Ellipsoidal modulation and multi-wavelength activity in the pre-cataclysmic binary RX J1553.0+4457

TL;DR

This study presents a comprehensive multi-wavelength analysis of the pre-cataclysmic binary RX J1553.0+4457, revealing ellipsoidal modulation, magnetic activity, and flaring behavior in a detached white dwarf and M-dwarf system.

Contribution

It provides the first detailed multi-wavelength characterization of RX J1553.0+4457, clarifying its nature as a detached pre-cataclysmic binary with magnetic activity-driven variability.

Findings

Detected short optical flares with amplitudes of 1-1.5 mag.

Identified stable orbital modulation consistent with ellipsoidal distortion.

Observed X-ray flux decline by a factor of about 4.

Abstract

RX J1553.0+4457 (TMTS J15530469+4457458) is a detached post-common-envelope binary containing a cool white dwarf and an active late-type companion. We present a multi-wavelength study combining BOOTES multi-band photometry, six sectors of public TESS full-frame imaging, Einstein Probe/FXT X-ray observations, CAFOS optical spectroscopy, and archival ultraviolet-to-mid-infrared photometry. The BOOTES data reveal two short optical flares separated by about 3 h, with amplitudes of roughly 1-1.5 mag and faster decay at shorter wavelengths. The combined TESS light curve shows a stable signal at P = 0.083782 d, consistent with the first harmonic of the known spectroscopic orbital period, and its folded morphology indicates ellipsoidal modulation from a tidally distorted late-type companion rather than an irradiation-dominated waveform. TESS flare energetics lie in the active M-dwarf regime. The Einstein Probe/FXT spectra show a factor of about 4 decline in the 0.3-10 keV flux, mainly associated with decreasing emission measures. The broadband SED is reproduced by a cool white dwarf plus a late-type M dwarf, with no clear hot-continuum or mid-infrared excess. RX J1553.0+4457 is therefore best interpreted as a detached pre-cataclysmic binary whose rapid optical variability is dominated by magnetic activity and whose orbital modulation is ellipsoidal, although a weak wind-fed or intermittent accretion contribution remains possible.