分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The ultra-short-period (USP) planets are exoplanets with very short orbital periods ($\textit{P} < 1$ day), and TOI-1807b is one such planet recently discovered by the TESS mission where it orbits in the TOI-1807 system that is still little known nowadays. In this paper, we re-analyzed the transit light curves of TOI-1807 using the latest TESS data from Sector 49, combined with previous data from Sector 22 and 23. By running the MCMC simulation through all three sectors, we found that our transit model fits the data from Sector 49 the best, and we deduced that TOI-1807b is a Super-Earth with a mass of $2.27^{+0.49}_{-0.58}\, M_\oplus$, a radius of $1.37^{+0.10}_{-0.09}\, R_\oplus$, a density of $0.875^{+0.264}_{-0.285}\, \rho_\oplus$, and a surface temperature of $1499^{+82}_{-129}\, \mathrm{K}$. We confirmed that TOI-1807b orbits at approximately $0.0135^{+0.0013}_{-0.0022}\, \mathrm{AU}$ with a period of $0.54929^{+0.00012}_{-0.00005}\, \mathrm{days}$, which raises the possibility of the planet being tidally locked due to spin-orbit synchronization. In addition, we suggest that TOI-1807b might slowly undergo its orbital decay process, and we further identify that TOI-1807b is in a circular, synchronous orbit and permanently deformed due to tides, leading to $\sim$4% correction in density. Since TOI-1807 is such a young star with an age of only $300 \pm 80\, \mathrm{Myr}$, we also imply that the radiation emitted from active TOI-1807 could be so intense that it might have destroyed most of the atmosphere over the surface of TOI-1807b.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： The ultra-short-period (USP) planets are exoplanets with very short orbital periods ($\textit{P} < 1$ day), and TOI-1807b is one such planet recently discovered by the TESS mission where it orbits in the TOI-1807 system that is still little known nowadays. In this paper, we re-analyzed the transit light curves of TOI-1807 using the latest TESS data from Sector 49, combined with previous data from Sector 22 and 23. By running the MCMC simulation through all three sectors, we found that our transit model fits the data from Sector 49 the best, and we deduced that TOI-1807b is a Super-Earth with a mass of $2.27^{+0.49}_{-0.58}\, M_\oplus$, a radius of $1.37^{+0.10}_{-0.09}\, R_\oplus$, a density of $0.875^{+0.264}_{-0.285}\, \rho_\oplus$, and a surface temperature of $1499^{+82}_{-129}\, \mathrm{K}$. We confirmed that TOI-1807b orbits at approximately $0.0135^{+0.0013}_{-0.0022}\, \mathrm{AU}$ with a period of $0.54929^{+0.00012}_{-0.00005}\, \mathrm{days}$, which raises the possibility of the planet being tidally locked due to spin-orbit synchronization. In addition, we suggest that TOI-1807b might slowly undergo its orbital decay process, and we further identify that TOI-1807b is in a circular, synchronous orbit and permanently deformed due to tides, leading to $\sim$4% correction in density. Since TOI-1807 is such a young star with an age of only $300 \pm 80\, \mathrm{Myr}$, we also imply that the radiation emitted from active TOI-1807 could be so intense that it might have destroyed most of the atmosphere over the surface of TOI-1807b.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Yongda Zhu
Hai-Xia Ma
Xiao-Bo Dong
Yang Huang
Tobias Mistele
Bo Peng
Qian Long
Tianqi Wang
Liang Chang
Xi Jin
摘要： Aiming at discriminating different gravitational potential models of the Milky Way, we perform tests based on the kinematic data powered by the Gaia DR2 astrometry, over a large range of $(R,z)$ locations. Invoking the complete form of Jeans equations that admit three integrals of motion, we use the independent $R$- and $z$-directional equations as two discriminators ($T_R$ and $T_z$). We apply the formula for spatial distributions of radial and vertical velocity dispersions proposed by Binney et al., and successfully extend it to azimuthal components, $\sigma_\theta(R,z)$ and $V_\theta(R,z)$; the analytic form avoids the numerical artifacts caused by numerical differentiation in Jeans-equations calculation given the limited spatial resolutions of observations, and more importantly reduces the impact of kinematic substructures in the Galactic disk. It turns out that whereas the current kinematic data are able to reject Moffat's Modified Gravity (let alone the Newtonian baryon-only model), Milgrom's MOND is still not rejected. In fact, both the carefully calibrated fiducial model invoking a spherical dark matter (DM) halo and MOND are equally consistent with the data at almost all spatial locations (except that probably both have respective problems at low-$|z|$ locations), no matter which a tracer population or which a meaningful density profile is used. Because there is no free parameter at all in the quasi-linear MOND model we use, and the baryonic parameters are actually fine-tuned in the DM context, such an effective equivalence is surprising, and might be calling forth a transcending synthesis of the two paradigms.
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