7,180 research outputs found
A Massive Bipolar Outflow and a Dusty Torus with Large Grains in the Pre-Planetary Nebula IRAS 22036+5306
We report high angular-resolution (~1") CO J=3--2 interferometric mapping,
using the Submillimeter Array (SMA), of IRAS22036+5306 (I22036), a bipolar
pre-planetary nebula (PPN) with knotty jets discovered in our HST SNAPshot
survey of young PPNs. In addition, we have obtained supporting lower-resolution
(~10") CO and 13CO J=1-0 observations with the Owens Valley Radio Observatory
(OVRO) interferometer, as well as optical long-slit echelle spectra at the
Palomar Observatory. The CO J=3-2 observations show the presence of a very fast
(~220 km/s), highly collimated, massive (0.03 Msun) bipolar outflow with a very
large scalar momentum (about 10^{39} g cm s^{-1}), and the characteristic
spatio-kinematic structure of bow-shocks at the tips of this outflow. The
Halpha line shows an absorption feature blue-shifted from the systemic velocity
by ~100 km/s, which most likely arises in neutral interface material between
the fast outflow and the dense walls of the bipolar lobes at low latitudes. The
fast outflow in I22036, as in most PPNs, cannot be driven by radiation
pressure. We find an unresolved source of submillimeter (and millimeter-wave)
continuum emission in I22036, implying a very substantial mass (0.02-0.04 Msun)
of large (radius >~1 mm), cold (< ~50 K) dust grains associated with I22036's
toroidal waist. We also find that the 13C/12C ratio in I22036 is very high
(0.16), close to the maximum value achieved in equilibrium CNO-nucleosynthesis
(0.33). The combination of the high circumstellar mass (i.e., in the extended
dust shell and the torus) and the high 13C/12C ratio in I22036 provides strong
support for this object having evolved from a massive (>~4 Msun) progenitor in
which hot-bottom-burning has occurred.Comment: to be published in the Astrophysical Journal, 2006, Dec 20, vol 653
23 Pages Text + 8 figures (4 Color
Further ALMA observations and detailed modeling of the Red Rectangle
We present new high-quality ALMA observations of the Red Rectangle (a well
known post-AGB object) in C17O J=6-5 and H13CN J=4-3 line emission and results
from a new reduction of already published 13CO J=3-2 data. A detailed model
fitting of all the molecular line data, including previous maps and single-dish
spectra, was performed using a sophisticated code. These observations and the
corresponding modeling allowed us to deepen the analysis of the nebular
properties. We also stress the uncertainties in the model fitting.
We confirm the presence of a rotating equatorial disk and an outflow, which
is mainly formed of gas leaving the disk. The mass of the disk is ~ 0.01 Mo,
and that of the CO-rich outflow is ~ 10 times smaller. High temperatures of ~
100 K are derived for most components. From comparison of the mass values, we
roughly estimate the lifetime of the rotating disk, which is found to be of
about 10000 yr. Taking data of a few other post-AGB composite nebulae into
account, we find that the lifetimes of disks around post-AGB stars typically
range between 5000 and more than 20000 yr. The angular momentum of the disk is
found to be high, ~ 9 Mo AU km/s, which is comparable to that of the stellar
system at present. Our observations of H13CN show a particularly wide velocity
dispersion and indicate that this molecule is only abundant in the inner
Keplerian disk, at ~ 60 AU from the stellar system. We suggest that HCN is
formed in a dense photodissociation region (PDR) due to the UV excess known to
be produced by the stellar system, following chemical mechanisms that are well
established for interstellar medium PDRs and disks orbiting young stars. We
further suggest that this UV excess could lead to the efficient formation and
excitation of PAHs and other C-bearing macromolecules, whose emission is very
intense in the optical counterpart.Comment: Astronomy & Astrohysics, in press; 17 pages, 18 figures, 1 tabl
Analysis of usage patterns in shared stocks: the red grouper fishery from the continental shelf of Yucatán
Effect of influenza-induced fever on human bioimpedance values
BACKGROUND AND AIMS:
Bioelectrical impedance analysis (BIA) is a widely used technique to assess body composition and nutritional status. While bioelectrical values are affected by diverse variables, there has been little research on validation of BIA in acute illness, especially to understand prognostic significance. Here we report the use of BIA in acute febrile states induced by influenza.
METHODS:
Bioimpedance studies were conducted during an H1N1 influenza A outbreak in Venezuelan Amerindian villages from the Amazonas. Measurements were performed on 52 subjects between 1 and 40 years of age, and 7 children were re-examined after starting Oseltamivir treatment. Bioelectrical Impedance Vector Analysis (BIVA) and permutation tests were applied.
RESULTS:
For the entire sample, febrile individuals showed a tendency toward greater reactance (p=0.058) and phase angle (p=0.037) than afebrile individuals, while resistance and impedance were similar in the two groups. Individuals with repeated measurements showed significant differences in bioimpedance values associated with fever, including increased reactance (p<0.001) and phase angle (p=0.007), and decreased resistance (p=0.007) and impedance (p<0.001).
