2025/11/20 by Bradley E. Schaefer, Schaefer, Bradley E., A. Pearce +11 · 1 citation
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics and Star Formation Studies #FOS: Physical sciences #Solar and Stellar Astrophysics (astro-ph.SR)
paper · pdf · doi:10.48550/arxiv.2511.16594
openalex publication_date 2025/11/20 · openalex created_date 2025/11/23 · openalex updated_date 2026/07/28
FQ Cir was an ordinary fast He/N classical nova, peaking at V=10.9. The pre-eruption and post-eruption counterpart was at V=14.0, making the smallest known classical nova amplitude of 3.1 mag. The nova light and the counterpart coincide to 0.034 arc-seconds, and the counterpart is a rare hot/blue emission-line star with flickering, so the identification of the quiescent nova is certain. The counterpart is a weak Be main sequence star, B1 V(n)(e). A coherent photometric period appears in all four \it TESS Sectors and in the AAVSO post-eruption light curve, as ellipsoidal modulation with orbital period 2.041738 days. The companion must have been spun-up to a fast rotation, and like all Be stars, a decretion disk is exuded. With the constraints of the blackbody radius and the main sequence, the companion mass is 13.0+0.2-0.5 M\odot, with radius 6.2±0.2 R\odot. This is the discovery of a cataclysmic variable with a high-mass companion, a new class that we call `High Mass Cataclysmic Variables'. The white dwarf mass is 1.25±0.10 M\odot and must have an accretion disk that supplies fuel for the nova eruption. FQ Cir represents a new mode of accretion in interacting binaries, with Roche lobe overflow from the decretion disk feeding mass into the usual accretion disk around the white dwarf, for disk-to-disk accretion. From the mass budget of the binary, the primary star must have its initial mass >7.6 M\odot, forming an ONe white dwarf, so FQ Cir can never become a Type Ia supernova.