\documentstyle[twoside, epsf, ibvs2]{article}


\begin{document}

\IBVShead{5339}{18 November 2002}

\IBVStitletl{Two New Eclipsing Binaries: V1626 O\lowercase{ri} (B\lowercase{rh} V38) and}{ GSC 0486-4828 (B\lowercase{rh} V64)}

\IBVSsubtitle{(BAV Mitteilungen Nr. 144)}

\IBVSauth{Lloyd, C.$^{1}$; Frank, P.$^{2,6}$; Bernhard, K.$^{3,6}$; Moschner, W.$^{4,6}$; Quester, W.$^{5,6}$}

\IBVSinst{Space Science \& Technology Department, Rutherford Appleton Laboratory, Chilton, Didcot, \\ Oxon. OX11 0QX, UK; e-mail: {\tt cl@astro1.bnsc.rl.ac.uk}}
\IBVSinst{D--84149 Velden, Germany; e-mail: {\tt frank.velden@t-online.de}}
\IBVSinst{A--4030 Linz, Austria; e-mail: {\tt kl.bernhard@aon.at}}
\IBVSinst{D-57368 Lennestadt, Germany; e-mail: {\tt wolfgang.moschner@t-online.de}}
\IBVSinst{D-73730 Esslingen, Germany; {\tt e-mail: wquester@aol.com}}
\IBVSinst{Bundesdeutsche Arbeitsge\-mein\-schaft f\"{u}r Ver\"{a}nderliche
Sterne e.V. (BAV), Munsterdamm 90,\\ D--12169~Berlin, Germany}

\SIMBADobjAliasJ2000{V1626 Ori}{Brh V38}{06 05 20.118 +10 04 25.54}
\SIMBADobjAliasJ2000{GSC 0486-4828}{Brh V64}{19 34 21.486 +03 54 43.33}

\IBVStyp{ EA }

\IBVSkey{Eclipsing binaries - variable stars - photometry}

\IBVSabs{V1626 Ori is an EA with a period of 1.137793 days containing a mid}
\IBVSabs{F-type main-sequence primary and an oversized early K-type}
\IBVSabs{secondary, which may or may not fill its Roche lobe. GSC 0486-4828}
\IBVSabs{has a period of 9.27850 days and contains two apparently unevolved} 
\IBVSabs{main-sequence stars of spectral types late B and early A.}  


\begintext

Further observations and analysis are presented of two suspected eclipsing
binaries recently discovered by Bernhard (2000a, 2000b). Further details
of the program are given by Bernhard \& Lloyd (2000) and an
up-to-date list of the variables can be found at {\tt
http://mitglied.lycos.de/klausbernhard/}. Details of the equipment used
are given by Lloyd et al. (2002) and Quester \& Bernhard (2001).

\vskip 6pt
V1626 Ori = BrhV38 = GSC 0721-2377 (06\hr05\mm20\fsec118
+10\deg04\arcm25\farcs54 Tycho-2) was initially reported as a possible
eclipsing system by Bernhard (2000a) on the basis of eight nights of
survey data. Further photometry on 16 nights have confirmed that it is an
eclipsing binary with a period of just over one day. The reference star
used was GSC~0721-0968 with $V\approx12\fmm2$. Two primary minimum have been
observed and the times are given in Table 1. The ephemeris of primary
minimum is given by

\[
\begin{array}{r@{}r@{}l}
HJD_{\rm MinI} = 2452223.5824 & {} + 1\fday137793 & {} \times E \\
\pm 29 & \pm 3 \\
\end{array}
\]

\IBVSfig{8cm}{5339-f1.eps}{The phase diagram of V1626 Ori = Brh V38
assuming that the reference star GSC~0721-0968 has $V=12\fmm2$. The CCD
observations of Moschner (open squares), Frank (filled circles) and
Bernhard (open circles) are folded with the ephemeris given in the
text. The fit is described in the text.}

V1626 Ori appears at the limit of the Tycho-2 catalogue (H\o g et al. 2000)
with a rather unreliable $V=12\fmm5\pm0\fmm3$ and $B-V=-0\fmm1\pm0\fmm4$ while the
USNO A2.0 catalogue gives $b=11\fmm6$ and $b-r=0\fmm7$ (Monet et al. 1998).

