Multi-epoch detections of the extended atmosphere and transmission spectra of KELT-9b with a 1.5 m telescope

TL;DR

This study uses multi-year ground-based observations to analyze the atmospheric variability of the ultra-hot Jupiter KELT-9b, confirming previous detections of atomic species and exploring potential seasonal changes in its extended atmosphere.

Contribution

First multi-epoch ground-based spectroscopic monitoring of KELT-9b's atmosphere, revealing consistent atomic signatures and analyzing temporal variability with a novel 'cometary tail' model.

Findings

Confirmed presence of Fe I, Fe II, Mg I across multiple epochs

Detected excess H-alpha absorption indicating mass-loss

No significant seasonal variations found in atmospheric signatures

Abstract

Irradiated Jovian atmospheres are complex, dynamic, and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been catalogued to date, KELT-9b is the hottest Gas Giant known, with an equilibrium temperature of 4050 K. We probe the temporal variability of transmission spectroscopic signatures from KELT-9b via a set of archival multi-year ground-based transit observations, performed with the TRES facility on the 1.5 m reflector at the Fred Lawrence Whipple Observatory. Our observations confirm past detections of Fe I, Fe II and Mg I over multiple epochs, in addition to excess absorption at H-alpha, which is an indicator for ongoing mass-loss. From our multi-year dataset, the H-alpha light curve consistently deviates from a standard transit, and follows a 'W' shape that is deeper near ingress and egress, and shallower mid-transit. To search for and quantify any seasonal variations that may be present, we parameterise a 'cometary tail' model to fit for the H-alpha transit. We find no detectable variations between the different observed epochs. Though a 'cometary tail' describes the H-alpha flux variations well, we note that such a scenario requires a high density of neutral hydrogen in the n = 2 excited state far beyond the planetary atmosphere. Other scenarios, such as centre-to-limb variations larger than that expected from 1-D atmosphere models, may also contribute to the observed H-alpha transit shape. These multi-epoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres.