The secular evolution of planetary nebula IC 418 and its implications for carbon star formation

Albert A. Zijlstra; Quentin A. Parker

REVIEW 3 major objections 6 minor 7 references

The secular evolution of planetary nebula IC 418 and its implications for carbon star formation

T0 review · 3 major / 6 minor · reviewed 2026-08-05 · deepseek-v4-flash

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Pith's one-line read IC 418's 130-year spectral record reveals real-time stellar evolution: the [Oiii]/Hβ ratio has risen linearly by 0.9% per year, which the authors attribute to the central star heating at 15–42 K/yr, implying a core mass of 0.560–0.583 solar

desk verdict Robust 130-year archival detection of a [Oiii]/Hβ rise in IC 418, but the carbon-star mass claim depends on the least physical atmosphere model and the abstract overreaches. read the letter →

arxiv 2508.14752 v1 pith:YWE2TM2H submitted 2025-08-20 astro-ph.SR astro-ph.GA

Albert A. Zijlstra , Quentin A. Parker This is my paper · ORCID

classification astro-ph.SRastro-ph.GA

keywords planetarynebulaIC418post-AGBevolutioncentralstarheatingratestellarcoremasscarbonformationarchivalspectroscopyphotoionizationmodeling

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

IC 418, one of the first planetary nebulae recognized as such, has left a 130-year trail of spectra, and the paper argues that trail records real-time stellar evolution. The ratio of the [Oiii] λ5007 line to Hβ has risen steadily—about 0.9% per year, a factor of ~2.5 in total—which the authors attribute to the central star heating up as it leaves the asymptotic giant branch and heads toward the white-dwarf cooling track. From photoionization models they convert this trend into a heating rate of 15–42 K/yr, and from post-AGB evolutionary tracks into a central-star mass of 0.560–0.583 solar masses and a main-sequence progenitor of 1.25–1.55 solar masses. Because the nebula is carbon-rich, the star must have been an AGB carbon star; if this mass range is right, carbon stars at solar metallicity form at lower masses than commonly assumed, and post-AGB evolution may be slower than recent models predict.

What carries the argument

The load-bearing tool is the [Oiii] λ5007/Hβ ratio as a spectroscopic thermometer: O++ requires 35.1 eV to form, so this ratio rises steeply and monotonically as the central star's effective temperature climbs from ~30 to ~45 kK, while Hβ changes more slowly. The paper assembles more than 30 historical and modern measurements (eye estimates, photographic plates, photoelectric scanners, CCD and IFU spectra), excludes non-representative slit data, and fits the integrated ratio against time. Cloudy photoionization models, run with blackbody, ATLAS, and WMBASIC stellar atmospheres, convert the observed ratio trend into a temperature evolution, and the Miller–Bertolami post-AGB tracks convert the

What would settle it

Continue high-precision spectroscopic monitoring of IC 418 for the next decade: the predicted [Oiii]/Hβ increase is ~0.009 per year, so a flat, negative, or strongly non-linear trend would refute the secular-heating interpretation. Independently, if a post-AGB-specific atmosphere model shifts the inferred heating rate outside 15–42 K/yr, the derived stellar mass and the carbon-star conclusion would change.

Watch

Extended reading notes

Core claim

The paper's central claim is that the [Oiii] λ5007/Hβ emission-line ratio in IC 418 has increased linearly at 0.0090 ± 0.0015 per year over 130 years (Equation 1), a change of roughly a factor 2.5, and that this secular trend is direct evidence of the central star's post-AGB evolution. From photoionization modeling with Cloudy, the authors derive a model-dependent heating rate of 15–42 K/yr, which they translate via the Miller–Bertolami post-AGB tracks into a central-star mass of 0.560–0.583 M☉ and a main-sequence progenitor mass of 1.25–1.55 M☉. Since IC 418 is carbon-rich and its central star originated from an AGB carbon star, the paper concludes that carbon star formation at solar metall

Load-bearing premise

The conversion from the observed line-ratio trend to a stellar heating rate is set by the choice of stellar atmosphere in the photoionization models; blackbody models give ~42 K/yr while wind-including models give ~15 K/yr, and the low-mass carbon-star conclusion requires the blackbody end.

