000005484 001__ 5484
000005484 005__ 20211216181633.0
000005484 0247_ $$2DOI$$a10.1093/mnras/stab383
000005484 037__ $$aSCART-2021-0144
000005484 100__ $$aGilkis, Avishai 
000005484 245__ $$aThe excess of cool supergiants from contemporary stellar evolution models defies the metallicity-independent Humphreys-Davidson limit
000005484 260__ $$c2021
000005484 520__ $$aThe Humphreys-Davidson (HD) limit empirically defines a region of high luminosities (log10(L/L⊙) ≳ 5.5) and low effective temperatures ($T_{\rm eff} \lesssim 20 \, {\rm kK}$ ) on the Hertzsprung-Russell diagram in which hardly any supergiant stars are observed. Attempts to explain this limit through instabilities arising in near- or super-Eddington winds have been largely unsuccessful. Using modern stellar evolution, we aim to re-examine the HD limit, investigating the impact of enhanced mixing on massive stars. We construct grids of stellar evolution models appropriate for the Small Magellanic Cloud (SMC) and Large Magellanic Cloud (LMC), as well as for the Galaxy, spanning various initial rotation rates and convective overshooting parameters. Significantly enhanced mixing apparently steers stellar evolution tracks away from the region of the HD limit. To quantify the excess of overluminous stars in stellar evolution simulations, we generate synthetic populations of massive stars and make detailed comparisons with catalogues of cool ( $T_\mathrm{eff} \le 12.5\, \mathrm{kK}$ ) and luminous (log10(L/L⊙) ≥ 4.7) stars in the SMC and LMC. We find that adjustments to the mixing parameters can lead to agreement between the observed and simulated red supergiant populations, but for hotter supergiants the simulations always overpredict the number of very luminous (log10(L/L⊙) ≥ 5.4) stars compared to observations. The excess of luminous supergiants decreases for enhanced mixing, possibly hinting at an important role mixing has in explaining the HD limit. Still, the HD limit remains unexplained for hotter supergiants.
000005484 594__ $$aNO
000005484 700__ $$aShenar, Tomer
000005484 700__ $$aRamachandran, Varsha
000005484 700__ $$aJermyn, Adam S.
000005484 700__ $$aMahy, Laurent
000005484 700__ $$aOskinova, Lidia M.
000005484 700__ $$aArcavi, Iair
000005484 700__ $$aSana, Hugues
000005484 773__ $$c1884-1896$$n2$$pMonthly Notices of the Royal Astronomical Society$$v503$$y2021
000005484 8560_ $$flaurent.mahy@ksb-orb.be
000005484 8564_ $$s5443181$$uhttp://publi2-as.oma.be/record/5484/files/Gilkis2021_Humphreys.pdf
000005484 8564_ $$s4365$$uhttp://publi2-as.oma.be/record/5484/files/Gilkis2021_Humphreys.gif?subformat=icon$$xicon
000005484 8564_ $$s8244$$uhttp://publi2-as.oma.be/record/5484/files/Gilkis2021_Humphreys.jpg?subformat=icon-180$$xicon-180
000005484 905__ $$apublished in
000005484 980__ $$aREFERD