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\IBVShead{6110}{26 June 2014}

\IBVStitletl{HD 106426, a new multiperiodic {\boldmath $\delta$} Scuti variable}

\begin{center}
\IBVSauth{Ho{\v n}kov{\'a}, K.$^{1}$; Jury{\v s}ek, J.$^{1}$; Ma{\v s}ek, M.$^{2}$; Paunzen, E.$^{3}$; Zejda, M.$^3$}
\end{center}

\IBVSinst{Variable Star and Exoplanet Section of Czech Astronomical Society}
\IBVSinst{Institute of Physics, Czech Academy of Sciences, 182 21 Praha, Czech Republic}
\IBVSinst{Department of Theoretical Physics and Astrophysics, Masaryk University,
Kotl\'a\v{r}sk{\'a} 2, 611~37 Brno, Czech Republic}

\SIMBADobj{HD 106426}

\IBVSkey{variables, CCD photometry, Delta Scuti stars}

\IBVStyp{ DSCT }

\IBVSabs{We present the time series analysis of CCD }
\IBVSabs{photometry from FRAM telescope at the Pierre Auger }
\IBVSabs{Observatory (PAO, Argentina) for HD 106426.}
\IBVSabs{In addition, we analysed the data from ASAS. HD 106426 is}
\IBVSabs{a new multiperiodic delta Scuti variable.}

\begintext

The class of $\delta$ Scuti stars comprise of pulsating variables of spectral types A to early F with 
luminosity classes V to III. They pulsate in radial and nonradial $p$ (and also $g$) modes with periods 
between about thirty minutes to eight hours and photometric amplitudes less than one magnitude (Breger et al. 2009).
Most $\delta$ Scuti stars do, however, show very small amplitudes; the smaller the amplitudes become, the more 
variables are found, for example in space mission data of the Kepler and CoRoT missions (Balona 2014).

During a survey to detect new rapidly rotating Ap stars (Paunzen et al. 2012), we discovered the variability
of HD 106426 (CP$-$62 2642, V\,=\,9.31\,mag). Although this star is rather bright, it was hardly investigated
in the past. It is also not included in the $Hipparcos$ catalogue. Houk \& Cowley (1975) list a spectral type of
A9\,V for this object.

We observed this star in two consecutive nights 18/19 March and 19/20 March 2014 with the 
F(/Ph)otometric Robotic Atmospheric Monitor (FRAM) telescope 
of the Pierre Auger Observatory which is located in the Mendoza province in Argentina, in the 
vicinity of the town Malarg{\"u}e. The telescope is a Meade 0.3m Schmidt-Cassegrain, with a CCD camera 
G4-16000 of Moravian Instruments which is also on the wide-field camera (300mm objective Nikkor). The 
telescope works in fully automated mode. We employed integration times of 40 seconds and a Johnson-Bessell
$B$ filter. In addition we analysed the data of the All Sky Automated Survey (ASAS) which are in the
$V$ band (Pojmanski 1997).

The basic image reduction (bias and flat correction) as well as the aperture photometry was done
within the Windows version of CMunipack\footnote{http://c-munipack.sourceforge.net/}. 
The final light curves of FRAM were generated using different comparison and check stars in order
to guarantee the statistical significance of the intrinsic variability of HD 106426. 

All light curves were examined in more detail using the Phase-Dispersion-Method within the 
software Peranso\footnote{http://www.peranso.com/}. An analysis with a discrete Fourier algorithm
gave the same frequencies and amplitudes. The observation log and the results are listed in Table~1.

The three data sets are of different time base and quality. However, we conclude from the analysis
that HD 106426 is multiperiodic. Figure 1 shows the phase folded light curve of the first observing night
from FRAM.

Perry (1991) published the following Str{\"o}mgren $uvby\beta$ photometry for our target:
$(b-y)$\,=\,0.307, $m_{1}$\,=\,0.137, $c_{1}$\,=\,0.883, and $\beta$\,=\,2.766, respectively.
Using the photometric calibration by Napiwotzki et al. (1993) gives $E(b-y)$\,=\,0.144\,mag, 
$T_{\mathrm eff}$\,=\,7250$\pm$250\,K, $\log g$\,=\,3.65\,$\pm0.15$\,dex, $M_{\mathrm V}$\,=\,1.50\,$\pm$0.2\,mag,
and solar metallicity. The bolometric correction and magnitude of the Sun taken
from Flower (1996) yields ${\log L/L_{\odot}}$\,=\,1.30\,dex. Interpolating in the evolutionary
grids for solar metallicity by Schaller et al. (1992), we derive a mass of about 1.9\,M$_{\odot}$
for HD 106426. It spent about 80\% of its main-sequence life-time. These values are typical of
an A5\,V star.

