First orbital elements for the lambda Bootis spectroscopic binary systems HD 84948 and HD 171948. Implications for the origin of the lambda Bootis stars
First orbital elements for the lambda Bootis spectroscopic binary systems HD 84948 and HD 171948. Implications for the origin of the lambda Bootis stars
复制标题
布提斯 lambda 光谱双星系统 HD 84948 和 HD 171948 的第一个轨道元素。对布提斯 lambda 星起源的影响
DOI：
10.1051/0004-6361:20011559
复制
发表时间：
2002
影响因子：
6.5
通讯作者：
C. Koen
中科院分区：
文献类型：
--
作者：
I. Iliev;E. Paunzen;I. Barzova;R. Griffin;I. Kamp;A. Claret;C. Koen
我们展示了两个 Bootis 型光谱双星系统 HD 84948 和 HD 171948 的高分辨率光谱观测。这两个系统都由两颗真正的 Bootis 星组成，这一点已经通过考虑双星性质的详细丰度分析所证明。尽管如此，我们还是获得了碳和氧的非 LTE 丰度，以便研究这些重要元素。这些丰度非常符合该族群的典型模式，毫无疑问所有四个组成部分都是真正的布蒂斯星。借助导出的轨道元素，可以确定两个系统的年龄。我们第一次可以估计银河场布提斯星的演化状态。那些非磁性、弱金属、I 族、晚期 B 型到早期 F 型恒星的起源仍然存在争议。解释布蒂斯现象（与星周物质的吸积或质量损失一起扩散）的两种广泛讨论的理论预测了这组物体的显着不同的演化阶段（接近零年龄主序列或终年龄主序列）。众所周知，该群中非常年轻的成员存在于猎户座 OBI 协会中，也可能存在于 NGC 2264 中。依巴谷数据确定了另外六颗靠近零年龄主序星的银河场布提斯星，而其他天体的演化状态仍未确定。依巴谷数据表明，我们在此讨论的两个系统的银河空间运动都是 I 族天体的典型运动。依帕谷任务的光度数据证实了之前发现的 HD 84948 脉动，其周期约为 110 分钟，V 振幅约为 14 毫米级。对于 HD 84948，我们根据质量比估计其年龄约为 1 Gyr，排除了可能的前主序状态。 HD 171948的年龄约为0.01至0.1 Gyr，接近零年龄主序。因此，我们得出的结论是，从非常早期阶段到终末主序，可以连续发现布提斯现象，这表明不同的机制可能在恒星演化的不同阶段发挥作用，产生相同的丰度模式。
We present high-resolution spectroscopic observations of the two Bootis type spectroscopic binary systems HD 84948 and HD 171948. Both systems consist of two true Bootis stars, as has already been proven by a detailed abundance analysis taking into account the binary nature. Nevertheless, we have obtained non- LTE abundances for carbon and oxygen in order to investigate those important elements. The abundances t excellently into the typical pattern for this group, leaving no doubt that all four components are true Bootis stars. With the help of the derived orbital elements it is possible to establish the ages of the two systems. For the rst time we can estimate the evolutionary status of Galactic eld Bootis stars. The origin of those nonmagnetic, metal-weak, Population I, late B- to early F-type stars is still controversial. The two widely discussed theories explaining the Bootis phenomenon (diusion together with either accretion of circumstellar matter or mass- loss) predict signicantly dierent evolutionary stages for this group of objects (close to either the Zero-Age Main Sequence or Terminal-Age Main Sequence). It is already known that very young members of the group exist in the Orion OBI association and probably in NGC 2264. Hipparcos data established six further Galactic eld Bootis stars which are close to the Zero-Age Main Sequence, whereas the evolutionary status for the other objects remained undetermined. The Hipparcos data reveal that the Galactic space motions of both the systems that we discuss here are typical of those of Population I objects. The photometric data from the Hipparcos mission conrm the pulsation previously discovered for HD 84948 with a period of about 110 min and a V -amplitude of about 14 mmag. For HD 84948, we estimate from the mass ratio an age of about 1 Gyr, ruling out a possible Pre-Main-Sequence status. HD 171948 has an age of about 0.01 to 0.1 Gyr which is close to the Zero-Age Main Sequence. We therefore conclude that the Bootis phenomenon can be found continuously from very early stages to the Terminal-Age Main Sequence, suggesting that dierent mechanisms might work at dierent stages of stellar evolution producing the same abundance pattern.