arXiv 1402.63082014-02-25astro-ph.EPastro-ph.SR

太阳型恒星周围Debris粒子的衰变

The Decay of Debris Disks around Solar-Type Stars

J. M. Sierchio, G. H. Rieke, K. Y. L. Su, Andras Gaspar

备注：: 46 pages. 7 figures. Accepted to ApJ
DOI：: 10.1088/0004-637X/785/1/33

摘要：

我们提出了一个斯皮策MIPS研究的24和70 $μ$ m的255颗F4 - K2型恒星的碎片盘过剩的衰变。我们已经使用了多种测试，包括色球和X射线活动之间的一致性，以及在HR图上的位置，来分配准确的恒星年龄。在这个光谱类型范围内，在24 $μ$ m处，小于5 Gyr的恒星的$13.6 \pm 2.8 \%$有超过3 $σ$或更高的水平，而没有老恒星，证实了以前的工作。在70 $μ$ m时，年轻恒星的$22.5 \pm 3.6\%$在$ \ge$ 3 $σ$显著性上有过量，而只有$4.7^{+3.7}_{-2.2}$ %的老恒星有过量。为了更有力地描述碎片盘的远红外行为，我们通过包括来自DEBRIS和DUNES调查的恒星来加倍样本。对于这个组合样本中的F4 - K4恒星，在光谱类型（检测到的分数为21.9 $^{+4.8}_{-4.3}\%$，晚期F; 16.5 $^{+3.9}_{-3.3}\%$，G;和16.9 $^{+6.3}_{-5.0}\%$，早期K）的远红外过量的发生率中只有微弱的（统计上不显著的）趋势。把这一光谱类型范围放在一起，在3 Gyr和4.5 Gyr之间，分数光度刚好低于$10^{-5}$的过度发生率有显著下降。有一个迹象表明，红外过剩的衰减时间尺度变化大致与光度的分数成反比。这种行为符合被动进化的理论预期。然而，在最古老的恒星周围检测到的过度行为比被动演化所预期的要多，这表明这些恒星周围存在后期动力学活动。

英文摘要：

We present a Spitzer MIPS study of the decay of debris disk excesses at 24 and 70 $μ$m for 255 stars of types F4 - K2. We have used multiple tests, including consistency between chromospheric and X-ray activity and placement on the HR diagram, to assign accurate stellar ages. Within this spectral type range, at 24 $μ$m, $13.6 \pm 2.8 \%$ of the stars younger than 5 Gyr have excesses at the 3$σ$ level or more, while none of the older stars do, confirming previous work. At 70 $μ$m, $22.5 \pm 3.6\%$ of the younger stars have excesses at $ \ge$ 3 $σ$ significance, while only $4.7^{+3.7}_{-2.2}$% of the older stars do. To characterize the far infrared behavior of debris disks more robustly, we double the sample by including stars from the DEBRIS and DUNES surveys. For the F4 - K4 stars in this combined sample, there is only a weak (statistically not significant) trend in the incidence of far infrared excess with spectral type (detected fractions of 21.9$^{+4.8}_{-4.3}\%$, late F; 16.5$^{+3.9}_{-3.3}\%$, G; and 16.9$^{+6.3}_{-5.0}\%$, early K). Taking this spectral type range together, there is a significant decline between 3 and 4.5 Gyr in the incidence of excesses with fractional luminosities just under $10^{-5}$. There is an indication that the timescale for decay of infrared excesses varies roughly inversely with the fractional luminosity. This behavior is consistent with theoretical expectations for passive evolution. However, more excesses are detected around the oldest stars than is expected from passive evolution, suggesting that there is late-phase dynamical activity around these stars.

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