论文标题
在低金属性下主序列附近的巨大恒星的光谱演变
Spectroscopic evolution of massive stars near the main sequence at low metallicity
论文作者
论文摘要
我们介绍沿z = 1/5 zsun和z = 1/30 zsun的进化轨道计算的合成光谱和SED，对于15至150 msun的质量。我们预测，最大的恒星都以亚磨性金属性为O2矮人开始进化。在较低的金属性下，在O2V期花费的寿命比例增加。我们在SMC中预测的矮人和巨人的分布准确地再现了观测值。超级巨人的有效温度比我们预期的略高。更大的恒星进入了更靠近ZAM的巨型和超级阶段，但不如太阳金属性那么接近。这是由于较低的金属性下的恒星风减少。我们的质量高于〜60 msun的模型应以O和B恒星的形式出现，而没有观察到这些物体，证实了最近文献中报道的趋势。在Z = 1/30 Zsun时，矮人覆盖了MS的一小部分，巨人和超级巨人的有效温度低于Z = 1/5 Zsun。这些低金属性星的紫外光谱只有弱的p-cygni曲线。 HEII 1640有时在最大的模型中显示出净排放，等效宽度达到〜1.2A。对于两组金属性，我们提供了在波长范围4500-8000 A中的合成光谱。此范围将由ELT的仪器Harmoni和Mosaics和Mosaics覆盖，并将其与Elt的Mosaics相关，并将其与地方集团相关。我们建议将HEI 7065与HEII 5412的比率用作光谱类型的诊断。我们表明该比率不取决于金属性。最后，我们讨论了模型的电离通量。每单位面积与有效温度的氢电离通量之间的关系仅取决于金属性。 HEI和HEII与电离通量的比率都取决于金属性，尽管以略有不同的方式。
We present synthetic spectra and SEDs computed along evolutionary tracks at Z=1/5 Zsun and Z=1/30 Zsun, for masses between 15 and 150 Msun. We predict that the most massive stars all start their evolution as O2 dwarfs at sub-solar metallicities. The fraction of lifetime spent in the O2V phase increases at lower metallicity. The distribution of dwarfs and giants we predict in the SMC accurately reproduces the observations. Supergiants appear at slightly higher effective temperatures than we predict. More massive stars enter the giant and supergiant phases closer to the ZAMS, but not as close as for solar metallicity. This is due to the reduced stellar winds at lower metallicity. Our models with masses higher than ~60 Msun should appear as O and B stars, whereas these objects are not observed, confirming a trend reported in the recent literature. At Z=1/30 Zsun, dwarfs cover a wider fraction of the MS and giants and supergiants appear at lower effective temperatures than at Z=1/5 Zsun. The UV spectra of these low-metallicity stars have only weak P-Cygni profiles. HeII 1640 sometimes shows a net emission in the most massive models, with an equivalent width reaching ~1.2 A. For both sets of metallicities, we provide synthetic spectroscopy in the wavelength range 4500-8000 A. This range will be covered by the instruments HARMONI and MOSAICS on the ELT and will be relevant to identify hot massive stars in Local Group galaxies with low extinction. We suggest the use of the ratio of HeI 7065 to HeII 5412 as a diagnostic for spectral type. We show that this ratio does not depend on metallicity. Finally, we discuss the ionizing fluxes of our models. The relation between the hydrogen ionizing flux per unit area versus effective temperature depends only weakly on metallicity. The ratios of HeI and HeII to H ionizing fluxes both depend on metallicity, although in a slightly different way.
