疏散星团成员星磁活动的观测研究
文献类型：学位论文
| 作者 | 房祥松 |
| 学位类别 | 博士 |
| 答辩日期 | 2013-05-29 |
| 授予单位 | 中国科学院研究生院（云南天文台） |
| 授予地点 | 北京 |
| 导师 | 李焱 ; 顾盛宏 |
| 关键词 | 疏散星团 晚型恒星 密近双星 恒星黑子 色球活动 |
| 其他题名 | A Study of Magnetic Activities for Stars in Open Clusters |
| 学位专业 | 天体物理 |
| 中文摘要 | 普遍认为，疏散星团成员星起源于同一块分子云，因而它们有相同的化学组成和年龄。另外，由于这些星团自身尺度一般远小于它们到地球的距离，所以可以近似认为这些成员星到地球的距离相同（因而星际消光也类似）。尤其是，大多数疏散星团分布在银河系中非常活跃的恒星形成区――旋臂区域。因此，疏散星团是一个理想的研究恒星形成与演化等物理过程的天然实验室。根据发电机理论，晚型恒星自转与对流相互耦合，从而产生磁场。对于年轻的疏散星团，其成员星角动量损失不大，具有较大的自转速率，于是磁活动水平较高，这为研究恒星磁活动带来了极大的方便，可以为我们提供更多的研究晚型恒星磁活动的素材。 在银河系中虽然已发现近两千个疏散星团，但是被详细研究过的星团却为数不多，迄今为止有关疏散星团成员星磁活动的研究资料还不多。为了在疏散星团中搜寻磁活动变星并对其进行活动性质等方面的研究，我们在2008年到2013年期间先后对三个年轻疏散星团NGC 1348、ASCC 5和NGC 1960进行了测光观测，目的是在其中搜寻磁活动变星。此外，我们对NGC 1960和Pleiades中的若干成员星进行了分光观测，以对其色球活动进行证认和研究。基于这些测光和分光观测研究，我们取得了有意义的研究结果。 我们对疏散星团NGC 1348进行了五个时段的多色测光观测，新发现了一颗相接双星：GSC2.3 NCB0032066。我们在该双星系统上观测到了O’Connell效应（?B?0.03 mag），表明该星是一个活动的相接双星系统。通过比较不同时期观测得到的光变曲线数据，我们发现从2008年11月到12月这段时间内其光变曲线形状发生了变化，这意味其黑子活动存在短时标的演化行为。 我们对ASCC 5进行了两个时段的测光观测，在其中发现了四颗食双星： 2MASS J00570305+5541588，2MASS J00572555+5546091，2MASS J00580602+5541451和2MASS J00583140+5539042（简记为2MJ5703，2MJ5725，2MJ5806和2MJ5831）。我们用Wilson-Devinney程序对它们进行了综合光变曲线分析，得到了其轨道参量等基本物理信息。 –2MJ5703是一个典型的A次型相接双星系统（质量比q ?0.5，相接度f?0.13），其光谱型为晚F型，轨道周期约为0.44天。 –2MJ5725可能是一个W次型的相接双星系统，其轨道周期大约为0.3天。它的光变曲线在极大附近不对称，说明该星上存在诸如黑子的磁活动现象。 –2MJ5806质量比约为0.9，是一个H次型的相接双星系统。该系统轨道周期为0.274天，其相接度比较小，约为0.1。 –2MJ5831可能是一个W次型的相接双星系统，其轨道周期为0.273天。该系统上存在明显的O’Connell效应，而且光变曲线形状存在快速变化，表明该系统子星磁活动比较剧烈。 对于NGC 1960，我们进行了三个时段的测光观测和分光证认，在其中发现了近十颗变星，包括几颗B型变星，一颗δScuti型脉动变星，几颗可能的磁活动变星。 我们对三颗昴星团成员星PELS 72、DH 679以及PELS 75进行了测光和中色散分光观测，分析表明它们都是磁活动变星，而且色球活动水平比较高。 –PELS 72表面长期存在两个大小可比的黑子区域，这两个黑子区域在经度方向都发生了移动，而且它们之间的距离不断发生变化，表现出了子午环流的迹象。 –DH 679短期内光变曲线形状比较稳定，存在两个相差约180度的活动经度带，这或许与跳变（flip-flop）活动现象有关。 –PELS 75的光变曲线的振幅发生快速的变化。短期内其黑子也在沿着经度方向移动，从长期数据来看，黑子倾向于只在同一个半球上出现。 以上的这些研究结果需要进一步的测光监测和分光观测以便对它们进行更深入细致的分析与研究。 |
| 英文摘要 | It is common knowledge that open clusters are dynamically associated systems of stars, in which the stars have formed together within the same molecular cloud. Therefore, apart from the coeval nature of the stars, they have the same chemical composition, and usually are assumed to be at the same distance from us and hence suffer from the same interstellar reddening. Particularly, open clusters are found mostly in the disk and especially the spiral arms, where many new stars are being formed. Hence it is a perfect place to study theories of stellar formation and evolution, and furthermore an ideal place to study stellar magnetic activities, taking into account that there are lots of low mass stars with rapid rotations in open clusters. Nearly 2000 open clusters have been detected in Galaxy, however, the magnetic activities are not understood well for the low mass stars in open clusters. Our aim is to search for magnetically active stars in open clusters, and study their magnetic activities. During 2008-2013, We carried out photometric observations of three young open clusters (NGC 1348, ASCC 5 and NGC 1960) with the purpose of searching for variable stars with magnetic activities; we also obtained spectroscopic observations for several stars in NGC 1960 and Pleiades to study their chromospheric activities. Based on these observations, we have obtained many interesting results, as follows. We carried out multi-color time-series photometric observations of the young, poorly studied open cluster NGC 1348, and discovered one contact binary star: GSC2.3 NCB0032066. The well known O’Connell effect (e.g., ?B?0.03 mag) was