KMS of Xinjiang Astronomical Observatory, CAS
| 恒星耀发探测与研究 | |
| Alternative Title | A Study of stellar Flares |
白建迎
| |
| Subtype | 博士 |
| Thesis Advisor | 艾力·伊沙木丁 |
| 2020-11-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 北京 |
| Degree Name | 理学博士 |
| Degree Discipline | 天体物理 |
| Keyword | 暂现事件探测 耀发 Ross 15 Kepler A型星 |
| Abstract | 恒星耀发是一种短时标暂现事件，通常耀发期间恒星亮度急剧抬升，之后慢速变暗，直到恢复至耀发前的恒星亮度水平，爆发持续时标一般从几秒到几个小时。这种爆发事件一般被认为起源于恒星磁场活动，由磁重联触发产生。对恒星耀发进行观测研究可以加深对耀发过程及其爆发机制的认识，促进对恒星活动和磁场的理解。本文围绕恒星耀发主要开展了两项研究工作：一、Ross 15耀发的测光及光谱观测研究；二、基于Kepler长曝光数据探测耀发星，并研究其中的A型星耀发。Ross 15是一颗耀发星，但到目前为止针对其耀发进行的观测研究很少。为了深入研究Ross 15的耀发属性，本研究对其进行了测光及光谱观测。在B波段128小时的测光观测共探测到28个耀发，得到了比前人研究更准确的爆发率（0.22±0.04个/小时）；Ross 15在B波段耀发能量范围为1029.5到1031.5 erg，没有探测到超级耀发（能量>1034erg），表明Ross 15可能不存在剧烈的磁活动。首次给出Ross 15耀发的累积频率分布（FFD）；比较了Ross 15与其它光谱型恒星在相同能量范围内的累积FFD，结果显示Ross 15的耀发频率低于同类型耀发恒星YZ CMi（M4.5）和GJ 1243（M4），与三颗M5型恒星大致相同，并且高于光谱型晚于M6的恒星，与同类型的两个源相比Ross 15呈现较低的磁场活动。本研究首次对Ross 15进行了同步的高时间分辨率光谱和测光观测，并探测到耀发样本中能量最高的一次耀发，分析显示该源耀发期连续谱与线谱（Hα、Hβ、Hγ和Hδ）强度都有所增强，且它们的强度变化存在显著相关，与前人对相似光谱型恒星的耀发研究结果一致，表明Ross 15的色球活动可能主要在色球中层。按照恒星演化的标准理论，正常的A型星没有表面对流层或者具有非常薄的对流层，预期没有磁场活动，应该没有恒星耀发。近几年多篇基于Kepler数据的研究发现少数A型星存在耀发现象，但是A型恒星耀发的机制还不清楚。为进一步扩充A型耀发星样本并深入研究其耀发属性，本研究分析了Kepler DR 25中有效温度在7000到10500 K的5435颗源的长曝光数据，共探测到103颗耀发星的682次耀发，其中72颗星有LAMOST（郭守敬望远镜）光谱数据。通过它们的光谱分类出51颗A型耀发星，其中17颗为本研究新发现的，另34颗是已知A型耀发星。在这些A型耀发星中共探测到352个耀发事件，并计算了这些耀发的持续时间、幅度以及在Kepler波段的能量，中值分别为2.5小时、2.1 mmag以及1035.8 erg。给出了这51颗星的耀发FFD，在相同的能量范围内，本文的FFD斜率与前人基于Kepler数据的研究给出的基本一致，但是爆发率比前人的要低，主要原因是本研究的探测标准略高于前人的。本文首次给出A型耀发星自转周期与耀发活动的关系，结果表明自转周期越长耀发活动越弱，说明A型耀发星自转越慢磁场活动相对越弱，这与前人针对晚型星的研究结果类似。本论文的创新点主要有：1、首次给出Ross 15耀发能量的累积频率分布，并首次对该源进行了测光和高时间分辨率光谱的同步观测，分析耀发属性。2、基于Kepler长曝光数据，新发现17颗A型耀发星，使A型耀发星样本数扩充了12%；分析51颗A型耀发星的光变曲线和耀发，首次给出A型耀发星自转周期与耀发活动的关系等。 |
| Other Abstract | A stellar flare is a short-time-scale transient event. In the flare phase, the brightness of the star rises sharply and then slowly dims until it returns to the star brightness before an explosion. The flare duration ranges from a few seconds to hours. This kind of event is considered to originate from magnetic activity and triggered by magnetic reconnection. Studies on stellar flares can improve the understanding of flare properties and explosion mechanisms, and also help promote the understanding of the magnetic activities. In this paper, two studies on stellar flares are conducted: 1. photometric and spectroscopic study of flares on Ross 15. 2. The detection of flare stars in Kepler long-cadence data and investgation of the flares on A-type stars. We conducted photometric and spectroscopic observations for Ross 15 in order to further study the flare properties of this less observed star. A total of 28 B-band flares are detected in 128 hours of photometric observations, leading to a total flare rate of 0.22(±0.04), more accurate than that provided by previous work. We give the energy range of the B-band flares (1029.5-1031.5 erg). Super flares are not detected (energy > 1034erg), which suggests that there may not exist strong magnetic activity. The FFD of the star is given for the first time. It is lower than that of GJ 1243 (M4) and YZ CMi (M4.5), roughly in the middle of that of three M5-type stars and higher than the average of spectral types ≥ M6. The results indicate that the magnetic activity of Ross 15 is weaker than that of GJ 1243 and YZ CMi, but stronger