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The expected linear residual correlation - - - with log R exhibits an rms scatter of 0. Various investigators have modeled the evolution of a star as it passes through the red giant phase, ejects significant mass, and becomes a white dwarf. The PN phase lies between the giant and WD stages in stellar evolution.
Also plotted are tracks of lower mass stars from Driebe et al. PNNi temperatures are from Napiwotzki We find that the four PNNi clump about a mass , in agreement with the peak of the WD mass distribution, 0. Interpolated individual masses are found in Table 6. These are listed in Table 7. We note that the mass of 40 Eri B from these tracks is , differing substantially from that listed in Provencal et al. Figure 9. Lower-mass dashed line tracks are from Driebe et al. The uncertainty in our log g is primarily due to the radius uncertainty.
Calculated values of log g for our four PNNi are listed in Table 6 and compared with the Napiwotzki line profile fitting values. Note that Figure 10 shows 40 Eri B to have a mass consistent with past estimates. Figure Symbol size is proportional to surface temperature. Companions with spectral types later than listed in Table 8 would not be detected by the FGS. For example, a companion 2 mag fainter than the DeHt 5 PNN an M1V star is at the limit of detectability for a separation of 15 mas, which for the parallax of DeHt 5 equates to 5. For another application of Table 8 we consider NGC Su et al.
A binary companion could provide an engine to sculpt a dust disk. If much asymmetrical PN structure is due to binarity Soker ; De Marco , then we would have the highest probability of detecting the companion to the PNN of. NGC , the most asymmetric of the PN we observed. Finally, in principle we can probe for very short period companions using the photometry in Figure 2. Companions with small separations could produce a single-peaked orbital light curve through heating of the companion star by the PNN e. As the companion star orbits the PNN, its heated face is alternately more or less visible, increasing and decreasing the observed flux from the PNN once per orbit.
Kawka et al. Assuming a similar inclination, we find from binary light curve modeling cf. Harrison et al. PNNi are too bright, washing out any variations due to reflection from companions. Napiwotzki has compiled PNe distances from a number of methods. Shklovski distances are only available for only three of our targets, and the Na D method has been applied only to two of our targets. The recent recalibration of the Shklovski distances by Stanghellini et al. The dashed line represents perfect agreement. The Shklovski approach has a tendency to underestimate the distances while the spectroscopic distances are a bit on the high side.
Objects are labeled to the right or top. Napiwotzki determined PNNi fundamental stellar parameters, temperature and surface gravity, from a fit of the hydrogen Balmer lines with profiles computed from NLTE model atmospheres. This technique is well established and tested for the analysis of hot white dwarfs e. However, when Napiwotzki applied this method to the even hotter central stars of old PNe, it became clear that for many stars no consistent fit of all Balmer lines could be achieved.
A strong temperature trend was present, with the fit of higher members of the Balmer series yielding higher temperatures. However, a physical explanation of the Balmer line problem remained elusive for some time. Models used for the Napiwotzki investigation were calculated in full NLTE but included only the two most abundant elements hydrogen and helium.
Tests carried out prior to the start of this project appeared to show that the impact of line blanketing of heavier elements on the temperature structure of the atmospheres had only minor impact on the hydrogen line profiles see discussion in Werner This treatment is very computer time intensive. For this reason, it was not included in previous calculations.
This method was then adapted by Napiwotzki Fitted surface gravities appeared to be unaffected by the Balmer line problem. All Balmer lines could be fitted with a single value of g using the Napiwotzki H and He models. Also, the Werner calculations did not indicate offsets in gravity. Napiwotzki compared his spectroscopic distance estimates with the results of other distance estimates including the best parallax measurements available at that time Harris et al. However, as pointed out by Napiwotzki , one has to take into account that the often significant relative errors of trigonometric parallaxes introduce sample biases.
