# HIP 65426 is a High-Frequency Delta Scuti Pulsator in Plausible Spin-Orbit Alignment with its Directly Imaged Exoplanet

**Authors:** Aldo G. Sepulveda, Daniel Huber, Timothy R. Bedding, Daniel R. Hey, Simon J. Murphy, Zhoujian Zhang, Michael C. Liu  
**arXiv:** [2312.05310](https://arxiv.org/abs/2312.05310)  
**Date:** 2023-12-08  
**Summary page:** https://www.summarizepaper.com/en/paper/2312.05310v1/

## Key points

- HIP 65426 hosts a young giant planet, the first exoplanet directly imaged with the JWST
- Classified as a high-frequency $\delta$ Scuti pulsator with a potential large frequency separation of $\Delta \nu =$7.23$\pm$0.02 cycles per day
- Dynamical mass upper limit of 12.8 Jupiter masses estimated for HIP 65426 b
- Stellar latitudinal differential rotation observed with periods of 7.85$\pm$0.08 hours and 6.67$\pm$0.04 hours
- Inclination of HIP 65426 measured to be $i_{\star}=105_{-9}^{+7}$$^\circ$, consistent with orbital inclination of HIP 65426 b at a confidence level of $68\%$
- Lack of significant evidence for spin-orbit misalignment within the HIP 65426 system noted
- Study contributes valuable insights into pulsation behavior and rotational dynamics, enhancing understanding of planetary systems beyond our solar system

## Summary

HIP 65426 is an intriguing system that has recently gained attention for hosting a young giant planet. This marks the first exoplanet to be directly imaged with the James Webb Space Telescope (JWST). In a study led by Aldo G. Sepulveda and his team, time-series photometry data from the Transiting Exoplanet Survey Satellite (TESS) was utilized to gain further insight into this captivating system. Through their analysis, HIP 65426 was classified as a high-frequency $\delta$ Scuti pulsator with a potential large frequency separation of $\Delta \nu =$7.23$\pm$0.02 cycles per day. The researchers also examined TESS data for pulsation timing variations but found no significant evidence, leading them to estimate a 95% dynamical mass upper limit of 12.8 Jupiter masses for HIP 65426 b. Furthermore, the team identified a low-frequency signal region in the data which they interpreted as indicative of stellar latitudinal differential rotation. This phenomenon was characterized by two rapid periods of 7.85$\pm$0.08 hours and 6.67$\pm$0.04 hours respectively, providing valuable insights into the rotational dynamics of HIP 65426. By combining their findings on TESS rotation periods with published values of radius and $v \sin{i}$, the team was able to jointly measure the inclination of HIP 65426 to $i_{\star}=105_{-9}^{+7}$$^\circ$. Interestingly, this stellar inclination was found to be consistent with the orbital inclination of HIP 65426 b ($108_{-3}^{+6}$$^{\circ}$) at a confidence level of $68\%$, based on their orbit fit using published relative astrometry. One particularly intriguing aspect highlighted in this study is the lack of significant evidence for spin-orbit misalignment within the HIP 65426 system. This observation aligns with an emerging trend suggesting preferential alignment between imaged long-period giant planets and their host stars, further underscoring the unique dynamics at play in this captivating exoplanetary system. Overall, these findings not only contribute valuable insights into the pulsation behavior and rotational dynamics of HIP 65426 but also add to our growing understanding of planetary systems beyond our solar system. The meticulous analysis conducted by Sepulveda et al. sheds new light on this enigmatic system and paves the way for future investigations into similar exoplanetary systems hosting young giant planets.