Revealing a Main-sequence Star that Consumed a Planet with JWST

April 2025 • 2025ApJ...983...87L

Authors • Lau, Ryan M. • Jencson, Jacob E. • Salyk, Colette • De, Kishalay • Fox, Ori D. • Hankins, Matthew J. • Kasliwal, Mansi M. • Keyes, Charles D. • Macleod, Morgan • Ressler, Michael E. • Rose, Sam

Abstract • The subluminous red nova (SLRN) Zwicky Transient Facility (ZTF) SLRN-2020 is the most compelling direct detection of a planet being consumed by its host star, a scenario known as a planetary engulfment event. We present JWST spectroscopy of ZTF SLRN-2020 taken +830 days after its optical emission peak using the NIRSpec fixed-slit 3–5 μm high-resolution grating and the MIRI 5–12 μm low-resolution spectrometer. NIRSpec reveals the ¹²CO fundamental band (ν = 1–0) in emission at ∼4.7 μm, Brackett-α emission, and the potential detection of PH₃ in emission at ∼4.3 μm. The JWST spectra are consistent with the claim that ZTF SLRN-2020 arose from a planetary engulfment event. We utilize DUSTY to model the late-time ∼1–12 μm spectral energy distribution (SED) of ZTF SLRN-2020, where the best-fit parameters indicate the presence of warm, K, circumstellar dust with a total dust mass of Log M_⊙. We also fit a DUSTY model to archival photometry taken +320 days after the peak that suggested the presence of a cooler, K, and more massive, Log , circumstellar dust component. Assuming the cool component originates from the ZTF SLRN-2020 ejecta, we interpret the warm component as fallback from the ejecta. From the late-time SED model, we measure a luminosity of L_⊙ for the remnant host star, which is consistent with a ∼0.7 M_⊙ K-type star that should not yet have evolved off the main sequence. If ZTF SLRN-2020 was not triggered by stellar evolution, we suggest that the planetary engulfment was due to orbital decay from tidal interactions between the planet and the host star.

Links

• PDF https://iopscience.iop.org/article/10.3847/1538-4357/adb429/pdf
• PREPRINT http://arxiv.org/abs/2504.07275
• DATA https://doi.org/10.17909/198x-0r66
• ELECTR https://iopscience.iop.org/article/10.3847/1538-4357/adb429/pdf