5,246 research outputs found
3-D Photoionization Structure and Distances of Planetary Nebulae III. NGC 6781
Continuing our series of papers on the three-dimensional (3-D) structures of
and accurate distances to Planetary Nebulae (PNe), we present our study of the
planetary nebula NGC6781. For this object we construct a 3-D photoionization
model and, using the constraints provided by observational data from the
literature we determine the detailed 3-D structure of the nebula, the physical
parameters of the ionizing source and the first precise distance. The procedure
consists in simultaneously fitting all the observed emission line morphologies,
integrated intensities and the 2-D density map from the [SII] line ratios to
the parameters generated by the model, and in an iterative way obtain the best
fit for the central star parameters and the distance to NGC6781, obtaining
values of 950+-143pc and 385 Lsun for the distance and luminosity of the
central star respectively. Using theoretical evolutionary tracks of
intermediate and low mass stars, we derive the mass of the central star of
NGC6781 and its progenitor to be 0.60+-0.03 Msun and 1.5+-0.5 Msun
respectively.Comment: 16 pp, 6 figues, 2 tables, submitted to the Ap
The large-scale ionised outflow of CH Cygni
HST and ground-based [OII} and [NII] images obtained from 1996 to 1999 reveal
the existence of a ionised optical nebula around the symbiotic binary CH Cyg
extending out to 5000 A.U. from the central stars. The observed velocity range
of the nebula, derived from long-slit echelle spectra, is of 130 km/s. In spite
of its complex appearence, the velocity data show that the basic morphology of
the inner regions of the optical nebula is that of a bipolar (or conical)
outflow extending nearly along the plane of the sky out to some 2000 A.U. from
the centre. Even if the extension of this bipolar outflow and its position
angle are consistent with those of the radio jet produced in 1984 (extrapolated
to the time of our optical imagery), no obvious counterpart is visible of the
original, dense radio bullets ejected by the system. We speculate that the
optical bipolar outflow might be the remannt of the interaction of the bullets
with a relatively dense circumstellar medium.Comment: 8 text pages + 3 figures (jpeg). ApJ in press. For a full PostScript
version with figures inline see
ftp://ftp.ll.iac.es/pub/research/preprints/PP252001.ps.g
Teaching about Madrid: A Collaborative Agents-Based Distributed Learning Course
Interactive art courses require a huge amount of computational resources to be running on real time. These computational resources are even bigger if the course has been designed as a Virtual Environment with which students can interact. In this paper, we present an initiative that has been develop in a close collaboration between two Spanish Universities: Universidad Politécnica de Madrid and Universidad Rey Juan Carlos with the aim of join two previous research project: a Collaborative Awareness Model for Task-Balancing-Delivery (CAMT) in clusters and the “Teaching about Madrid” course, which provides a cultural interactive background of the capital of Spain
Why a Single-Star Model Cannot Explain the Bipolar Nebula of Eta Carinae
I examine the angular momentum evolution during the 1837-1856 Great Eruption
of the massive star Eta Carinae. I find that the new estimate of the mass blown
during that eruption implies that the envelope of Eta Car substantially
spun-down during the 20 years eruption. Single-star models, most of which
require the envelope to rotate close to the break-up velocity, cannot account
for the bipolar nebula (the Homunculus) formed from matter expelled in that
eruption. The kinetic energy and momentum of the Homunculus further constrains
single-star models. I discuss how Eta Car can fit into a unified model for the
formation of bipolar lobes where two oppositely ejected jets inflate two lobes
(or bubbles). These jets are blown by an accretion disk, which requires stellar
companions in the case of bipolar nebulae around stellar objects.Comment: ApJ, in press. New references and segments were adde
A three-dimensional view of the remnant of Nova Persei 1901 (GK Per)
We present a kinematical study of the optical ejecta of GK Per. It is based
on proper motions measurements of 282 knots from ~20 images spanning 25 years.
Doppler-shifts are also computed for 217 knots. The combination of proper
motions and radial velocities allows a unique 3-D view of the ejecta to be
obtained. The main results are: (1) the outflow is a thick shell in which knots
expand with a significant range of velocities, mostly between 600 and 1000
km/s; (2) kinematical ages indicate that knots have suffered only a modest
deceleration since their ejection a century ago; (3) no evidence for anisotropy
in the expansion rate is found; (4) velocity vectors are generally aligned
along the radial direction but a symmetric pattern of non-radial velocities is
also observed at specific directions; (5) the total Halpha+[NII] flux has been
linearly decreasing at a rate of 2.6 % per year in the last decade. The Eastern
nebular side is fading at a slower rate than the Western one. Some of the knots
displayed a rapid change of brightness during the 2004-2011 period. Over a
longer timescale, a progressive circularization and homogenization of the
nebula is taking place; (6) a kinematic distance of 400+-30 pc is determined.
These results raise some problems to the previous interpretations of the
evolution of GK Per. In particular, the idea of a strong interaction of the
outflow with the surrounding medium in the Southwest quadrant is not supported
by our data.Comment: Accepted for publication in The Astrophysical Journal (19 pages, 17
figures). Higher resolution version of this article (2.5 MB) is available at
http://www.aai.ee/~sinope/ApJ89291_liimets.pd
New insights into the outflows from R Aquarii
R Aquarii is a symbiotic binary surrounded by a large and complex nebula with
a prominent curved jet. It is one of the closest known symbiotic systems, and
therefore offers a unique opportunity to study the central regions of these
systems and the formation and evolution of astrophysical jets. We studied the
evolution of the central jet and outer nebula of R Aqr taking advantage of a
long term monitoring campaign of optical imaging, as well as of high-resolution
integral field spectroscopy. Narrow-band images acquired over a period of more
than 21 years are compared in order to study the expansion and evolution of all
components of the R Aqr nebula. The magnification method is used to derive the
kinematic ages of the features that appear to expand radially. Integral field
spectroscopy of the OIII 5007A emission is used to study the velocity structure
of the central regions of the jet. New extended features, further out than the
previously known hourglass nebula, are detected. The kinematic distance to R
Aqr is calculated to be 178 pc using the expansion of the large hourglass
nebula. This nebula of R Aqr is found to be roughly 650 years old, while the
inner regions have ages ranging from 125 to 290 years. The outer nebula is
found to be well described by a ballistic expansion, while for most components
of the jet strong deviations from such behaviour are found. We find that the
Northern jet is mostly red-shifted while its Southern part is blue-shifted,
apparently at odds with findings from previous studies but almost certainly a
consequence of the complex nature of the jet and variations in ionisation and
illumination between observations.Comment: 13 pages, 8 figures, accepted for publication in A&
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