1
|
Uga CI, Gautam SP, Seba EB. TEC disturbances caused by CME-triggered geomagnetic storm of September 6-9, 2017. Heliyon 2024; 10:e30725. [PMID: 38784557 PMCID: PMC11112271 DOI: 10.1016/j.heliyon.2024.e30725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Revised: 05/02/2024] [Accepted: 05/02/2024] [Indexed: 05/25/2024] Open
Abstract
This study investigates the ionospheric response to a geomagnetic storm triggered by a Coronal Mass Ejection (CME) during 6-9 September 2017, across GPS stations located in diverse geographical regions. We analyze the changes in the magnetic field component (ΔH), the Prompt Penetration Electric Fields (PPEF), and the Total Electron Content (TEC). We find that ΔH exhibits latitude-dependent responses during the storm, with high-latitude stations experiencing more significant reductions compared to low-latitude stations. The PPEF behavior is found to be directly correlated with solar wind disturbances. Particularly during the main phase of the storm, fluctuations in PPEF were clearly associated with negative values in the Dst index. The KIRU station, located at a high latitude, shows the most pronounced PPEF effects, indicating the increased susceptibility of high-latitude regions to solar wind interactions. The time series plot of TEC, covering a full month at different stations, shows a distinct diurnal pattern driven by solar ionization. Equatorial stations such as HYDE, BOU, HON (HNLC), and DODM exhibit the highest daily TEC values. During the geomagnetic storm, TEC disturbances are evident across all stations, with significant disturbances and varying trends in TEC depletion rate observed at different locations. The TEC values differ by 5-25 TECU during the storm period, suggesting intricate ionospheric responses to geomagnetic storms at different stations. This highlights the importance of considering different geographical regions to fully understand the ionospheric dynamics related to solar activities.
Collapse
Affiliation(s)
- Chali Idosa Uga
- Jimma University, College of Natural and Computational Science, Department of Physics, Jimma, Ethiopia
- University of Alabama in Huntsville, Department of Space Science, Huntsville, AL, United States
| | - Sujan Prasad Gautam
- University of Alabama in Huntsville, Department of Space Science, Huntsville, AL, United States
| | - Ephirem Beshir Seba
- Ethiopian Space Science and Geospatial Institute, Department of Space Science and Research Application, Addis Ababa, Ethiopia
- KU Leuven, Department Wiskunde, Centre for Mathematical Plasma-Astrophysics, Leuven, Belgium1
| |
Collapse
|
2
|
Dai L, Zhu M, Ren Y, Gonzalez W, Wang C, Sibeck D, Samsonov A, Escoubet P, Tang B, Zhang J, Branduardi-Raymont G. Global-scale magnetosphere convection driven by dayside magnetic reconnection. Nat Commun 2024; 15:639. [PMID: 38245508 PMCID: PMC10799867 DOI: 10.1038/s41467-024-44992-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2023] [Accepted: 01/11/2024] [Indexed: 01/22/2024] Open
Abstract
Plasma convection on a global scale is a fundamental feature of planetary magnetosphere. The Dungey cycle explains that steady-state convection within the closed part of the magnetosphere relies on magnetic reconnection in the nightside magnetospheric tail. Nevertheless, time-dependent models of the Dungey cycle suggest an alternative scenario where magnetospheric convection can be solely driven by dayside magnetic reconnection. In this study, we provide direct evidence supporting the scenario of dayside-driven magnetosphere convection. The driving process is closely connected to the evolution of Region 1 and Region 2 field-aligned currents. Our global simulations demonstrate that intensified magnetospheric convection and field-aligned currents progress from the dayside to the nightside within 10-20 minutes, following a southward turning of the interplanetary magnetic field. Observational data within this short timescale also reveal enhancements in both magnetosphere convection and the ionosphere's two-cell convection. These findings provide insights into the mechanisms driving planetary magnetosphere convection, with implications for the upcoming Solar-Wind-Magnetosphere-Ionosphere Link Explorer (SMILE) mission.
