Signatures of CH${}_4$ and NH${}_3$ in the atmosphere of $\beta$ Pictoris b

Abstract

$\beta$ Pictoris is a nearby (19.7 pc), young ($\sim$ 24 Myr), bright ($V=3.85$) planetary system hosting three directly imaged planets. Previous high-resolution spectroscopy of $\beta$ Pic b has detected H${}_2$O and CO, but not CH${}_4$ or NH${}_3$. Combining observations across a broad wavelength range has been shown to maximise sensitivity to such weak molecular signals. We searched for previously undetected molecular species in the atmosphere of $\beta$ Pic b using high-resolution near-infrared spectra. We combined 44 CRIRES+ spectral settings covering the H, K, L, and M bands and cross-correlated the extracted planetary spectra with molecular templates. For species with uncertain detectability, we weighted the observations by their molecular information content and data quality, independent of the measured candidate-species cross-correlation functions. We recover H${}_2$O and CO at cross-correlation S/N values of approximately 200 and 50, respectively. We additionally identify tentative CH${}_4$ and NH${}_3$ signals near the expected radial velocity of $\beta$ Pic b, with S/N values of approximately 5.3 and 5.7. Equivalent extractions at the same projected separation on the opposite side of the star show no comparable peaks. We classify the CH${}_4$ and NH${}_3$ signals as tentative because their cross-correlation S/N values do not fully account for possible residual systematics. If confirmed, these would be the first detections of both species in the atmosphere of $\beta$ Pic b.

arXiv commentAccepted for publication in Astronomy & Astrophysics. 7 pages, 3 figures