First Doppler Limits on Binary Planets and Exomoons in the HR 8799 System

Abstract

We place the first constraints on binary planets and exomoons from Doppler monitoring of directly imaged exoplanets. We model radial velocity observations of HR 8799 b, c, and d from Ruffio et al. (2021) and determine upper limits on the $m\sin i$ of short-period binary planets and satellites. At 95% confidence, we rule out companions orbiting the three planets more massive than $m\sin i=2M_J$ with orbital periods shorter than 5 days. We achieve our tightest constraints on moons orbiting HR 8799 c, where with 95% confidence we rule out out edge-on Jupiter-mass companions in periods shorter than 5 days and edge-on half-Jupiter-mass moons in periods shorter than 1 day. These radial velocity observations come from spectra with resolution 20 times lower than typical radial velocity instruments and were taken using a spectrograph that was designed before the first directly imaged exoplanet was discovered. Similar datasets from new and upcoming instruments will probe significantly lower exomoon masses.

8 pages, 2 figures, 1 table, and one .csv file of mass upper limits as a function of orbital period included in the source code. Accepted for publication in ApJ Letters

References in corpus (10)

• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Transit timing effects due to an exomoon
• First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
• HEK VI: On the Dearth of Galilean Analogs in Kepler and the Exomoon Candidate Kepler-1625b I
• EXOFASTv2: A public, generalized, publication-quality exoplanet modeling code
• Detecting companions to extrasolar planets using mutual events
• Extrasolar Binary Planets I: Formation by tidal capture during planet-planet scattering
• Possibility of Detecting Moons of Pulsar Planets Through Time-of-Arrival Analysis
• Extrasolar Binary Planets II: Detectability by Transit Observations
• On The Feasibility of Exomoon Detection Via Exoplanet Phase Curve Spectral Contrast

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• Measuring the variability of directly imaged exoplanets using vector Apodizing Phase Plates combined with ground-based differential spectrophotometry
• Exomoon search with VLTI/GRAVITY around the substellar companion HD 206893 B
• Direct detectability of tidally heated exomoons by photometric orbital modulation
• Astrometric exomoon detection by means of optical interferometry
• Transit Duration and Timing Variations from Binary Planets