KEPLER MONITORING OF AN L DWARF I. THE PHOTOMETRIC PERIOD AND WHITE LIGHT FLARES
KEPLER MONITORING OF AN L DWARF I. THE PHOTOMETRIC PERIOD AND WHITE LIGHT FLARES
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L 矮星的开普勒监测 I. 光度周期和白光耀斑
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发表时间：
2013
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通讯作者：
S. Metchev
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作者：
J. Gizis;A. Burgasser;E. Berger;P. Williams;F. Vrba;K. Cruz;S. Metchev
我们报告了开普勒任务对附近L1矮星WISEP J190648.47+401106.8 （W1906+40）进行15个月监测的结果。Karl G. Jansky甚大阵列和双子座北望远镜的观测结果显示，这颗L矮星具有磁性活动，具有静止的射电和可变的Hα发射。初步的三角视差显示W1906+40位于pc的距离，所有的观测结果都表明W1906+40是一颗古老的盘状恒星，刚好在氢燃烧极限之上。这颗恒星的光度变化周期为8.9小时，幅度为1.5%，全年都有一个一致的相位。我们从观测到的周期、光度（10−3.67±0.03 L☉）、有效温度（2300±75 K）和vsin i（11.2±2.2 km s−1）推断其半径为0.92±0.07RJ和sini > 0.57。光曲线可以用一个大的高纬度黑点来模拟。与许多l型棕矮星不同，没有证据表明在< 2%的水平上存在其他的变化，无论是非周期的还是短暂的周期的，这些变化掩盖了潜在的旋转周期。我们认为长期存在的表面特征可能是由于恒星黑子，但如果没有进一步的多波长观测，就不能排除云变化的可能性。在双子座光谱学中，我们观察到有史以来在L矮星上看到的最强大的耀斑，估计白光发射能量为1.6 × 1032 erg。利用开普勒的数据，我们发现了类似的耀斑，并估计W1906+40上的光学/紫外能量为1031尔格或更高的白光耀斑每月经常出现1-2次。
We report on the results of 15 months of monitoring the nearby field L1 dwarf WISEP J190648.47+401106.8 (W1906+40) with the Kepler mission. Supporting observations with the Karl G. Jansky Very Large Array and Gemini North Telescope reveal that the L dwarf is magnetically active, with quiescent radio and variable Hα emission. A preliminary trigonometric parallax shows that W1906+40 is at a distance of pc, and all observations are consistent with W1906+40 being an old disk star just above the hydrogen-burning limit. The star shows photometric variability with a period of 8.9 hr and an amplitude of 1.5%, with a consistent phase throughout the year. We infer a radius of 0.92 ± 0.07RJ and sin i > 0.57 from the observed period, luminosity (10−3.67 ± 0.03 L☉), effective temperature (2300 ± 75 K), and vsin i (11.2 ± 2.2 km s−1). The light curve may be modeled with a single large, high latitude dark spot. Unlike many L-type brown dwarfs, there is no evidence of other variations at the ≳ 2% level, either non-periodic or transient periodic, that mask the underlying rotation period. We suggest that the long-lived surface features may be due to starspots, but the possibility of cloud variations cannot be ruled out without further multi-wavelength observations. During the Gemini spectroscopy, we observed the most powerful flare ever seen on an L dwarf, with an estimated energy of ∼1.6 × 1032 erg in white light emission. Using the Kepler data, we identify similar flares and estimate that white light flares with optical/ultraviolet energies of 1031 erg or more occur on W1906+40 as often as 1–2 times per month.