GONG p-Mode Parameters Through Two Solar Cycles.

We investigate the parameters of global solar p-mode oscillations, namely damping width Γ , amplitude A , mean squared velocity 〈 v 2 〉 , energy E , and energy supply rate d E / d t , derived from two solar cycles' worth (1996 - 2018) of Global Oscillation Network Group (GONG) time series for harmonic degrees l = 0 - 150 . We correct for the effect of fill factor, apparent solar radius, and spurious jumps in the mode amplitudes. We find that the amplitude of the activity-related changes of Γ and A depends on both frequency and harmonic degree of the modes, with the largest variations of Γ for modes with 2400 µ Hz ≤ ν ≤ 3300 µ Hz and 31 ≤ l ≤ 60 with a minimum-to-maximum variation of 26.6 ± 0.3 % and of A for modes with 2400 µ Hz ≤ ν ≤ 3300 µ Hz and 61 ≤ l ≤ 100 with a minimum-to-maximum variation of 27.4 ± 0.4 % . The level of correlation between the solar radio flux F 10.7 and mode parameters also depends on mode frequency and harmonic degree. As a function of mode frequency, the mode amplitudes are found to follow an asymmetric Voigt profile with ν max = 3073.59 ± 0.18 µ Hz . From the mode parameters, we calculate physical mode quantities and average them over specific mode frequency ranges. In this way, we find that the mean squared velocities 〈 v 2 〉 and energies E of p modes are anticorrelated with the level of activity, varying by 14.7 ± 0.3 % and 18.4 ± 0.3 % , respectively, and that the mode energy supply rates show no significant correlation with activity. With this study we expand previously published results on the temporal variation of solar p-mode parameters. Our results will be helpful to future studies of the excitation and damping of p modes, i.e., the interplay between convection, magnetic field, and resonant acoustic oscillations.

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).