Tidally Excited Modes and $\delta$ Scuti Pulsations in the Eclipsing Triple Star IM Persei

TL;DR

This study analyzes the IM Persei triple star system using TESS data, revealing tidally excited modes and δ Scuti pulsations in the eclipsing pair, with detailed modeling confirming stellar parameters and pulsation characteristics.

Contribution

It provides the first detailed analysis of tidally excited modes and δ Scuti pulsations in IM Per, combining binary modeling with pulsation analysis based on high-quality TESS data.

Findings

Eclipsing pair consists of twin dwarfs with nearly equal masses and radii.

Detected 22 significant pulsation signals, including tidally excited modes.

Confirmed the pulsating star as a δ Scuti variable within the Cepheid instability strip.

Abstract

IM Per is a triple star system whose eclipsing pair masses and radii are accurate to within 1 \%. The TESS light curve of the program target exhibits partial eclipses and multiple oscillations with mmag-level amplitudes. It is found that the oscillations affect eclipse timing measurements. Binary modeling of the high-quality TESS data indicates that the eclipsing components of the triple system are twin dwarfs with parameters of $M_2$/$M_1$ = 0.995, $R_2$/$R_1$ = 0.901, and $\Delta$($T_{\rm eff,1}$--$T_{\rm eff,2}$) = 12 K in an eccentric ($e$ = 0.049), detached configuration. The third light of $l_3$ = 0.054 may mostly come from a G-type tertiary companion. Our predicted parallax of 1.52 $\pm$ 0.09 mas is concurrent with the Gaia measurement of 1.52 $\pm$ 0.05 mas. Multifrequency analysis of the outside-eclipse residuals reveals 22 significant pulsation signals: four in the gravity-mode region (0.03$-$2.22 day$^{-1}$) and 18 in the pressure-mode region (9.19$-$25.12 day$^{-1}$). Of the low frequencies, $f_{11}$ and $f_{14}$ are orbital harmonics that can be identified as tidally excited modes. The pulsation periods and constants for the high frequencies, and the position in the Cepheid instability strip demonstrate that the pulsating component of IM Per is a $\delta$ Sct variable.