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\IBVShead{6123}{12 December 2014}

\IBVStitle{Investigation of the eclipsing binary system OT L\lowercase{yr}}

\centerline{\uppercase{BAV Mitteilungen Nr.\ 237}}
\bigskip

\IBVSauth{Agerer, F.}

\IBVSinsto{Bundesdeutsche Arbeitsgemeinschaft f\"{u}r Ver\"{a}nderliche Sterne e.V. (BAV), Munsterdamm 90, D-12169 Berlin, Germany, email: agerer.zweik@t-online.de}

\SIMBADobj{OT Lyr}

\IBVStyp{  EA  }
\IBVSkey{binaries: eclipsing}

\begintext

This star (AN 61.1930 = USNO-B1.0 1192-0326799 = 2MASS J19081152+2913576) was discovered to be a variable of Algol type by Hoffmeister (1930). A range from 14 to 15 mag was given. The same author gave this variable the 1855.0 coordinates RA = 19\hr02\mm28\sec, Dec = +29\deg0\farcm1. Richter (1961) determined the first ephemeris as 
\begin{equation}
{\rm Min~I = JD~} 2425303.646  + 0\fday471095  \times E \\
\end{equation}
and a magnitude range between 13\fmm9 and 14\fmm9. 

OT Lyr is listed in the GCVS with these information (Samus et al.\ 2014). 
OT Lyr has been included in \lq A Catalogue of Eclipsing Variables\rq
(Malkov et al.~2006). In 2007 a minimum of OT Lyr was observed by the author (H\"{u}bscher 2007). Further observations of this variable showed only small amplitude
variation of DSCT-type. 

Extensive photoelectric monitoring (C14, -IR and -UV-filter, KAF 1603 CCD) has confirmed the Algol type of variability and revealed a period of approximately 8.3 days (Figure 1).  TYC 2135-2336 (12\fmm597) and GSC 2135-1552 (12\fmm5) has been used as comparison star and check star, respectively. 

\begin{table}[!hb]
\centerline{Observed minima }
\vskip 3mm
\begin{center}
\begin{tabular}{cr@{.}lcr@{.}lr@{.}lc}
\hline
 Number & \multicolumn{2}{c}{HJD hel.} & Weight &
 \multicolumn{2}{c}{Epoch} &
 \multicolumn{2}{l}{$(O-C)$} & Source \\
\hline
1 & 2425303 & 646  &  0 &$ -3692$& 0 &$   -1$&  346  & [1] \\
2 & 2454222 & 4568 &  1 &$  -222$& 0 &$   +0$&  001  & [2] \\
3 & 2456072 & 5023 &  1 &$     0$& 0 &$   -0$&  004  & [3] \\
4 & 2456897 & 5191 &  1 &$    99$& 0 &$   -0$&  010  & [3] \\
5 & 2456918 & 360  &  0 &$   101$& 5 &$   -0$&  003  & [3] \\
6 & 2456964 & 210  &  1 &$   107$& 0 &$   +0$&  012  & [3] \\
\hline\\
\end{tabular}

{\normalsize Sources: [1] Richter (1961), [2] H\"{u}bscher (2007), 
 [3] Agerer (this paper).}
\end{center}
\end{table}


Using only CCD-measured primary minimum timings the following first ephemeris
could be derived: 
\begin{equation}
\begin{array}{r@{}r@{}l}
{\rm Min~I = HJD~} 2456072.5063 & {} + 8\fday333563 & {} \times E \\
\pm 13 & \pm 10 \\
\end{array}
\end{equation}

\IBVSfig{8cm}{6123-f1.eps}{Photoelectric observations folded with
  the ephemeris (2), after removing the variations caused by the DSCT
  component.}
\IBVSfigKey{6123-f1.eps}{OT Lyr}{light curve}
 

In the instrumental system, OT Lyr is 13\fmm45 out of eclipse and
14\fmm75 in primary minimum. 
The secondary minimum seems to be somewhat displaced at a phase about 0.48 and
is about 0\fmm07 deep. 


A closer view to the data made clear, that the $\delta$ Scuti variations can be followed
through the whole period of the eclipsing binary. During primary minima
the amplitude of the light variation is reduced to about $\pm$0\fmm2 (Figure~2),
whereas in normal light and in times of secondary eclipses the amplitude is
about $\pm$0\fmm4 (Figure~3). 

\IBVSfig{5.5cm}{6123-f2.eps}{The $\delta$ Scuti variations in primary eclipse, after
  removing the variation caused by the eclipse.}  
  \IBVSfigKey{6123-f2.eps}{OT Lyr}{light curve}

\IBVSfig{5.5cm}{6123-f3.eps}{DSCT component in secondary eclipse,
after removing the variation caused by the eclipse.}  
\IBVSfigKey{6123-f3.eps}{OT Lyr}{light curve}

From this it is obvious that the hotter component of the binary is the
pulsating one and that the eclipse is not total.

The following first elements for the $\delta$ Scuti component could be derived: 

\begin{equation}
{\rm Max = HJD~} 2455451.3375  + 0\fday086495 \times E.
\end{equation}


Figure 4 shows the corresponding phased light curve.

\IBVSfig{5.5cm}{6123-f4.eps}{The $\delta$ Scuti component out of eclipse, folded with
  the ephemeris (3), and displayed with respect to the constant brightness level.} 
\IBVSfigKey{6123-f4.eps}{OT Lyr}{light curve}


\textbf{Acknowledgements:} This research made use of the SIMBAD data base, operated by the CDS
at Strasbourg, France.


\references

Hoffmeister, C., 1930, {\it AN}, {\bf 238}, 189

Hoffmeister, C., 1933, {\it Sonn.\ Mitt.}, {\bf N22}, 191

H\"{u}bscher, J., 2007, {\it IBVS}, {\bf 5802}

Malkov O.Y., et al., 2006, {\it A\&A}, {\bf 446}, 785

Richter, G., 1961, {\it MVS}, {\bf 565}

Samus, N.~N.~et al., 2014, {\it General Catalogue of Variable Stars}, Moscow

\endreferences

\IBVSCorrectedVersion{Thu Dec 18 13:34:50 CET 2014}

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