English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present absolute parallaxes and relative proper motions for the centralstars of the planetary nebulae NGC 6853 (The Dumbbell), NGC 7293 (The Helix),Abell 31, and DeHt 5. This paper details our reduction and analysis using DeHt5 as an example. We obtain these planetary nebula nuclei (PNNi) parallaxes withastrometric data from Fine Guidance Sensors FGS 1R and FGS 3, white-lightinterferometers on the Hubble Space Telescope (HST). Proper motions, spectralclassifications and VJHKT_2M and DDO51 photometry of the stars comprising theastrometric reference frames provide spectrophotometric estimates of referencestar absolute parallaxes. Introducing these into our model as observations witherror, we determine absolute parallaxes for each PNN. Weighted averaging withprevious independent parallax measurements yields an average parallaxprecision, \sigma_{\pi}/\pi = 5 %. Derived distances are: d_{NGC6853}=405^{+28}_{-25}pc, d_{NGC 7293}=216^{+14}_{-12} pc, d_{Abell 31} =621^{+91}_{-70} pc, and d_{DeHt 5} = 345^{+19}_{-17} pc. These PNNi distancesare all smaller than previously derived from spectroscopic analyses of thecentral stars. Derived absolute magnitudes and previously measured effectivetemperatures permit estimates of PNNi radii, through both the Stefan-Boltzmannrelation and Eddington fluxes. Comparing absolute magnitudes with post-AGBmodels provides mass estimates. Masses cluster around 0.57 M(sun), close to thepeak of the white dwarf mass distribution. Adding a few more PNNi withwell-determined distances and masses, we compare all the PNNi with cooler whitedwarfs of similar mass, and confirm, as expected, that PNNi have larger radiithan white dwarfs that have reached their final cooling tracks. (Abridged)

Astrometry with the Hubble Space Telescope: Trigonometric Parallaxes of Planetary Nebula Nuclei: NGC 6853, NGC 7293, Abell 31, and DeHt 5