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\input ibvs2.sty

\begin{document}
\IBVShead{5045}{14 March 2001}

\IBVStitletl{V404 Lyrae in the Field}{ of the Very Old Galactic Cluster NGC 6791}

\IBVSauth{Csizmadia, Sz.; S\'andor, Zs.}

\IBVSinsto{Konkoly Observatory of the Hungarian Academy of Sciences,
H-1525 Budapest, P.O. Box 67, Hungary\\ \indent e-mail: csizmadia@konkoly.hu}

\SIMBADobj{V404 Lyrae}
\IBVStyp{ EB }
\IBVSkey{photometry}
\IBVSabs{V404 Lyr was observed on seven nights. We report two new times of minima.}
\IBVSabs{New period was determined.}

\begintext

V404~Lyrae was listed as a $\beta$ Lyrae type eclipsing binary by Popova
and Kraicheva (1984) in the field of the old galactic cluster NGC 6791
(its age is $t=8 \pm 0.5$ Gyr, $m-M = 13\fmm42$, $E_{B-V}=0.10$, Chaboyer
et al.\ 1999). In the GCVS (Kholopov et al.\ 1985) the following ephemeris
is found: 
\begin{equation}
{\rm Min.~I = HJD}~ 2435836.462 + 0\fday73094585 \times E.
\end{equation}
According to our knowledge neither spectroscopic information nor light 
curve is available for V404~Lyr and there are only observations of minima 
published in the literature. 

Therefore we observed the star on seven nights using the 1-m RCC-telescope
of the Konkoly Observatory. The detector was a $1024 \times 1024$
electronically cooled Photometrics CCD-camera and we applied a $2 \times
2$ binning on the chip. We used Johnson--Cousins $V(I)_C$ filters. All
frames were cleaned from cosmic ray events and we made bias and flat-field
corrections. Dome-flats were used. The dark-current was negligible. The
average seeing was about $2\farcs4$. The log of observations can be found
in Table 1. In order to determine the instrumental magnitudes we used the
IRAF/DAOPHOT package. From our observations we could determine two new
moments of minima (see Table 2). 

\begin{table}[h]
\caption{Log of observations}
\begin{center}
\begin{tabular}{crrcl}
\hline
Date of observation & $V$ & $I$ & Phase coverage & Note \\
\hline
JD~2451691 &92 & 91 & 0.04 - 0.24 & \\
\phantom{JD~}2451692 &72 & 72 & 0.38--0.52 & \\ 
\phantom{JD~}2451725 &60 & 60 & 0.59--0.72 & \\
\phantom{JD~}2451728 & 9 & 9 & 0.82--0.83 & thin clouds \\
\phantom{JD~}2451729 &30 & 30 & 0.16--0.22 & \\
\phantom{JD~}2451772 &170& 174 & 0.82--0.17 & full moon \\
\phantom{JD~}2451773 &21 & 48 & 0.25--0.35 & \\
\hline
\end{tabular}
\end{center}
\end{table}

In Table 2 the $(O-C)_{\rm GCVS}$ represent the residuals using ephemeris (1).
A linear fit to the data has been yielded better elements: 
\begin{equation}
\begin{array}{r@{}r@{}l}
{\rm Min.~I = HJD}~2435836.448 & {} + 0\fday7309432 & {} \times E \\
{}\pm0.014 & {}\pm0.0000006 \\
\end{array}
\end{equation}
and the residuals are listed in Table 2 as $(O-C)_{2}$.

