In our previous work,we searched for superflares on different types of stars while focusing on G-type dwarfs using entire Kepler data to study statistical properties of the occurrence rate of superflares.Using these n...In our previous work,we searched for superflares on different types of stars while focusing on G-type dwarfs using entire Kepler data to study statistical properties of the occurrence rate of superflares.Using these new data,as a byproduct,we found 14 cases of superflare detection on 13 slowly rotating Sun-like stars with rotation periods of24.5–44 days.This result supports the earlier conclusion by others that the Sun may possibly undergo a surprise superflare.Moreover,we found 12 and seven new cases of detection of exceptionally large amplitude superflares on six and four main sequence stars of G-and M-type,respectively.No large-amplitude flares were detected in A,F or K main sequence stars.Here we present preliminary analysis of these cases.The superflare detection,i.e.,an estimation of flare energy,is based on a more accurate method compared to previous studies.We fit an exponential decay function to flare light curves and study the relation between e-folding decay time,τ,versus flare amplitude and flare energy.We find that for slowly rotating Sun-like stars,large values ofτcorrespond to small flare energies and small values ofτcorrespond to high flare energies considered.Similarly,τis large for small flare amplitudes andτis small for large amplitudes considered.However,there is no clear relation between these parameters for large amplitude superflares in the main sequence G-and M-type stars,as we could not establish clear functional dependence between the parameters via standard fitting algorithms.展开更多
The Closeby Habitable Exoplanet Survey(CHES) mission is proposed to discover habitable-zone Earth-like planets of nearby solar-type stars(~10 pc away from our solar system) via microarcsecond relative astrometry.The m...The Closeby Habitable Exoplanet Survey(CHES) mission is proposed to discover habitable-zone Earth-like planets of nearby solar-type stars(~10 pc away from our solar system) via microarcsecond relative astrometry.The major scientific objectives of CHES are:to search for Earth Twins or terrestrial planets in habitable zones orbiting100 FGK nearby stars;further to conduct a comprehensive survey and extensively characterize nearby planetary systems.The primary payload is a high-quality,low-distortion,high-stability telescope.The optical subsystem is a coaxial three-mirror anastigmat(TMA) with a 1.2 m-aperture,0°.44 × 0°.44 field of view and 500 nm-900 nm working wave band.The camera focal plane is composed of a mosaic of 81 scientific CMOS detectors each with4 k × 4 k pixels.The heterodyne laser interferometric calibration technology is employed to ensure microarcsecond level(1 μas) relative astrometry precision to meet the requirements for detection of Earth-like planets.The CHES satellite operates at the Sun-Earth L2 point and observes all the target stars for 5 yr.CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on microarcsecond astrometry from space.This will definitely enhance our understanding of the formation of diverse nearby planetary systems and the emergence of other worlds for solar-type stars,and finally provide insights to the evolution of our own solar system.展开更多
为提高温室骨架受力性能,证明装配式骨架在日光温室结构中的可行性,并优化日光温室骨架的装配设计,以陕西省杨凌区某日光温室为研究对象,选取椭圆形单管骨架结构,在内置与外置装配件2种不同连接方式下进行节点设计及有限元分析。分别选...为提高温室骨架受力性能,证明装配式骨架在日光温室结构中的可行性,并优化日光温室骨架的装配设计,以陕西省杨凌区某日光温室为研究对象,选取椭圆形单管骨架结构,在内置与外置装配件2种不同连接方式下进行节点设计及有限元分析。分别选取8、9、10 cm 3种常见规格的装配件与椭圆钢管进行组装,运用ANSYS软件分别计算装配式椭圆管跨中连接部位在5、7、10 kN的集中力作用下节点的受力和变形情况,再设置未截断椭圆钢管作为对照组进行比对。结果表明,当装配式日光温室椭圆管内置10 cm长连接件时结构变形量最小。此外,当主管截面角度取10°时所受应力最小。研究开发出椭圆形装配式骨架并为其开发装配节点,通过静力试验研究装配式骨架受力性能,最后通过有限元数值模拟验证静力试验的可靠性和日光温室骨架装配化设计的可行性。该研究可为日光温室椭圆骨架的装配式开发及装配式节点的优化提供依据。展开更多
