5,638 research outputs found
3D Photoionisation Modelling of NGC 6302
We present a three-dimensional photoionisation and dust radiative transfer
model of NGC 6302, an extreme, high-excitation planetary nebula. We use the 3D
photoionisation code Mocassin} to model the emission from the gas and dust. We
have produced a good fit to the optical emission-line spectrum, from which we
derived a density distribution for the nebula. A fit to the infrared coronal
lines places strong constraints on the properties of the unseen ionising
source. We find the best fit comes from using a 220,000 K hydrogen-deficient
central star model atmosphere, indicating that the central star of this PN may
have undergone a late thermal pulse.
We have also fitted the overall shape of the ISO spectrum of NGC 6302 using a
dust model with a shallow power-law size distribution and grains up to 1.0
micron in size. To obtain a good fit to the infrared SED the dust must be
sufficiently recessed within the circumstellar disk to prevent large amounts of
hot dust at short wavelengths, a region where the ISO spectrum is particularly
lacking. These and other discoveries are helping to unveil many properties of
this extreme object and trace it's evolutionary history.Comment: 8 pages, 4 figures; for the proceedings of "Asymmetric Planetary
Nebuale IV," R. L. M. Corradi, A. Manchado, N. Soker ed
Isolated tau leptons in events with large missing transverse momentum at HERA
A search for events containing isolated tau leptons and large missing
transverse momentum, not originating from the tau decay, has been performed
with the ZEUS detector at the electron-proton collider HERA, using 130 pb^-1 of
integrated luminosity. A search was made for isolated tracks coming from
hadronic tau decays. Observables based on the internal jet structure were
exploited to discriminate between tau decays and quark- or gluon-induced jets.
Three tau candidates were found, while 0.40 +0.12 -0.13 were expected from
Standard Model processes, such as charged current deep inelastic scattering and
single W-boson production. To search for heavy-particle decays, a more
restrictive selection was applied to isolate tau leptons produced together with
a hadronic final state with high transverse momentum. Two candidate events
survive, while 0.20 +-0.05 events are expected from Standard Model processes.Comment: 28 pages, 4 figures, 3 tables, accepted by Phys. Lett. B. Updated
with minor changes to the text requested by the journal refere
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
Discovery of a planetary nebula surrounding the symbiotic star DT Serpentis
We report the discovery of a planetary nebula centered on the poorly studied
symbiotic binary star DT Ser. In a few other symbiotic stars spatially resolved
nebulae have been discovered: however, only one of them might be a genuine
planetary nebula, while the others are likely to originate in complex mass
ejections episodes from the interacting binary central stars, possibly related
to nova-like outbursts. The rim of the planetary nebula around DT Ser is
severely distorted toward a brighter star, 5 arcsec away. In infrared WISE
data, this star shows the presence of a detached cold dust shell such as those
observed in post-AGB stars. The apparent association of the symbiotic star and
its planetary nebula with the nearby possible post-AGB object is discussed. We
also discuss the sparse and conflicting literature data that could support an
observed variability of the surface brightness of the planetary nebula. The
puzzling and intriguing characteristics displayed by DT Ser are surely worth
further and more detailed investigations.Comment: in press in A&
K 3-22: a D-type symbiotic star
A goal of the IPHAS survey is to determine the frequency and nature of
emission-line sources in the Galactic plane. According to our selection
criteria, K 3-22 is a candidate symbiotic star, but it was previously
classified as a planetary nebula. To determine its nature, we acquired a
low-resolution optical spectrum of K 3-22. Our analysis of our spectroscopy
demonstrates that K 3-22 is indeed a D-type symbiotic star, because of its high
excitation nebular spectrum and the simultaneous presence of Raman-scattered O
VI emission at 6825 and 7082 angstrom, which is detected primarily in symbiotic
stars.Comment: 3 pages, 1 figure. Accepted for publication on Astronomy and
Astrophysic
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