171 research outputs found
The enigmatic central star of the planetary nebula PRTM 1
The central star of the planetary nebula PRTM 1 (PN G243.8-37.1) was
previously found to be variable by M. Pena and colleagues. As part of a larger
programme aimed towards finding post common-envelope binary central stars we
have monitored the central star of PRTM 1 spectroscopically and photometrically
for signs of variability. Over a period of ~3 months we find minimal radial
velocity (<10 km/s) and photometric (< 0.2 mag) variability. The data suggest a
close binary nucleus can be ruled out at all but the lowest orbital
inclinations, especially considering the spherical morphology of the nebula
which we reveal for the first time. Although the current data strongly support
the single star hypothesis, the true nature of the central star of PRTM 1
remains enigmatic and will require further radial velocity monitoring at higher
resolution to rule out a close binary. If in the odd case that it is a close
binary, it would be the first such case in a spherical planetary nebula, in
contradiction to current thinking.Comment: A&A, in pres
Binary planetary nebulae nuclei towards the Galactic bulge. II. A penchant for bipolarity and low-ionisation structures
Considerable effort has been applied towards understanding the precise
shaping mechanisms responsible for the diverse range of morphologies exhibited
by planetary nebulae (PNe). A binary companion is increasingly gaining support
as a dominant shaping mechanism, however morphological studies of the few PNe
that we know for certain were shaped by binary evolution are scarce or biased.
Newly discovered binary central stars (CSPN) from the OGLE-III photometric
variability survey have significantly increased the sample of post
common-envelope (CE) nebulae available for morphological analysis. We present
Gemini South narrow-band images for most of the new sample to complement
existing data in a qualitative morphological study of 30 post-CE nebulae.
Nearly 30% of nebulae have canonical bipolar morphologies, however this rises
to 60% once inclination effects are incorporated with the aid of geometric
models. This is the strongest observational evidence yet linking CE evolution
to bipolar morphologies. A higher than average proportion of the sample shows
low-ionisation knots, filaments or jets suggestive of a binary origin. These
features are also common around emission-line nuclei which may be explained by
speculative binary formation scenarios for H-deficient CSPN.Comment: Accepted for publication in A&
Searching for binary central stars of planetary nebulae with Kepler
The Kepler Observatory offers unprecedented photometric precision (<1 mmag)
and cadence for monitoring the central stars of planetary nebulae, allowing the
detection of tiny periodic light curve variations, a possible signature of
binarity. With this precision free from the observational gaps dictated by
weather and lunar cycles, we are able to detect companions at much larger
separations and with much smaller radii than ever before. We have been awarded
observing time to obtain light-curves of the central stars of the six confirmed
and possible planetary nebulae in the Kepler field, including the newly
discovered object Kn 61, at cadences of both 30 min and 1 min. Of these six
objects, we could confirm for three a periodic variability consistent with
binarity. Two others are variables, but the initial data set presents only weak
periodicities. For the central star of Kn 61, Kepler data will be available in
the near future
From Bipolar to Elliptical: Simulating the Morphological Evolution of Planetary Nebulae
The majority of Proto-planetary nebulae (PPN) are observed to have bipolar
morphologies. The majority of mature PN are observed to have elliptical shapes.
In this paper we address the evolution of PPN/PN morphologies attempting to
understand if a transition from strongly bipolar to elliptical shape can be
driven by changes in the parameters of the mass loss process. To this end we
present 2.5D hydrodynamical simulations of mass loss at the end stages of
stellar evolution for intermediate mass stars. We track changes in wind
velocity, mass loss rate and mass loss geometry. In particular we focus on the
transition from mass loss dominated by a short duration jet flow (driven during
the PPN phase) to mass loss driven by a spherical fast wind (produced by the
central star of the PN). We address how such changes in outflow characteristics
can change the nebula from a bipolar to an elliptical morphology. Our results
show that including a period of jet formation in the temporal sequence of PPN
to PN produces realistic nebular synthetic emission geometries. More
importantly such a sequence provides insight, in principle, into the apparent
difference in morphology statistics characterizing PPN and PN systems. In
particular we find that while jet driven PPN can be expected to be dominated by
bipolar morphologies, systems that begin with a jet but are followed by a
spherical fast wind will evolve into elliptical nebulae. Furthermore, we find
that spherical nebulae are highly unlikely to ever derive from either bipolar
PPN or elliptical PN.Comment: Accepted for publication in the MNRAS, 15 pages, 7 figure
Multi-Object Spectroscopy Field Configuration by Simulated Annealing
Multi-object spectroscopy (MOS) instruments, such as the Two-degree Field
(2dF) facility of the Anglo-Australian Observatory (AAO), have facilitated
large-scale redshift surveys. Yet despite their acclaim, instrument design has
been suspected of introducing subtle selection effects into surveys.
Investigation into these selection effects has been overshadowed by instrument
complexity. We identify the field configuration algorithm (FCA) used to select
targets for observation as mainly responsible for such effects. A FCA can
imprint artificial structure on observed target distributions, which may accrue
over large angular scales, potentially to the detriment of statistical analyses
applied to such surveys. We present here a new FCA developed for 2dF that is
based on simulated annealing (SA), a generic method commonly used to solve
constrained optimisation problems. We generate synthetic fields and utilise
mock 2dF volumes to contrast the behaviour of previous strategies with the SA
FCA. The angular two-point correlation function and other sensitive techniques
reveal that the new FCA achieves unprecedented sampling uniformity and target
yield with improved target priority handling and observational flexibility over
current FCAs. The SA FCA is generic enough to be used by current 2dF-like and
potentially next-generation MOS instruments with little modification.Comment: 14 pages, 16 figures, accepted to MNRA
- …