Editorial extensions

If this is right

Continued monitoring of IC 418 will trace the central star's heating along the post-AGB track in real time, testing whether the linear trend persists.
The derived core mass range (0.560–0.583 M☉) and progenitor mass (1.25–1.55 M☉) tighten the initial–final mass relation at the low-mass end.
The result implies the lower-mass cutoff for carbon star formation at solar metallicity may be below the ~1.65 M☉ found by Marigo et al. (2020), challenging AGB third-dredge-up models.
The instantaneous heating rate is comparable to the average rate implied by the nebula's kinematic age (~25 K/yr), suggesting post-AGB evolutionary models may over-predict heating speeds.
The demonstrated method—mining 130-year-old archival spectra for a single line ratio—can be applied to other young planetary nebulae with long observational records.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

If the low-mass carbon-star conclusion holds, galactic chemical evolution calculations that place carbon and s-process production only in stars above roughly 1.5–2 solar masses at solar metallicity would need to include lower-mass yields, changing the inferred carbon enrichment history of the Galaxy.
The same archival ratio-fitting approach could be applied to other young, low-excitation planetary nebulae with long spectroscopic records, such as NGC 6572 and IC 4997, to build a small sample of independently measured heating rates and test the mass–heating-rate relation statistically.
A decisive check on the model dependence would be a new stellar-atmosphere grid built specifically for post-AGB stars with winds; if it moves the inferred heating rate outside 15–42 K/yr, the derived mass range and the carbon-star implication would need revision.
Since the 1893 eye estimate dominates the fit's uncertainty, re-reducing the earliest photographic plates with modern calibration techniques could substantially tighten the trend's zero point and the inferred heating rate.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

Jim,

You should know two things about this one. First, the archival data work is genuinely impressive: they've assembled a 130-year record of [Oiii]/Hβ measurements for IC 418, carefully corrected for the quirks of eye, photographic, and photoelectric detectors, and the secular rise (roughly a factor of 2.5, linear slope ~0.009 per year) survives excluding the earliest, least certain point. That's a real result, and it's the longest baseline yet for spectroscopic evolution in a PN. Second, the mass and carbon-star conclusions are much softer than the abstract implies. The heating rate inferred from the line ratio depends on the stellar atmosphere model: blackbody gives ~42 K/yr, while ATLAS and WMBASIC (which include winds and are 'may be more realistic') give ~15-16 K/yr. That factor-of-four spread translates directly to core masses 0.583 vs 0.560 Msun and progenitor masses 1.55 vs 1.25 Msun. The carbon-star conclusion only holds at the blackbody end, and the paper itself says the atmosphere models give masses below the carbon-star range. So the abstract overstates what the body supports.

The paper deserves credit for laying this out openly: Section 6.1 quantifies the spread, and Section 7 flags 'this important contradiction.' That's honest. The problem isn't the analysis; it's that the abstract and the mass range 0.560–0.583 give the impression of a firm result when the model systematics are the dominant uncertainty.

Minor quibbles: the 1893 Campbell point carries a lot of weight in the fit uncertainty, but the slope is robust to excluding it. The 1-D Cloudy simplification is reasonable for this mildly elliptical nebula, and the density dependence is shown to be small. The use of Miller-Bertolami tracks is fine, and the circularity burden is low because the secular trend is measured independently of the models.

Who should read it: anyone working on post-AGB evolution, PN central stars, or carbon star formation. The observational detection is worth taking seriously, and the method (heating rate → mass) is a clever way to break degeneracies that luminosity alone can't. But the carbon-star claim should be treated as provisional until the atmosphere-model issue is resolved.

My recommendation: send it to peer review. A good referee can push for a more balanced abstract and a clearer statement that the low-mass carbon star conclusion is conditional on the blackbody model. The paper is solid enough and important enough that it deserves that round of feedback, not a desk reject.

Best, [Name]

Referee Report

3 major / 6 minor

Summary. The paper reports a secular, approximately linear increase of ~0.9% per year in the [OIII] λ5007/Hβ ratio of the planetary nebula IC 418 over 1938–2024 (with a controversial 1893 visual point), based on a careful re-analysis of historical and modern spectroscopy. The authors interpret this as real-time heating of the central star, use Cloudy photoionization models with different stellar atmospheres to convert the ratio trend into a heating rate (15–42 K/yr), and hence derive a central-star mass of 0.560–0.583 M☉ and a main-sequence progenitor mass of 1.25–1.55 M☉ via Miller–Bertolami evolutionary tracks. They argue that because IC 418 is a carbon-rich PN, carbon-star formation at solar metallicity extends to lower initial masses than commonly assumed.

