在这第一项工作中，试图分析解释对磁制动指数$q$的影响，这是由de Freitas \& De Medeiros（2013）估计的主序星中恒星速度的演化引起的。我们发现，$q$的效应是理解控制恒星自旋下降的微妙机制的决定性因素，这种机制是恒星质量的函数。我们注意到，我们的模型预测，计算的年龄是不同的陀螺年代学年龄。实际上，仅考虑Skumanich关系的规范值（$q$ =3）来测量陀螺年龄。结果表明，当$q$为自由参数时，可以很好地确定恒星的年龄。我们还证实，对于旋转周期小于$\sim$ 5天（即，快速旋转体）在不同的指标$q$之间存在很大的差异。此外，根据选取的质量范围，陀螺年代学模型测得的年龄可能被低估。总之，我们认为，广义陀螺仪年龄磁制动指数可以是一个有趣的方式来更好地理解旋转的想法作为一个时钟。
英文摘要：
In this first work attempts to analytically explain the effects on the magnetic braking index, $q$, caused by the evolution of stellar velocity in main-sequence stars, and estimated by de Freitas \& De Medeiros (2013). We have found that the effect of $q$ is here a determining factor for understanding the delicate mechanisms that control the spin-down of stars as a function of the mass of stars. We note that our models predict that the calculated ages are distinct from gyrochronology ages. Indeed, the gyro-ages are measured considering only the canonical value of the Skumanich relation ($q$=3). As a result, we find that the age of stars can be well-determined when $q$ is free parameter. We also verified that for rotation periods less than $\sim$ 5 days (i.e., fast rotators) there is a strong discrepancy among the different indexes $q$. In addition, the ages measured by gyrochronology model can be underestimated according to mass range selected. In conclusion, we suggest that the generalized gyro-ages by magnetic braking index can be an interesting way to better understand the idea of rotation as a clock.
Estimating stellar ages is important for advancing our understanding of stellar and exoplanet evolution and investigating the history of the Milky Way. However, ages for low-mass stars are hard to infer as they evolve slowly on the main sequence. In addition, empirical dating methods are difficult to calibrate for low-mass stars as they are faint. In this work, we calculate ages for Kepler F, G, and crucially K and M dwarfs, using their rotation and kinematic properties. We apply the simple assumption that the velocity dispersion of stars increases over time and adopt an age--velocity--dispers…
Rotation, differential rotation, and gyrochronology of active Kepler stars
CoRoT和开普勒卫星的高精度测光测量了数万颗恒星的表面旋转周期。我们的主要目标是推导出成千上万的场星的年龄使用一致的旋转周期测量在不同的gyrochronology关系。多个旋转周期被解释为表面差异旋转（DR）。我们重新分析了Reinhold等人（2013）的24，124颗开普勒恒星的样本，使用基于Lomb-Scargle周期图的不同方法。每个乳区（Q1-Q14）使用预美白方法单独处理。此外，分析了完整的时间序列及其不同的片段。对于超过18，500颗恒星，我们的结果与McQuillan et al.（2014）的旋转周期一致。其中，超过12，300颗恒星显示出多个显著的峰值，我们将其解释为DR。使用不同的陀螺年代学关系，对超过17，000颗恒星推导出1亿年至10亿年的陀螺年代学年龄。在3200-4700 K之间，Teff的年龄分布为双峰型.导出的年龄揭示了一个经验的活动年龄关系，光度变化作为恒星活动代理。此外，我们还发现了1079颗周期非常稳定（大部分是短周期）的恒星。这些周期的一半可能与非食伴星稳定的自转有关，另一半可能是由于脉动。由于超过93.0%的恒星似乎比太阳年轻，因此导出的陀螺年代学年龄受到很好的限制，其中校准是最可靠的。解释年龄分布中的双峰性是具有挑战性的，并且限制了准确的恒星年龄预测。在超过三年的观测中，存在着自转周期几乎恒定的冷恒星，这可能是因为它们与伴星同步，或…
Accurate stellar ages are essential for our understanding of the star formation history of the Milky Way, Galactic chemical evolution, and to constrain exoplanet formation models. Gyrochronology, a relationship between stellar rotation and age, appears to offer a reliable age indicator for main sequence (MS) stars over the mass range of approximately 0.6 to 1.3 $M_\odot$. Those stars lose their angular momentum due to magnetic braking and as a result, their rotation speeds decrease with age. Although current gyrochronology relations are fairly well tested for young MS stars with masses greater…
Rotation periods for cool stars in the 4 Gyr-old open cluster M67, the solar-stellar connection, and the applicability of gyrochronology to at least solar age
Recent observations reveal the surprising breakdown of stellar gyrochronology relations at about the Sun's age hinting that middle-aged, solar-like stars transition to a magnetically inactive future. We provide a theoretical basis for these intriguing observations inspired by simulations with a mathematical dynamo model that can explore long-term solar cycle fluctuations. We reproduce the observed bimodal distribution of sunspot numbers, but only for subcritical dynamos. Based on a bifurcation analysis, we argue that ageing of solar-like stars makes the magnetically-weak dynamo regime readily …
Age is a stellar parameter that is both fundamental and difficult to determine. Among middle-aged M dwarfs, the most prolific hosts of close-in and detectable exoplanets, gyrochronology is the most promising method to assign ages, but requires calibration by rotation-temperature sequences (gyrochrones) in clusters of known ages. We curated a catalog of 249 late K- and M-type (($T_{eff}$=3200-4200K) exoplanet host stars with established rotation periods, and applied empirical, temperature-dependent rotation-age relations based on relevant published gyrochrones, including one derived from observ…
