Circumstellar masers in the Magellanic Clouds

We have searched for 22 GHz H2O and 43/86/129 GHz SiO masers in bright IRAS point sources in the SMC and LMC, to test whether the kinematics of the mass loss from these stars depends on metallicity. H2O masers were detected in the red supergiants IRAS04553-6825 and IRAS05280-6910, and tentatively in the luminous IR object IRAS05216-6753 and the AGB star IRAS05329-6708. SiO masers were detected in IRAS04553-6825. The outflow velocity increases between the H2O masing zone near the dust-formation region and the more distant OH masing zone from 18 to 26 km/s for IRAS04553-6825 and from 6 to 17 km/s for IRAS05280-6910. The total sample of LMC targets is analysed in comparison with circumstellar masers in the Galactic Centre. The photon fluxes of circumstellar masers in the LMC are very similar to those in the Galactic Centre. The expansion velocities in the LMC appear to be 20% lower than for similarly bright OH masers in the Galactic Centre, but the data are consistent with no difference in expansion velocity. OH/IR stars in the LMC appear to have slower accelerating envelopes than OH/IR stars in the Galactic Centre. Masers in the LMC have blue-asymmetric emission profiles. This may be due to the amplification of stellar and/or free-free radiation, rather than the amplification of dust emission, and may be more pronounced in low metallicity envelopes. SiO maser strength increases with the photometric amplitude at 2.2 micron but is independent of the photometric amplitude at 10 micron. This suggests a strong connection between shocks in the dust-free SiO masing zone and the dust formation process. Appendices describe H2O maser emission from R Dor in the Milky Way, optical echelle spectroscopy of IRAS04553-6825, and the properties of masers in the Galactic Centre (Abridged).Comment: 19 pages, 17 figures. Accepted for publication in Astronomy & Astrophysics Main Journa

The AGB superwind speed at low metallicity

We present the results of a survey for OH maser emission at 1612 MHz from dust-enshrouded AGB stars and supergiants in the LMC and SMC, with the Parkes radio telescope, aimed at deriving the speed of the superwind from the double-peaked OH maser profiles. Out of 8 targets in the LMC we detected 5, of which 3 are new detections - no maser emission was detected in the two SMC targets. We detected for the first time the redshifted components of the OH maser profile in the extreme red supergiant IRAS 04553-6825, confirming the suspicion that its wind speed had been severely underestimated. Despite a much improved spectrum for IRAS 04407-7000, which was known to exhibit a single-peaked OH maser, no complementary peak could be detected. The new detection in IRAS 05003-6712 was also single-peaked, but for two other new detections, IRAS 04498-6842 and IRAS 05558-7000, wind speeds could be determined from their double-peaked maser profiles. The complete sample of known OH/IR stars in the LMC is compared with a sample of OH/IR stars in the galactic centre. The LMC sources generally show a pronounced asymmetry between the bright blueshifted maser emission and weaker redshifted emission, which we attribute to the greater contribution of amplification of radiation coming directly from the star itself as the LMC sources are both more luminous and less dusty than their galactic centre counterparts. We confirm that the OH maser strength is a measure of the dust (rather than gas) mass-loss rate. At a given luminosity or pulsation period, the wind speed in LMC sources is lower than in galactic centre sources, and the observed trends confirm simple radiation-driven wind theory if the dust-to-gas ratio is approximately proportional to the metallicity.Comment: 13 pages, 18 figures. Accepted for publication in MNRA

A Southern Hemisphere Sea Level Pressure-Based Precursor for ENSO Warm and Cold Events

Past studies have described large-scale sea level pressure (SLP) variations in the Southern Hemisphere that lead to El Nino-Southern Oscillation (ENSO) warm and cold events (WE and CE). By relying on this description and the importance of the related variability in the lead up to WE and CE, Southern Hemisphere SLP variations in May-June-July (MJJ) are shown here to be excellent predictors for the peak warm/cold events in sea-surface temperatures (SST) and sea level pressure that mark the mature phase of a warm/cold event in November-January of the same year. Cyclostationary empirical orthogonal functions (CSEOFs) are used to extract the variability associated with this description of SLP evolution leading to extreme events, underscoring the importance of this signal in the build-up to ENSO events. Using the CSEOF decomposition, an MJJ precursor is established and shown to precede impending warm and cold events in the past sixty years. Furthermore, the precursor developed in this study would have suggested that a significant WE for the latter half of 2014 was unlikely

