678 research outputs found
Understanding angular momentum transport in red giants: the case of KIC 7341231
Context. Thanks to recent asteroseismic observations, it has been possible to
infer the radial differential rotation profile of subgiants and red giants.
Aims. We want to reproduce through modeling the observed rotation profile of
the early red giant KIC 7341231 and constrain the physical mechanisms
responsible for angular momentum transport in stellar interiors.
Methods. We compute models of KIC 7341231 including a treatment of shellular
rotation and we compare the rotation profiles obtained with the one derived by
Deheuvels et al. (2012). We then modify some modeling parameters in order to
quantify their effect on the obtained rotation profile. Moreover, we mimic a
powerful angular momentum transport during the Main Sequence and study its
effect on the evolution of the rotation profile during the subgiant and red
giant phases.
Results. We show that meridional circulation and shear mixing alone produce a
rotation profile for KIC 7341231 too steep compared to the observed one. An
additional mechanism is then needed to increase the internal transport of
angular momentum. We find that this undetermined mechanism has to be efficient
not only during the Main Sequence but also during the much quicker subgiant
phase. Moreover, we point out the importance of studying the whole rotational
history of a star in order to explain its rotation profile during the red giant
evolution.Comment: 8 pages, 8 figures, 5 table
Massive star evolution in close binaries:conditions for homogeneous chemical evolution
We investigate the impact of tidal interactions, before any mass transfer, on
various properties of the stellar models. We study the conditions for obtaining
homogeneous evolution triggered by tidal interactions, and for avoiding any
Roche lobe overflow during the Main-Sequence phase. We consider the case of
rotating stars computed with a strong coupling mediated by an interior magnetic
field. In models without any tidal interaction (single stars and wide
binaries), homogeneous evolution in solid body rotating models is obtained when
two conditions are realized: the initial rotation must be high enough, the loss
of angular momentum by stellar winds should be modest. This last point favors
metal-poor fast rotating stars. In models with tidal interactions, homogeneous
evolution is obtained when rotation imposed by synchronization is high enough
(typically a time-averaged surface velocities during the Main-Sequence phase
above 250 km s), whatever the mass losses. In close binaries, mixing is
stronger at higher than at lower metallicities. Homogeneous evolution is thus
favored at higher metallicities. Roche lobe overflow avoidance is favored at
lower metallicities due to the fact that stars with less metals remain more
compact. We study also the impact of different processes for the angular
momentum transport on the surface abundances and velocities in single and close
binaries. In models where strong internal coupling is assumed, strong surface
enrichments are always associated to high surface velocities in binary or
single star models. In contrast, models computed with mild coupling may produce
strong surface enrichments associated to low surface velocities. Close binary
models may be of interest for explaining homogeneous massive stars, fast
rotating Wolf-Rayet stars, and progenitors of long soft gamma ray bursts, even
at high metallicities.Comment: 21 pages, 13 figures, 3 tables, accepted for publication in Astronomy
and Astrophysic
Thermohaline instability and rotation-induced mixing. III - Grid of stellar models and asymptotic asteroseismic quantities from the pre-main sequence up to the AGB for low- and intermediate-mass stars at various metallicities
The availability of asteroseismic constraints for a large sample of stars
from the missions CoRoT and Kepler paves the way for various statistical
studies of the seismic properties of stellar populations. In this paper, we
evaluate the impact of rotation-induced mixing and thermohaline instability on
the global asteroseismic parameters at different stages of the stellar
evolution from the Zero Age Main Sequence to the Thermally Pulsating Asymptotic
Giant Branch to distinguish stellar populations. We present a grid of stellar
evolutionary models for four metallicities (Z = 0.0001, 0.002, 0.004, and
0.014) in the mass range between 0.85 to 6.0 Msun. The models are computed
either with standard prescriptions or including both thermohaline convection
and rotation-induced mixing. For the whole grid we provide the usual stellar
parameters (luminosity, effective temperature, lifetimes, ...), together with
the global seismic parameters, i.e. the large frequency separation and
asymptotic relations, the frequency corresponding to the maximum oscillation
power {\nu}_{max}, the maximal amplitude A_{max}, the asymptotic period spacing
of g-modes, and different acoustic radii. We discuss the signature of
rotation-induced mixing on the global asteroseismic quantities, that can be
detected observationally. Thermohaline mixing whose effects can be identified
by spectroscopic studies cannot be caracterized with the global seismic
parameters studied here. But it is not excluded that individual mode
frequencies or other well chosen asteroseismic quantities might help
constraining this mixing.Comment: 15 pages, 11 figures, accepted for publication in A&
Are the stars of a new class of variability detected in NGC~3766 fast rotating SPB stars?
A recent photometric survey in the NGC~3766 cluster led to the detection of
stars presenting an unexpected variability. They lie in a region of the
Hertzsprung-Russell (HR) diagram where no pulsation are theoretically expected,
in between the Scuti and slowly pulsating B (SPB) star instability
domains. Their variability periods, between 0.1--0.7~d, are outside the
expected domains of these well-known pulsators. The NCG~3766 cluster is known
to host fast rotating stars. Rotation can significantly affect the pulsation
properties of stars and alter their apparent luminosity through gravity
darkening. Therefore we inspect if the new variable stars could correspond to
fast rotating SPB stars. We carry out instability and visibility analysis of
SPB pulsation modes within the frame of the traditional approximation. The
effects of gravity darkening on typical SPB models are next studied. We find
that at the red border of the SPB instability strip, prograde sectoral (PS)
modes are preferentially excited, with periods shifted in the 0.2--0.5~d range
due to the Coriolis effect. These modes are best seen when the star is seen
equator-on. For such inclinations, low-mass SPB models can appear fainter due
to gravity darkening and as if they were located between the ~Scuti and
SPB instability strips.Comment: 6 pages, 2 figures, to appear in the proceedings of the IAU Symposium
307, New windows on massive stars: asteroseismology, interferometry, and
spectropolarimetr
Asteroseismology of red-clump stars with CoRoT and Kepler
The availability of asteroseismic constraints for a large number of red
giants with CoRoT and in the near future with Kepler, paves the way for
detailed studies of populations of galactic-disk red giants. We investigate
which information on the observed population can be recovered by the
distribution of the observed seismic constraints: the frequency of maximum
power of solar-like oscillations () and the large frequency
separation (). We use the distribution of and of
observed by CoRoT in nearly 800 red giants in the first long
observational run, as a tool to investigate the properties of galactic
red-giant stars through the comparison with simulated distributions based on
synthetic stellar populations.
