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ATEL # 1640; D.V. Denisenko (IKI, Moscow), T.V. Kryachko, B.L. Satovskiy (Astrotel Observatory, KSU/AST)
on 31 Jul 2008; 17:08 UT
Password Certification: S.A.Grebenev (firstname.lastname@example.org)
Subjects: Optical, X-ray, Cataclysmic Variables, Variables
During the systematic search for optical identifications of the poorly studied ROSAT sources a variable object was found within 20" from 1RXS J180834.7+101041. The star USNO-B1 1001-0317189 at the following coordinates: R.A.=18h08m35.80s, Dec.=+10o10'30.2" (J2000.0) has varied by about 0.8m between two Red Palomar plates. Photometric follow-up with the 0.30-m Astrotel-Caucasus robotic telescope (Kazan State University Mountain Station, Karachay-Cherkessia, Russia) has confirmed the star to be a cataclysmic variable with a period of 0.070037(1)d. More than 220 unfiltered exposures, each 300 sec long, were obtained between JD 2454608 and 2454648. USNO-A2.0 0975-10560020 (R=15.8) was used as a comparison star and USNO-A2.0 0975-10561808 as a check star. During four observing nights between 2008 May 21 and 31 the object was showing very prominent short eclipses from 17.1m to 18.4m. Light curve of J1808+1010 obtained on May 22 with four eclipses is presented at http://hea.iki.rssi.ru/~denis/J1808+1010-LC-May22.gif . Between June 13 and 30, however, the variable appeared in a higher state with eclipses from 16.1m to 17.0m. Judging from the orbital period and variations of the light curve we suppose the object to be a cataclysmic variable of AM Her type - that is, a polar variable.
Color-combined (BRIR) 10'x9' DSS finder chart is available at http://hea.iki.rssi.ru/~denis/J1808+1010-comps.gif (position of CV is marked with dashes). The folded light curves (separately for May and June) are shown at http://hea.iki.rssi.ru/~denis/J1808+1010-LC2008.gif .
During single night observation on July 26.95 UT the object was measured at unfiltered CR=15.7 magnitude. The variable still appears to be in the active state. Spectroscopic and photometric follow-up is encouraged.