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Recent optical activity of V4641 Sgr

ATEL # 1797; Akira Arai, Makoto Uemura, Masayuki Yamanaka, Mahito Sasada, Yuki Ikejiri, and Kiyoshi Sakimoto (Hiroshima Univ.)
on 21 Oct 2008; 20:48 UT
Password Certification: Kazutaka Yamaoka (

Subjects: Optical, Binaries, Black Holes, Transients

Optical observations were performed by the "KANATA" 1.5-m telescope at Higashi-Hiroshima Observatory. Our preliminary analysis shows the object was V=13.4 on Oct. 14, 13.7 on Oct. 15, and 13.5 on Oct. 16. It has remained in a slightly active phase in which the V-band flux was 0.1-0.2 mag brighter than its quiescent level (the quiescent state was dominated by the ellipsoidal modulations of the seconary star). The V-band light curve can be seen at:*[XRB]

We also took low resolution spectra on 15, 16, and 17. The obtained spectra show no prominent emission lines, such as reported in (Lindstrom, et al., 2005, MNRAS, 363, 882L). Most recently, on 20 and 21 Oct, the V-magnitudes were almost on the ellipsoidal modulations. It may imply a weakening of the current activity.

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