1,696 research outputs found
Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
We report a detection of water in emission in the spectrum of the M2
supergiant atar mu Cep (M2Ia) observed by the Short Wavelength Spectrometer
(SWS) aboard Infrared Space Observatory (ISO) and now released as the ISO
Archives. The emission first appears in the 6 micron region (nu2 fundamental)
and then in the 40 micron region (pure rotation lines) despite the rather
strong dust emission. The intensity ratios of the emission features are far
from those of the optically thin gaseous emission. Instead, we could reproduce
the major observed emission features by an optically thick water sphere of the
inner radius about two stellar radii (1300Rsun), Tex = 1500K, and Ncol (H2O) =
3.0E+20/cm2. This model also accounts for the H2O absorption bands in the near
infrared (1.4, 1.9, and 2.7 micron) as well. The detection of water in emission
provides strong constraints on the nature of water in the early M supergiant
stars, and especially its origin in the outer atmosphere is confirmed against
other models such as the large convective cell model. We finally confirm that
the early M supergiant star is surrounded by a huge optically thick sphere of
the warm water vapor, which may be referred to as MOLsphere for simplicity.
Thus, the outer atmosphere of M supergiant stars should have a complicated
hierarchical and/or hybrid structure with at least three major constituents
including the warm MOLsphere (T about 1.0E+3K) together with the previously
known hot chromosphere (T about 1.0E+4K) and cool expanding gas-dust envelope
(T about 1.0E+2K).Comment: 14 pages, 5 postscript figures, to appear in ApJ
Herschel/PACS observations of the 69 band of crystalline olivine around evolved stars
We present 48 Herschel/PACS spectra of evolved stars in the wavelength range
of 67-72 m. This wavelength range covers the 69 m band of crystalline
olivine (). The width and
wavelength position of this band are sensitive to the temperature and
composition of the crystalline olivine. Our sample covers a wide range of
objects: from high mass-loss rate AGB stars (OH/IR stars,
M/yr), through post-AGB stars with and without circumbinary disks, to
planetary nebulae and even a few massive evolved stars. The goal of this study
is to exploit the spectral properties of the 69 m band to determine the
composition and temperature of the crystalline olivine. Since the objects cover
a range of evolutionary phases, we study the physical and chemical properties
in this range of physical environments. We fit the 69 m band and use its
width and position to probe the composition and temperature of the crystalline
olivine. For 27 sources in the sample, we detected the 69 m band of
crystalline olivine (). The
69 m band shows that all the sources produce pure forsterite grains
containing no iron in their lattice structure. The temperature of the
crystalline olivine as indicated by the 69 m band, shows that on average
the temperature of the crystalline olivine is highest in the group of OH/IR
stars and the post-AGB stars with confirmed Keplerian disks. The temperature is
lower for the other post-AGB stars and lowest for the planetary nebulae. A
couple of the detected 69 m bands are broader than those of pure
magnesium-rich crystalline olivine, which we show can be due to a temperature
gradient in the circumstellar environment of these stars. continued...Comment: Accepted for publication in A&
Spectral and morphological analysis of the remnant of Supernova 1987A with ALMA & ATCA
We present a comprehensive spectral and morphological analysis of the remnant
of Supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and
the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and
thermal components of the radio emission are investigated in images from 94 to
672 GHz ( 3.2 mm to 450 m), with the assistance of a
high-resolution 44 GHz synchrotron template from the ATCA, and a dust template
from ALMA observations at 672 GHz. An analysis of the emission distribution
over the equatorial ring in images from 44 to 345 GHz highlights a gradual
decrease of the east-to-west asymmetry ratio with frequency. We attribute this
to the shorter synchrotron lifetime at high frequencies. Across the transition
from radio to far infrared, both the synchrotron/dust-subtracted images and the
spectral energy distribution (SED) suggest additional emission beside the main
synchrotron component () and the thermal component
originating from dust grains at K. This excess could be due to
free-free flux or emission from grains of colder dust. However, a second
flat-spectrum synchrotron component appears to better fit the SED, implying
that the emission could be attributed to a pulsar wind nebula (PWN). The
residual emission is mainly localised west of the SN site, as the spectral
analysis yields across the western regions,
with around the central region. If there is a PWN in the remnant
interior, these data suggest that the pulsar may be offset westward from the SN
