27 research outputs found
A catalogue of integrated H-alpha fluxes for 1,258 Galactic planetary nebulae
We present a catalogue of new integrated H-alpha fluxes for 1258 Galactic
planetary nebulae (PNe), with the majority, totalling 1234, measured from the
Southern H-Alpha Sky Survey Atlas (SHASSA) and/or the Virginia Tech
Spectral-line Survey (VTSS). Aperture photometry on the continuum-subtracted
digital images was performed to extract H-alpha + [NII] fluxes in the case of
SHASSA, and H-alpha fluxes from VTSS. The [NII] contribution was then
deconvolved from the SHASSA flux using spectrophotometric data taken from the
literature or derived by us. Comparison with previous work shows that the flux
scale presented here has no significant zero-point error. Our catalogue is the
largest compilation of homogeneously derived PN fluxes in any waveband yet
measured, and will be an important legacy and fresh benchmark for the
community. Amongst its many applications, it can be used to determine
statistical distances for these PNe, determine new absolute magnitudes for
delineating the faint end of the PN luminosity function, provide baseline data
for photoionization and hydrodynamical modelling, and allow better estimates of
Zanstra temperatures for PN central stars with accurate optical photometry. We
also provide total H-alpha fluxes for another 75 objects which were formerly
classified as PNe, as well as independent reddening determinations for ~270
PNe, derived from a comparison of our H-alpha data with the best literature
H-beta fluxes. In an appendix, we list corrected H-alpha fluxes for 49 PNe
taken from the literature, including 24 PNe not detected on SHASSA or VTSS,
re-calibrated to a common zero-point.Comment: 49 pages, 7 figures, 10 tables, to appear in MNRAS. This version
includes full-length tables 1 and
HASH: the Hong Kong/AAO/Strasbourg H-alpha planetary nebula database
By incorporating our major recent discoveries with re-measured and verified
contents of existing catalogues we provide, for the first time, an accessible,
reliable, on-line SQL database for essential, up-to date information for all
known Galactic PNe. We have attempted to: i) reliably remove PN mimics/false
ID's that have biased previous studies and ii) provide accurate positions,
sizes, morphologies, multi-wavelength imagery and spectroscopy. We also provide
a link to CDS/Vizier for the archival history of each object and other valuable
links to external data. With the HASH interface, users can sift, select,
browse, collate, investigate, download and visualise the entire currently known
Galactic PNe diversity. HASH provides the community with the most complete and
reliable data with which to undertake new science.Comment: 8 pages, 4 figures; accepted to appear in refereed proceedings of the
11th Pacific Rim Conference held in Hong-kong in Dec 201
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 and their mimics: the MASH-MEN Project
The total number of true, likely and possible planetary nebulae (PN) now
known in the Milky Way is about 3000, approximately twice 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. The
two most important are the AAO/UKST SuperCOSMOS H-alpha survey - SHS and the
Isaac Newton photometric H-alpha survey - IPHAS, which are responsible for most
of the new discoveries. A serious problem with previous PN catalogues is that
several different kinds of astrophysical objects are able to mimic PN in some
of their observed properties leading to significant contamination. These
objects include H II regions and Stromgren zones around young O/B stars,
reflection nebulae, Wolf-Rayet ejecta, supernova remnants, Herbig-Haro objects,
young stellar objects, B[e] stars, symbiotic stars and outflows, late-type
stars, cataclysmic variables, low redshift emission-line galaxies, and even
image/detector flaws. PN catalogues such as the Macquarie/AAO/Strasbourg
H-alpha Planetary Nebula catalogue (MASH) have been carefully vetted to remove
these mimics using the wealth of new wide-field multi-wavelength data and our
100% follow-up spectroscopy to produce a compilation of new PN discoveries of
high purity. During this process significant numbers of PN mimics have been
identified. The aim of this project is to compile these MASH rejects into a
catalogue of Miscellaneous Emission Nebulae (MEN) and to highlight the most
unusual and interesting examples. A new global analysis of these MEN objects is
underway before publishing the MEN catalogue online categorizing objects by
type together with their spectra and multi-wavelength images.Comment: 2 pages, IAU 283: An Eye To The Future proceeding
New light on Galactic post-asymptotic giant branch stars. I. First distance catalogue
We have commenced a detailed analysis of the known sample of Galactic
post-asymptotic giant branch (PAGB) objects compiled in the Toru\'n catalogue
of Szczerba et al., and present, for the first time, homogeneously derived
distance determinations for the 209 likely and 87 possible catalogued PAGB
stars from that compilation. Knowing distances are essential in determining
meaningful physical characteristics for these sources and this has been
difficult to determine for most objects previously. The distances were
determined by modelling their spectral energy distributions (SED) with multiple
black-body curves, and integrating under the overall fit to determine the total
distance-dependent flux. This method works because the luminosity of these
central stars is very nearly constant from the tip of the AGB phase to the
beginning of the white-dwarf cooling track. This then enables us to use a
standard-candle luminosity to estimate the SED distances. For Galactic thin
disk PAGB objects, we use three luminosity bins based on typical observational
characteristics, ranging between 3500 and 12000 L_sun. We further adopt a
default luminosity of 1700 L_sun for all halo PAGB objects. We have also
applied the above technique to a further sample of 69 related nebulae not in
the current edition of the Toru\'n catalogue. In a follow-up paper we will
estimate distances to the subset of RV Tauri variables using empirical
period-luminosity relations, and to the R\,CrB stars, allowing a population
comparison of these objects with the other subclasses of PAGB stars for the
first time.Comment: 24 pages, 8 tables, 4 figures. Submitted to MNRAS. Appendix B
containing full list of SED figures excluded in this versio
New Galactic Planetary Nebulae selected by radio and multi-wavelength characteristics
We have used the Cornish radio catalogue combined with the use of
multi-wavelength data to identify 62 new Planetary Nebula (PN) candidates close
to the Galactic mid-plane. Of this sample 11 have weak optical counterparts in
deep narrow band H imaging that allows their spectroscopic follow-up.
