X-ray Emission from Magnetically Torqued Disks of Oe/Be Stars

We focus attention on the Oe/Be stars to test the concept that the disks of these stars form by magnetic channeling of wind material toward the equator. Calculations are made of the X-rays expected from the Magnetically Torqued Disk (MTD) model for Be stars discussed by Cassinelli et al. (2002), by Maheswaran (2003), and by Brown et al. (2004). The dominant parameters in the model are the $\beta$ value of the velocity law, the rotation rate of the star, $S_o$, and the ratio of the magnetic field energy density to the disk gravitational energy density, $\gamma$. The model predictions are compared with the $ROSAT$ observations obtained for an O9.5 star $\zeta$ Oph from \Berghofer et al. (1996) and for 7 Be stars from Cohen et al. (1997). Extra considerations are also given here to the well studied Oe star $\zeta$ Oph for which we have $Chandra$ observations of the X-ray line profiles of the triad of He-like lines from the ion Mg XI.Comment: 28 pages with 6 figures. Accepted for publication in Ap

New Challenges For Wind Shock Models: The Chandra Spectrum Of The Hot Star Delta Orionis

The Chandra spectrum of delta Ori A shows emission lines from hydrogen- and helium-like states of Si, Mg, Ne, and O, along with N VII Lyalpha and lines from ions in the range Fe XVII-Fe XXI In contrast to the broad lines seen in zeta Pup and zeta Ori (850 +/- 40 and 1000 +/- 240 km s(-1) half-width at half-maximum [HWHM], respectively), these lines are broadened to only 430 +/- 60 km s(-1) HWHM. This is much lower than the measured wind terminal velocity of 2000 km s(-1). The forbidden, intercombination, and resonance (fir) lines from He-like ions indicate that the majority of the X-ray line emission does not originate at the base of the wind, in agreement with the standard wind shock models for these objects. However, in that model the X-ray emission is distributed throughout an expanding, X-ray-absorbing wind, and it is therefore surprising that the emission lines appear relatively narrow, unshifted, and symmetric. We compare the observed line profiles to recent detailed models for X-ray line pro le generation in hot stars, but none of them offers a fully satisfactory explanation for the observed line profiles

The Effects of Clumps in Explaining X-ray Emission Lines from Hot Stars

It is now well established that stellar winds of hot stars are fragmentary and that the X-ray emission from stellar winds has a strong contribution from shocks in winds. Chandra high spectral resolution observations of line profiles of O and B stars have shown numerous properties that had not been expected. Here we suggest explanations by considering the X-rays as arising from bow shocks that occur where the stellar wind impacts on spherical clumps in the winds. We use an accurate and stable numerical hydrodynamical code to obtain steady-state physical conditions for the temperature and density structure in a bow shock. We use these solutions plus analytic approximations to interpret some major X-ray features: the simple power-law distribution of the observed emission measure derived from many hot star X-ray spectra and the wide range of ionization stages that appear to be present in X-ray sources throughout the winds. Also associated with the adiabatic cooling of the gas around a clump is a significant transverse velocity for the hot plasma flow around the clumps, and this can help to understand anomalies associated with observed line widths, and the differences in widths seen in stars with high and low mass-loss rates. The differences between bow shocks and the planar shocks that are often used for hot stars are discussed. We introduce an ``on the shock'' (OTSh) approximation that is useful for interpreting the X-rays and the consequences of clumps in hot star winds and elsewhere in astronomy.Comment: to appear in the Astrophysical Journa

High Resolution X-ray Spectra of the Brightest OB Stars in the Cygnus OB2 Association