Lutz—Kelker biases are one way to estimate the size of the effect. Napiwotzki performed a Monte Carlo simulation trying to model the properties of the Harris et al. The conclusion at that time was that both distance scales are marginally consistent, but large uncertainties remained. Improved accuracy of recent trigonometric parallax measurements have changed the situation dramatically. A straightforward reading from Table A.
Both estimates confirm that remaining systematic errors are now much smaller, in line with the small Lutz—Kelker biases given in our Table 6. Thus it is a good time to reassess the spectroscopic distance scale. This offset is smaller than that found by Napiwotzki , but due to the smaller errors and biases it is now highly significant. This translates into an average log g offset. In Table 6 we find DeHt 5 anomalous, the difference between gravity derived from our radius and from the analysis of stellar atmospheres larger than for the other three PNNi.
DeHt 5 is of special interest and will be discussed below. The temperature and gravity derived by Napiwotzki place the central star of DeHt 5 in a region of the temperature gravity diagram inconsistent with a post-AGB origin. The parameters of this central star were better matched to those of a star that lost its envelope at the end of the first red giant branch and is now evolving into a low mass He-core white dwarf.
Barstow et al. The derived temperature is 57, K—lower than the Napiwotzki result—partly due to the inclusion of metal line blanketing and partly due to a different fit algorithm and philosophy. The resulting abundances are higher than those of the well-known hot "template" white dwarf G —B2B, which appears to have typical abundances for that parameter range Barstow et al. One could be tempted to speculate that unusual metal abundances could explain the unusual large differences between trigonometric and spectral analysis results.
More detailed abundance analyses of more PNNi would be needed to decide this question. In any case one conclusion is that even the metal blanketed atmospheres of Barstow et al. Parker et al. A more detailed investigation of the nebula will clarify this issue. Weighted averages with previous ground-based determinations Harris et al.
Our results confirm that statistical distances methods of the Shklovski type underestimate the distances of old planetary nebulae. On the other hand, the improved accuracy of our trigonometric parallaxes now show that previous spectroscopic distances significantly overestimated the distances.
Results from Napiwotzki and similar studies should be corrected accordingly. We use these parallaxes and estimates of interstellar extinction from our own spectrophotometry and other investigations to derive PNNi absolute magnitudes.
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These four PNNi along with two others with well-determined distances and five WD satisfy theoretical linear correlations between absolute bolometric magnitude, log temperature, and log radius. Estimating from post-AGB evolutionary models, we find PNNi masses that agree with those typically found for white dwarf stars. These results are based partially on observations obtained with the Apache Point Observatory 3.
We thank an anonymous referee for a careful reading and suggestions that improved the presentation. Parallax factors are projections along R. The HST has a full compliment of six rate gyros, two per axis, that provide coarse pointing control. By the time these observations were in progress, three of the gyros had failed.
To find out more, see our Privacy and Cookies policy. Close this notification. Download Article PDF. Article data. Share this article. Article information. Author affiliations. Related links. Table 1. Zoom In Zoom Out Reset image size. The DeHt 5 Astrometric Model With the positions measured by FGS 1r, we determine the scale, rotation, and offset "plate constants" relative to an arbitrarily adopted constraint epoch the so-called "master plate" for each observation set the data acquired at each epoch.
Table 4. Table 5. Table 6. Radii: PNNi Versus WDs Our four parallaxes, along with measured temperatures and apparent luminosities have resulted in four newly estimated radii for PNNi that, according to theory, should eventually descend to a WD cooling track. Table 7. If much asymmetrical PN structure is due to binarity Soker ; De Marco , then we would have the highest probability of detecting the companion to the PNN of Table 8.
Barker, T. Barstow, M. Benedict, G.
Bergeron, P. Bessell, M. Bohlin, R. Bond, H. Bradley, A.
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Burstein, D. Ciardullo, R. Cox, A. De Marco, O. Driebe, T. Finley, D. Flower, P. Franz, O. Girard, T. Hamada, T. Hanson, R. Harris, H.