We have observed eight of these candidates spectroscopically, leading to the
confirmation of 7 out of 8 as PNe. All but one of our sample of newly detected
PNe appear to be of Type I chemistry with very large [NII]/H ratios.
This indicates that our selection method heavily favours detection of this kind
of PN. Cornish is a low Galactic latitude survey where young objects and Type I
PNe (thought to derive from higher mass progenitors) are more plentiful, but
where optical extinction is large. The very high success rate in correctly
identifying PNe in this zone proves the efficacy of our radio and multiple
multi-wavelength diagnostic tools used to successfully predict and then confirm
their PN nature, at least in the cases where an optical counterpart is found
and has been observed. The study reinforces the effective use of a combination
of multi-wavelength and optical data in the identification of new Galactic PNe
and especially those of Type I chemistries whose dusty environments often
prevents their easy detection in the optical regime alone.Comment: 13 pages, 5 figure
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
Kathryns Wheel: A spectacular galaxy collision discovered in the Galactic neighbourhood
We report the discovery of the closest collisional ring galaxy to the Milky
Way. Such rare systems occur due to "bulls-eye" encounters between two
reasonably matched galaxies. The recessional velocity of about 840 km/s is low
enough that it was detected in the AAO/UKST Survey for Galactic H
emission. The distance is only 10.0 Mpc and the main galaxy shows a full ring
of star forming knots, 6.1 kpc in diameter surrounding a quiescent disk. The
smaller assumed "bullet" galaxy also shows vigorous star formation. The
spectacular nature of the object had been overlooked because of its location in
the Galactic plane and proximity to a bright star and even though it is the
60 brightest galaxy in the HI Parkes All Sky Survey (HIPASS) HI
survey.
The overall system has a physical size of 15 kpc, a total mass of
M (stars + HI), a metallicity of
[O/H], and a star formation rate of 0.2-0.5 M\,yr,
making it a Magellanic-type system. Collisional ring galaxies therefore extend
to much lower galaxy masses than commonly assumed. We derive a space density
for such systems of , an order of magnitude
higher than previously estimated. This suggests Kathryn's Wheel is the nearest
such system. We present discovery images, CTIO 4-m telescope narrow-band
follow-up images and spectroscopy for selected emission components. Given its
proximity and modest extinction along the line of sight, this spectacular
system provides an ideal target for future high spatial resolution studies of
such systems and for direct detection of its stellar populations.Comment: 18 pages, 12 figures, accepted for publication in MNRA
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
Discovery of planetary nebulae using predictive mid-infrared diagnostics
We demonstrate a newly developed mid-infrared planetary nebula (PN) selection
technique. It is designed to enable efficient searches for obscured, previously
unknown, PN candidates present in the photometric source catalogues of Galactic
plane MIR sky surveys. Such selection is now possible via new, sensitive,
high-to-medium resolution, MIR satellite surveys such as those from the Spitzer
Space Telescope and the all-sky Wide-Field Infrared Survey Explorer (WISE)
satellite missions. MIR selection is based on how different colour-colour
planes isolate zones (sometimes overlapping) that are predominately occupied by
different astrophysical object types. These techniques depend on the
reliability of the available MIR source photometry. In this pilot study we
concentrate on MIR point source detections and show that it is dangerous to
take the MIR GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire)
photometry from Spitzer for each candidate at face value without examining the
actual MIR image data. About half of our selected sources are spurious
detections due to the applied source detection algorithms being affected by
complex MIR backgrounds and the de-blending of diffraction spikes around bright
MIR point sources into point sources themselves. Nevertheless, once this
additional visual diagnostic checking is performed, valuable MIR selected PN
candidates are uncovered. Four turned out to have faint, compact, optical
counterparts in our H-alpha survey data missed in previous optical searches. We
confirm all of these as true PNe via our follow-up optical spectroscopy. This
lends weight to the veracity of our MIR technique. It demonstrates sufficient
robustness that high-confidence samples of new Galactic PN candidates can be
extracted from these MIR surveys without confirmatory optical spectroscopy and
imaging. This is problematic or impossible when the extinction is large.Comment: 14 pages, 7 figures, 7 tables; accepted for publication in MNRA