Photospheric C,N,and O abundances of 118 solar-analog stars were determined by applying the synthetic-fitting analysis to their spectra in the blue or near-UV region comprising lines of CH,NH,and OH molecules,with an ...Photospheric C,N,and O abundances of 118 solar-analog stars were determined by applying the synthetic-fitting analysis to their spectra in the blue or near-UV region comprising lines of CH,NH,and OH molecules,with an aim of clarifying the behaviors of these abundances in comparison with[Fe/H].It turned out that,in the range of-0.6■[Fe/H]■+0.3,[C/Fe]shows a marginally increasing tendency with decreasing[Fe/H]with a slight upturn around[Fe/H]~0,[N/Fe]tends to somewhat decrease toward lower[Fe/H],and[O/Fe]systematically increases (and thus[C/O]decreases) with a decrease in[Fe/H].While these results are qualitatively consistent with previous determinations mostly based on atomic lines,the distribution centers of these[C/Fe],[N/Fe],and[O/Fe]at the near-solar metallicity are slightly negative by several hundredths of dex,which is interpreted as due to unusual solar abundances possibly related to the planetary formation of our solar system.However,clear anomalies are not observed in the[C,N,O/Fe]ratios of planet-host stars.Three out of four very Be-deficient stars were found to show anomalous[C/Fe]or[N/Fe]which may be due to mass transfer from the evolved companion,though its relation to the Be depletion mechanism is still unclear.展开更多
In our previous work,we investigated the occurrence rate of super-flares on various types of stars and their statistical properties,with a particular focus on G-type dwarfs,using entire Kepler data.The said study also...In our previous work,we investigated the occurrence rate of super-flares on various types of stars and their statistical properties,with a particular focus on G-type dwarfs,using entire Kepler data.The said study also considered how the statistics change with stellar rotation period,which in turn,had to be determined.Using such new data,as a by-product,we found 138 Kepler IDs of F-and G-type main sequence stars with rotation periods less than a day(P_(rot)<1 day).On one hand,previous studies have revealed short activity cycles in F-type and G-type stars and the question investigated was whether or not short-term activity cycles are a common phenomenon in these stars.On the other hand,extensive studies exist which establish an empirical connection between a star's activity cycle and rotation periods.In this study,we compile all available Kepler data with P_(rot)<1 day,and rely on an established empirical relation between P_(cyc)and P_(rot)with the aim to provide predictions for very short 5.09≤P_(cyc)≤38.46 day cases in a tabular form.We propose an observation to measure P_(cyc)using a monitoring program of stellar activity(e.g.,activity-related chromospheric emission S-index)or a similar means for the Kepler IDs found in this study in order put the derived empirical relations between P_(cyc)and P_(rot)derived here to the test.We also propose an alternative method for measuring very short P_(cyc),using flare-detection algorithms applied to future space mission data.展开更多
基金Support for MAST for non-HST data is provided by the NASA Office of Space Science via grant NNX13AC07G and by other grants and contractsRiyadh,Saudi Arabia and the Royal Embassy of Saudi Arabia Cultural Bureau in London,UK for the financial support of her PhD scholarship,held at Queen Mary University of London。
文摘In our previous work,we searched for superflares on different types of stars while focusing on G-type dwarfs using entire Kepler data to study statistical properties of the occurrence rate of superflares.Using these new data,as a byproduct,we found 14 cases of superflare detection on 13 slowly rotating Sun-like stars with rotation periods of24.5–44 days.This result supports the earlier conclusion by others that the Sun may possibly undergo a surprise superflare.Moreover,we found 12 and seven new cases of detection of exceptionally large amplitude superflares on six and four main sequence stars of G-and M-type,respectively.No large-amplitude flares were detected in A,F or K main sequence stars.Here we present preliminary analysis of these cases.The superflare detection,i.e.,an estimation of flare energy,is based on a more accurate method compared to previous studies.We fit an exponential decay function to flare light curves and study the relation between e-folding decay time,τ,versus flare amplitude and flare energy.We find that for slowly rotating Sun-like stars,large values ofτcorrespond to small flare energies and small values ofτcorrespond to high flare energies considered.Similarly,τis large for small flare amplitudes andτis small for large amplitudes considered.However,there is no clear relation between these parameters for large amplitude superflares in the main sequence G-and M-type stars,as we could not establish clear functional dependence between the parameters via standard fitting algorithms.
