Black Mirror: The impact of rotational broadening on the search for reflected light from 51 Pegasi b with high resolution spectroscopy

Abstract

The extreme contrast ratios between stars and their planets at optical wavelengths make it challenging to isolate the light reflected by exoplanet atmospheres. Yet, these reflective properties reveal key processes occurring in the atmospheres, and they also span wavelengths that include the potential O${}_2$ biosignature. High resolution cross-correlation spectroscopy (HRCCS) offers a robust avenue for developing techniques to extract exoplanet reflection spectra. We aimed to extract the optical reflected light spectrum of the non-transiting hot Jupiter 51 Peg b by adapting techniques designed to remove tellurics in infrared HRCCS to instead remove optical stellar lines. Importantly, we investigated the so far neglected impact of the broadening of the reflected host star spectrum due to the difference between the stellar rotation and the planet's orbital velocity. We used 484, R=115000 optical spectra of 51 Peg b from HARPS-N and HARPS, which we aligned to the exact stellar rest frame in order to effectively remove the contaminating host star. However, some stellar residuals remained, likely due to stellar activity. We cross-correlated with an appropriately broadened synthetic stellar model to search for the planet's Doppler-shifting spectrum. We detect no significant reflected light from 51 Peg b and report a S/N=3 upper limit on the contrast ratio of 76.0 ppm (7.60x10${}^{-5}$) when including broadening, and 24.0 ppm (2.40x10${}^{-5}$) without. These upper limits rule out radius and albedo combinations of previously claimed detections. Broadening can significantly impact the ability of HRCCS to extract reflected light spectra and must be considered when determining the contrast ratio, radius, and albedo of the planet. Asynchronous systems (Prot,${}_{\star }\ne$ Porb) are most affected, including most hot Jupiters as well as Earth-size planets in the traditional habitable zones of some M-dwarfs.

25 pages, 18 figures in main text, accepted for publication in A&A on 30/12/2021

References in corpus (36)

• The NumPy array: a structure for efficient numerical computation
• Molecfit: A general tool for telluric absorption correction. I. Method and application to ESO instruments
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT X-Shooter spectra
• Measuring the rotation period distribution of field M-dwarfs with Kepler
• The fast spin-rotation of a young extrasolar planet
• A new list of thorium and argon spectral lines in the visible
• SOAP 2.0: A tool to estimate the photometric and radial velocity variations induced by stellar spots and plages
• Combining high-dispersion spectroscopy (HDS) with high contrast imaging (HCI): Probing rocky planets around our nearest neighbors
• A spectral survey of an ultra-hot Jupiter: Detection of metals in the transmission spectrum of KELT-9 b
• The Very Low Albedo of an Extrasolar Planet: MOST Spacebased Photometry of HD 209458
• Detection of Fe I in the atmosphere of the ultra-hot Jupiter WASP-121b, and a new likelihood-based approach for Doppler-resolved spectroscopy
• A new library of theoretical stellar spectra with scaled-solar and alpha-enhanced mixtures
• Changing Phases of Alien Worlds: Probing Atmospheres of Kepler Planets with High-Precision Photometry
• Atmospheric characterization of Proxima b by coupling the Sphere high-contrast imager to the Espresso spectrograph
• High-Resolution Spectroscopic Detection of TiO and Stratosphere in the Day-side of WASP-33b
• Discovery of water at high spectral resolution in the atmosphere of 51 Peg b
• Neutral Iron Emission Lines From The Day-side Of KELT-9b -- The GAPS Programme With HARPS-N At TNG XX
• Clouds on the hot Jupiter HD189733b: constraints from the reflection spectrum
• Evidence for a spectroscopic direct detection of reflected light from 51 Peg b
• HARPS-N Solar Radial-Velocity Variations Are Dominated By Large, Bright Magnetic Regions
• A temperature inversion with atomic iron in the ultra-hot dayside atmosphere of WASP-189b
• The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity
• First Detection of Hydroxyl Radical Emission from an Exoplanet Atmosphere: High-dispersion Characterization of WASP-33b using Subaru/IRD
• Variability of stellar granulation and convective blueshift with spectral type and magnetic activity. I. K and G main sequence stars
• Detection of Fe\,{\sc i} Emission in the Day-side Spectrum of WASP-33b
• Visible-light Phase Curves from the Second Year of the TESS Primary Mission
• Impact of micro-telluric lines on precise radial velocities and its correction
• Detection of Ionized Calcium in the Atmosphere of the Ultra-Hot Jupiter WASP-76b
• Testing the Detectability of Extraterrestrial ${\mathrm{O}}_2$ with the ELTs using Real Data with Real Noise
• Planet and star synergy at high spectral resolution. A rationale for the characterisation of exoplanet atmospheres. I. The Infrared
• M-Dwarf Fast Rotators and the Detection of Relatively Young Multiple M-Star Systems
• High Resolution Spectroscopy and High Contrast Imaging with the ELT : looking for O${}_2$ in Proxima b
• The GAPS Programme at TNG. XXIX. No detection of reflected light from 51 Peg b using optical high-resolution spectroscopy
• Spectroscopic Transit Search: a self-calibrating method for detecting planets around bright stars
• Extreme Precision Radial Velocity Working Group Final Report