Non-conservative evolution in Algols: where is the matter?

Abstract

There is gathering indirect evidence suggesting non-conservative evolutions in Algols. However, the systemic mass-loss rate is poorly constrained by observations and generally set as a free parameter in binary-star evolution simulations. Moreover, systemic mass loss may lead to observational signatures that are still to be found. We investigate the impact of the outflowing gas and the possible presence of dust grains on the spectral energy distribution (SED). We used the 1D plasma code Cloudy and compared the results with the 3D Monte-Carlo radiative transfer code Skirt for dusty simulations. The circumbinary mass-distribution and binary parameters are computed with state-of-the-art binary calculations done with the Binstar evolution code. The outflowing material reduces the continuum flux-level of the stellar SED in the optical and UV. Due to the time-dependence of this effect, it may help to distinguish between different ejection mechanisms. Dust, if present, leads to observable infrared excesses even with low dust-to-gas ratios and traces the cold material at large distances from the star. By searching for such dust emission in the WISE catalogue, we found a small number of Algols showing infrared excesses, among which the two rather surprising objects SX Aur and CZ Vel. We find that some binary B[e] stars show the same strong Balmer continuum as we predict with our models. However, direct evidence of systemic mass loss is probably not observable in genuine Algols, since these systems no longer eject mass through the hotspot mechanism. Furthermore, owing to its high velocity, the outflowing material dissipates in a few hundred years. If hot enough, the hotspot may produce highly ionised species such as SiIV and observable characteristics that are typical of W Ser systems.

Accepted for piblications in A&A; 21 pages, 19 figures

References in corpus (10)

• A Grid of NLTE Line-Blanketed Model Atmospheres of Early B-type Stars
• SKIRT: an Advanced Dust Radiative Transfer Code with a User-Friendly Architecture
• Mass loss out of close binaries. II
• Spin-up and hot spots can drive mass out of a binary
• Two extremely luminous WN stars in the Galactic center with circumstellar emission from dust and gas
• The eclipsing LMC star OGLE05155332--6925581: a clue for Double Periodic Variables
• A Spectroscopic Study of the Algol-type Binaries S Equulei and KO Aquilae: Absolute Parameters and Mass Transfer
• The data mining III: An analysis of 21 eclipsing binary light-curves observed by the INTEGRAL/OMC
• Phase-dependent X-ray observations of the beta Lyrae system: No eclipse in the soft band
• The data mining: An analysis of 20 eclipsing binary light-curves observed by the INTEGRAL/OMC