Photometric determination of the mass accretion rates of pre-main sequence stars. II. NGC346 in the Small Magellanic Cloud

[Abridged] We have studied the properties of the stellar populations in the field of the NGC346 cluster in the Small Magellanic Cloud, using a novel self-consistent method that allows us to reliably identify pre-main sequence (PMS) objects actively undergoing mass accretion, regardless of their age. The method does not require spectroscopy and combines broad-band V and I photometry with narrow-band Halpha imaging to identify all stars with excess Halpha emission and derive the accretion luminosity Lacc and mass accretion rate Macc for all of them. The application of this method to existing HST/ACS photometry of the NGC346 field has allowed us to identify and study 680 bona-fide PMS stars with masses from ~0.4 to ~4 Msolar and ages in the range from ~1 to ~30 Myr. This is the first study to reveal that, besides a young population of PMS stars (~ 1 Myr old), in this field there is also an older population of PMS objects with a median age of ~20 Myr. We provide for all of them accurate physical parameters. We study the evolution of the mass accretion rate as a function of stellar parameters and find that logMacc ~ -0.6 Log t + Log m + c, where t is the age of the star, m its mass and c a quantity that is higher at lower metallicity. The high mass accretion rates that we find suggest that a considerable fraction of the stellar mass is accreted during the PMS phase and that PMS evolutionary models that do not account for this effect will systematically underestimate the true age when compared with the observations.Comment: Accepted for publication in the ApJ. 14 pages, 11 figures. Corrected typos and reference

Identifying Inhibitors of Inflammation:A Novel High-Throughput MALDI-TOF Screening Assay for Salt-Inducible Kinases (SIKs)

Matrix-assisted laser desorption/ionization time-of-flight (MALDI TOF) mass spectrometry has become a promising alternative for high-throughput drug discovery as new instruments offer high speed, flexibility and sensitivity, and the ability to measure physiological substrates label free. Here we developed and applied high-throughput MALDI TOF mass spectrometry to identify inhibitors of the salt-inducible kinase (SIK) family, which are interesting drug targets in the field of inflammatory disease as they control production of the anti-inflammatory cytokine interleukin-10 (IL-10) in macrophages. Using peptide substrates in in vitro kinase assays, we can show that hit identification of the MALDI TOF kinase assay correlates with indirect ADP-Hunter kinase assays. Moreover, we can show that both techniques generate comparable IC50 data for a number of hit compounds and known inhibitors of SIK kinases. We further take these inhibitors to a fluorescence-based cellular assay using the SIK activity-dependent translocation of CRTC3 into the nucleus, thereby providing a complete assay pipeline for the identification of SIK kinase inhibitors in vitro and in cells. Our data demonstrate that MALDI TOF mass spectrometry is fully applicable to high-throughput kinase screening, providing label-free data comparable to that of current high-throughput fluorescence assays.</p

Confirming the Primarily Smooth Structure of the Vega Debris Disk at Millimeter Wavelengths

Clumpy structure in the debris disk around Vega has been previously reported at millimeter wavelengths and attributed to concentrations of dust grains trapped in resonances with an unseen planet. However, recent imaging at similar wavelengths with higher sensitivity has disputed the observed structure. We present three new millimeter wavelength observations that help to resolve the puzzling and contradictory observations. We have observed the Vega system with the Submillimeter Array (SMA) at a wavelength of 880 μm and an angular resolution of 5"; with the Combined Array for Research in Millimeter-wave Astronomy (CARMA) at a wavelength of 1.3 mm and an angular resolution of 5"; and with the Green Bank Telescope (GBT) at a wavelength of 3.3 mm and angular resolution of 10". Despite high sensitivity and short baselines, we do not detect the Vega debris disk in either of the interferometric data sets (SMA and CARMA), which should be sensitive at high significance to clumpy structure based on previously reported observations. We obtain a marginal (3σ) detection of disk emission in the GBT data; the spatial distribution of the emission is not well constrained.We analyze the observations in the context of several different models, demonstrating that the observations are consistent with a smooth, broad, axisymmetric disk with inner radius 20–100 AU and width ≾50 AU. The interferometric data require that at least half of the 860 μm emission detected by previous single-dish observations with the James Clerk Maxwell Telescope be distributed axisymmetrically, ruling out strong contributions from flux concentrations on spatial scales of ≾100 AU. These observations support recent results from the Plateau de Bure Interferometer indicating that previous detections of clumpy structure in the Vega debris disk were spurious

The R136 star cluster hosts several stars whose individual masses greatly exceed the accepted 150 Msun stellar mass limit

