标题： 围绕行星状星云中心双星KV Vel运行的棕矮星 显示英文标题

标题： A brown dwarf orbiting around the planetary-nebula central binary KV Vel

摘要： KV Vel是一个非食的短周期（P = 0.3571天）密近双星，包含一个非常热的次矮星主星（77000 K）和一个温度较低质量较小的伴星（3400 K），该系统位于行星状星云DS 1的中心。 基于262个新的光极大时刻以及文献中收集的数据分析了密近双星的轨道周期变化。 发现O-C曲线显示出一个振幅较小（0.0034天）的周期性变化，周期为29.55年。 通过冷组分的类太阳磁活动周期来解释这一现象被排除，因为所需的能量远大于该组分在一个完整周期内的总辐射能量。 因此，这种周期性变化被合理地解释为由于存在第三天体而产生的光行时效应，这得到了TESS获得的O-C曲线的周期性变化以及相当对称和稳定的光变曲线的支持。 第三天体的质量确定为M_3sini' = 0.060(7) M_sun。 如果第三天体与中心双星共面（即i' = 62.5{\deg }），则第三天体的质量计算为M_3 ~ 0.068 M\sun ，因此它将低于稳定氢燃烧的极限，是一个棕矮星。 轨道分离小于9.35天文单位（AU）。 KV Vel及其周围的行星状星云和棕矮星伴星可能是在主星在早期渐近巨星分支阶段充满洛希瓣后通过共同包层演化形成的。 显示英文摘要

摘要： KV Vel is a non-eclipsing short-period (P = 0.3571 days) close binary containing a very hot subdwarf primary (77000 K) and a cool low-mass secondary star (3400 K) that is located at the center of the planetary nebula DS 1. The changes in the orbital period of the close binary were analyzed based on 262 new times of light maximum together with those compiled from the literature. It is discovered that the O-C curve shows a small-amplitude (0.0034 days) cyclic period variation with a period of 29.55 years. The explanation by the solar-type magnetic activity cycles of the cool component is ruled out because the required energies are much larger than the total radiant energy of this component in a whole cycle. Therefore, the cyclic variation was plausibly explained as the light-travel time effect via the presence of a tertiary component, which is supported by the periodic changes of the O-C curve and the rather symmetric and stable light curves obtained by TESS. The mass of the tertiary companion is determined to be M_3sini' = 0.060(7) M_sun. If the third body is coplanar with the central binary (i.e., i' = 62.5{\deg}), the mass of the tertiary component is computed as M_3 ~ 0.068 M\sun, and thus it would be below the stable hydrogen-burning limit and is a brown dwarf. The orbital separation is shorter than 9.35 astronomical units (AU). KV Vel together with its surrounding planetary nebula and the brown-dwarf companion may be formed through the common-envelope evolution after the primary filled its Roche lobe during the early asymptotic giant branch stage.