When the disc’s away, the stars will play: dynamical masses in the nova-like variable KR Aur with a pinch of accretion

2020/02/24 by P. Rodríguez-Gil, T. Shahbaz, M. A. P. Torres +11 · 15 citations
Earth and Planetary Sciences · Physics and Astronomy · #Accretion (finance) #Accretion disc #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Star Formation Studies #Cataclysmic variable star #High-pressure geophysics and materials #Intermediate polar #Nova (rocket) #Nuclear physics #Physics #Pinch #Stars #Variable star #White dwarf #astro-ph.HE #astro-ph.SR

paper · pdf · doi:10.1093/mnras/staa612

published in Monthly Notices of the Royal Astronomical Society 494(1), 425-441 (Oxford University Press) · 18 pages, 17 figures, 6 tables, accepted for publication in MNRAS (2020 Feb 19)

arxiv created 2020/02/24 · openalex publication_date 2020/02/29 · openalex created_date 2020/03/06 · arxiv updated 2020/04/08 · openalex updated_date 2026/08/05

Abstract

ABSTRACT We obtained time-resolved optical photometry and spectroscopy of the nova-like variable KR Aurigae in the low state. The spectrum reveals a DAB white dwarf (WD) and a mid-M dwarf companion. Using the companion star’s i-band ellipsoidal modulation we refine the binary orbital period to be P = 3.906519 ± 0.000001 h. The light curve and the spectra show flaring activity due to episodic accretion. One of these events produced brightness oscillations at a period of 27.4 min, that we suggest to be related with the rotation period of a possibly magnetic WD at either 27.4 or 54.8 min. Spectral modelling provided a spectral type of M4–5 for the companion star and T₁=27 148 ± 496 K, log g=8.90 ± 0.07, and log (He/H)= -0.79^+0.07_-0.08 for the WD. By simultaneously fitting absorption- and emission-line radial velocity curves and the ellipsoidal light curve, we determined the stellar masses to be M₁ = 0.94^+0.15_-0.11 \rmM_{\rm \odot} and M₂ = 0.37^+0.07_-0.07 \rmM_{\rm \odot} for the WD and the M-dwarf companion, respectively, and an orbital inclination of 47^+1^{\rm o}_{-2^{\rm o}}. Finally, we analyse time-resolved spectroscopy acquired when the system was at an i-band magnitude of 17.1, about 1.3 mag brighter than it was in the low state. In this intermediate state, the line profiles contain an emission S-wave delayed by ≃0.2 orbital cycle relative to the motion of the WD, similar to what is observed in SW Sextantis stars in the high state.

Citations

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• The NextGen Model Atmosphere Grid for \documentclassaastex \usepackageamsbsy \usepackageamsfonts \usepackageamssymb \usepackagebm \usepackagemathrsfs \usepackagepifont \usepackagestmaryrd \usepackagetextcomp \usepackageportland,xspace \usepackageamsmath,amsxtra \usepackage[OT2,OT1]fontenc \newcommand\cyr \renewcommand\rmdefaultwncyr \renewcommand\sfdefaultwncyss \renewcommand\encodingdefaultOT2 \normalfont \selectfont \DeclareTextFontCommand\textcyr\cyr \pagestyleempty \DeclareMathSizes10976 \begindocument \landscape 3000≤ T_eff ≤ 10,000 \enddocument K