2,310 research outputs found
A multi-wavelength study of the young star V1118 Orionis in outburst
Abriged version for astroph: The young late-type star V1118 Orionis was in
outburst from 2005 to 2006. We followed the outburst with optical and
near-infrared photometry; the X-ray emission was further probed with
observations taken with XMM-Newton and Chandra during and after the outburst.
In addition, we obtained mid-infrared photometry and spectroscopy with Spitzer
at the peak of the outburst and in the post-outburst phase. The spectral energy
distribution of V1118 Ori varied significantly over the course of the outburst.
The optical flux showed the largest variations, most likely due to enhanced
emission by a hot spot. The latter dominated the optical and near-infrared
emission at the peak of the outburst, while the disk emission dominated in the
mid-infrared. The X-ray flux correlated with the optical and infrared fluxes,
indicating that accretion affected the magnetically active corona and the
stellar magnetosphere. The thermal structure of the corona was variable with
some indication of a cooling of the coronal temperature in the early phase of
the outburst with a gradual return to normal values. Color-color diagrams in
the optical and infrared showed variations during the outburst, with no obvious
signature of reddening due to circumstellar matter. Using MC realizations of
star+disk+hotspot models to fit the SED in ``quiescence'' and at the peak of
the outburst, we determined that the mass accretion rate varied from about
2.5E-7 Msun/yr to 1E-6 Msun/yr; in addition the fractional area of the hotspot
increased significantly as well. The multi-wavelength study of the V1118 Ori
outburst helped us to understand the variations in spectral energy
distributions and demonstrated the interplay between the disk and the stellar
magnetosphere in a young, strongly accreting star.Comment: Accepted in A&A, Tables will be published onlin
Local recurrences in western low rectal cancer patients treated with or without lateral lymph node dissection after neoadjuvant (chemo) radiotherapy: An international multi-centre comparative study
Background: In the West, low rectal cancer patients with abnormal lateral lymph nodes (LLNs) are commonly treated with neoadjuvant (chemo)radiotherapy (nCRT) followed by total mesorectal excision (TME). Additionally, some perform a lateral lymph node dissection (LLND). To date, no comparative data (nCRT vs. nCRT + LLND) are available in Western patients. Methods: An international multi-centre cohort study was conducted at six centres from the Netherlands, US and Australia. Patients with low rectal cancers from the Netherlands and Australia with abnormal LLNs (â„5 mm short-axis in the obturator, internal iliac, external iliac and/or common iliac basin) who underwent nCRT and TME (LLND-group) were compared to similarly staged patients from the US who underwent a LLND in addition to nCRT and TME (LLND + group). Results: LLND + patients (n = 44) were younger with higher ASA-classifications and ypN-stages compared to LLND-patients (n = 115). LLND + patients had larger median LLNs short-axes and received more adjuvant chemotherapy (100 vs. 30%; p < 0.0001). Between groups, the local recurrence rate (LRR) was 3% for LLND + vs. 11% for LLND- (p = 0.13). Disease-free survival (DFS, p = 0.94) and overall survival (OS, p = 0.42) were similar. On multivariable analysis, LLND was an independent significant factor for local recurrences (p = 0.01). Sub-analysis of patients who underwent long-course nCRT and had adjuvant chemotherapy (LLND-n = 30, LLND + n = 44) demonstrated a lower LRR for LLND + patients (3% vs. 16% for LLND-; p = 0.04). DFS (p = 0.10) and OS (p = 0.11) were similar between groups. Conclusion: A LLND in addition to nCRT may improve loco-regional control in Western patients with low rectal cancer and abnormal LLNs. Larger studies in Western patients are required to evaluate its contribution
Illumination in symbiotic binary stars: Non-LTE photoionization models. II. Wind case
We describe a non-LTE photoionization code to calculate the wind structure
and emergent spectrum of a red giant wind illuminated by the hot component of a
symbiotic binary system. We consider spherically symmetric winds with several
different velocity and temperature laws and derive predicted line fluxes as a
function of the red giant mass loss rate, \mdot. Our models generally match
observations of the symbiotic stars EG And and AG Peg for \mdot about 10^{-8}
\msunyr to 10^{-7} \msunyr. The optically thick cross- section of the red giant
wind as viewed from the hot component is a crucial parameter in these models.
Winds with cross-sections of 2--3 red giant radii reproduce the observed
fluxes, because the wind density is then high, about 10^9 cm^{-3}. Our models
favor winds with acceleration regions that either lie far from the red giant
photosphere or extend for 2--3 red giant radii.Comment: 51 pages, LaTeX including three tables, requires 15 Encapsulated
Postscript figures, to appear in Ap
Debris Disks: Probing Planet Formation
Debris disks are the dust disks found around ~20% of nearby main sequence
stars in far-IR surveys. They can be considered as descendants of
protoplanetary disks or components of planetary systems, providing valuable
information on circumstellar disk evolution and the outcome of planet
formation. The debris disk population can be explained by the steady
collisional erosion of planetesimal belts; population models constrain where
(10-100au) and in what quantity (>1Mearth) planetesimals (>10km in size)
typically form in protoplanetary disks. Gas is now seen long into the debris
disk phase. Some of this is secondary implying planetesimals have a Solar
System comet-like composition, but some systems may retain primordial gas.
