[论文解读] An incisive look at the symbiotic star SS Leporis -- Milli-arcsecond imaging with PIONIER/VLTI

Nicolas Blind, H. M. J. Boffin+5 more|arXiv (Cornell University)|Dec 7, 2011

Stellar, planetary, and galactic studies参考文献 40被引用 22

一句话总结

使用甚长基线干涉仪PIONIER/VLTI的毫角秒高分辨率干涉测量，本研究解析了共生双星SS Leporis的内层结构，发现M型巨星并未充满其洛希瓣。相反，质量转移通过风洛希瓣溢出发生，且有强烈证据表明A型恒星周围存在吸积盘，与先前模型相比，显著修正了该系统的质量比和恒星尺寸。

ABSTRACT

Context. Determining the mass transfer in a close binary system is of prime importance for understanding its evolution. SS Leporis, a symbiotic star showing the Algol paradox and presenting clear evidence of ongoing mass transfer, in which the donor has been thought to fill its Roche lobe, is a target particularly suited to this kind of study. Aims. Since previous spectroscopic and interferometric observations have not been able to fully constrain the system morphology and characteristics, we go one step further to determine its orbital parameters, for which we need new interferometric observations directly probing the inner parts of the system with a much higher number of spatial frequencies. Methods. We use data obtained at eight different epochs with the VLTI instruments AMBER and PIONIER in the H- and K-bands. We performed aperture synthesis imaging to obtain the first model-independent view of this system. We then modelled it as a binary (whose giant is spatially resolved) that is surrounded by a circumbinary disc. Results. Combining these interferometric measurements with previous radial velocities, we fully constrain the orbit of the system. We then determine the mass of each star and significantly revise the mass ratio. The M giant also appears to be almost twice smaller than previously thought. Additionally, the low spectral resolution of the data allows the flux of both stars and of the dusty disc to be determined along the H and K bands, and thereby extracting their temperatures. Conclusions. We find that the M giant actually does not stricto sensus fill its Roche lobe. The mass transfer is more likely to occur through the accretion of an important part of the giant wind. We finally rise the possibility for an enhanced mass loss from the giant, and we show that an accretion disc should have formed around the A star.

研究动机与目标

• 使用高角分辨率干涉测量解析共生双星SS Leporis的轨道与结构参数。
• 确定M型巨星是否如先前假设的那样充满其洛希瓣，或质量转移是否通过其他机制发生。
• 通过无模型成像约束双星成员的质量和环双星盘的几何结构。
• 基于动力学与运动学约束，研究A型星周围是否存在吸积盘及其特性。
• 评估该系统的演化状态及其对后-AGB演化与行星状星云形成的影响。

提出的方法

• 在H波段和K波段使用VLTI上的PIONIER和AMBER仪器获取了8个历元的干涉数据，实现了高空间频率采样。
• 执行孔径综合成像，以毫角秒分辨率生成系统亮度分布的无模型视图。
• 将干涉数据与径向速度测量相结合，完全约束轨道元素（周期、偏心率、倾角、半长轴）。
• 将系统建模为一个被中心A型恒星和周围环双星尘埃盘包围的解析巨星。
• 利用径向速度曲线和干涉可见度，推导质量函数并推断个体质量和质量比。
• 基于角动量守恒和洛希瓣溢出动力学，估算吸积盘的最小半径。

实验结果

研究问题

• RQ1 SS Leporis中的M型巨星是否如先前光谱和干涉数据所推断的那样充满其洛希瓣？
• RQ2 该双星系统的真正质量比是多少，与先前估计相比如何？
• RQ3 是否存在A型星周围吸积盘的直接证据，其预期大小和结构如何？
• RQ4 质量转移机制的本质是什么——洛希瓣溢出还是风洛希瓣溢出？其对系统演化有何影响？
• RQ5 环双星盘的存在及其潜在质量损失如何影响系统的长期演化？

主要发现

• SS Leporis中的M型巨星并未严格充满其洛希瓣，与先前基于洛希瓣溢出模型的假设相矛盾。
• 质量比被修正为 q = 1.85 ± 0.25，显著低于先前估计的 1/q = 3.50 ± 0.57，表明A星比先前认为的更重。
• M型巨星的半径约为 15 R☉，接近先前估计值的一半，表明其恒星尺寸小于先前认知。
• 该系统最合理的解释是风洛希瓣溢出，其中巨星光球风的相当大一部分被A星吸积。
• A星周围很可能已形成吸积盘，预测半径约为 ~33 R☉，表观直径为 0.8–1 mas，未来高分辨率仪器可探测。
• 该系统正处于演化为后-AGB系统的临界点，预计M型巨星将在约17万年内演化为白矮星，可能形成非球对称的行星状星云。