19,808 research outputs found
Radio-continuum detections of Galactic Planetary Nebulae I. MASH PNe detected in large-scale radio surveys
We present an updated and newly compiled radio-continuum data-base for MASH
PNe detected in the extant large scale "blind" radio-continuum surveys (NVSS,
SUMSS/MGPS-2 and PMN) and, for a small number of MASH PNe, observed and
detected in targeted radio-continuum observations. We found radio counterparts
for approximately 250 MASH PNe. In comparison with the percentage of previously
known Galactic PNe detected in the NVSS and MGPS-2 radio-continuum surveys and
according to their position on the flux density-angular diameter and the radio
brightness temperature evolutionary diagrams we conclude, unsurprisingly, that
the MASH sample presents the radio-faint end of the known Galactic PNe
population. Also, we present radio-continuum spectral properties of a small
sub-sample of MASH PNe located in the strip between declinations -30arcdeg and
-40arcdeg, that are detected in both the NVSS and MGPS-2 radio surveys.Comment: 13 figures and 7 tables, accepted for publication in MNRA
Planetary Nebula Surveys: Past, Present and Future
In this review we cover the detection, identification and astrophysical
importance of planetary nebulae (PN). The legacy of the historic Perek &
Kohoutek and Acker et al. catalogues is briefly covered before highlighting the
more recent but significant progress in PN discoveries in our Galaxy and the
Magellanic Clouds. We place particular emphasis on the major MASH and the IPHAS
catalogues, which, over the last decade alone, have essentially doubled
Galactic and LMC PN numbers. We then discuss the increasing role and importance
that multi-wavelength data is playing in both the detection of candidate PN and
the elimination of PN mimics that have seriously biased previous PN
compilations. The prospects for future surveys and current efforts and
prospects for PN detections in external galaxies are briefly discussed due to
their value both as cosmic distance indicators and as kinematical probes of
galaxies and dark matter properties.Comment: 8 pages, 1 figure, Proceedings of the Asymmetric Planetary Nebula V
Conference (Invited Review, Lake District, England, June 2010
Flux calibration of the AAO/UKST SuperCOSMOS H-alpha Survey
The AAO/UKST SuperCOSMOS H Survey (SHS) was, when completed in 2003,
a powerful addition to extant wide-field surveys. The combination of areal
coverage, spatial resolution and sensitivity in a narrow imaging band, still
marks it out today as an excellent resource for the astronomical community. The
233 separate fields are available online in digital form, with each field
covering 25 square degrees. The SHS has been the motivation for equivalent
surveys in the north, and new digital H surveys now beginning in the
south such as VPHAS+. It has been the foundation of many important discovery
projects with the Macquarie/AAO/Strasbourg H planetary nebula project
being a particularly successful example. However, the full potential of the SHS
has been hampered by lack of a clear route to acceptable flux calibration from
the base photographic data. We have determined the calibration factors for 170
individual SHS fields, and present a direct pathway to the measurement of
integrated H fluxes and surface brightnesses for resolved nebulae
detected in the SHS. We also include a catalogue of integrated H fluxes
for 100 planetary and other nebulae measured from the SHS, and use these
data to show that fluxes, accurate to 0.10 - 0.14 dex (25-35 per
cent), can be obtained from these fields. For the remaining 63 fields, a mean
calibration factor of 12.0 counts pix R can be used, allowing the
determination of reasonable integrated fluxes accurate to better than 0.2
dex (50 per cent). We outline the procedures involved and the caveats
that need to be appreciated in achieving such flux measurements. This paper
forms a handy reference source that will significantly increase the scientific
utility of the SHS.Comment: 14 pages, 12 figures, 2 tables (plus 7 pp. of supplementary online
information). Version to appear in MNRA
Are planetary nebulae derived from multiple evolutionary scenarios?
Our understanding of planetary nebulae has been significantly enhanced as a
result of several recent large surveys (Parker et al., these proceedings).