The Cygnus OB2 Association contains some of the most luminous OB stars in our Galaxy, the brightest of which are also among the most luminous in X-rays. We have obtained a Chandra High Energy Transmission Grating Spectrometer (HETGS) observation centered on Cyg OB2 No. 8a, the most luminous X-ray source in the Association. Although our analysis will focus on the X-ray properties of Cyg OB2 No. 8a, we also present limited analyses of three other OB stars (Cyg OB2 Nos. 5, 9, and 12). Applying standard diagnostic techniques as used in previous studies of early-type stars, we find that the X-ray properties of Cyg OB2 No. 8a are very similar to those of other OB stars that have been observed using high-resolution X-ray spectroscopy. From analyses of the He-like ion "fir" emission lines, we derive radial distances of the He-like line emission sources and find these fir-inferred radii are consistent with their corresponding X-ray continuum optical depth unity radii. Contrary to other O-star results, the emission lines of Cyg OB2 No. 8a show a large range in line centroid shifts (roughly -800 to +250 km/s). We discuss the implications of our results in light of the fact that Cyg OB2 No. 8a is a member of a rather tight stellar cluster, and shocks could arise at interfaces with the winds of these other stars.Comment: 36 pages (including 4 tables and 12 figures). LaTeX. Submitted to Ap

X-Atlas: An Online Archive of Chandra's Stellar High Energy Transmission Gratings Observations

The high-resolution X-ray spectroscopy made possible by the 1999 deployment of the Chandra X-ray Observatory has revolutionized our understanding of stellar X-ray emission. Many puzzles remain, though, particularly regarding the mechanisms of X-ray emission from OB stars. Although numerous individual stars have been observed in high-resolution, realizing the full scientific potential of these observations will necessitate studying the high-resolution Chandra dataset as a whole. To facilitate the rapid comparison and characterization of stellar spectra, we have compiled a uniformly processed database of all stars observed with the Chandra High Energy Transmission Grating (HETG). This database, known as X-Atlas, is accessible through a web interface with searching, data retrieval, and interactive plotting capabilities. For each target, X-Atlas also features predictions of the low-resolution ACIS spectra convolved from the HETG data for comparison with stellar sources in archival ACIS images. Preliminary analyses of the hardness ratios, quantiles, and spectral fits derived from the predicted ACIS spectra reveal systematic differences between the high-mass and low-mass stars in the atlas and offer evidence for at least two distinct classes of high-mass stars. A high degree of X-ray variability is also seen in both high and low-mass stars, including Capella, long thought to exhibit minimal variability. X-Atlas contains over 130 observations of approximately 25 high-mass stars and 40 low-mass stars and will be updated as additional stellar HETG observations become public. The atlas has recently expanded to non-stellar point sources, and Low Energy Transmission Grating (LETG) observations are currently being added as well

\u27It promoted a positive culture around falls prevention\u27: staff response to a patient education programme—a qualitative evaluation

Objectives: The purpose of this study was to understand how staff responded to individualized patient falls prevention education delivered as part of a cluster randomised trial, including how they perceived the education contributed to falls prevention on their wards. Design: A qualitative explanatory study. Methods: 5 focus groups were conducted at participatory hospital sites. The purposive sample of clinical staff (including nurses, physiotherapists and quality improvement staff ) worked on aged care rehabilitation wards when a cluster randomised trial evaluating a patient education programme was conducted. During the intervention period, an educator, who was a trained health professional and not a member of staff, provided individualised falls prevention education to patients with good levels of cognition (Mini-Mental State Examination \u3e23/30). Clinical staff were provided with training to support the programme and their feedback was sought after the trial concluded, to understand how they perceived the programme impacted on falls prevention. Data were thematically analysed using NVivo qualitative data analysis software. Results: 5 focus groups were conducted at different hospitals (n=30 participants). Staff perceived that the education created a positive culture around falls prevention and further, facilitated teamwork, whereby patients and staff worked together to address falls prevention. The educator was perceived to be a valuable member of the team. Staff reported that they developed increased knowledge and awareness about creating a safe ward environment. Patients being proactive and empowered to engage in falls prevention strategies, such as ringing the bell for assistance, was viewed as supporting staff falls prevention efforts and motivating staff to change practice. Conclusions: Staff responded positively to patient falls prevention education being delivered on their wards. Providing individualised patient education to older patients with good levels of cognition can empower staff and patients to work as a team to address falls prevention on hospital rehabilitation wards

Educators’ perspectives about how older hospital patients can engage in a falls prevention education programme: a qualitative process evaluation

