Special Notice #208: Optical transient in Pegasus

May 8, 2010: CBET 2273 (D.W.E. Green, editor) reports the discovery of a bright transient in Pegasus by Dae-Am Yi (Yeongwol-kun, Gangwon-do, Korea). The object was discovered at magnitude 10.8 on 2010 May 6.77 (JD 2455323.27) on an image taken with a Canon 5D + 93-mm camera lens. The object brightened to magnitude 8.4 as observed on 2010 May 7.76 (2455324.26) on an image taken with a 400-mm lens. The transient object appears to be concident with GSC 2197:886 on discovery images, but this identification is not yet proven. The GSC star has a NOMAD catalog V magnitude of 13.84 and is a close double with a separation of about 3 arcseconds. Based upon an examination of the POSS-I and POSS-II plates by Arne Henden, it is possible that the double is composed of two unassociated stars, one with a high proper motion. Observations of this field are strongly encouraged both to obtain astrometry of the source and to follow the progress of this outburst. It was noted by H. Yamaoka (Kyushu University) that there is a bright ROSAT X-ray source within seven arcseconds of the GSC star, and so the object may be a cataclysmic variable of some kind.
CBET 2273 gives the coordinates of the GSC star for the object, which are
RA: 21 38 06.571 , Dec: +26 19 57.33
Charts for this object may be plotted using AAVSO VSP (http://www.aavso.org/vsp).
Please promptly submit all observations to the AAVSO using the name "VSX J213806.5+261957".
This AAVSO Special Notice was prepared by M. Templeton.
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