Angelos Karakonstantakis (NCAC, Warsaw)
Based on https://arxiv.org/abs/2501.04094 from Golden et al. (Jan 2025)
Weronika Narloch (NCAC, Warsaw)
based on https://arxiv.org/pdf/2412.09783 from Clontz et al. (Dec 2024)
Vincent Hocdé (NCAC, Warsaw)
Cepheid circumstellar emissions have previously been detected via both infrared excess and infrared interferometric observations at a few stellar radii. Those studies have shown that these circumstellar emission can be produced by ionized gas, however there is no direct observational evidence to confirm this hypothesis. In this letter we explore the continuum emission and a spectrum of the bright and long-period Cepheid, ℓ~Car (P=35.56day) at millimeter-wavelengths in order to detect possible effects of ionized gas emission. We presented ALMA observations of ℓ Car in two spectral setups in Band~6 (near 212 and 253\,GHz, respectively) and we compared the measured flux density to one expected for the stellar continuum. We also derived the spectral index and probed the presence of Radio Recombination Lines (RRL). We report statistically significant emission of about 3.5mJy in the two spectral ranges, which is about 2.5 times the stellar continuum emission. For the first time, we are also able to derive the spectral index of the flux density (Sν∝να), α=+1.26±0.44 (∼3σ error), which is characteristic of partially optically thick ionized gas emission. Additionally, we discovered an emission line from a RRL of hydrogen H29α centered on the stellar rest velocity, smaller in spatial extent than about 0\farcs2 (≲100AU), with a symmetric profile with a width at half power of 55.3±7.5\,\kms (1σ error). It confirms the presence of ionized gas emission near ℓ~Car. The millimeter emission detected from ℓ Car can be attributed to ionized gas emission from the Cepheid's chromosphere. Further radio interferometric observations are necessary to confirm the occurrence of these ionized gas envelopes around Cepheids of different pulsation periods.
Andrzej Sołtan (NCAC, Warsaw)
https://arxiv.org/abs/2501.19236 (Unveiling the largest structures in the nearby Universe: Discovery of the Quipu superstructure)
