# The Directly-Imaged Exoplanet Host Star 51 Eridani is a Gamma Doradus Pulsator

**Authors:** Aldo G. Sepulveda, Daniel Huber, Zhoujian Zhang, Gang Li, Michael C. Liu, Timothy R. Bedding  
**arXiv:** [2205.01103](https://arxiv.org/abs/2205.01103)  
**Date:** 2022-05-02  
**Summary page:** https://www.summarizepaper.com/en/paper/2205.01103v1/

## Key points

- Star 51 Eri is a well-known exoplanet host and member of the $\beta$ Pictoris moving group
- Recent observations using two-minute cadence photometry from TESS have revealed multi-periodic variability in 51 Eri consistent with pulsations of Gamma Doradus ($\gamma$ Dor) stars
- Identified pulsation modes include dipole and quadrupole gravity-modes, as well as Rossby modes previously observed in Kepler $\gamma$ Dor stars
- Previously reported variability attributed to stellar rotation may instead be due to $\gamma$ Dor pulsations
- Detected pulsations enabled estimation of plausible stellar core rotation period of 0.9$^{+0.3}_{-0.1}$ days for 51 Eri, using mean frequency of $l=1$ gravity-modes and empirical trends of Kepler $\gamma$ Dor population
- No evidence for transiting companions around 51 Eri was found in residual light curve; future TESS observations could allow constraint on stellar core rotation rate, which would trace its surface rotation rate and help clarify whether or not the stellar equatorial plane and orbit of 51 Eri b are coplanar
- Findings highlight that 51 Eri is not only a directly-imaged exoplanet host but also a $\gamma$ Dor pulsator - making it an important benchmark system for studying both exoplanets and stellar astrophysics

## Summary

The star 51 Eri is a well-known exoplanet host and member of the $\beta$ Pictoris moving group. Recent observations using two-minute cadence photometry from the Transiting Exoplanet Survey Satellite (TESS) have revealed multi-periodic variability in 51 Eri that is consistent with pulsations of Gamma Doradus ($\gamma$ Dor) stars. The most significant pulsation modes identified include dipole and quadrupole gravity-modes, as well as Rossby modes, which have been previously observed in Kepler $\gamma$ Dor stars. These results suggest that previously reported variability attributed to stellar rotation may instead be due to $\gamma$ Dor pulsations. The detected pulsations have enabled an estimation of a plausible stellar core rotation period of 0.9$^{+0.3}_{-0.1}$ days for 51 Eri, using the mean frequency of the $l=1$ gravity-modes and empirical trends of the Kepler $\gamma$ Dor population. Further follow-up observations and modeling may enable determination of an asteroseismic age for this benchmark system. No evidence for transiting companions around 51 Eri was found in the residual light curve; however, future TESS observations could allow a constraint on the stellar core rotation rate, which would trace its surface rotation rate and help clarify whether or not the stellar equatorial plane and orbit of 51 Eri b are coplanar. In conclusion, these findings highlight that 51 Eri is not only a directly-imaged exoplanet host but also a $\gamma$ Dor pulsator - making it an important benchmark system for studying both exoplanets and stellar astrophysics.