A He3 driven instability near the fully convective boundary

Abstract

We report on the discovery of an instability in low mass stars just above the threshold ($\sim 0.35{\text{M}}_{\odot }$) where they are expected to be fully convective on the main sequence. Non-equilibrium He3 burning creates a convective core, which is separated from a deep convective envelope by a small radiative zone. The steady increase in central He3 causes the core to grow until it touches the surface convection zone, which triggers fully convective episodes in what we call the "convective kissing instability". These episodes lower the central abundance and cause the star to return to a state in which is has a separate convective core and envelope. These periodic events eventually cease when the He3 abundance throughout the star is sufficiently high that the star is fully convective, and remains so for the rest of its main sequence lifetime. The episodes correspond to few percent changes in radius and luminosity, over Myr to Gyr timescales. We discuss the physics of the instability, as well as prospects for detecting its signatures in open clusters and wide binaries. Secondary stars in cataclysmic variables (CVs) will pass through this mass range, and this instability could be related to the observed paucity of such systems for periods between two and three hours. We demonstrate that the instability can be generated for CV secondaries with mass-loss rates of interest for such systems, and discuss potential implications.

6 pages, 3 figures. Submitted to ApJ. For a brief video explaining the key result of this paper, see http://www.youtube.com/user/OSUAstronomy

References in corpus (4)

• Modules for Experiments in Stellar Astrophysics (MESA)
• The Evolution of Cataclysmic Variables as Revealed by their Donor Stars
• An asteroseismic study of the O9V star HD 46202 from CoRoT space-based photometry
• OPserver: interactive online-computations of opacities and radiative accelerations

Cited by in corpus (29)

• Modules for Experiments in Stellar Astrophysics (MESA): Giant Planets, Oscillations, Rotation, and Massive Stars
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• A discontinuity in the $T_{\mathrm{eff}}$-radius relation of M-dwarfs
• A closer look at the transition between fully convective and partly radiative low mass stars
• TOI-5205 b: A Short-period Jovian Planet Transiting a Mid-M Dwarf
• The relative emission from chromospheres and coronae: dependence on spectral type and age
• Bridging the gap -- the disappearance of the intermediate period gap for fully convective stars, uncovered by new ZTF rotation periods
• Gaia Gaps and the Physics of Low-Mass Stars. I. The Fully Convective Boundary
• Star-in-a-box simulations of fully convective stars
• TOI-3235 b: a transiting giant planet around an M4 dwarf star
• An explanation for the gap in the Gaia HRD for M dwarfs
• Stellar Cycles in Fully Convective Stars and a New Interpretation of Dynamo Evolution
• Astrophysical properties of 600 bonafide single stars in the Hyades open cluster
• Benchmarking MESA isochrones against the Hyades single star sequence
• Stellar Characterization and Radius Inflation of Hyades M Dwarf Stars From the APOGEE Survey
• The LHS 1678 System: Two Earth-Sized Transiting Planets and an Astrometric Companion Orbiting an M Dwarf Near the Convective Boundary at 20 pc
• Rotation at the Fully Convective Boundary: Insights from Wide WD + MS Binary Systems
• Bridging the Gap between Intermediate and Massive Stars I: Validation of MESA against the State-of-the-Art Monash Stellar Evolution Program for a 2$M_{\odot }$ AGB Star
• Mind the Gap I: H$\alpha$ Activity of M Dwarfs Near the Partially/Fully Convective Boundary and a New H$\alpha$ Emission Deficiency Zone on the Main Sequence
• The Solar Neighborhood XLVII: Comparing M Dwarf Models with Hubble Space Telescope Dynamical Masses and Spectroscopy
• A transition of dynamo modes in M dwarfs: narrowing down the spectral range where the transition occurs*
• A discontinuity in the luminosity-mass relation and fluctuations in the evolutionary tracks of low-mass and low-metallicity stars at the Gaia M-dwarf gap
• Estimating the Convective Turnover Time
• Validation of a Third Planet in the LHS 1678 System
• Updated High-Temperature Opacities for the Dartmouth Stellar Evolution Program and their Effect on the Jao Gap Location
• The convective kissing instability in low-mass M-dwarf models: convective overshooting, semi-convection, luminosity functions, surface abundances and star cluster age dating
• A deep HST view of the open cluster NGC2158: binaries, mass functions, and M-dwarf discontinuity
• The Solar Neighborhood. LV. M Dwarf Twin Binaries -- One in Five Twin Sibling Pairs Are Mismatched in Activity and/or Rotation
• The M-dwarf Ultraviolet Spectroscopic Sample I. Determining Stellar Parameters for Field Stars