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Magnetic fields can drastically change predictions of evolutionary models of massive stars via mass-loss quenching, magnetic braking, and efficient angular momentum transport, which we aim to quantify in this work. We use the MESA software instrument to compute an extensive main-sequence grid of stellar structure and evolution models, as well as isochrones, accounting for the effects attributed to a surface fossil magnetic field. The grid is densely populated in initial mass (3-60 M$_\odot$), surface equatorial magnetic field strength (0-50 kG), and metallicity (representative of the Solar neighbourhood and the Magellanic Clouds). We use two magnetic braking and two chemical mixing schemes and compare the model predictions for slowly-rotating, nitrogen-enriched ("Group 2") stars with observations in the Large Magellanic Cloud. We quantify a range of initial field strengths that allow for producing Group 2 stars and find that typical values (up to a few kG) lead to solutions. Between the subgrids, we find notable departures in surface abundances and evolutionary paths. In our magnetic models, chemical mixing is always less efficient compared to non-magnetic models due to the rapid spin-down. We identify that quasi-chemically homogeneous main sequence evolution by efficient mixing could be prevented by fossil magnetic fields. We recommend comparing this grid of evolutionary models with spectropolarimetric and spectroscopic observations with the goals of i) revisiting the derived stellar parameters of known magnetic stars, and ii) observationally constraining the uncertain magnetic braking and chemical mixing schemes., Comment: Accepted for publication in MNRAS. A full reproduction package is available on Zenodo at https://doi.org/10.5281/zenodo.7069766

5 pages, 6 figures.--PACS nrs.:23.40.-s, 21.60.Jz, 26.30.Ca, 27.50.+e.--ArXiv pre-print available at: http://arxiv.org/abs/0910.1021v1, Weak interaction rates are studied in neutron deficient Kr and Sr waiting-point isotopes in ranges of densities and temperatures relevant for the rp process. The nuclear structure is described within a microscopic model (deformed QRPA) that reproduces not only the half-lives but also the Gamow–Teller strength distributions recently measured. The various sensitivities of the decay rates to both density and temperature are discussed. Continuum electron capture is shown to contribute significantly to the weak rates at rp-process conditions., This work was supported by Ministerio de Ciencia e Innovación (Spain) under Contract No. FIS2008-01301.

The (d,He-2) charge-exchange reaction on the double-beta decay (beta beta) nucleus Zn-64 has been studied at an incident energy of 183 MeV. The two protons in the S-1(0) state (indicated as He-2) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. He-2 spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus Cu-64 with high precision. Zn-64 is one of the rare cases undergoing a beta beta decay in beta(+) direction. In the experiment presented here, Gamow-Teller (GT(+)) transition strengths have been extracted. Together with the GT(-) transition strengths from Ni-64(He-3,t) data to the same intermediate nucleus Cu-64, the nuclear matrix elements of the beta beta decay of Zn-64 have been evaluated. Finally, the GT(+/-) distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

The (d,He-2) charge-exchange reaction on the double-beta decay (beta beta) nucleus Zn-64 has been studied at an incident energy of 183 MeV. The two protons in the S-1(0) state (indicated as He-2) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. He-2 spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus Cu-64 with high precision. Zn-64 is one of the rare cases undergoing a beta beta decay in beta(+) direction. In the experiment presented here, Gamow-Teller (GT(+)) transition strengths have been extracted. Together with the GT(-) transition strengths from Ni-64(He-3,t) data to the same intermediate nucleus Cu-64, the nuclear matrix elements of the beta beta decay of Zn-64 have been evaluated. Finally, the GT(+/-) distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell.

The (d,2He) charge-exchange reaction on the double-beta decay (beta beta) nucleus 64Zn has been studied at an incident energy of 183 MeV. The two protons in the 1S0 state (indicated as 2He) were both momentum analyzed and detected simultaneously by the BBS magnetic spectrometer and its position-sensitive detector. 2He spectra with a resolution of about 115 keV (FWHM) have been obtained allowing identification of many levels in the residual nucleus 64Cu with high precision. 64Zn is one of the rare cases undergoing a beta beta decay in beta+ direction. In the experiment presented here, Gamow-Teller (GT+) transition strengths have been extracted. Together with the GT- transition strengths from 64Ni(3He,t) data to the same intermediate nucleus 64Cu, the nuclear matrix elements of the beta beta decay of 64Zn have been evaluated. Finally, the GT± distributions are compared with shell-model calculations and a critical assessment is given of the various residual interactions presently employed for the pf shell

