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A search for variability in exoplanet analogues and low-gravity brown dwarfs

Abstract : We report the results of a J-band survey for photometric variability in a sample of young, low-gravity objects using the New Technology Telescope (NTT) and the United Kingdom Infrared Telescope (UKIRT). Surface gravity is a key parameter in the atmospheric properties of brown dwarfs and this is the first large survey that aims to test the gravity dependence of variability properties. We do a full analysis of the spectral signatures of youth and assess the group membership probability of each target using membership tools from the literature. This results in a 30 object sample of young low-gravity brown dwarfs. Since we are lacking in objects with spectral types later than L9, we focus our statistical analysis on the L0-L8.5 objects. We find that the variability occurrence rate of L0-L8.5 low-gravity brown dwarfs in this survey is 30^{+16}_{-8}{{ per cent}}. We reanalyse the results of Radigan (2014) and find that the field dwarfs with spectral types L0-L8.5 have a variability occurrence rate of 11^{+13}_{-4}{{ per cent}}. We determine a probability of 98{{ per cent}} that the samples are drawn from different distributions. This is the first quantitative indication that the low-gravity objects are more likely to be variable than the field dwarf population. Furthermore, we present follow-up JS and KS observations of the young, planetary-mass variable object PSO 318.5-22 over three consecutive nights. We find no evidence of phase shifts between the JS and KS bands and find higher JS amplitudes. We use the JS light curves to measure a rotational period of 8.45 ± 0.05 h for PSO 318.5-22.
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Submitted on : Friday, June 24, 2022 - 4:10:35 PM
Last modification on : Saturday, June 25, 2022 - 9:30:01 AM

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Johanna M. Vos, Beth A. Biller, Mariangela Bonavita, Simon Eriksson, Michael C. Liu, et al.. A search for variability in exoplanet analogues and low-gravity brown dwarfs. Monthly Notices of the Royal Astronomical Society, 2019, 483, pp.480-502. ⟨10.1093/mnras/sty3123⟩. ⟨insu-03704141⟩

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