PHL 1445：一个在周期极小值附近有一个亚恒星施主的食激变变星
PHL 1445: An eclipsing cataclysmic variable with a substellar donor near the period minimum
摘要：
本文介绍食矮新星PHL 1445的高速三色测光。PHL 1445的轨道周期为76.3分钟，刚好低于激变变星的最小周期~82分钟。平均四次日食揭示了白矮星和亮点的日食。我们通过拟合参数化的日食模型来确定系统参数的平均光曲线。我们得到质量比q = 0.087 ± 0.006，倾角i = 85.2 ± 0.9度。发现原始和供体质量分别为Mw = 0.73 ± 0.03 Msun和Md = 0.064 ± 0.005 Msun。通过多色测光，我们测定了白矮星的温度Tw = 13200 ± 700 K，距离220 ± 50 pc。PHL 1445的进化状态是不确定的。我们可以排除一个明显进化的捐赠者，但不是一个轻微进化的捐赠者。与褐矮星供体的形成是合理的;虽然褐矮星在质量转移开始时需要不超过6亿年，需要一个极低的质量比（q = 0.025）的祖系统。PHL 1445加入SDSS 1433，是一个次周期最小的CV，有一个亚恒星施主。两个这样的系统的存在提出了另一种可能性，即当前对固有散射和/或周期最小值位置的估计可能是错误的。
英文摘要：
We present high-speed, three-colour photometry of the eclipsing dwarf nova PHL 1445, which, with an orbital period of 76.3 min, lies just below the period minimum of ~82 min for cataclysmic variable stars. Averaging four eclipses reveals resolved eclipses of the white dwarf and bright spot. We determined the system parameters by fitting a parameterised eclipse model to the averaged lightcurve. We obtain a mass ratio of q = 0.087 +- 0.006 and inclination i = 85.2 +- 0.9 degrees. The primary and donor masses were found to be Mw = 0.73 +- 0.03 Msun and Md = 0.064 +- 0.005 Msun, respectively. Through multicolour photometry a temperature of the white dwarf of Tw = 13200 +- 700 K and a distance of 220 +- 50 pc were determined. The evolutionary state of PHL 1445 is uncertain. We are able to rule out a significantly evolved donor, but not one that is slightly evolved. Formation with a brown dwarf donor is plausible; though the brown dwarf would need to be no older than 600 Myrs at the start of mass transfer, requiring an extremely low mass ratio (q = 0.025) progenitor system. PHL 1445 joins SDSS 1433 as a sub-period minimum CV with a substellar donor. These existence of two such systems raises an alternative possibility; that current estimates for the intrinsic scatter and/or position of the period minimum may be in error.
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