分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qichun Liu
Jie Lin
Xiaofeng Wang
Shenghong Gu
Jianrong Shi
Liyun Zhang
Gaobo Xi
Jun Mo
Yongzhi Cai
Liyang Chen
Zhihao Chen
Fangzhou Guo
Xiaojun Jiang
Gaici Li
Wenxiong Li
Han Lin
Weili Lin
Jialian Liu
Cheng Miao
Xiaoran Ma
摘要： Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jie Lin
Chengyuan Wu
Xiaofeng Wang
Péter Németh
Herang Xiong
Tao Wu
Alexei Filippenko
Yongzhi Cai
Thomas Brink
Shengyu Yan
Xiangyun Zeng
Yangpin Luo
Danfeng Xiang
Jujia Zhang
Weikang Zheng
Yi Yang
Jun Mo
Gaobo Xi
Jicheng Zhang
Abdusamatjan Iskandar
摘要： Blue large-amplitude pulsators (BLAPs) represent a new and rare class of hot pulsating stars with unusually large amplitudes and short periods. Up to now, only 24 confirmed BLAPs have been identified from more than one billion monitored stars, including a group with pulsation period longer than $\sim 20$ min (classical BLAPs, hereafter) and the other group with pulsation period below $\sim 8$ min. The evolutionary path that could give rise to such kinds of stellar configurations is unclear. Here we report on a comprehensive study of the peculiar BLAP discovered by the Tsinghua University - Ma Huateng Telescopes for Survey (TMTS), TMTS J035143.63+584504.2 (TMTS-BLAP-1). This new BLAP has an 18.9 min pulsation period and is similar to the BLAPs with a low surface gravity and an extended helium-enriched envelope, suggesting that it is a low-gravity BLAP at the shortest-period end. In particular, the long-term monitoring data reveal that this pulsating star has an unusually large rate of period change, P_dot/P=2.2e-6/yr. Such a significant and positive value challenges its origins from both helium-core pre-white-dwarfs and core helium-burning subdwarfs, but is consistent with that derived from shell helium-burning subdwarfs. The particular pulsation period and unusual rate of period change indicate that TMTS-BLAP-1 is at a short-lived (~10^6 yr) phase of shell-helium ignition before the stable shell-helium burning; in other words, TMTS-BLAP-1 is going through a "Hertzsprung gap" of hot subdwarfs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Qichun Liu
Jie Lin
Xiaofeng Wang
Shenghong Gu
Jianrong Shi
Liyun Zhang
Gaobo Xi
Jun Mo
Yongzhi Cai
Liyang Chen
Zhihao Chen
Fangzhou Guo
Xiaojun Jiang
Gaici Li
Wenxiong Li
Han Lin
Weili Lin
Jialian Liu
Cheng Miao
Xiaoran Ma
摘要： Tsinghua University-Ma Huateng Telescopes for Survey (TMTS) aims to detect fast-evolving transients in the Universe, which has led to the discovery of thousands of short-period variables and eclipsing binaries since 2020. In this paper, we present the observed properties of 125 flare stars identified by the TMTS within the first two years, with an attempt to constrain their eruption physics. As expected, most of these flares were recorded in late-type red stars with $G_{\rm BP}-G_{\rm RP}$ > 2.0 mag, however, the flares associated with bluer stars tend to be on average more energetic and have broader profiles. The peak flux (F_peak) of the flare is found to depend strongly on the equivalent duration (ED) of the energy release, i.e., $F_{{\rm peak}} \propto {\rm ED}^{0.72\pm0.04}$, which is consistent with results derived from the Kepler and Evryscope samples. This relation is likely related to the magnetic loop emission, while -- for the more popular non-thermal electron heating model -- a specific time evolution may be required to generate this relation. We notice that flares produced by hotter stars have a flatter $F_{{\rm peak}} \propto {\rm ED}$ relation compared to that from cooler stars. This is related to the statistical discrepancy in light-curve shape of flare events with different colors. In spectra from LAMOST, we find that flare stars have apparently stronger H alpha emission than inactive stars, especially at the low temperature end, suggesting that chromospheric activity plays an important role in producing flares. On the other hand, the subclass having frequent flares are found to show H alpha emission of similar strength in their spectra to that recorded with only a single flare but similar effective temperature, implying that the chromospheric activity may not be the only trigger for eruptions.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jie Lin
Chengyuan Wu
Xiaofeng Wang
Péter Németh
Herang Xiong
Tao Wu
Alexei Filippenko
Yongzhi Cai
Thomas Brink
Shengyu Yan
Xiangyun Zeng
Yangpin Luo
Danfeng Xiang
Jujia Zhang
Weikang Zheng
Yi Yang
Jun Mo
Gaobo Xi
Jicheng Zhang
Abdusamatjan Iskandar
摘要： Blue large-amplitude pulsators (BLAPs) represent a new and rare class of hot pulsating stars with unusually large amplitudes and short periods. Up to now, only 24 confirmed BLAPs have been identified from more than one billion monitored stars, including a group with pulsation period longer than $\sim 20$ min (classical BLAPs, hereafter) and the other group with pulsation period below $\sim 8$ min. The evolutionary path that could give rise to such kinds of stellar configurations is unclear. Here we report on a comprehensive study of the peculiar BLAP discovered by the Tsinghua University - Ma Huateng Telescopes for Survey (TMTS), TMTS J035143.63+584504.2 (TMTS-BLAP-1). This new BLAP has an 18.9 min pulsation period and is similar to the BLAPs with a low surface gravity and an extended helium-enriched envelope, suggesting that it is a low-gravity BLAP at the shortest-period end. In particular, the long-term monitoring data reveal that this pulsating star has an unusually large rate of period change, P_dot/P=2.2e-6/yr. Such a significant and positive value challenges its origins from both helium-core pre-white-dwarfs and core helium-burning subdwarfs, but is consistent with that derived from shell helium-burning subdwarfs. The particular pulsation period and unusual rate of period change indicate that TMTS-BLAP-1 is at a short-lived (~10^6 yr) phase of shell-helium ignition before the stable shell-helium burning; in other words, TMTS-BLAP-1 is going through a "Hertzsprung gap" of hot subdwarfs.
分类： 工程与技术科学 >> 工程与技术科学其他学科 提交时间： 2023-01-10 合作期刊: 《Art & Design Research》
摘要： In the past 30 years, the development of brownland into green land has become an important way for the sustainable development and management of urban land. Fully understanding the various application scenarios and values of this approach is helpful to explore its efforts in providing ecosystem services and meet the development needs of different types of cities. This paper reviews the practice and literature of brownfield redevelopment from the perspective of landscape architecture, and obtains the process of its theoretical development and its understanding deepening. Through sorting out the relevant discipline literature, the seven main green space types and their potential broad benefits are summarized, and we realize that the brownfield itself has many values that cannot be ignored in the development process. On this basis, it proposes that there is a new cognition of the relationship between brownfield and green space.
分类： 其他 >> 综合 提交时间： 2023-01-02 合作期刊: 《Art & Design Research》
摘要： In the past 30 years, the development of brownland into green land has become an important way for the sustainable development and management of urban land. Fully understanding the various application scenarios and values of this approach is helpful to explore its efforts in providing ecosystem services and meet the development needs of different types of cities. This paper reviews the practice and literature of brownfield redevelopment from the perspective of landscape architecture, and obtains the process of its theoretical development and its understanding deepening. Through sorting out the relevant discipline literature, the seven main green space types and their potential broad benefits are summarized, and we realize that the brownfield itself has many values that cannot be ignored in the development process. On this basis, it proposes that there is a new cognition of the relationship between brownfield and green space.
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