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Individual distances

Distance is one of the most fundamental parameters and appears in nearly all studies of PNe. There exist several ``statistical'' distances based on various assumptions concerning the system of PNe. The differences of the statistical distances for a given object are large mainly because of the differences of individual objects called planetary nebulae. A better situation exists with ``individual'' distances which are more or less reliable and are given basically by: trigonometric parallaxes of central stars, spectroscopic parallaxes of the companions of central stars, membership of clusters, expansion of nebulae and extinction of nebulae compared with the extinction in their vicinity. There are further methods which use some general conceptions, described mainly by Acker (1978), Sabbadin (1986) and Pottasch (1996), such as e.g. his ``gravity'' distances, depending on the correctness of the model atmosphere used.

We have divided the PNe with known individual distances into two categories according to the accuracy of the distances: the first category of distances is accurate up to 50% or less; we estimate the accuracy of the second category of distances to be within 50-150%. We would like to point out that the individual values given in the following table need not be wholly independent of each other, but we give them again in order to show the scatter of distances which is not small at all for some objects. However the present situation is much better than that some years ago because now almost 10% of all planetaries have known individual distances (77 in the first and 63 in the second category).

List of planetary nebulae with individual distances

REFERENCES:

  1. Sabbadin F., 1986, A&AS 64, 579. (Table 1: column 10)
  2. Harris H.C., Dahn C.C., Monet D.G., Pier J.R., 1997, Proc. IAU Symp.180, 40.
    (Table 2: Trigonometric parallaxes)
  3. Acker A., Fresneau A., Pottasch S.R., Jasniewicz G., 1998, A&A 337, 253.
    (Table 1: HIPPARCOS, reliable trigonometric parallaxes)
  4. Cahn J.H., Kaler J.B., Stanghellini L., 1992, A&AS 94, 399. (Table 3: Calibration nebulae)
  5. Terzian Y., 1997, Proc. IAU Symp.180, 29. (Table 1: Expansion distances - mean)
  6. Pottasch S.R., 1996, A&A 307, 561:
    1. (Table 3: Spectroscopic distances)
    2. (Table 5: Expansion distances)
    3. (Table 6: ``Gravity'' distances)
    4. (Table 8: Extinction distances)
  7. Gutierrez-Moreno A., Anguita C., Loyola P., Moreno H., 1999, PASP 111, 1163. (Table 3: Trigonometric parallaxes)
  8. Napiwotzki R., Schönberner D., 1995, A&A 301, 545. (Table 6: Na D extinction distances)
  9. Gathier R., Pottasch S.R., Pel J.W., 1986, A&A 157, 171. (Table 12: Extinction distances)
  10. Martin W., 1994, A&A 281, 526. (Table 4: Extinction distances)
  11. Saurer W., 1995, A&A 297, 261. (Extinction distances)
  12. Acker A., 1978, A&AS 33, 367. (Table 4: Extinction distances D(ABS))



next up previous
Nächste Seite: Binary central stars Aufwärts: Elementary Statistics Vorherige Seite: Discoveries
Lubos Kohoutek
2001-04-02