These new discoveries suggest that the `PN phenomenon' is in fact more
heterogeneous than previously envisaged. Even after the careful elimination of
mimics from Galactic PN catalogues, there remains a surprising diversity in the
population of PNe and especially their central stars. Indeed, several
evolutionary scenarios are implicated in the formation of objects presently
catalogued as PNe. We provide a summary of these evolutionary pathways and give
examples of each. Eventually, a full census of local PNe can be used to
confront both stellar evolution theory and population synthesis models.Comment: 4 pages, 1 figure. To be published in Planetary Nebulae: an Eye to
the Future, Proceedings of IAU Symposium 283, held in Puerto de la Cruz,
Tenerife, Spain, July 25-29 201
The planetary nebula Abell 48 and its [WN] nucleus
We have conducted a detailed multi-wavelength study of the peculiar nebula
Abell 48 and its central star. We classify the nucleus as a helium-rich,
hydrogen-deficient star of type [WN4-5]. The evidence for either a massive WN
or a low-mass [WN] interpretation is critically examined, and we firmly
conclude that Abell 48 is a planetary nebula (PN) around an evolved low-mass
star, rather than a Population I ejecta nebula. Importantly, the surrounding
nebula has a morphology typical of PNe, and is not enriched in nitrogen, and
thus not the `peeled atmosphere' of a massive star. We estimate a distance of
1.6 kpc and a reddening, E(B-V) = 1.90 mag, the latter value clearly showing
the nebula lies on the near side of the Galactic bar, and cannot be a massive
WN star. The ionized mass (~0.3 M_Sun) and electron density (700 cm^-3) are
typical of middle-aged PNe. The observed stellar spectrum was compared to a
grid of models from the Potsdam Wolf-Rayet (PoWR) grid. The best fit
temperature is 71 kK, and the atmospheric composition is dominated by helium
with an upper limit on the hydrogen abundance of 10 per cent. Our results are
in very good agreement with the recent study of Todt et al., who determined a
hydrogen fraction of 10 per cent and an unusually large nitrogen fraction of ~5
per cent. This fraction is higher than any other low-mass H-deficient star, and
is not readily explained by current post-AGB models. We give a discussion of
the implications of this discovery for the late-stage evolution of
intermediate-mass stars. There is now tentative evidence for two distinct
helium-dominated post-AGB lineages, separate to the helium and carbon dominated
surface compositions produced by a late thermal pulse. Further theoretical work
is needed to explain these recent discoveries.Comment: 19 pages, 10 figures, to appear in MNRAS. Version 3 incorporates
proof correction
The H surface brightness radius plane as a diagnostic tool for photoionized nebulae
The H surface brightness radius () relation is a robust
distance indicator for planetary nebulae (PNe), further enhanced by different
populations of PNe having distinct loci in space. Other types of
photoionized nebulae also plot in quite distinct regions in the plane,
allowing its use as a diagnostic tool. In particular, the nova shells and
massive star ejecta (MSE) plot on relatively tight loci illustrating their
evolutionary sequences. For the MSE, there is potential to develop a distance
indicator for these objects, based on their trend in space. As
high-resolution, narrowband surveys of the nearest galaxies become more
commonplace, the plane is a potentially useful diagnostic tool to help
identify the various ionized nebulae in these systems.Comment: 4 pages, 2 figures. To appear in the proceedings of the 11th Pacific
Rim Conference on Stellar Astrophysics: Physics and Chemistry of the Late
Stages of Stellar Evolution, held in Hong Kong, Dec 201
Planetary Nebulae: Observational Properties, Mimics, and Diagnostics
The total number of true, likely and possible planetary nebulae (PN) now
known in the Milky Way is nearly 3000, double the number known a decade ago.
The new discoveries are a legacy of the recent availability of wide field,
narrowband imaging surveys, primarily in the light of H-alpha. In this paper,
we summarise the various PN discovery techniques, and give an overview of the
many types of objects which mimic PN and which appear as contaminants in both
Galactic and extragalactic samples. Much improved discrimination of classical
PN from their mimics is now possible based on the wide variety of high-quality
multiwavelength data sets that are now available. We offer improved taxonomic
and observational definitions for the PN phenomenon based on evaluation of
these better diagnostic capabilities. However, we note that evidence is
increasing that the PN phenomenon is heterogeneous, and PN are likely to be
formed from multiple evolutionary scenarios. In particular, the relationships
between some collimated symbiotic outflows and bipolar PN remain uncertain.Comment: 25 pages, 6 figures; presentation at the workshop on the Legacies of
the Macquarie/AAO/Strasbourg H-alpha Planetary Nebula project, accepted by
the Publications of the Astronomical Society of Australia (PASA
K 1-6: an asymmetric planetary nebula with a binary central star
We present new imaging data and archival multiwavelength observations of the
little studied emission nebula K 1-6 and its central star. Narrow-band images
in H-alpha (+ [NII]) and [OIII] taken with the Faulkes Telescope North reveal a
stratified, asymmetric, elliptical nebula surrounding a central star which has
the colours of a late G- or early K-type subgiant or giant. GALEX ultraviolet
images reveal a very hot subdwarf or white dwarf coincident in position with
this star. The cooler, optically dominant star is strongly variable with a
period of 21.312 +/- 0.008 days, and is possibly a high amplitude member of the
RS CVn class, although an FK Com classification is also possible. Archival
ROSAT data provide good evidence that the cool star has an active corona. We
conclude that K 1-6 is most likely an old bona fide planetary nebula at a
distance of ~1.0 kpc, interacting with the interstellar medium, and containing
a binary or ternary central star. The observations and data analyses reported
in this paper were conducted in conjunction with Year 11 high school students
as part of an Australian Research Council Linkage Grant science education
project, denoted Space To Grow, conducted jointly by professional astronomers,
educational researchers, teachers, and high-school students.Comment: 13 pages, 5 figures, accepted by the Publications of the Astronomical
Society of Australia (PASA
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