# Accretion Funnel Reconfiguration during an Outburst in a Young Stellar Object: EX Lupi

**Authors:** Koshvendra Singh, Joe P. Ninan, Marina M. Romanova, David A. H. Buckley, Devendra K. Ojha, Arpan Ghosh, Andrew Monson, Malte Schramm, Saurabh Sharma, Daniel E. Reichart, Joanna Mikolajewska, Juan Carlos Beamin, J. Borissova, Valentin D. Ivanov, Vladimir V. Kouprianov, Franz-Josef Hambsch, Andrew Pearce  
**arXiv:** [2404.05420](https://arxiv.org/abs/2404.05420)  
**Date:** 2024-04-08  
**Summary page:** https://www.summarizepaper.com/en/arxiv-id/2404.05420v1/

## Key points

- EX Lupi, a low-mass young stellar object, experienced an accretion-driven outburst in March 2022
- Significant phase change of approximately 112$^{\circ}$ $\pm$ 5$^{\circ}$ in its multiband lightcurves
- Consistent phase shift in radial velocities observed through high-resolution spectra obtained with HRS on SALT
- Increase in amplitude of various emission lines indicating reconfiguration of accretion funnel geometry over the stellar surface
- Detailed 3D MHD simulations successfully replicated the observed phase change for EX Lupi

## Summary

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EX Lupi, a low-mass young stellar object, experienced an accretion-driven outburst in March of 2022, leading to a significant phase change of approximately 112$^{\circ}$ $\pm$ 5$^{\circ}$ in its periodically oscillating multiband lightcurves. This event was accompanied by a consistent phase shift in the radial velocities observed through high-resolution spectra obtained with HRS on SALT, as well as an increase in the amplitude of various emission lines. These changes in phase and velocity amplitude indicated a reconfiguration of the accretion funnel geometry over the stellar surface, suggesting a shift in the azimuthal and latitudinal location of the accretion hotspot. Furthermore, detailed 3D MHD simulations successfully replicated the observed phase change for EX Lupi. To explain these phenomena, researchers explored potential scenarios such as forward shifting of the dipolar accretion funnel or the emergence of a new accretion funnel during the outburst. During this period, evidence emerged of the hotspot's morphology extending azimuthally in an asymmetric manner with a leading hot edge and cold tail along the stellar rotation axis. High cadence photometry revealed clumpiness in the accretion flow, with short timescale variabilities indicating discrete clumps within the system. This clumpiness was further supported by observations from HRS spectra showing episodic highly blue-shifted wings in prominent emission lines like Ca II IRT and Balmer H.

Overall, these findings shed light on the dynamic nature of accretion processes in young stellar objects during outburst events and highlight the complex interplay between accretion funnels, hotspots, and clumpy flows. The comprehensive study conducted by Koshvendra Singh et al., accepted for publication in The Astrophysical Journal, provides valuable insights into how these systems evolve and interact under extreme conditions.