Significance. If the empirical trend and its interpretation hold, this is a rare and valuable direct measurement of post-AGB stellar evolution on human timescales. The archival work—assembling and cross-checking 130 years of heterogeneous observations, including corrections for emulsion sensitivity, slit coverage, and known line-ratio issues—is a significant contribution in itself. The slope is robust to exclusion of the earliest datum, and the authors are transparent about the model dependence of the heating rate. The paper also demonstrates the diagnostic power of the [OIII]/Hβ ratio as a stellar-temperature probe. However, the astrophysical conclusion about low-mass carbon-star formation depends heavily on which stellar-atmosphere model is used, and the paper's own discussion acknowledges this tension.

major comments (3)

[§6.1 and §7] The central astrophysical claim—that carbon-star formation extends to initial masses 1.25–1.55 M☉—is carried entirely by the blackbody end of the atmosphere-model grid. Equations (3)–(5) give dTeff/dt = 38.8±2.5 K/yr (blackbody), 41.7±2.7 K/yr (blackbody with the Morisset & Georgiev density), 16.1±1.0 K/yr (ATLAS), and 15.2±1.0 K/yr (WMBASIC). Section 7 states that the wind-including models 'may be more realistic' and place the star below the carbon-star range of Marigo et al. (2020) and of Rees et al. (2024). The abstract's unqualified statement that carbon-star formation 'extends to these low masses' is thus not supported by the models the authors themselves consider more physical. This needs to be either resolved with new atmosphere models (e.g., a CSPN-specific grid) or the conclusion must be reframed as conditional on the blackbody assumption.
[§6.2] The quoted mass range 0.560–0.583 M☉ is presented as a seemingly tight constraint, but it is the union of two disjoint model predictions separated by the atmosphere-model choice, not a propagated uncertainty. The statement that 'both lower and higher masses can be excluded at good confidence' is not justified, because the factor-of-2.7 spread in heating rate corresponds to a systematic, not statistical, uncertainty. Without propagating the atmosphere-model spread into the mass determination, the initial-mass range 1.25–1.55 M☉ and the carbon-star conclusion inherit an unquantified systematic error.
[§4.2, Eq. (1)–(2)] The error analysis of the linear fit is based on assumed noise sigma values (σ=0.3 for 1893, σ=0.1 for all other points) with no justification or sensitivity test. The slope itself is robust to the 1893 point, as stated, but the reported uncertainty of ±0.0015 yr⁻¹ is entirely controlled by that ad hoc σ choice. A more transparent approach would be to report a bootstrap or Monte Carlo uncertainty using the actual measurement uncertainties (where known) and to discuss how the assumed σ affects the significance of the trend.

minor comments (6)

[Abstract/Introduction] Typos: 'over an 130 year' should be 'over a 130 year'; 'on it’s way' should be 'on its way'.
[Table 1, footnote 11] The MUSE footnote contains 'Oiii 50007 Å'—the wavelength should be 5007 Å.
[§4.2 and Table 1] The criteria for excluding points from the fit are not consistently defined. Eq. (1) excludes 'narrow slits', Eq. (2) excludes Aller & Czyzak (1979) and Hyung et al. (1994), and the text says the fit 'excludes the data from narrow slits'. Please clarify which data are used in which fit and whether the 1979 point is narrow-slit or otherwise flagged.
[§5, Figure 3 caption] The caption reads 'The lines are for constant density models; the points shows the location...'—grammar should be 'points show'.
[§5] The notation 'logn_e = 3.95 cm⁻³' is ambiguous; use log₁₀(n_e/cm⁻³) = 3.95.
[§6.1] The text says the conversion uncertainty is 'a factor of four', while the ratio of the extreme heating rates is 41.7/15.2 ≈ 2.7. Either define the range more carefully (e.g., 10–40 K/yr) or correct the wording.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the secular trend is an independent empirical measurement, and the model-based conversions are standard inversions using external codes and tracks.

full rationale

The paper's central empirical result, the secular increase in [Oiii]/Hβ (Eq. 1), is a direct fit to archival data and is independent of any model. The conversion to a heating rate is a standard photoionization-model inversion using Cloudy with publicly available atmosphere models; the paper explicitly aims to model relative changes rather than reproduce the full spectrum, so the observed trend is not an input used to calibrate the model. The stellar mass is inferred by comparing the measured heating rate to the independent Miller-Bertolami evolutionary tracks, and the initial mass follows from the same tracks' initial-final mass relation; this is a self-consistent use of external models, not a logical circle. Self-citations (e.g., Gesicki & Zijlstra 2007; Hajduk et al. 2015) are used as supporting evidence for the method and prior examples of secular changes, but the argument does not reduce to these citations. The atmosphere-model spread (15–42 K/yr) is a quantified systematic uncertainty, honestly acknowledged in Sections 6.1 and 7, and does not constitute a fitted parameter disguised as a prediction. No equation or claim is equivalent to its own input by construction.

