27 research outputs found
Tomographic Separation of Composite Spectra. VIII. The Physical Properties of the Massive Compact Binary in the Triple Star System HD 36486 (delta Orionis A)
Double-lined spectroscopic orbital elements have recently been found for the
central binary in the massive triple, delta Orionis A based on radial
velocities from cross-correlation techniques applied to IUE high dispersion
spectra and He I 6678 spectra obtained at Kitt Peak. The primary and secondary
velocity amplitudes were found to be 94.9 +/- 0.6 km/s and 186 +/- 9 km/s
respectively. Tomographic reconstructions of the primary and secondary stars'
spectra confirm the O9.5 II classification of the primary and indicate a B0.5
III type for the secondary. The widths of the UV cross-correlation functions
are used to estimate the projected rotational velocities, Vsin i = 157 +/- 6
km/s and 138 +/- 16 km/s for the primary and secondary, respectively implying
that both stars rotate faster than their orbital motion. We used the
spectroscopic results to make a constrained fit of the Hipparcos light curve of
this eclipsing binary, and the model fits limit the inclination to the range
between 67 and 77 degrees. The i = 67 degrees solution, which corresponds to a
near Roche-filling configuration, results in a primary mass of 11.2 solar
masses and a secondary mass of 5.6 solar masses, both of which are
substantially below the expected masses for stars of their luminosity. This
binary may have experienced a mass ratio reversal caused by Case A Roche lobe
overflow, or the system may have suffered extensive mass loss through a binary
interaction, perhaps during a common envelope phase, in which most of the
primary's mass was lost from the system rather than transferred to the
secondary.Comment: 27 pages, 15 figures in press, the Astrophysical Journal, February 1,
200
A quantitative study of O stars in NGC2244 and the Mon OB2 association
Our goal is to determine the stellar and wind properties of seven O stars in
the cluster NGC2244 and three O stars in the OB association MonOB2. These
properties give us insight into the mass loss rates of O stars, allow us to
check the validity of rotational mixing in massive stars, and to better
understand the effects of the ionizing flux and wind mechanical energy release
on the surrounding interstellar medium and its influence on triggered star
formation. We collect optical and UV spectra of the target stars which are
analyzed by means of atmosphere models computed with the code CMFGEN. The
spectra of binary stars are disentangled and the components are studied
separately. All stars have an evolutionary age less than 5 million years, with
the most massive stars being among the youngest. Nitrogen surface abundances
show no clear relation with projected rotational velocities. Binaries and
single stars show the same range of enrichment. This is attributed to the youth
and/or wide separation of the binary systems in which the components have not
(yet) experienced strong interaction. A clear trend of larger enrichment in
higher luminosity objects is observed, consistent with what evolutionary models
with rotation predict for a population of O stars at a given age. We confirm
the weakness of winds in late O dwarfs. In general, mass loss rates derived
from UV lines are lower than mass loss rates obtained from Ha. The UV mass loss
rates are even lower than the single line driving limit in the latest type
dwarfs. These issues are discussed in the context of the structure of massive
stars winds. The evolutionary and spectroscopic masses are in agreement above
25 Msun but the uncertainties are large. Below this threshold, the few
late-type O stars studied here indicate that the mass discrepancy still seems
to hold.Comment: 20 pages, 12 figures. A&A accepte
Instabilities in the Envelopes and Winds of Very Massive Stars
The high luminosity of Very Massive Stars (VMS) means that radiative forces
play an important, dynamical role both in the structure and stability of their
stellar envelope, and in driving strong stellar-wind mass loss. Focusing on the
interplay of radiative flux and opacity, with emphasis on key distinctions
between continuum vs. line opacity, this chapter reviews instabilities in the
envelopes and winds of VMS. Specifically, we discuss how: 1) the iron opacity
bump can induce an extensive inflation of the stellar envelope; 2) the density
dependence of mean opacity leads to strange mode instabilities in the outer
envelope; 3) desaturation of line-opacity by acceleration of near-surface
layers initiates and sustains a line-driven stellar wind outflow; 4) an
associated line-deshadowing instability leads to extensive small-scale
structure in the outer regions of such line-driven winds; 5) a star with
super-Eddington luminosity can develop extensive atmospheric structure from
photon bubble instabilities, or from stagnation of flow that exceeds the
"photon tiring" limit; 6) the associated porosity leads to a reduction in
opacity that can regulate the extreme mass loss of such continuum-driven winds.
