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\IBVSheadDOI{63}{6238}{7 March 2018}


\IBVStitletl{Discovery of short-period oscillations}{ in the mass-accreting component of TT\,V\lowercase{el}}

\IBVSauth{Mkrtichian, D. E.$^1$;  Gunsriwiwat, K.$^1$; Reichart, D. E.$^2$;   Haislip, J. B.$^2$; \\ Kouprianov, V. V.$^2$;   Poshyachinda, S.$^1$}
\IBVSinst{National Astronomical Research Institute of Thailand (NARIT)
260 Moo 4, T. Donkaew, A. Maerim, Chiangmai, 50180
Thailand}
\IBVSinst{University of North Carolina 269 Phillips Hall, CB 3255 Chapel Hill, NC 27599}

\SIMBADobj{TT Vel}

\begintext

The ``Thai Sky Survey for oEA Stars" (THASSOS) project is focused on
searching for and studying new mass-accreting pulsating components of
semi-detached Algol-type systems, the class of pulsators  called
oEA stars (Mkrtichian et al., 2002, 2004). Up to now, within the frame of the THASSOS
project, four new oEA stars, VY Hya (Gunsriwiwat \& Mkrtichian, 2016), GQ
TrA (Mkrtichian et al., 2016), BD Vir (Mkrtichian et al., 2017a), and UW
Vir (Mkrtichian et al., 2017b) were discovered.

TT\,Vel is a semi-detached Algol-type eclipsing binary system with a
2.1084 day orbital period. The system is photometrically-neglected and
there is no accurate photometric light curve of the system. The A5\,V
primary component of the system can be pulsating as it is within in the
instability strip. For these reasons it was included to the THASSOS oEA
candidate list.

12 nights of photometric observations for TT\,Vel were acquired from
March 28  to  April 16, 2014 using the 0.6-meter Thai Southern
Hemisphere Telescope (TST) PROMPT8 at Cerro Tololo Inter-American
Observatory (CTIO). The telescope is equipped with an Apogee Alta E42
CCD camera. Three second exposure times through Johnson $B$ filter were
used. All stars in the field of view were reduced with the MaxIm DL 5 software
using aperture photometry. HD 89623 ($V=8.09$ mag, $B-V=0.00$ mag) was used as a
comparison star. The phased differential light curve, folded according to
HJD = 2456751.320 + 2.1083805$\times$E, is shown in Figure 1.

During the search for pulsational variations in the primary component, we
omitted all data at primary minima. The slow orbital variations in
out-of-eclipse parts of light curves were removed using low-order
polynomial fits. The residual light curves are shown in Figure 2.

\begin{table}[b!]
\centering
\caption{Pulsation frequencies and amplitudes.}
 	\begin{tabular}{cc}
        \hline
        \hline
Frequency (c/d)    &   Amplitude (mag)   \\
         \hline
$f_1$=16.455$\pm$0.002	&	0.0046$\pm$ 0.0003\\
$f_2$=15.485$\pm$0.003	&	0.0023$\pm$ 0.0003      \\
	\hline
	\hline
		\end{tabular}
\label{tab:dataobserve}
\end{table}

\IBVSfig{8cm}{6238-f1.eps}{The phased orbital light curve  of TT Vel (dots).}
\IBVSfig{12cm}{6238-f2.eps}{The nightly residual light variations of TT Vel (dots). The solid line is a two-frequency fit to the data.}
\IBVSfigKey{6238-f1.eps}{TT Vel data}{light curve}
\IBVSfigKey{6238-f2.eps}{TT Vel data}{light curve}


 The periodic signals in the residual data were analysed using the
 Period04 software (Lenz \& Breger, 2005), designed for the Discrete
 Fourier Transform (DFT) analysis and the pre-whitening technique for
 consecutive detection of signals in the data. The frequency spectra of
 consecutive steps of the  DFT analysis are shown in Figure 3, from top
 to bottom. As a result, we detected two periodic signals at frequencies
 16.455~c/d and 15.485~c/d.  The frequencies and amplitudes of signals
 are given in Table 1.
 
\IBVSfig{9cm}{6238-f3.eps}{The DFT frequency spectra of the primary component. Top panel - the DFT of the residual light curve, highest peak is at 16.455 c/d.  Middle panel - the DFT of the residuals after removal of 16.455 c/d, the highest peak is at 15.485 c/d. Bottom panel - the DFT after removal of 16.455 and 15.485 c/d.}
\IBVSfigKey{6238-f3.eps}{TT Vel data}{periodogram}


Conclusion: We discovered short-period, $\delta$ Scuti-type
multiperiodic pulsations in the primary component of the semi-detached, Algol-type binary
system TT Vel. We conclude that TT Vel is a new member
of the oEA group of pulsators.


\noindent {\bf Acknowledgements:} We acknowledge this work as part of the research activity supported by
the National Astronomical Research Institute of Thailand (NARIT),
Ministry of Science and Technology of Thailand.


\references

Gunsriwiwat K., Mkrtichian D.~E., 2016, {\it IBVS}, {\bf 6178}

Lenz P., Breger M., 2005, {\it Communications in Asteroseismology}, {\bf 146}, 53 \DOI{10.1553/cia146s53}

Mkrtichian D. et al., 2002, {\it ASP Conf. Ser}, {\bf 259}, 96 

Mkrtichian, D.E., Kusakin, A.V., Rodriguez, E., et al., 2004, {\it A\&A}, {\bf 419}, 1015 \DOI{10.1051/0004-6361:20040095}

Mkrtichian D.~E., Gunsriwiwat K., Komonjinda S., 2016, {\it IBVS}, {\bf 6182}

Mkrtichian D.~E., A-thano N., Awiphan S., 2017a, {\it IBVS}, {\bf 6210} \DOI{10.22444/IBVS.6210}

Mkrtichian D.~E., et al., 2017b, {\it IBVS}, {\bf 6221} \DOI{10.22444/IBVS.6221}

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