中国巡天空间望远镜(China Space Survey Telescope,CSST)是中国载人航天工程规划建设的以大规模天文巡天为主任务的2m口径空间光学望远镜,兼具高空间分辨率与大视场特性,性能优异。暂现源是CSST的重要科学目标之一.CSST作为空间望远镜...中国巡天空间望远镜(China Space Survey Telescope,CSST)是中国载人航天工程规划建设的以大规模天文巡天为主任务的2m口径空间光学望远镜,兼具高空间分辨率与大视场特性,性能优异。暂现源是CSST的重要科学目标之一.CSST作为空间望远镜,与地面望远镜的图像噪声组成有着明显不同。因此,不能直接套用先前地基巡天项目的暂现源探测方案,需要针对性开发专属的探测方法.CSST的暂现源探测方法以CSST仿真数据为基础进行开发。验证,旨在尽可能准确地识别CSST主巡天数据中的暂现源,方法以图像相减法为基础,首先获得观测图像所对应残差图像,并利用滤波方法给出残差图像泊松噪声分布;然后使用渐变阈值间接统一背景噪声水平,对残差图像进行目标源测光得到候选源列表;最后,通过判断候选源与当地泊松噪声的偏差对真实暂现源进行筛选,结合原始图像信息与观测图像测光分类信息后,进一步对候选源列表的假源进行剔除,最终输出暂现源星表。方法在共计20000个暂现源的多轮仿真测试中,能够以平均95.9%的准确率对观测图像中的暂现源进行筛选,相较于先前工作,还更加全面且定量地给出了测试所得的不同亮度暂现源所对应的探测率,测试结论验证了CSST暂现源探测方法的可行性、泛化能力与稳定性。该方法也为空间望远镜暂现源探测任务提供了理论与编程基础.展开更多
Polycyclic aromatic hydrocarbons(PAHs),PANHs,and peptoids dust spectral calculations from the interstellar medium(ISM)are important for dust observations and theory.Our goal is to calculate the radiation spectrum of s...Polycyclic aromatic hydrocarbons(PAHs),PANHs,and peptoids dust spectral calculations from the interstellar medium(ISM)are important for dust observations and theory.Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field.We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures.By the Vienna Ab-initio Simulation Package code,the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust.When the radius of spherical dust clusters is~[0.009-0.042]μm,the dust radiation spectrum agrees well with the Z=0.02 mMMP stellar spectra,and the PAHs radiation spectrum of NGC 4676 at wavelengths of(0-5]μm and(5-10]μm,respectively.In the ionized state,the N-PAH,C_(10)H_(9)N,2(C_(4)H_(4))^(1+),and peptoids 4(CHON),(C_(8)H_(10)N_(2)O_(5))^(1+)dust clusters at 3.3μm,while the 2(C_(22)H_(21)N_(3)O_(2))^(1+),4(CHON)dust clusters at 5.2μm have obvious peaks.There is a characteristic of part of PAHs and peptoids clusters radiation at the nearinfrared wavelength of 2μm.However,especially after applying an electric field to the dust,the emission spectrum of the dust increases significantly in the radiation wavelength range[3-10]μm.Consequently,the dust clusters of PAHs,PANHs,and peptoids of the radius size~[0.009-0.042]μm are likely to exist in the ISM.展开更多
A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction...A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction to the EPIC effective area.To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction,in this work,we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei(AGN).The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures(merging good time intervals(GTIs)from two missions)to avoid bias due to the rapid spectral variability of the AGN.Before the correction,the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by■subsequently yielding significantly underestimated cutoff energy E_(cut)and the strength of reflection component R when performing joint-fitting.We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fitΓ,E_(cut),and R.We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra,but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included.Besides,we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time,in many cases,joint-fitting yields no advantage compared with utilizing NuSTAR data alone.Finally,We present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the small window(SW)mode.展开更多
