KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau
Abstract
Transiting exoplanets provide a unique laboratory for studying stellar surface heterogeneities via starspot or facular occultations. When observed at multiple wavelengths, this configuration enables spectroscopic characterization of spot thermal contrasts, distributions, and morphology. In this work, we leverage JWST NIRISS/SOSS transit observations of the 20--30~Myr planets V1298~Tau~bcd to study the surface properties of their solar analog host star V1298~Tau. We identify 14 starspot crossing events across two visits. We derive 0.8−2.8μm starspot contrast spectra and demonstrate the contrasts can only be explained when accounting for the umbral and penumbral components of the starspots, robust to which stellar model grid is assumed. The spot temperatures are broadly consistent between visits, suggesting that V1298~Tau (Tphot=4866±33\,K) has starspots with Tumbra = 3300--3600\,K umbrae and Tpenumbra = 4400--4600\,K penumbrae, and are ∼25--30\% umbrae by area. The differences between these spot components and the stellar photosphere are consistent with sunspots. Additionally, the relation between the spot contrast and the ratio of umbral to penumbral area is similar to that of the Sun. Combining these JWST observations with long baseline multi-band photometry from the Las Cumbres Observatory, we also estimated the global unocculted spot distribution, revealing at least 5 additional large unocculted active regions. Altogether, these measurements suggest that while the total spot coverage evolves in time, the relative temperatures of surface heterogeneities on Sun-like stars may be consistent throughout their lifetimes. Furthermore, these results demonstrate that JWST exoplanet transit observations can be useful for starspot substructure characterization.
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BibTeX
@misc{murphy2026kronos,
title = {{KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau}},
author = {Matthew M. Murphy and Adina D. Feinstein and Meir E. Schochet and Benjamin V. Rackham and Luis Welbanks and Darryl Z. Seligman and Girish M. Duvvuri and Eva-Maria Ahrer and John H. Livingston and Saugata Barat and Jean-Michel Désert and Rafael Luque and Catriona Murray and Matthew C. Nixon and Sydney Petz and Michael Radica and Hinna Shivkumar},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2606.16782},
eprint = {2606.16782},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.16782},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - KRONOS II: Solar-like Umbra and Penumbra Properties on the Young Sun V1298~Tau
AU - Matthew M. Murphy
AU - Adina D. Feinstein
AU - Meir E. Schochet
AU - Benjamin V. Rackham
AU - Luis Welbanks
AU - Darryl Z. Seligman
AU - Girish M. Duvvuri
AU - Eva-Maria Ahrer
AU - John H. Livingston
AU - Saugata Barat
AU - Jean-Michel Désert
AU - Rafael Luque
AU - Catriona Murray
AU - Matthew C. Nixon
AU - Sydney Petz
AU - Michael Radica
AU - Hinna Shivkumar
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2606.16782
UR - https://arxiv.org/abs/2606.16782
AB - Transiting exoplanets provide a unique laboratory for studying stellar surface heterogeneities via starspot or facular occultations. When observed at multiple wavelengths, this configuration enables spectroscopic characterization of spot thermal contrasts, distributions, and morphology. In this work, we leverage JWST NIRISS/SOSS transit observations of the 20--30~Myr planets V1298~Tau~bcd to study the surface properties of their solar analog host star V1298~Tau. We identify 14 starspot crossing events across two visits. We derive 0.8−2.8μm starspot contrast spectra and demonstrate the contrasts can only be explained when accounting for the umbral and penumbral components of the starspots, robust to which stellar model grid is assumed. The spot temperatures are broadly consistent between visits, suggesting that V1298~Tau (T_phot=4866±33\,K) has starspots with T_umbra = 3300--3600\,K umbrae and T_penumbra = 4400--4600\,K penumbrae, and are ∼25--30\% umbrae by area. The differences between these spot components and the stellar photosphere are consistent with sunspots. Additionally, the relation between the spot contrast and the ratio of umbral to penumbral area is similar to that of the Sun. Combining these JWST observations with long baseline multi-band photometry from the Las Cumbres Observatory, we also estimated the global unocculted spot distribution, revealing at least 5 additional large unocculted active regions. Altogether, these measurements suggest that while the total spot coverage evolves in time, the relative temperatures of surface heterogeneities on Sun-like stars may be consistent throughout their lifetimes. Furthermore, these results demonstrate that JWST exoplanet transit observations can be useful for starspot substructure characterization.
ER -