LCO对roAp恒星J0855（TYC 2488-1241-1）超临界扭曲脉动的观测
LCO observations of a super-critical distorted pulsation in the roAp star J0855 (TYC 2488-1241-1)
摘要：
我们报告了一颗快速振荡的Ap星J 0855（TYC 2488-1241-1）的60小时测光活动的结果。我们利用多站点Las Cumbres天文台（LCO）的0.4米望远镜获得了以前缺乏详细研究的roAp星的短节奏B波段观测。我们的观测证实了发现该恒星（$P_{\rm rot}=3.0918$ d）的论文中提出的自转周期，并揭示了该恒星以扭曲的模式脉动。B的数据显示这颗星是振幅最高的roAp星之一，峰间振幅为24毫等。在197.2714 d $^{-1}$（2283 $μ$ Hz; P=7.30 min）的脉动频率的模型表明，这颗恒星属于超临界振荡器的子组，在那里观测到的频率高于理论上的声学截止频率。从模型中，我们推断，恒星的旋转轴是倾斜角约$30^\circ$的视线，与旋转轴的磁轴的倾斜角的$40^\circ$或$24^\circ$取决于脉动模式是偶极或四极，分别。
英文摘要：
We report the results of a 60-hr photometric campaign of a rapidly oscillating Ap star, J0855 (TYC 2488-1241-1). We have utilised the multi-site Las Cumbres Observatory's (LCO) 0.4-m telescopes to obtain short cadence B-band observations of an roAp star previously lacking detailed study. Our observations confirm the rotation period presented in the discovery paper of this star ($P_{\rm rot}=3.0918$ d), and reveal the star to be pulsating in a distorted mode. The B data show this star to be among the highest amplitude roAp stars, with a peak-to-peak amplitude of 24 mmag. Modelling of the pulsation frequency at 197.2714 d$^{-1}$ (2283 $μ$Hz; P=7.30 min) shows that this star belongs to the subgroup of super-critical pulsators, where the observed frequencies are above the theoretical acoustic cutoff frequency. From the modelling, we deduce that the star's rotation axis is inclination angle of about $30^\circ$ to the line-of-sight, with an angle of obliquity of the magnetic axis to the rotation axis of either $40^\circ$ or $24^\circ$ depending on whether the pulsation mode is dipole or quadrupole, respectively.
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