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arXiv 0905.2512astro-ph.GA
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重新审视太阳邻居的动力学和历史

Kinematics and history of the solar neighbourhood revisited

Michael Aumer, James J. Binney

备注：
18 pages, 18 figures, accepted for publication in MNRAS
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摘要：

我们使用自行和自行车从新的减少依巴谷数据和日内瓦-哥本哈根径向速度的一个完整的样本~15000主序星和次巨星，和新的帕多瓦等时线约束的运动学和恒星形成历史的太阳附近。我们重新推导了太阳运动和局部速度椭球的结构。当主速度频散随时间t^β增加时，σ_W（β_W~0.45）的指数β大于σ_U（β_U~0.31）的指数β。对于三维速度弥散，我们得到β=0.35。我们排除了Quillen和Garnett（2000）提出的~3 Gyr后的盘加热饱和。对于最老的恒星，不能排除在>~4 Gyr之后的饱和以及速度色散的突然增加。对于我们所有的模型，恒星形成率都在下降，现在比开始时低2-7倍。SFR呈指数下降的模型有利于非常高的盘年龄在11.5和13 Gyr之间，并排除年龄低于10.5 Gyr，因为它们产生更差的拟合数量密度和速度分散的红星。SFR是代表薄盘和厚盘的两个递减指数之和的模型倾向于年龄在10.5和12 Gyr之间，下限为~10.0 Gyr。虽然在我们的模型中，恒星形成速率的峰值早得令人惊讶，但太阳邻域恒星的平均形成时间要晚于星系形成的从头算模型，这可能是由于这种模型的弱点。

英文摘要：

We use proper motions and parallaxes from the new reduction of Hipparcos data and Geneva-Copenhagen radial velocities for a complete sample of ~15000 main-sequence and subgiant stars, and new Padova isochrones to constrain the kinematics and star-formation history of the solar neighbourhood. We rederive the solar motion and the structure of the local velocity ellipsoids. When the principal velocity dispersions are assumed to increase with time as t^β, the index βis larger for σ_W (β_W~0.45) than for σ_U (β_U~0.31). For the three-dimensional velocity dispersion we obtain β=0.35. We exclude saturation of disc heating after ~3 Gyr as proposed by Quillen & Garnett(2000). Saturation after >~4 Gyr combined with an abrupt increase in velocity dispersion for the oldest stars cannot be excluded. For all our models the star-formation rate is declining, being a factor 2-7 lower now than it was at the beginning. Models in which the SFR declines exponentially favour very high disc ages between 11.5 and 13 Gyr and exclude ages below ~10.5 Gyr as they yield worse fits to the number density and velocity dispersion of red stars. Models in which the SFR is the sum of two declining exponentials representing the thin and thick discs favour ages between 10.5 and 12 Gyr with a lower limit of ~10.0 Gyr. Although in our models the star-formation rate peaked surprisingly early, the mean formation time of solar-neighbourhood stars is later than in ab-initio models of galaxy formation, probably on account of weaknesses in such models.

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