Time dependent accretion onto a black hole in a disk plus corona system

Hard X-ray lightcurves exhibit delays of 1 s with respect to the soft X-ray lightcurves when the microquasar GRS 1915+105 is in the state of frequent, regular outbursts. Such outbursts are supposed to be driven by the radiation pressure instability of the inner disk parts. The hard X-ray delays are then caused by the time needed for the adjustment of the corona to changing conditions in the underlying disk. We support this claim by the computation of the time evolution of the disk, including a non-stationary evaporation of the disk and mass exchange with the corona.     

Magnetohydrodynamics in solar and space physics

Because of its proximity, our Sun provides a unique opportunity to perform high resolution observations of its outer layers throughout the whole electromagnetic spectrum. We can also theoretically model most of the fascinating physical phenomena taking place on the Sun, as well as their impact on the solar system.     

ICMEs in the Outer Heliosphere and at High Latitudes: An Introduction

Interplanetary coronal mass ejections (ICMEs) are observed at all latitudes and distances from which data are available. We discuss the radial evolution of ICMEs out to large distances and ICME properties at high latitudes. The internal pressure of ICMEs initially exceeds the ambient solar wind pressure and causes the ICMEs to expand in radial width to about 15~AU. Large ICMEs and series of ICMEs compress the leading plasma and form merged interaction regions (MIRs) which dominate the structure of the outer heliosphere at solar maximum. The distribution of high-latitude ICMEs is solar cycle dependent. A few overexpanding ICMEs are observed at high-latitude near solar minimum. Near solar maximum ICMEs are observed at all latitudes, but those above 40° do not have high charge states.     

The Strength and Structure of the Coronal Magnetic Field

I discuss a method for determining the strength and spatial structure of the coronal magnetic field by observations of the Faraday rotation of a radio galaxy which is in conjunction with the Sun. Given a knowledge of the plasma density in the outer corona, and the magnetic field sector structure (both independently available), the strength of the coronal field can be determined, as well as the magnitude of spatial variations on scales of 1000 km to several solar radii. Such knowledge is crucial for testing computational models of the solar corona, which are prominently featured in this meeting. Results are presented from observations with the Very Large Array radio telescope of the radio galaxy 3C228 on August 16, 2003, when the line of sight to the source was at heliocentic distances of 7.1−6.2R _⊙. The observations are consistent with a coronal magnetic field which is proportional to the inverse square of the distance in the range 6 ≤ r ≤ 10R _⊙, and has a value of 39 mG at 6.2R _⊙. The Faraday rotation is uniform across the source, indicating an absence of strong plasma inhomogeneity on spatial scales up to 35,000 km.     

Two sources of magnetosheath ions observed by Cluster in the mid-altitude polar cusp

Double cusps have been observed on a few occasions by polar orbiting spacecraft and ground-based observatories. The four Cluster spacecraft observed two distinct regions, showing characteristics of a double cusp, during a mid-altitude cusp pass on 7 August 2004. The Wind spacecraft detected a southward turning of the Interplanetary Magnetic Field (IMF) at the beginning of the cusp crossings and IMF–Bz stayed negative throughout. Cluster 4 observed a high energy step in the ion precipitation around 1 keV on the equatorward side of the cusp and a dense ion population in the cusp centre. Cluster 1, entering the cusp around 1 min later, observed only a partial ion dispersion with a low energy cutoff reaching 100 eV, together with the dense ion population in the cusp centre. About 9 min later, Cluster 3 entered the cusp and observed full ion dispersion from a few keV down to around 50 eV, together with the dense ion population in the centre of the cusp. The ion flow was directed poleward and eastward in the step/dispersion, whereas in the centre of the cusp the flow was directed poleward and westward. In addition the altitude of the source region of ion injection in the step/dispersion was found 50% larger than in the cusp centre. This event could be explained by the onset of dayside reconnection when the IMF turned southward. The step would be the first signature of component reconnection near the subsolar point, and the injection in the centre of the cusp a result of anti-parallel reconnection in the northern dusk side of the cusp. A three-dimensional magnetohydrodynamic (MHD) simulation is used to display the topology of the magnetic field and locate the sources of the ions during the event.     

Spatial distribution and orbital properties of interplanetary dust at high latitudes

Although the interplanetary dust cloud is assumed to be mainly concentrated in the ecliptic plane, there is a component of dust particles on highly inclined orbits that forms the out-of-ecliptic distribution. The ULYSSES mission for the first time makes this component accessible to in-situ, detection. Evidence for this dust component is also provided from the analysis of the Zodiacal light brightness and especially from the spherical shape of the solar F — corona. An obvious source for an out-of-ecliptic dust population is the activity of comets on high eccentric, highly inclined orbits. We discuss the dynamical conditions of particles under the influence of the radiation pressure when released from the comet and discuss their input to the dust cloud based on brightness analysis and in-situ results.     

