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

摘要Hrivnak AST 99- 00846中低质量恒星的观测性质在它们演化的大多数阶段，从主序星到白色矮星阶段，都有很好的记录。 然而，观测最少的演化阶段是从红巨星到行星状星云的过渡，即所谓的原行星状星云（PPN）阶段。这是因为这种转变发生得相对较快;恒星经常被星周尘埃显著遮蔽;而且直到最近还没有有效的手段来识别这样的物体。然而，在过去的十年中，作为IRAS卫星红外巡天观测的结果，根据尘埃壳层的红外辐射，已经确定了大约50个好的PPN候选者，本项目的目标是定量地确定这一过渡阶段中具有代表性的一些物体的中心星和拱星壳层的观测特性。 将获得可见光和近红外波长的高分辨率光谱观测。根据这些观测数据，将确定光球丰度和星周包层的化学和动力学。这些结果将有助于检验中低质量恒星的核合成和质量损失理论。人们发现，大多数原行星状星云的亮度变化很大，而且也有脉动。 脉动速度是通过观测来自恒星的观测辐射中的多普勒效应来测量的。 这个监测原行星状星云这种变化的独特方案将在今后三年内进行。 原则上，所获得的结果可能导致这些物体内部结构的信息

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