Assumptions & free parameters 4 free parameters · 6 assumptions · 0 invented entities

No new entities are introduced. The chain relies on published photoionization and stellar evolution models; the main free choice is the stellar atmosphere SED, which causes a factor-of-four spread in the derived heating rate.

free parameters (4)

Stellar luminosity input = log L = 37.30 erg/s (blackbody) or 37.40 erg/s (other models)
Chosen from literature to match IC 418. Affects the absolute Teff scale but not the secular trend.
Nebular density = log n_e = 3.95 cm^-3
Adopted from Morisset & Georgiev (2009). The paper states the heating-rate result is little affected by density for IC 418's parameters.
Fit noise sigma = sigma = 0.3 for 1893 point, sigma = 0.1 for all others
Assigned by hand to compute uncertainties on the linear slope. No per-point error analysis is provided.
Inner radius = log r_in = 16.09 cm
Scaled from Morisset & Georgiev (2009) to the Gaia DR3 distance. Minor effect on the modeled ratios.

assumptions (6)

domain assumption Cloudy v23.01 correctly solves the photoionization and radiative transfer for IC 418 parameters
Used throughout Section 5 to compute [Oiii]/Hβ as a function of Teff.
domain assumption The nebula can be approximated as a 1-D spherical shell despite an axial ratio of 0.85
Section 5: 'equivalent to assuming a spherical nebula. This is a reasonable approximation for this mildly elliptical PN'.
domain assumption Miller-Bertolami post-AGB evolutionary tracks correctly predict dTeff/dt as a function of core mass
Section 6.2: heating rates from these models are used to convert the measured heating rate into a mass.
domain assumption The initial-final mass relation from the same Miller-Bertolami models maps core mass to progenitor mass
Section 6.2: 'Using the initial masses in the models of Miller Bertolami (2016)'.
domain assumption The observed line-ratio change is due to Teff evolution, not to changing extinction or nebular density
Sections 4.2 and 5; shocks contribute only about 2 to 2.5%.
ad hoc to paper Adopted noise sigma values are representative of the historical data errors
Section 4.2: sigma=0.3 for the 1893 point and sigma=0.1 for all others are assumed without a detailed error analysis of each measurement.

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Cite this review

Pith. "Pith review of The secular evolution of planetary nebula IC 418 and its implications for carbon star formation." pith.science (2026). https://pith.science/paper/YWE2TM2H

@misc{pith2026250814752,
  author       = {Pith},
  title        = {Pith review of: The secular evolution of planetary nebula IC 418 and its implications for carbon star formation},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/YWE2TM2H}},
  note         = {Machine review of arXiv:2508.14752}
}

read the original abstract

The rate of stellar evolution can rarely be measured in real time. The fastest evolution (excluding event-driven evolution), where stars may evolve measurably over decades, is during the post-AGB phase. In this paper we provide direct evidence for such a case. A secular, linear, factor of ~2.5 increase is found in the strength of the [O III] lines relative to H-beta over an 130 year period in the young, well-known, low excitation planetary nebula IC 418. The increase is caused by the rising temperature of the central star. We use photo-ionization models to derive a model dependent heating rate for the central star in the range 15-42 K\/yr. These derived heating rates are very sensitive to the stellar mass, and yield a central-star mass of 0.560-0.583 solar masses. Initial-final mass relations based on the Miller-Bertolami models give a progenitor main-sequence mass of 1.25-1.55 solar masses. IC 418 is a carbon rich planetary nebula and its central star, HD 35914, has evolved from an AGB carbon star. This result shows that carbon star formation at solar metallicity extends to these low masses. This is lower than commonly assumed and suggests that post-AGB evolution may be slower than recent post-AGB models predict.

Figures

Figures reproduced from arXiv: 2508.14752 by the authors.