The mass-loss return from evolved stars to the Large Magellanic Cloud V. The GRAMS carbon-star model grid

The total dust return rate from AGB and RSG star outflows is an important constraint to galactic chemical evolution models. However, this requires detailed radiative transfer (RT) modeling of individual stars, which becomes impractical for large data sets. Another approach is to select the best-fit spectral energy distribution (SED) from a grid of dust shell models, allowing for a faster determination of the luminosities and mass-loss rates for entire samples. We have developed the Grid of RSG and AGB ModelS (GRAMS) to measure the mass-loss return from evolved stars. The models span the range of stellar, dust shell and grain properties relevant to evolved stars. In this paper we present the carbon-star grid and compare our results with data of Large Magellanic Cloud (LMC) carbon stars from the SAGE and SAGE-Spec programs. We generate spherically symmetric dust shell models using the 2Dust code, with hydrostatic models for the central stars. We explore five values of the inner radius R_in of the dust shell (1.5, 3, 4.5, 7 and 12 R_star). We use amorphous carbon dust mixed with 10% silicon carbide by mass. The grain sizes follows a KMH distribution. The models span 26 values of 11.3 um optical depth, ranging from 0.001 to 4. For each model, 2Dust calculates the output SED from 0.2 to 200 um. Over 12,000 models have dust temperatures below 1800 K. The GRAMS synthetic photometry is in good agreement with SAGE photometry for LMC carbon-rich and extreme AGB star candidates, as well as spectroscopically confirmed carbon stars from the SAGE-Spec study. Our models reproduce the IRAC colors of most of the extreme AGB star candidates, consistent with the expectation that a majority of these enshrouded stars have carbon-rich dust. Finally, we fit the SEDs of some well-studied carbon stars and compare the resulting luminosities and mass-loss rates with those from previous studies.Comment: 16 pages, 13 figures, accepted for publication in Astronomy & Astrophysic

The Physical Properties of the Red Supergiant WOH G64: The Largest Star Known?

WOH G64 is an unusual red supergiant (RSG) in the Large Magellanic Cloud (LMC), with a number of properties that set it apart from the rest of the LMC RSG population, including a thick circumstellar dust torus, an unusually late spectral type, maser activity, and nebular emission lines. Its reported physical properties are also extreme, including the largest radius for any star known and an effective temperature that is much cooler than other RSGs in the LMC, both of which are at variance with stellar evolutionary theory. We fit moderate-resolution optical spectrophotometry of WOH G64 with the MARCS stellar atmosphere models, determining an effective temperature of 3400 +/- 25 K. We obtain a similar result from the star's broadband V - K colors. With this effective temperature, and taking into account the flux contribution from the aysmmetric circumstellar dust envelope, we calculate log(L/L_sun) = 5.45 +/- 0.05 for WOH G64, quite similar to the luminosity reported by Ohnaka and collaborators based on their radiative transfer modeling of the star's dust torus. We determine a radius of R/R_sun = 1540, bringing the size of WOH G64 and its position on the H-R diagram into agreement with the largest known Galactic RSGs, although it is still extreme for the LMC. In addition, we use the Ca II triplet absorption feature to determine a radial velocity of 294 +/- 2 km/s for the star; this is the same radial velocity as the rotating gas in the LMC's disk, which confirms its membership in the LMC and precludes it from being an unusual Galactic halo giant. Finally, we describe the star's unusual nebula emission spectrum; the gas is nitrogen-rich and shock-heated, and displays a radial velocity that is significantly more positive than the star itself by 50 km/s.Comment: 25 pages, 5 figures; accepted for publication in The Astronomical Journa

Exercise-Induced splanchnic hypoperfusion results in gut dysfunction in healthy men

