论文标题
Cygnus Extreme B-Supergiant 2Mass J20395358+4222505的性质
The nature of the Cygnus extreme B-supergiant 2MASS J20395358+4222505
论文作者
论文摘要
2MASS J20395358+4222505是庞大的OB恒星关联cyg ob2附近的一个被遮盖的早期B超级巨人。尽管其明亮的红外幅度（k $ _ {s} $ = 5.82），由于其昏暗的光学幅度（b = 16.63，v = 13.68），它仍然在很大程度上被忽略了。在上一篇论文中，我们将其归类为高度发红的，可能极具发光的早期B型超级巨人。在使用乐器Megara@GTC进行调试期间，我们在U，B和R光谱频段中获得了光谱。它显示了其光谱类型B1 IA的特别强大的H $α$排放。这位恒星似乎处于超级和超级巨星之间的中间阶段，这一群体可能会在近乎（天文学的）未来中加入。我们观察到单个观察值之间的径向速度差并确定恒星参数，获得T $ _ {eff} $ = 24000 K，LOGG $ _ {C} $ = 2.88 $ \ $ \ pm $ 0.15。对于b-supergiant，发现的旋转速度很大，vsini = 110 $ \ pm $ 25 km s $^{ - 1} $。丰度模式与太阳能一致，c轻度C不足（基于单线）。 Assuming that J20395358+4222505 is at the distance of Cyg OB2 we derive the radius from infrared photometry, finding R= 41.2 $\pm$ 4.0 R$_{\odot}$, log(L/L$_{\odot}$)= 5.71 $\pm$ 0.04 and a spectroscopic mass of 46.5 $\pm$ 15.0 m $ _ {\ odot} $。对于频谱类型，$ \ dot {m} $ = 2.4x10 $^{ - 6} $ m $ _ {\ odot} $高旋转速度和质量损失率将恒星放在双稳定性跳跃的热侧。连同几乎太阳CNO的丰度模式，它们也可能指向二进制系统中的进化，J20395358+42222505是初始次级。
2MASS J20395358+4222505 is an obscured early B supergiant near the massive OB star association Cyg OB2. Despite its bright infrared magnitude (K$_{s}$=5.82) it has remained largely ignored because of its dim optical magnitude (B=16.63, V=13.68). In a previous paper we classified it as a highly reddened, potentially extremely luminous, early B-type supergiant. We obtained its spectrum in the U, B and R spectral bands during commissioning observations with the instrument MEGARA@GTC. It displays a particularly strong H$α$ emission for its spectral type, B1 Ia. The star seems to be in an intermediate phase between super- and hypergiant, a group that it will probably join in the near (astronomical) future. We observe a radial velocity difference between individual observations and determine the stellar parameters, obtaining T$_{eff}$ = 24000 K, logg$_{c}$= 2.88 $\pm$ 0.15. The rotational velocity found is large for a B-supergiant, vsini= 110 $\pm$ 25 km s$^{-1}$. The abundance pattern is consistent with solar, with a mild C underabundance (based on a single line). Assuming that J20395358+4222505 is at the distance of Cyg OB2 we derive the radius from infrared photometry, finding R= 41.2 $\pm$ 4.0 R$_{\odot}$, log(L/L$_{\odot}$)= 5.71 $\pm$ 0.04 and a spectroscopic mass of 46.5 $\pm$ 15.0 M$_{\odot}$. The clumped mass-loss rate (clumping factor 10) is very high for the spectral type, $\dot{M}$ = 2.4x10$^{-6}$ M$_{\odot}$ a$^{-1}$. The high rotational velocity and mass-loss rate place the star at the hot side of the bi-stability jump. Together with the nearly solar CNO abundance pattern, they may also point to evolution in a binary system, J20395358+4222505 being the initial secondary.
