\documentstyle[twoside, epsfig]{article}

\input ibvs2.sty

\begin{document}

\IBVShead{5725}{11 September 2006}

\IBVStitle{The Bright Cepheid V411 Lacertae}

\IBVSauth{Szabados, L.}

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

\SIMBADobj{V411 Lac}
\GCVSobj{V411 Lac}

\IBVStyp{ DCEPS }
\IBVSkey{Variable stars, Cepheids, Hipparcos, O-C}
\IBVSabs{$UBV$ photometric data of the small amplitude classical Cepheid}
\IBVSabs{are published. The pulsation period has been updated.}
\IBVSabs{It is suspected that V411 Lac is a double-mode pulsator.}

\begintext

Photometric variability of V411~Lacertae (HD~213233, HIP~110968,
SAO~34498) was first detected by the Tycho instrument during the Hipparcos
project (Woitas, 1997). Surprisingly enough, variability of such a bright
star had escaped the observers' attention before. There are three such
bright (between 7-8 mag. in $V$) Cepheids discovered from the photometric
data of this astrometric satellite: CK~Cam, V898~Cen, and V411~Lac. While
the first two have been observed more or less regularly since then, no
more recent observational data are available on V411~Lac. There exist,
however, several earlier photometric data obtained between October 1981
and January 1982 whose mean value (averaged from two to four observations)
is $V=9\fmm80$ (Scharlach and Craine, 1983). Because the real value is
$7\fmm80$, this figure is either a typographic error or the result of a
misidentification (both the $V-R$ and $V-I$ colour indices assigned to
SAO~34498 are too red for a Cepheid).

In the discovery paper, Woitas (1997) reported a 2\fday91 periodicity.
This value was then refined in the Hipparcos Catalogue (ESA, 1997) to be
2.90816 days. In order to have more information (light curve in more than
one colour, precise pulsation period and its possible changes),
V411~Lacertae was put on the photometric observational program of
monitoring bright northern Cepheids in the Konkoly Observatory.

\begin{table}
\centerline{Table 1. New photometric observations of V411~Lacertae}
\label{Tab_phot}
\begin{center}
\begin{tabular}{lcccclccc}
\hline
\hline
\noalign{\smallskip}
JD\,Hel. & $V$ & $B-V$ & $U-B$ && JD\,Hel. & $V$ & $B-V$ & $U-B$ \\
2\,400\,000+ & [mag] & [mag] & [mag] &&2\,400\,000+ & [mag] & [mag] & [mag] \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
50749.2969 & 7.709 & 0.697 & - && 52198.3900 & 7.826 & 0.788 & 0.341 \\
50749.3804 & 7.720 & 0.686 & - && 52199.4228 & 7.855 & 0.785 & 0.321\\
50750.2973 & 7.865 & 0.764 & - && 52200.3657 & 7.681 & 0.708 & 0.286\\
50750.3841 & 7.877 & 0.794 & - && 52589.2790 & 7.831 & 0.752 & 0.319\\
50751.2700 & 7.836 & 0.748 & - && 52618.3074 & 7.839 & 0.760 & 0.324\\
50751.3396 & 7.810 & 0.736 & - && 52619.2581 & 7.705 & 0.702 & 0.294\\
50832.2514 & 7.918 & 0.769 & - && 52620.2554 & 7.806 & 0.807 & 0.372\\
51052.4423 & 7.810 & 0.762 & - && 52673.2423 & 7.928 & 0.780 & 0.365\\
51758.4083 & 7.674 & 0.704 & 0.289 && 52901.4175 & 7.697 & 0.688 & 0.313\\
51759.4032 & 7.845 & 0.794 & 0.358 && 52902.3468 & 7.844 & 0.799 & 0.362\\
51838.3429 & 7.955 & 0.821 & 0.363 && 52903.3790 & 7.821 & 0.754 & 0.315\\
51839.3167 & 7.741 & 0.724 & 0.287 && 52904.3444 & 7.683 & 0.713 & 0.299\\
51840.3195 & 7.719 & 0.723 & 0.318 && 52906.3452 & 7.802 & 0.740 & 0.314\\
52194.4521 & 7.700 & 0.705 & 0.285 && 52948.3702 & 7.747 & 0.732 & 0.336\\
52195.3596 & 7.788 & 0.771 & 0.332 && 53266.3669 & 7.900 & 0.815 & 0.387\\
52197.3657 & 7.695 & 0.705 & 0.291 && 53286.3753 & 7.868 & 0.795 & 0.370\\
\noalign{\smallskip}
\hline
\end{tabular}
\end{center}
\end{table}


\begin{table}
\centerline{Table 2. $O-C$ residuals for V411~Lacertae}
\label{Tab_oc}
\begin{center}
\begin{tabular}{lcccl}
\hline
\hline
\noalign{\smallskip}
Normal Max & $E$ & $O-C$ & Band & Source  \\
JD\,$_\odot$ 2\,400\,000+ &  & [day] & & \\
\noalign{\smallskip}
\hline
\noalign{\smallskip}
47995.0192 & $-$210 & +0.0181 & H$_{\rm P}$ & Hipparcos\\
48256.7478 & $-$120 & +0.0026 & H$_{\rm P}$ & Hipparcos\\
48605.7357 & 0 & $-$0.0018 & H$_{\rm P}$ & Hipparcos\\
48969.2470 & 125 & $-$0.0241 & H$_{\rm P}$ & Hipparcos\\
50798.5727 & 754 & +0.0004 & $V$ & present paper\\
52031.6791 & 1178 & +0.0007 & $V$ & present paper\\
52860.5396 & 1463 & +0.0046 & $V$ & present paper\\
\noalign{\smallskip}
\hline
\end{tabular}
\end{center}
\end{table}

