The First Ground-Level Enhancement of Solar Cycle 24 on 17 May 2012 and Its Real-Time Detection

Ground-level enhancements (GLEs) are defined as sudden increases in the recorded intensity of cosmic-ray particles, usually by neutron monitors (NMs). In this work we present a time-shifting analysis (TSA) for the first arriving particles that were detected at Earth by NMs. We also present an automated real-time GLE alert that has been developed and is operating via the Neutron Monitor Database (NMDB), which successfully identified the 17 May 2012 event, designated as GLE71. We discuss the time evolution of the real-time GLE alert that was issued for GLE71 and present the event onset-time for NMs that contributed to this GLE alert based on their archived data. A comparison with their real-time time-stamp was made to illustrate the necessity for high-resolution data (e.g. 1-min time resolution) made available at every minute. The first results on the propagation of relativistic protons that have been recorded by NMs, as inferred by the TSA, imply that they are most probably accelerated by the coronal-mass-ejection-driven shock. Furthermore, the successful usage of NM data and the corresponding achievement of issuing a timely GLE alert are discussed.     

Investigation of the possible source for the solar energetic particle event on 2017 September 10

According to the solar proton data observed by Geostationary Operational Environmental Satellites(GOES), ground-based neutron monitors on Earth and near-relativistic electron data measured by the ACE spacecraft, the onset times of protons with different energies and near-relativistic electrons have been estimated and compared with the time of solar soft and hard X-ray and radio burst data.The results show that first arriving relativistic and non-relativistic protons and electrons may have been accelerated by the concurrent flare. The results also suggest that release times of protons with different energies may be different, and the protons with lower energy may have been released earlier than those with higher energy. Some protons accelerated by concurrent flares may be further accelerated by the shock driven by the associated CME.     

1979年9月19日3B级耀斑光谱分析:金属线的不对称性和线心位移

本文研究了1979年9月19日3B级耀斑金属谱线的不对称性和线心位移.结果表明:强金属线红不对称占主要地位,少数弱金属线也有蓝不对称存在;不对称程度极大发生于线心强度极大之前;不对称性有时可由蓝变红;不管不对称程度如何,线心的位移却很小,总体上仅表现为极微弱的蓝移.文中认为,耀斑爆发时色球压缩区的向下扩展及由此引起的温度极小区上下的物质运动这个动力学过程可基本解释这些观测现象.金属线的研究是对H_α和CaIIK线光谱研究的补充.     

Spectral analysis of the 3B flare on September 19, 1979: asymmetries and shifts of metallic lines

The asymmetries and Doppler shifts of metallic lines of the 3B flare on September 19, 1979 are investigated in this paper. The results show that: (1) red asymmetries dominate in strong metallic lines, but blue asymmetries also exist in some weak lines; (2) the maximum of the line asymmetry always precedes the maximum of the line intensity; (3) the blue asymmetry occurs generally in the early phase, and can occasionally turn to a red one in the later phase; and (4) the line center has no obvious shift, regardless of the line asymmetry. It is proposed that, the mass motions around the temperature minimum region caused by the impulsive heating or the propagation of the chromospheric condensation can explain these observational results. The study on metallic lines has an auxiliary help for understanding the dynamic process in the lower atmosphere of solar flares.     

First Images of Impulsive Millimeter Emission and Spectral Analysis of the 1994 August 18 Solar Flare

We present here the first images of impulsive millimeter emission of a flare. The flare on 1994 August 18 was simultaneously observed at millimeter (86 GHz), microwave (1-18 GHz), and soft and hard X-ray wavelengths. Images of millimeter, soft and hard X-ray emission show the same compact ( 8) source. Both the impulsive and the gradual phases are studied in order to determine the emission mechanisms. During the impulsive phase, the radio spectrum was obtained by combining the millimeter with simultaneous microwave emission. Fitting the nonthermal radio spectra as gyrosynchrotron radiation from a homogeneous source model with constant magnetic field yields the physical properties of the flaring source, that is, total number of electrons, power-law index of the electron energy distribution, and the nonthermal source size. These results are compared to those obtained from the hard X-ray spectra. The energy distribution of the energetic electrons inferred from the hard X-ray and radio spectra is found to follow a double power-law with slope 6–8 below 50 keV and 3–4 above those energies. The temporal evolution of the electron energy spectrum and its implication for the acceleration mechanism are discussed. Comparison of millimeter and soft X-ray emissions during the gradual phase implies that the millimeter emission is free-free radiation from the same hot soft X-ray emitting plasma, and further suggests that the flare source contains multiple temperatures.     

