Robustness Measures for Molecular Detections using High-Resolution Transmission Spectroscopy of Exoplanets

Abstract

Ground-based high-resolution transmission spectroscopy has emerged as a promising technique for detecting chemicals in transiting exoplanetary atmospheres. Despite chemical inferences in several exoplanets and previous robustness studies, a robust and consistent detrending method to remove telluric and stellar features from transmission spectra has yet to be agreed upon. In this work we investigate the robustness of metrics used to optimise PCA-based detrending for high-resolution transmission spectra of exoplanets in the near-infrared. As a case study, we consider observations of the hot Jupiter HD 189733 b obtained using the CARMENES spectrograph on the 3.5 m CAHA telescope. We confirm that optimising the detrending parameters to maximise the S/N of a cross-correlation signal in the presence of noise has the potential to bias the detection significance at the planetary velocity of optimisation. However, we find that optimisation using the difference between a signal-injected cross-correlation function and the direct cross-correlation function (CCF) is more robust against over-optimisation of noise and spurious signals. We additionally examine the robustness of weighting the contribution of each order to the final CCF, and of S/N calculations. Using a prescribed robust methodology, we confirm H2O in the atmosphere of HD 189733 b (S/N = 6.1). We then investigate two further case studies, of exoplanets HD 209458 b and WASP-76 b, confirming OH in the atmosphere of WASP-76 b (S/N = 4.7), and demonstrating how non-robust methods may induce false positive or inflated detections. Our findings pave the way towards a robust framework for homogeneous characterisation of exoplanetary atmospheres using high-resolution transmission spectroscopy in the near-infrared.

arXiv commentAccepted for publication in MNRAS

References in corpus (60)

• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Detection of Planetary Transits Across a Sun-like Star
• Detection of an Extrasolar Planet Atmosphere
• The false positive rate of Kepler and the occurrence of planets
• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b
• Theoretical Transmission Spectra During Extrasolar Giant Planet Transits
• A high accuracy computed water line list
• Obliquities of Hot Jupiter host stars: Evidence for tidal interactions and primordial misalignments
• Correcting systematic effects in a large set of photometric lightcurves
• Improved parameters for extrasolar transiting planets
• ELODIE metallicity-biased search for transiting Hot Jupiters II. A very hot Jupiter transiting the bright K star HD189733
• Sodium Absorption From the Exoplanetary Atmosphere of HD189733b Detected in the Optical Transmission Spectrum
• The signature of orbital motion from the dayside of the planet tau Bootis b
• ExoMol line lists IV: The rotation-vibration spectrum of methane up to 1500 K
• Detection of water absorption in the day side atmosphere of HD 189733 b using ground-based high-resolution spectroscopy at 3.2 microns
• A variationally computed line list for hot NH3
• The climate of HD 189733b from fourteen transits and eclipses measured by Spitzer
• Exoplanetary Atmospheres: Key Insights, Challenges and Prospects
• ExoMol line lists III: An improved hot rotation-vibration line list for HCN and HNC
• Spectrally resolved detection of sodium in the atmosphere of HD189733b with the HARPS spectrograph
• Nightside condensation of iron in an ultra-hot giant exoplanet
• The Spectroscopic Orbit of the Planetary Companion Transiting HD209458
• Chemical consequences of the C/O ratio on hot Jupiters: Examples from WASP-12b,CoRoT-2b, XO-1b, and HD 189733b
• Retrieving Temperatures and Abundances of Exoplanet Atmospheres with High-Resolution Cross-Correlation Spectroscopy
• Ground-based detection of sodium in the transmission spectrum of exoplanet HD209458b
• Using Stellar Limb-Darkening to Refine the Properties of HD 209458b
• Atomic iron and titanium in the atmosphere of the exoplanet KELT-9b
• Rotation and winds of exoplanet HD 189733 b measured with high-dispersion transmission spectroscopy
• Improved HCN/HNC linelist, model atmospheres and synthetic spectra for WZ Cas
• Detection of carbon monoxide in the high-resolution day-side spectrum of the exoplanet HD 189733b
• Exoplanetary Atmospheres - Chemistry, Formation Conditions, and Habitability
• The Rossiter-McLaughlin effect of CoRoT-3b & HD189733b
• Five carbon- and nitrogen-bearing species in a hot giant planet's atmosphere
• Line-profile tomography of exoplanet transits I: The Doppler shadow of HD 189733b
• SPIRou: nIR velocimetry & spectropolarimetry at the CFHT
• High-Resolution Spectroscopic Detection of TiO and Stratosphere in the Day-side of WASP-33b
• Retrieval of planetary and stellar properties in transmission spectroscopy with Aura
• Discovery of water at high spectral resolution in the atmosphere of 51 Peg b
• Flat-relative optimal extraction. A quick and efficient algorithm for stabilised spectrographs
• GENESIS: New Self-Consistent Models of Exoplanetary Spectra
• Three irradiated and bloated hot Jupiters: WASP-76b, WASP-82b & WASP-90b
• Exoplanet atmospheres with GIANO. I. Water in the transmission spectrum of HD 189733b
• Hot Jupiters: Origins, Structure, Atmospheres
• Minerva-Australis I: Design, Commissioning, & First Photometric Results
• PLATON II: New Capabilities And A Comprehensive Retrieval on HD 189733b Transit and Eclipse Data
• On the robustness of analysis techniques for molecular detections using high resolution exoplanet spectroscopy
• Decomposing the Iron Cross-Correlation Signal of the Ultra-Hot Jupiter WASP-76b in Transmission using 3D Monte-Carlo Radiative Transfer
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Exoplanet atmospheres with GIANO II. Detection of molecular absorption in the dayside spectrum of HD 102195b
• Evidence for multiple molecular species in the hot Jupiter HD 209458b
• Multiple water band detections in the CARMENES near-infrared transmission spectrum of HD 189733 b
• Water vapor detection in the transmission spectra of HD 209458 b with the CARMENES NIR channel
• The GAPS Programme at TNG XXXVIII. Five molecules in the atmosphere of the warm giant planet WASP-69b detected at high spectral resolution
• Black Mirror: The impact of rotational broadening on the search for reflected light from 51 Pegasi b with high resolution spectroscopy
• The GAPS Programme at TNG XXXIX -- Multiple molecular species in the atmosphere of the warm giant planet WASP-80 b unveiled at high resolution with GIANO-B
• Exoplanetary Atmospheres
• Searching for the origin of the Ehrenreich effect in ultra-hot Jupiters: Evidence for strong C/O gradients in the atmosphere of WASP-76b?
• SPIRou: a nIR spectropolarimeter / high-precision velocimeter for the CFHT
• Searching for reflected light from $\tau$ Bootis b with high-resolution ground-based spectroscopy: Approaching the $10^{-5}$ contrast barrier

