BRITE-Constellation观测到的roAp星$α$ Circini
The roAp star $α$ Circini as seen by BRITE-Constellation
摘要：
我们报告的分析高精度，多色光度观测的快速振荡的Ap（roAp）明星$α$ Cir。这些观测是通过BRITE-Constellation获得的，这是一个由五颗纳米卫星组成的协调飞行任务，每次以两种颜色（Johnson B和R）连续收集数十颗明亮恒星的毫米级精度测光，时间长达180天。BRITE是BRight Target Explorer的缩写。物体$α$ Cir是最亮的roAp星，也是进行此类调查的理想目标，有助于以高分辨率确定振荡频率。这颗恒星足够明亮，可以进行互补干涉测量和时间分辨光谱学。四颗BRITE卫星对$α$ Cir进行了146天或33个旋转周期的观测。根据4.4790 d的旋转周期分阶段的测光揭示了定性不同的光变化在两个光度带。相控的红波段测光与先前发表的WIRE数据吻合良好，显示出关于相位0.5对称的光变曲线，其中第一谐波的贡献很大。相反，相位蓝波段数据显示基本上是正弦变化。我们用贝叶斯光度成像对这两个光变曲线进行建模，这表明存在两个大规模的光度明亮（相对于周围的光球）点。我们还研究了高频脉动光谱编码的BRITE测光。我们的分析建立了过去20年的主脉动频率的稳定性，确认了在2006年之前未检测到的频率f7的存在（或未激发的模式），并排除了主脉动频率的四极模式。
英文摘要：
We report on an analysis of high-precision, multi-colour photometric observations of the rapidly-oscillating Ap (roAp) star $α$ Cir. These observations were obtained with the BRITE-Constellation, which is a coordinated mission of five nanosatellites that collects continuous millimagnitude-precision photometry of dozens of bright stars for up to 180 days at a time in two colours (Johnson B and R). BRITE stands for BRight Target Explorer. The object $α$ Cir is the brightest roAp star and an ideal target for such investigations, facilitating the determination of oscillation frequencies with high resolution. This star is bright enough for complementary interferometry and time-resolved spectroscopy. Four BRITE satellites observed $α$ Cir for 146 d or 33 rotational cycles. Phasing the photometry according to the 4.4790 d rotational period reveals qualitatively different light variations in the two photometric bands. The phased red-band photometry is in good agreement with previously-published WIRE data, showing a light curve symmetric about phase 0.5 with a strong contribution from the first harmonic. The phased blue-band data, in contrast, show an essentially sinusoidal variation. We model both light curves with Bayesian Photometric Imaging, which suggests the presence of two large-scale, photometrically bright (relative to the surrounding photosphere) spots. We also examine the high-frequency pulsation spectrum as encoded in the BRITE photometry. Our analysis establishes the stability of the main pulsation frequency over the last 20 years, confirms the presence of frequency f7, which was not detected (or the mode not excited) prior to 2006, and excludes quadrupolar modes for the main pulsation frequency.
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