Analysis of the orbit of Cosmos 72 (1965-53B) near 15th-order resonance

Cosmos 72 (1965-53B) was launched on 16 April 1965 into a near-circular orbit with an average height of 570 km and inclination 56°. Over the years, the orbit has contracted slowly under the influence of air drag, and On 27 June 1972 passed through exact 15th-order resonance, when successive equator crossings are 24° apart in longitude and the ground track repeats after 15 rev. The orbit has been determined at seven epochs between April 1972 and February 1973, using the RAE orbit refinement program PROP, with 544 optical and radar observations: the average orbital accuracy is about 50 m in height and 0.0008° in inclination.For Cosmos 72 the change in inclination at 15th-order resonance, due to perturbations by 15th-order harmonics in the geopotential, is greater than for any satellite previously analysed— nearly 0.07°—and analysis of the change, using the seven PROP orbits and 45 U.S. Navy orbits, yields equations accurate to 4 per cent for the geopotential coefficients of order 15 and odd degree (15, 17, 19 …). A similar analysis of the variation in eccentricity gives less accurate equations for coefficients of order 15 and even degree (16, 18 …). The variations in right ascension of the node and argument of perigee have also been analysed.     

近地小行星(10302) 1989 ML和(4660) Nereus的轨道特征及演化分析

近地小行星(10302) 1989 ML和(4660) Nereus作为下一代深空探测的候选目标一直备受关注. 在考虑太阳系主要天体的动力学背景下, 通过计算最大Lyapunov指数(MLE)及MEGNO (Mean Exponential Growth factor of Nearby Orbits)指数讨论它们的稳定性. 同时, 对每个小行星, 在其观测误差范围内按多元正态分布各选取1000个克隆粒子, 通过统计分析显示这两个小行星在10万年内可能的运动范围, 给出半长径-偏心率空间中的出现次数分布图, 并统计小行星与地球或其他大行星之间的密近交汇及碰撞的概率. 此外还对这两个小行星的标称轨道进行长期共振、Kozai共振及平运动共振的动力学分析. 综上得出结论, 1989 ML处在平运动共振主导的区域, 发生密近交汇的概率较小, 从而其轨道相对较稳定; 而Nereus处在地球的密近交汇区域, 轨道极不稳定.     

Analysis of Orbital Characteristics and Evolution of Near-Earth Asteroids (10302) 1989 ML and (4660) Nereus

Near-Earth asteroids (10302) 1989 ML and (4660) Nereus have attracted much attention as candidates for the next generation of deep space explorations. In the study, the maximum Lyapunov exponent (MLE) and MEGNO (Mean Exponential Growth factor of Nearby Orbits) index are calculated after considering the effects of major objects in the Solar system, and the stabilities of these two asteroids are discussed. For each asteroid, 1000 clonal particles consistent with the observational uncertainties are generated from a multivariate normal distribution. Statistical results display probably emerging regions of each asteroid within 0.1 million years, and provide distributions of occurrence times in the phase space of semi-major axis versus eccentricity. We estimate the probability of close encounters and collisions between the asteroid and Earth or other planets. Furthermore, secular resonances, Kozai resonance, and mean motion resonances are analyzed for nominal orbits of the two asteroids. We conclude that 1989 ML is in the region dominated by mean motion resonances with terrestrial planets. The probability of close encounters with them is relatively small, therefore its orbit is relatively stable. Nereus is located in a region that can have close-encounters with the Earth, and it has an extremely unstable orbit.     

Spectral properties and composition of potentially hazardous Asteroid (99942) Apophis

The known close approach of Asteroid (99942) Apophis in April 2029 provides the opportunity for the case study of a potentially hazardous asteroid in advance of its encounter. The visible to near-infrared (0.55 to 2.45 μm) reflectance spectrum of Apophis is compared and modeled with respect to the spectral and mineralogical characteristics of likely meteorite analogs. Apophis is found to be an Sq-class asteroid that most closely resembles LL ordinary chondrite meteorites in terms of spectral characteristics and interpreted olivine and pyroxene abundances, although we cannot rule out some degree of partial melting. A meteorite analog allows some estimates and conjectures of Apophis' possible range of physical properties such as the grain density and micro-porosity of its constituent material. Composition and size similarities of Apophis with (25143) Itokawa suggest a total porosity of 40% as a “current best guess” for Apophis. Applying these parameters to Apophis yields a mass estimate of 2×¹⁰¹⁰ kg with a corresponding energy estimate of 375 Mt for its potential hazard. Substantial unknowns, most notably the total porosity, allow uncertainties in these mass and energy estimates to be as large as factors of two or three.     

