| 摘要 | 脉动变星是变星中数量最多的，脉动变星是物理变星的一种。盾牌座 $\delta$ 型脉动变星又称矮造父变星，位于赫罗图中经典造父脉动 不稳定带的下部和主序交叉的地方，是一类短周期脉动变星。大振幅δ scuti (HADS)脉动变星，是V波段脉动振幅超过0.3星等，其转动很慢。除了白矮星，盾牌座 $\delta$ 型脉动变星的脉动成分是我们银河系内第二丰富的脉动变星。 HADS包括处于主序演化阶段星族I恒星和演化了的星族II恒星（这些星也被称为凤凰座SX型变星，SX Phe type variables）。HADS变星的脉动周期几小时（$<0.3$天），脉动振幅$0.3-0.7$星等，很低的转动速度（$\rm{v \sin i < 30\,km\,s^{-1}}$）。我们通过分析盾牌座变星的星表 (Chang et al. 2013)\citep{Chang20131}，得到四分之一的盾牌座变星是大振幅盾牌座脉动变星（406,1473）。 大振幅脉动变星的观测研究对望远镜的口径要求比较低，因此HADS是非常重要一类研究目标。 本文的研究主要是利用国内小口径望远镜群对大振幅盾牌座脉动变星进行了监测。我们通过$\rm{O-C}$的方法对监测的目标的脉动周期进行了分析，主要的结果如下： 1、DE Lac是脉动周期为0.253694天的大振幅盾牌座脉动变星。我们应用云南天文台的1米反射式望远镜，在2013年12月18日和2014年1月5日对目标星进行了CCD测光监测，同时， 也采用国家天文台兴隆观测站85公分望远镜对DE Lac进行了测光观测。通过在文献中收集的光度极大时刻值，结合我们自己的观测数据，我们用经典的$\rm{O-C}$方法对DE Lac的 脉动周期进行了分析。分析所有的光度极大时刻值，我们发现DE Lac的脉动周期是长期增加的，周期变化率为$\dot{P}=+3.7\times{10^{-8}}$\,天/年。这个脉动周期变化率和 理论模型预测的脉动周期变化率是相符合的，我们同时收集了其他有长周期变化的大振幅盾牌座脉动变星，并分析了所收集样本的脉动周期变化率。 2、BP Peg是一颗有着很长监测历史的大振幅盾牌座脉动变星。对BP Peg新的CCD测光监测是在2013年12月4日利用云南天文台1米反射式望远镜，以及在2013年12月29利用国家天文台兴隆观测站 85公分望远镜开展。研究目标星的脉动周期$0.109543574$天。我们收集了所有已知的光度极大时刻值，结合我们自己的最新的观测数据，对BP Peg的脉动周期应用$\rm{O-C}$的方法来进行了研究。通过研究发现，BP Peg的脉动周期显示出周期性的变化，其周期性变化的周期为$24.5$\,年，周期性变化的振幅为$0.0060$\,天。 如果这种周期性变化是由于双星轨道运动的光时效应引起的，那么就会存在一颗看不见的暗伴星天体，我们推断这个暗伴星天体质量很可能为0.20 $\rm{M_{\odot}}$，并且它最可能 是一颗M型恒星。 3、GW UMa是一颗由依巴谷卫星在1997年发现的大振幅盾牌座脉动变星，它的脉动周期是$0.20319367$天。结合我们观测得到的新的光极大时刻值，采用$\rm{O-C}$图的方法对GW UMa进行了 脉动周期的分析。周期性的变化明显的显示在$\rm{O-C}$图上，从图上我们可以看出周期性变化的半振幅为$0.0023$\,天，通过简单计算，推算出周期性变化的周期为$13.2$\,年。 我们认为引起这种周期性变化的原因可能是，存在伴星天体，双星轨道运动的光时效应造成的。如果我们的假设为真，那么伴星的质量是由质量函数： $M_{2}\sin i = 0.11(\pm 0.01)\,\rm{M_{\odot}}$确定的。我们采用$1.76 \,\rm{ M_{\odot}}$为GW UMa的质量，那么两颗星是相互绕转在一起的双星系统，两子星间距为$6.5(\pm0.8)$\,AU。 如果我们取轨道倾角$i \geq 22.6^{\circ}$，可以推算出伴星质量$M_{2}<0.3 \,\rm{M_{\odot}}$，它就是一颗完全对流的恒星。这个结论提示我们，对于亮天体恒星来说，存在隐藏的暗 伴星天体不是那么的不正常。 |
| 其他摘要 | Many variables are pulsation variables, it is one kinds of physical variables. Today, the former ``dwarf cepheids'' of the disk population are mostly called ``high-amplitude Delta Scuti stars''. The $\delta$ Scuti stars are pulsators situated in the classical cepheid instability strip on the main sequence or are moving from the main sequence to the giant branch. In general, it is one kinds of short-period pulsating variable star. After white dwarfs, they are the second most abundant pulsating variables in our Galaxy. High-amplitude $\delta$ Scuti ( HADS ) stars include Pop.I stars close to the main sequence and evolved Pop.II stars (these are also known as SX Phe type variables). HADS are characterized by pulsating periods of several hours ($<0.3$ days), amplitudes of variability of $0.3-0.7$ magnitudes, and low rotational velocities ($\rm{v \sin i < 30\,km\,s^{-1}}$). These pulsations exhibit multiple modes and possibly non-radial modes, and many of them are primarily fundamental-mode pulsators. In history, the stars of HADS had ever been called Dwarf Cepheids, Al Vel stars or RRs stars. Through