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\IBVShead{5714}{17 July 2006}

\IBVStitle{Accurate BV lightcurve of the eclipsing binary V1898 C\lowercase{yg}}

\IBVSauth{Dallaporta, S.$^1$; Munari, U.$^2$}

\IBVSinst{Via Filzi 9, I-38034 Cembra (TN), Italy}
\IBVSinst{INF Osservatorio Astronomico di Padova, Sede di Asiago, I-36032 Asiago (VI), Italy}

\SIMBADobj{V1898 Cyg}
\IBVSabs{Spectroscopic and photometric orbital periods published for the}
\IBVSabs{early type (B) eclipsing binary V1898 Cyg cluster around 3 days. Our}
\IBVSabs{extensive and accurate photoelectric photometry (r.m.s. 0.007 mag) has for}
\IBVSabs{the first time mapped the complete lightcurve of this binary and}
\IBVSabs{shows that previously published orbital periods are in error, the correct}
\IBVSabs{one being half of the previously published values.  The orbital ephemeris in}
\IBVSabs{V band is Min (I) = 2452901.3740 (+/- 0.0001) + 1.51311 (+/- 0.000005) x E.}

\begintext

\IBVSTnam{V1898 Cyg =  HD 200776}

\IBVSTcoo{21\hr 03\mm 53\fsec8}{+46\deg 19\arcm 50\arcs}{2000}

\IBVSTobs{28-cm Schmidt--Cassegrain telescope}

\IBVSTdet{Optec SSP5 photoelectric photometer}

\IBVSTfil{$BV$}

\IBVSTdateobs{From July 22, 2003 to September 17, 2004}

\IBVSTcomp{HD 200595 (B3V);  adopted magnitudes $V = 6.486$,   $B-V = -0.137$ 
           transformed from Tycho-2 $V_T$, $B_T$ values following Bessell (2000); 
           the same comparison star adopted by McCrosky and Whitney (1982) and Halbedel (1985)}

\IBVSTchk{HD 201666 (B2V); adopted magnitudes $V = 7.643$,   $B-V = -0.013$ 
          transformed from Tycho-2 $V_T$, $B_T$ values following Bessell (2000)}

\IBVSTdata{Available at the IBVS website and http://ulisse.pd.astro.it/V1898Cyg/index.html}

\IBVSedata{5714-t1.txt}
\IBVSdataKey{5714-t1.txt}{V1898 Cyg}{photometry}
\IBVSedata{5714-t2.txt}
\IBVSdataKey{5714-t2.txt}{V1898 Cyg}{photometry}
\IBVSedata{5714-t3.txt}
\IBVSdataKey{5714-t3.txt}{V1898 Cyg}{minima times}

\IBVSTtyp{ EB }

\IBVSTsys{Yes}{}

\IBVSTrem{Abt et al.\ (1972) discovered V1898 Cyg as a single lined
spectroscopic binary with a period of 2.9258 days. 
Photoelectric photometry by McCrosky and Whitney (1982) fitted to this
period was unable to provide a reasonable light curve.
Later on, Halbedel (1985) obtained 110 pairs of $B$, $V$ photoelectric
measurements and indicated an orbital period of 3.0239 days with nearly equally deep eclipses. 
The Variability Annex to the Hipparcos Catalog
suggests that the depth of primary and secondary eclipses should be markedly different
and that the orbital period should be around half of the previously published values.
Our extensive (607 points in $V$ band, 559 in $B$ band) and accurate (r.m.s.\ error
0.006 mag in $B$, 0.008 mag in $V$) photoelectric photometry provides the first
complete mapping of the light and color curves (see Figure~1) of this
interesting early type binary (B2III, Fehrenbach et al.\ 1962). The data show
that the correct orbital ephemeris for primary minimum in $V$ band is:
$${\rm  Min~(I)} = 2452901.3740 (\pm 0.0001) + 1.51311 (\pm 0.000005)\times E.$$
Heliocentric times of primary minima are 2452895.3220 ($\pm$ 0.0002) and
2452901.3740 ($\pm$ 0.0001) in $V$ band, 2453246.3663 ($\pm$ 0.0005) in $B$
band.}

\IBVSfig{9.1cm}{5714-f1.ps}{The complete $B$ and $V$ light curves and $B-V$ color curve for V1898 Cyg}
\IBVSfigKey{5714-f1.ps}{V1898 Cyg}{light curve}

\references

Abt, H.A., Levy, S.G., Gandet, T.L., 1972, {\it AJ}, 77, 138

Bessell, M.S., 2000, {\it PASP}, 112, 961

Fehrenbach, C. et al., 1962, {\it J. Obs.}, 45, 349 

Halbedel, E.M., 1985, {\it IBVS}, No.\ 2663

McCrosky, R.E., Whitney, C.A., 1982, {\it IBVS}, No.\ 2186

\endreferences

\bigskip

%From: IBVS 5726
\IBVSerratum{5714}

The true shape of the eclipsing binary light curve and the modified, 
correct period of V1898 Cyg was already published in IBVS 5699/76 
(2005, July 20) by Caton \& Smith \hfill\break (http://www.konkoly.hu/cgi-bin/IBVS?5699\#76).

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The Editors

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