Two overall themes are the potential links of such instabilities to Luminous
Blue Variable (LBV) stars, and the potential role of radiation forces in
establishing the upper mass limit of VMS.Comment: 44 pages, 13 figures. Chapter to appear in the book "Very Massive
Stars in the Local Universe", Springer, J.S. Vink, e
Spatially resolved STIS spectra of WR+OB binaries with colliding winds
We present spatially resolved spectra of the visual WR+OB massive binaries
WR86, WR146, and WR147, obtained with the Space Telescope Imaging Spectrograph
on board the Hubble Space Telescope. The systems are classified as follows:
WR86 = WC7 + B0 III, WR146 = WC6 + O8 I-IIf, WR147 = WN8 + O5-7 I-II(f). Both
WR146 and WR147 are known to have strong non-thermal radio emission arising in
a wind-wind collision shock zone between the WR and OB components. We find that
the spectra of their O companions show Halpha profiles in emission, indicative
of large mass-loss rates, and consistent with the colliding-wind model. Our
spectra indicate that the B component in WR86 has a low mass-loss rate, which
possibly explains the fact that WR86, despite being a long period WR+OB binary,
was not found to be a strong non-thermal radio emitter. Because of the small
mass-loss rate of the B star component in WR86, the wind collision region must
be closer to the B star and smaller in effective area, hence generating smaller
amounts of non-thermal radio emission. Absolute magnitudes for all the stars
are estimated based on the spectral types of the components (based on the
tables by Schmidt-Kaler for OB stars, and van der Hucht for WR stars), and
compared with actual, observed magnitude differences. While the derived
luminosities for the WC7 and B0 III stars in WR86 are consistent with the
observed magnitude difference, we find a discrepancy of at least 1.5 magnitudes
between the observed luminosities of the components in each of WR146 and WR147
and the absolute magnitudes expected from their spectral types. In both cases,
it looks as though either the WR components are about 2 magnitudes too bright
for their spectral types, or that the O components are about 2 magnitudes too
faint. We discuss possible explanations for this apparent discrepancy.Comment: Accepted for publication in the Astronomical Journa
L-band spectroscopy of Galactic OB-stars
Context. Mass-loss, occurring through radiation driven supersonic winds, is a
key issue throughout the evolution of massive stars. Two outstanding problems
are currently challenging the theory of radiation-driven winds: wind clumping
and the weak-wind problem. Aims. We seek to obtain accurate mass-loss rates of
OB stars at different evolutionary stages to constrain the impact of both
problems in our current understanding of massive star winds. Methods. We
perform a multi-wavelength quantitative analysis of a sample of ten Galactic
OB-stars by means of the atmospheric code CMFGEN, with special emphasis on the
L-band window. A detailed investigation is carried out on the potential of
Br\alpha\ and Pf\gamma\ as mass-loss and clumping diagnostics. Results. For
objects with dense winds, Br\alpha\ samples the intermediate wind while
Pf\gamma\ maps the inner one. In combination with other indicators (UV,
H\alpha, Br\gamma) these lines enable us to constrain the wind clumping
structure and to obtain "true" mass-loss rates. For objects with weak winds,
Br\alpha\ emerges as a reliable diagnostic tool to constrain the mass-loss
rates. The emission component at the line Doppler-core superimposed on the
rather shallow Stark absorption wings reacts very sensitively to mass loss
already at very low mass-loss values. On the other hand, the line wings display
similar sensitivity to mass loss as H\alpha, the classical optical mass loss
diagnostics. Conclusions. Our investigation reveals the great diagnostic
potential of L-band spectroscopy to derive clumping properties and mass-loss
rates of hot star winds. We are confident that Br\alpha\ will become the
primary diagnostic tool to measure very low mass-loss rates with unprecedented
accuracyComment: Accepted by A&
The most massive stars in the Arches cluster
We study a sample composed of 28 of the brightest stars in the Arches
cluster. We analyze K-band spectra obtained with the integral field
spectrograph SINFONI on the VLT. Atmosphere models computed with the code
CMFGEN are used to derive the effective temperatures, luminosities, stellar
abundances, mass loss rates and wind terminal velocities. We find that the
stars in our sample are either H-rich WN7-9 stars (WN7-9h) or O supergiants,
two being classified as OIf+. All stars are 2-4 Myr old. There is marginal
evidence for a younger age among the most massive stars. The WN7-9h stars reach
luminosities as large as 2 x 1e6 Lsun, consistent with initial masses of ~ 120
Msun. They are still quite H-rich, but show both N enhancement and C depletion.
