A solar-like magnetic cycle on the mature K-dwarf 61 Cyg A (HD 201091)
S. Boro Saikia, S. V. Jeffers, J. Morin, P. Petit, C. P. Folsom, S. C. Marsden, J. -F. Donati, R. Cameron, J. C. Hall, V. Perdelwitz, A. Reiners, A. A. Vidotto
The long-term monitoring of magnetic cycles in cool stars is a key diagnostic in understanding how dynamo generation and amplification of magnetic fields occur in stars similar in structure to the Sun. We investigate the temporal evolution of a possible magnetic cycle, determined from its large-scale field, of 61 Cyg A over its activity cycle using spectropolarimetric observations and compare it to the solar case. We use Zeeman Doppler imaging (ZDI) to reconstruct the large-scale magnetic geometry over multiple observational epochs spread over a time span of nine years. We investigate the time evolution of the different components of the large-scale field and compare it with the evolution of its chromospheric activity by measuring the flux in three different chromospheric indicators: Ca II H&K, H-alpha and Ca II infra red triplet lines. We also compare our results with the star's coronal activity using XMM-Newton observations. The large-scale magnetic geometry of 61 Cyg A exhibits polarity reversals in both poloidal and toroidal field components, in phase with the chromospheric activity cycle. We also detect weak solar-like differential rotation with a shear level similar to the Sun. During our observational time span of nine years, 61 Cyg A exhibits solar-like variations in its large-scale field geometry as it evolves from minimum activity to maximum activity and vice versa. During its activity minimum in epoch 2007.59, ZDI reconstructs a simple dipolar geometry which becomes more complex close to activity maximum in epoch 2010.55. The radial field flips polarity and reverts back to a simple geometry in epoch 2013.61. The field is strongly dipolar and the evolution of the dipole component of the field is reminiscent of the solar behaviour. The polarity reversal of the large-scale field indicates a magnetic cycle that is in phase with the chromospheric and coronal cycle.
A 682-second X-ray Periodicity in CH Cygni: Evidence for a Magnetic White Dwarf
Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Fisk University（菲斯克大学）；Vanderbilt University（范德堡大学）；Texas Tech University（得克萨斯理工大学）；University of Texas Rio Grande Valley（德克萨斯里奥格兰德河谷大学）
Differences in the fast optical variability of the dwarf nova V1504 Cyg between quiescence and outbursts detected in Kepler data and simulations of the rms-flux relations
White dwarf and subdwarf stars in the Sloan Digital Sky Survey Data Release 16
白矮星是超过97%的恒星演化的终态，因此通过它们的光度函数和初末质量关系携带着银河系结构和演化的信息。通过研究斯隆数字巡天数据第16版中所有白色或蓝色恒星的新光谱，我们报告了2410颗恒星的光谱分类，直到我们的识别截止值信噪比等于3。我们新发现了1404个DA，189个DZ，103个DC，12个DB和9个CV。剩下的天体是碳或L星（dC/L），窄线氢主导星（sdA），矮F星和P Cyg天体的混合体。由于SDSS DR 16没有瞄准白矮星，新发现的数量比以前的版本要少得多。我们还报告了大气参数和质量的一个子集，包括555个新的DA，10个新的DB，和85个DZ的光谱与信噪比大于10。
