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arXiv 2302.09084astro-ph.SRastro-ph.GA
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利用 Gaia 过量不确定性作为恒星变率和年龄的代理指标

Using the Gaia excess uncertainty as a proxy for stellar variability and age

Madyson G. Barber, Andrew W. Mann

备注：
Accepted to ApJ. 19 pages, 9 figures, 3 tables. For associated code, see https://github.com/madysonb/EVA
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AI总结：

本文提出用 Gaia 过量测光不确定性 $Var$ 表征恒星变率并校准年龄，验证其可用于测定年轻星协、识别真实共动同龄群组。

摘要：

众所周知，恒星在年轻时更加活跃，因此年龄与测光变率之间存在很强的相关性。在给定年龄下，不同恒星之间的振幅变化很大，但在大型恒星群中，年龄—变率关系会变得显著。我们利用 Gaia 测光中的过量测光不确定性（$Var_{G}$、$Var_{BP}$ 和 $Var_{RP}$）作为变率的代理指标来探索这一关系。这些指标遵循类似 Skumanich 的关系，标度约为 $\simeq t^{-0.4}$。通过对一组已知年龄的星协进行校准，我们展示了群体成员的 $Var$ 如何能够为年龄小于约 2.5 Gyr 的星协预测群体年龄，误差在 10–20% 以内。在实际应用中，年龄不确定性更大，主要原因是群体规模有限。该指数在最年轻的年龄阶段（$<$100 Myr）最有用，此时其不确定性与从颜色—星等图得到的结果相当，甚至更好。该指数还具有覆盖广泛、易于计算的特点，并可用于主序前或主序后恒星很少甚至不存在的中等年龄阶段。我们进一步展示了如何利用 $Var$ 寻找新的星协，并检验一组共同运动恒星是否为真正的同代星群体。我们将方法应用于 350 pc 以内的 Theia 群组，发现不少于约 90% 的群组与从场星中抽取恒星的情况不一致，且约 80% 的群组的变率年龄与从 CMD 推导出的年龄相符。我们的发现表明，这些群组中的绝大多数包含真实的恒星群体。

英文摘要：

Stars are known to be more active when they are young, resulting in a strong correlation between age and photometric variability. The amplitude variation between stars of a given age is large, but the age-variability relation becomes strong over large groups of stars. We explore this relation using the excess photometric uncertainty in Gaia photometry ($Var_{G}$, $Var_{BP}$, and $Var_{RP}$) as a proxy for variability. The metrics follow a Skumanich-like relation, scaling as $\simeq t^{-0.4}$. By calibrating against a set of associations with known ages, we show how $Var$ of population members can predict group ages within 10-20% for associations younger than $\simeq$2.5 Gyr. In practice, age uncertainties are larger, primarily due to finite group size. The index is most useful at the youngest ages ($<$100 Myr), where the uncertainties are comparable to or better than those derived from a color-magnitude diagram. The index is also widely available, easy to calculate, and can be used at intermediate ages where there are few or no pre- or post-main-sequence stars. We further show how $Var$ can be used to find new associations and test if a group of co-moving stars is a real co-eval population. We apply our methods on the Theia groups within 350 pc and find $\gtrsim$90% are inconsistent with drawing stars from the field and $\simeq$80% have variability ages consistent with those derived from the CMD. Our finding suggest the great majority of these groups contain real populations.

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