Space weather service activities and initiatives at LAMP (Argentinean Space Weather Laboratory group)

Since more than one decade ago, several institutions started to offer a large variety of Operative Space Weather (SWx) products. This is of major importance because Space Weather events can affect aviation communications, global positioning systems, grid electric power, satellite technologies, and human health in space. The scientific potential on solar-terrestrial physics in Argentina motivated the creation of an interdisciplinary Laboratory of Space Weather in Argentina. The Argentinean Space Weather Laboratory (in Spanish ‘Laboratorio Argentino de Meteorología del esPacio’, LAMP) was initiated in 2016, and it carries out daily monitoring of real-time information (space and ground-based instruments) on Space Weather. The information is synthesized on a weekly bulletin as a summary of the Space Weather conditions, and it is posted on a website (spaceweather.at.fcen.uba.ar). The analyzed information includes own data and of other centers that offer them publicly, and it is also analyzed and discussed later on, during monthly briefings. In particular, one of the regional products that is included in the briefing discussions and it was developed by LAMP in collaboration with INPE-EMBRACE, involves Vertical Total Electron Content (VTEC) maps in the Argentinean region. LAMP set up a Space Weather Laboratory in the Antarctic peninsula, in the Argentine Marambio base, where a Water Cherenkov radiation Detector (WCD) was installed during the Argentinean Antarctic campaign (January-March of 2019). This detector is the southern node of a Latin American Collaboration (LAGO, Latin American Giant Observatory), which is a network of WCDs installed throughout more than 10 Latin American countries.     

Two successive partial mini-filament confined ejections

Active region (AR) NOAA 11476 produced a series of confined plasma ejections, mostly accompanied by flares of X-ray class M, from 08 to 10 May 2012. The structure and evolution of the confined ejections resemble that of EUV surges; however, their origin is associated to the destabilization and eruption of a mini-filament, which lay along the photospheric inversion line (PIL) of a large rotating bipole. Our analysis indicate that the bipole rotation and flux cancellation along the PIL have a main role in destabilizing the structure and triggering the ejections. The observed bipole emerged within the main following AR polarity. Previous studies have analyzed and discussed in detail two events of this series in which the mini-filament erupted as a whole, one at 12:23 UT on 09 May and the other at 04:18 UT on 10 May. In this article we present the observations of the confined eruption and M4.1 flare on 09 May 2012 at 21:01 UT (SOL2012-05-09T21:01:00) and the previous activity in which the mini-filament was involved. For the analysis we use data in multiple wavelengths (UV, EUV, X-rays, and magnetograms) from space instruments. In this particular case, the mini-filament is seen to erupt in two different sections. The northern section erupted accompanied by a C1.6 flare and the southern section did it in association with the M4.1 flare. The global structure and direction of both confined ejections and the location of a far flare kernel, to where the plasma is seen to flow, suggest that both ejections and flares follow a similar underlying mechanism.     

飞向晕轨道的探测器轨道优化

晕轨道的稳定流形为从地球到晕轨道的转移轨道设计提供了便利．以往都采用在晕轨道上的目标点施加脉冲,这样,稳定流形只是为转移轨道的设计提供一个初始猜想,探测器并没有运行在稳定流形上,因而并未真正利用稳定流形节省燃料的优势．利用基于序优化理论的微分修正法,研究从晕轨道近地点稳定流形上不同点进入稳定流形所需要的燃料消耗,寻找燃耗最少的转移轨道．仿真表明,对于晕轨道近地点入轨,找到的稳定流形射入点机动比以往的晕轨道入轨点机动节省约33％的燃料消耗．此外,还对晕轨道上不同入轨点的入轨代价进行了研究,得到了晕轨道近地点入轨的最小燃耗解．     

行星际小推力轨道Lambert解及应用

 为提高行星际小推力转移轨道初始设计精度,提出了基于N次逆多项式逼近的半解析Lambert算法,并基于该算法发展了一种转移轨道初始设计方法。首先,采用N次逆多项式近似小推力轨道形状,应用推力方向假设和位置速度边界条件推导出部分系数及推力大小解析式。接着,分析了飞行时间约束和轨道动力学约束下解的存在性,并给出了关键系数的可行域。然后,利用探测器质量消耗方程建立了Lambert问题求解模型并加以解决。最后,基于所提Lambert算法,通过对连续推力约束进行降维,提出一种求解多圈非固定时间的行星际小推力转移轨道初始设计方法。分别以固定和非固定时间转移任务为例对所提Lambert算法和初始轨道设计方法进行了数学仿真,数值结果表明：相比传统6阶方法,所提Lambert算法在目标轨道半长轴为5 AU时可减少速度增量需求36.63%;所提初始设计方法与最优化方法设计结果接近,可为转移轨道的精确设计提供可行的设计初值。