We write to report the discovery that Deneb is a large amplitude polarization variable. Over a ~400 d time span from August 2022 Deneb's polarization was typically around 3900 parts-per-million (ppm) in the SDSS g'-band. Yet, it varied by several hundred ppm in an irregular way on a timescale of weeks. The largest polarization change, amounting to 2500 ppm, occurred shortly after the last pulsation ``resumption'' event identified by Abt et al. (2023) in TESS photometry. The relationship between the observed polarization -- particularly corresponding to the resumption event -- and its brightness and H-alpha spectra suggests a mechanism involving density changes in its wind and/or extended atmosphere. Smaller effects due to pulsations are not ruled out and further study is recommended.
Cite
@article{arxiv.2404.17707,
title = {Deneb is a Large Amplitude Polarimetric Variable},
author = {Daniel V. Cotton and Jeremy Bailey and Jean Perkins and Derek L. Buzasi and Ievgeniia Boiko},
journal= {arXiv preprint arXiv:2404.17707},
year = {2024}
}