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KIC 6220497: a new Algol-type eclipsing binary with multiperiodic Pulsations

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Jae Woo Lee

14.07.2016

Co-author

Jae Woo Lee, Kyeongsoo Hong, Seung-Lee Kim, and Jae-Rim Koo

Affiliation

Korea Astronomy and Space Science Institute

Main category

Natural Sciences (Astrophysics and Astrononmy)

Abstract

We present both binarity and pulsation of KIC 6220497 from the {\it Kepler} observations. The light curve synthesis shows that the eclipsing system is a semi-detached Algol with parameters of

q

$q$ = 0.243

\pm

$\pm$ 0.001,

i

$i$ = 77.3

\pm

$\pm$ 0.3 deg, and

Δ T

$\Delta T$ = 3,372

\pm

$\pm$ 58 K, in which the detached primary component fills its Roche lobe by

\sim

$\sim$ 87\%. A multiple frequency analysis of the eclipse-subtracted light residuals reveals 33 frequencies in the range of 0.75

-

$-$ 20.22 d

^{- 1}

$^{-1}$ with amplitudes between 0.27 and 4.56 mmag. Among these, four are pulsation frequencies in fundamental (

f_{1}

$f_1$ ,

f_{5}

$f_5$ ) and

p

$p$ (

f_{2}

$f_2$ ,

f_{7}

$f_7$ ) modes, and six are orbital frequency (

f_{8}

$f_8$ ,

f_{31}

$f_{31}$ ) and its harmonics (

f_{6}

$f_6$ ,

f_{11}

$f_{11}$ ,

f_{20}

$f_{20}$ ,

f_{24}

$f_{24}$ ), which can be attributed to tidally excited modes. For the pulsation frequencies, the pulsation constants of 0.16

-

$-$ 0.33 d and the period ratios of

P_{p u l} / P_{o r b}

$P_{\rm pul}/P_{\rm orb}$ = 0.042

-

$-$ 0.089 indicate that the primary component is a

δ

$\delta$ Sct pulsating star and, thus, KIC 6220497 is an oscillating eclipsing Algol (oEA) star. The dominant pulsation period of 0.1174051

\pm

$\pm$ 0.0000004 d is significantly longer than that expected from empirical relations that link the pulsation period with the orbital period. The surface gravity of

log g_{1}

$\log g_1$ = 3.78

\pm

$\pm$ 0.03 is clearly smaller than those of the other oEA stars with similar orbital periods. The pulsation period and the surface gravity of the pulsating primary demonstrate that KIC 6220497 would be the more evolved EB, compared with normal oEA stars.

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