position.Comment: ApJ accepted. 21 pages, emulateapj. References update
Brownian Motions on Metric Graphs
Brownian motions on a metric graph are defined. Their generators are
characterized as Laplace operators subject to Wentzell boundary at every
vertex. Conversely, given a set of Wentzell boundary conditions at the vertices
of a metric graph, a Brownian motion is constructed pathwise on this graph so
that its generator satisfies the given boundary conditions.Comment: 43 pages, 7 figures. 2nd revision of our article 1102.4937: The
introduction has been modified, several references were added. This article
will appear in the special issue of Journal of Mathematical Physics
celebrating Elliott Lieb's 80th birthda
Carbon Monoxide in the Cold Debris of Supernova 1987A
We report spectroscopic and imaging observations of rotational transitions of
cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a
supernova remnant. In addition to line luminosities for the CO J=1-0, 2-1, 6-5,
and 7-6 transitions, we present upper limits for all other transitions up to
J=13-12, collectively measured from the Atacama Large Millimeter Array (ALMA),
the Atacama Pathfinder EXperiment (APEX), and the Herschel Spectral and
Photometric Imaging REceiver (SPIRE). Simple models show the lines are emitted
from at least 0.01 solar masses of CO at a temperature > 14 K, confined within
at most 35% of a spherical volume expanding at ~ 2000 km/s. Moreover, we locate
the emission within 1'' of the central debris. These observations, along with a
partial observation of SiO, confirm the presence of cold molecular gas within
supernova remnants and provide insight into the physical conditions and
chemical processes in the ejecta. Furthermore, we demonstrate the powerful new
window into supernova ejecta offered by submillimeter observations.Comment: Accepted to the Astrophysical Journal Letters, 6 pages, 3 figure
Spectral and morphological analysis of the remnant of supernova 1987A with alma and atca
published_or_final_versio
DNA resection in eukaryotes: deciding how to fix the break
DNA double-strand breaks are repaired by different mechanisms, including homologous
recombination and nonhomologous end-joining. DNA-end resection, the first step in
recombination, is a key step that contributes to the choice of DSB repair. Resection, an
evolutionarily conserved process that generates single-stranded DNA, is linked to checkpoint
activation and is critical for survival. Failure to regulate and execute this process results in
defective recombination and can contribute to human disease. Here, I review recent findings on
the mechanisms of resection in eukaryotes, from yeast to vertebrates, provide insights into the
regulatory strategies that control it, and highlight the consequences of both its impairment and its
deregulation
A Spitzer Space Telescope far-infrared spectral atlas of compact sources in the Magellanic Clouds. I. The Large Magellanic Cloud
[abridged] We present 52-93 micron spectra obtained with Spitzer in the
MIPS-SED mode, of a representative sample of luminous compact far-IR sources in
the LMC. These include carbon stars, OH/IR AGB stars, post-AGB objects and PNe,
RCrB-type star HV2671, OH/IR red supergiants WOHG064 and IRAS05280-6910, B[e]
stars IRAS04530-6916, R66 and R126, Wolf-Rayet star Brey3a, Luminous Blue
Variable R71, supernova remnant N49, a large number of young stellar objects,
compact HII regions and molecular cores, and a background galaxy (z~0.175). We
use the spectra to constrain the presence and temperature of cold dust and the
excitation conditions and shocks within the neutral and ionized gas, in the
circumstellar environments and interfaces with the surrounding ISM. Evolved
stars, including LBV R71, lack cold dust except in some cases where we argue
that this is swept-up ISM. This leads to an estimate of the duration of the
prolific dust-producing phase ("superwind") of several thousand years for both
RSGs and massive AGB stars, with a similar fractional mass loss experienced
despite the different masses. We tentatively detect line emission from neutral
oxygen in the extreme RSG WOHG064, with implications for the wind driving. In
N49, the shock between the supernova ejecta and ISM is revealed by its strong
[OI] 63-micron emission and possibly water vapour; we estimate that 0.2 Msun of
ISM dust was swept up. Some of the compact HII regions display pronounced
[OIII] 88-micron emission. The efficiency of photo-electric heating in the
interfaces of ionized gas and molecular clouds is estimated at 0.1-0.3%. We
confirm earlier indications of a low nitrogen content in the LMC. Evidence for
solid state emission features is found in both young and evolved object; some
of the YSOs are found to contain crystalline water ice.Comment: Accepted for publication in The Astronomical Journal. This paper
accompanies the Summer 2009 SAGE-Spec release of 48 MIPS-SED spectra, but
uses improved spectrum extraction. (Fig. 2 reduced resolution because of
arXiv limit.
