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arXiv 1209.5316astro-ph.SR
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变色龙II低质量恒星形成区：径向速度、元素丰度和吸积特性

The Chamaeleon II low-mass star-forming region: radial velocities, elemental abundances, and accretion properties

K. Biazzo, J. M. Alcalá, E. Covino, A. Frasca, F. Getman, L. Spezzi

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21 Pages, 15 Figures, 7 Tables. Accepted for publication in Astronomy and Astrophysics. Abstract shortened
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摘要：

恒星形成区（SFR）成员的径向速度、元素丰度和吸积性质对于理解恒星和行星形成具有重要意义。虽然红外观测揭示了圆盘的演化状态，但光谱学对于获取中心恒星的属性和吸积特征的信息至关重要。2 MASS存档数据和斯皮策对变色龙II暗云的c2 d巡天提供了大量年轻恒星的盘性质。我们补充这些数据与光谱的目的是提供物理恒星参数和吸积特性。我们使用FLAMES/UVES+GIRAFFE观测的40名成员Cha II测量径向速度通过互相关技术，锂丰度的生长曲线，并为一个合适的恒星元素丰度的Fe，Al，Si，Ca，Ti和Ni使用代码MOOG。从Halpha，Hbeta，和HeI-5876，6678，7065埃发射线的等效宽度，我们估计的质量吸积率，dMacc/dt，为所有的对象。我们得到了Cha II星的径向速度分布（<Vrad>=11.4 ± 2.0 km/s）。我们发现，在0.1-1.0兆太阳质量范围内，dMacc/dt与M星^[1.3]和年龄^[-0.82]相关，而Cha II的平均dMacc/dt约为7*10^（-10）兆太阳/年。我们还建立了HeI-7065埃谱线发射与吸积光度之间的关系。Cha II恒星和气体的径向速度分布是一致的。在给定的恒星质量下，dMacc/dt的扩散大约是一个数量级，不能完全归因于短时间尺度的变化。通过分析dMacc/dt与Spitzer和2 MASS波段颜色的关系，发现在dMacc/dt~10^（-10）Msun/yr时，内盘由光学厚向光学薄转变。最后，圆盘部分与Cha II的年龄一致。

英文摘要：

Radial velocities, elemental abundances, and accretion properties of members of star-forming regions (SFRs) are important for understanding star and planet formation. While infrared observations reveal the evolutionary status of the disk, optical spectroscopy is fundamental to acquire information on the properties of the central star and on the accretion characteristics. 2MASS archive data and the Spitzer c2d survey of the Chamaeleon II dark cloud have provided disk properties of a large number of young stars. We complement these data with spectroscopy with the aim of providing physical stellar parameters and accretion properties. We use FLAMES/UVES+GIRAFFE observations of 40 members of Cha II to measure radial velocities through cross-correlation technique, Li abundances by means of curves of growth, and for a suitable star elemental abundances of Fe, Al, Si, Ca, Ti, and Ni using the code MOOG. From the equivalent widths of the Halpha, Hbeta, and the HeI-5876, 6678, 7065 Angstrom emission lines, we estimate the mass accretion rates, dMacc/dt, for all the objects. We derive a radial velocity distribution for the Cha II stars (<Vrad>=11.4+-2.0 km/s). We find dMacc/dt prop. to Mstar^1.3 and to Age^(-0.82) in the 0.1-1.0 Msun mass regime, and a mean dMacc/dt for Cha II of ~7*10^(-10) Msun/yr. We also establish a relationship between the HeI-7065 Angstrom line emission and the accretion luminosity. The radial velocity distributions of stars and gas in Cha II are consistent. The spread in dMacc/dt at a given stellar mass is about one order of magnitude and can not be ascribed entirely to short timescale variability. Analyzing the relation between dMacc/dt and the colors in Spitzer and 2MASS bands, we find indications that the inner disk changes from optically thick to optically thin at dMacc/dt~10^(-10) Msun/yr. Finally, the disk fraction is consistent with the age of Cha II.

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