Collapse
Affiliation(s)
- Lei Dai
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China.
| | - Minghui Zhu
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
| | - Yong Ren
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
| | - Walter Gonzalez
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
- National Institute for Space Research (INPE), São José dos Campos, São Paulo, Brazil
| | - Chi Wang
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
| | - David Sibeck
- Goddard Space Flight Center, NASA, Greenbelt, US
| | - Andrey Samsonov
- Mullard Space Science Laboratory, University College London, Dorking, UK
| | - Philippe Escoubet
- European Space Research and Technology Centre, European Space Agency (ESA), Noordwijk, Netherlands
| | - Binbin Tang
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
| | - Jiaojiao Zhang
- National Space Science Center, Chinese Academy of Sciences, Beijing, 100190, China
| | | |
Collapse
|
3
|
Dagnall N, Drinkwater KG, O’Keeffe C, Ventola A, Laythe B, Jawer MA, Massullo B, Caputo GB, Houran J. Things That Go Bump in the Literature: An Environmental Appraisal of "Haunted Houses". Front Psychol 2020; 11:1328. [PMID: 32595577 PMCID: PMC7304295 DOI: 10.3389/fpsyg.2020.01328] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Accepted: 05/19/2020] [Indexed: 01/05/2023] Open
Abstract
This paper contains a narrative overview of the past 20-years of environmental research on anomalous experiences attributed to "haunted house." This exercise served as a much-needed update to an anthology of noteworthy overviews on ghosts, haunts, and poltergeists (Houran and Lange, 2001b). We also considered whether new studies had incorporated certain recommendations made in this anthology. Our search revealed a relative paucity of studies (n = 66) on environmental factors that ostensibly stimulate haunt-type experiences. This literature was diverse and often lacked methodological consistency and adherence to the prior suggestions. However, critical consideration of the content revealed a recurring focus on six ambient variables: embedded (static) cues, lighting levels, air quality, temperature, infrasound, and electromagnetic fields. Their relation to the onset or structure of witness reports showed mostly null, though sometimes inconsistent or weak outcomes. However, such research as related to haunts is arguably in its infancy and new designs are needed to account better for environmental and architectural phenomenology. Future studies should therefore address four areas: (i) more consistent and precise measurements of discrete ambient variables; (ii) the potential role of "Gestalt influences" that involve holistic environment-person interactions; (iii) individual differences in attentional or perceptual sensitivities of percipients to environmental variables; and (iv) the role of attitudinal and normative influences in the interpretation of environmental stimuli. Focused scrutiny on these issues should clarify the explanatory power of evolutionary-environmental models for these and related anomalous experiences.
Collapse
Affiliation(s)
- Neil Dagnall
- Department of Psychology, Manchester Campus, Manchester Metropolitan University, Manchester, United Kingdom
| | - Kenneth G. Drinkwater
- Department of Psychology, Manchester Campus, Manchester Metropolitan University, Manchester, United Kingdom
| | - Ciarán O’Keeffe
- School of Human & Social Sciences, Buckinghamshire New University, Buckinghamshire, United Kingdom
| | | | - Brian Laythe
- Institute for the Study of Religious and Anomalous Experience, Jeffersonville, IN, United States
| | | | | | | | - James Houran
- Laboratory for Statistics and Computation, ISLA—Instituto Politécnico de Gestão e Tecnologia, Vila Nova de Gaia, Portugal
- Integrated Knowledge Systems, Dallas, TX, United States
| |
Collapse
|
4
|
He F, Guo RL, Dunn WR, Yao ZH, Zhang HS, Hao YX, Shi QQ, Rong ZJ, Liu J, Tian AM, Zhang XX, Wei Y, Zhang YL, Zong QG, Pu ZY, Wan WX. Plasmapause surface wave oscillates the magnetosphere and diffuse aurora. Nat Commun 2020; 11:1668. [PMID: 32245960 PMCID: PMC7125146 DOI: 10.1038/s41467-020-15506-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 03/16/2020] [Indexed: 11/09/2022] Open
Abstract
Energy circulation in geospace lies at the heart of space weather research. In the inner magnetosphere, the steep plasmapause boundary separates the cold dense plasmasphere, which corotates with the planet, from the hot ring current/plasma sheet outside. Theoretical studies suggested that plasmapause surface waves related to the sharp inhomogeneity exist and act as a source of geomagnetic pulsations, but direct evidence of the waves and their role in magnetospheric dynamics have not yet been detected. Here, we show direct observations of a plasmapause surface wave and its impacts during a geomagnetic storm using multi-satellite and ground-based measurements. The wave oscillates the plasmapause in the afternoon-dusk sector, triggers sawtooth auroral displays, and drives outward-propagating ultra-low frequency waves. We also show that the surface-wave-driven sawtooth auroras occurred in more than 90% of geomagnetic storms during 2014-2018, indicating that they are a systematic and crucial process in driving space energy dissipation.
