arXiv subjects

Yiren Lin

Publications and source records attributed to Yiren Lin.

5 recordsLinked to original sources

arXiv2026

Modeling the Dynamics and Thermochemistry for the Outer Atmospheres of the Ultra-hot Jupiter WASP-121b

We present three-dimensional simulations of the ultra-hot Jupiter (UHJ) WASP-121b from the planetary surface to extended outflows, coupling hydrodynamics with consistent non-equilibrium thermochemistry, ray-tracing radiative transfer, and hydrodynamics using the GPU-accelerated Kratos framework. The fiducial model exhibits several atmospheric layers, including the lower atmospheres controlled by day-night circulation, and transonic photoevaporative outflows at higher altitudes shaped into two spiral arms by the stellar gravity and orbital motion effects. Different species could trace different regions: Fe probes rotation-dominated inner layers, Na maps dense spiral arms where recombination balances photoionization, and H$\alpha$ and He 10830 A features trace progressively more extended, ionized gas. With spiral arm velocities reaching ~ 40 km/s projected along the line of sight, this morphology naturally reproduces the velocity pattern of observed high-velocity Na and H$\alpha$ absorption features without requiring significant super-rotation jet streams, although the absolute absorption amplitudes could carry uncertainties from stellar UV luminosity and trace elemental abundances. Parametric studies reveal complex dependencies on stellar irradiation: enhanced FUV intensifies outflows and extends spiral arms spatially and kinematically, while EUV and X-ray expands spiral structures into attenuated, ionized regions. Stellar wind confinement compresses the dayside outflow and enhances metastable helium absorption. This work demonstrates that current and future transmission spectral observations that probe multiple species can provide important constraints on astrophysical environments of UHJs by comparing state-of-the-art simulations.

astro-ph.EP↗

arXiv2024

SgrA* spin and mass estimates through the detection of multiple extremely large mass-ratio inspirals

We analyze the parameter estimation accuracy that can be achieved for the mass and spin of SgrA$^\ast$, the SMBH in our Galactic Center, by detecting multiple extremely large mass-ratio inspirals (XMRIs). XMRIs are formed by brown dwarfs (BD) inspiraling into a supermassive black hole (SMBH), thus emitting gravitational waves (GWs) inside the detection band of future space-based detectors such as LISA and TianQin. Theoretical estimates suggest the presence of approximately 10 XMRIs emitting detectable GWs, making them some of the most promising candidates for space-based GW detectors. Our analysis indicates that even if individual sources have low SNRs ($\approx10$), high-precision parameter estimates can still be achieved by detecting multiple sources. In this case, the accuracy of the parameter estimates increases by approximately one to two orders of magnitude, at least. Moreover, by analyzing a small sample of 400 initial conditions for XMRIs formed in the Galactic Center, we estimate that almost 80\,\% of the detectable XMRIs orbiting SgrA$^\ast$ will have eccentricities between 0.43 to 0.95 and an $\mathrm{SNR}\in [10,100]$. The remaining $\sim$20\,\% of the sources have an $\mathrm{SNR}\in [100,1000]$ and eccentricities ranging from 0.25 to 0.92. Additionally, some XMRIs with high SNR are far from being circular. These loud sources with $\mathrm{SNR}\approx 1000$ can have eccentricities as high as $e\approx0.7$; although their detection chances are low, representing $\lesssim$2\,\% of the detectable sources, their presence is not ruled out.

astro-ph.HE↗

arXiv2024

Mono- and oligochromatic extreme-mass ratio inspirals

The gravitational capture of a stellar-mass object by a supermassive black hole represents a unique probe of warped spacetime. The small object, typically a stellar-mass black hole, describes a very large number of cycles before crossing the event horizon. Because of the mass difference, we call these captures extreme-mass ratio inspirals (EMRIs). Their merger event rate at the Galactic Centre is negligible, but the amount of time spent in the early inspiral is not. Early EMRIs (E-EMRIs) spend hundreds of thousands of years in band during this phase. At very early stages, the peak of the frequency will not change during an observational time. At later stages, it will change a bit and finally the EMRI explores a wide range of them when it is close to merger. We distinguish between "monocromatic" E-EMRIs, which do not change their (peak) frequency, oligochromatic E-EMRIs, which explore a short range and polychromatic ones, the EMRIs which have been discussed so far in the literature. We derive the number of E-EMRIs at the Galactic Centre, and their signal-to-noise ratios (SNR) and perform a study of parameter extraction. We show that parameters such as the spin and the mass can be extracted with an error which can be as small as $10^{-11}$ and $10^{-5}\,M_{\odot}$. There are between hundreds and thousands of E-EMRIs in their monochromatic stage at the GC, and tens in their oligochromatic phase. The SNR ranges from a minimum of $10$ (larger likelihood) to a maximum of $10^6$ (smaller likelihood). Moreover, we derive the contribution signal corresponding to the incoherent sum of continuous with two representatives masses; $10\,M_{\odot}$ and $40\,M_{\odot}$ and show that their curves will cover a significant part of LISA's sensitivity curve. Depending on their level of circularisation, they might be detected as individual sources or form a foreground population.

astro-ph.CO↗

arXiv2024

Photoevaporation from Inner Protoplanetary Disks Confronted with Observations

The decades-long explorations on the dispersal of protoplanetary disks involve many debates about photoevaporation versus magnetized wind launching mechanisms. This letter argues that the observed winds originating from the inner disk ($R\lesssim 0.3$ AU) cannot be explained by the photoevaporative mechanism. Energy conservation requires the presumed photoevaporative winds to be heated to $\gtrsim 10^5$ K when launched from inner disks. However, due to efficient thermal accommodation with dust grains and cooling processes at high densities, X-ray irradiation at energies above 1 keV cannot efficiently launch winds in the first place because of its high penetration. Some studies claiming X-ray wind launching have oversimplified the thermochemical couplings. Furthermore, heating the gas to escape velocity will over-ionize it, suppressing the species responsible for observed forbidden lines (e.g., [OI] 6300 $\r{A}$ ). Confirmed by semi-analytic integrations of thermochemical fluid structures, such high ionizations contradict the observed emission of neutral and singly-ionized atoms from the winds originating from the inner disks.

astro-ph.EP↗

arXiv2022

SgrA$^{*}$ spin and mass estimates through the detection of an extremely large mass-ratio inspiral

Estimating the spin of ${\rm SgrA^\ast}$ is one of the current challenges we face in understanding the center of our Galaxy. In the present work, we show that detecting the gravitational waves (GWs) emitted by a brown dwarf inspiraling around ${\rm SgrA^\ast}$ will allow us to measure the mass and the spin of ${\rm SgrA^\ast}$ with unprecedented accuracy. Such systems are known as extremely large mass-ratio inspirals (XMRIs) and are expected to be abundant and loud sources in our galactic center. We consider XMRIs with a fixed orbital inclination and different spins of ${\rm SgrA^\ast}$ ($s$) between 0.1 and 0.9. For both cases, we obtain the number of circular and eccentric XMRIs expected to be detected by space-borne GW detectors like LISA and TianQin. We find that if the orbit is eccentric, then we expect to always have several XMRIs in band while for almost circular XMRIs, we only expect to have one source in band if ${\rm SgrA^\ast}$ is highly spinning. We later perform a Fisher matrix analysis to show that by detecting a single XMRI the mass of ${\rm SgrA^\ast}$ can be determined with an accuracy of the order $10^{-2}\,\text{M}_{\odot}$, while the spin can be measured with an accuracy between $10^{-7}$ and $10^{-4}$ depending on the orbital parameters of the XMRI.

astro-ph.HE↗