found in November 2008, which indicates that this object is an active binary star. We compared the light curves derived in different observing runs, and found that there existed a slight change from November to December, 2008, which indicates the evolution of spot activity on at least one component in a time scale of about one month. We carried out Rc-band time-series photometric observations of the young open cluster ASCC 5, and discovered four eclipsing binaries: 2MASS J00570305+5541588, 2MASS J00572555+5546091, 2MASS J00580602+5541451 and 2MASS J00583140+5539042 (hereafter 2MJ5703, 2MJ5725, 2MJ5806 and 2MJ5831 respectively). We analyzed their light curves using the Wilson-Devinney light curve modeling technique and derived their basic physical parameters. –2MJ5703 is a typical A subtype contact binary system (mass ratio q?0.5, the degree of contact f?0.13) with a late F spectral type, having an orbital period of 0.44 days. –2MJ5725 is more likely a W subtype contact binary with a very low variation amplitude of about 0.07 mag. It has an orbital period of about 0.302 days. There are asymmetric distortions in its light curves, suggesting the presence of starspots on the components. –2MJ5806 is an H subtype contact binary system with a high mass ratio around 0.9 and a small degree of contact of about 0.1, and it has a short orbital period of about 0.274 days. –2MJ5831 is probably a W subtype contact binary with a low light variation amplitude around 0.11 mag and a short orbital period of 0.273 days. The presence of remarkable O’Connell effect and rapid variations of light curves indicate presence of strong magnetically activities on the components of this binary. We undertook photometric observations of the open cluster NGC 1960 in 2012 November, December and in 2013 February, and discovered nearly 10 variable stars in this field. Among these variables, several ones are variable B stars, one is a δ Scuti Star, the others may be the magnetically active stars. We made photometric and spectroscopic observations of three member stars of Pleiades (PELS 72, DH 679 and PELS 75). Our observations indicate that all of them are magnetically active stars, being in very active states –PELS 72: There are at least two spots on the surface of this star in great part of observing runs, and the longitude separation between the two spots varies quickly. Furthermore, they are moving oppositely with respect to longitude, which gives us a clue of the presence of the meridian circulation. –DH 679: It shows no rapid variation in its light curve shapes on a short time scale, however, it seems that there are two active longitudes 180 degrees apart, based on longer data baselines, which usually relates to so-called“flip-flop”activity phenomenon. –PELS 75: There are rapid variations in its light curve amplitudes, and the primary spot shifts along longitude on a short time scale. More interestingly, spots in all datasets concentrate in a longitude range of about 180 degrees, indicating that the spots are inclined to emerge on the same hemisphere. It should be pointed out that further observations are needed to understand better their basic physical parameters and magnetic activities for these stars mentioned above. |
| 学科主题 | 天文学 |
| 语种 | 中文 |
| 源URL | [http://ir.ynao.ac.cn/handle/114a53/5335]  |
| 专题 | 云南天文台_恒星物理研究组 |
| 推荐引用方式 GB/T 7714 | 房祥松. 疏散星团成员星磁活动的观测研究[D]. 北京. 中国科学院研究生院（云南天文台）. 2013. |
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来源：云南天文台
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