摘要：Context. We have obtained multi-wavelength observations of compact
Galactic planetary nebulae (PNe) to probe post-asymptotic giant branch (AGB) evolution
from the onset of nebular ejection. Here we analyze new observations from HST to derive
the masses and evolutionary status of their central stars (CSs).
Aims. Our objective here is to derive the masses of the CSs hosted by
compact PNe in order to better understand the relationship between the CS properties and
those of the surrounding nebulae. We also compare this sample with others we obtained
using the same technique in different metallicity environments: the Large and Small
Magellanic Clouds.
Methods. This paper is based on HST/WFC3 images of 51 targets obtained
in a snapshot survey (GO–11657). The high spatial resolution of HST allows us to resolve
these compact PNe and distinguish the CS emission from that of their surrounding PNe. We
derive CS bolometric luminosities and effective temperatures using the Zanstra technique,
from a combination of HST photometry and ground-based spectroscopic data. The targets were
imaged through the filters F200LP, F350LP, and
F814W from which we derive Johnson V and I magnitudes. We infer CS
masses by placing the stars on a temperature-luminosity diagram and compare their location
with the best available, single star post-AGB evolutionary tracks.
Results. We present new, unique photometric measurements of 50 CSs, and
we derive effective temperatures and luminosities for most of them. Central star masses
for 23 targets were derived with the evolutionary track technique; the remaining masses
were indeterminate most likely because of underestimates of the stellar temperature, or
because of substantial errors in the adopted statistical distances to these objects. We
expect these problems will be largely overcome when the Gaia distance
catalog becomes available. We find that objects with the higher ratios of Zanstra
temperatures T(H i)/T( He ii ) tend to
have lower-mass progenitors.
Conclusions. The distribution of CS masses in this sample of compact PNe
is remarkably different from samples in the LMC and SMC, but with a median mass of 0.59
M⊙ it is similar to other Galatic samples.
Finally, we conclude from the typically advanced evolutionary state of the CSs on the log
L, log
Teff plane that the compact nature of many
of the PNe is a result of their large distance, rather than their physical dimension.
关键词：Galaxy: disk;planetary nebulae: general;stars: AGB and post-AGB;stars: evolution;stars: fundamental parameters
