Studies of luminous stars in nearby galaxies. III. Comments on the evolution of the most massive stars in the Milky Way and the large magellanic cloud-猫眼课题宝

对附近星系中发光恒星的研究。

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1979

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作者：

R. Humphreys;K. Davidson

对我们银河系和大麦哲伦星云区域的超巨星观测到的H-R图进行经验比较，揭示了这两个星系的光谱类型和光度分布相当。光谱类型相似的超巨星具有相同的光度，除了A型星，在那里选择效应可能很重要。这些结果表明，两个星系中质量最大的恒星的演化受相同的基本物理过程控制，蓝红超巨星的比率随星系中心距离和光度的变化涉及到化学成分梯度和质量损失率的变化。由于最亮恒星的相对数量对质量损失更敏感，因此亮度较低的超巨星的B/R比可能是银河系丰度梯度的更好指标。银河系和LMC超巨星的光度上限都表现为：（1）最热恒星的光度随着温度的降低而降低; =-9.5至-10等，对于温度低于15，000 K的恒星。我们认为，观测到的光度极限主要是由于大质量恒星演化过程中的大质量损失的影响。eta Car和P Cyg的例子表明，质量损失率可能非常迅速和不稳定-平均比目前观察到的大多数热超巨星更高。因此，大于60 M/太阳下/到较冷温度的恒星的演化受到不稳定性和伴随的高质量损失的限制。初始质量接近50- 60 M/太阳/可能是星星演化到M超巨星区域的质量的经验上限，并可能解释了观测到的较冷超巨星光度的上限。«少

An empirical comparison of the observed H-R diagrams for the supergiants in our region of the Galaxy and the Large Magellanic Cloud reveals comparable distributions of spectral types and luminosities in the two galaxies. Supergiants of similar spectral types have the same luminosities, except for the A-type stars, where selection effects may be important. These results suggest that the same basic physical processes govern the evolution of the most massive stars in the two galaxies.Variations in the blue-to-red supergiant ratio with galactocentric distance and with luminosity involve chemical composition gradients and varying rates of mass loss. Since the relative numbers of the most luminous stars are more sensitive to mass loss, the B/R ratio from the less luminous supergiants may be a better indicator of galactic abundance gradients.The upper luminosity boundary for both the galactic and the LMC supergiants is characterized by (1) decreasing luminosity with decreasing temperature for the hottest stars and (2) an upper limit to the luminosity near M/sub bol/approx. =-9.5 to -10 mag for stars cooler than 15,000 K. We suggest that the observed luminosity limits are due primarily to the effects of large mass loss on the evolution of the most massive stars. The examplesmore » of eta Car and P Cyg suggest that mass-loss rates can be very rapid and unsteady--higher on the average than presently observed for most of the hot supergiants. The evolution of stars greater than 60 M/sub sun/ to cooler temperatures is consequently limited by instabilities and the accompanying high mass loss. An initial mass near 50--60 M/sub sun/ may be an empirical upper limit to the mass at which a star can evolve to the region of the M supergiants and probably accounts for the observed upper bound to the luminosities of the cooler supergiants.« less

Studies of luminous stars in nearby galaxies. III. Comments on the evolution of the most massive stars in the Milky Way and the large magellanic cloud

对附近星系中发光恒星的研究。

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