Gyrochronology is one of the methods currently used to estimate the age of stellar open clusters. Hundreds of new clusters, associations, and moving groups unveiled by Gaia and complemented by accurate rotation period measurements provided by recent space missions such as Kepler and TESS are allowing us to significantly improve the reliability of this method. We use gyrochronology, that is, the calibrated age-mass-rotation relation valid for low-mass stars, to measure the age of the recently discovered moving group Group X. We extracted the light curves of all candidate members from the TESS f…
We present a catalog of ~100,000 periodic variable stars in TESS FFI data among members of widely distributed moving groups identified with Gaia in the previous papers in the series. By combining the periods from our catalog attributable to rotation with previously derived rotation periods for benchmark open clusters, we develop an empirical gyrochronology relation of angular momentum evolution that is valid for stars with ages 10-1000 Myr. Excluding stars rotating faster than 2 days, which we find are predominantly binaries, we achieve a typical age precision of ~0.2-0.3 dex and improving at …
The presence of a massive close-in planet with an orbital period of a few days or less around a low-mass star can possibly results in a strong variation of the properties of the central star. Indeed, star-planet tidal interactions generate exchanges of angular momentum that can results in tidal spin-up. This effect could then lead to gyrochronological ages biased towards younger ages. Aims. This article provides the community with TATOO, a standalone tool based on tidal-chronology, to estimate the age of a massive close-in planetary system by only using its observed properties: mass of the pla…
Gyrochronology allows the derivation of ages for cool main sequence stars based on their observed rotation periods and masses, or a suitable proxy thereof. It is increasingly well-explored for FGK stars, but requires further measurements for older ages and K-M-type stars. We study the nearby, 3 Gyr-old open cluster Ruprecht 147 to compare it with the previously-studied, but far more distant, NGC 6819 cluster, and especially to measure cooler stars than was previously possible there. We constructed an inclusive list of 102 cluster members from prior work, including Gaia DR2, and for which light…
A Test of Substellar Evolutionary Models with High-Precision Ages from Asteroseismology and Gyrochronology for the Benchmark System HR 7672AB
Institute for Astronomy, University of Hawai‘i（夏威夷大学天文研究所）；Institute for Astronomy, University of Edinburgh, Royal Observatory（爱丁堡大学皇家天文台天文研究所）；Department of Physics, University of California, Santa Barbara（加州大学圣塔芭芭拉分校物理系）；Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto（波尔图大学空间天体物理研究所）；Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto（波尔图大学理学院物理与天文系）；Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University（奥胡斯大学物理与天文系恒星天体物理学中心）
We present stellar rotation periods for late K- and early M-dwarf members of the 4 Gyr old open cluster M67 as calibrators for gyrochronology and tests of stellar spin-down models. Using Gaia EDR3 astrometry for cluster membership and Pan-STARRS (PS1) photometry for binary identification, we build this set of rotation periods from a campaign of monitoring M67 with the Canada-France-Hawaii Telescope's MegaPrime wide field imager. We identify 1807 members of M67, of which 294 are candidate single members with significant rotation period detections. Moreover, we fit a polynomial to the period ver…
ChronoFlow: A Data-Driven Model for Gyrochronology
David A. Dunlap Department of Astronomy & Astrophysics, University of Toronto, Toronto, ON, Canada（多伦多大学天文学与天体物理学系）；Dunlap Institute of Astronomy & Astrophysics, University of Toronto, Toronto, ON, Canada（多伦多大学杜拉普天文与天体物理学研究所）；Department of Statistical Sciences, University of Toronto, Toronto, ON M5S 3G3, Canada（多伦多大学统计科学系）；Data Sciences Institute, University of Toronto, Toronto, ON, Canada（多伦多大学数据科学研究所）；Department of Physics, Lafayette College, Easton, PA, United States（拉法叶学院物理系）；Center for Astrophysics — Harvard & Smithsonian, Cambridge, MA 02138, USA（哈佛—史密松天体物理中心）；Department of Astronomy, The Ohio State University, Columbus, 140 W 18th Ave, OH 43210, USA（俄亥俄州立大学天文学系）；Center for Cosmology and Astroparticle Physics (CCAPP), The Ohio State University, 191 W. Woodruff Ave., Columbus, OH 43210, USA（俄亥俄州立大学宇宙学与天体粒子物理中心）；American Museum of Natural History, Central Park West, Manhattan, NY, USA（美国自然历史博物馆）；Center for Computational Astrophysics, Flatiron Institute, Manhattan, NY, USA（Flatiron研究所计算天体物理学中心）
Extreme-ultraviolet and X-ray emissions from stellar coronae drive mass loss from exoplanet atmospheres, and ultraviolet emission from stellar chromospheres drives photo-chemistry in exoplanet atmospheres. Comparisons of the spectral energy distributions of host stars are, therefore, essential for understanding the evolution and habitability of exoplanets. The large number of stars observed with the MUSCLES, Mega-MUSCLES, and other recent HST observing programs has provided for the first time a large sample (79 stars) of reconstructed Lyman-alpha fluxes that we compare with X-ray fluxes to ide…
