3,982 research outputs found
A FUSE View of the Stellar Winds of Planetary Nebula Central Stars
Since the IUE satellite produced a vast collection of high-resolution UV
spectra of central stars of planetary nebulae (CSPNe), there has not been any
further systematic study of the stellar winds of these stars. The high spectral
resolution, sensitivity and large number of archival observations in the FUSE
archive allow the study of the stellar winds of CSPNe in the far UV domain
where lines of species spanning a wide excitation range can be observed. We
present here a preliminary analysis of the P Cygni profiles of a sample of 60
CSPNe observed by FUSE. P Cygni profiles evidencing fast stellar winds with
velocities between 200 and 4,300 km/s have been found in 40 CSPNe. In many
cases, this is the first time that fast stellar winds have been reported for
these PNe. A detailed study of these far-UV spectra is on-going.Comment: 4 pages, 3 figures; accepted, to appear in Publications of the
Astronomical Society of Australi
Hidden IR structures in NGC 40: signpost of an ancient born-again event
We present the analysis of infrared (IR) observations of the planetary nebula
NGC 40 together with spectral analysis of its [WC]-type central star HD 826.
Spitzer IRS observations were used to produce spectral maps centred at
polycyclic aromatic hydrocarbons (PAH) bands and ionic transitions to compare
their spatial distribution. The ionic lines show a clumpy distribution of
material around the main cavity of NGC 40, with the emission from [Ar II] being
the most extended, whilst the PAHs show a rather smooth spatial distribution.
Analysis of ratio maps shows the presence of a toroidal structure mainly seen
in PAH emission, but also detected in a Herschel PACS 70 mic image. We argue
that the toroidal structure absorbs the UV flux from HD 826, preventing the
nebula to exhibit lines of high-excitation levels as suggested by previous
authors. We discuss the origin of this structure and the results from the
spectral analysis of HD 826 under the scenario of a late thermal pulse.Comment: 10 pages, 10 figures; Accepted to MNRA
WISE morphological study of Wolf-Rayet nebulae
We present a morphological study of nebulae around Wolf-Rayet (WR) stars
using archival narrow-band optical and Wide-field Infrared Survey Explorer
(WISE) infrared images. The comparison among WISE images in different bands and
optical images proves to be a very efficient procedure to identify the nebular
emission from WR nebulae, and to disentangle it from that of the ISM material
along the line of sight. In particular, WR nebulae are clearly detected in the
WISE W4 band at 22 m. Analysis of available mid-IR Spitzer spectra shows
that the emission in this band is dominated by thermal emission from dust
spatially coincident with the thin nebular shell or most likely with the
leading edge of the nebula. The WR nebulae in our sample present different
morphologies that we classified into well defined WR bubbles (bubble -type nebulae), clumpy and/or disrupted shells (clumpy/disrupted -type nebulae), and material mixed with the diffuse medium (mixed -type nebulae). The variety of morphologies presented by WR nebulae shows a
loose correlation with the central star spectral type, implying that the
nebular and stellar evolutions are not simple and may proceed according to
different sequences and time-lapses. We report the discovery of an obscured
shell around WR35 only detected in the infrared.Comment: 11 pages, 6 figures, plus 23 appendix figures; to appear in Astronomy
and Astrophysic
Kn 26, a New Quadrupolar Planetary Nebula
Once classified as an emission line source, the planetary nebula (PN) nature
of the source Kn 26 has been only recently recognized in digital sky surveys.
To investigate the spectral properties and spatio-kinematical structure of Kn
26, we have obtained high spatial-resolution optical and near-IR narrow-band
images, high-dispersion long-slit echelle spectra, and intermediate-resolution
spectroscopic observations. The new data reveal an hourglass morphology typical
of bipolar PNe. A detailed analysis of its morphology and kinematics discloses
the presence of a second pair of bipolar lobes, making Kn 26 a new member of
the subclass of quadrupolar PNe. The time-lap between the ejection of the two
pairs of bipolar lobes is much smaller than their dynamical ages, implying a
rapid change of the preferential direction of the central engine. The chemical
composition of Kn 26 is particularly unusual among PNe, with a low N/O ratio
(as of type II PNe) and a high helium abundance (as of type I PNe), although
not atypical among symbiotic stars. Such an anomalous chemical composition may
have resulted from the curtail of the time in the Asymptotic Giant Branch by
the evolution of the progenitor star through a common envelope phase.Comment: 9 pages, 5 figures, accepted for publication in A&
Rings and arcs around evolved stars. II. The Carbon Star AFGL 3068 and the Planetary Nebulae NGC 6543, NGC 7009 and NGC 7027
We present a detailed comparative study of the arcs and fragmented ring-like
features in the haloes of the planetary nebulae (PNe) NGC 6543, NGC 7009, and
NGC 7027 and the spiral pattern around the carbon star AFGL 3068 using
high-quality multi-epoch HST images. This comparison allows us to investigate
the connection and possible evolution between the regular patterns surrounding
AGB stars and the irregular concentric patterns around PNe. The radial proper
motion of these features, ~15 km/s, are found to be consistent with the AGB
wind and their linear sizes and inter-lapse times (500-1900 yr) also agree with
those found around AGB stars, suggesting a common origin. We find evidence
using radiative-hydrodynamic simulations that regular patterns produced at the
end of the AGB phase become highly distorted by their interactions with the
expanding PN and the anisotropic illumination and ionization patterns caused by
shadow instabilities. These processes will disrupt the regular (mostly spiral)
patterns around AGB stars, plausibly becoming the arcs and fragmented rings
observed in the haloes of PNe.Comment: 13 pages, 9 figures, accepted for publication in MNRA
The Unusual Distributions of Ionized Material and Molecular Hydrogen in NGC 6881: Signposts of Multiple Events of Bipolar Ejection in a Planetary Nebula
The planetary nebula NGC 6881 displays in the optical a quadrupolar
morphology consisting of two pairs of highly collimated bipolar lobes aligned
along different directions. An additional bipolar ejection is revealed by the
hydrogen molecular emission, but its wide hourglass morphology is very
different from that of the ionized material. To investigate in detail the
spatial distribution of molecular hydrogen and ionized material within NGC
6881, and to determine the prevalent excitation mechanism of the H2 emission,
we have obtained new near-IR Br-gamma and H2 and optical H-alpha and [N II]
images, as well as intermediate resolution JHK spectra. These observations
confirm the association of the H2 bipolar lobes to NGC 6881 and find that the
prevalent excitation mechanism is collisional. The detailed morphology and very
different collimation degree of the H2 and ionized bipolar lobes of NGC 6881
not only imply that multiple bipolar ejections have occurred in this nebula,
but also that the dominant shaping agent is different for each bipolar
ejection: a bipolar stellar wind most likely produced the H2 lobes, while
highly collimated outflows are carving out the ionized lobes into the thick
circumstellar envelope. The asymmetry between the southeast and northwest H2
bipolar lobes suggests the interaction of the nebula with an inhomogeneous
interstellar medium. We find evidence that places NGC 6881 in the H II region
Sh 2-109 along the Orion local spiral arm.Comment: 9 pages, 7 figures, 4 table
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