Original title: Rotational broadening of exoplanet spectra in arbitrarily oriented systems: Application to reflected light
Sophia R. Vaughan, Laura Kreidberg · September 2026
When astronomers study light bouncing off an exoplanet, the spinning of both the host star and the planet alters the observed light waves. This spin causes spectral linesSpecific colors in a spectrum that are missing or extra strong, acting like barcodes for atoms.—specific fingerprints of light—to stretch out and broaden. If scientists ignore how a system tilts, their measurements will be wrong. In this study, researchers created mathematical formulas to track this rotational broadeningSpinning objects spread out the colors they send us, making each spectral line wider. for systems tilted in any arbitrary direction. They mapped how their new math connects to standard planetary orbit measurements. They discovered that if a system is misaligned, this line broadening can differ by on the order of 50 km s$^{-1}$ compared to an aligned orbit. These formulas could also be adapted to study heat radiated directly by planets.
You are trying to describe how much a dancer's costume blurs in a photo. If the dancer is spinning on the spot, the blur is simple. But if the stage itself is also turning, and the dancer is not standing in the middle, the blur changes depending on where she stands and which way she faces. In this paper the dancer is an exoplanet, the stage is its orbit, and the equations describe how reflected starlight gets smeared by the combined spin of the star and planet when the orbit is tilted.
Astronomers use the shape of reflected starlight to learn what exoplanet atmospheres are made of. If a planet's orbit is tilted, that tilt changes the light's shape by up to 50 km/s and can distort those readings. This work gives the correction needed to measure the tilt instead of being fooled by it.
The abstract does not specify what assumptions the kernels rely on, only that their limitations are investigated. It also does not show the kernels applied to real observational data. The extension to thermal emission is only suggested as a possible modification, not demonstrated.
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Rotational broadening of exoplanet spectra in arbitrarily oriented systems: Application to reflected light — Sophia R. Vaughan, Laura Kreidberg
Abstract licence: CC0
Explanation generated by Synthesis from the abstract — it is not the original paper. This is a preprint, so it hasn't necessarily been peer reviewed.