Department of Physics and Astronomy, Vanderbilt University, 1807 Station B, Nashville, Tennessee 37235, USA.
Nature. 2013 Aug 22;500(7463):427-30. doi: 10.1038/nature12419.
Surface gravity is a basic stellar property, but it is difficult to measure accurately, with typical uncertainties of 25 to 50 per cent if measured spectroscopically and 90 to 150 per cent if measured photometrically. Asteroseismology measures gravity with an uncertainty of about 2 per cent but is restricted to relatively small samples of bright stars, most of which are giants. The availability of high-precision measurements of brightness variations for more than 150,000 stars provides an opportunity to investigate whether the variations can be used to determine surface gravities. The Fourier power of granulation on a star's surface correlates physically with surface gravity: if brightness variations on timescales of hours arise from granulation, then such variations should correlate with surface gravity. Here we report an analysis of archival data that reveals an observational correlation between surface gravity and root mean squared brightness variations on timescales of less than eight hours for stars with temperatures of 4,500 to 6,750 kelvin, log surface gravities of 2.5 to 4.5 (cgs units) and overall brightness variations of less than three parts per thousand. A straightforward observation of optical brightness variations therefore allows a determination of the surface gravity with a precision of better than 25 per cent for inactive Sun-like stars at main-sequence to giant stages of evolution.
表面重力是恒星的基本属性，但很难准确测量，如果通过光谱法测量，其典型不确定性为 25%至 50%；如果通过光度法测量，其典型不确定性为 90%至 150%。星震学以约 2%的不确定性测量重力，但它仅限于相对较小的亮星样本，其中大多数是巨星。对于超过 150,000 颗恒星的亮度变化进行高精度测量的方法提供了一个机会，可以研究这些变化是否可用于确定表面重力。恒星表面的颗粒状结构的傅里叶功率与表面重力在物理上相关：如果亮度变化的时间尺度为小时，是由颗粒状结构引起的，那么这种变化应该与表面重力相关。在这里，我们报告了对档案数据的分析结果，该分析结果显示，对于温度在 4500 到 6750 开尔文之间、对数表面重力在 2.5 到 4.5（cgs 单位）之间且整体亮度变化小于千分之三的恒星，其表面重力与小于八小时时间尺度上的均方根亮度变化之间存在观测相关性。因此，通过对光学亮度变化的直接观测，可以以优于 25%的精度确定处于主序到巨星演化阶段的非活动类似太阳恒星的表面重力。