Spectral evolution of Nova V400 Per (1974) and Nova V373 Sct (1975)

Photographic and spectroscopic observations of the two galactic novae, V400 Per and V373 Sct, which appeared in 1974 and 1975, have been carried out at Asiago. The light curves of the two novae were characterized by the presence of brightness oscillations during the early decline. The spectral evolution was quite normal: the spectra showed at first, over a relatively strong continuum, wide emission bands of moderate excitation, accompanied by blueshifted absorptions, with radial velocities of –1760 km s^–1 (Nova Per) and –1260 km s^–1 (Nova Sct). Later, after the novae entered the nebular stage, the continuum weakened, the absorption disappeared and the novae displayed the usual emission spectrum, with permitted and forbidden lines of high excitation ([Oiii], Niii, Hei, Heii). Forbidden lines of Fevi and Fevii-and in Nova Sct, also Fex and Ax-were present for a time, but they soon disappeared, so that at the end the spectrum was dominated by the [Oiii] nebular lines, even stronger than H.     

Effect of Continuum Scattering on the Statistical and Temporal Characteristics of Spectral Line Formation

Astrophysics - Some new results from our study of the effect of continuum scattering on different observed characteristics of spectral lines are presented. The main purpose is to study temporal...     

Spectral characteristics of iron-bearing phyllosilicates: Comparison to Orgueil (CI1), Murchison and Murray (CM2)

Abstract— Phyllosilicate alteration minerals are commonly found in low petrologic types of carbonaceous chondrites. Previous spectral studies have examined Mg-bearing phyllosilicates with limited success in matching the spectral properties of CM and CI chondrites. Transmission electron microscope and other analytical techniques suggest that Fe-bearing clays are more abundant in CI and CM chondrites than magnesian varieties. Here, we present the results of an examination of the reflectance spectra of Fe-phyllosilicates, including serpentines and berthierines, of which the latter were formerly known as septechlorites. We have measured the diffuse reflectance spectra of powdered samples from 0.3 to 25 μn. We find that these minerals provide a better spectral match to many of the features seen in CI and CM chondrites, and simple linear combinations of the spectra of both Fe- and Mg-phyllosilicates closely approximate the spectra of CM and CI chondrites.     

Analysis of OMEGA/Mars Express data hyperspectral data using a Multiple-Endmember Linear Spectral Unmixing Model (MELSUM): Methodology and first results

The mineralogical composition of the Martian surface is investigated by a Multiple-Endmember Linear Spectral Unmixing Model (MELSUM) of the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) imaging spectrometer onboard Mars Express. OMEGA has fully covered the surface of the red planet at medium to low resolution (2–4 km per pixel). Several areas have been imaged at a resolution up to 300 m per pixel. One difficulty in the data processing is to extract the mineralogical composition, since rocks are mixtures of several components. MELSUM is an algorithm that selects the best linear combination of spectra among the families of minerals available in a reference library. The best fit of the observed spectrum on each pixel is calculated by the same unmixing equation used in the classical Spectral Mixture Analysis (SMA). This study shows the importance of the choice of the input library, which contains in our case 24 laboratory spectra (endmembers) of minerals that cover the diversity of the mineral families that may be found on the Martian surface. The analysis is restricted to the 1.0–2.5 μm wavelength range. Grain size variations and atmospheric scattering by aerosols induce changes in overall albedo level and continuum slopes. Synthetic flat and pure slope spectra have therefore been included in the input mineral spectral endmembers library in order to take these effects into account. The selection process for the endmembers is a systematic exploration of whole set of combinations of four components plus the straight line spectra. When negative coefficients occur, the results are discarded. This strategy is successfully tested on the terrestrial Cuprite site (Nevada, USA), for which extensive ground observations exist. It is then applied to different areas on Mars including Syrtis Major, Aram Chaos and Olympia Undae near the North Polar Cap. MELSUM on Syrtis Major reveals a region dominated by mafic minerals, with the oldest crustal regions composed of a mixing between low-calcium pyroxenes (LCPs) (orthopyroxenes (OPx)) and high-calcium pyroxenes (HCPs) (clinopyroxenes (CPx)). The Syrtis volcanic edifice appears depleted in LCP (OPx) and enriched in HCP (CPx), which is consistent with materials produced with a lower partial fusion degree at an age younger to the surrounding crust. Strong olivine signatures are found between the two calderas Nili Patera and Meroe Patera and in Nili Fossae. A strong signature of iron oxides is found within Aram Chaos, with a spatial distribution also consistent with thermal emission spectrometer (TES). Gypsum is unambiguously detected in the northern polar region, in agreement with the study of Langevin et al. [2005. Sulfates in the north polar region of Mars detected by OMEGA/Mars Express. Science 307(5715), 1584–1586]. Our results show that the linear spectral unmixing provides good first order results in a variety of mineralogical contexts, and can therefore confidently be used on a wider scale to analyze the complete archive of OMEGA data.     

