Year: 2026
Type: preprint
Abstract: Granulation is a persistent feature of stars with outer convective layers and is the photospheric signature of near-surface convective energy transport. In disk-integrated observations, it produces stochastic brightness variations that contribute substantially to stellar variability on timescales of minutes to hours. High-precision, observations with JWST provide an opportunity to study the chromatic signatures of stellar granulation. This work aims to measure the amplitude and characteristic timescale of granulation-induced variability for solar-type stars and to investigate whether the granulation signal shows significant chromatic variation in the near-infrared. We accessed publicly available JWST/NIRISS SOSS time-series observations of LTT-9779 (G7V) and WASP-121 (F6V) and de-trended the light curves by fitting the transits, eclipses, and planetary phase curves. We computed power spectra from the de-trended light curves and fit them with a Harvey granulation profile. We first analyzed the broadband light curves to measure and fix the granulation timescale and then repeated the power-spectrum analysis in individual wavelength channels to measure the chromatic dependence of the granulation amplitude. For LTT-9779, we measure a broadband granulation amplitude of σ$=53.8^{+4.1}_{-4.0}$ppm at a timescale of τ$=4.8^{+1.5}_{-1.3}$min. For WASP-121, we measure σ$=59.3\pm4.3$ppm and τ$=6.3^{+2.1}_{-1.8}$min. We also measure peak oscillation frequencies of ν$=3382^{+166}_{-191}μ$Hz and $1649^{+55}_{-69}μ$Hz in the bandpass-integrated power spectra of LTT-9779 and WASP-121, respectively. In the spectroscopic fits, we find $σ$ decreases with wavelength. Our results demonstrate a new observational window on short-timescale stellar variability and provides a way to characterize chromatic stellar noise in transit light curves.
Source: arXiv (Cornell University)
Institutions: Max Planck Institute for Solar System Research, Universitat Politècnica de Catalunya, Instituto de Astrofísica de Andalucía, Center for Astrophysics Harvard & Smithsonian, Space Telescope Science Institute, Institute of Space Sciences, Institut d'Estudis Espacials de Catalunya, University of Toronto, Canadian Institute for Theoretical Astrophysics
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: National Aeronautics and Space Administration, Space Telescope Science Institute, Ministerio de Ciencia, Innovación y Universidades, Centres de Recerca de Catalunya, European Commission, Deutsche Forschungsgemeinschaft, Volkswagen Foundation, Agence Nationale de la Recherche, Generalitat de Catalunya, Deutsches Zentrum für Luft- und Raumfahrt, HORIZON EUROPE Framework Programme, European Regional Development Fund, Agencia Estatal de Investigación, European Social Fund
Awards: G103270039, G1105844351, G1426358987, G1622782223, G2064873908, G223336455, G2462415295, G256731684, G3005324705, G302750986, G3546882995, G3696727022, G3715634343, G373897614, G3772858555, G3817602061, G390761925, G410571670, G451917667, G463062595, G491712853, G5195188938, G5404395142, G5434874113, G546199279, G5539308778, G5568641063, G5635532810, G5881647929, G5894067328, G5967599077, G617610489, G6217019444, G6218905885, G624877701, G6465668149, G6513613686, G6656126374, G6731524417, G69051668, G6996428894, G717256432, G7205067785, G7805626310, G7863371703, Stellare Schmetterlingsdiagramme, G8118709007, G8172319115, G8284171658, G8497050386, G8637226926, G8777606647, G8888022036, G929308097
OpenAlex ID: W7223029681