中国巡天空间望远镜(Chinese Survey Space Telescope,CSST)是中国的首个大型空间光学望远镜,将对包括系外行星探测在内的诸多科学目标开展研究,有望取得前沿科学进展.时序测光精度是CSST重要的性能指标,受到物理噪声和仪器噪声的影响,...中国巡天空间望远镜(Chinese Survey Space Telescope,CSST)是中国的首个大型空间光学望远镜,将对包括系外行星探测在内的诸多科学目标开展研究,有望取得前沿科学进展.时序测光精度是CSST重要的性能指标,受到物理噪声和仪器噪声的影响,需要通过数值模拟对其分析和评估.模拟基于目前公布的CSST主要技术参数,建立了时序的恒星信号和噪声模型,以CSST的i波段为例,分析凝视观测模式下的测光精度.通过数值仿真,展示了孔径测光中各项噪声的贡献,特别是由指向抖动和像素响应不均匀性导致的抖动噪声.模拟结果还给出了测光孔径的推荐范围.为了获得更高的信噪比,可以减小仪器抖动振幅和像素不均匀性,或者采用参考星较差测光的方式.结果为CSST后续的时序测光精度与不同指标参数的相关性分析、系外行星探测能力评估以及测光数据处理提供了模拟数据的支撑.展开更多
Being one of the most fundamental physical parameter of astronomical objects,mass plays a vital role in the study of exoplanets,including their temperature structure,chemical composition,formation,and evolution.Howeve...Being one of the most fundamental physical parameter of astronomical objects,mass plays a vital role in the study of exoplanets,including their temperature structure,chemical composition,formation,and evolution.However,nearly a quarter of the known confirmed exoplanets lack measurements of their masses.This is particularly severe for those discovered via the radial velocity(RV)technique,which alone could only yield the minimum mass of planets.In this study,we use published RV data combined with astrometric data from a cross-calibrated Hipparcos-Gaia Catalog of Accelerations to jointly constrain the masses of 115 RV-detected substellar companions,by conducting full orbital fits using the public tool orvara.Among them,9 exoplanets with M_(p)sini<13.5M_(Jup)are reclassified to the brown dwarf(BD)regime,and 16 BD candidates(13.5≤Mp sini<80M_(Jup))turn out to be low-mass M dwarfs.We point out the presence of a transition in the BD regime as seen in the distributions of host star metallicity and orbital eccentricity with respect to planet masses.We confirm the previous findings that companions with masses below 42.5 M_(Jup)might primarily form in the protoplanetary disk through core accretion or disk gravitational instability,while those with masses above 42.5 M_(Jup)formed through the gravitational instability of a molecular cloud like stars.Selection effects and detection biases,which may affect our analysis to some extent,are discussed.展开更多
耀变体(Blazar)的光谱能量分布(Spectral Energy Distribution,SED)中显示有两个明显的峰,其中低能峰为同步辐射峰。耀变体同步辐射峰的峰值功率与峰值频率存在反相关关系,因此与光谱能量分布峰值有关的多波段复合光谱指数构建的谱指数...耀变体(Blazar)的光谱能量分布(Spectral Energy Distribution,SED)中显示有两个明显的峰,其中低能峰为同步辐射峰。耀变体同步辐射峰的峰值功率与峰值频率存在反相关关系,因此与光谱能量分布峰值有关的多波段复合光谱指数构建的谱指数平面可以作为耀变体的两个亚类(平谱射电类星体(Flat Spectrum Radio Quasar,FSRQ)和蝎虎座BL型天体(BL Lac))的分类器。通过斯特拉斯堡天文台的数据库为费米4期目录(4FGL-DR3)中的耀变体进行了多波段数据的交叉匹配,得到多波段数据样本。在此基础上发现,耀变体的8个宽波段谱指数(α_(rw1),α_(rw2),α_(rw3),αro,αrγ,α_(w1w2),α_(w1w3)和α_(w3x))分布具有双峰结构,且明显区分耀变体的两个亚类。通过机器学习中的支持向量机(Support Vector Machine,SVM)模型,进一步分析了谱指数平面对耀变体亚类的分类作用,发现大部分谱指数平面分类的准确率在80%以上。展开更多
文摘中国巡天空间望远镜(China Space Survey Telescope,CSST)是中国载人航天工程规划建设的以大规模天文巡天为主任务的2m口径空间光学望远镜,兼具高空间分辨率与大视场特性,性能优异。暂现源是CSST的重要科学目标之一.CSST作为空间望远镜,与地面望远镜的图像噪声组成有着明显不同。因此,不能直接套用先前地基巡天项目的暂现源探测方案,需要针对性开发专属的探测方法.CSST的暂现源探测方法以CSST仿真数据为基础进行开发。验证,旨在尽可能准确地识别CSST主巡天数据中的暂现源,方法以图像相减法为基础,首先获得观测图像所对应残差图像,并利用滤波方法给出残差图像泊松噪声分布;然后使用渐变阈值间接统一背景噪声水平,对残差图像进行目标源测光得到候选源列表;最后,通过判断候选源与当地泊松噪声的偏差对真实暂现源进行筛选,结合原始图像信息与观测图像测光分类信息后,进一步对候选源列表的假源进行剔除,最终输出暂现源星表。方法在共计20000个暂现源的多轮仿真测试中,能够以平均95.9%的准确率对观测图像中的暂现源进行筛选,相较于先前工作,还更加全面且定量地给出了测试所得的不同亮度暂现源所对应的探测率,测试结论验证了CSST暂现源探测方法的可行性、泛化能力与稳定性。该方法也为空间望远镜暂现源探测任务提供了理论与编程基础.
基金the Independent Innovation Project for Postgraduates of Central South University(No.160171008)the National Natural Science Foundation of China(project No.U2031204)the project of Xinjiang(No.2021D01C075)。
