519 research outputs found
The Herschel Planetary Nebula Survey (HerPlaNS) I. Data Overview and Analysis Demonstration with NGC 6781
This is the first of a series of investigations into far-IR characteristics
of 11 planetary nebulae (PNs) under the Herschel Space Observatory Open Time 1
program, Herschel Planetary Nebula Survey (HerPlaNS). Using the HerPlaNS data
set, we look into the PN energetics and variations of the physical conditions
within the target nebulae. In the present work, we provide an overview of the
survey, data acquisition and processing, and resulting data products. We
perform (1) PACS/SPIRE broadband imaging to determine the spatial distribution
of the cold dust component in the target PNs and (2) PACS/SPIRE
spectral-energy-distribution (SED) and line spectroscopy to determine the
spatial distribution of the gas component in the target PNs. For the case of
NGC 6781, the broadband maps confirm the nearly pole-on barrel structure of the
amorphous carbon-richdust shell and the surrounding halo having temperatures of
26-40 K. The PACS/SPIRE multi-position spectra show spatial variations of
far-IR lines that reflect the physical stratification of the nebula. We
demonstrate that spatially-resolved far-IR line diagnostics yield the (T_e,
n_e) profiles, from which distributions of ionized, atomic, and molecular gases
can be determined. Direct comparison of the dust and gas column mass maps
constrained by the HerPlaNS data allows to construct an empirical gas-to-dust
mass ratio map, which shows a range of ratios with the median of 195+-110. The
present analysis yields estimates of the total mass of the shell to be 0.86
M_sun, consisting of 0.54 M_sun of ionized gas, 0.12 M_sun of atomic gas, 0.2
M_sun of molecular gas, and 4 x 10^-3 M_sun of dust grains. These estimates
also suggest that the central star of about 1.5 M_sun initial mass is
terminating its PN evolution onto the white dwarf cooling track.Comment: 27 pages, 16 figures, accepted for publication in A&
Arcsecond-resolution 12CO mapping of the yellow hypergiants IRC +10420 and AFGL 2343
IRC +10420 and AFGL 2343 are the unique, known yellow hypergiants (YHGs)
presenting a heavy circumstellar envelope (CSE). We aim to study the
morphology, exceptional kinematics, and excitation conditions of their CSEs,
and the implications for mass-loss processes. We have mapped the 12CO J=2-1 and
1-0 emission in these YHGs with the IRAM Plateau de Bure interferometer and the
30m telescope. We developed LVG models in order to analyze their circumstellar
characteristics. The maps show that the overall shape of both CSEs is
approximately spherical, although they also reveal several aspherical features.
The CSE around IRC +10420 shows a rounded extended halo surrounding a bright
inner region, with both components presenting aspherical characteristics. It
presents a brightness minimum at the center. The envelope around AFGL 2343 is a
detached shell, showing spherical symmetry and clumpiness at a level of about
15% of the maximum brightness. The envelopes expand isotropically at about 35
km/s, about two or three times faster than typical CSEs around AGB stars. High
temperatures (~ 200 K) are derived for the innermost regions in IRC +10420,
while denser and cooler (~ 30 K) gas is found in AFGL 2343. The mass-loss
processes in these YHGs have been found to be similar. The deduced mass-loss
rates (~ 10E-4 - 10E-3 Msun/yr) are much higher than those obtained in AGB
stars, and they present significant variations on time scales of ~ 1000 yr
Interactions of Heavy Hadrons using Regge Phenomenology and the Quark Gluon String Model
The search for stable heavy exotic hadrons is a promising way to observe new
physics processes at collider experiments. The discovery potential for such
particles can be enhanced or suppressed by their interactions with detector
material. This paper describes a model for the interactions in matter of stable
hadrons containing an exotic quark of charges or
using Regge phenomenology and the Quark Gluon String Model. The influence of
such interactions on searches at the LHC is also discussed
The ALMA detection of CO rotational line emission in AGB stars in the Large Magellanic Cloud
Context. Low- and intermediate-mass stars lose most of their stellar mass at the end of their lives on the asymptotic giant branch (AGB). Determining gas and dust mass-loss rates (MLRs) is important in quantifying the contribution of evolved stars to the enrichment of the interstellar medium.
