NSF Young Investigator: Binarity in Young Stars

[457458] Ghez对恒星形成的研究常常是为了解释太阳系的形成和演化。因此，目前恒星形成的范式集中在一颗恒星的产生上，这颗恒星在年轻的时候被气体和尘埃盘包围，大约有几百个天文单位（au）大小，行星可能从这里形成。然而，盖兹等人最近对银河系中金牛座和蛇夫座的恒星形成区域进行的调查得出的结论是，大多数（如果不是全部的话）年轻的低质量恒星都有伴星。此外，大多数双星之间的距离都小于通常假设的星周盘的大小。在离金牛座和蛇夫座最近的星系形成地点（距离= 150秒差距）的距离上，星周盘的角度范围预计大约为1-2秒弧。不幸的是，由于大气中的湍流，传统成像技术的角分辨率被限制在1弧秒，比4米望远镜的理论分辨率差10-30倍。因此，为了研究这些复杂而又普遍存在的近距离双星，将使用散斑成像的高分辨率成像技术。目前的研究重点是研究这些紧密的双星对星周盘形成和演化的影响。星周盘的存在及其性质主要是从测量的金牛座T星的光谱能量分布（SED）推断出来的。特别是，过量的紫外线和红外波段的辐射被认为是由圆盘过程引起的。最近，在模拟这些影响方面的努力增加，导致SED的倾角被解释为行星形成的证据。然而，到目前为止，对紧密双星的SED是观察来自两个组成部分的联合光的结果。在一种方法中，为了回答有关紧密伴星对星周盘的影响的问题，Ghez博士正在使用高空间分辨率成像技术测量这些紧密双星系统中每个单独组成部分的SED，从光学波长到红外波长。这将允许确定(1)，有多少先前观测到的过剩可以归因于次级源的存在，而不是星周盘的存在；(2)，如果过剩存在，是两个组成部分还是只有一个显示了星周盘的证据；(3)，SED的下降是否由两颗具有不同表观温度的恒星的存在造成。在第二种方法中，Ghez博士还将比较经典金牛座T星（CTTS）的双星频率，后者被认为有一个内部吸积盘，而弱线金牛座T星（WTTS）的双星频率，后者被认为没有内部吸积盘。在他们最初的工作中，Ghez博士和她的合作者在3西格玛水平上观察到一个区别；距离小于35au的双星在WTTS中比在CTTS中更常见。这些观测结果表明，与许多金牛座T星相关的近伴星明显干扰了盘吸积过程。这个结果是一个令人兴奋的可能性，但需要对更多的金牛座T星进行后续观测才能获得统计意义。这将通过(1)扩大观察到的金牛座T星的样本到更多的恒星形成区域和使用更灵敏的相机到更暗的系统；(2)最终使用更大的望远镜（直径5米，如凯克望远镜）来进一步探索这种关系。如果Ghez博士的假设是正确的，那么CTTS和WTTS双星数量之间的差异应该在更小的距离上增加。这个奖项是为了表彰在科学和工程领域杰出的年轻教员。该奖项将通过为研究和教育活动提供灵活的支持，提高教师的职业生涯。鼓励与支持研究和教育的工业和机构合作。

9457458 Ghez The study of star formation is often motivated by the desire to explain the formation and evolution of the solar system. Thus, the current paradigm for star formation is centered on the production of a single star that, at a young age, is surrounded by a disk of gas and dust, roughly a few hundred astronomical units (AUs) in size, from which planets may form. However, recent surveys, carried out by Dr. Ghez and others, of the star forming regions of Taurus and Ophiuchus in our Galaxy have led to the conclusion that most, if not all, young low mass stars have companion stars. Furthermore, the majority of these binary stars are separated by distances that are smaller than the size typically assumed for a circumstellar disk. At the distance to Taurus and Ophiuchus, the nearest sites of star formation in our Galaxy (Distance = 150 parsec), the angular extent of a circumstellar disk is expected to be roughly 1-2 seconds of arc. Unfortunately, due to turbulence in the atmosphere, the angular resolution of traditional imaging techniques is limited to 1 second of arc, a factor of 10-30 times worse than the theoretical resolution of a 4-m telescope. Thus, to study these perplexing and yet prevalent close binary stars, the high resolution imaging technique of speckle imaging will be used. The current research effort is focussed on studying the effect of these close binary stars on the formation and evolution of circumstellar disks. The presence of a circumstellar disk and its properties are primarily inferred from the measured spectral energy distribution (SED) of T Tauri stars. In particular, it is the excesses of radiation at ultra-violet and infrared wavelengths that have been attributed to disk processes. More recently, increased efforts in modeling the effects have resulted in the interpretation of dips in the SED as evidence for planetary formation. However, the SED's for close binary stars have so far been the result of observing the co mbined light from both components. In one approach to answering questions regarding the consequence of close companion stars for circumstellar disks, Dr. Ghez is measuring the SED, from optical to infrared wavelengths, of each individual component within these close binary star systems using high spatial resolution imaging techniques. This will allow a determination of (1), how much of the previously observed excess can be attributed to the presence of a secondary source as opposed to a circumstellar disk (2), if the excess remains, whether both components or only one shows evidence for a circumstellar disk and (3), whether or not the dips in the SED are created by the presence of two stars with different apparent temperatures. In a second approach, Dr. Ghez will also compare the binary star frequency of the classical T Tauri stars (CTTS), which are thought to have an inner accretion disk, with that of the weak-lined T Tauri stars (WTTS), which are thought to lack an inner accretion disk. In their initial work, Dr. Ghez and her collaborators observed a distinction at the 3 sigma level; at separations less than 35 AU binary stars are more frequent among the WTTS than the CTTS. These observations suggest that close companions significantly interfere with the disk accretion process associated with many T Tauri stars. This result is an exciting possibility but requires follow up observations of more T Tauri stars to gain statistical significance. This will be accomplished by (1), expanding the sample of observed T Tauri stars to additional star forming regions and to fainter systems with the use of a more sensitive camera and (2), eventually using larger telescopes (Diameter 5-m, such as the Keck telescope) to probe this relationship further. If Dr. Ghez' hypothesis is correct, then the difference between the CTTS and WTTS binary star populations should increase at smaller separations. This award is to recognize an outstanding young faculty member in s cience and engineering. The award will enhance the career of the faculty member by providing flexible support for research and educational activities. Cooperation with industry and institutions that support research and education is encouraged.