1,084 research outputs found
Nebular Abundance Errors
The errors inherent to the use of the standard "ionization correction factor"
("i_CF") method of calculating nebular conditions and relative abundances of H,
He, N, O, Ne, S, and Ar in emission line nebulae have been investigated under
conditions typical for planetary nebulae. The photoionization code CLOUDY was
used to construct a series of model nebulae with properties spanning the range
typical of PNe. Its radial "profiles" of bright, frequently observed optical
emission lines were then summed over a variety of "apertures" to generate sets
of emission line measurements. These resulting line ratios were processed using
the i_CF method to "derive" nebular conditions and abundances. We find that for
lines which are summed over the entire nebula the i_CF-derived abundances
differ from the input abundances by less than 5% for He and O up to 25% or more
for Ne, S, and Ar. For resolved observations, however, the discrepancies are
often much larger and are systematically variable with radius. This effect is
especially pronounced in low-ionization zones where nitrogen and oxygen are
neutral or once-ionized such as in FLIERs, ansae and ionization fronts. We
argue that the reports of stellar-enriched N in the FLIERs of several PNe are
probably specious.Comment: 22 pages, 4 tables, and 1 figure. Accepted for publication in the
Astronomical Journal. Replaced to correct a referenc
The evolution of M 2-9 from 2000 to 2010
M 2-9, the Butterfly nebula, is an outstanding representative of extreme
aspherical flows. It presents unique features such as a pair of high-velocity
dusty polar blobs and a mirror-symmetric rotating pattern in the inner lobes.
Imaging monitoring of the evolution of the nebula in the past decade is
presented. We determine the proper motions of the dusty blobs, which infer a
new distance estimate of 1.3+-0.2 kpc, a total nebular size of 0.8 pc, a speed
of 147 km/s, and a kinematical age of 2500 yr. The corkscrew geometry of the
inner rotating pattern is quantified. Different recombination timescales for
different ions explain the observed surface brightness distribution. According
to the images taken after 1999, the pattern rotates with a period of 92+-4 yr.
On the other hand, the analysis of images taken between 1952 and 1977 measures
a faster angular velocity. If the phenomenon were related to orbital motion,
this would correspond to a modest orbital eccentricity (e=0.10+-0.05), and a
slightly shorter period (86+-5 yr). New features have appeared after 2005 on
the west side of the lobes and at the base of the pattern. The geometry and
travelling times of the rotating pattern support our previous proposal that the
phenomenon is produced by a collimated spray of high velocity particles (jet)
from the central source, which excites the walls of the inner cavity of M 2-9,
rather than by a ionizing photon beam. The speed of such a jet would be
remarkable: between 11000 and 16000 km/s. The rotating-jet scenario may explain
the formation and excitation of most of the features observed in the inner
nebula, with no need for additional mechanisms, winds, or ionization sources.
All properties point to a symbiotic-like interacting binary as the central
source of M 2-9.Comment: Accepted for publication on Astronomy and Astrophysics (10 pages, 8
figures
The Planetary Nebula Luminosity Function: Pieces of the Puzzle
Extragalactic surveys in the emission line of [O III] 5007 have provided us
with the absolute line strengths of large, homogeneous sets of planetary
nebulae. These data have been used to address a host of problems, from the
measurement of the extragalactic distance scale, to the study of stellar
populations. I review our current understanding of the [O III] planetary nebula
luminosity function (PNLF), and discuss some of the physical processes that
effect its structure. I also describe the features of the H-alpha PNLF, a
function that, upon first glance, looks similar to the [O III] PNLF, but which
includes a very different set of objects. Finally, I discuss recent
measurements of alpha, the number of PNe found in a stellar population,
normalized to that population's bolometric luminosity. I show that, contrary to
expectations, the values of alpha found in actively star-forming spirals is
essentially the same as those measured in late-type elliptical and lenticular
systems. I discuss how this result sheds light on the physics of the planetary
nebula phenomenon.Comment: 7 pages, including 7 figures; presentation at the workshop on the
Legacies of the Macquarie/AAO/Strasbourg H-alpha Planetary Nebula project,
accepted for publication in PAS
- …