Multiepoch Detections of the Extended Atmosphere and Transmission Spectra of KELT-9b with a 1.5 m Telescope

• Published in: The Astronomical journal Vol. 165; no. 3; pp. 101 - 116
• Main Authors: Lowson, Nataliea, Zhou, George, Wright, Duncan J., Huang, Chelsea X., Mendonça, João M., Cabot, Samuel H. C., Pudmenzky, Christa, Wittenmyer, Robert A., Latham, David W., Bieryla, Allyson, Esquerdo, Gilbert A., Berlind, Perry, Calkins, Michael L.
• Format: Journal Article
• Language: English
• Published: Madison The American Astronomical Society 01.03.2023; IOP Publishing
• Subjects: Astronomy; Atmospheric models; Comet tails; Exoplanet atmospheric composition; Exoplanet atmospheric variability; Exoplanet evolution; Exoplanets; Extrasolar planets; Gas giant planets; Ground-based observation; H alpha line; Hot Jupiters; Jupiter atmosphere; Light curve; Planetary atmospheres; Seasonal variations; Stellar systems; Telescopes; Temporal variability; Transit
• ISSN: 0004-6256; 1538-3881
• DOI: 10.3847/1538-3881/acacf3

Abstract Irradiated Jovian atmospheres are complex and dynamic and can undergo temporal variations due to the close proximity of their parent stars. Of the Jovian planets that have been cataloged 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 multiyear 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 α , which is an indicator for ongoing mass loss. From our multiyear data set, the H α light curve consistently deviates from a standard transit and follows a “W” shape that is deeper near ingress and egress and shallower midtransit. To search for and quantify any seasonal variations that may be present, we parameterize a “cometary tail” model to fit for the H α transit. We find no detectable variations between the different observed epochs. Though a “cometary tail” describes the H α 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 center-to-limb variations larger than that expected from 1D atmosphere models, may also contribute to the observed H α transit shape. These multiepoch observations highlight the capabilities of small telescopes to provide temporal monitoring of the dynamics of exoplanet atmospheres.