An alternative to mode fitting

The space mission CoRoT provides us with a large amount of high-duty cycle long-duration observations. Mode fitting has proven to be efficient for the complete and detailed analysis of the oscillation pattern, but remains time consuming. Furthermore, the photometric background due to granulation severely complicates the analysis. Therefore, we attempt to provide an alternative to mode fitting, for the determination of large separations. With the envelope autocorrelation function and a dedicated filter, it is possible to measure the variation of the large separation independently for the ridges with even and odd degrees. The method appears to be as accurate as the mode fitting. It can be very easily implemented and is very rapid.Comment: Proceedings of the 4th HELAS International Conference held in Lanzarote, 201

Sounding stellar cores with mixed modes

The space-borne missions CoRoT and Kepler have opened a new era in stellar physics, especially for evolved stars, with precise asteroseismic measurements that help determine precise stellar parameters and perform ensemble astero seismology. This paper deals with the quality of the information that we can retrieve from the oscillations. It focusses on the conditions for obtaining the most accurate measurement of the radial and non-radial oscillation patterns. This accuracy is a prerequisite for making the best with asteroseismic data. From radial modes, we derive proxies of the stellar mass and radii with an unprecedented accuracy for field stars. For dozens of subgiants and thousands of red giants, the identification of mixed modes (corresponding to gravity waves propagating in the core coupled to pressure waves propagating in the envelope) indicates unambiguously their evolutionary status. As probes of the stellar core, these mixed modes also reveal the internal differential rotation and show the spinning down of the core rotation of stars ascending the red giant branch. A toy model of the coupling of waves constructing mixed modes is exposed, for illustrating many of their features.Comment: Meeting: New advances in stellar physics: from microscopic to macroscopic processes Roscoff, 27-31 May 201

Testing the cores of first ascent red-giant stars using the period spacing of g modes

In the context of the determination of stellar properties using asteroseismology, we study the influence of rotation and convective-core overshooting on the properties of red-giant stars. We used models in order to investigate the effects of these mechanisms on the asymptotic period spacing of gravity modes ($\Delta \Pi_1$) of red-giant stars that ignite He burning in degenerate conditions (M$\lesssim$2.0 M$_{\odot}$). We also compare the predictions of these models with Kepler observations. For a given $\Delta\nu$, $\Delta \Pi_1$ depends not only on the stellar mass, but also on mixing processes that can affect the structure of the core. We find that in the case of more evolved red-giant-branch (RGB) stars and regardless of the transport processes occurring in their interiors, the observed $\Delta \Pi_1$ can provide information as to their stellar luminosity, within ~10-20%. In general, the trends of $\Delta \Pi_1$ with respect to mass and metallicity that are observed in Kepler red-giant stars are well reproduced by the models.Comment: 5pages, 6 figure

The red giants in NGC 6633 as seen with CoRoT, HARPS and SOPHIE

The open cluster NGC 6633 was observed with CoRoT in 2011 and simultaneous high-resolution spectroscopy was obtained with the SOPHIE and HARPS spectrographs. One of the four targets was not found to be a cluster member. For all stars we provide estimates of the seismic and spectroscopic parameters.Comment: Proc. of the workshop "Asteroseismology of stellar populations in the Milky Way" (Sesto, 22-26 July 2013), Astrophysics and Space Science Proceedings, (eds. A. Miglio, L. Girardi, P. Eggenberger, J. Montalban

Stellar oscillations - the adiabatic case

This lecture on adiabatic oscillations is intended to present the basis of asteroseismology and to serve as an introduction for other lectures of the EES 2014. It also exposes the state-of-the-art of solar-like oscillation analysis, as revealed by the space missions CoRoT and Kepler. A large part of the lecture is devoted to the interpretation of the modes with a mixed character that reveal the properties of the radiative cores of subgiants and red giants.Comment: 103 page

Inflammation and the coagulation system in tuberculosis: Tissue Factor leads the dance

Mycobacterium tuberculosis, the causative agent of tuberculosis, drives the formation of granulomas, structures in which both immune cells and the bacterial pathogen cohabit. The most abundant cells in granulomas are macrophages, which contribute as both cells with bactericidal activity and as targets for M. tuberculosis infection and proliferation during the entire course of infection. The mechanisms and factors involved in the regulation and control of macrophage microenvironment-specific polarization and plasticity are not well understood, as some granulomas are able to control bacteria growth and others fail to do so, permitting bacterial spread. In this issue of the European Journal of Immunology, Venkatasubramanian et al. [Eur. J. Immunol. 2016. 46: 464-479] show that mice lacking the tissue factor gene in myeloid cells have augmented M. tuberculosis growth and increased inflammation in the lungs. This suggests that tissue factor, an initiator of coagulation, is important for the generation of fibrin, which supports granuloma formation. This article demonstrates for the first time the involvement of tissue factor in inducing effective immunity against M. tuberculosis, and sheds new lights on the complex interplay between host inflammatory response, the coagulation system, and the control of M. tuberculosis infection

Gravity modes as a way to distinguish between hydrogen- and helium-burning red giant stars

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. Outstanding issues in our understanding of red giants include uncertainties in the amount of mass lost at the surface before helium ignition and the amount of internal mixing from rotation and other processes. Progress is hampered by our inability to distinguish between red giants burning helium in the core and those still only burning hydrogen in a shell. Asteroseismology offers a way forward, being a powerful tool for probing the internal structures of stars using their natural oscillation frequencies. Here we report observations of gravity-mode period spacings in red giants that permit a distinction between evolutionary stages to be made. We use high-precision photometry obtained with the Kepler spacecraft over more than a year to measure oscillations in several hundred red giants. We find many stars whose dipole modes show sequences with approximately regular period spacings. These stars fall into two clear groups, allowing us to distinguish unambiguously between hydrogen-shell-burning stars (period spacing mostly about 50 seconds) and those that are also burning helium (period spacing about 100 to 300 seconds).Comment: to appear as a Letter to Natur