We discuss properties of oscillatory convective modes in low-mass red giants, and compare them with observed properties of the long secondary periods (LSPs) of semi-regular red giant variables. Oscillatory convective modes are very nonadiabatic g$^{-}$ modes and they are present in luminous stars, such as red giants with $\log L/{\rm L}_\odot \ga 3$. Finite amplitudes for these modes are confined to the outermost nonadiabatic layers, where the radiative energy flux is more important than the convective energy flux. The periods of oscillatory convection modes increase with luminosity, and the growth times are comparable to the oscillation periods. The LSPs of red giants in the Large Magellanic Cloud (LMC) are observed to lie on a distinct period-luminosity sequence called sequence D. This sequence D period-luminosity relation is roughly consistent with the predictions for dipole oscillatory convective modes in AGB models if we adopt a mixing length of 1.2 pressure scale height ($α= 1.2$). However, the effective temperature of the red-giant sequence of the LMC is consistent to models with $α=1.9$, which predict periods too short by a factor of two.
Harmonic phase diagnostics of long secondary periods. Testing predictions of oscillatory convective dipole modes in the OGLE sample
European Southern Observatory（欧洲南方天文台）；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天文学与天体物理研究学院）；Australian Astronomical Optics & School of Mathematical and Physical Sciences, Macquarie University（麦考瑞大学天文光学与数理科学学院）
Interferometric view into RT Pav's long secondary period. binary vs oscillatory convective modes
European Southern Observatory（欧洲南方天文台）；Research School of Astronomy and Astrophysics, Australian National University（澳大利亚国立大学天文学与天体物理研究学院）；Institut d’Astronomie et d’Astrophysique, Université Libre de Bruxelles (ULB)（布鲁塞尔自由大学天文学与天体物理学研究所）；Astronomical Observatory, University of Warsaw（华沙大学天文台）；Institute of Astronomy, KU Leuven（荷语鲁汶大学天体物理研究所）；Departamento de Física, Universidad de Santiago de Chile（智利圣地亚哥大学物理系）；Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS), USACH（智利圣地亚哥大学天体物理与空间探索跨学科研究中心）
National Astronomical Observatory of Japan, National Institutes of Natural Sciences（日本国立天文台，国立自然科学研究院）；Department of Astronomy, Graduate University for Advanced Studies（高级研究院天文学系）
We discuss low-frequency g modes excited by resonant couplings with weakly unstable oscillatory convective modes in the rotating convective core in early-type main-sequence stars. Our non-adiabatic pulsation analyses including the effect of Coriolis force for $2\,M_\odot$ main-sequence models show that if the convective core rotates slightly faster than the surrounding radiative layers, g modes in the radiative envelope are excited by a resonance coupling. The frequency of the excited g mode in the inertial frame is close to $|mΩ_{\rm c}|$ with $m$ and $Ω_{\rm c}$ being the azimuthal order of …
The origin of long secondary periods (LSPs) in red giant variables is unknown. We investigate whether stellar pulsations in red giants can explain the properties of the LSP variability. VIJHKs light curves obtained by OGLE and the IRSF/SIRIUS survey in the Small Magellanic Cloud are examined. The sample of oxygen-rich LSP stars show evidence of a phase lag between the light curves of optical and near- IR band. The change in radius contributes the bolometric change roughly half as much as the change in temperature, implying that the change in effective temperature plays an important role in the…
We study the role of nonlinear effects on tidally-excited internal gravity waves in stellar radiation zones in exoplanetary or binary systems. We are partly motivated to study tides due to massive short-period hot Jupiters, which preferentially orbit stars with convective cores, for which wave breaking near the stellar centre cannot operate. We develop a theory (and test it with numerical calculations) for the nonlinear excitation of super-harmonic "secondary" waves (with frequencies $2ω_p$) by a "primary" tidal wave (with frequency $ω_p$) near the interface between the radiation zone and conv…
One of the most important problems in the context of cataclysmic variables (CVs) is the lack of observations of systems with periods between 2 and 3.12 hours, known as the period gap. The orbital evolution of CVs with periods shorter than those in the gap is dominated by gravitational radiation while for periods exceeding those of the gap it is dominated by magnetic braking of the secondary star. Spruit & Ritter (1983) showed that as periods approach 3 hours and secondary stars become fully convective a sharp decline in magnetic dynamo and braking efficiency would result in such a gap. Recent …
Radial differential rotation leading to dipole collapse in pre-main-sequence stars
Universitat Politècnica de Catalunya (UPC)（加泰罗尼亚理工大学）；Observatoire de Paris, Université PSL, Sorbonne Université, Université Paris cité, CY Cergy Paris Université, CNRS（巴黎天文台、巴黎文理研究大学、索邦大学、巴黎西岱大学、塞吉-蓬图瓦兹大学、法国国家科学研究中心）；Institut d’Astrophysique Spatiale, Université Paris-Saclay（空间天体物理研究所、巴黎萨克雷大学）
