毕宿星团和昂宿星团恒星变率的GALEX紫外线观测
GALEX ultraviolet observations of stellar variability in the Hyades and Pleiades clusters
摘要：
本文介绍了利用GALEX近紫外（NUV：1750 - 2750 A）和远紫外（FUV：1350 - 1750 A）成像观测毕宿星团和昂宿星团疏散星团中两个直径为1.2度的视场，以探测成员星可能的紫外光变。我们已经进行了详细的软件搜索短期紫外线通量的变化，在这些观测过程中的约400个来源，在每个毕宿星团和昴星团领域，以确定耀斑（dMe）恒星物体。这次搜索发现了16个紫外线可变源，其中13个可能与M型恒星直接相关。其他的紫外源是G型星和一颗新发现的天琴座RR星，USNOB1.0 1069-0046050，周期为0.624天，距离为4.5-7.0 kpc。给出了6颗可能的dMe星上记录的7个耀斑事件的光子通量随时间变化的光变曲线。这些耀斑的紫外线能量范围为2 E27至5E 29尔格，相应的NUV变化为1.82马格。只有一个耀斑事件（在恒星Cl* Melotte 25 LH 129上）可以肯定地与毕宿星团本身的一个成员的起源有关。最后，我们的许多M型候选者显示出长时间的增强紫外线活动，但没有相关的快速增加通量，通常与耀斑事件。然而，在这种活动增加期间的总紫外线能量输出大于许多短期紫外线耀斑。这些增强的低水平紫外线活动的间隔同意的想法，即使在静止，紫外线发射从dMe星可能与叠加的许多小耀斑事件拥有广泛的能量。
英文摘要：
We present GALEX near ultraviolet (NUV:1750 - 2750A) and far ultraviolet (FUV: 1350 - 1750A) imaging observations of two 1.2 degree diameter fields in the Hyades and Pleiades open clusters in order to detect possible UV variability of the member stars. We have performed a detailed software search for short-term UV flux variability during these observations of the approx 400 sources detected in each of the Hyades and Pleiades fields to identify flare-like (dMe) stellar objects. This search resulted in the detection of 16 UV variable sources, of which 13 can be directly associated with probable M-type stars. The other UV sources are G-type stars and one newly discovered RR Lyrae star, USNOB1.0 1069-0046050, of period 0.624 day and distance 4.5-7.0 kpc. Light curves of photon flux versus time are shown for 7 flare events recorded on six probable dMe stars. UV energies for these flares span the range 2E27 to 5E29 erg, with a corresponding NUV variability change of 1.82 mag. Only one of these flare events (on the star Cl* Melotte 25 LH129) can definitely be associated with an origin on a member the Hyades cluster itself. Finally, many of our M-type candidates show long periods of enhanced UV activity but without the associated rapid increase in flux that is normally associated with a flare event. However, the total UV energy output during such periods of increased activity is greater than that of many short-term UV flares. These intervals of enhanced low-level UV activity concur with the idea that, even in quiescence, the UV emission from dMe stars may be related to a superposition of many small flare events possessing a wide range of energies.
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