Spectroscopic analyses of H-rich WN5-6 stars within the young star clusters NGC 3603 and R136 are presented, using archival HST & VLT spectroscopy, & high spatial resolution near-IR photometry. We derive high T* for the WN stars in NGC 3603 (T*~42+/-2 kK) & R136 (T*~53+/-3 kK) plus clumping-corrected dM/dt ~ 2-5x10^-5 Msun/yr which closely agree with theoretical predictions. These stars make a disproportionate contribution to the global budget of their host clusters. R136a1 alone supplies ~7% of N(LyC) of the entire 30 Dor region. Comparisons with stellar models calculated for the main-sequence evolution of 85-500 Msun suggest ages of ~1.5 Myr & M_init in the range 105 - 170 Msun for 3 systems in NGC 3603, plus 165-320 Msun for 4 stars in R136. Our high stellar masses are supported by dynamical mass determinations for the components of NGC 3603 A1. We consider the predicted L_X of the R136 stars if they were close, colliding wind binaries. R136c is consistent with a colliding wind binary system. However, short period, colliding wind systems are excluded for R136a WN stars if mass ratios are of order unity. Widely separated systems would have been expected to harden owing to early dynamical encounters with other massive stars in such a dense environment. From simulated star clusters, whose constituents are randomly sampled from the Kroupa IMF, both clusters are consistent with a tentative upper mass limit of ~300 Msun. The Arches cluster is either too old, exhibits a deficiency of very massive stars, or more likely stellar masses have been underestimated - M_init for the most luminous stars in the Arches cluster approach 200 Msun according to contemporary stellar & photometric results. The potential for stars greatly exceeding 150 Msun within metal-poor galaxies suggests that such pair-instability SNe could occur within the local universe, as has been claimed for SN 2007bi (abridged).Comment: 20 pages, 14 figures, accepted for MNRAS. Version with higher resolution figures is available from http://pacrowther.staff.shef.ac.uk/R136.pdf See also http://www.eso.org/public/news/eso1030/ from Wed 21 from noon (CEST

Employing a coaching model of supervision during physiotherapy placements: Charting the student experience

Purpose Placement capacity during physiotherapy degree programmes is presently under unprecedented stress. In the wake of COVID-19, Health Education England has moved to increase university places across all Allied Health Professions (AHPs) by 50%, without any reduction in quality of education. In order to facilitate this increase in student numbers, Higher Education Institutions (HEIs) and healthcare teams are being asked to change their ways of working and consider alternative supervision models. One such model is the group-based ‘coaching’ approach which is commonly used in the education of medical students but seldom employed on AHP programmes, where one-to-one supervision remains the default. The research reported herein was tasked with qualitatively elucidating student experiences of such a coaching supervision initiative, introduced by the research team across a set of undergraduate and postgraduate physiotherapy placements in two NHS Trusts the north of England during 2020 and 2021. Methods The research team contacted all students who had (a) completed a placement using the coaching supervision model, while also (b) having prior experience of placement(s) using the more conventional one-to-one approach. These students, registered at a number of UK HEIs, were informed that participation would involve sitting for a semi-structured interview in which they would be afforded the opportunity to critically discuss their experiences of the coaching placement. In accordance with time and budgetary constrictions, the first N=20 students to register interest in participating were invited to take part in an online interview. All invited students provided interviews, with a mean duration of 25 minutes. Interviews were transcribed verbatim, with redactions made only for participant identity protection. Transcripts were investigated coordinatively by the full research team using Reflexive Thematic Analysis. Results Analysis yielded four global themes. 1. Teamwork and Camaraderie; the collective experience engendered by the coaching model was widely lauded and cited as a source of confidence and support, though some participants were conscious that they were too often deferring to the more ‘experienced’ students in their group. 2. Leadership; all students cited opportunities to lead and delegate within their group as important to their professional development, though the experience of being led - and delegated to - by other students was more difficult for some than others. 3. Safety Nets; it was commonly asserted that the coaching model exposed both strengths and weaknesses in performance much more than one-to-one supervision, which was taken to simultaneously boost and undermine confidence. 4. Acceleration and Inertia; while all students argued that they initially learned more quickly in the group environment, a few contended that, as time passed, it began to hold them back. Conclusion(s) Findings indicated that although the coaching model was generally very popular with students, these successes did not come without caveats. Future research might specifically investigate links between these caveats and student profiles over a wider population. Impact These findings have clear import for nuancing in design of future coaching placements, particularly regarding how to maintain the strengths while further improving the student experience

Expanding physiotherapy placement capacity: Clinical Educators’ experiences of implementing a coaching approach to supervision