They are thus identified as core H-burning objects showing products of the CNO
equilibrium at their surface. Their progenitors are most likely supergiants of
spectral types earlier than O4-6 and initial masses > 60 Msun. Their winds
follow a well defined modified wind momentum - luminosity relation (WLR): this
is a strong indication that they are radiatively driven. Stellar abundances
tend to favor a slightly super solar metallicity, at least for the lightest
metals. We note however that the evolutionary models seem to under-predict the
degree of N enrichment.Comment: 19 pages, 15 figures. A&A accepte
The Effect of Particulate Air Pollution on Emergency Admissions for Myocardial Infarction: A Multicity Case-Crossover Analysis
Recently, attention has focused on whether particulate air pollution is a specific trigger of myocardial infarction (MI). The results of several studies of single locations assessing the effects of ambient particular matter on the risk of MI have been disparate. We used a multicity case-crossover study to examine risk of emergency hospitalization associated with fine particulate matter (PM) with aerodynamic diameter < 10 μm (PM(10)) for > 300,000 MIs during 1985–1999 among elderly residents of 21 U.S. cities. We used time-stratified controls matched on day of the week or on temperature to detect possible residual confounding by weather. Overall, we found a 0.65% [95% confidence interval (CI), 0.3–1.0%] increased risk of hospitalization for MI per 10 μg/m(3) increase in ambient PM(10) concentration. Matching on apparent temperature yielded a 0.64% increase in risk (95% CI, 0.1–1.2%). We found that the effect size for PM(10) doubled for subjects with a previous admission for chronic obstructive pulmonary disease or a secondary diagnosis of pneumonia, although these differences did not achieve statistical significance. There was a weaker indication of a larger effect on males but no evidence of effect modification by age or the other diagnoses. We also found that the shape of the exposure–response relationship between MI hospitalizations and PM(10) is almost linear, but with a steeper slope at levels of PM(10) < 50 μg/m(3). We conclude that increased concentrations of ambient PM(10) are associated with increased risk of MI among the elderly
Facilitating family needs and support at the end of life in hospital: A descriptive study
Background:
Caring for family members of dying patients is a vital component of end-of-life care, yet family members’ needs at the end of life may be unmet.
Aim:
To explore hospital clinician assessment and facilitation of family needs and practices to support families at the end of life.
Design:
Descriptive study utilising a retrospective medical record audit.
Setting and Sample:
Undertaken in a large public hospital, the sample included 200 deceased patients from four specialities; general medicine (n = 50), intensive care (n = 50), inpatient palliative care (n = 50) and aged rehabilitation (n = 50). Data were analysed according to age; under 65-years and 65-years or over.
Results:
Deceased patients’ mean age was 75-years, 60% were Christian and Next-of-Kin were documented in 96% of cases. 79% spoke English, yet interpreters were used in only 6% of cases. Formal family meetings were held in 64% of cases. An assessment of family needs was undertaken in 52% of cases, and more likely for those under 65-years (p = 0.027). Cultural/religious practices were supported/facilitated in only 6% of all cases. Specialist palliative care involvement was more likely for those aged 65-years or over (p = 0.040) and social work involvement more likely for those under 65-years (p = 0.002). Pastoral care and bereavement support was low across the whole sample.
Conclusions:
Prioritising family needs should be core to end-of-life care. Anticipation of death should trigger routine referral to support personnel/services to ensure practice is guided by family needs. More research is needed to evaluate how family needs assessment can inform end-of-life care, supported by policy
An XMM-Newton observation of the Lagoon Nebula and the very young open cluster NGC 6530
We report the results of an XMM-Newton observation of the Lagoon Nebula (M8). Our EPIC images of this region reveal a cluster of point sources, most of which have optical counterparts inside the very young open cluster NGC6530. The bulk of these X-ray sources are probably associated with low and intermediate mass pre-main sequence stars. One of the sources experienced a flare-like increase of its X-ray flux making it the second brightest source in M8 after the O4 star 9 Sgr. The X-ray spectra of most of the brightest sources can be fitted with thermal plasma models with temperatures of kT similar to a few keV. Only a few of the X-ray selected PMS candidates are known to display Halpha emission and were previously classified as classical T Tauri stars. This suggests that most of the X-ray emitting PMS stars in NGC6530 are weak-line T Tauri stars. In addition to 9 Sgr, our EPIC field of view contains also a few early-type stars. The X-ray emission from HD 164816 is found to be typical for an O9.5 III-IV star. At least one of the known Herbig Be stars in NGC6530 ( LkHalpha 115) exhibits a relatively strong X-ray emission, while most of the main sequence stars of spectral type B1 and later are not detected. We also detect ( probably) diffuse X-ray emission from the Hourglass Region that might reveal a hot bubble blown by the stellar wind of Herschel 36, the ionizing star of the Hourglass Region