR, cloud-free models, solar-abundance models with a high cloud deck, or sub-solar abundance models with a moderate cloud deck. This is a broader range compared to published results from low-resolution spectroscopy, but is also compatible with them at a 1σ level.

Spandan Dash, Matteo Brogi, Siddharth Gandhi, Marina Lafarga, Annabella Meech, Aaron Bello-Arufe, Peter J. Wheatley

Comments: 18 pages, 8 figures, Accepted for publication in Monthly Notices of the Royal Astronomical Society Main Journal on April 9, 2024
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2404.06648 [astro-ph.EP] (or arXiv:2404.06648v1 [astro-ph.EP] for this version)
Submission history
From: Spandan Dash
[v1] Tue, 9 Apr 2024 22:56:05 UTC (24,296 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