Reversal of the /O III/lambda 4363/H[SUB]gamma[/SUB] lambda 4340 ratio in the planetary nebula IC 4997

Feibelman, W. A.; Hobbs, R. W.; Mccracken, C. W.; Brown, L. W.

doi:10.1086/157167

Cited by 10 publications

(9 citation statements)

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“…If smaller (greater) distances are assumed, the kinematical age would be smaller (larger) accordingly. For instance, if we assume that the formation of the inner shell coincides with the reversal of the [O III] 4363/H␥ intensity ratio observed from 1962 (Feibelman et al 1979;Kiser & Daub 1982), the distance would be 31300 pc. On the other hand, we have assumed a constant expansion velocity for the inner shell.…”

Section: Discussionmentioning

confidence: 99%

“…It is reasonable to assume that large amounts of kinetic energy are being transferred from the stellar wind of the Wolf-Rayet-type central star to the inner shell. If the temperature of the central star varies (Feibelman et al 1979;Ferland 1979), the wind velocity might be variable. In fact, this is suggested by the very different total velocity width of the H␣ wings measured by Feibelman et al (1992) and by us (see above).…”

Section: Discussionmentioning

confidence: 99%

“…The planetary nebula (PN) IC 4997 has attracted attention since Liller & Aller (1957) and Aller & Liller (1966) reported on variability of the [O III] 4363/H␥ line intensity ratio in the nebula (see also Feibelman et al 1979;Purgathofer & Stoll 1981). More recent observations have shown that many emission lines from IC 4997 are also variable (Feibelman, Aller, & Hyung 1992).…”

Section: Introductionmentioning

confidence: 99%

“…However, the interpretation of the observations presents many problems. The variability of the [O III] 4363/H␥ intensity ratio is probably caused by variations of T e , which would ultimately be due to changes in the stellar flux (Feibelman et al 1979 and references therein ;Ferland 1979;Purgathofer & Stoll 1981). Other authors consider that the expansion alone of the PN is enough to explain that variability (Aller & Liller 1966;Kiser & Daub 1982).…”

Section: Introductionmentioning

confidence: 99%

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The Double-Shell Structure of the Variable Young Planetary Nebula IC 4997

Miranda

Torrelles

Eiroa

1996

The Astrophysical Journal

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VLA-A 3.6 cm continuum and H92␣ observations and long-slit optical spectroscopy of IC 4997 are presented. The radio continuum map shows that IC 4997 is a double-shell planetary nebula consisting of a faint, knotty outer shell of size 32"7 ϫ 1"4, elongated at position angle 354Њ, and a bright, circular inner shell of 30"28 in diameter. The outer shell presents an hourglass-like morphology and exhibits a striking mirror symmetry with respect to its minor axis. The deduced mean electron densities are 31.2 ϫ 10 4 cm Ϫ3 and 31.4 ϫ 10 5 cm Ϫ3 in the outer and inner shells, respectively. The knots in the outer shell present electron densities of 33-4 ϫ 10 4 cm Ϫ3 , somewhat higher than the mean. The analysis of the H␣, [N II], and [S II] emission lines, spatially and spectrally resolved in the spectrum, allows us to deduce the basic kinematical properties of the two shells. The outer shell presents bipolar motions, expands at 312 km s Ϫ1 in the equatorial plane, and was formed several hundred years ago. The inner shell expands at 325 km s Ϫ1 and was ejected some decades ago. The H␣ emission from the central star presents extremely wide wings that can be traced up to 35375 km s Ϫ1 . This value is much higher than those previously reported for IC 4997. Our results suggest that the two shells are interacting and that a dense region may have been formed between the two shells. The physical conditions in this dense region could vary as the inner shell expands, and, therefore, variations of the emitted spectrum from this region are expected. This interaction should be taken into account in order to explain the observed variability of the emission lines in the nebula. Subject headings: ISM: kinematics and dynamics -planetary nebulae: individual (IC 4997)

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Double-Shell Structure of the Variable Young Planetary Nebula IC 4997

Miranda

Torrelles

Eiroa

1996

The Astrophysical Journal

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“…An interesting question regards the origin of a variable CS wind in IC 4997. The variation in the [O iii]λ4363/Hγ ratio suggests that, in addition to its maximum value around 1995, another maximum may have existed around 1938−1940 when that ratio reached values very similar to those in 1995 (Feibelman et al 1979;A+20, their Fig. 4).…”

Section: Discussionmentioning

confidence: 88%

An episodically variable stellar wind in the planetary nebula IC 4997

Miranda

Torrelles

Lillo-Box

2022

A&A

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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.

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Periodicity in spectral variations of IC 4997?

Gurzadyan

1992

Astrophys Space Sci

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Reversal of the /O III/lambda 4363/H[SUB]gamma[/SUB] lambda 4340 ratio in the planetary nebula IC 4997

Cited by 10 publications

References 0 publications

The Double-Shell Structure of the Variable Young Planetary Nebula IC 4997

The Double-Shell Structure of the Variable Young Planetary Nebula IC 4997

An episodically variable stellar wind in the planetary nebula IC 4997

Periodicity in spectral variations of IC 4997?

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