激变变星轨道周期间隙：比以往更加明显
The cataclysmic variable orbital period gap: More evident than ever
AI总结：
本研究基于SDSS样本，通过区分极化星与非极化星，以超过98%置信度确认非极化CV存在轨道周期间隙（147-191分钟），并揭示极化星因磁场减弱磁制动而无此间隙，支持标准CV演化理论。
摘要：
近期，斯隆数字巡天（SDSS）识别出的大规模且均匀的激变变星（CVs）样本已发表。在这些样本中，著名的轨道周期间隙——即轨道周期范围约2-3小时内系统缺失的现象，也是大多数CV演化模型的定义性特征——据称并未清晰呈现。若此说法属实，将彻底改变我们对CV演化的认识。在本快报中，我们聚焦于白矮星磁场强到足以与伴星磁场相连的CV（即所谓的极化星）与非极化CV之间在轨道周期间隙上的潜在差异，因为已有预测认为极化星中白矮星的磁场会减弱通过磁制动导致的角动量损失强度。我们将SDSS I-IV样本中的CV分为极化星和非极化系统，并进行统计检验以评估周期分布是否符合标准CV演化模型所预测的双峰分布。我们以超过98%的置信度确认了SDSS I-IV样本中非极化CV存在周期间隙。轨道周期间隙的边界为147分钟和191分钟，其中下边界与先前发表的值（129分钟）不同。SDSS I-IV中极化星的轨道周期分布明显不同，并未显示出类似的周期间隙。SDSS样本以及之前的CV样本均与标准CV演化理论一致。磁制动确实似乎在完全对流边界附近被中断，这导致CV演化过程中出现分离阶段。在极化星中，白矮星磁场减弱了磁制动的强度，因此极化星的轨道周期分布并未显示出与非极化星同样深刻且广泛的周期间隙。
英文摘要：
Recently, large and homogeneous samples of cataclysmic variables (CVs) identified by the Sloan Digital Sky Survey (SDSS) were published. In these samples, the famous orbital period gap, which is a dearth of systems in the orbital period range ~2-3 hr and the defining feature of most evolutionary models for CVs, has been claimed not to be clearly present. If true, this finding would completely change our picture of CV evolution. In this Letter we focus on potential differences with respect to the orbital period gap between CVs in which the magnetic field of the white dwarf is strong enough to connect with that of the donor star, so-called polars, and non-polar CVs as the white dwarf magnetic field in polars has been predicted to reduce the strength of angular momentum loss through magnetic braking. We separated the SDSS I-IV sample of CVs into polars and non-polar systems and performed statistical tests to evaluate whether the period distributions are bimodal as predicted by the standard model for CV evolution or not. We confirm the existence of a period gap in the SDSS I-IV sample of non-polar CVs with >98 per cent confidence. The boundaries of the orbital period gap are 147 and 191 minutes, with the lower boundary being different to previously published values (129 min). The orbital period distribution of polars from SDSS I-IV is clearly different and does not show a similar period gap. The SDSS samples as well as previous samples of CVs are consistent with the standard theory of CV evolution. Magnetic braking does indeed seem get disrupted around the fully convective boundary, which causes a detached phase during CV evolution. In polars, the white dwarf magnetic field reduces the strength of magnetic braking and consequently the orbital period distribution of polars does not display an equally profound and extended period gap as non-polars.
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