Criteria for Dynamical Timescale Mass Transfer of Metal-poor Intermediate-mass Stars

Abstract

The stability criteria of rapid mass transfer and common-envelope evolution are fundamental in binary star evolution. They determine the mass, mass ratio, and orbital distribution of many important systems, such as X-ray binaries, type Ia supernovae, and merging gravitational-wave sources. We use our adiabatic mass-loss model to systematically survey intermediate-mass (IM) stars’ thresholds for dynamical timescale mass transfer. The impact of metallicity on the stellar responses and critical mass ratios is explored. Both tables (Z = 0.001) and fitting formulae (Z = 0.001 and Z = 0.02) of the critical mass ratios of IM stars are provided. An application of our results to intermediate-mass X-ray binaries (IMXBs) is discussed. We find that the predicted upper limit to mass ratios, as a function of orbital period, is consistent with the observed IMXBs that undergo thermal or nuclear timescale mass transfer. According to the observed peak X-ray luminosity, L X, we predict the range of L X for IMXBs as a function of the donor mass and the mass-transfer timescale.

A New Route to Massive Hot Subdwarfs: Common Envelope Ejection from Asymptotic Giant Branch Stars

“…In the AGB CE ejection channel, the progenitor of a hot subdwarf fills its Roche lobe at the AGB. The binary may enter the CE phase (depending on the critical mass ratios as functions of the donors' masses and evolutionary stages; see Ge et al 2010Ge et al , 2015Ge et al , 2020Ge et al , 2023. If the CE is successfully ejected by the released energy of orbital shrinkage, an sdO/B binary is born.…”

The Common Envelope Evolution Outcome. II. Short-orbital-period Hot Subdwarf B Binaries Reveal a Clear Picture

“…Notably, a critical mass ratio for instability q crit ≡ M donor /M accretor = 1.2 or 1.5 is typically adopted, independent of the progenitor mass of an sdB. Recent studies by Ge et al (2020aGe et al ( , 2020bGe et al ( , 2023 show that the critical mass ratios for dynamically unstable q ad or thermal timescale mass transfer q th depend on both the progenitor mass and evolutionary stage (the radius).…”

“…With the model grids, we trace the radius response and the total energy change (Equation ( 13)) of the donor using the adiabatic mass-loss code (Ge et al 2010a(Ge et al , 2010b(Ge et al , 2015(Ge et al , 2020a(Ge et al , 2023. We first assume the progenitor masses of eight sdB binaries with a WD companion in Table 1 are 1 .00, 1.14, 1.30, 1.44, 1.50, 1.60, 1.80, 1.91, and 2.00 M e .…”

The Distribution of Semidetached Binaries. I. An Efficient Pipeline

“…The red star markers and black dots represent our SD candidates and the literature samples, respectively. Ge et al (2015Ge et al ( , 2020aGe et al ( , 2020bGe et al ( , 2023 have proposed relationships between the critical mass ratio limits ( ) q ad and orbital periods for stars of different masses. In Figure 12, we have selected the critical mass ratio limits for dynamical-timescale (gray lines) and thermal-timescale (blue lines) mass transfer at some significant evolutionary stages, including the ZAMS, the late H-R gap (LHG), and the base of the red giant branch (BRGB), represented by dashed, dotted, and solid lines, respectively.…”

“…The distribution of mass ratio (q = M donor /M accretor ) and orbital period for SDs with early-type accretors (a) and late-type accretors (b). The colored lines represent the theoretical critical mass ratio limits for dynamical-timescale (gray lines) and thermal-timescale (blue lines) mass transfer at different evolutionary stages from Ge et al (2015Ge et al ( , 2020aGe et al ( , 2020bGe et al ( , 2023, including the ZAMS in dashed lines, the LHG in dotted lines, and the BRGB in solid lines. The red star markers represent our SD candidates, while the black dots correspond to the literature samples.…”