Title: Discovery of the pre-main-sequence eclipsing binary MML 48 Show Chinese title

Title: MML 48的前主序食双星的发现

Abstract: We present the discovery of the eclipsing binary MML 48, which is a member of Upper Centaurus Lupus, has an associated age of 16 Myr, and is composed of two young, low-mass stars. We used space- and ground-based observations to characterize the system with both time-series photometry and spectroscopy. Given the extreme mass ratio between the stars, q_EB = 0.209 +- 0.014, we modeled a single-lined spectroscopic and eclipsing binary system. The orbital period, 2.0171068 +- 0.0000004 d, is measured from the highest precision light curves. We derive a primary mass of 1.2 +- 0.07 Msun using stellar models, and with radial velocities we measured a secondary mass of 0.2509 +- 0.0078 Msun. The radii are large, as expected for pre-main-sequence stars, and are measured as 1.574 +- 0.026 +- 0.050 Rsun and 0.587 +- 0.0095 +- 0.050 Rsun, for the primary and secondary stars, respectively. MML 48 joins the short list of known low-mass, pre-main-sequence eclipsing binaries (EBs), being one of only five systems with intermediate ages (15-25 Myr), and the system with the most extreme mass ratio. The primary star is currently at the "fusion bump", undergoing an over-production of energy in the core due to the build-up of 3He before reaching its equilibrium abundance set by the proton-proton (p-p) I chain. MML 48 A is the first young star in an eclipsing system that has been found during its fusion bump. MML 48 is thus an important benchmark for low-mass stellar evolution at a time when the stars are rapidly changing, which allows for a tight constraint on the corresponding isochrone given the uneven mass ratio. Show Chinese abstract

Abstract: 我们发现了食双星MML 48，它是上半人马- Lupus星协的成员，年龄约为16 Myr，并由两颗年轻的低质量恒星组成。我们使用空间和地面观测来通过时间序列测光和光谱学来表征该系统。鉴于恒星之间的极端质量比，q_EB = 0.209 +- 0.014，我们建模了一个单线光谱食双星系统。轨道周期为2.0171068 +- 0.0000004 d，这是从最高精度的光曲线中测量得到的。我们使用恒星模型得出主星的质量为1.2 +- 0.07 Msun，通过径向速度我们测得次星的质量为0.2509 +- 0.0078 Msun。由于这是前主序星，半径较大，分别测得主星和次星的半径为1.574 +- 0.026 +- 0.050 Rsun和0.587 +- 0.0095 +- 0.050 Rsun。MML 48加入了已知的低质量前主序食双星（EBs）的短列表中，是仅有的五个具有中等年龄（15-25 Myr）的系统之一，并且是质量比最极端的系统。主星目前处于“融合凸起”阶段，由于在达到由质子-质子（p-p）I链设定的平衡丰度之前3He的积累，核心正在产生过量的能量。MML 48 A是第一个在融合凸起阶段被发现的食双星系统中的年轻恒星。因此，MML 48是在恒星快速变化时期的重要基准，这使得在不均匀质量比的情况下可以对相应的等时线进行严格约束。