[vsnet-campaign 1643] Orbital period of the new EW-type star GSC 04370-0026 in the field of RXS J062518.2+733433

[Ivan L.Andronov]

Orbital period of the new EW-type star GSC 04370-0026 in the field of RXS J062518.2+733433

I.L.Andronov (ONU, Ukraine), L.L.Chinarova (ONU, Ukraine), J.Foote (CBA Utah, USA), C.H.Kim (CBNU, Korea), Y.Kim (CBNU, Korea), N.I.Ostrova (ONU, Ukraine), S.S.Park (CBNU, Korea), S.Zola (UJ, Poland)

The <a href="http://www.konkoly.hu/cgi-bin/IBVS?5700">variability</a> of GSC 04370-0026 (R.A.=06h25m58.2s, Dec=+73 31'15.4", 2000) was discovered by S.S.Park. The star is apparently close to the intermediate polar RXS J062518.2+733433, and was studied in the same field of CCD images. Y.Kim, I.L.Andronov, S.S.Park and C.H.Kim have <a href="http://uavso.pochta.ru/TA492.pdf"> classified</a> the object as the EW-type star. 
The brightness of the <a href="http://ksss.or.kr/dtp/J200509/ykkim.ps"> comparison</a> stars for both variables was determined by Kim, Andronov et al. (2005). The observations have been obtained at the 60-cm and 1m telescopes of the Korean Institute of Astronomy and Space Science (filter R), 60-cm telescope of the Jagiellonian University (Poland, filters VRI) and 25-cm of the CBA Utah observatory (no filter).
Altogether 2040 observations during 9 nights have been obtained.<br>

The sine-based periodogram analysis using the program FO (<a href="http://il-a.pochta.ru/oap7_049.ps"> Andronov 1994</a>, Odessa Astron. Publ. 7, 49) has shown a highest peak at the period 0.22132s, which is definitely half of the orbital period. This value was corrected using the non-linear trigonometric polynomial fit (program FDCN described in the same paper). The ephemeris is <br>
Min.I.HJD=2453667.2697(6)+0.4426426(8)*E,<br>
where the numbers in brackets are error estimates in the units of a last decimal digit.
The R brightness of the fit at the minimum and maximum are 13.314(5) and 12.936(6), respectively, with an amplitude of 0.378(5) mag. However, the curve seems to be unstable at the phases 0.5-1.0, what possibly can argue for presence of an asymmetric accretion stream.

Because GSC 04370-0026 is close to RXS J062518.2+733433, further observations of both stars in the same field are appreciated.