CONCLUSIONS:
There are bioelectrical variations induced by influenza that can be related to dehydration, with lower extracellular to intracellular water ratio in febrile individuals, or a direct thermal effect. Caution is recommended when interpreting bioimpedance results in febrile states
Adaptive Optics Imaging of IRAS 18276-1431: a bipolar pre-planetary nebula with circumstellar "searchlight beams" and "arcs"
We present high-angular resolution images of the post-AGB nebula
IRAS18276-1431 (also known as OH17.7-2.0) obtained with the Keck II Adaptive
Optics (AO) system in its Natural Guide Star (NGS) mode in the Kp, Lp, and Ms
near-infrared bands. We also present supporting optical F606W and F814W HST
images as well as interferometric observations of the 12CO(J=1-0), 13CO(J=1-0),
and 2.6mm continuum emission with OVRO. The envelope of IRAS18276-1431 displays
a clear bipolar morphology in our optical and NIR images with two lobes
separated by a dark waist and surrounded by a faint 4.5"x3.4" halo. Our Kp-band
image reveals two pairs of radial ``searchlight beams'' emerging from the
nebula center and several intersecting, arc-like features. From our CO data we
derive a mass of M>0.38[D/3kpc]^2 Msun and an expansion velocity v_exp=17km/s
for the molecular envelope. The density in the halo follows a radial power-law
proportional to r^-3, which is consistent with a mass-loss rate increasing with
time. Analysis of the NIR colors indicates the presence of a compact central
source of ~300-500K dust illuminating the nebula in addition to the central
star. Modeling of the thermal IR suggests a two-shell structure in the dust
envelope: 1) an outer shell with inner and outer radius R_in~1.6E16cm and
R_out>~1.25E17cm, dust temperature T_d~105-50K, and a mean mass-loss rate of
Mdot~1E-3Msun/yr; and 2) an inner shell with R_in~6.3E14cm, T_dust~500-105K,
and Mdot~3E-5Msun/yr. An additional population of big dust grains (radius
a>~0.4mm) with T_dust=150-20K and mass M_dust=(0.16-1.6)E-3 [D/3kpc]^2 Msun can
account for the observed sub-mm and mm flux excess. The mass of the envelope
enclosed within R_out=1.25E17cm derived from SED modeling is ~1[D/3kpc]^2 Msun.Comment: 46 pages, 14 figures, 3 tables, accepted for publication in ApJ.
Figures 12 & 13 in low resolution. Full resolution versions are available
upon request to the first autho
ALMA observations of the Red Rectangle, a preliminary analysis
We aim to study equatorial disks in rotation and axial outflows in post-AGB
objects, as to disclose the formation and shaping mechanisms in planetary
nebulae. So far, both disks and outflows had not been observed simultaneously.
We have obtained high-quality ALMA observations of 12CO and 13CO J=3-2 and
12CO J=6-5 line emission in the Red Rectangle, the only post-AGB/protoplanetary
object in which a disk in rotation has been mapped up to date.
These observations provide an unprecedented description of the complex
structure of this source. Together with an equatorial disk in rotation, we find
a low-velocity outflow that occupies more or less the region placed between the
disk and the optical X-shaped nebula. From our observations and preliminary
modeling of the data, we confirm the previously known properties of the disk
and obtain a first description of the structure, dynamics, and physical
conditions of the outflow.Comment: 5 pages, 5 figure
High-resolution observations of IRAS 08544-4431. Detection of a disk orbiting a post-AGB star and of a slow disk wind
We are studying a class of binary post-AGB stars that seem to be
systematically surrounded by equatorial disks and slow outflows. Although the
rotating dynamics had only been well identified in three cases, the study of
such structures is thought to be fundamental to the understanding of the
formation of nebulae around evolved stars. We present ALMA maps of 12CO and
13CO J=3-2 lines in one of these sources, IRAS08544-4431. We analyzed the data
by means of nebula models, which account for the expectedly composite source
and can reproduce the data. From our modeling, we estimated the main nebula
parameters, including the structure and dynamics and the density and
temperature distributions. We discuss the uncertainties of the derived values
and, in particular, their dependence on the distance.
Our observations reveal the presence of an equatorial disk in rotation; a
low-velocity outflow is also found, probably formed of gas expelled from the
disk. The main characteristics of our observations and modeling of
IRAS08544-4431 are similar to those of better studied objects, confirming our
interpretation. The disk rotation indicates a total central mass of about 1.8
Mo, for a distance of 1100 pc. The disk is found to be relatively extended and
has a typical diameter of ~ 4 10^16 cm. The total nebular mass is ~ 2 10^-2 Mo,
of which ~ 90% corresponds to the disk. Assuming that the outflow is due to
mass loss from the disk, we derive a disk lifetime of ~ 10000 yr. The disk
angular momentum is found to be comparable to that of the binary system at
present. Assuming that the disk angular momentum was transferred from the
binary system, as expected, the high values of the disk angular momentum in
this and other similar disks suggest that the size of the stellar orbits has
significantly decreased as a consequence of disk formation.Comment: 10 pages, 7 figures, accepted by A&
The constant-velocity highly collimated outflows of the planetary nebula He 2-90
We present high-dispersion echelle spectroscopic observations and a
narrow-band [N II] image of the remarkable jet-like features of He 2-90. They
are detected in the echelle spectra in the H-alpha and [N II] lines but not in
other nebular lines. The [N II]/H-alpha ratio is uniformly high, ~1. The
observed kinematics reveals bipolar collimated outflows in the jet-like
features and shows that the southeast (northwest) component expands towards
(away from) the observer at a remarkably constant line-of-sight velocity,
26.0+-0.5 km/s. The observed expansion velocity and the opening angle of the
jet-like features are used to estimate an inclination angle of ~5 degrees with
respect to the sky plane and a space expansion velocity of ~290 km/s. The
spectrum of the bright central nebula reveals a profusion of Fe lines and
extended wings of the H-alpha line, similar to those seen in symbiotic stars
and some young planetary nebulae that are presumed to host a mass-exchanging
binary system. If this is the case for He 2-90, the constant velocity and
direction of the jets require a very stable dynamic system against precession
and warping.Comment: 8 pages (emulate ApJ), 5 figure, 1 tabl
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