# A High-Contrast Search for Variability in HR 8799bc with VLT-SPHERE

**Authors:** B. A. Biller, D. Apai, M. Bonnefoy, S. Desidera, R. Gratton, M. Kasper, M. Kenworthy, A. M. Lagrange, C. Lazzoni, D. Mesa, A. Vigan, K. Wagner, J. M. Vos, A. Zurlo  
**arXiv:** [2101.08514](https://arxiv.org/abs/2101.08514)  
**Date:** 2021-01-21  
**Summary page:** https://www.summarizepaper.com/en/paper/2101.08514v1/

## Key points

- Study used VLT-SPHERE instrument for high-contrast search for variability in planets HR8799bc
- Planets have similar colors and spectra to other young exoplanet analogues known to be variable
- 5-epoch SPHERE IRDIS broadband-$H$ search conducted for variability in the two planets
- Results showed similarities between HR 8799b aperture photometry and HR 8799bc negative simulated planet photometry trends
- Satellite spot lightcurves followed same trends as planet lightcurves in August 2018 epochs but diverged in October 2017 epochs
- Analysis of $\Delta(mag)_{b} - \Delta(mag)_{c}$ traced non-shared variations between the two planets, ruling out non-shared variability at a level of 10-20% over a period of 4-5 hours
- Sensitivity to variability: HR 8799b sensitive to amplitudes >5% for periods <10 hours; HR 8799c limited to variability >25% for similar periods
- Study provides insights into potential variability of HR8799bc and emphasizes the need for further observations

## Summary

A recent study used data from the VLT-SPHERE instrument to conduct a high-contrast search for variability in the planets HR8799bc. These planets have similar colors and spectra to other young exoplanet analogues known to be variable, suggesting that they may also display variability. The study involved a 5-epoch SPHERE IRDIS broadband-$H$ search for variability in these two planets. The results showed that both HR 8799b aperture photometry and HR 8799bc negative simulated planet photometry exhibited similar trends within uncertainties. However, satellite spot lightcurves followed the same trends as the planet lightcurves in the August 2018 epochs but diverged in the October 2017 epochs. By analyzing $\Delta(mag)_{b} - \Delta(mag)_{c}$, researchers were able to trace non-shared variations between the two planets and ruled out non-shared variability at a level of 10-20$\%$ over a period of 4-5 hours. To assess their sensitivity to variability, researchers simulated variable lightcurves by inserting and retrieving a suite of simulated planets positioned at similar radii from the star as HR8799bc but offset in position angle. They found that for HR 8799b, they were sensitive to variability with amplitudes $>5\%$ for periods less than 10 hours. In contrast, sensitivity for HR 8799c was limited to variability $>25\%$ for similar periods. Overall, this study provides valuable insights into the potential variability of HR8799bc and highlights the importance of further observations to better understand the dynamics of these intriguing exoplanets.