A New Approach to Identifying Massive Young Stellar Objects (MYSOs)

最近斯皮策太空望远镜红外线阵列照相机（IRAC）对银道面的调查揭示了一类新的物体，其特征是在IRAC 4.5微米波段的明亮扩展发射。 Edward Churchwell博士（威斯康星州-麦迪逊大学）和他的小组已经对其中300多个天体（指定EGO =扩展绿色天体，因为在三色IRAC图像中4.5微米波段的共同编码是绿色）进行了编目。 对EGO的中红外光谱能量分布（SED）的分析表明，它们是大质量的年轻恒星天体（MYSO）。激发4.5微米发射的机制，被认为是在超音速外流中的冲击H2或CO气体，表明EGO是处于活跃吸积状态的MYSO。 研究人员将进行一套全面的多波长研究，旨在描述新发现的EGO的特性，并对大质量星星形成的理论提出限制;特别是吸积、外流和集群如何同时运作。将在该项目下进行的研究将通过近红外至厘米波长的高角分辨率研究，对精心挑选的30个EGO样品的流出特性、光度、质量和聚集特性进行表征。 其中包括扩展甚大阵列（EVLA）搜索44 GHz I类CH 3OH脉泽，已知与分子流出，这将与低分辨率分子线调查（HCO+和SiO）结合使用，以测试假设的流出起源IRAC 4.5微米的排放和测量流出特性。EVLA搜索6.7 GHz的II类CH 3OH脉泽，已知是与MYSO，将使用沿着同时获得的高分辨率3.6厘米和7毫米的连续数据，以建立质量范围的EGO。运动学距离将被确定为样本中的所有源，允许光度，恒星质量和信封吸积率被提取从他们的SED使用网格的原恒星模型。对这类新天体的这些后续观测将为迄今为止隐藏的高质量原恒星演化阶段提供急需的信息。除了更好地了解MYSO性质的主要研究目标外，该项目将在项目期间支持培训一名全日制研究生和几名本科生，并通过几个当地组织促进公众宣传，包括威斯康星州航天中心的大学，天文学系的校外推广中心，每周天文广播节目。

Recent Spitzer Space Telescope Infrared Array Camera (IRAC) surveys of the Galactic Plane have revealed a new class of objects that are characterized by bright extended emission in the IRAC 4.5 micron band. Over 300 of these objects (designated EGOs=extended green objects, for the common coding of the 4.5 micron band as green in 3-color IRAC images) have been catalogued by Dr. Edward Churchwell (University of Wisconsin - Madison) and his team. Analysis of the mid-infrared spectral energy distributions (SEDs) of EGOs indicates that they are massive young stellar objects (MYSOs). The mechanism for exciting the 4.5 micron emission, thought to be shocked H2 or CO gas in supersonic outflows, suggests that EGOs are MYSOs in a state of active accretion. The investigators will carry out a comprehensive set of multiwavelength studies designed to characterize the properties of the newly discovered EGOs and to place constraints on theories of massive star formation; in particular how accretion, outflows and clustering operate simultaneously.Very little is currently known about EGOs other than the mid-Infrared properties derived from Spitzer data. The studies that will be carried out under this project will characterize the outflow properties, luminosities, masses, and clustering properties of a well-chosen sample of 30 EGOs, via high angular resolution studies at near-Infrared through centimeter wavelengths. These include an Extended-Very Large Array (EVLA) search for 44 GHz Class I CH3OH masers, known to be associated with molecular outflows, which will be used in conjunction with lower-resolution molecular line surveys (HCO+ and SiO) to test the hypothesis of an outflow origin for the IRAC 4.5 micron emission and measure outflow properties. An EVLA search for 6.7 GHz Class II CH3OH masers, known to be associated with MYSOs, will be used along with simultaneously obtained high-resolution 3.6 cm and 7 mm continuum data to establish the mass range of EGOs. Kinematic distances will be determined for all the sources in the sample, permitting the luminosity, stellar mass, and envelope accretion rate to be extracted from their SEDs using a grid of protostar models. These follow-up observations on this new class of objects will add much needed information on this heretofore hidden stage of high-mass protostellar evolution.In addition to the primary research goals of better understanding the nature of MYSOs, this project will support the training of one full time graduate student and several undergraduate students over its duration as well as contributing to public outreach through several local organizations, including the University of Wisconsin Space Place, the off-campus outreach center of the Department of Astronomy, and a weekly astronomy radio program.