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• JWST transmission spectroscopy of HD 209458b: a super-solar metallicity, a very low C/O, and no evidence of CH4, HCN, or C2H2
• CRIRES${}^{+}$ transmission spectroscopy of WASP-127b. Detection of the resolved signatures of a supersonic equatorial jet and cool poles in a hot planet
• Retrieval of the dayside atmosphere of WASP-43b with CRIRES+
• A sub-solar metallicity on the ultra-short period planet HIP 65Ab
• A formally motivated retrieval framework applied to the high resolution transmission spectrum of HD 189733 b
• Retrieving day- and nightside atmospheric properties of the ultra-hot Jupiter TOI-2109b. Detection of Fe and CO emission lines and evidence for inefficient heat transport
• ATMOSPHERIX: III- Estimating the C/O ratio and molecular dynamics at the limbs of WASP-76 b with SPIRou
• Exploring the atmosphere of GJ 1132 b with CRIRES+
• Tighter constraints on the atmosphere of GJ 436 b from combined high-resolution CARMENES and CRIRES${}^{+}$ observations
• Ground-based Atmospheric Characterization of Super-Earth L 98-59 d at High Spectral Resolution
• Quantifying thermal water dissociation in the dayside photosphere of WASP-121 b using NIRPS
• Open Source High-Resolution Exoplanet Atmosphere Retrievals with POSEIDON
• A Measurement of the Water Abundance in the Atmosphere of the Hot Jupiter WASP-43b with High-resolution Cross-correlation Spectroscopy
• Assessing robustness and bias in 1D retrievals of 3D Global Circulation Models at high spectral resolution: a WASP-76 b simulation case study in emission
• First Results from WINERED: Detection of Emission Lines from Neutral Iron and a Combined Set of Trace Species on the Dayside of WASP-189 b