Abstract
ABSTRACT The planets HR8799bc display nearly identical colours and spectra as variable young exoplanet analogs such as VHS 1256-1257ABb and PSO J318.5-22, and are likely to be similarly variable. Here we present results from a 5-epoch SPHERE IRDIS broadband-H search for variability in these two planets. HR 8799b aperture photometry and HR 8799bc negative simulated planet photometry share similar trends within uncertainties. Satellite spot lightcurves share the same trends as the planet lightcurves in the August 2018 epochs, but diverge in the October 2017 epochs. We consider Δ(mag)b − Δ(mag)c to trace non-shared variations between the two planets, and rule out non-shared variability in Δ(mag)b − Δ(mag)c to the 10–20 ${{\ \rm per\ cent}}$ level over 4–5 h. To quantify our sensitivity to variability, we simulate variable lightcurves by inserting and retrieving a suite of simulated planets at similar radii from the star as HR 8799bc, but offset in position angle. For HR 8799b, for periods <10 h, we are sensitive to variability with amplitude $\gt 5{{\ \rm per\ cent}}$. For HR 8799c, our sensitivity is limited to variability $\gt 25{{\ \rm per\ cent}}$ for similar periods.
Highlights
Over the last 15 years, a small but growing cohort of young, widelyseparated giant planets, such as HR 8799bcde (Marois et al 2008, 2010) and β Pic b (Lagrange et al 2010), have been directly imaged via their own thermal emission in the infrared
Quasiperiodic variability is commonly found in field L and T type brown dwarfs, with periods from 1.5-30 hours, and amplitudes ranging from 0.01-27% (Radigan et al 2012, 2014; Radigan 2014; Wilson et al 2014; Metchev et al 2015; Eriksson et al 2019)
This means that the satellite spots do not always provide appropriate photometric references for detrending the broadband H exoplanet lightcurves; this seems to be correlated to the observing conditions and may be due to the fact that the planet spectra are similar to each other, but much redder than the spectrum of the star
Summary
Citation for published version: Biller, BA, Apai, D, Bonnefoy, M, Desidera, S, Gratton, R, Kasper, M, Kenworthy, M, Lagrange, AM, Lazzoni, C, Mesa, D, Vigan, A, Wagner, K, Vos, JM & Zurlo, A 2021, 'A High-Contrast Search for Variability in HR 8799bc with VLT-SPHERE', Monthly Notices of the Royal Astronomical Society , vol 503, no.
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