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$^{-1}$), 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 $\delta$ Scuti and slowly pulsating B (SPB) star instability domains. Their variability periods, between $\sim$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 $\delta$~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 ($\nu_{max}$) and the large frequency separation ($\Delta\nu$). We use the distribution of $\nu_{max}$ and of $\Delta\nu$ 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 $\nu_{max}$ and of $\Delta\nu$ 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&

Physics of massive stars relevant for the modeling of Wolf-Rayet populations

Key physical ingredients governing the evolution of massive stars are mass losses, convection and mixing in radiative zones. These effects are important both in the frame of single and close binary evolution. The present paper addresses two points: 1) the differences between two families of rotating models, i.e. the family of models computed with and without an efficient transport of angular momentum in radiative zones; 2) The impact of the mass losses in single and in close binary models.Comment: 5 pages, 4 figures, to appear in the proceedings of the international Wolf-Rayet stars workshop held in Potsdam (2015