Objectives - Falls are the most frequent adverse event reported in hospitals. Patient and staff education delivered by trained educators significantly reduced falls and injurious falls in an older rehabilitation population. The purpose of the study was to explore the educators’ perspectives of delivering the education and to conceptualise how the programme worked to prevent falls among older patients who received the education. Design - A qualitative exploratory study. Methods - Data were gathered from three sources: conducting a focus group and an interview (n=10 educators), written educator notes and reflective researcher field notes based on interactions with the educators during the primary study. The educators delivered the programme on eight rehabilitation wards for periods of between 10 and 40 weeks. They provided older patients with individualised education to engage in falls prevention and provided staff with education to support patient actions. Data were thematically analysed and presented using a conceptual framework. Results - Falls prevention education led to mutual understanding between staff and patients which assisted patients to engage in falls prevention behaviours. Mutual understanding was derived from the following observations: the educators perceived that they could facilitate an effective three-way interaction between staff actions, patient actions and the ward environment which led to behaviour change on the wards. This included engaging with staff and patients, and assisting them to reconcile differing perspectives about falls prevention behaviours. Conclusions - Individualised falls prevention education effectively provides patients who receive it with the capability and motivation to develop and undertake behavioural strategies that reduce their falls, if supported by staff and the ward environment

It promoted a positive culture around falls prevention': Staff response to a patient education programme-a qualitative evaluation

Objectives: The purpose of this study was to understand how staff responded to individualised patient falls prevention education delivered as part of a cluster randomised trial, including how they perceived the education contributed to falls prevention on their wards. Design: A qualitative explanatory study. Methods: 5 focus groups were conducted at participatory hospital sites. The purposive sample of clinical staff (including nurses, physiotherapists and quality improvement staff) worked on aged care rehabilitation wards when a cluster randomised trial evaluating a patient education programme was conducted. During the intervention period, an educator, who was a trained health professional and not a member of staff, provided individualised falls prevention education to patients with good levels of cognition (Mini-Mental State Examination >23/30). Clinical staff were provided with training to support the programme and their feedback was sought after the trial concluded, to understand how they perceived the programme impacted on falls prevention. Data were thematically analysed using NVivo qualitative data analysis software. Results: 5 focus groups were conducted at different hospitals (n=30 participants). Staff perceived that the education created a positive culture around falls prevention and further, facilitated teamwork, whereby patients and staff worked together to address falls prevention. The educator was perceived to be a valuable member of the team. Staff reported that they developed increased knowledge and awareness about creating a safe ward environment. Patients being proactive and empowered to engage in falls prevention strategies, such as ringing the bell for assistance, was viewed as supporting staff falls prevention efforts and motivating staff to change practice.Conclusions: Staff responded positively to patient falls prevention education being delivered on their wards. Providing individualised patient education to older patients with good levels of cognition can empower staff and patients to work as a team to address falls prevention on hospital rehabilitation wards

A Coordinated X-ray and Optical Campaign of the Nearby Massive Binary δ\delta Orionis Aa: II. X-ray Variability

We present time-resolved and phase-resolved variability studies of an extensive X-ray high-resolution spectral dataset of the $\delta$ Orionis Aa binary system. The four observations, obtained with Chandra ACIS HETGS, have a total exposure time of ~479 ks and provide nearly complete binary phase coverage. Variability of the total X-ray flux in the range 5-25 $\AA$ is confirmed, with maximum amplitude of about +/-15% within a single ~125 ks observation. Periods of 4.76d and 2.04d are found in the total X-ray flux, as well as an apparent overall increase in flux level throughout the 9-day observational campaign. Using 40 ks contiguous spectra derived from the original observations, we investigate variability of emission line parameters and ratios. Several emission lines are shown to be variable, including S XV, Si XIII, and Ne IX. For the first time, variations of the X-ray emission line widths as a function of the binary phase are found in a binary system, with the smallest widths at phase=0.0 when the secondary $\delta$ Orionis Aa2 is at inferior conjunction. Using 3D hydrodynamic modeling of the interacting winds, we relate the emission line width variability to the presence of a wind cavity created by a wind-wind collision, which is effectively void of embedded wind shocks and is carved out of the X-ray-producing primary wind, thus producing phase-locked X-ray variability.Comment: 36 pages, 14 Tables, 19 Figures, accepted by ApJ, one of 4 related papers to be published togethe