标题： 长周期中间极性天体 1RXSJ154814.5-452845 显示英文标题

标题： The long period Intermediate Polar 1RXSJ154814.5-452845

摘要： 我们展示了最近发现的特殊中间极（IP）1RXSJ154814.5-452845的首次时间分辨中等分辨率光学光谱观测，这使我们能够精确确定双星轨道周期（Porb=9.87+/-0.03小时）和白矮星自转周期Pspin=693.01+/-0.06秒）。该系统是第三个位于假定的6-10小时IP轨道周期间隙之外的系统，也是长周期IPs中的第五个系统，具有相对较高的异步性。从弱红吸收特征的存在，我们将伴星识别为光谱型K2+/-2V，它似乎已经演化到核时标上。通过发射线和红吸收线的轨道径向速度测量，得到质量比q=0.65+/-0.12。两分量的质量估计为Mwd >= 0.5Msun和Msec=0.4-0.79Msun，轨道倾角25deg < i <=58deg。距离估计为540-840pc。在这个距离上，围绕巴尔默发射线的特殊吸收特征的存在不能归因于白矮星光球的贡献，它们的自转调制表明起源于磁约束吸积流。对于其轨道周期而言，白矮星的吸积率也不高（Mdot<5x10**16g/s）。自旋与轨道周期比Pspin/Porb=0.02和低质量吸积率表明该系统远离自旋平衡。吸积白矮星的磁矩被发现小于4.1x10**32 Gcm**3，表明这是一个低磁场系统。 显示英文摘要

摘要： We present the first time resolved medium resolution optical spectroscopy of the recently identified peculiar Intermediate Polar (IP) 1RXSJ154814.5-452845, which allows us to precisely determine the binary orbital period (Porb=9.87+/-0.03hr) and the white dwarf spin period Pspin=693.01+/-0.06s). This system is then the third just outside the purported 6-10hr IP orbital period gap and the fifth of the small group of long period IPs, which has a relatively high degree of asynchronism. From the presence of weak red absorption features, we identify the secondary star with a spectral type K2+/-2V, which appears to have evolved on the nuclear timescale. From the orbital radial velocities of emission and the red absorption lines a mass ratio q=0.65+/-0.12 is found. The masses of the components are estimated to be Mwd >= 0.5Msun and Msec=0.4-0.79Msun and the binary inclination 25deg < i <=58deg . A distance between 540-840pc is estimated. At this distance, the presence of peculiar absorption features surrounding Balmer emissions cannot be due to the contribution of the white dwarf photosphere and their spin modulation suggests an origin in the magnetically confined accretion flow. The white dwarf is also not accreting at a particularly high rate (Mdot<5x10**16g/s), for its orbital period. The spin-to-orbit period ratio Pspin/Porb=0.02 and the low mass accretion rate suggest that this system is far from spin equilibrium. The magnetic moment of the accreting white dwarf is found to be < 4.1x10**32 Gcm**3, indicating a low magnetic field system.