\vskip 6pt
A photometric model of the system has been derived using the {\sc Light}2
code (see Hill et al., 1989). In this system there is nothing to guide to
choice of mass ratio but given the difference in the eclipse depths it is
likely that $q<0.5$. A range of mass ratios, $1.0>q>0.1$, and
temperatures have been explored and it must be conceded that a wide
variety of photometric parameters provide almost identical fits to the
light curve. However, only a small range of models are physically
consistent with the primary being a main-sequence star, and these have
$T_1\sim6600$ and $q<0.5$, corresponding to an F5\,V star. The parameters
are only weakly dependent on $q$, but with $q < 0.2$ the secondary fills
its Roche lobe.

The fit to the light curve shown in Figure 1 was obtained with $q=0.3$
and $T_{1}=6600$~K (fixed), yielding $T_{2}=4600\pm100$ K,
$i=77\deg\pm1\deg$, $R_{1}/a_{0}=0.23\pm0.01$ and
$R_{2}/a_{0}=0.24\pm0.02$. A star of spectral type F5\,V, has
$M=1.4$${\rm M_{\odot}}$\ and $R=1.3$${\rm R_{\odot}}$\ (Cox 2000), giving $a_{0}=5.8$
${\rm R_{\odot}}$, and $R_1=1.3$${\rm R_{\odot}}$\ from the model. The temperature of the secondary
corresponds to an early K-type star with a radius, $R_2=1.4$${\rm R_{\odot}}$, which
is substantially larger than expected for an early K-type star. For
$q<0.5$ there is little to separate the solutions so the secondary may
fill its Roche lobe or is close to it. If it does fill its Roche lobe
then $q<0.2$, implying $M_2<0.3$${\rm M_{\odot}}$.


\begin{table}[!h]\centering
\normalsize
\caption{Brh V38 - Times of minima}
\vskip 2pt
\begin{tabular}{lcclcc} \hline
~~~~~HJD & $O-C$ & Min & ~~~~~HJD & $O-C$ & Min \\ \hline
2451957.3379(12) & $-$0.0009 & I & 2452223.5824(3)    &+0.0000 & I \\ \hline
\end{tabular}
\end{table}

\IBVSfig{8cm}{5339-f2.eps}{The phase diagram of BrhV64 = GSC 0486-4828
assuming that the reference star GSC~0486-3453 has $V=12\fmm3$. The CCD
observations of Frank (open squares), Quester (open circles) and
Bernhard (filled circles) are folded with the ephemeris given in the
text. The fit is described in the text.}

BrhV64 = GSC 0486-4828 (19\hr34\mm21\fsec486 +03\deg54\arcm43\farcs33)
was initially reported as a probable eclipsing system by Bernhard (2000b)
following several long runs of observations. Further extensive photometry
during the 2000 and 2001 observing seasons has confirmed that it is an
eclipsing binary, with a period of just under ten days. In total four
minima have been observed and they are given in Table 2. The reference
star used was GSC~0486-3453 with $V\approx12\fmm3$. The ephemeris of primary
minimum is given by

\[
\begin{array}{r@{}r@{}l}
HJD_{\rm MinI} = 2452137.5441 & {} + 9\fday27850 & {} \times E \\
\pm 103 & \pm 5 \\
\end{array}
\]

\begin{table}[!t]\centering
\normalsize
\caption{Brh V64 - Times of minima}
\vskip 2pt
\begin{tabular}{lcclcc} \hline
~~~~~HJD & $O-C$ & Min & ~~~~~HJD & $O-C$ & Min \\ \hline
2452137.5441(17) & +0.0000& I~ & 2452179.3590(7) &+0.0013 & II\\ 
2452151.5251(11) & +0.0029& II & 2452448.4309(29)&$-0.0033$& II \\ \hline
\end{tabular}
\end{table}

\IBVSfig{8cm}{5339-f3.eps}{Detail of the primary and secondary minima. The 
symbols are as in Figure 2.}

The light curve, given in Figure 2, shows that both eclipses are nearly
equal in depth, at close to 0\fmm7, indicating that the system contains
two similar stars. Figure 3 shows that there is a small but clear
difference in the eclipses, which eliminates the half period, but also
that the secondary eclipse is slightly displaced, to $\phi=0.5065$,
indicating a small eccentricity.

