\documentstyle[epsfig,twoside]{article}

\input ibvs2.sty

\begin{document}


\IBVShead{5646}{24 August 2005}

\IBVStitletl{Partial Eclipses in BR Cygni}

\IBVSauth{Terrell, Dirk$^1$; Gross, John$^2$}

\IBVSinst{Dept. of Space Studies, Southwest Research Institute,
1050 Walnut St., Suite 400,\\ \indent  Boulder, CO 80302, USA,
e-mail: terrell@boulder.swri.edu}

\IBVSinst{Sonoita Research Observatory, Box 131, Sonoita, AZ 85637, USA,
e-mail: johngross3@msn.com}

\SIMBADobj{BR Cyg}
\IBVStyp{  EB  }
\IBVSkey{photometry}
\IBVSabs{New BVRcIc photometry of BR Cygni shows that the primary eclipse}
\IBVSabs{is partial and does not show the unusual filter-dependent behavior}
\IBVSabs{published by Wehinger.}


\begintext

\vspace*{-1cm}

BR Cygni ($\alpha_{2000} = 19\hr 40\mm 54\fsec7$, $\delta_{2000} = +46\deg 47\arcm 05\farcs6$, $V=9.98$) is a classical 
Algol with a period of about 1.33 days. The SIMBAD database lists its spectral type 
as A3V and $B-V=0.05 \pm 0.03$ from Tycho observations, a color consistent with the spectral type. 
Wehinger (1968) published photometry
in yellow and blue filters that showed an odd dependence of the nature of the primary eclipse on wavelength.
The yellow light curve showed an apparent totality that lasted approximately 38 minutes while the blue 
light curve exhibited a partial primary eclipse and Wehringer was unable to explain this unusual behavior.
Koch et al. (1979) expressed surprise that no further study of the system had been done.

In order to explore this potentially unusual system, we began observing BR Cyg with $BVR_{c}I_{c}$ filters 
at the Sonoita Research Observatory. We used the 0.35m telescope equipped with a Santa Barbara Instrument Group 
Research STL-1001XE CCD camera. Calibration (bias, dark, flat) and aperture photometry were done with IRAF.

Observations were made on eight nights in June 2005 with a total of
776 observations with the $B$ filter, 742 in $V$, 737 in $R_c$ and 738 in $I_c$. GSC 3556-3216 
($B-V=0.03 \pm 0.03$ from Tycho) was used as the comparison star. The standard deviation of individual 
measurements in each filter was about 0.01 magnitudes. 
The instrumental differential magnitudes for BR Cyg are available from the IBVS web site as 
5646-t2.txt ($B$), 5646-t3.txt ($V$), 5646-t4.txt ($R_c$) and 5646-t5.txt ($I_c$). 

\IBVSedata{5646-t2.txt} 
\IBVSedata{5646-t3.txt}
\IBVSedata{5646-t4.txt}
\IBVSedata{5646-t5.txt} 

\IBVSdataKey{5646-t2.txt}{BR Cyg}{photometry}
\IBVSdataKey{5646-t3.txt}{BR Cyg}{photometry}
\IBVSdataKey{5646-t4.txt}{BR Cyg}{photometry}
\IBVSdataKey{5646-t5.txt}{BR Cyg}{photometry}

Inspection of Figure 1 shows that the primary eclipse is partial in all filters. The light curves show
no indications of the odd morphology seen in the Wehinger (1968) data. BR Cyg thus appears to be a 
normal Algol with the typical small night-to-night variability most likely related to mass transfer from
the lobe-filling secondary component. We see no evidence of pulsations (with amplitude greater than the 1\%
precision of our photometry) as seen in some other Algols (e.g. IU Per observations by Kim, et al., 2005).

We analyzed our observations with the 2003 version of the Wilson-Devinney program (WD; Wilson \& Devinney, 1971;
Wilson, 1979). The analysis must be viewed as preliminary since the eclipses are partial and we have
no radial velocity from which to determine the mass ratio, which is only weakly constrained by the
photometry (Terrell \& Wilson, 2005). Initial experiments showed that the light curve fits required the 
secondary to fill its Roche lobe, so we used WD's mode 5 and adjusted the parameters shown
in Table 1. We set the mean effective temperature of star 1 (the star eclipsed at primary minimum) equal to
8900 K based on the $B-V$ value and the calibration of Flower (1996). Unadjusted parameters such as the gravity
darkening exponents and bolometric albedos were set to their theoretically expected values for radiative and 
convective envelopes for the primary and secondary respectively. Limb darkening coefficients for the
logarithmic limb darkening law were interpolated from the Van Hamme (1993) tables. 

Figure 1 shows the fits to the observations. The errors in Table 1 are the formal errors from the differential
corrections solution and are probably too optimistic given the actual uncertainty in the mass ratio. The error
estimate for $T_2$ is more correctly interpreted as the error in $T_1-T_2$ as the assumption of fixing $T_1$ based 
on the $B-V$ value involves an uncertainty of the order of 300 K. A spectroscopic study of the system 
is needed before further progress can be made.

\begin{table}[!hr]
\centerline{Table 1. Adjusted Parameters for the Light Curve Solution}
\begin{center}
\begin{tabular}{ccc}
\hline
Parameter & Value & Std. Error\IBVSfm{}\\ 
\hline
$i$ & 81\fdeg87 & 0\fdeg04 \\ 
$T_2$ & 5698 K & 5 K \\ 
$q$ & 0.532 & 0.003 \\ 
$\Omega_1$ & 3.872 & 0.008 \\ 
$HJD_0$ & 2452501.0124 & 0.0004 \\
$P$ & 1\fday3327286 & 0\fday0000006 \\
$L_1/(L_1+L_2)_B$ & 0.905 & 0.001 \\
$L_1/(L_1+L_2)_V$ & 0.840 & 0.001 \\
$L_1/(L_1+L_2)_{R_c}$ & 0.791 & 0.001 \\
$L_1/(L_1+L_2)_{I_c}$ & 0.738 & 0.001 \\
\hline
\end{tabular}
\end{center}
\end{table}
\IBVSfoot{Formal errors from the differential corrections solution.}

\IBVSfig{8cm}{5646-f1.eps}{$BVR_cI_c$ light curves of BR Cyg and the fits from the Wilson-Devinney solution.}
\IBVSfigKey{5646-f1.eps}{BR Cyg}{light curve}

\newpage

\references

Flower, P.J., 1996, {\it ApJ}, {\bf 469}, 355

Kim, S.-L., Lee, J.W., Koo, J.-R., Kang, Y. B. and Mkrtichian, D. E., 2005, {\it IBVS}, 5629

Koch R.H., Wood F.B., Florkowski D.R. \& Oliver J.P., 1979, {\it IBVS}, 1708

Terrell, D. and Wilson, R.E., 2005, {\it ApSpSc},  {\bf 296}, 221

Van Hamme, W., 1993, {\it AJ}, {\bf 106}, 2096

Wehinger, P.A., 1968, {\it AJ}, {\bf 73}, 159

Wilson, R.E., 1979, {\it ApJ}, {\bf 234}, 1054

Wilson, R.E. and Devinney, E.J. (WD), 1971, {\it ApJ}, {\bf 166}, 605

\endreferences



\end{document}
