RUI: High-Resolution Observational Study of Proto-Planetary Nebulae

Hrivnak AST 99-00846在中低质量恒星从主序到白矮星演化的大多数阶段都有很好的观测记录。然而，最少被观测到的演化阶段是从红巨星向行星星云的过渡，这一阶段被称为原始行星星云(PPN)阶段。这是因为这一转变发生得相对较快；恒星经常被恒星周围的尘埃严重遮盖；而且直到最近，还没有有效的手段来识别这类天体。然而，在过去的十年里，由于从IRAS卫星红外天空测量获得的观测结果，根据尘埃壳的红外发射已经确定了大约50个良好的PPN候选者。该项目的目标是定量地确定在这一过渡阶段中具有代表性的若干天体的中心恒星和星周壳层的观测性质。将在可见光和近红外波长获得高分辨率光谱观测。根据这些观测数据，将确定光球层的丰度以及星周包层的化学和动力学。这些结果将有助于检验低质量和中等质量恒星的核合成和质量损失理论。人们已经发现，大多数原行星星云的亮度不同，也是脉动的。脉动速度是通过观察观测到的恒星辐射中的多普勒效应来测量的。这项监测原行星星云变化的独特计划将在未来三年内实施。原则上，所获得的结果可能导致关于这些对象的内部结构的信息

Abstract Hrivnak AST 99-00846The observational properties of intermediate and low mass stars have been well documented in most phases of their evolution, from the main sequence to the white dwarf phase. The most poorly observed phase of evolution, however, is the transition from red giants to planetary nebulae, in what is known as the proto-planetary nebulae (PPN) phase. This is because the transition occurs relatively rapidly; the stars are often significantly obscured by circumstellar dust; and because until recently there was not efficient means to identify such objects. In the past decade, however, as a result of observations obtained from the IRAS satellite infrared sky survey, about 50 good PPN candidates have been identified based upon the infrared emission from their dust shells.The goal of this project is to determine quantitatively the observational properties of the central stars and circumstellar shells of a representative number of objects in this transitional phase. High-resolution spectroscopic observations will be obtained at visible and near-infrared wavelengths. From the data of these observations, the photospheric abundances and the chemistry and dynamics of the circumstellar envelopes will be determined. The results will help test theories of nucleosynthesis and mass loss in low- and medium-mass stars. It has been found that most proto-planetary nebulae vary in brightness and also pulsate. The pulsation velocity is measured by observing the Doppler effects in the observed emissions from the stars. This unique program to monitor this variability of the proto-planetary nebulae will be carried out over the next three years. In principle, the results obtained may lead to information on the internal structure of these objects