arXiv subjects

Eritas Yang

Publications and source records attributed to Eritas Yang.

5 recordsLinked to original sources

arXiv2026

Steady-state Stellar Winds Driven by Recombination

Hydrogen and helium recombination energy has been proposed as a potential driver of mass ejection in common-envelope evolution and other eruptive stellar phenomena. We investigate whether recombination can by itself launch a steady, transonic wind from near a stellar surface. Using a tabulated equation of state, we explore steady-state, adiabatic wind solutions over a broad range of stellar mass, density, and temperature. We classify a wind as recombination-driven only if the gas is gravitationally bound prior to recombination and if the released energy remains trapped until the flow becomes unbound. Only a small fraction of the solutions satisfy both conditions. In most cases, the gas is either already unbound without recombination or loses the released energy through radiative diffusion while still bound. The subset of valid solutions require outflow velocities $\gtrsim 10\,{\rm km\,s^{-1}}$ at $10\,R_\odot$, inconsistent with a wind launched from a hydrostatic star. We conclude that recombination energy alone is unlikely to produce steady stellar winds. It can, however, accelerate and unbind a pre-existing outflow generated by processes such as binary orbital decay, producing mass-loss rates of $\sim \rm M_\odot\,yr^{-1}$.

astro-ph.SR↗

arXiv2026

A Massive Hot-Jupiter Companion that Disfavors Giant Planet Formation Beyond the Water-Ice Line

We report evidence for a brown-dwarf companion with mass $34^{+30}_{-11}~M_{\rm J}$ in the KELT-20 system, in which an ultra-hot Jupiter transits an A2-type star. The companion's properties are inferred from a joint analysis of astrometric accelerations and transit timing variations, and its present-day orbit imposes dynamical limits on where the hot Jupiter could have formed. Given the star's current luminosity, the water-ice line is expected at $\sim$8-15 au, but the companion's inferred pericenter distance of a few au would lead to orbit crossing or long-term instability for any planet formed at such distances. If the companion formed early and remained near its current orbit over the system's lifetime, the proto-hot Jupiter must have formed within $\sim$3.7 au to avoid orbit crossing, and within $\sim$1.5 au to remain dynamically stable over the system's lifetime. These results disfavor formation beyond the ice line and point instead to formation at smaller orbital distances followed by inward migration.

astro-ph.EP↗

arXiv2025

An Analytical Model for the Eccentricity Cascade: Hot Jupiter Formation via S-type Instability

A widely explored pathway for hot Jupiter (HJ) formation is high-eccentricity migration driven by von Zeipel-Lidov-Kozai cycles induced by an exterior companion. However, for a distant or low-mass companion, this mechanism typically demands that the planet's initial orbit be very nearly perpendicular to that of the companion. In previous work (Yang et al. 2025), we demonstrated that such fine-tuning can be circumvented in the HAT-P-7 system due to the presence of an intermediate body that efficiently couples the orbits of the planet and the distant companion -- a mechanism we termed the eccentricity cascade (EC). In this work, we analytically characterize the dynamics governing the EC and delineate the parameter space within which it effectively operates. Our qualitative results are as follows: (i) The proto-HJ's eccentricity is most efficiently excited when the inner triple is on the verge of dynamical instability, (ii) the addition of a distant fourth body allows this instability to be approached gradually, and (iii) the instability mechanism is closely related to the stability of circumstellar (S-type) planets in binaries. By deriving an analytic criterion for S-type instability, we obtain closed-form expressions describing the onset of the EC. Our results show that efficient HJ formation via the EC occurs across a broad range of intermediate perturbers, highlighting its potential as a robust migration channel.

astro-ph.EP↗

arXiv2025

Discovery of a dwarf planet candidate in an extremely wide orbit: 2017 OF201

We report the discovery of a dwarf planet candidate, 2017 OF201, currently located at a distance of 90 au. Its orbit is extremely wide and extends to the inner Oort cloud, with a semi-major axis of 830 au and a perihelion of 45 au, precisely determined from 24 observations over 20 years. Assuming a typical albedo of 0.13, we estimate a diameter about 700 km, making it the second-largest known object in this dynamical population and a dwarf planet candidate with the widest orbit. Its high eccentricity suggests that an unseen population of similar objects would total about 1% of Earth's mass. Notably, the longitude of perihelion of 2017 OF201 lies outside the clustering observed in extreme trans-Neptunian objects, posing a challenge to the proposed dynamical evidence for the hypothetical Planet Nine.

astro-ph.EP↗

arXiv2025

A third star in the HAT-P-7 system, and a new dynamical pathway to misaligned hot Jupiters

The retrograde orbit of the hot Jupiter HAT-P-7b is suggestive of high-eccentricity migration caused by dynamical interactions with a massive companion. However, the only other known body in the system is an M dwarf located $\sim$10$^3$~AU away, too distant to cause high-eccentricity migration without fine tuning. Here we present transit-timing and radial-velocity evidence for an additional stellar companion with semi-major axis $32^{+16}_{-11}$~AU, eccentricity $0.76^{+0.12}_{-0.26}$, and minimum mass $0.19^{+0.11}_{-0.06}$~$\rm M_\odot$. We investigate several dynamical routes by which this nearby companion star could have played a role in converting a cold Jupiter into the retrograde hot Jupiter that is observed today. Of particular interest is a novel "eccentricity cascade" mechanism involving both of the companion stars: the outer companion periodically excites the eccentricity of the inner companion through von Zeipel-Lidov-Kozai (ZLK) cycles, and this eccentricity excitation is slowly transferred to the cold Jupiter via successive close encounters, eventually triggering its high-eccentricity migration. The plausibility of this mechanism in explaining HAT-P-7b shows that stellar companions traditionally considered too distant to cause hot Jupiter formation might nevertheless be responsible, with the aid of closer-orbiting massive companions. With these developments, HAT-P-7b is one of the few hot Jupiters for which a complete high-eccentricity migration history can be simulated based only on observed bodies, rather than invoking bodies that are beneath detection limits or that are no longer in the system.

astro-ph.EP↗