The S-32(d,He-2)P-32 charge-exchange reaction has been studied at forward angles and at an incident energy of E-d=170 MeV. The two protons in the S-1(0)(pp) state (indicated as He-2) were both momentum analyzed and detected by the same spectrometer and detector. High resolution He-2 spectra have been obtained allowing identification of many levels in the residual nucleus with high precision. The (d,He-2) reaction selectively excites spin-isospin-flip transitions, and at vanishing momentum transfer these are largely governed by the Gamow-Teller transition operator for the beta(+) direction. In the case of the self-conjugate nucleus S-32, the (d,He-2) probe is calibrated against the elementary (p,n) probe going into the mirror beta(-) direction. The deduced results are compared with those obtained from (p,p(')) and (e,e(')) reactions, which excite the same levels in the isospin multiplet. Angular distributions of cross sections for the (d,He-2) reaction are presented and compared with DWBA calculations. A level-by-level comparison with shell-model calculations using the USD interaction has been performed, and the structure of the l-forbidden ground state transition is discussed. From the comparison with (p,p(')), (e,e(')), and (p,n) data the isospin-analog J(pi)=1(+) levels in the triplet of the A=32 nuclei are deduced.

The S-32(d,He-2)P-32 charge-exchange reaction has been studied at forward angles and at an incident energy of E-d=170 MeV. The two protons in the S-1(0)(pp) state (indicated as He-2) were both momentum analyzed and detected by the same spectrometer and detector. High resolution He-2 spectra have been obtained allowing identification of many levels in the residual nucleus with high precision. The (d,He-2) reaction selectively excites spin-isospin-flip transitions, and at vanishing momentum transfer these are largely governed by the Gamow-Teller transition operator for the beta(+) direction. In the case of the self-conjugate nucleus S-32, the (d,He-2) probe is calibrated against the elementary (p,n) probe going into the mirror beta(-) direction. The deduced results are compared with those obtained from (p,p(')) and (e,e(')) reactions, which excite the same levels in the isospin multiplet. Angular distributions of cross sections for the (d,He-2) reaction are presented and compared with DWBA calculations. A level-by-level comparison with shell-model calculations using the USD interaction has been performed, and the structure of the l-forbidden ground state transition is discussed. From the comparison with (p,p(')), (e,e(')), and (p,n) data the isospin-analog J(pi)=1(+) levels in the triplet of the A=32 nuclei are deduced.

The V-51(d,He-2)Ti-51 charge-exchange reaction has been investigated at an incident energy of 171 MeV and scattering angles near 0degrees. The two protons in the S-1(0)(pp) state (denoted as He-2) were both momentum analyzed and detected by the same spectrometer and detector. Spectra with a resolution of about 125 keV (full width at half maximum) have been obtained allowing identification of many levels in Ti-51 with high precision. The GT(+) strength distribution for transitions to levels up to about 6 MeV of excitation energy has been extracted. The results are compared with a large-scale shell-model calculation in the full pf shell.

The V-51(d,He-2)Ti-51 charge-exchange reaction has been investigated at an incident energy of 171 MeV and scattering angles near 0degrees. The two protons in the S-1(0)(pp) state (denoted as He-2) were both momentum analyzed and detected by the same spectrometer and detector. Spectra with a resolution of about 125 keV (full width at half maximum) have been obtained allowing identification of many levels in Ti-51 with high precision. The GT(+) strength distribution for transitions to levels up to about 6 MeV of excitation energy has been extracted. The results are compared with a large-scale shell-model calculation in the full pf shell.

The Humphreys-Davidson (HD) limit empirically defines a region of high luminosities (log L > 5.5) and low effective temperatures (T < 20kK) on the Hertzsprung-Russell Diagram in which hardly any supergiant stars are observed. Attempts to explain this limit through instabilities arising in near- or super-Eddington winds have been largely unsuccessful. Using modern stellar evolution we aim to re-examine the HD limit, investigating the impact of enhanced mixing on massive stars. We construct grids of stellar evolution models appropriate for the Small and Large Magellanic Clouds (SMC, LMC), as well as for the Galaxy, spanning various initial rotation rates and convective overshooting parameters. Significantly enhanced mixing apparently steers stellar evolution tracks away from the region of the HD limit. To quantify the excess of over-luminous stars in stellar evolution simulations we generate synthetic populations of massive stars, and make detailed comparisons with catalogues of cool (T < 12.5kK) and luminous (log L > 4.7) stars in the SMC and LMC. We find that adjustments to the mixing parameters can lead to agreement between the observed and simulated red supergiant populations, but for hotter supergiants the simulations always over-predict the number of very luminous (log L > 5.4) stars compared to observations. The excess of luminous supergiants decreases for enhanced mixing, possibly hinting at an important role mixing has in explaining the HD limit. Still, the HD limit remains unexplained for hotter supergiants., accepted for publication in MNRAS