Global Time-Series Photometry of Collapsed Variable Stars

脉动物体对物理学家来说很重要，因为对它们的分析可以提供有关物体内部结构的信息；这是研究地震扰动以确定地球内部结构的基本原理。天文学家已经发现，太阳和其他种类的恒星经历了许多类型的“非径向脉动”，对这些观测结果的分析现在是太阳物理学中发展最快的学科。许多白矮星是恒星演化的最常见的产物，也经历了许多类型的非径向振荡。这些恒星中大量的脉动模式，加上它们简单的“简并”状态（允许用很少的物理变量来制定模型），已经将白矮星的地震学研究推向了变星研究的前沿。首席研究员（PI）使用了之前的五年总统青年研究员奖，以帮助资助全球一组天文学家同时观测白矮星的不同寻常的兴趣。通过汇集他们的观测数据，他们能够规避地球昼夜旋转周期造成的严重数据缺口，并进行数天的观测——在最好的情况下，连续观测近10天。PI和他的合作者使用如此超长的数据串来探测和识别白矮星PG+1159-035中超过100个独立的脉动模式。这些脉动的识别使天文学家能够估计这颗恒星的质量在0.4%以内（除了太阳之外最精确的恒星质量测定），估计恒星的自转速度，包括恒星旋转轴在天空中的倾斜，并推断出该恒星至少存在三个不同化学成分的区域。国家科学基金会的奖金将支持对其他特殊兴趣的白矮星的国际观测活动的继续。该研究将特别强调其化学结构的细节以及旋转对NRP模式激发的影响。最终，这些研究可能还允许测量一些白矮星的大小随时间的变化。反过来，这将使我们能够准确地估计这些恒星演化为“冷烬”时的冷却速度。这样的冷却速率将使我们能够估计这些恒星的年龄。由于这些恒星是我们银河系盘中最古老的恒星之一，因此这些年龄将为我们银河系的年龄以及宇宙的年龄提供强有力的限制。

Pulsating objects are important to physicists because an analysis of them gives information about the interior structure of the object; this is the principle underlying the study of seismic disturbances to determine the Earth's interior structure. Astronomers have discovered that the Sun and other classes of stars undergo many types of "nonradial pulsations", and the analysis of these observations is now responsible for the most rapidly developing disciplines of solar physics. Many white dwarf stars, which are the most common product of stellar evolution, undergo many types of nonradial oscillations as well. The large number of pulsation modes in these stars, together with their simple "degenerate" state (which allows a model to be formulated with very few physical variables), has moved the study of seismology of white dwarfs to the forefront of variable star research. The Principal Investigator (PI) has used a previous, five-year Presidential Young Investigator award to help underwrite simultaneous observing of white dwarfs of unusual interest by a group of astronomers located around the globe. By pooling their observations they are able to circumvent the severe data-gaps imposed by the Earth's day/night rotation cycle and conduct observations for several days -- in the best case over nearly 10 continuous days. The PI and his collaborators have used such extraordinarily long data strings to detect and identify over 100 independent pulsation modes in the white dwarf PG+1159-035. The identification of these pulsations has permitted astronomers to estimate the mass of this star to within 0.4% (the most accurate determination of a stellar mass other than the Sun's), to estimate the star's rotation rate including the tilt of the star's rotational axis in the sky, and to infer the presence of at least three regions of the star with different chemical compositions. The NSF award will support a continuation of international observing campaigns on other white dwarfs of special interest. The study will emphasis emphasis in particular the details of their chemical structure as well as the effect of rotation of the excitation of the NRP modes. Eventually, these studies may also permit the measurement of the change of some white dwarfs' sizes with time. This would allow in turn an accurate estimate of the cooling rate of these stars as they evolve to "cold embers". Such cooling rates will permit an estimate of the ages of these stars. Since these stars are among the oldest stars in the disk of our Milky Way Galaxy, these ages will provide strong constraints on the age of our Galaxy and hence of the Universe.