A Paradigm Shift in Exoplanet False Positive Identification with HIP-44302

TL;DR

This study reclassifies HIP-44302 (TOI-568) from a potential exoplanet host to a hierarchical triple-star system by integrating TESS transit data, broad-band photometry, and high-resolution imaging with a novel EXOFASTv2 modeling approach. The authors extend EXOFASTv2 with multi-star linking and orbit linking, enabling a self-consistent fit to three stars (A,B,C) and two bound orbits using SEDs, MIST isochrones, and eclipse/dilution constraints, without relying on radial velocities. They find Stars B and C form an eclipsing binary with $P = 9.599214$ d and $e ≈ 0.198$, orbiting Star A at $ ho ≈ 0.2946''$, while Star A appears pole-on with $v\sin i ≈ 2.3$ km/s; the primary transit is diluted by the single star, and a robust isochrone-based age constraint ties all stars to a common age. This methodology provides a paradigm shift in false positive identification, reducing vetting resources for planet candidates and yielding precise characterizations of complex stellar architectures. The work has broad implications for exoplanet demographics, stellar formation, and the interpretation of transit signals in multi-star environments.

Abstract

Through detailed modeling of all three stars, we show that HIP-44302 is a false positive triple-star system. While the Transiting Exoplanet Survey Satellite initially designated the object as a planetary candidate, observing a 10-day transit and secondary eclipse in Sectors 8 and 35, we definitively exclude this scenario, finding instead that the transit comes from eclipsing stellar companions with $P = 9.599214$ days and $a = 0.1415$ AU. This binary orbits a single star at a wide separation of $ρ= 0.2946''$, determined through high-resolution AO and speckle imaging and corresponding to a $\sim$297 AU, $\sim$1886-year orbit at a distance of 1010 pc. Using transit data and photometry, we use EXOFASTv2 to fit the transit light curve, spectral energy distribution, and MIST evolutionary models of the three stars. We find that the isolated star and the larger binary star are massive A stars, with the single star having evolved off the main sequence, while the smaller companion is a G star. We also found an unusually low rotational velocity of 2.3 km/s from the single A star, observed from MINERVA and TRES RVs, implying a pole-on orientation. The triple-star architecture derived from multiple data sources made this target a complex system that required new capabilities within EXOFASTv2 to properly model. Our successful modeling demonstrates a new paradigm for false positive identification and classification that incorporates imaging, photometry, transits, and global modeling to definitively rule out false positives that may otherwise pollute candidate catalogs without extensive follow-up observations.

Figures (12)

• Figure 1: Transit light curve from TESS of HIP-44302, which shows the primary transit at a 10-day period and a shallow secondary eclipse at roughly half the period. Red and blue arrows identify the primary and secondary transit respectively, and red points represent binned data. For a more detailed view of the transits, see our models in Figures \ref{['fig:transit']} and \ref{['fig:secondary']}.
• Figure 2: NIRC AO imaging and sensitivity curve. Insets: Images of the central portion of the images.
• Figure 3: Gemini speckle image from January 8th, 2020 at 562 nm and 832 nm shows the two stars seen in Figure \ref{['fig:nirc2_imaging']}.
• Figure 4: Gemini speckle image from March 4th, 2023 indicates no discernible movement, although the proper motion is smaller than our uncertainty.
• Figure 5: TRES average line profile shows a narrow line from primary star (indicating a low rotational velocity) and a broad shoulder, presumably from the massive companions.