An episodically variable stellar wind in the planetary nebula IC 4997

IC 4997 is a planetary nebula well known by its variability. We present high-resolution spectra of IC 4997 obtained in 1993, 2019, and 2020 that reveal changes in the Hα and [N » II] emission line profiles, which had never been reported for this object. The Hα P Cygni emission profile observed in 1993 changed to a single-peaked profile in 2019-2020, implying that the stellar wind has largely weakened. The very broad Hα emission wings narrowed by a factor of ∼2 between 1993 and 2019-2020, indicating that the efficiency of the Rayleigh-Raman scattering has noticeably decreased. A high-velocity [N » II] nebular component detected in 1993 is missing in 2019 and 2020, probably due to a decrease in its electron density. A correlation exists between the strength of the stellar wind and the episodic (∼50-60 yr) variation in the [O » III]λ4363/Hγ line intensity ratio, suggesting that an episodic, smoothly variable stellar wind is the main cause of the variability of IC 4997. Monitoring of that intensity ratio and of the Hα emission line profile in the coming years and new multiwavelength observations are key to unveiling the ongoing processes in IC 4997 and constraining the origin of the wind variability. © ESO 2022.
We thank Calar Alto Observatory for allocation of director’s discretionary time to this programme. LFM is partially supported by MCIU grant AYA2017-84390-C2-1-R (co-funded by FEDER) and PID2020-114461GB-I00 of AEI (10.13039/501100011033), and acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). J.M.T. acknowledges partial support from the PID2020-117710GB-I00 grant funded by MCIN/AEI/10.13039/501100011033. J.L.-B. acknowledges financial support received from “la Caixa” Foundation (ID 100010434) and from the European Unions Horizon 2020 research and innovation programme under the Marie Slodowska-Curie grant agreement No 847648, with fellowship code LCF/BQ/PI20/11760023. This research has also been partly funded by the Spanish State Research Agency (AEI) Projects No.ESP2017-87676-C5-1-R and No. MDM-2017-0737 Unidad de Excelencia “María de Maeztu”- Centro de Astrobiología (INTA-CSIC).