Volume 416, Number 2, March III 2004
|Page(s)||623 - 629|
|Section||Interstellar and circumstellar matter|
|Published online||27 February 2004|
On expansion parallax distances for planetary nebulae
Sterrewacht Leiden, PO Box 9513, 2300 RA, Leiden, The Netherlands
Corresponding author: mellema@strw.LeidenUniv.nl
Accepted: 2 December 2003
The distances to individual wind-driven bubbles such as Planetary Nebulae (PNe) can be determined using expansion parallaxes: the angular expansion velocity in the sky is compared to the radial velocity of gas measured spectroscopically. Since the one is a pattern velocity, and the other a matter velocity, these are not necessarily the same. Using the jump conditions for both shocks and ionization fronts, I show that for typical PNe the pattern velocity is 20 to 30% larger than the material velocity, and the derived distances are therefore typically 20 to 30% too low. I present some corrected distances and suggest approaches to be used when deriving distances using expansion parallaxes.
Key words: shock waves / planetary nebulae / stars: distances / stars: AGB and post–AGB / hydrodynamics / ISM: planetary nebulae: general
© ESO, 2004
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