11,379 research outputs found
Fast, low-ionization emission regions of the planetary nebula M2-42
Spatially resolved observations of the planetary nebula M2-42 (PN
G008.2-04.8) obtained with the Wide Field Spectrograph on the Australian
National University 2.3 m telescope have revealed the remarkable features of
bipolar collimated jets emerging from its main structure. Velocity-resolved
channel maps derived from the [N II] 6584 emission line disentangle
different morphological components of the nebula. This information is used to
develop a three-dimensional morpho-kinematic model, which consists of an
equatorial dense torus and a pair of asymmetric bipolar outflows. The expansion
velocity of about 20 km s is measured from the spectrum integrated over
the main shell. However, the deprojected velocities of the jets are found to be
in the range of 80-160 km s with respect to the nebular center. It is
found that the mean density of the collimated outflows, 595 125
cm, is five times lower than that of the main shell, 3150 cm,
whereas their singly ionized nitrogen and sulfur abundances are about three
times higher than those determined from the dense shell. The results indicate
that the features of the collimated jets are typical of fast, low-ionization
emission regions.Comment: 6 pages, 4 figures, 4 tables, accepted for publication in The
Astronomical Journa
Newly confirmed and high quality candidate Galactic SNRs uncovered from the AAO/UKST HAlpha survey
We present a catalogue of 18 new Galactic supernova remnants (SNRs) uncovered
in the optical regime as filamentary emissions and extended nebulosities on
images of the Anglo Australian Observatory/United Kingdom Schmidt Telescope
(AAO/UKST) HAlpha survey of the southern Galactic plane. Our follow-up spectral
observations confirmed classical optical SNR emission lines for these 18
structures via detection of very strong [SII] at 6717 and 6731A relative to
HAlpha ([SII]/HAlpha> 0.5). Morphologically, 10 of these remnants have
coherent, extended arc or shell structures, while the remaining objects are
more irregular in form but clearly filamentary in nature, typical of optically
detected SNRs.
In 11 cases there was a clear if not complete match between the optical and
radio structures with H filamentary structures registered inside and along the
presumed radio borders. Additionally, ROSAT X-ray sources were detected inside
the optical/radio borders of 11 of these new remnants and 3 may have an
associated pulsar.
The multi-wavelength imaging data and spectroscopy together present strong
evidence to confirm identification of 18 new, mostly senile Galactic SNRs. This
includes G288.7-6.3, G315.1+2.7 and G332.5-5.6, identified only as possible
remnants from preliminary radio observations. We also confirm existence of
radio quiet but optically active supernova remnants.Comment: In original form 21 pages, 29 figures Accepted for MNRA
A fast and portable Re-Implementation of Piskunov and Valenti's Optimal-Extraction Algorithm with improved Cosmic-Ray Removal and Optimal Sky Subtraction
We present a fast and portable re-implementation of Piskunov and Valenti's
optimal-extraction algorithm (Piskunov & Valenti, 2002} in C/C++ together with
full uncertainty propagation, improved cosmic-ray removal, and an optimal
background-subtraction algorithm. This re-implementation can be used with IRAF
and most existing data-reduction packages and leads to signal-to-noise ratios
close to the Poisson limit. The algorithm is very stable, operates on spectra
from a wide range of instruments (slit spectra and fibre feeds), and has been
extensively tested for VLT/UVES, ESO/CES, ESO/FEROS, NTT/EMMI, NOT/ALFOSC,
STELLA/SES, SSO/WiFeS, and finally, P60/SEDM-IFU data.Comment: 23 pages, 12 figure
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
The H\alpha\ surface brightness - radius relation: a robust statistical distance indicator for planetary nebulae
Measuring the distances to Galactic planetary nebulae (PNe) has been an
intractable problem for many decades. We have now established a robust optical
statistical distance indicator, the H surface brightness- radius or S-r
relation, which addresses this problem. We developed this relation from a
critically evaluated sample of primary calibrating PNe. The robust nature of
the method results from our revised calibrating distances with significantly
reduced systematic uncertainties, and the recent availability of high-quality
data, including updated nebular diameters and integrated H fluxes. The
S-r technique is simple in its application, requiring only an angular size, an
integrated H\alpha\ flux, and the reddening to the PN. From these quantities,
an intrinsic radius is calculated, which when combined with the angular size,
yields the distance directly. Furthermore, we have found that optically thick
PNe tend to populate the upper bound of the trend, while optically-thin PNe
fall along the lower boundary in the S-r plane. This enables sub-trends to be
developed which offer even better precision in the determination of distances,
as good as 18 per cent in the case of optically-thin, high-excitation PNe. This
is significantly better than any previous statistical indicator. We use this
technique to create a catalogue of statistical distances for over 1100 Galactic
PNe, the largest such compilation in the literature to date. Finally, in an
appendix, we investigate both a set of transitional PNe and a range of PN
mimics in the S-r plane, to demonstrate its use as a diagnostic tool.
Interestingly, stellar ejecta around massive stars plot on a tight locus in S-r
space with the potential to act as a separate distance indicator for these
objects.Comment: 49 pages, 17 tables, 8 figures. Published in MNRAS; supplementary
tables are included at end of this manuscrip
Are the Perseus-Pisces chain and the Pavo-Indus wall connected?
A significant empty region was found between the southern Pavo- Indus (PI)
wall and the northern Perseus-Pisces (PP) chain. This survey tests the reality
of this void which may simply reflect previous poor sampling of the galaxies in
this region. Redshifts for a magnitude selected sample of 379 galaxies were
obtained covering the four UKST/SERC survey fields with Bt <= 17.0. All
redshifts were obtained with the FLAIR multi-object spectroscopy system on the
1.2 m U.K. Schmidt Telescope at Siding Spring, Australia. Two highly
significant density enhancements were found in the galaxy distribution at 133
Mpc and 200 Mpc (Ho=75 km/s/Mpc). We claim that no connexion exists between PP
and PI. However, a southern extension of PP was detected and makes the total
length of this chain of more than 150 Mpc.Comment: 14 pages, postscript including tables and figures
New Structure In The Shapley Supercluster
We present new radial velocities for 189 galaxies in a 91 sq. deg region of
the Shapley supercluster measured with the FLAIR-II spectrograph on the UK
Schmidt Telescope. The data reveal two sheets of galaxies linking the major
concentrations of the supercluster. The supercluster is not flattened in
Declination as was suggested previously and it may be at least 30 percent
larger than previously thought with a correspondingly larger contribution to
the motion of the Local Group.Comment: LaTex: 2 pages, 1 figure, includes conf_iap.sty style file. To appear
in proceedings of The 14th IAP Colloquium: Wide Field Surveys in Cosmology,
held in Paris, 1998 May 26--30, eds. S.Colombi, Y.Mellie
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&
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