The VLTI/MIDI survey of massive young stellar objects: Sounding the inner regions around intermediate-and high-mass young stars using mid-infrared interferometry
The VLTI/MIDI survey of massive young stellar objects: Sounding the inner regions around intermediate-and high-mass young stars using mid-infrared interferometry
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DOI：
10.1051/0004-6361/201321539
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发表时间：
2013-08
影响因子：
6.5
通讯作者：
P. Boley;H. Linz;R. Boekel;T. Henning;M. Feldt;L. Kaper;C. Leinert;A. Mueller;I. Pascucci;M. Robberto;B. Stecklum;L. Waters;H. Zinnecker
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作者：
P. Boley;H. Linz;R. Boekel;T. Henning;M. Feldt;L. Kaper;C. Leinert;A. Mueller;I. Pascucci;M. Robberto;B. Stecklum;L. Waters;H. Zinnecker
上下文由于大质量恒星形成的观测和数值模拟存在固有的困难，对这些天体早期演化阶段的理解仍然是难以捉摸的。特别是，观测探测距离中央星星100 Au的星周物质是非常困难的，因为这样的物体很罕见（因此，平均来说，很远），通常嵌入很深。长基线中红外干涉测量法提供了一种在适当波长获得研究这类物体所需的空间分辨率的方法;然而，由于空间频率覆盖范围稀疏，解释这类观测结果往往很困难。目标。我们的目标是描述年轻大质量恒星周围星周物质的分布和组成，并通过长基线中红外干涉观测来研究这些物体中的物理结构。方法.我们使用欧洲南方天文台甚大望远镜干涉仪的双望远镜干涉仪，在N波段（8-13 μm）观测了24个中等质量和高质量的年轻恒星天体样本。我们有成功的条纹探测20个对象，目前光谱分辨相关通量和能见度水平的预测基线高达128米。我们用几何模型拟合了星周物质的体积，得到了发射区的大小，以及星周物质的取向和伸长。样品中的14个物体在总通量谱和相关通量谱中显示出10 μm硅酸盐吸收特征。对于其中的13个天体，我们能够用一个简单的吸收模型拟合相关通量谱，从而限制星周物质的成分和吸收特性。结果几乎所有观测到的大质量年轻恒星天体在中红外波长下都表现出明显的球对称性偏差。一般来说，中红外辐射既能追踪气盘，也能追踪外流，但在许多情况下，由于目前的长基线干涉仪通常提供的空间频率覆盖范围很小，因此仅凭干涉测量数据可能难以理清这些成分。对于这个样本中的大多数物体，吸收发生在比探测器探测的更大的空间尺度上。最后，这些光源周围的中红外辐射的物理范围与总光度相关，尽管有显著的散射。结论.星周物质在年轻的大质量恒星周围距离Au 100天文单位处无处不在。长基线中红外干涉测量法提供了直接观测这种物质所需的分辨能力。然而，特别是对于深埋源，当试图将中红外辐射归因于特定的物理结构时，必须谨慎，例如拱星盘或外流。
Context. Because of inherent difficulties involved in observations and numerical simulations of the formation of massive stars, an understanding of the early evolutionary phases of these objects remains elusive. In particular, observationally probing circumstellar material at distances ≲100 AU from the central star is exceedingly difficult, as such objects are rare (and thus, on average, far away) and typically deeply embedded. Long-baseline mid-infrared interferometry provides one way of obtaining the necessary spatial resolution at appropriate wavelengths for studying this class of objects; however, interpreting such observations is often difficult due to sparse spatial-frequency coverage. Aims. We aim to characterize the distribution and composition of circumstellar material around young massive stars and to investigate exactly which physical structures in these objects are probed by long-baseline mid-infrared interferometric observations. Methods. We used the two-telescope interferometric instrument MIDI of the Very Large Telescope Interferometer of the European Southern Observatory to observe a sample of 24 intermediate- and high-mass young stellar objects in the N band (8-13 μm). We had successful fringe detections for 20 objects and present spectrally-resolved correlated fluxes and visibility levels for projected baselines of up to 128 m. We fit the visibilities with geometric models to derive the sizes of the emitting regions, as well as the orientation and elongation of the circumstellar material. Fourteen objects in the sample show the 10 μm silicate feature in absorption in the total and correlated flux spectra. For 13 of these objects, we were able to fit the correlated flux spectra with a simple absorption model, allowing us to constrain the composition and absorptive properties of the circumstellar material. Results. Nearly all of the massive young stellar objects observed show significant deviations from spherical symmetry at mid-infrared wavelengths. In general, the mid-infrared emission can trace both disks and outflows, and in many cases it may be difficult to disentangle these components on the basis of interferometric data alone, because of the sparse spatial frequency coverage normally provided by current long-baseline interferometers. For the majority of the objects in this sample, the absorption occurs on spatial scales larger than those probed by MIDI. Finally, the physical extent of the mid-infrared emission around these sources is correlated with the total luminosity, albeit with significant scatter. Conclusions. Circumstellar material is ubiquitous at distances ≲100 AU around young massive stars. Long-baseline mid-infrared interferometry provides the resolving power necessary for observing this material directly. However, in particular for deeply-embedded sources, caution must be used when attempting to attribute mid-infrared emission to specific physical structures, such as a circumstellar disk or an outflow.