文摘Polycyclic aromatic hydrocarbons(PAHs),PANHs,and peptoids dust spectral calculations from the interstellar medium(ISM)are important for dust observations and theory.Our goal is to calculate the radiation spectrum of spherical PAHs dust clusters in a vacuum containing ionized and applied in the presence of an electric field.We propose a new simple computational model to calculate the size of three-dimensional spherical dust clusters formed by different initial dust structures.By the Vienna Ab-initio Simulation Package code,the density functional theory with the generalized approximation was used to calculate the electron density gradient and obtain the radiation spectrum of dust.When the radius of spherical dust clusters is~[0.009-0.042]μm,the dust radiation spectrum agrees well with the Z=0.02 mMMP stellar spectra,and the PAHs radiation spectrum of NGC 4676 at wavelengths of(0-5]μm and(5-10]μm,respectively.In the ionized state,the N-PAH,C_(10)H_(9)N,2(C_(4)H_(4))^(1+),and peptoids 4(CHON),(C_(8)H_(10)N_(2)O_(5))^(1+)dust clusters at 3.3μm,while the 2(C_(22)H_(21)N_(3)O_(2))^(1+),4(CHON)dust clusters at 5.2μm have obvious peaks.There is a characteristic of part of PAHs and peptoids clusters radiation at the nearinfrared wavelength of 2μm.However,especially after applying an electric field to the dust,the emission spectrum of the dust increases significantly in the radiation wavelength range[3-10]μm.Consequently,the dust clusters of PAHs,PANHs,and peptoids of the radius size~[0.009-0.042]μm are likely to exist in the ISM.
基金supported by the National Natural Science Foundation of China(12033006,12192221,123B2042).
文摘A recently released XMM-Newton note revealed a significant calibration issue between nuclear spectroscopic telescope array(NuSTAR)and XMM-Newton European Photon Imaging Camera(EPIC)and provided an empirical correction to the EPIC effective area.To quantify the bias caused by the calibration issue in the joint analysis of XMM-NuSTAR spectra and verify the effectiveness of the correction,in this work,we perform joint-fitting of the NuSTAR and EPIC-pn spectra for a large sample of 104 observation pairs of 44 X-ray bright active galactic nuclei(AGN).The spectra were extracted after requiring perfect simultaneity between the XMM-Newton and NuSTAR exposures(merging good time intervals(GTIs)from two missions)to avoid bias due to the rapid spectral variability of the AGN.Before the correction,the EPIC-pn spectra are systematically harder than the corresponding NuSTAR spectra by■subsequently yielding significantly underestimated cutoff energy E_(cut)and the strength of reflection component R when performing joint-fitting.We confirm that the correction is highly effective and can commendably erase the discrepancy in best-fitΓ,E_(cut),and R.We thus urge the community to apply the correction when joint-fitting XMM-NuSTAR spectra,but note that the correction is limited to 3–12 keV and therefore not applicable when the soft X-ray band data are included.Besides,we show that as merging GTIs from two missions would cause severe loss of NuSTAR net exposure time,in many cases,joint-fitting yields no advantage compared with utilizing NuSTAR data alone.Finally,We present a technical note on filtering periods of high background flares for XMM-Newton EPIC-pn exposures in the small window(SW)mode.
