arXiv subjects

Wata Tubthong

Publications and source records attributed to Wata Tubthong.

4 recordsLinked to original sources

arXiv2026

EBLM XVII - Tidal Synchronization and Circularization in Tight Stellar Binaries

Tidal interactions in close stellar binaries are central to their orbital and rotational evolution, making observational tests of theoretical predictions essential for our understanding of the evolution of these, as well as close exoplanetary systems. Such tests require precise measurements of the orbital eccentricity and stellar rotation. The EBLM (Eclipsing Binary Low Mass) survey delivers a homogeneous sample of eclipsing binaries, composed of F/G/K primaries and M-dwarf (or low-mass K-dwarf) secondaries. We analyze 68 unequal mass binaries ($0.1 \leq q \leq 0.6$, where $q$ is the mass ratio), with measurable primary star rotation rates from TESS, and over a decade of radial velocity observations. This sample probes the critical regime where tidal effects are expected to transition between being efficient and inefficient. We find that ~75% of our sample has circularized, with eccentric systems confined to $P_{\rm orb} \gtrsim 3$ days, with modest eccentricities (e < 0.25). Roughly ~78% of our sample is synchronized, with nearly all binaries within a 3-day orbital period residing in a well-defined "synchronization zone". Beyond this, a minority of asynchronous systems persist, which cannot be easily explained by our application of current tidal mechanisms or by differential rotation.

astro-ph.SR↗

arXiv2025

Starspots and Flares are Generally Not Correlated

Sunspots and solar flares are two different manifestations of magnetic activity on the surface of the Sun. On the Sun, flares typically occur close to spots. In this paper we test this the connection between spots and flares on other stars. We detect 218,386 stellar flares on 14,163 spotted stars using a new algorithm called \textsc{toffee}. Inhomogeneous spot distributions mean that as stars rotate they become brighter when less spots are facing the observer, and dimmer when more spots are facing the observer. We determine that flares occur when the star is brighter $49.97\pm 0.21\%$ of the time, i.e. there is an equal preference for the flares to occur when the star is relatively bright or dim. We therefore find no evidence for a correlation between flare rate and spot occurrence, contrary to what is seen on the Sun.

astro-ph.SR↗

arXiv2025

The EBLM Project XVIII. 3D Obliquities of Five Low-Mass Eclipsing Binaries

The formation of tight stellar binaries remains an unsolved problem. There is too much angular momentum in a collapsing and fragmenting protostellar cloud to form a stellar binary in situ with a separation less than an AU, yet thousands of these short-period binaries have been discovered. One indication of a binary's formation is the angle between the stellar spin and orbital axes --- its obliquity. The classical method for determining projected stellar obliquities is the Rossiter-McLaughlin effect. This has been applied to 132 hot Jupiters, but only a handful of stellar binaries. Of the binary systems with measured projected obliquities, even fewer have measured 3D obliquities. In this paper, we add five more short-period binary 3D obliquity measurements to the sample previously consisting of one system. We present Rossiter-McLaughlin measurements for EBLM J0239-20, EBLM J0941-31, EBLM J1037-25, EBLM J1141-37, and EBLM J2025-45. These systems consist of an M-dwarf eclipsing an F/G type primary. We combine CORALIE and HARPS spectroscopy with TESS photometry of primary and secondary eclipses. We show that even though the sky-projected obliquities seem to be aligned, there is modest but non-zero spin-orbit misalignment ($\psi$ between 5 and 20$^{\circ}$). Our primary stars straddle the Kraft break at $\sim 6250K$. We derive the M-dwarf masses and radii to precisions better than 3\%. With the exception of EBLM J0941-31, each system has an inflated radius, exceeding stellar model predictions by more than 5$\sigma$.

astro-ph.SR↗

arXiv2025

Exomoons of Circumbinary Planets

Confirmation of the first exomoon remains elusive. Although several exomoon candidates exist around single stars, there are currently no candidates around circumbinary planets (CBPs). Most circumbinary planets are thought to form far from the host binary and migrate through the protoplanetary disc. Therefore, an exomoon of a CBP represents a fascinating yet complex and evolving four-body system. Their existence (or absence) would shed light on the robustness of moon formation and evolution in dynamically active planetary systems. In this work, we simulate the orbital evolutions of exomoons around migrating CBPs. We show that for fully migrated CBPs, a moon is capable of surviving the migration if it is formed within $\sim5-10\%$ of the planet's Hill Radius, well within the currently proposed range at which moons are thought to settle in the planetary disc for giant planets. Even though all known CBPs are gas giants, 18\% of the surviving moons in our sample are within the habitable zone, giving credence to circumbinary habitability, albeit hosted by moons rather than planets. $38\%$ of moons escape their host planet early in the migration and become long-period CBPs (i.e a multi-planet circumbinary system). Nearly one-third of exomoons collide with their host planet, and $1\%$ are ejected from the system entirely. This last class presents another pathway for producing free-floating planetary mass objects, like those discovered recently and expected from the Roman microlensing survey.

astro-ph.EP↗