# The Effelsberg survey of FU~Orionis and EX~Lupi objects II. -- H$_2$O maser observations

**Authors:** Zs. M. Szabó, Y. Gong, W. Yang, K. M. Menten, O. S. Bayandina, C. J. Cyganowski, Á. Kóspál, P. Ábrahám, A. Belloche, F. Wyrowski  
**arXiv:** [2305.00736](https://arxiv.org/abs/2305.00736)  
**Date:** 2023-05-01  
**Summary page:** https://www.summarizepaper.com/en/paper/2305.00736v1/

## Key points

- FU Orionis (FUor) and EX Lupi (EXor) are rare pre-main sequence low-mass stars that undergo powerful accretion outbursts during their early stellar evolution.
- Water masers can serve as powerful probes of mass accretion and ejection in star-forming regions.
- A team of researchers performed the first systematic search for the 22.2 GHz water maser line in FUors/EXors to determine its overall incidence and perform follow-up high angular resolution observations.
- Using the Effelsberg 100-m radio telescope, the team observed the 22.2 GHz H2O maser towards a sample of 51 objects.
- They detected five water masers, three of which were associated with eruptive stars resulting in a 6% detection rate for eruptive sources.
- The team also detected water maser emission in their pointing towards the FUor binary RNO 1B/1C and H$_2$O(B), a Class 0 source ~30'' from the EXor V512 Per.
- The presence of 22.2 GHz water maser emission in FUor/EXor systems was demonstrated, opening the way to radio interferometric observations to study these eruptive stars on small scales.
- This study provides important insights into the prevalence of water masers towards FUors/EXors and highlights their potential as probes for studying accretion and ejection processes in these rare pre-main sequence low-mass stars.

## Summary

FU Orionis (FUor) and EX Lupi (EXor) are two groups of rare pre-main sequence low-mass stars that undergo powerful accretion outbursts during their early stellar evolution. Water masers, which are widespread in star-forming regions, can serve as powerful probes of mass accretion and ejection. However, little is known about the prevalence of water masers towards FUors/EXors. To address this gap, a team of researchers performed the first systematic search for the 22.2 GHz water maser line in FUors/EXors to determine its overall incidence and perform follow-up high angular resolution observations. Using the Effelsberg 100-m radio telescope, the team observed the 22.2 GHz H2O maser towards a sample of 51 objects. They detected five water masers, three of which were associated with eruptive stars resulting in a 6% detection rate for eruptive sources. These detections included one EXor, V512 Per (also known as SVS 13 or SVS 13A), and two FUors, Z CMa and HH 354 IRS. This is the first reported detection of water maser emission towards HH 354 IRS. The team also detected water maser emission in their pointing towards the FUor binary RNO 1B/1C, which most likely originates from the nearby deeply embedded source IRAS 00338+6312 (~4'', from RNO 1B/1C). Emission was also detected from H$_2$O(B) (also known as SVS 13C), a Class 0 source ~30'' from the EXor V512 Per. The peak flux density of H$_2$O(B) in their observations was found to be at an all-time high at 498.7 Jy. In addition to these detections, the team also found maser emission towards one Class 0/I (HH 354 IRS) and two Class I (V512 Per and Z CMa) eruptive stars. The presence of 22.2 GHz water maser emission in FUor/EXor systems was demonstrated, opening the way to radio interferometric observations to study these eruptive stars on small scales. Comparing their data with historical observations, the team suggests that multiple water maser flares have occurred in both V512 Per and H$_2$O(B). Overall, this study provides important insights into the prevalence of water masers towards FUors/EXors and highlights their potential as probes for studying accretion and ejection processes in these rare pre-main sequence low-mass stars.