Background Splanchnic hypoperfusion is common in various pathophysiological conditions and often considered to lead to gut dysfunction. While it is known that physiological situations such as physical exercise also result in splanchnic hypoperfusion, the consequences of flow redistribution at the expense of abdominal organs remained to be determined. This study focuses on the effects of splanchnic hypoperfusion on the gut, and the relationship between hypoperfusion, intestinal injury and permeability during physical exercise in healthy men. Methods and Findings Healthy men cycled for 60 minutes at 70% of maximum workload capacity. Splanchnic hypoperfusion was assessed using gastric tonometry. Blood, sampled every 10 minutes, was analyzed for enterocyte damage parameters (intestinal fatty acid binding protein (I-FABP) and ileal bile acid binding protein (I-BABP)). Changes in intestinal permeability were assessed using sugar probes. Furthermore, liver and renal parameters were assessed. Splanchnic perfusion rapidly decreased during exercise, reflected by increased gapg-apCO2 from −0.85±0.15 to 0.85±0.42 kPa (p < 0.001). Hypoperfusion increased plasma I-FABP (615±118 vs. 309±46 pg/ml, p < 0.001) and I-BABP (14.30±2.20 vs. 5.06±1.27 ng/ml, p < 0.001), and hypoperfusion correlated significantly with this small intestinal damage (rS = 0.59; p < 0.001). Last of all, plasma analysis revealed an increase in small intestinal permeability after exercise (p < 0.001), which correlated with intestinal injury (rS = 0.50; p < 0.001). Liver parameters, but not renal parameters were elevated. Conclusions Exercise-induced splanchnic hypoperfusion results in quantifiable small intestinal injury. Importantly, the extent of intestinal injury correlates with transiently increased small intestinal permeability, indicating gut barrier dysfunction in healthy individuals. These physiological observations increase our knowledge of splanchnic hypoperfusion sequelae, and may help to understand and prevent these phenomena in patients

Barriers and facilitators perceived by physicians when using prediction models in practice

Objectives Prediction models may facilitate risk-based management of health care conditions. In a large cluster-randomized trial, presenting calculated risks of postoperative nausea and vomiting (PONV) to physicians (assistive approach) increased risk-based management of PONV. This increase did not improve patient outcome - that is, PONV incidence. This prompted us to explore how prediction tools guide the decision-making process of physicians. Study Design and Setting Using mixed methods, we interviewed eight physicians to understand how predicted risks were perceived by the physicians and how they influenced decision making. Subsequently, all 57 physicians of the trial were surveyed for how the presented risks influenced their perceptions. Results Although the prediction tool made physicians more aware of PONV prevention, the physicians reported three barriers to use predicted risks in their decision making. PONV was not considered an outcome of utmost importance; decision making on PONV prophylaxis was mostly intuitive rather than risk based; prediction models do not weigh benefits and risks of prophylactic drugs. Conclusion Combining probabilistic output of the model with their clinical experience may be difficult for physicians, especially when their decision-making process is mostly intuitive. Adding recommendations to predicted risks (directive approach) was considered an important step to facilitate the uptake of a prediction tool

Detailed maps of interstellar clouds in front of omega Centauri: Small-scale structures in the Galactic Disc-Halo interface

We used the multiplex capabilities of the AAOmega spectrograph at the Anglo-Australian Telescope to create a half-square-degree map of the neutral and low-ionized ISM in front of the nearby (~5 kpc), most massive Galactic globular cluster, omega Centauri. Its redshifted, metal-poor and hot horizontal branch stars probe the medium-strong Ca II K and Na I D2 line absorption, and weak absorption in the lambda5780 and lambda5797 Diffuse Interstellar Bands (DIBs), on scales around a parsec. The kinematical and thermodynamical picture emerging from these data is that we predominantly probe the warm neutral medium and weakly-ionized medium of the Galactic Disc-Halo interface, ~0.3-1 kpc above the mid-plane. A comparison with Spitzer Space Telescope 24-micron and DIRBE/IRAS maps of the warm and cold dust emission confirms that both Na I and Ca II trace the overall column density of the warm neutral and weakly-ionized medium. Clear signatures are seen of the depletion of calcium atoms from the gas phase into dust grains. Curiously, the coarse DIRBE/IRAS map is a more reliable representation of the relative reddening between sightlines than the Na I and Ca II absorption-line measurements, most likely because the latter are sensitive to fluctuations in the local ionization conditions. The behaviour of the DIBs is consistent with the lambda5780 band being stronger than the lambda5797 band in regions where the ultraviolet radiation level is relatively high, as in the Disc-Halo interface. This region corresponds to a sigma-type cloud. In all, our maps and simple analytical model calculations show in unprecedented detail that small-scale density and/or ionization structures exist in the extra-planar gas of a spiral galaxy. (abridged)Comment: Accepted for publication in MNRA