\begin{center}
\normalsize
Table 2: Times of minima of V404~Lyr
\vskip2mm
\begin{tabular}{llllrl}
\hline
HJD & $E$ & Error &$(O-C)_{\rm GCVS}$ & $(O-C)_{2}$ & Reference \\ 
\hline
2449787.5943 & 19086.5 & & $-0.0657$ & $-0.0011$ & Agerer \& Huebscher (1997a) \\ 
2449799.6564 & 19103 & & $-0.0642$ & $+0.0005$ & " \\
2449857.3968 & 19182 & & $-0.0685$ & $-0.0037$ & " \\
2449865.4441 & 19193 & & $-0.0616$ & $+0.0033$ & " \\
2450158.5502 & 19594 & & $-0.0648$ & $+0.0011$ & Agerer \& Huebscher (1997b) \\ 
2450248.4586 & 19717 & $\pm .0001$ & $-0.0627$ & $+0.0035$ & " \\
2450346.4006 & 19851 & $\pm .0021$ & $-0.0675$ & $-0.0086$ & Agerer \& Huebscher (1998) \\ 
2450379.2939 & 19896 & $\pm .0014$ & $-0.0667$ & $~0.0000$ & " \\
2450593.4582 & 20189 & $\pm .0011$ & $-0.0696$ & $-0.0021$ & Agerer \& Huebscher (1999) \\ 
2450894.6115 & 20601 & $\pm .0007$ & $-0.0660$ & $+0.0026$ & " \\ 
2451299.5501 & 21155 & $\pm .0007$ & $-0.0714$ & $-0.0013$ & Agerer \& Huebscher (2000) \\
2451308.698~ & 21167.5 & $\pm .004~$ & $-0.060 $ & $+0.0098$ & Diethelm (2001)\\
2451312.7094 & 21173 & $\pm .0012$ & $-0.0691$ & $+0.0010$ & " \\
2451692.4324 & 21692.5 & $\pm .0005$ & $-0.0724$ & $-0.0010$ & this paper \\
2451772.4730 & 21802 & $\pm .0002$ & $-0.0704$ & $+0.0012$ & this paper \\ 
\hline 
\end{tabular}
\end{center}

\bigskip

The comparison and check stars were GSC 3121-1597 and USNO 1275-1113
0035, respectively. These stars were standardized as given in Table 3
using our observations on some Landolt-standards located in the SA 113
area (Landolt 1983).

\addtocounter{table}{1}
\begin{table}[h]
\caption{Comparison stars for V404~Lyrae}
\begin{center}
\begin{tabular}{lcc}
\hline
Star & $V$ & $V-I_C$ \\
\hline
GSC 3121-1597 & 11.82 & +0.51 \\
USNO 1275-1113~0035 & 13.53 & +0.78 \\
\hline
\end{tabular}
\end{center}
\end{table}

To get the light-curve we used differential photometry. In order to
determine the transformation constants for differential photometry, we
applied the observations of Messier 67 which were made with the same
instrument during January and February, 2000 on three nights by I. T\'oth. 
Using the method described in Henden and Kaitchuck (1982) we got the
transformation equations. The $V$ light curve and the $V-I_C$ colour curve
are shown in Figs.~1-2. The individual data points 
are available on the IBVS homepage.

\IBVSedata{5045-t4.txt}

At maximum light the brightness and colour index of V404~Lyr are
$V=11.39$, and $V-I_C=0.47$, respectively. In order to estimate the
distance modulus we used the method described in Dworak (1975). The
interstellar reddening was estimated as $A_V = 3.0 \times E_{B-V} =
0\fmm30$ and the $E_{B-V}$ was taken from Chaboyer et al.\ (1999). The
distance modulus is $9.0\pm1$ magnitudes (its error comes mainly from the
uncertainty of the inclination) which is significantly smaller than the
distance modulus of NGC 6791 (i.e.\ $13\fmm42$, see above). Therefore
V404~Lyr is not a member of this cluster. 

\IBVSfig{12.76cm}{5045-f1.eps}{$V$-light curve of V404~Lyr} 

\IBVSfig{7.24cm}{5045-f2.eps}{$V-I_C$ colour curve of V404~Lyr. Note that the
system is redder at primary minimum and bluer at secondary one} 

\newpage

{\it Acknowledgements.} We thank to I. T\'oth for the
observations of Messier 67. 

\references

Agerer F., Huebscher J., 1997a, {\it IBVS}, No.\ 4383

Agerer F., Huebscher J., 1997b, {\it IBVS}, No.\ 4472

Agerer F., Huebscher J., 1998, {\it IBVS}, No.\ 4562

Agerer F., Huebscher J., 1999, {\it IBVS}, No.\ 4711

Agerer F., Huebscher J., 2000, {\it IBVS}, No.\ 4912

Chaboyer, B., Green, E. M., Liebert, J., 1999, {\it AJ}, {\bf 117}, 1360

Dworak, T. Z., 1975, {\it AcA}, {\bf 25}, 383

Diethelm, R., 2001, {\it IBVS}, No.\ 5027

Henden, A. A., Kaitchuck, R. H., 1982, Astronomical Photometry, van 
Nostrand Reinhold Company

Kholopov, P. N. et al., 1985, General Catalogue of Variable Stars, 4th 
edition, Moscow 

Landolt, A. U., 1983, {\it AJ}, {\bf 88}, 439 

Popova, M., Kraicheva, Z., 1984, {\it Astrofiz.\ Issled.\ SAO} {\bf 18}, 64

\endreferences

\end{document}