文摘中国巡天空间望远镜(Chinese Survey Space Telescope,CSST)是中国的首个大型空间光学望远镜,将对包括系外行星探测在内的诸多科学目标开展研究,有望取得前沿科学进展.时序测光精度是CSST重要的性能指标,受到物理噪声和仪器噪声的影响,需要通过数值模拟对其分析和评估.模拟基于目前公布的CSST主要技术参数,建立了时序的恒星信号和噪声模型,以CSST的i波段为例,分析凝视观测模式下的测光精度.通过数值仿真,展示了孔径测光中各项噪声的贡献,特别是由指向抖动和像素响应不均匀性导致的抖动噪声.模拟结果还给出了测光孔径的推荐范围.为了获得更高的信噪比,可以减小仪器抖动振幅和像素不均匀性,或者采用参考星较差测光的方式.结果为CSST后续的时序测光精度与不同指标参数的相关性分析、系外行星探测能力评估以及测光数据处理提供了模拟数据的支撑.
基金supported by the National Key R&D Program of China Nos.2019YFA0405102 and 2019YFA0405502supported by the National Natural Science Foundation of China(NSFC,Grant Nos.12073044 and 11988101)。
文摘Being one of the most fundamental physical parameter of astronomical objects,mass plays a vital role in the study of exoplanets,including their temperature structure,chemical composition,formation,and evolution.However,nearly a quarter of the known confirmed exoplanets lack measurements of their masses.This is particularly severe for those discovered via the radial velocity(RV)technique,which alone could only yield the minimum mass of planets.In this study,we use published RV data combined with astrometric data from a cross-calibrated Hipparcos-Gaia Catalog of Accelerations to jointly constrain the masses of 115 RV-detected substellar companions,by conducting full orbital fits using the public tool orvara.Among them,9 exoplanets with M_(p)sini<13.5M_(Jup)are reclassified to the brown dwarf(BD)regime,and 16 BD candidates(13.5≤Mp sini<80M_(Jup))turn out to be low-mass M dwarfs.We point out the presence of a transition in the BD regime as seen in the distributions of host star metallicity and orbital eccentricity with respect to planet masses.We confirm the previous findings that companions with masses below 42.5 M_(Jup)might primarily form in the protoplanetary disk through core accretion or disk gravitational instability,while those with masses above 42.5 M_(Jup)formed through the gravitational instability of a molecular cloud like stars.Selection effects and detection biases,which may affect our analysis to some extent,are discussed.
文摘耀变体(Blazar)的光谱能量分布(Spectral Energy Distribution,SED)中显示有两个明显的峰,其中低能峰为同步辐射峰。耀变体同步辐射峰的峰值功率与峰值频率存在反相关关系,因此与光谱能量分布峰值有关的多波段复合光谱指数构建的谱指数平面可以作为耀变体的两个亚类(平谱射电类星体(Flat Spectrum Radio Quasar,FSRQ)和蝎虎座BL型天体(BL Lac))的分类器。通过斯特拉斯堡天文台的数据库为费米4期目录(4FGL-DR3)中的耀变体进行了多波段数据的交叉匹配,得到多波段数据样本。在此基础上发现,耀变体的8个宽波段谱指数(α_(rw1),α_(rw2),α_(rw3),αro,αrγ,α_(w1w2),α_(w1w3)和α_(w3x))分布具有双峰结构,且明显区分耀变体的两个亚类。通过机器学习中的支持向量机(Support Vector Machine,SVM)模型,进一步分析了谱指数平面对耀变体亚类的分类作用,发现大部分谱指数平面分类的准确率在80%以上。