**Figure 1.** Observed values of λ5007/Hβ over a 130 year time period. The most reliable data, based on integrated flux across the full PN, are plotted as filled triangles. Open triangles refer to less reliable measurements usually derived from wide slits or apertures that do not cover all of the nebula. Open squares show limits. The off-centre data of S. Hyung et al. (1994) is not included. The best fit and limits are shown; thi… view at source ↗

**Figure 2.** The predicted [O iii] 5007/Hβ ratio as function of Teff , for different stellar atmosphere models and assuming a constant density nebula. Top panel: Hydrostatic ATLAS and blackbody models. Bottom panel: WMBASIC models which include stellar winds, and the Cloudy fit for a single CMFGEN model with stellar winds from V. Escalante et al. (2012) (also shown in the top panel). The red parallelogram encompasses the range o… view at source ↗

**Figure 3.** The change in stellar temperature needed for increasing [O iii]/Hβ from 1.0 to 2.0, for blackbody and ATLAS models at constant density. The drawn line is for blackbody models and the dashed line for ATLAS stellar atmospheres. The points indicate the location of the C. Morisset & L. Georgiev (2009) (left) and M. A. Dopita et al. (2017) (right) density models, shown at the density of their main inner shell, where the … view at source ↗

Figures from the paper (2 more)

**Figure 4.** Figure 4: The derived central star temperature evolution of IC 418 based on changes in the observed [O iii]/Hβ line ratios. The drawn lines correspond to the linear fit of Eq. 2. The lower panel gives blackbody SEDs from the density distributions of C. Morisset & L. Georgiev (20…

**Figure 5.** Figure 5: Selected historical examples of 2-D spectra of IC418 covering the Hβ and [O iii] region from years 1918 to 2016. The change in the [O iii] to Hβ ratio is clear, notwithstanding corrections for emulsion sensitivity for the 1918 and 1942 photographic plates. From top to …

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Reference graph

Works this paper leans on

7 extracted references · 5 canonical work pages

[1]

1992, The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae

Acker, A., Marcout, J., Ochsenbein, F., et al. 1992, The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae. Parts I, II. (European Southern Observatory, Garching (Germany)) Ali, A., Amer, M. A., Dopita, M. A., Vogt, F. P. A., & Basurah, H. M. 2015, A&A, 583, A83, doi: 10.1051/0004-6361/201526223 Aller, L., & Kaler, J. B. 1964, ApJ, 140, 936, doi: 10....

arXiv doi:10.48550/arxiv.astro-ph/0405087 1992
[5]

photographic region

The exact observation time is not always known, and some papers give a range of dates. This is reflected in the uncertainties on years given in the table. Some measurements did not integrate along the slit but present ratios from the PN’s centre where [Oiii] is stronger due to ionisation stratification (e.g. S. Torres-Peimbert & M. Peimbert 1977). The dee...

work page 1977
[137]

A., Gon¸ calves, D

https://arxiv.org/abs/1302.4485 Fragkou, V., V´ azquez, R., Parker, Q. A., Gon¸ calves, D. R., & Lomel ´ ı-N´ u˜ nez, L. 2025, A&A, 696, A146, doi: 10.1051/0004-6361/202453031 Frew, D. J., Bojiˇ ci´ c, I. S., & Parker, Q. A. 2013, MNRAS, 431, 2, doi: 10.1093/mnras/sts393 The secular evolution of planetary nebula IC 41811 Frew, D. J., Parker, Q. A., & Boji...

arXiv 2025
[1894]

nebulium

appears to have made the first recorded spectral observation on Nov 2, 1893, with a visual spectroscope with a wide slit to include all the PN. He noticed that the two “nebulium” lines N1 (4949 ˚A) and N2 (5007˚A) (unidentified then, but now known to be the [Oiii] lines) were slightly less extended and more centrally condensed than Hβ. He measured a brigh...

work page 1951
[2009]

tabulated values in SIMBAD where V=9.01 from UCAC4 data of the system N

Mcore 0.560–0.583M ⊙ this work Mprogenitor 1.25–1.55 M⊙ this work *nebular contribution removed from photometric estimates of the star c.f. tabulated values in SIMBAD where V=9.01 from UCAC4 data of the system N. Zacharias et al. (2012). B.THE HISTORICAL SPECTROSCOPIC ARCHIVE To assess evidence for secular evolution in line intensity ratios and of the dia...

work page 2012
[2016]

