* Astronomy

Title: Lightcurves of the Karin family asteroids
Authors: Fumi Yoshida, Takashi Ito, Budi Dermawan, Tsuko Nakamura, Shigeru Takahashi, Mansur A. Ibrahimov, Renu Malhotra, Wing Huen Ip, Wen Ping Chen, Yu Sawabe, Masashige Haji, Ryoko Saito, Masanori Hirai, Seidai Miyasaka, Hideo Fukushima, Hideo Sato, Yusuke Sato

The Karin family is the first recognised very young asteroid family that was created by an asteroid breakup only 5.8 Myr ago. As the members of this family probably have not experienced significant orbital or collisional evolution yet, it is possible that they still preserve properties of the original collisional event in terms of their rotational status and surface colour. We have been carrying out a series of photometric observations of the Karin family asteroids, and here we report the analysis result of lightcurves including the rotation period of eleven members as well as those of an interloper asteroid: (832) Karin, (4507) 1990 FV (an interloper), (7719) 1997 GT36, (10783) 1999 RB9, (11728) Einer, (13765) Nansmith, (16706) Svojsik, (28271) 1999 CK16, (40917) 1999 TR171, (43032) 1999 VR26, (69880) 1998 SQ81, and (71031) 1999 XE68. As for four of them we estimated their absolute magnitudes H_R and the slope parameter G_R of the solar phase curves: (832) Karin, (4507) 1990 FV, (13765) Nansmith, and (69880) 1998 SQ81. Relation between the reduced peak-to-peak variation magnitude and the rotation period of the asteroids indicates that there is a general trend that elongated members have lower spin rate, and less elongated members have higher spin rate. The mean rotation rate of the Karin family members turned out to be much lower than those of NEAs (near-Earth asteroids) or smaller MBAs (main belt asteroids; diameter D<12 km), and even lower than that of larger MBAs (D>130 km), suggesting the existence of post-disruption evolution process over the spin state of the older asteroids, such as the YORP effect.

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