The Validity of Mass Functions for the Central Stars of Planetary Nebulae

Monthly Notices of the Royal Astronomical Society

2005

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The central stars of highly evolved planetary nebulae (PNe) are expected to have closely similar absolute visual magnitudes MV. This enables us to determine approximate distances to these sources where one knows their central star visual magnitudes, and levels of extinction. We find that such an analysis implies values of D which are similar to those determined by Phillips; Cahn, Kaler & Stanghellin; Acker, and Daub. However, our distances are very much smaller than those of Zhang; Bensby & Lundstrom, and van de Steene & Zijlstra. The reasons for these differences are discussed, and can be traced to errors in the assumed relation between brightness temperature and radius. Finally, we determine that the binary companions of such stars can be no brighter than MV∼ 6 mag, implying a spectral type of K0 or later in the case of main‐sequence stars.

Section: The Evolutionary Characteristics Of Pne Central Starsmentioning

confidence: 99%

The distances of highly evolved planetary nebulae

Monthly Notices of the Royal Astronomical Society

2005

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“…Much here depends upon whether their value of M ENV is plausible, however. Pottasch (1996) and Phillips (2000) suggest that values of M ENV may be greater, for instance, and this would push the phase of optical thinness to much later stages of evolution. Even where shells are optically thick to He ii ionizing radiation, the Zanstra temperature may underestimate central star effective temperatures where T EFF > 100 kK (Gruenwald & Viegas 2000). This disparity may be of order 13 per cent where T EFF = 150 kK, increasing to ∼25 per cent where T EFF = 400 kK. Observations of optical extinction (Phillips 1998) and near and far infrared emission (Pottasch 1984; Phillips & Cuesta 1994) testify to the importance of dust within the shells of PNe.…”

Section: The Relation Between Tz and Teffmentioning

confidence: 99%

Section: The Relation Between Tz and Teffmentioning

confidence: 99%

The relation between Zanstra temperature and morphology in planetary nebulae

2003

Monthly Notices RAS

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We have created a master list of Zanstra temperatures for 373 galactic planetary nebulae based upon a compilation of 1575 values taken from the published literature. These are used to evaluate mean trends in temperature for differing nebular morphologies. Among the most prominent results of this analysis is the tendency for η=TZ(He ii)/TZ(He i) to increase with nebular radius, a trend which is taken to arise from the evolution of shell optical depths. We find that as many as 87 per cent of nebulae may be optically thin to H ionizing radiation where radii exceed ∼0.16 pc. We also note that the distributions of values η and TZ(He ii) are quite different for circular, elliptical and bipolar nebulae. A comparison of observed temperatures with theoretical H‐burning tracks suggests that elliptical and circular sources arise from progenitors with mean mass 〈MPG〉≅ 1 M⊙ (although the elliptical progenitors are probably more massive). Higher‐temperature elliptical sources are likely to derive from progenitors with mass ≅2 M⊙, however, implying that these nebulae (at least) are associated with a broad swathe of progenitor masses. Such a conclusion is also supported by trends in mean galactic latitude. It is found that higher‐temperature elliptical sources have much lower mean latitudes 〈b〉 than those with smaller TZ(He ii), a trend which is explicable where there is an increase in 〈MPG〉 with increasing TZ(He ii). This latitude–temperature variation also applies for most other sources. Bipolar nebulae appear to have mean progenitor masses ≅2.5 M⊙, whilst jets, Brets and other highly collimated outflows are associated with progenitors at the other end of the mass range (〈MPG〉∼ 1 M⊙). Indeed it is possible, given their large mean latitudes and low peak temperatures, that the latter nebulae are associated with the lowest‐mass progenitors of all. The present results appear fully consistent with earlier analyses based upon nebular scale heights, shell abundances and the relative proportions of differing morphologies, and offer further evidence for a link between progenitor mass and morphology.

“…There is some alternative and largely independent evidence to support this presumption. Thus Phillips (2000a) has noted that ratios of Zanstra temperatures T z (HeII)/T z (HI) imply quite large optical depths in sources having radii R < 2 pc. Not all such sources are optically thick, but it is clear that many of them are.…”

Section: Implications Of the Deduced Radial Functionmentioning

confidence: 99%

The radial distribution function in planetary nebulae

2003

Astron Nachr

Abstract. We have investigated the variation of planetary nebula number densities as a function of nebular radius, taking account of uncertainties arising from interstellar extinction. We find that the trend is composed of two components: one (a "spike" component) located at radii R < 0.035 pc, and the other (a "plateau" component) extending to larger radii. The plateau component appears to follow a Gaussian fall-off law with scale radius R0 = 0.28 pc. It is shown that this latter trend is not consistent with the assumption that larger shells are optically thin and density bounded. Rather, it seems likely that many of the larger sources have appreciable Lyman continuum optical depths and are ionization bounded. The deduced variation in N (R) then suggests that the velocities of the ionization fronts increase with radius. The nature of the spike component is less easy to fathom, and this may arise as a result of sharply lower ionization front velocities at radii R < 0.035 pc, or through contraction of the shells following a down-turn in central star luminosities.