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arXiv 1302.0358astro-ph.SR
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双星系统EP Andromedae及其环双星伴星

The Eclipsing System EP Andromedae and its Circumbinary Companions

Jae Woo Lee, Tobias Cornelius Hinse, Jang-Ho Park

摘要:

我们提出了新的长期CCD测光EP和期间获得2007年至2012年。光变曲线显示了在主极小值和季节到季节的光变化的日全食。综合所有光变曲线表明,食对是一个W型过接触双星,参数q = 2.578,i = 83.3 deg,$ΔT$ = 27 K,f = 28%,l3 = 2~3%. 2007年的非对称光变曲线,可以用一台磁发电机上的两个食分上的冷点来模拟。包括我们的95个定时测量,共414次最小光跨越约82年的周期研究。对日食时序图的详细分析表明,EP And的轨道周期是一个向上张开的抛物线和两个周期变化的组合,周期长度分别为P3 = 44.6年和P4 = 1.834年,半振幅分别为K3 = 0.0100 d和K4 = 0.0039 d。观测到的周期以+1.39x10 ^{-10}的分数速率增加,与W-D程序计算的结果非常一致,并且可以用从主星到副星的质量转移和由于磁制动引起的角动量损失的某种组合来解释。对这两个周期的最合理的解释是一对光旅行时间效应,这是由可能存在的第三和第四分量驱动的,其投影质量分别为M3 = 0.25 Msun和M4 = 0.90 Msun。质量更大的伴星可以通过几年内的高分辨率光谱数据来揭示,也可能是一个双星。环联星可能在食双星的形成和演化过程中扮演了重要的角色,这可能会导致食双星的初始轨道周期较短,从而通过角动量损失而演化成过接触的构型。

英文摘要:

We present new long-term CCD photometry for EP And acquired during the period 2007 to 2012. The light curves display total eclipses at primary minima and season-to-season light variability. Our synthesis for all available light curves indicates that the eclipsing pair is a W-type overcontact binary with parameters of q=2.578, i=83.3 deg, $ΔT$=27 K, f=28 %, and l3=2~3 %. The asymmetric light curves in 2007 were satisfactorily modeled by a cool spot on either of the eclipsing components from a magnetic dynamo. Including our 95 timing measurements, a total of 414 times of minimum light spanning about 82 yr were used for a period study. A detailed analysis of the eclipse timing diagram revealed that the orbital period of EP And has varied as a combination of an upward-opening parabola and two periodic variations, with cycle lengths of P3=44.6 yr and P4=1.834 yr and semi-amplitudes of K3=0.0100 d and K4=0.0039 d, respectively. The observed period increase at a fractional rate of +1.39x10^{-10} is in excellent agreement with that calculated from the W-D code and can be plausibly explained by some combination of mass transfer from the primary to the secondary star and angular momentum loss due to magnetic braking. The most reasonable explanation for both cycles is a pair of light-travel-time effects driven by the possible existence of a third and fourth component with projected masses of M3=0.25 Msun and M4=0.90 Msun. The more massive companion could be revealed using high-resolution spectroscopic data extending over the course of a few years and could also be a binary itself. It is possible that the circumbinary objects may have played an important role in the formation and evolution of the eclipsing pair, which would cause it to have a short initial orbital period and thus evolve into an overcontact configuration by angular momentum loss.

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