A photometric model of the system has again been derived using the {\sc
Light}2 code (see Hill et al., 1989). The mass ratio is unknown but given
the similarity of the eclipses it is reasonable to assume initially that
$q\sim1.0$. Similar fits to the light curve are found for a range of
temperatures, so $T_1$ and $T_2$ are unconstrained, but the relative
radii are found to be almost independent of temperature. A temperature
for the primary, $T_{1}=10\,500$~K has been adopted as this provides a
physically consistent set of values for both stars, assuming that they
lie on the main sequence.

Adopting $q=1$ and $T_{1}=10\,500$ K (fixed), gives $T_{2}=10\,000\pm100$
K, $R_{1}/a_{0}=0.080\pm0.002$, $R_{2}/a_{0}=0.063\pm0.002$,
$i=89\fdeg8\pm0\fdeg2$, $e=0.04\pm0.01$ and $\omega=74\deg\pm6\deg$. This
fit is plotted in Figures 2 and 3. The primary corresponds to a
main-sequence star near spectral type B9, which has $M=3.3$ ${\rm M_{\odot}}$\ and
$R=2.7$ ${\rm R_{\odot}}$\ (Cox 2000), giving $a_{0}=34.0$ ${\rm R_{\odot}}$, and $R_1=2.7$ from
the model. The secondary is marginally cooler and smaller, with $R_2=2.2$
${\rm R_{\odot}}$, making it an early A-type star. This result is also consistent
with the Tycho-2 photometry which gives $V=11\fmm96\pm0\fmm13$ and
$B-V=0\fmm08\pm0\fmm23$. As the system is detached, apparently unevolved, and
has $i = 90\deg$ it would appear to be an ideal candidate for testing the
fundamental parameters of main-sequence stars.

\vskip 6pt
{\it Acknowledgements.} It is a pleasure the acknowledge the use of the 
SIMBAD database, operated by the CDS at Strasbourg, France.


\references

Bernhard, K., 2000a, vsnet-newvar, No. 290\\ 
{\tt http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-newvar/msg00290.html}
%%BeV38

Bernhard, K., 2000b, vsnet-newvar, No. 642\\
{\tt http://www.kusastro.kyoto-u.ac.jp/vsnet/Mail/vsnet-newvar/msg00642.html}
%%BeV64

Bernhard, K., Lloyd, C., 2000, {\it IBVS}, No.\ 4920

Cox, A. N., 2000, (ed) {\it Allen's Astrophysical Quantities}, fourth
edition. Springer-Verlag

Hill, G., Fisher, W. A., Holmgren, D., 1989, {\it A\&A}, {\bf 211}, 81

H\o g, E., Fabricius, C., Makarov, V. V., Urban, S., Corbin, T., Wycoff, G.,
Bastian, U., Schwekendiek, P., Wicenec, A., 2000, {\it A\&A}, {\bf 355}, L27
%%Tycho-2

Lloyd, C., Frank, P., Bernhard, K., Moschner, W., 2002, {\it IBVS}, No.\ 5260

Monet, D., Bird, A., Canzian, B., Dahn, C., Guetter, H., Harris, H., Henden, A., Levine, S., Luginbuhl, C., Monet, A. K. B., Rhodes, A., Riepe, B., Sell, S.,
Stone, R., Vrba, F., Walker, R., 1998, {\it The USNO-A2.0 Catalogue}

Quester, W., Bernhard, K., 2001, {\it IBVS}, No.\ 5161

\endreferences


\end{document}