From top to bottom we show a slitless IC 418 spectrum given in W

The change in the [Oiii] to Hβratio is clear, notwithstanding corrections for emulsion sensitivity for the 1918 and 1942 photographic plates. From top to bottom we show a slitless IC 418 spectrum given in W. H. Wright (1918); a slit spectrum from A. B. Wyse (1942); an electronic camera spectrum from L. Aller & M. Walker (1970) and finally a 2-D extract fr...

work page 1918
[6572]

the theoretical ratio of 3.0

to 2.96 (NGC 6826), c.f. the theoretical ratio of 3.0. The value for IC 418 is 2.78 from the reported intensities of 13.9 and 5.0 – the weakest for all PNe in the sample. The secular evolution of planetary nebula IC 41815 Plate XLIX from Wright 1918 for IC418 slitless spectrogram photographic plate Plate XIII from Wyse 1942 for IC418 Extract of Fig1. from...

work page 1918

Pith tools

Reviewed August 5, 2026 · model on record in the stance chip above.

[1] [1]

1992, The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae

Acker, A., Marcout, J., Ochsenbein, F., et al. 1992, The Strasbourg-ESO Catalogue of Galactic Planetary Nebulae. Parts I, II. (European Southern Observatory, Garching (Germany)) Ali, A., Amer, M. A., Dopita, M. A., Vogt, F. P. A., & Basurah, H. M. 2015, A&A, 583, A83, doi: 10.1051/0004-6361/201526223 Aller, L., & Kaler, J. B. 1964, ApJ, 140, 936, doi: 10....

arXiv doi:10.48550/arxiv.astro-ph/0405087 1992

[2] [5]

photographic region

The exact observation time is not always known, and some papers give a range of dates. This is reflected in the uncertainties on years given in the table. Some measurements did not integrate along the slit but present ratios from the PN’s centre where [Oiii] is stronger due to ionisation stratification (e.g. S. Torres-Peimbert & M. Peimbert 1977). The dee...

work page 1977

[3] [137]

A., Gon¸ calves, D

https://arxiv.org/abs/1302.4485 Fragkou, V., V´ azquez, R., Parker, Q. A., Gon¸ calves, D. R., & Lomel ´ ı-N´ u˜ nez, L. 2025, A&A, 696, A146, doi: 10.1051/0004-6361/202453031 Frew, D. J., Bojiˇ ci´ c, I. S., & Parker, Q. A. 2013, MNRAS, 431, 2, doi: 10.1093/mnras/sts393 The secular evolution of planetary nebula IC 41811 Frew, D. J., Parker, Q. A., & Boji...

arXiv 2025

[4] [1894]

nebulium

appears to have made the first recorded spectral observation on Nov 2, 1893, with a visual spectroscope with a wide slit to include all the PN. He noticed that the two “nebulium” lines N1 (4949 ˚A) and N2 (5007˚A) (unidentified then, but now known to be the [Oiii] lines) were slightly less extended and more centrally condensed than Hβ. He measured a brigh...

work page 1951

[5] [2009]

tabulated values in SIMBAD where V=9.01 from UCAC4 data of the system N

Mcore 0.560–0.583M ⊙ this work Mprogenitor 1.25–1.55 M⊙ this work *nebular contribution removed from photometric estimates of the star c.f. tabulated values in SIMBAD where V=9.01 from UCAC4 data of the system N. Zacharias et al. (2012). B.THE HISTORICAL SPECTROSCOPIC ARCHIVE To assess evidence for secular evolution in line intensity ratios and of the dia...

work page 2012

[6] [2016]

From top to bottom we show a slitless IC 418 spectrum given in W

The change in the [Oiii] to Hβratio is clear, notwithstanding corrections for emulsion sensitivity for the 1918 and 1942 photographic plates. From top to bottom we show a slitless IC 418 spectrum given in W. H. Wright (1918); a slit spectrum from A. B. Wyse (1942); an electronic camera spectrum from L. Aller & M. Walker (1970) and finally a 2-D extract fr...

work page 1918

[7] [6572]

the theoretical ratio of 3.0

to 2.96 (NGC 6826), c.f. the theoretical ratio of 3.0. The value for IC 418 is 2.78 from the reported intensities of 13.9 and 5.0 – the weakest for all PNe in the sample. The secular evolution of planetary nebula IC 41815 Plate XLIX from Wright 1918 for IC418 slitless spectrogram photographic plate Plate XIII from Wyse 1942 for IC418 Extract of Fig1. from...

work page 1918