First occurrence of pyrophanite (MnTi03) and baddeleyite (ZrO2) in an ordinary chondrite

Abstract A 220 × 430 μm Mg-Al-chromite fragment in the Raguli H3.8 ordinary chondrite exhibits distinct optical and compositional zoning. The dark central region of the Mg-Al-chromite is enriched in MgO, Al₂O₃ and ZnO and depleted in TiO₂, Cr₂O₃, FeO and MnO relative to the lighter outer region. A subhedral olivine grain attached to radiating euhedral ilmenites is present in the central region of the fragment. One of the ilmenite crystals contains a tiny grain (0.5 × 5.8 μm) of baddeleyite (ZrO₂). Two end-member pyrophanite grains (MnTiO₃) occur in the outer portion of the fragment This is the first occurrence of pyrophanite and baddeleyite in an ordinary chondrite. Although it is possible that the Mg-Al-chromite fragment was derived from an achondritic projectile of unusual composition, we offer two alternative models for its formation. These include (a) a multi-stage process involving nebular melting of a chromian-spinel chondrule that had accreted some olivine-bearing, Mn-rich material followed by metamorphism on the parent body, and (b) formation of the fragment on a metamorphosed parent body from an impact melt of a chromite-rich assemblage containing Mn-rich ilmenite. We favor the latter alternative.     

LAMOST Medium-Resolution Spectral Survey of Galactic Nebulae(LAMOST MRS-N):An overview of scientific goals and survey plan

Since Sep.2018,LAMOST has started the medium-resolution(R～7500) spectral survey(MRS).We proposed the spectral survey of Galactic nebulae,including H Ⅱ regions,HH objects,supernova remnants,planetary nebulae and the special stars with MRS(LAMOST MRS-N).LAMOST MRS-N covers about 1700 square degrees of the northern Galactic plane within 40°l215° and-5° b5°.In this 5-year survey,we plan to observe about 500 thousand nebulae spectra.According to the commissioning observations,the nebulae spectra can provide precise radial velocity with uncertainty less than 1 km s~(-1).These high-precision spectral data are of great significance to our understanding of star formation and evolution.     

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Optimization of the Spectral Line Inversion Code

The Very Fast Inversion of the Stokes Vector (VFISV) is a Milne–Eddington spectral line inversion code used to determine the magnetic and thermodynamic parameters of the solar photosphere from observations of the Stokes vector in the 6173 Å Fe i line by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We report on the modifications made to the original VFISV inversion code in order to optimize its operation within the HMI data pipeline and provide the smoothest solution in active regions. The changes either sped up the computation or reduced the frequency with which the algorithm failed to converge to a satisfactory solution. Additionally, coding bugs which were detected and fixed in the original VFISV release are reported here.     

The Surface Structure of the M-Type Asteroid 21 Lutetia: Spectral and Frequency Analysis

A preliminary study of the surface of the asteroid 21 Lutetia with ground-based methods is of significant importance, because this object is included into the Rosetta space mission schedule. From August 31 to November 20, 2000, about 50 spectra of Lutetia and the same number of spectra of the solar analog HD10307 (G2V) and regional standards were obtained with a resolution of 4 and 3 nm at the MTM-500 telescope television system of the Crimean astrophysical observatory. From these data, the synthetic magnitudes of the asteroid in the BRV color system have been obtained, the reflected light fluxes have been determined in absolute units, and its reflectance spectra have been calculated for a range of 370–740 nm. In addition, from the asteroid reflectance spectra obtained at different rotation phases, the values of the equivalent width of the most intensive absorption band centered at 430–440 nm and attributed to hydrosilicates of the serpentine type have been calculated. A frequency analysis of the values V(1, 0) confirmed the rotation period of Lutetia 0.^d3405 (8.^h172) and showed a two-humped light curve with a maximal amplitude of 0.^m25. The color indices B-V and V-R showed no noticeable variations with this period. A frequency analysis of the equivalent widths of the absorption band of hydrosilicates near 430–440 nm points to the presence of many significant frequencies, mainly from 15 to 20 c/d (c/d is the number of cycles per day), which can be caused by a heterogeneous distribution of hydrated material on the surface of Lutetia. The sizes of these heterogeneities (or spots) on the asteroid surface have been estimated at 3–5 to 70 km with the most frequent value between 30 and 40 km.     

Analysis of the Distribution,Rotation and Scale Characteristics of Solar Wind Switchbacks:Comparison between the First and Second Encounters of Parker Solar Probe

The S-shaped magnetic structure in the solar wind formed by the twisting of magnetic field lines is called a switchback,whose main characteristics are the rever...