8 research outputs found

    Magnetic braking with MESA evolutionary models in the single star and LMXB regimes

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    Magnetic braking has a prominent role in driving the evolution of close low mass binary systems and heavily influences the rotation rates of low mass F- and later type stars with convective envelopes. Several possible prescriptions that describe magnetic braking in the context of 1D stellar evolution models currently exist. We test four magnetic braking prescriptions against both low mass X-ray binary orbital periods from the Milky Way and single star rotation periods observed in open clusters. We find that data favors a magnetic braking prescription that follows a rapid transition from fast to slow rotation rates, exhibits saturated (inefficient) magnetic braking below a critical Rossby number, and that is sufficiently strong to reproduce ultra compact X-ray binary systems. Of the four prescriptions tested, these conditions are satisfied by a braking prescription that incorporates the effect of high order magnetic field topology on angular momentum loss. None of the braking prescriptions tested are able to replicate the stalled spin down observed in open cluster stars aged 700 - 1000 Myr or so, with masses \lesssim 0.8 M\rm M_{\odot}.Comment: 20 pages, 5 figure

    The Effects of Wind Roche-lobe Overflow on Binary Evolution

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    Wind Roche-Lobe Overflow (WRLOF) is a mass-transfer mechanism for stellar binaries wherein the wind acceleration zone of the donor star exceeds its Roche lobe radius, allowing material to be transferred to the accretor. WRLOF may explain characteristics observed in blue lurkers and blue stragglers, such as their fast rotation rate. While WRLOF has been implemented in rapid population synthesis codes, it has yet to be explored thoroughly in detailed binary models such as MESA, and over a wide range of initial binary configurations. We incorporate WRLOF accretion in MESA using the POSYDON infrastructure and investigate wide low-mass binaries at solar metallicity, and perform a parameter study over initial orbital period and star mass. In most of the models where we consider angular momentum transfer during accretion, the accretor is spun up to the critical rotation rate and develops a boosted wind. Balanced by boosted wind loss, the accretor only gains 2%\sim 2\% of its total mass due to wind accretion, but can maintain a near-critical rotation rate during WRLOF. Notably, the mass transfer efficiency is significantly smaller than in previous studies in which the rotation of the accretor star is ignored. We compare our results to observational data of blue lurkers in M67 and find that the WRLOF mechanism can qualitatively explain their rapid rotation speed, their location on the HR diagram and their orbital periods.Comment: 17 pages, 11 figures, 3 tables, submitted to AAS Journal

    Combined Effects of Rotation and Age Spreads on Extended Main-Sequence Turn Offs

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    The extended main-sequence turn offs (eMSTOs) of several young to intermediate age clusters are examined in the Magellanic Clouds and the Milky Way. We explore the effects of extended star formation (eSF) and a range of stellar rotation rates on the behavior of the color–magnitude diagram, paying particular attention to the MSTO. We create synthetic stellar populations based on MESA stellar models to simulate observed Hubble Space Telescope and Gaia star cluster data. We model the effect of rotation as a nonparametric distribution, allowing for maximum flexibility. In our models the slow rotators comprise the blueward, and fast rotators the redward portion of the eMSTO. We simulate data under three scenarios: nonrotating eSF, a range of rotation rates with a single age, and a combination of age and rotation effects. We find that two of the five clusters (the youngest and oldest) favor an age spread, but these also achieve the overall worst fits of all clusters. The other three clusters show comparable statistical evidence between rotation and an age spread. In all five cases, a rotation-rate distribution alone is capable of qualitatively matching the observed eMSTO structure. In future work, we aim to compare our predicted VsiniV\sin i with observations in order to better constrain the physics related to stellar rotation