We can clearly identify the bulk of the red giants observed by CoRoT as
red-clump stars, i.e. post-flash core-He-burning stars. The distribution of
and of give us access to the distribution of the
stellar radius and mass, and thus represent a most promising probe of the age
and star formation rate of the disk, and of the mass-loss rate during the
red-giant branch.
This approach will be of great utility also in the interpretation of
forthcoming surveys of variability of red giants with CoRoT and Kepler. In
particular, an asteroseismic mass estimate of clump stars in the old-open
clusters observed by Kepler, would represent a most valuable observational test
of the poorly known mass-loss rate on the giant branch, and of its dependence
on metallicity.Comment: 5 pages, 6 figures, proceeding for "Stellar Pulsation: Challenges for
Theory and Observation", Santa Fe 200
Engagement of families in ICU from the nursing staff perspective
Background:
Family engagement in intensive care units (ICU) is proposed as a way to increase active partnership with patients and move away from paternalism (Burns et al 2018). Family engagement and family-centred care are closely linked to improve the quality of care. The term and practice of ‘family engagement’ is complex but Burns et al (2018) viewed patient and family engagement as a way to achieve family centred care. Promoting family engagement within the ICU setting is recognised as more challenging to nursing practice because of the added emotional aspects for families of acutely ill patients (Brown et al 2015).
This research was part of an international collaboration supported by the Family Care in Acute and Critical Illness Research Cluster which is supported by the International Family Nursing Association. This presentation will focus on the findings of the UK aspect of the research.
Research Question:
How do nurses from one English setting describe their nursing engagement with families of adults admitted in intensive care units?
Methods:
A social ecological approach (Bronfenbrenner, 1979) was used for this study. Social ecology acknowledges that families are complex groups that interact with other people and their world to provide meaning.
Data were collected including demographic information, individual semi-structured qualitative interviews which were transcribed, and a questionnaire ‘Factors That Influence Family Engagement (QFIFE)’ (Hetland, Hickman, McAndrew, & Daly, 2017).
One intensive care unit in the South East of England was used for this study. Permanent members of the nursing team were invited to participate. Analysis was undertaken using a statistic package (SPSS version 21) for questionnaire data and a content analysis approach for qualitative data.
Ethical approval was gained from the University and Gray Area Project approval from the healthcare organisation.
Results:
Seven participants completed all aspects of the data collection. All participants rated that family engagement was important. Engagement varied depending of the acuity of the patient with nurses deciding the level of family engagement at a particular point in the patient journey. As the patients’ illness stabilised the involvement of the family was promoted. The family engagement role can be described as observers, encouragers, supporter or active participants in patient care. Staff were particularly concerned about maintaining the safety of the patient during any family activities and developing good communication.
Initial analysis suggests that nurses regulate family engagement to ensure safety of patients and to promote recovery. Families need encouragement from ICU nurses to engage in a meaningful way. Building rapport and setting boundaries are skills needed by nurses and families value explanation of care.
Conclusions:
Family engagement needs careful consideration about the amount and type of activities that are appropriate and safe for families to undertake at a particular point. However, family engagement is seen as positive contribution to the patient recovery journey. This international project will continue to compare and combine results across the world. Consideration of future initiatives to family engagement in ICU will be further outlined
Stellar mass and age determinations - I. Grids of stellar models from Z=0.006 to 0.04 and M=0.5 to 3.5 Msun
We present dense grids of stellar models suitable for comparison with
observable quantities measured with great precision, such as those derived from
binary systems or planet-hosting stars. We computed new Geneva models without
rotation at metallicities Z=0.006, 0.01, 0.014, 0.02, 0.03 and 0.04 (i.e.
[Fe/H] from -0.33 to +0.54) and with mass in small steps from 0.5 to 3.5 Msun.
Great care was taken in the procedure for interpolating between tracks in order
to compute isochrones. Several properties of our grids are presented as a
function of stellar mass and metallicity. Those include surface properties in
the Hertzsprung-Russell diagram, internal properties including mean stellar
density, sizes of the convective cores, and global asteroseismic properties. We
checked our interpolation procedure and compared interpolated tracks with
computed tracks. The deviations are less than 1% in radius and effective
temperatures for most of the cases considered. We also checked that the present
isochrones provide nice fits to four couples of observed detached binaries and
to the observed sequences of the open clusters NGC 3532 and M67. Including
atomic diffusion in our models with M<1.1 Msun leads to variations in the
surface abundances that should be taken into account when comparing with
observational data of stars with measured metallicities. For that purpose,
iso-Zsurf lines are computed. These can be requested for download from a
dedicated web page together with tracks at masses and metallicities within the
limits covered by the grids. The validity of the relations linking Z and FeH is
also re-assessed in light of the surface abundance variations in low-mass
stars.Comment: Accepted for publication in A&
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