Aims: This study attempts to spectrally resolve CO thermal line emission in a small sample of AGB stars in the Large Magellanic Cloud (LMC).
Methods: The Atacama Large Millimeter Array was used to observe two OH/IR stars and four carbon stars in the LMC in the CO J = 2-1 line.
Results: We present the first measurement of expansion velocities in extragalactic carbon stars. All four C stars are detected and wind expansion velocities and stellar velocities are directly measured. Mass-loss rates are derived from modelling the spectral energy distribution and Spitzer/IRS spectrum with the DUSTY code. The derived gas-to-dust ratios allow the predicted velocities to agree with the observed gas-to-dust ratios. The expansion velocities and MLRs are compared to a Galactic sample of well-studied relatively low MLRs stars supplemented with extreme C stars with properties that are more similar to the LMC targets. Gas MLRs derived from a simple formula are significantly smaller than those derived from dust modelling, indicating an order of magnitude underestimate of the estimated CO abundance, time-variable mass loss, or that the CO intensities in LMC stars are lower than predicted by the formula derived for Galactic objects. This could be related to a stronger interstellar radiation field in the LMC.
Conclusions: Although the LMC sample is small and the comparison to Galactic stars is non-trivial because of uncertainties in their distances (hence luminosities), it appears that for C stars the wind expansion velocities in the LMC are lower than in the solar neighbourhood, while the MLRs appear to be similar. This is in agreement with dynamical dust-driven wind models
Herschel/HIFI observations of O-rich AGB stars : molecular inventory
Spectra, taken with the heterodyne instrument, HIFI, aboard the Herschel
Space Observatory, of O-rich asymptotic giant branch (AGB) stars which form
part of the guaranteed time key program HIFISTARS are presented. The aim of
this program is to study the dynamical structure, mass-loss driving mechanism,
and chemistry of the outflows from AGB stars as a function of chemical
composition and initial mass.
We used the HIFI instrument to observe nine AGB stars, mainly in the H2O and
high rotational CO lines We investigate the correlation between line
luminosity, line ratio and mass-loss rate, line width and excitation energy.
A total of nine different molecules, along with some of their isotopologues
have been identified, covering a wide range of excitation temperature. Maser
emission is detected in both the ortho- and para-H2O molecules. The line
luminosities of ground state lines of ortho- and para-H2O, the high-J CO and
NH3 lines show a clear correlation with mass-loss rate. The line ratios of H2O
and NH3 relative to CO J=6-5 correlate with the mass-loss rate while ratios of
higher CO lines to the 6-5 is independent of it. In most cases, the expansion
velocity derived from the observed line width of highly excited transitions
formed relatively close to the stellar photosphere is lower than that of lower
excitation transitions, formed farther out, pointing to an accelerated outflow.
In some objects, the vibrationally excited H2O and SiO which probe the
acceleration zone suggests the wind reaches its terminal velocity already in
the innermost part of the envelope, i.e., the acceleration is rapid.
Interestingly, for R Dor we find indications of a deceleration of the outflow
in the region where the material has already escaped from the star.Comment: 6 Figures in the main paper + 12 further figures in the appendix (to
be printed in electronic form) Accepted for publication by A&
Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
Aims. We present near-infrared interferometry of the carbon-rich asymptotic giant branch (AGB) star R Sculptoris (R Scl)
Drinking behaviour and alcohol-related harm amongst older adults: analysis of existing UK datasets.
Older adults experience age-related physiological changes that increase sensitivity and decrease tolerance to alcohol and there are a number of age-related harms such as falls, social isolation and elder abuse, which are compounded by alcohol misuse. Despite this unique vulnerability and the fact that the number of older adults is increasing, the literature on drinking behaviour and alcohol-related harm in older adults is sparse. This article describes a secondary analysis of UK data to address this knowledge gap
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