Maria Pia di Mauro

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 by 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 ∼50 seconds) and those that are also burning helium (period spacing ∼100 to 300 seconds).

OSCILLATING RED GIANTS OBSERVED DURING CAMPAIGN 1 OF THE KEPLER K2 MISSION: NEW PROSPECTS FOR GALACTIC ARCHAEOLOGY

NASA’s re-purposed Kepler mission ‐ dubbed K2 ‐ has brought new scientific opportunitie s that were not anticipated for the original Kepler mission. One science goal that makes optimal use of K2’s capa bilities, in particular its 360-degree ecliptic field of view, is galacti c archaeology ‐ the study of the evolution of the Galaxy from the fossil stellar record. The thrust of this research i s to exploit high-precision, time-resolved photometry from K2 in order to detect oscillations in red giant stars. Th is asteroseismic information can provide estimates of stellar radius (hence distance), mass and age of vast numbers of stars across the Galaxy. Here we present the initial analysis of a subset of red giants, observed towards the North Galactic Gap, during the mission’s first full science campaign. We investigate the feasibility of us ing K2 data for detecting oscillations in red giants that span a range in apparent magnitude and evolutionary state (hence intrinsic luminosity). We demonstrate that oscillations are detectable for essentially all cool g iants within the logg range � 1.9‐3.2. Our detection is complete down to Kp � 14.5, which results in a seismic sample with little or no detectio n bias. This sample is ideally suited to stellar population studies that seek to investigate potential shortcomings of contemporary Galaxy models. Subject headings:stars: fundamental parameters — stars: oscillations — stars: interiors

Synergies between solar and stellar modelling

Asteroseismology of solar and stellar models.- New results on standard solar models.- Low heavy-element photospheric abundance: a challenge for solar modeling.- Comparisons between stellar models and reliability of the theoretical models.- Modeling the solar irradiance background via numerical simulation.- Helioseismology as a diagnostic of the solar interior.- Prospects for asteroseismology.- How asteroseismology can constrain the global parameters of solar-like star models.- Asteroseismology and the degeneracy of model solutions for subgiant stars.- Determining stellar radii using large separations: an error analysis.- The red-giant CoRoT target HR?7349.- ??Cas: a new candidate ??Cephei star. Atmospheric characterization and variability analysis.- CoRoT 102931335: a candidate ? Dor in an eclipsing binary.- A complex asteroseismic study of the hybrid B-type pulsator ? Eridani.- Asteroseismic modelling of the solar-like star ? Hydri.- Spectroscopic mode identification of main-sequence non-radially pulsating stars.- The PMS ? Scuti star PDS2.- Investigating the semi-regular light variations of the bright M5 supergiant: ? Herculis.- CoRoT observations of the young open cluster Dolidze 25.- Pulsation period changes as a tool to identify pre-zero age horizontal branch stars.- Semiconvective mixing in low-mass stars.- Sensitivity of the sub-photospheric flow fields inferred from ring-diagram analysis to the change on the solar model.- Accurate and versatile equations of state for the Sun and Sun-like stars.- Application of SAHA-S EOS to solar modeling.- Dynamic screening in solar and stellar nuclear reactions.- Charged-particle induced thermonuclear reaction rates of 3He(3He,2p)4He, 3He(4He,?)7Be and 7Be(p,?)8B by using the exact tunneling probability.- Effects of new nuclear reaction rates on the solar neutrino fluxes.- The role of the equation of state in models of very low-mass stars.- Elemental diffusion and segregation processes in partially ionized solar plasma.- Emulating the OPAL equation of state.- The chemical composition of the Sun.- The chemical composition of solar-type stars in comparison with that of the Sun.- The solar, exoplanet and cosmological lithium problems.- Helium and metal diffusion in the Sun and in cluster stars.- Radiative accelerations, accumulation of iron and thermohaline convection inside stars.- Convection in stellar models.- Some properties of the kinetic energy flux and dissipation in turbulent stellar convection zones.- Overshooting and semiconvection: structural changes and asteroseismic signatures.- Stellar turbulence and mode physics.- Numerical simulations of the ?-mechanism with convection.- Stochastic excitation of gravity modes in massive main-sequence stars.- New insights on the interior of solar-like pulsators thanks to CoRoT: the case of HD 49385.- Smooth models of overshooting at the base of the solar convective zone.- The solar differential rotation: a historical view.- A semi-analytic approach to angular momentum transport in stellar radiative interiors.- Effect of stellar rotation on oscillation frequencies.- 2-D models of rapidly rotating stars.- 2D solar modeling.- The butterfly diagram internal structure.- The discontinuous nature of chromospheric-activity evolution.- Future instrumentation for solar physics: a double channel MOF imager on board ASI Space Mission ADAHELI.- A new opportunity from space: PLATO mission.- Planning magneto-optical filters for the study of magnetic oscillations of the Sun.- Synthetic stellar and SSP libraries as templates for Gaia simulations.- Differential photometry of ? Scuti stars at Maidanak observatory.- Unveiling stellar cores via their flattening.- Interpreting the solar cycle changes in p-mode velocity amplitudes as seen in Sun-as-a-star observations.- Nuclear reactions.

A Study of the Solar-Like Properties of β Hydri

We investigate properties of the internal structure of HR2021, better known as β Hydri, a G2 IV subgiant with mass close to solar and for which observations by Bedding et al. (2001) have shown the presence of solar-like oscillations. We have computed models of β Hydri, based on updated global parameters, and compared the computed frequencies for the models with the observed oscillation spectrum.

The Rotational Shear Layer inside the Early Red-giant Star KIC 4448777

We present the asteroseismic study of the early red-giant star KIC 4448777, complementing and integrating a previous work (Di Mauro et al. 2016), aimed at characterizing the dynamics of its interior by analyzing the overall set of data collected by the {\it Kepler} satellite during the four years of its first nominal mission. We adopted the Bayesian inference code DIAMOND (Corsaro \& De Ridder 2014) for the peak bagging analysis and asteroseismic splitting inversion methods to derive the internal rotational profile of the star. The detection of new splittings of mixed modes, more concentrated in the very inner part of the helium core, allowed us to reconstruct the angular velocity profile deeper into the interior of the star and to disentangle the details better than in Paper I: the helium core rotates almost rigidly about 6 times faster than the convective envelope, while part of the hydrogen shell seems to rotate at a constant velocity about 1.15 times lower than the He core. In particular, we studied the internal shear layer between the fast-rotating radiative interior and the slow convective zone and we found that it lies partially inside the hydrogen shell above

Interpretation of the solar-like pulsational behaviour of η Bootis

r \simeq 0.05R

Differential rotation of the solar interior: new helioseismic results by inversion of the SOI-MDI/SOHO data

and extends across the core-envelope boundary. Finally, we theoretically explored the possibility for the future to sound the convective envelope in the red-giant stars and we concluded that the inversion of a set of splittings with only low-harmonic degree

Rotation of the Solar Interior: New Results by Helioseismic Data Inversions

l\leq 3

Mass and angular momentum loss of the Sun by magnetically driven winds

, even supposing a very large number of modes, will not allow to resolve the rotational profile of this region in detail.