DY Pegasi — a SX Phoenicis Star in a Binary System with an Evolved Companion. (arXiv:2008.02542v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Xue_H/0/1/0/all/0/1">Hui-Fang Xue</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Niu_J/0/1/0/all/0/1">Jia-Shu Niu</a>
In this work, the photometric data from AAVSO are collected and analyzed on
the SX Phoenicis star DY Pegasi (DY Peg). From the frequency analysis, we get 3
independent frequencies: $f_0 = 13.71249 rm{c days^{-1}}$, $f_1 = 17.7000
rm{c days^{-1}}$, and $f_2 =18.138 rm{c days^{-1}}$, in which $f_0$ and
$f_1$ are the radial fundamental and first overtone mode respectively, while
$f_2$ is detected for the first time and should belong to a non-radial mode.
The $O-C$ diagram of the times of maximum light shows that DY Peg has a period
change rate $(1/P_0)(mathrm{d} P_0/mathrm{d} t) = -(5.87 pm 0.03) times
10^{-8} mathrm{yr^{-1}}$ for its fundamental pulsation mode, and should
belong to a binary system which has a orbital period $P_{mathrm{orb}} =
15425.0 pm 205.7 mathrm{days}$. Based on the spectroscopic information,
single star evolutionary models are constructed to fit the observed
frequencies. However, some important parameters of the fitted models are not
consistent with that from observations. Combing with the information from
observation and theoretical calculation, we conclude that DY Peg should be a SX
Phoenicis star in a binary system and accreting mass from a dust disk, which
was the residue of its evolved companion (most probability a hot white dwarf at
the present stage) produced in the AGB phase. Further observations are needed
to confirm this inference, and it might be potentially a universal formation
mechanism and evolutionary history for SX Phoenicis stars.
In this work, the photometric data from AAVSO are collected and analyzed on
the SX Phoenicis star DY Pegasi (DY Peg). From the frequency analysis, we get 3
independent frequencies: $f_0 = 13.71249 rm{c days^{-1}}$, $f_1 = 17.7000
rm{c days^{-1}}$, and $f_2 =18.138 rm{c days^{-1}}$, in which $f_0$ and
$f_1$ are the radial fundamental and first overtone mode respectively, while
$f_2$ is detected for the first time and should belong to a non-radial mode.
The $O-C$ diagram of the times of maximum light shows that DY Peg has a period
change rate $(1/P_0)(mathrm{d} P_0/mathrm{d} t) = -(5.87 pm 0.03) times
10^{-8} mathrm{yr^{-1}}$ for its fundamental pulsation mode, and should
belong to a binary system which has a orbital period $P_{mathrm{orb}} =
15425.0 pm 205.7 mathrm{days}$. Based on the spectroscopic information,
single star evolutionary models are constructed to fit the observed
frequencies. However, some important parameters of the fitted models are not
consistent with that from observations. Combing with the information from
observation and theoretical calculation, we conclude that DY Peg should be a SX
Phoenicis star in a binary system and accreting mass from a dust disk, which
was the residue of its evolved companion (most probability a hot white dwarf at
the present stage) produced in the AGB phase. Further observations are needed
to confirm this inference, and it might be potentially a universal formation
mechanism and evolutionary history for SX Phoenicis stars.
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