6,557 research outputs found
Local Interstellar Medium Kinematics towards the Southern Coalsack and Chamaeleon-Musca dark clouds
The results of a spectroscopic programme aiming to investigate the kinematics
of the local interstellar medium components towards the Southern Coalsack and
Chamaeleon-Musca dark clouds are presented. The analysis is based upon
high-resolution (R ~ 60,000) spectra of the insterstellar NaI D absorption
lines towards 63 B-type stars (d < 500 pc) selected to cover these clouds and
the connecting area defined by the Galactic coordinates: 308 > l > 294 and -22
< b < 5. The radial velocities, column densities, velocity dispersions, colour
excess and photometric distances to the stars are used to understand the
kinematics and distribution of the interstellar cloud components. The analysis
indicates that the interstellar gas is distributed in two extended sheet-like
structures permeating the whole area, one at d < 60 pc and another around
120-150 pc from the Sun. The dust and gas feature around 120-150 pc seem to be
part of an extended large scale feature of similar kinematic properties,
supposedly identified with the interaction zone of the Local and Loop I
bubbles.Comment: 19 pages, accepted for MNRA
High-velocity collimated outflows in planetary nebulae: NGC 6337, He 2-186, and K 4-47
We have obtained narrow-band images and high-resolution spectra of the
planetary nebulae NGC 6337, He 2-186, and K 4-47, with the aim of investigating
the relation between their main morphological components and several
low-ionization features present in these nebulae. The data suggest that NGC
6337 is a bipolar PN seen almost pole on, with polar velocities higher than 200
km/s. The bright inner ring of the nebula is interpreted to be the "equatorial"
density enhancement. It contains a number of low-ionization knots and outward
tails that we ascribe to dynamical instabilities leading to fragmentation of
the ring or transient density enhancements due to the interaction of the
ionization front with previous density fluctuations in the ISM. The lobes show
a pronounced point-symmetric morphology and two peculiar low-ionization
filaments whose nature remains unclear. The most notable characteristic of He
2-186 is the presence of two high-velocity (higher than 135 km/s) knots from
which an S-shaped lane of emission departs toward the central star. K 4-47 is
composed of a compact core and two high-velocity, low-ionization blobs. We
interpret the substantial broadening of line emission from the blobs as a
signature of bow shocks, and using the modeling of Hartigan, Raymond, & Hartman
(1987), we derive a shock velocity of 150 km/s and a mild inclination of the
outflow on the plane of the sky. We discuss possible scenarios for the
formation of these nebulae and their low-ionization features. In particular,
the morphology of K 4-47 hardly fits into any of the usually adopted mass-loss
geometries for single AGB stars. Finally, we discuss the possibility that
point-symmetric morphologies in the lobes of NGC 6337 and the knots of He 2-186
are the result of precessing outflows from the central stars.Comment: 16 pages plus 7 figures, ApJ accepted. Also available at
http://www.iac.es/publicaciones/preprints.htm
Cystic fibrosis transmembrane conductance regulator (CFTR): closed and open state channel models.
The cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP binding cassette (ABC) transporter superfamily. CFTR controls the flow of anions through the apical membrane of epithelia. Dysfunctional CFTR causes the common lethal genetic disease cystic fibrosis. Transitions between open and closed states of CFTR are regulated by ATP binding and hydrolysis on the cystosolic nucleotide binding domains (NBDs), which are coupled with the transmembrane domains (TMDs) forming the pathway for anion permeation. Lack of structural data hampers a global understanding of CFTR, and thus the development of rational approaches directly targeting defective CFTR. In this work, we explored possible conformational states of the CFTR gating cycle by means of homology modeling. As templates, we used structures of homologous ABC transporters, namely TM287- 288, ABC-B10, McjD and Sav1866. In the light of published experimental results, structural analysis of the transmembrane cavity suggests that the TM287-288-based CFTR model could correspond to a commonly occupied closed state, while the McjD-based model could represent an open state. The models capture the important role played by Phe337 as a filter/gating residue and provide structural information on the conformational transition from closed to open channel
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
Knots in the outer shells of the planetary nebulae IC 2553 and NGC 5882
We present images and high-resolution spectra of the planetary nebulae IC
2553 and NGC 5882. Spatio-kinematic modeling of the nebulae shows that they are
composed of a markedly elongated inner shell, and of a less aspherical outer
shell expanding at a considerably higher velocity than the inner one. Embedded
in the outer shells of both nebulae are found several low-ionization knots. In
IC 2553, the knots show a point-symmetric distribution with respect to the
central star: one possible explanation for their formation is that they are the
survivors of pre-existing point-symmetric condensations in the AGB wind, a fact
which would imply a quite peculiar mass-loss geometry from the giant
progenitor. In the case of NGC 5882, the lack of symmetry in the distribution
of the observed low-ionization structures makes it possible that they are the
result of in situ instabilities.Comment: 20 pages including 1 table and 6 figures. ApJ accepted. Also
available at http://andromeda.roque.ing.iac.es/~sanchez/ingpub/index2000.htm
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
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