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2020年

圖: CLASH星系團的徑向加速關係

田雍 博士後研究員: 我們首次接露了一個緊密的徑向加速關係在20個CLASH星系團。在本圖中,兩軸分別來自兩個獨立的測量:總加速度(gtot)來自弱重力透鏡和強重力透鏡效應;重子加速度(gbar)來自X射線氣體、恆星質量和星團最亮星系。方程gtot=(gbar g)1/2可描述徑向加速關係,其中g=(2.02±0.11)×10−9 ms−2。其斜率和星系中徑向加速關係的低加速度極限一致,但是截距則暗示了一個更大的加速度尺度。

Fig. Asteroid Discovery and Light Curve Extraction Using the Hough Transform: A Rotation Period Study for Subkilometer Main-belt Asteroids

Dr. Chan-Kao Chang: Using the Hough transform, a line detecting algorithm, more than 3000 new asteroids were discovered from a high-cadence observation of the Pan-STARRS 1 (PS1). This observation was originally planned to collected asteroid lightcurves for rotation period measurement and conducted in October 2016. Because of the high cadence observation (i.e., images were continuously taken one after one for the entire night), the detections of an asteroid would line up as a straight line and, therefore, these line-up detections can be used to identify asteroids.

With the collected lightcurves of these new asteroids, 122 reliable rotation periods were obtained and 13 of them are super-fast rotators (i.e., asteroids in the size range of rubble-pile structure, a weak aggregate of large and small components held together by gravity rather than material strength, have rotation periods < 2 hr). This kind of asteroids is not expected because they suppose to be destroyed due to the exceedingly centrifugal force introduced by a rotation period of < 2hr. How these super-fast rotators can survive is still a mystery. (Lo, Kai-Jie, et al. (including Chan-Kao Chang; Wing-Huen Ip; Wen-Ping Chen) 2020, AJ, 159, 25L)