than that of the stars with spectra type ≥ M6. We performed, for the first time, simultaneous high-cadence spectroscopic and photometric observations, detecting the most energetic flare in our sample. The intensities of the continuum and Balmer lines (Hα，Hβ，Hγ，Hδ) are calculated and they Significant enhancements of the intensities are shown and correlations between them are detected during the flare, which is same with that of the other deeply studied flare stars of the similar spectral type. The result indicates that the chromospheric activities of Ross 15 occur in the middle chromosphereAccording to the standard theory of stellar evolution, normal A-type stars have no convective zone, expecting to have no magnetic activity. Thus there should be no stellar flares on A-type stars. Some A-type flare stars are detected in previous researches based on Kepler data, indicating A-type stars have flares. The flare mechanism of A-type stars is still unclear. In order to expand the sample of A-type flare stars and to further study their flare properties, this work analyzes the long-cadence light curves of 5435 stars with effective temperatures of 7000 to 10500 K in Data Release 25 of Kepler. A total of 103 flare stars and 682 flares are detected, of which 72 have LAMOST (the Large Sky Area Multi-Object fiber Spectroscopic Telescope) spectral types, resulting in 51 A-type stars, including 17 new found and 34 known. A total of 352 flares are detected from the A-type stars. Their flare durations, amplitudes and energies in Kepler band are calculated, with the medians of 2.5 h, 2.1 mmag and 1035.8 erg, respectively. The FFD of the A-type stars is given. Within same energy range, the FFD slope is consistent with that in the previous researches also based on Kepler data, but the FFD is lower than that given by those researches. The lower FFD is probably due to our detection criteria, which is higher than that of the previous works. The activity-rotation relation of the A-type flare stars is shown for the first time, in which the flare activity decreases as the rotation period increases. The result suggests that the magnetic activity get weaker as the rotation period getting longer, same with that of the late-type stars in previous studies. The innovation points of this paper are as follows: 1. Through a long-term observation, the cumulative frequency distribution of flares on Ross 15 is given for the first time. The simultaneous observations of photometry and high-time resolution spectrum of the star are conducted for the first time in order to study the properties of the star’s flare. 2. A total of 17 newly discovered A-type flare stars are presented, which expanded the sample of A-type flare stars by 12%. For A-type flare stars, the relationship between their rotation periods and flare activities is given for the first time. |
| Pages | 85 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xao.ac.cn/handle/45760611-7/4729 |
| Collection | 研究生学位论文 |
| Affiliation | 中国科学院新疆天文台 |
| First Author Affilication | Xinjiang Astronomical Observatory, Chinese Academy of Sciences |
| Recommended Citation GB/T 7714 | 白建迎. 恒星耀发探测与研究[D]. 北京. 中国科学院大学,2020. |
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| 白建迎.pdf（4539KB） | 学位论文 | 暂不开放 | CC BY-NC-SA | Application Full Text | ||
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