Herschel Detects a Massive Dust Reservoir in Supernova 1987A
We report far-infrared and submillimeter observations of Supernova 1987A, the
star that exploded on February 23, 1987 in the Large Magellanic Cloud, a galaxy
located 160,000 lightyears away. The observations reveal the presence of a
population of cold dust grains radiating with a temperature of ~17-23 K at a
rate of about 220 solar luminosity. The intensity and spectral energy
distribution of the emission suggests a dust mass of ~0.4-0.7 solar mass. The
radiation must originate from the SN ejecta and requires the efficient
precipitation of all refractory material into dust. Our observations imply that
supernovae can produce the large dust masses detected in young galaxies at very
high redshifts.Comment: This is the author's version of the work. It is posted here by
permission of the AAAS for personal use, not for redistribution. To appear in
Science; available in Science Express on 7th July,
DOI:10.1126/science.1205983 at
http://www.sciencemag.org/lookup/doi/10.1126/science.1205983 ; 14 pages, 2
figures, 4 tables. High resolution images are available from the author
Quantitative analysis of WC stars: Constraints on neon abundances from ISO/SWS spectroscopy
Neon abundances are derived in four Galactic WC stars -- gamma Vel (WR11,
WC8+O7.5III), HD156385 (WR90, WC7), HD192103 (WR135, WC8), and WR146 (WC5+O8) -
using mid-infrared fine structure lines obtained with ISO/SWS. Stellar
parameters for each star are derived using a non-LTE model atmospheric code
(Hillier & Miller 1998) together with ultraviolet (IUE), optical (INT, AAT) and
infrared (UKIRT, ISO) spectroscopy. In the case of gamma Vel, we adopt results
from De Marco et al. (2000), who followed an identical approach.
ISO/SWS datasets reveal the [NeIII] 15.5um line in each of our targets, while
[NeII] 12.8um, [SIV] 10.5um and [SIII] 18.7um are observed solely in gamma Vel.
Using a method updated from Barlow et al. (1988) to account for clumped winds,
we derive Ne/He=3-4x10^-3 by number, plus S/He=6x10^-5 for gamma Vel. Neon is
highly enriched, such that Ne/S in gamma Vel is eight times higher than cosmic
values. However, observed Ne/He ratios are a factor of two times lower than
predictions of current evolutionary models of massive stars. An imprecise
mass-loss and distance were responsible for the much greater discrepancy in
neon content identified by Barlow et al.
Our sample of WC5--8 stars span a narrow range in T* (=55--71kK), with no
trend towards higher temperature at earlier spectral type, supporting earlier
results for a larger sample by Koesterke & Hamann (1995). Stellar luminosities
range from 100,000 to 500,000 Lo, while 10^-5.1 < Mdot/(Mo/yr) < 10^-4.5,
adopting clumped winds, in which volume filling factors are 10%. In all cases,
wind performance numbers are less than 10, significantly lower than recent
estimates. Carbon abundances span 0.08 < C/He < 0.25 by number, while oxygen
abundances remain poorly constrained.Comment: 16 pages,7 figures accepted for MNRA
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