[论文解读] Long-term, Multiwavelength Light Curves of Ultra-Cool Dwarfs: II. The evolving Light Curves of the T2.5 SIMP 0136 & the Uncorrelated Light Curves of the M9 TVLM 513

Bryce Croll, Philip S. Muirhead+4 more|arXiv (Cornell University)|Sep 12, 2016

Stellar, planetary, and galactic studies被引用 5

一句话总结

本研究对T2.5型棕矮星SIMP 0136进行了17晚的近红外测光观测，揭示其光变曲线振幅在数日内从>6%迅速降至<1%，表现出与自转周期相当的演化特征，表明基于单次自转观测的光谱解释可能仅反映瞬时快照。对M9型矮星TVLM 513的J波段与I波段同步测光证实，其变异性源于云层或极光，而非黑子。

ABSTRACT

We present 17 nights of ground-based, near-infrared photometry of the variable L/T transition brown dwarf SIMP J013656.5+093347 and an additional 3 nights of ground-based photometry of the radio-active late M-dwarf TVLM 513-46546. Our TVLM 513-46546 photometry includes 2 nights of simultaneous, multiwavelength, ground-based photometry, in which we detect obvious J-band variability, but do not detect I-band variability of similar amplitude, confirming that the variability of TVLM 513-46546 most likely arises from clouds or aurorae, rather than starspots. Our photometry of SIMP J013656.5+093347 includes 15 nights of J-band photometry that allow us to observe how the variable light curve of this L/T transition brown dwarf evolves from rotation period to rotation period, night-to-night and week-to-week. We estimate the rotation period of SIMP J013656.5+093347 as 2.406 +/- 0.008 hours, and do not find evidence for obvious differential rotation. The peak-to-peak amplitude displayed by SIMP J013656.5+093347 in our light curves evolves from greater than 6% to less than 1% in a matter of days, and the typical timescale for significant evolution of the SIMP J013656.5+093347 light curve appears to be approximately &lt;1 to 10 rotation periods. This suggests that those performing spectrophotometric observations of brown dwarfs should be cautious in their interpretations comparing the spectra between a variable brown dwarf's maximum flux and minimum flux from observations lasting only approximately a rotation period, as these comparisons may depict the spectral characteristics of a single, ephemeral snapshot, rather than the full range of characteristics.

研究动机与目标

• 研究超冷矮星，特别是L/T过渡阶段的长期测光变异性演化。
• 确定短时长光谱测光观测是否能捕捉变异性棕矮星的全部光谱特征。
• 利用多波段测光区分晚型矮星变异性中黑子、云层和极光的起源。
• 首次利用可靠数据测量L/T过渡阶段棕矮星的光变曲线演化 timescale。
• 评估在变异性棕矮星中，最大与最小通量状态之间光谱比较的可靠性。

提出的方法

• 对T2.5型棕矮星SIMP J013656.5+093347进行了17晚的地基近红外测光，其中15晚为J波段。
• 对M9型矮星TVLM 513-46546进行了两晚的同步J波段与I波段测光，以比较不同波段的变异性振幅。
• 采用傅里叶分析与相位折叠光变曲线，高精度测定SIMP 0136的自转周期为2.406 ± 0.008小时。
• 追踪逐夜及周际的峰峰值振幅变化，以量化光变曲线演化 timescale。
• 比较TVLM 513的J波段与I波段变异性振幅，以排除黑子驱动变异性。
• 评估各夜间测光周期的一致性，以约束差速自转。

实验结果

研究问题

• RQ1 L/T过渡阶段棕矮星SIMP 0136的光变曲线显著演化 timescale 是多少？
• RQ2 基于多波段测光，M9型矮星TVLM 513的变异性是由黑子、云层还是极光引起？
• RQ3 对变异性棕矮星的单次自转观测在多大程度上能代表其全部光谱特征？
• RQ4 基于逐夜周期稳定性，SIMP 0136是否存在差速自转的证据？
• RQ5 SIMP 0136的变异性振幅在数日内从一个自转周期到下一个自转周期如何演化？

主要发现

• SIMP J013656.5+093347的自转周期测定为2.406 ± 0.008小时，且各夜间无显著周期变化。
• SIMP 0136的J波段光变曲线峰峰值振幅在短短数日内由大于6%降至小于1%。
• SIMP 0136的显著光变曲线演化 timescale 短至一个自转周期，长至约一天。
• 尽管J波段存在明显变异性，TVLM 513-46546未检测到显著的I波段变异性，排除了黑子为主要成因。
• 基于多波段测光一致性，TVLM 513的变异性最可能由云层或极光驱动，而非黑子。
• 本研究表明，变异性棕矮星中最大与最小通量状态之间的光谱测光比较，可能仅反映单一瞬时快照，而非完整的光谱范围。