CPD-82 291: Multi-sector TESS Photometry and SED Analysis of an Active Eclipsing Binary

Abstract

We present a multi-sector $TESS$ photometric and spectral energy distribution analysis of the eclipsing binary CPD--82~291 (RX~J0853.1--8244). Eight $TESS$ sectors reveal well-defined eclipses and substantial, changing out-of-eclipse modulation. The asymmetries are reproduced by different surface-brightness configurations at different epochs, consistent with strong and evolving stellar activity, although the fitted circular regions are not unique maps of individual starspots. A detached-binary light-curve model yields an orbital inclination of $i\simeq 82.1^{\circ }$ and a photometric mass ratio of $q_{\mathrm{phot}}\simeq 0.464$. Without a spectroscopic radial-velocity orbit, the mass ratio and absolute parameters are model-dependent rather than dynamical measurements. Combining the light-curve geometry with the SED radius scale and \textit{Gaia} distance gives $R_1\simeq 1.25R_{\odot }$ and $R_2\simeq 3.70R_{\odot }$; the corresponding model-inferred masses remain substantially less secure than the dimensionless light-curve parameters. The stellar photospheres reproduce the observed SED from the optical region through WISE W4, with no statistically significant mid-infrared excess. The only positive long-wavelength deviation is a low-significance $60\mu$m measurement, while the $90\mu$m result is an upper limit. A cool circumbinary-dust model can reproduce this tentative signal, but such a component is not required by the photometry, and its inferred mass and radial extent are non-unique and strongly model dependent. Evolutionary tracks place the primary close to the zero-age main sequence and the secondary well above the main-sequence locus. However, the absence of radial velocities and spectroscopic youth indicators, together with $Gaia$ astrometry inconsistent with Chamaeleon~I membership, prevents a secure pre-main-sequence classification.

Accepted for publication in PASP. 41 pages, 18 figures, and 6 tables