Ongoing planet formation processes are invoked for some debris disks, such as
the continued growth of dwarf planets in an unstirred disk, or the growth of
terrestrial planets through giant impacts. Planets imprint structure on debris
disks in many ways; images of gaps, clumps, warps, eccentricities and other
disk asymmetries, are readily explained by planets at >>5au. Hot dust in the
region planets are commonly found (<5au) is seen for a growing number of stars.
This dust usually originates in an outer belt (e.g., from exocomets), although
an asteroid belt or recent collision is sometimes inferred.Comment: Invited review, accepted for publication in the 'Handbook of
Exoplanets', eds. H.J. Deeg and J.A. Belmonte, Springer (2018
Star formation in Perseus: II. SEDs, classification and lifetimes
Working with the submillimetre continuum map of the Perseus molecular cloud
(Hatchell et al. 2005), we aimed to determine the evolutionary stage of each
submm core in Perseus, and investigate the lifetimes of these phases. We
compile spectral energy distributions (SEDs) from 2MASS, Spitzer IRAC,
Michelle, IRAS, SCUBA and Bolocam data. Sources are classified
starless/protostellar on the basis of infrared and/or outflow detections and
Class I/Class 0 on the basis of Tbol, Lbol/Lsmm and F_{3.6}/F_{850}. In order
to investigate the dependence of these evolutionary indicators on mass, we
construct radiative transfer models of Class 0 sources. Of the submm cores,
56/103 (54%) are confirmed protostars on the basis of infrared emission or
molecular outflows. Of these, 22 are classified Class 1 on the basis of three
evolutionary indicators, 34 are Class 0, and the remaining 47 are assumed
starless. Perseus contains a much greater fraction of Class 0 sources than
either Taurus or Rho Oph. Comparing the protostellar with the T Tauri
population, the lifetime of the protostellar phase in Perseus is 0.25-0.67 Myr
(95% confidence limits). The relative lifetime of the Class 0 and Class 1
phases are similar. We find that for the same source geometry but different
masses, evolutionary indicators such as Tbol vary their value. It is therefore
not always appropriate to use a fixed threshold to separate Class 0 and Class I
sources. More modelling is required to determine the observational
characteristics of the Class 0/Class I boundary over a range of masses.Comment: A&A accepted. 35 pages, 24 figures. Version with original figures
available at http://www.astro.ex.ac.uk/people/hatchell/publications.htm
Fragmentation and mass segregation in the massive dense cores of Cygnus X
We present Plateau de Bure interferometer observations obtained in continuum
at 1.3 and 3.5 mm towards the six most massive and young (IR-quiet) dense cores
in Cygnus X. Located at only 1.7 kpc, the Cygnus X region offers the
opportunity of reaching small enough scales (of the order of 1700 AU at 1.3 mm)
to separate individual collapsing objects. The cores are sub-fragmented with a
total of 23 fragments inside 5 cores. Only the most compact core, CygX-N63,
could actually be a single massive protostar with an envelope mass as large as
60 Msun. The fragments in the other cores have sizes and separations similar to
low-mass pre-stellar and proto-stellar condensations in nearby protoclusters,
and are probably of the same nature. A total of 9 out of these 23 protostellar
objects are found to be probable precursors of OB stars with envelope masses
ranging from 6 to 23 Msun. The level of fragmentation is globally higher than
in the turbulence regulated, monolithic collapse scenario, but is not as high
as expected in a pure gravo-turbulent scenario where the distribution of mass
is dominated by low-mass protostars/stars. Here, the fractions of the total
core masses in the high-mass fragments are reaching values as high as 28, 44,
and 100 % in CygX-N12, CygX-N53, and CygX-N63, respectively, much higher than
what an IMF-like mass distribution would predict. The increase of the
fragmentation efficiency as a function of density in the cores is proposed to
be due to the increasing importance of self-gravity leading to gravitational
collapse at the scale of the dense cores. At the same time, the cores tend to
fragment into a few massive protostars within their central regions. We are
therefore probably witnessing here the primordial mass segregation of clusters
in formation.Comment: 14 pages, 16 figures, submitted for publication in A&
AMI Large Array radio continuum observations of Spitzer c2d small clouds and cores
We perform deep 1.8 cm radio continuum imaging towards thirteen protostellar
regions selected from the Spitzer c2d small clouds and cores programme at high
resolution (25") in order to detect and quantify the cm-wave emission from
deeply embedded young protostars. Within these regions we detect fifteen
compact radio sources which we identify as radio protostars including two
probable new detections. The sample is in general of low bolometric luminosity
and contains several of the newly detected VeLLO sources. We determine the 1.8
cm radio luminosity to bolometric luminosity correlation, L_rad -L_bol, for the
sample and discuss the nature of the radio emission in terms of the available
sources of ionized gas. We also investigate the L_rad-L_IR correlation and
suggest that radio flux density may be used as a proxy for the internal
luminosity of low luminosity protostars.Comment: submitted MNRA
On the nature of candidate luminous blue variables in M33
Luminous blue variables (LBVs) are expected to play an important role in
massive stellar evolution as well as being the progenitors of some of the most
luminous supernovae known. In this paper we provide a multiwavelength study of
the population of (candidate) LBVs identified within M33. New spectra provide
an observational baseline of >4yr with respect to published data, which is well
suited to identifying LBV outbursts. Multi-epoch optical and mid-IR surveys of
M33 further constrain the variability of the sample and permit a search for
dusty circumstellar ejecta. Spectroscopic and photometric variability appears
common amongst the sample, although in many cases further observations will be
required to determine its physical origin. Nevertheless, we report a new
outburst of M33 Var C, while the transition of the WNLh star B517 to a cooler B
supergiant phase between 1993-2010 confirms an LBV classification.
