We present the orbital solution of a peculiar double-lined spectroscopic and eclipsing binary system, 2M17091769+3127589. This solution was obtained by a simultaneous fit of both APOGEE radial velocities and TESS and ASAS-SN light curves to determine masses and radii. This system consists of an M _⊙, R _⊙ red giant and a hotter M _⊙, R _⊙ subgiant. Modeling with the MESA evolutionary codes indicates that the system likely formed 5.26 Gyrs ago, with a M = 1.2 M _⊙ primary that is now the system’s red giant and a M = 1.11 M _⊙ secondary that is now a more massive subgiant. Due to Roche-lobe overflow as the primary ascends the red giant branch, the more evolved “primary” (i.e., originally the more massive star of the pair) is now only one sixth as massive as the “secondary.” Such a difference between the initial and the current mass ratio is one of the most extreme detected so far. Evolutionary modeling suggests the system is still engaged in mass transfer, at a rate of M _⊙/yr, and it provides an example of a less evolved precursor to some of the systems that consist of white dwarfs and blue stragglers.

我们提出了一个特殊的双线光谱和食双星系统的轨道解，2M17091769+3127589。该解决方案是通过同时拟合 APOGEE 径向速度和 TESS 和 ASAS-SN 光曲线来确定质量和半径而获得的。该系统由一颗 M _⊙ , R _⊙红巨星和一颗温度更高的 M _⊙ , R _{⊙ 次}巨星组成。使用 MESA 演化代码建模表明该系统可能在 5.26 Gyrs 之前形成，M = 1.2 M _⊙主星现在是系统的红巨星，M = 1.11 M _⊙次巨星现在是一个更大的次巨星。由于当主星上升到红巨星分支时罗氏叶溢出，进化程度更高的“主星”（即原来质量更大的恒星对）现在只有“次星”质量的六分之一。初始质量比和当前质量比之间的这种差异是迄今为止检测到的最极端的差异之一。进化模型表明该系统仍在以 M _⊙ /yr的速率进行质量传递，并且它提供了一个由白矮星和蓝落后者组成的系统的进化程度较低的前体的例子。