An episodically variable stellar wind in the planetary nebula IC 4997

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Table 1.

Velocity width (km s⁻¹) of the Hα emission line at different intensity levels in the three epochs.

Full width ^(a)	1993.7.16	2019.7.31	2020.9.21
FWZI	7000 ± 300 ^(b)	3900 ± 350	3850 ± 200
FW5σ	4270 ± 160 ^(b)	1900 ± 170	1890 ± 100
FW0.002	2400 ± 100	404 ± 30	400 ± 20
FW0.0035	1020 ± 40	290 ± 17	282 ± 12
FW0.005	340 ± 23	235 ± 12	231 ± 10

Notes.

^(a)

FWZI = full width at the continuum level; FW5σ = full width at 5σ level from the continuum; FW0.002/0.0035/0.005 = full width at the 0.002/0.0035/0.005 level from the peak intensity.

^(b)

From the f/3 coudé spectrum assuming symmetry of the wings with respect to the radial velocity centroid of the Hα emission line (see text).

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