The new photometric observations were obtained with the 50\,cm Cassegrain
telescope located at Piszk\'estet\H{o} Mountain Station, equipped with a
refrigerated photoelectric photometer. The observations were made through
$UBV$ filters of Johnson's system. 34 observations were obtained on 31
nights between 1997 and 2004. HD~213159 served as the comparison star
whose constancy was regularly checked against the brightness of HD~213243.
Moreover, Hipparcos photometry also testifies photometric constancy of
this star (HIP~110924). The instrumental magnitude differences have been
converted into the standard photometric system using the average
transformation coefficients determined for the $V$ magnitude, $B-V$ and
$U-B$ colour indices by observing photometric standard stars. The
following magnitudes were used for the comparison star, HD~213159:
$V=7\fmm73$, $B-V=0\fmm0$, and $U-B=-0\fmm34$ (Scharlach and Craine,
1983). The individual observational data are listed in Table~1. The
internal accuracy of the photometric data is better than 0\fmm01 in $V$
and $B$ bands and is about 0\fmm01 in $U$. The phased light curve in $V$
band, the $B-V$ and $U-B$ phase curves are shown plotted in Figures~1-3,
respectively. The photometric data have been folded on the period value of
2\fday908269, obtained from the $O-C$ diagram as discussed below.

\begin{center}
\IBVSfig{8.6cm}{5725-f1.eps}{The $V$ light curve of V411~Lacertae}
\IBVSfigKey{5725-f1.eps}{V411 Lac}{light curve}
\vskip -1.5cm

\IBVSfig{4.2cm}{5725-f2.eps}{The $B-V$ colour index curve of V411~Lacertae}
\IBVSfigKey{5725-f2.eps}{V411 Lac}{colour curve}
\vskip -1.5cm

\IBVSfig{4.2cm}{5725-f3.eps}{The $U-B$ colour index curve of V411~Lacertae}
\IBVSfigKey{5725-f3.eps}{V411 Lac}{colour curve}

\end{center}


Availability of the Hipparcos photometric data covering about three years
as well as our new data distributed in almost a decade, allow the
construction of an $O-C$ diagram. The seasonal normal maxima were
determined using the well covered Hipparcos normal light curve. The $O-C$
residuals obtained are listed in Table~2 with respect to the ephemeris:

$$
\begin{array}{r@{}r@{}l}
C = 2448605.7375 & {} + 2\fday908269 & {} \times E. \\
 \pm .0064 &  \pm .000008 \\
\end{array}
$$

The value of the period appearing in this ephemeris was obtained from the
least squares fit to the $O-C$ residuals (using equal weights). The new
value of the pulsation period is somewhat longer and more precise than
that deduced from the Hipparcos data alone.

Future observations of V411~Lac are important, since as is seen in Fig.~1,
the light curve shows some excessive scatter which cannot be explained by
observational uncertainties. The pulsation period of V411~Lac is well
within the range where double-mode pulsation occurs among Galactic
Cepheids. Therefore, observers having an access to small photometric
telescopes in the northern hemisphere are urged to monitor closely
V411~Lacertae already in this observing season.

Acknowledgements: This work was supported by the Hungarian OTKA grant
T~046207.

\references

ESA, 1997, The Hipparcos Catalogue, ESA SP-1200

Scharlach, W.W.G., Craine E.R., 1983, {\it PASP}, {\bf 95}, 876

Woitas, J., 1997, {\it IBVS}, No.\,4444

\endreferences

\vspace{2.5cm}

\IBVSerrata{5425, 5431, 5455, 5458, 5489, 5500, 5532, 5586, 5700}

Geert Hoogeveen reported the following errors in various IBVS issues:

\begin{table}[h!]
\normalsize
\begin{tabular}{c l l l}
\hline
IBVS No. & item & printed & correct \\
\hline
5425 & identifier (BD -4\deg 2739) & 1RXS J0950391.1-053029 & 1RXS
J095039.1-053029 \\

5431 & RA (BD +20\deg 2890)  & 13\hr53\mm53\fsec848 & 13\hr53\mm13\fsec848 
\\

5455 & Decl. (GSC 4709-1250) & -00 18 05.4 & -01 18 05.4 \\

5458 & identifier (FASTT 1195) & GSC 0449-0455 & GSC 0449-0456 \\

5458 & Epoch column header & 2400000 & 2450000 \\

5489 & identifier & GSC 7758-1126 & GSC 7758-1162 \\

5500 & identifier  (\# 5) & GSC 3328-0163 & GSC 6328-0163 \\

5532 & identifier (NSV 14532) & HD 214505 & HD 220345 \\

5586 & identifier (NSV 20599) & HIP 80022 & HIP 80222 \\

5586 & identifier (NSV 1916) & GSC 8959-0532 & GSC 1859-0532 \\

5700 & identifier (\# 44) & GSC 4207-1658 & GSC 4433-1658 \\

\hline
\end{tabular}
\end{table}



\end{document}