the analysis of the $\delta$ Scuti stars catalogue (Chang et al. 2013), we find that about a quarter of $\delta$ Scuti stars (406 from 1473) are HADS and ten percent of $\delta$ Scuti stars (141 from 1473) are in binary or multiple systems. As large amplitude pulsating variable stars are easy to monitor using the small telescope, so, HADS is a kind of very important research objectives. In this paper, we use some small telescope located in China to monitor some high-amplitude $\delta$ Scuti ( HADS ) stars. $\rm{O-C}$ method was used to study the period changes, The results are as follows: 1. DE Lac is a high-amplitude ${\delta}$ Scuti variable with a period of $0.253694$ days. New CCD photometric monitor of DE Lac were carried out on December 18, 2013 and January 5, 2014 by using the 1.0-m reflecting telescope at Yunnan Observatories. Photometric observations of DE Lac were also gained by using the 85-cm telescope at Xinglong Station of National Astronomical Observatory. By using a few new determined times of light maximum together with those collected from the literature, the period changes in Observed-Calculated ($\rm{O-C}$) diagram are analyzed. We discover that the pulsating period of DE Lac is increasing continuously at a rate of $\dot{P}=+3.7\times{10^{-8}}$\,days/year. It is compatible with the prediction from the stellar evolution model calculation. Meanwhile, We collect other ${\delta}$ Scuti star that have period change. 2. New CCD photometric monitoring on the high-amplitude ${\delta}$ Scuti variable BP Peg was carried out on November 4, 2013 by using the 1.0-m reflecting telescope of Yunnan Observatories in China as well as on December 29, 2013 by using the 85-cm telescope at Xinglong Station of National Astronomical Observatory in China. BP Peg is a new high-amplitude ${\delta}$ Scuti variable with a period of $0.10954357$ day. We have collected all the times of light maximum from the literature together with our data, and the pulsation period changes are analyzed through Observed-Calculated $\rm{O-C}$ method. With the available data, we discover that the pulsating period of BP Peg shows a cyclic oscillation with a period of $24.5$ years and an amplitude of 0.0060 days. If the cyclic period changes are caused by light-time effect in a binary system, the reckoned mass of the hidden companion could be 0.20 $\rm{M_{\odot}}$ and possibly, it is an M-type star. 3. GW UMa is a new high-amplitude $\delta$ Scuti variable with a period of $0.^{d}20319367$, it was discovered as a high-amplitude pulsating variable star by the Hipparcos satellite in 1997. By using a few new determined times of light maximum together with those collected from the literature, the changes in Observed-Calculated ($\rm{O-C}$) diagram were analyzed. It is discovered that the $\rm{O-C}$ curve of GW UMa shows a cyclic variation with a peri |
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