Proof-of-concept quantitative analysis is provided for Romano's star; the
results being consistent with the finding that its bolometric luminosity varies
during its LBV excursions. The combination of the temperature and luminosity of
two stars, the B hypergiant [HS80] 110A and the cool hypergiant B324, appears
to be in violation of the empirical Humphreys-Davidson limit. Mid-IR
observations demonstrate that a number of candidates appear associated with hot
circumstellar dust, although no objects as extreme as Eta Carinae are
identified. The combined multiwavelength dataset suggests that the population
of LBVs studied is contaminated by stars demonstrating the B[e] phenomenon. Of
these, a subset of optically faint, low luminosity stars associated with hot
dust are of particular interest since they appear similar to the likely
progenitors of SN 2008S and the 2008 NGC300 transient, albeit suffering less
intrinsic extinction. [ABRIDGED]Comment: 23 pages, 14 figures, accepted for publication in Astronomy and
Astrophysic
Association between Chronic Arsenic Exposure and Nutritional Status among the Women of Child Bearing Age: A Case-Control Study in Bangladesh
The role of nutritional factors in arsenic metabolism and toxicity is yet to be fully elucidated. A low protein diet results in decreased excretion of DMA and increased tissue retention of arsenic in experimental studies. Malnourished women carry a higher risk of adverse pregnancy outcomes. Chronic exposure to high arsenic (>50 ÎŒg/L) through drinking water also increases the risk of adverse pregnancy outcomes. The synergistic effects (if any) of malnutrition and chronic arsenic exposure may worsen the adverse pregnancy outcomes. This population based case control study reports the association between chronic arsenic exposure and nutritional status among the rural women in Bangladesh. 348 cases (BMI < 18.5) and 360 controls (BMI 18.5â24.99) were recruited from a baseline survey conducted among 2,341 women. An excess risk for malnutrition was observed among the participants chronically exposed to higher concentrations of arsenic in drinking water after adjusting for potential confounders such as participantâs age, religion, education, monthly household income and history of oral contraceptive pills. Women exposed to arsenic >50 ÎŒg/L were at 1.9 times (Odds Ratio = 1.9, 95% CI = 1.1â3.6) increased risk of malnutrition compared to unexposed. The findings of this study suggest that chronic arsenic exposure is likely to contribute to poor nutritional status among women of 20â45 years
Genotyping Validates the Efficacy of Photographic Identification in a Capture-Mark-Recapture Study Based on the Head Scale Patterns of the Prairie Lizard (\u3ci\u3eSceloporus consobrinus\u3c/i\u3e)
Population studies often incorporate captureâmarkârecapture (CMR) techniques to gather information on longâterm biological and demographic characteristics. A fundamental requirement for CMR studies is that an individual must be uniquely and permanently marked to ensure reliable reidentification throughout its lifespan. Photographic identification involving automated photographic identification software has become a popular and efficient noninvasive method for identifying individuals based on natural markings. However, few studies have (a) robustly assessed the performance of automated programs by using a doubleâmarking system or (b) determined their efficacy for longâterm studies by incorporating multiâyear data. Here, we evaluated the performance of the program Interactive Individual Identification System (I3S) by crossâvalidating photographic identifications based on the head scale pattern of the prairie lizard (Sceloporus consobrinus) with individual microsatellite genotyping (N = 863). Further, we assessed the efficacy of the program to identify individuals over time by comparing error rates between withinâyear and betweenâyear recaptures. Recaptured lizards were correctly identified by I3S in 94.1% of cases. We estimated a false rejection rate (FRR) of 5.9% and a false acceptance rate (FAR) of 0%. By using I3S, we correctly identified 97.8% of withinâyear recaptures (FRR = 2.2%; FAR = 0%) and 91.1% of betweenâyear recaptures (FRR = 8.9%; FAR = 0%). Misidentifications were primarily due to poor photograph quality (N = 4). However, two misidentifications were caused by indistinct scale configuration due to scale damage (N = 1) and ontogenetic changes in head scalation between capture events (N = 1). We conclude that automated photographic identification based on head scale patterns is a reliable and accurate method for identifying individuals over time. Because many lizard or reptilian species possess variable head squamation, this method has potential for successful application in many species
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