CoRoT外场中暗弱Be星样本研究。第三部分：中心恒星的全球光谱表征与天体物理参数
Study of a Sample of Faint Be Stars in the Exofield of CoRoT. Part III. Global Spectroscopic Characterization and Astrophysical Parameters of the Central Stars
AI总结：
本文利用VLT/FLAMES光谱和GIRFIT拟合，校正19颗B/Be星的快速旋转效应并分析星周盘发射线，确定其质量、距离、亚临界旋转状态及盘密度结构。
摘要：
本工作致力于研究CoRoT在第四次长运行（LRA02）中观测到的暗弱Be星。天体物理参数是利用ESO的VLT/FLAMES仪器观测的光谱确定的。使用我们的GIRFIT软件包，以恒星大气模型拟合光谱。λ 6400–7200 Å波段的光谱使我们能够确认或首次识别Be星候选体。对一组19颗B型星和Be星的表观参数（Teff、log g、V sin i）进行了快速旋转所诱导效应的校正。这些校正使我们能够确定：1）与分离双星系统中测得的质量相一致的质量；2）与GAIA视差相符的距离；以及3）约0.6–0.7的赤道离心力/重力比，这表明我们的Be星是亚临界旋转体。对Balmer线Hα、Hγ和Hδ发射线的研究给出了：与其他Be星的干涉测量推断相符的星周盘（CD）发射区尺度；CD径向密度分布随R变化的指数n(R)；以及CD底部密度。Hγ和Hδ发射线形成于靠近中心恒星的CD层中。这些线给出的指数n(R)值不同于针对Hα所假定的值。未来对Hγ和Hδ发射线的详细研究可能揭示向CD其余区域进行角动量粘性输运很可能起源的区域的物理性质。Be星的亚临界旋转表明，其巨大的离散质量抛射及相伴的非径向脉动可能在因旋转而对对流变得不稳定的恒星包层区域中具有共同起源。由可能存在的被剥离的亚矮O/B伴星在估计Teff时诱导的误差，不太可能超过其当前的不确定度。
英文摘要：
The present work is devoted to the study of faint Be stars observed by CoRoT in the fourth long run (LRA02). The astrophysical parameters were determined from the spectra observed with the VLT/FLAMES instruments at ESO. Spectra were fitted with models of stellar atmospheres using our GIRFIT package. Spectra in the lambda-lambda 6400-7200$ AA domain enabled the confirmation or a first identification of Be star candidates. The apparent parameters (Teff,log g,Vsin i) for a set of 19 B and Be stars were corrected for the effects induced by the rapid rotation. These allowed us to determine: 1) masses that are in agreement with those measured for detached binary systems; 2) distances that agree with the GAIA parallaxes; and 3) centrifugal/gravity equatorial force ratios of ~0.6-0.7, which indicate that our Be stars are subcritical rotators. A study of the Balmer Halpha, Hgamma and Hdelta emission lines produced: extents of the circumstellar disk (CD) emitting regions that agree with the interferometric inferences in other Be stars; R-dependent exponents n(R) of the CD radial density distributions; CD base densities. The Hgamma and Hdelta emission lines are formed in CD layers close to the central star. These lines produced a different value of the exponent n(R) than assumed for Halpha. Further detailed studies of Hgamma and Hdelta emission lines could reveal the physical properties of regions where the viscous transport of angular momentum to the remaining CD regions is likely to originate from. The subcritical rotation of Be stars suggests that their huge discrete mass-ejections and concomitant non-radial pulsations might have a common origin in stellar envelope regions that become unstable to convection due to rotation. The errors induced on the estimated Teff by the possible presence of stripped sub-dwarf O/B companions are not likely to exceed their present uncertainties.
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