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arXiv 0907.2380astro-ph.SR
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猎户座郊区的恒星和原行星盘特性

Star and protoplanetary disk properties in Orion's suburbs

M. Fang, R. van Boekel, W. Wang, A. Carmona, A. Sicilia-Aguilar, Th. Henning

备注：
52 pages, 16 tables, 29 figures. Accepted by A&A. Table numbering error corrected
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摘要：

(Note：这是原始“结构化”A&A格式摘要的缩短版本。）我们对Lynds~ 1630 N和1641云进行了大规模的光学分光和光度测量。我们提供了L1630 N中132颗已确认的年轻恒星和L1641中267个这样的天体的目录。我们确定了28个过渡盘系统，其中20个是以前未知的，以及42个新的过渡盘候选人，我们有宽带测光，但没有光学光谱。我们从H_α、H_β和HeI 5876 α发射线的等效宽度估算了质量吸积率M_acc，并发现M_acc与恒星质量的依赖关系，在我们探测的亚太阳质量范围内，α约为3.1。通过对大量文献中质量吸积率估算样本的研究，在太阳下区域得到了类似的α ~2.8的斜率，但如果包括0.04 Msun-5 Msun的整个质量范围，则α ~2.0的斜率较浅。在过渡盘天体中，与仍然具有光学厚盘的恒星相比，显示出显著吸积活动的恒星比例相对较低（分别为26 \pm 11%和57 \pm 6%）。然而，那些确实表现出显著吸积的过渡盘具有与正常光学厚盘相同的吸积率中值，为3-4*10^{-9} M_sun/yr。我们发现，过渡磁盘和WTTS没有磁盘的年龄是统计上无法区分的，这两组都显着老于CTTS。这些结果反对盘二进制相互作用或引力不稳定的机制，导致过渡盘外观。我们的观察表明，磁盘的寿命在集群人口短于分布人口。我们提出了改进的Halpha等效宽度标准来区分WTTTS和CTTS。

英文摘要：

(Note: this is a shortened version of the original "structured" A&A format abstract.) We performed a large optical spectroscopic and photometric survey of the Lynds~1630N and 1641 clouds. We provide a catalog of 132 confirmed young stars in L1630N and 267 such objects in L1641. We identify 28 transition disk systems, 20 of which were previously unknown, as well as 42 new transition disk candidates for which we have broad-band photometry but no optical spectroscopy. We estimate mass accretion rates M_acc from the equivalent widths of the H_alpha, H_beta, and HeI 5876Åemission lines, and find a dependence on stellar mass of M_acc propto Mstar^alpha, with alpha~3.1 in the subsolar mass range that we probe. An investigation of a large literature sample of mass accretion rate estimates yields a similar slope of alpha~2.8 in the subsolar regime, but a shallower slope of alpha~2.0 if the whole mass range of 0.04 M_sun-5 Msun is included. Among the transition disk objects, the fraction of stars that show significant accretion activity is relatively low compared to stars with still optically thick disks (26\pm11% vs. 57\pm6%, respectively). However, those transition disks that do show significant accretion have the same median accretion rate as normal optically thick disks of 3-4*10^{-9} M_sun/yr. We find that the ages of the transition disks and the WTTSs without disks are statistically indistinguishable, and both groups are significantly older than the CTTSs. These results argue against disk-binary interaction or gravitational instability as mechanisms causing a transition disk appearance. Our observations indicate that disk lifetimes in the clustered population are shorter than in the distributed population. We propose refined Halpha equivalent width criteria to distinguish WTTSs from CTTSs.

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