Because $\delta$ Scuti stars obey a period-luminosity-color relationship, we are able to compare our
results with the ``heuristic'' one published by Breger (1979): \\
\begin{center}
$M_{\mathrm V}$\,=\,$-$3.05\,$\log P$\,+\,8.46\,$(b-y)_{\mathrm 0}$\,$-$\,3.12.
\end{center}
We used a mean logarithmic period of $-$1 resulting in $M_{\mathrm V}$\,=\,1.3\,mag. Within the errors,
this value excellently agrees with that from the photometric calibration.
Finally, we calculated the pulsation constant as given by Stellingwerf (1979): \\
\begin{center}
$\log Q$\,=\,$-$6.456\,+\,0.5\,$\log g$\,+\,0.1$M_{\mathrm Bol}$\,+\,$\log T_{\mathrm eff}$\,+\,$\log P$.
\end{center}
The resulting Q-value of 0.024 for our target would suggest a pulsation in the second
or third overtone (Stellingwerf 1979). Further photometric and spectroscopic observations
are needed to shed more light on the nature of HD 106426.

\begin{table}[!t]
\centerline{\bf Table 1: Observation log and results.}
\begin{center}
\small
\begin{tabular}{lccccc}\hline
Source & HJD(start) & HJD(end)   & $N$ & Freq. & Ampl.  \\
       & 2450000+   & 2450000+   &     & [c/d] & [mmag] \\
\hline
ASAS   & 1899.84343 & 5048.51607 & 521 & 11.54 & 11     \\
FRAM   & 6735.76575 & 6735.88587 & 125 & 10.87 & 33     \\
       & 6736.53343 & 6736.66705 & 112 &  6.48 & 29     \\
\hline
\end{tabular}
\normalsize
\end{center}
\end{table}

\IBVSfig{10cm}{6110-f1.ps}{Folded phased light curve of the first observing night from FRAM.}
\IBVSfigKey{6110-f1.ps}{HD 106426}{light curve}

\bigskip

{\bf Acknowledgements:} This project is financed by the SoMoPro II programme \linebreak
(3SGA5916). The research leading to these results has acquired a financial grant
from the People Programme (Marie Curie action) of the Seventh Framework Programme
of EU according to the REA Grant Agreement No. 291782. The research
is further co-financed by the South-Moravian Region. It was also supported by
the grants GA {\v C}R P209/12/0217, 14-26115P, 7AMB12AT003, 7AMB14AT015,
and the financial contributions of the Austrian Agency for International Cooperation
in Education and Research (BG-03/2013, CZ-10/2012, and CZ-09/2014).
The operation of the robotic telescope FRAM is supported by the EU grant GLORIA 
(No. 283783 in FP7-Capacities program) and by the grant of the Ministry of Education 
of the Czech Republic (MSMT-CR LG13007). 

\references

Balona, L. A. 2014, {\it MNRAS}, {\bf 437}, 1476

Breger, M. 1979, {\it PASP}, {\bf 91}, 5

Breger, M., Lenz, P., Pamyatnykh, A. A. 2009, {\it MNRAS}, {\bf 396}, 291

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

Houk, N., Cowley, A. P. 1975, University of Michigan Catalogue of two-dimensional spectral types for the HD stars. Volume I \BIBCODE{1975mcts.book.....H}

Lenz, P., Breger, M. 2005, {\it CoAst}, {\bf 146}, 53

Napiwotzki, R., Schoenberner, D., Wenske, V. 1993, {\it A\&A}, {\bf 268}, 653

Paunzen, E., Netopil, M., Rode-Paunzen, M., et al. 2012, {\it A\&A}, {\bf 542}, A89

Perry, C. L. 1991, {\it PASP}, {\bf 103}, 494 

Pojmanski, G. 1997, {\it Acta Astronomica}, {\bf 47}, 467

Schaller, G., Schaerer, D., Meynet, G., Maeder, A. 1992, {\it A\&AS}, {\bf 96}, 269

Stellingwerf, R. F. 1979, {\it ApJ}, {\bf 227}, 935

\endreferences

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