Ultraviolet Spectropolarimetry:Conservative and Nonconservative Mass Transfer in OB Interacting Binaries

Abstract

One objective of the Polstar spectropolarimetry mission is to characterize the degree of nonconservative mass transfer that occurs at various stages of binary evolution, from the initial mass reversal to the late Algol phase. The proposed instrument combines spectroscopic and polarimetric capabilities, where the spectroscopy can resolve Doppler shifts in UV resonance lines with 10 km/s precision, and polarimetry can resolve linear polarization with 10 −3 precision or better. The spectroscopy will identify absorption by mass streams seen in projection against the stellar disk as a function of orbital phase, as well as scattering from extended splash structures and a circumbinary disk of material that fails to be transferred conservatively. The polarimetry affects more the light coming from material not seen against the stellar disk, allowing the geometry of the scattering to be tracked, resolving ambiguities left by the spectroscopy and light-curve information. For example, nonconservative mass streams ejected in the polar direction will produce polarization of the opposite sign from conservative transfer accreting in the orbital plane. Also, time domain coverage over a range of phases of the binary orbit are well supported by the Polstar observing strategy. Combining these elements will significantly improve our understanding of the mass transfer process and the amount of mass that can escape from the system, an important channel for changing the final mass, and ultimate supernova, of the large number of massive stars found in binaries at close enough separation to undergo interaction.

Ultraviolet spectropolarimetry with polstar: interstellar medium science

“…Polstar's broad wavelength coverage will enable a wide variety of investigations in addition to interstellar medium studies, in the physics of hot stars involving mass loss, the effect of binarity on winds, magnetospheres, and rapid rotation (Gayley et al 2021;Peters et al 2021;St-Louis et al 2021a;Jones et al 2021;Shultz et al 2021), and in the properties of protoplanetary disks (Wisniewski et al 2021).…”

“…However, the general procedure outlined here is likely to be able to decompose the main components, given high-enough signal-to-noise data. Deviation from flat continuum stellar polarization is discussed in the other Polstar white papers (Peters et al 2021;Gayley et al 2021;St-Louis et al 2021b;Jones et al 2021;Shultz et al 2021). At moderate signal to noise, these analyses may not provide complete or high-quality decomposition of the source terms.…”

Revisiting the high-mass transfer close binary star system AU Monocerotis

“…The first one represents the radius of a stable accretion disk for different mass ratios, while the second is the distance of closest approach of the gas stream from the center of the gainer. From this diagnostic, an accretion disk can develop in this system (Peters et al 2021). The impact of the gas stream on the accretion disk produces an hot spot.…”

Evolution of Close Binary System Parameter Distributions

“…As a result, there are observational evidences for both conservative and nonconservative mass transfer in close binaries (Podsiadlowski et al 2001;Yakut 2006;Manzoori 2011;Pols 2012). More recent discussions on observational proves of conservative and non-conservative scenarios of mass transfer can be found in (Qian et al 2020;Dervisoglu et al 2018;Peters et al 2021;Vidante and Malasan 2022;Miszuda et al 2022), while these and other problems related to the evolution of close bianries are reviewed in (Tutukov and Cherepashchuk 2020;Offner et al 2022).…”