基金financially supported by the Strategic Priority Research Program on Space Science of the Chinese Academy of Sciences (Grant No. XDA 15020800)the National Natural Science Foundation of China (Grant Nos. 12033010, 41604152 and U1938111)Foundation of Minor Planets of the Purple Mountain Observatory and Youth Innovation Promotion Association CAS (Grant No. 2018178)。
文摘The Closeby Habitable Exoplanet Survey(CHES) mission is proposed to discover habitable-zone Earth-like planets of nearby solar-type stars(~10 pc away from our solar system) via microarcsecond relative astrometry.The major scientific objectives of CHES are:to search for Earth Twins or terrestrial planets in habitable zones orbiting100 FGK nearby stars;further to conduct a comprehensive survey and extensively characterize nearby planetary systems.The primary payload is a high-quality,low-distortion,high-stability telescope.The optical subsystem is a coaxial three-mirror anastigmat(TMA) with a 1.2 m-aperture,0°.44 × 0°.44 field of view and 500 nm-900 nm working wave band.The camera focal plane is composed of a mosaic of 81 scientific CMOS detectors each with4 k × 4 k pixels.The heterodyne laser interferometric calibration technology is employed to ensure microarcsecond level(1 μas) relative astrometry precision to meet the requirements for detection of Earth-like planets.The CHES satellite operates at the Sun-Earth L2 point and observes all the target stars for 5 yr.CHES will offer the first direct measurements of true masses and inclinations of Earth Twins and super-Earths orbiting our neighbor stars based on microarcsecond astrometry from space.This will definitely enhance our understanding of the formation of diverse nearby planetary systems and the emergence of other worlds for solar-type stars,and finally provide insights to the evolution of our own solar system.
文摘为提高温室骨架受力性能,证明装配式骨架在日光温室结构中的可行性,并优化日光温室骨架的装配设计,以陕西省杨凌区某日光温室为研究对象,选取椭圆形单管骨架结构,在内置与外置装配件2种不同连接方式下进行节点设计及有限元分析。分别选取8、9、10 cm 3种常见规格的装配件与椭圆钢管进行组装,运用ANSYS软件分别计算装配式椭圆管跨中连接部位在5、7、10 kN的集中力作用下节点的受力和变形情况,再设置未截断椭圆钢管作为对照组进行比对。结果表明,当装配式日光温室椭圆管内置10 cm长连接件时结构变形量最小。此外,当主管截面角度取10°时所受应力最小。研究开发出椭圆形装配式骨架并为其开发装配节点,通过静力试验研究装配式骨架受力性能,最后通过有限元数值模拟验证静力试验的可靠性和日光温室骨架装配化设计的可行性。该研究可为日光温室椭圆骨架的装配式开发及装配式节点的优化提供依据。
文摘Photospheric C,N,and O abundances of 118 solar-analog stars were determined by applying the synthetic-fitting analysis to their spectra in the blue or near-UV region comprising lines of CH,NH,and OH molecules,with an aim of clarifying the behaviors of these abundances in comparison with[Fe/H].It turned out that,in the range of-0.6■[Fe/H]■+0.3,[C/Fe]shows a marginally increasing tendency with decreasing[Fe/H]with a slight upturn around[Fe/H]~0,[N/Fe]tends to somewhat decrease toward lower[Fe/H],and[O/Fe]systematically increases (and thus[C/O]decreases) with a decrease in[Fe/H].While these results are qualitatively consistent with previous determinations mostly based on atomic lines,the distribution centers of these[C/Fe],[N/Fe],and[O/Fe]at the near-solar metallicity are slightly negative by several hundredths of dex,which is interpreted as due to unusual solar abundances possibly related to the planetary formation of our solar system.However,clear anomalies are not observed in the[C,N,O/Fe]ratios of planet-host stars.Three out of four very Be-deficient stars were found to show anomalous[C/Fe]or[N/Fe]which may be due to mass transfer from the evolved companion,though its relation to the Be depletion mechanism is still unclear.
基金Princess Nourah Bint Abdulrahman University,Riyadh,Saudi ArabiaRoyal Embassy of Saudi Arabia Cultural Bureau in London,UK for the financial support。
文摘In our previous work,we investigated the occurrence rate of super-flares on various types of stars and their statistical properties,with a particular focus on G-type dwarfs,using entire Kepler data.The said study also considered how the statistics change with stellar rotation period,which in turn,had to be determined.Using such new data,as a by-product,we found 138 Kepler IDs of F-and G-type main sequence stars with rotation periods less than a day(P_(rot)<1 day).On one hand,previous studies have revealed short activity cycles in F-type and G-type stars and the question investigated was whether or not short-term activity cycles are a common phenomenon in these stars.On the other hand,extensive studies exist which establish an empirical connection between a star's activity cycle and rotation periods.In this study,we compile all available Kepler data with P_(rot)<1 day,and rely on an established empirical relation between P_(cyc)and P_(rot)with the aim to provide predictions for very short 5.09≤P_(cyc)≤38.46 day cases in a tabular form.We propose an observation to measure P_(cyc)using a monitoring program of stellar activity(e.g.,activity-related chromospheric emission S-index)or a similar means for the Kepler IDs found in this study in order put the derived empirical relations between P_(cyc)and P_(rot)derived here to the test.We also propose an alternative method for measuring very short P_(cyc),using flare-detection algorithms applied to future space mission data.
