[HP99] 159 -- Properties of the first Supersoft X-ray Source with a Helium star donor

Abstract

[HP99] 159 is remarkable as the first supersoft X-ray source (SSS) identified with an evolved helium star donor. With a likely orbital period of 1.164 d or 2.327 d, the origin of the SSS component is controversial, with the two current models being either steady He-burning on the white dwarf surface, or that it is a helium nova in the decaying phase. To help resolve this issue we present extensive new long-term spectroscopy (with SALT) and photometry (at SAAO and with OGLE) of [HP99] 159 which (a) supports 2.327 d as the orbital period, and (b) finds only a small He II radial velocity modulation. The latter is surprising as it implies a very low inclination system, whereas our light curve modelling suggests $i\sim 50^{\circ }$, and hence that the He II must be produced in outflowing material further above, or beyond, the disc. We find that the decaying nova model cannot fit our OGLE light curve and the observed SSS flux level. [HP99] 159 has been essentially constant as an SSS over several decades, implying a sustained high level of mass-transfer from its He star donor, making it the only confirmed single-degenerate scenario SN Ia progenitor. We have updated the known SSS binary parameters and find a clear $\sim$1.5 mag difference in their $M_{\mathrm{V}}$ when compared to the $M_{\mathrm{V}}-\Sigma$ properties of LMXBs, likely due to the larger irradiated areas and more luminous donors.

arXiv comment8 pages, 8 figures, Accepted for publication in MNRAS

References in corpus (25)

• A method for optimal image subtraction
• Physics Of Eclipsing Binaries. II. Towards the Increased Model Fidelity
• A New Evolutionary Path to Type Ia Supernovae: Helium-Rich Super-Soft X-Ray Source Channel
• Spectral models for binary products: Unifying Subdwarfs and Wolf-Rayet stars as a sequence of stripped-envelope stars
• OGLE-IV: Fourth Phase of the Optical Gravitational Lensing Experiment
• The hot subdwarf B + white dwarf binary KPD 1930+2752 - a Supernova Type Ia progenitor candidate
• The expanding bipolar shell of the helium nova V445 Puppis
• MN48: a new Galactic bona fide luminous blue variable revealed by Spitzer and SALT
• The nature of the supersoft X-ray source RX~J0513--69
• The photometric-amplitude and mass-ratio distributions of contact binary stars
• The shortest period sdB plus white dwarf binary CD-30 11223 (GALEX J1411-3053)
• Helium accreting CO white dwarfs with rotation: helium novae instead of double detonation
• Helium Nova on a Very Massive White Dwarf -- A Light Curve Model of V445 Puppis (2000) Revised
• A limit cycle model for long-term optical variations of V Sagittae: The second example of accretion wind evolution
• Microlensing optical depth and event rate toward the Large Magellanic Cloud based on 20 years of OGLE observations
• V445 Puppis -- Helium nova on a massive white dwarf
• Type Ia Supernova Sub-classes and Progenitor Origin
• Discovery of a double detonation thermonuclear supernova progenitor
• Astrokit -- an Efficient Program for High-Precision Differential CCD Photometry and Search for Variable Stars
• Evolution of Helium Star - White Dwarf Binaries Leading up to Thermonuclear Supernovae
• HD 49798: Its History of Binary Interaction and Future Evolution
• Period--luminosity relation for persistent LMXBs in the near-infrared
• A helium-burning white dwarf binary as a supersoft X-ray source
• SALT spectroscopy of evolved massive stars
• A helium nova in the Large Magellanic Cloud -- the faint supersoft X-ray source [HP99]159