Mass transfer from giant donors

Abstract

The stability of mass transfer in binaries with convective giant donors remains an open question in modern astrophysics. There is a significant discrepancy between what the existing methods predict for a response to mass loss of the giant itself, as well as for the mass transfer rate during the Roche lobe overflow. Here we show that the recombination energy in the superadiabatic layer plays an important and hitherto unaccounted-for role in the donor's response to mass loss, in particular on its luminosity and effective temperature. Our improved optically thick nozzle method to calculate the mass transfer rate via L 1 allows us to evolve binary systems for a substantial Roche lobe overflow. We propose a new, strengthened criterion for the mass transfer instability, basing it on whether the donor experiences overflow through its outer Lagrangian point. We find that with the new criterion, if the donor has a well-developed outer convective envelope, the critical initial mass ratio for which a binary would evolve stably through the conservative mass transfer varies from 1.5 to 2.2, which is about twice as large as previously believed. In underdeveloped giants with shallow convective envelopes this critical ratio may be even larger. When the convective envelope is still growing, and in particular for most cases of massive donors, the critical mass ratio gradually decreases to this value, from that of radiative donors.

Constraining Mass-transfer Histories of Blue Straggler Stars with COS Spectroscopy of White Dwarf Companions

“…While closer, these criteria for stability still yield a q c too low for our formation model. Pavlovskii & Ivanova (2015) compare the adiabatic treatment of giant donor stars to 1D stellar models and adopt a different stability condition for whether there is overflow through the L2/L3 Lagrangian points. Importantly for this work, the L2/L3 overflow criteria can allow for stable mass transfer in binaries that fail the criteria set by the adiabatic response of the giant star.…”

The Formation of EL CVn-type Binaries

“…where M1 and R1 are the mass and radius of the donor and ω is its rotational angular velocity which is assumed to 2 Extensive effort has been put into developing reliable criteria to distinguish between dynamically stable and unstable mass transfer (Hjellming & Webbink 1987;Webbink 1988;Soberman, Phinney & van den Heuvel 1997;Han et al 2002;Chen & Han 2008;Woods et al 2012;Pavlovskii & Ivanova 2015;Ge et al 2015), but there are still many problems and no consensus on this issue.…”

Summary of Eighth Meeting on Hot Subdwarfs and Related Objects

“…Stability of a Roche lobe filling star against mass-loss on a dynamical time scale is determined by its adiabatic response to mass-loss, thresholds which Hjellming & Webbink (1987) explore with polytropic models. More detailed calculations of mass transfer staCorresponding Author: Anthony Eugene Lynas-Gray: Department of Physics, University of Oxford, United Kingdom; Email: aelg@astro.ox.ac.uk bility are given by Ge et al (2010Ge et al ( , 2015 while Pavlovskii & Ivanova (2015) and Pavlovskii et al (2017) model the asymptotic response of donor stars in interacting binary systems to very rapid mass-loss, characterised by adiabatic expansion throughout their interiors. Han's conclusions were: a) the Roche model may be invalid for extreme mass ratios, b) Roche lobe overflow (RLOF) may be more stable than previously supposed and c) Common Envelope (CE) ejection may be more efficient for red giant -Main Sequence (MS) binaries than for red giant -white dwarf binaries.…”