Purpose Increasing by 50% the UK’s capacity for training students in the Allied Health Professions (AHPs), as recently mandated by Health Education England, represents a significant challenge for universities and healthcare providers alike. This challenge is, perhaps, felt most acutely in the domain of placement provision, where resources are not necessarily available to support the clinical supervision of large numbers of additional students. In response to this, a trial ‘coaching’ model of clinical supervision in physiotherapy was introduced by the researchers across two NHS Trusts in the North of England in 2020 and 2021. Commonly used in the practical training of medical students, this entails extensive group-based learning activity, rather than the one-to-one approach traditional across most AHP areas. The research reported herein explores the experiences of Clinical Educators (CEs) in implementing this approach for the first time, with a view to more clearly understanding its impacts upon their own working practices and those within their departments. Methods The research team contacted all CEs who had (a) supervised one full cohort of students using the coaching model, while also (b) having prior experience of supervising using the traditional approach, inviting them to take part in an online semi-structured interview addressing their experiences. In line with pragmatic restraints, the first N=10 to register interest were formally recruited, and all provided interviews (with a mean duration of 31 minutes). These interviews were transcribed verbatim, with redactions made only where essential for the protection of participants’ identities. The full research team undertook investigation of the transcripts using Reflexive Thematic Analysis. Results Four global themes emerged from the data. 1. Oversight and Management; all participants maintained initial apprehension around the workload involved in monitoring a group of students rather than an individual. In practice, most found that the students’ monitoring and support of each other was highly effective. This ultimately provided the participants more time to work with individual problems, although some of these did relate to intra-group dynamics. 2. Teamworking and Learning; all participants found that they were largely facilitating learning, rather than being expected to simply ‘deliver’ it. Most students were reported to take stronger ownership of their own learning when working in teams, although those that did not could be proportionately more demanding on supervisory resources. 3. Patient Contact; universally, participants maintained that each student received more overall hands-on time with patients, and each patient received more overall physiotherapy, when the coaching approach was used. 4. Multi-Disciplinarity; while all students were reported to have profited in learning and confidence from greater opportunities to work with Multi-Disciplinary Teams, the participants described similar personal gains from having worked closely with university staff to coordinatively develop the coaching approach itself. Conclusion(s) Findings indicate that, despite initial misgivings, and some student teamworking difficulties that should not be overlooked, participants’ experiences of implementing the coaching approach were overwhelmingly positive, indicating clear benefits for their own workloads, student learning and patient contact. Impact This research indicates that the coaching approach is worth further investigation as a tool in expanding physiotherapy placement capacity

Bright OB stars in the Galaxy IV. Stellar and wind parameters of early to late B supergiants

We apply the NLTE atmosphere code FASTWIND to perform a spectroscopic study of a small sample of Galactic B-supergiants from B0 to B9. By means of the resulting data and incorporating additional datasets from alternative studies, we investigate the properties of OB-supergiants and compare our findings with theoretical predictions. As a result we find that due to the combined effects of line- and wind-blanketing, the temperature scale of Galactic B-supergiants needs to be revised downwards, by 10 to 20 percent, the latter value being appropriate for stronger winds. In fair accordance with recent results, our sample furthermore indicates a gradual decrease in wind terminal velocities over the bi-stability region, where the limits of this region are located at lower temperatures than the predicted ones. Introducing a distance-independent quantity Q' related to wind-strength, we also show that this quantity is a well defined, monotonically increasing function of Teff outside this region. Inside and from hot to cool, the mass loss rate changes by a factor (in between 0.4 and 2.5) which is (much) smaller than the predicted factor of 5. All this indicates that the decrease in wind terminal velocity over the bi-stability region is not over-compensated by an increase of mass loss rate, as frequently argued (provided the wind-clumping properties on both sides of this region do not differ substantially).Comment: 23 pages and 14 figures accepted for publication in A & A; the Fig. 1 title and the last para of Sec. 4.1 modified; a new reference adde

Nitrogen line spectroscopy in O-stars -- III. The earliest O-stars

This is the third paper in a series aiming at the analysis of nitrogen abundances in O-type stars, to enable further constraints on the early evolution of massive stars. We provide first theoretical predictions for the NIV4058/NIII4640 emission line ratio in dependence of various parameters, and confront them with results from the analysis of a sample of early LMC/SMC O-stars. Stellar and wind parameters are determined by line profile fitting of H/He/N lines, exploiting the helium and nitrogen ionization balance. Corresponding synthetic spectra are calculated using the NLTE atmospheric code FASTWIND. Though there is a monotonic relationship between the emission line ratio and Teff, all other parameters being equal, theoretical predictions indicate additional dependencies, most notably, on the nitrogen abundance. These basic predictions are confirmed by results from atmospheric code CMFGEN. The effective temperatures for the earliest O-stars, inferred from the nitrogen ionization balance, are partly considerably hotter than indicated by previous studies. Consistent with earlier results, effective temperatures increase from supergiants to dwarfs for all spectral types in the LMC. The relation between observed NIV4058/NIII4640 emission line ratio and Teff, for a given luminosity class, turned out to be quite monotonic for our sample stars, and fairly consistent with our model predictions. The scatter within a spectral sub-type is mainly produced by abundance effects. Our findings suggest that the Walborn et al. (2002) classification scheme is able to provide a meaningful relation between spectral type and Teff, provided that it is possible to discriminate for the luminosity class. This might be difficult to achieve in low-Z environments such as the SMC, owing to rather low wind-strengths. According to our predictions, the major bias of the classification scheme is due to nitrogen content.Comment: Main paper: 23 pages, 14 figures. Appendix: 20 pages, 20 figures. Accepted by Astronomy & Astrophysic