分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: The spectrograph ESPRESSO recently obtained a limit on the variation of the fine-structure constant, $\alpha$, through measurements along the line of sight of a bright quasar with a precision of $1.36$ ppm at $1\sigma$ level. This imposes new constraints on cosmological models with a varying $\alpha$. We assume such a model where the electromagnetic sector is coupled to a scalar field dark energy responsible for the current acceleration of the Universe. We parametrise the variation of $\alpha$ with two extra parameters, one defining the cosmological evolution of the quintessence component and the other fixing the coupling with the electromagnetic field. The objective of this work is to constrain these parameters with both astrophysical and local probes. We also carried out a comparative analysis of how each data probe may constrain our parametrisation. We performed a Bayesian analysis by comparing the predictions of the model with observations. The astrophysical datasets are composed of quasar spectra measurements, including the latest ESPRESSO data point, as well as Planck observations of the cosmic microwave background. We combined these with local results from atomic clocks and the MICROSCOPE experiment. The constraints placed on the quintessence parameter are consistent with a null variation of the field, and are therefore compatible with a $\Lambda$CDM cosmology. The constraints on the coupling to the electromagnetic sector are dominated by the E\"otv\"os parameter local bound. More precise measurements with ESPRESSO will be extremely important to study the cosmological evolution of $\alpha$ as it probes an interval of redshift not accessible to other types of observations. However, for this particular model, current available data favour a null variation of $\alpha$ resulting mostly from the strong MICROSCOPE limits.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: We report the discovery and characterization of a nearby (~ 85 pc), older (27 +/- 3 Myr), distributed stellar population near Lower-Centaurus-Crux (LCC), initially identified by searching for stars co-moving with a candidate transiting planet from TESS (HD 109833; TOI 1097). We determine the association membership using Gaia kinematics, color-magnitude information, and rotation periods of candidate members. We measure it's age using isochrones, gyrochronology, and Li depletion. While the association is near known populations of LCC, we find that it is older than any previously found LCC sub-group (10-16 Myr), and distinct in both position and velocity. In addition to the candidate planets around HD 109833 the association contains four directly-imaged planetary-mass companions around 3 stars, YSES-1, YSES-2, and HD 95086, all of which were previously assigned membership in the younger LCC. Using the Notch pipeline, we identify a second candidate transiting planet around HD 109833. We use a suite of ground-based follow-up observations to validate the two transit signals as planetary in nature. HD 109833 b and c join the small but growing population of <100 Myr transiting planets from TESS. HD 109833 has a rotation period and Li abundance indicative of a young age (< 100 Myr), but a position and velocity on the outskirts of the new population, lower Li levels than similar members, and a CMD position below model predictions for 27 Myr. So, we cannot reject the possibility that HD 109833 is a young field star coincidentally nearby the population.
分类: 天文学 >> 天文学 提交时间: 2023-02-19
摘要: Hot jupiters (P 60 $\mathrm{M}_\oplus$) are almost always found alone around their stars, but four out of hundreds known have inner companion planets. These rare companions allow us to constrain the hot jupiter's formation history by ruling out high-eccentricity tidal migration. Less is known about inner companions to hot Saturn-mass planets. We report here the discovery of the TOI-2000 system, which features a hot Saturn-mass planet with a smaller inner companion. The mini-neptune TOI-2000 b ($2.70 \pm 0.15 \,\mathrm{R}_\oplus$, $11.0 \pm 2.4 \,\mathrm{M}_\oplus$) is in a 3.10-day orbit, and the hot saturn TOI-2000 c ($8.14^{+0.31}_{-0.30} \,\mathrm{R}_\oplus$, $81.7^{+4.7}_{-4.6} \,\mathrm{M}_\oplus$) is in a 9.13-day orbit. Both planets transit their host star TOI-2000 (TIC 371188886, V = 10.98, TESS magnitude = 10.36), a metal-rich ([Fe/H] = $0.439^{+0.041}_{-0.043}$) G dwarf 174 pc away. TESS observed the two planets in sectors 9-11 and 36-38, and we followed up with ground-based photometry, spectroscopy, and speckle imaging. Radial velocities from CHIRON, FEROS, and HARPS allowed us to confirm both planets by direct mass measurement. In addition, we demonstrate constraining planetary and stellar parameters with MIST stellar evolutionary tracks through Hamiltonian Monte Carlo under the PyMC framework, achieving higher sampling efficiency and shorter run time compared to traditional Markov chain Monte Carlo. Having the brightest host star in the V band among similar systems, TOI-2000 b and c are superb candidates for atmospheric characterization by the JWST, which can potentially distinguish whether they formed together or TOI-2000 c swept along material during migration to form TOI-2000 b.