Collapse
Affiliation(s)
- Fei He
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| | - Rui-Long Guo
- Laboratoire de Physique Atmosphérique et Planétaire, STAR Institute, Université de Liège, Liège, B-4000, Belgium
| | - William R Dunn
- Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Holmbury St Mary, Dorking, RH5 6NT, UK
| | - Zhong-Hua Yao
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| | - Hua-Sen Zhang
- Institute of Applied Physics and Computational Mathematics, Beijing, 100088, China
| | - Yi-Xin Hao
- Institute of Space Physics and Applied Technology, Peking University, Beijing, 100871, China
| | - Quan-Qi Shi
- School of Space Science and Physics, Shandong University, Weihai, 264209, China
| | - Zhao-Jin Rong
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| | - Jiang Liu
- Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA, 90095, USA
| | - An-Min Tian
- School of Space Science and Physics, Shandong University, Weihai, 264209, China
| | - Xiao-Xin Zhang
- Key Laboratory of Space Weather, National Center for Space Weather, China Meteorological Administration, Beijing, 100081, China.
| | - Yong Wei
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China.
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China.
| | - Yong-Liang Zhang
- Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
| | - Qiu-Gang Zong
- Institute of Space Physics and Applied Technology, Peking University, Beijing, 100871, China
| | - Zu-Yin Pu
- Institute of Space Physics and Applied Technology, Peking University, Beijing, 100871, China
| | - Wei-Xing Wan
- Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, 100029, China
- Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing, 100029, China
| |
Collapse
|
5
|
Borovsky JE, Valdivia JA. The Earth's Magnetosphere: A Systems Science Overview and Assessment. SURVEYS IN GEOPHYSICS 2018; 39:817-859. [PMID: 30956375 PMCID: PMC6428226 DOI: 10.1007/s10712-018-9487-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2018] [Accepted: 07/07/2018] [Indexed: 05/20/2023]
Abstract
A systems science examination of the Earth's fully interconnected dynamic magnetosphere is presented. Here the magnetospheric system (a.k.a. the magnetosphere-ionosphere-thermosphere system) is considered to be comprised of 14 interconnected subsystems, where each subsystem is a characteristic particle population: 12 of those particle populations are plasmas and two (the atmosphere and the hydrogen geocorona) are neutrals. For the magnetospheric system, an assessment is made of the applicability of several system descriptors, such as adaptive, nonlinear, dissipative, interdependent, open, irreversible, and complex. The 14 subsystems of the magnetospheric system are cataloged and described, and the various types of magnetospheric waves that couple the behaviors of the subsystems to each other are explained. This yields a roadmap of the connectivity of the magnetospheric system. Various forms of magnetospheric activity beyond geomagnetic activity are reviewed, and four examples of emergent phenomena in the Earth's magnetosphere are presented. Prior systems science investigations of the solar-wind-driven magnetospheric system are discussed: up to the present these investigations have not accounted for the full interconnectedness of the system. This overview and assessment of the Earth's magnetosphere hopes to facilitate (1) future global systems science studies that involve the entire interconnected magnetospheric system with its diverse time and spatial scales and (2) connections of magnetospheric systems science with the broader Earth systems science.
Collapse
Affiliation(s)
- Joseph E. Borovsky
- Center for Space Plasma Physics, Space Science Institute, Boulder, CO 80301 USA
| | | |
Collapse
|
6
|
Lotko W, Smith RH, Zhang B, Ouellette JE, Brambles OJ, Lyon JG. Space weather. Ionospheric control of magnetotail reconnection. Science 2014; 345:184-7. [PMID: 25013068 DOI: 10.1126/science.1252907] [Citation(s) in RCA: 64] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail.
Collapse
Affiliation(s)
- William Lotko
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA. Research Affiliate, High Altitude Observatory, National Center for Atmospheric Research, Boulder, CO, USA.
| | - Ryan H Smith
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Binzheng Zhang
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Jeremy E Ouellette
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA. Department of Computer and Information Systems, Vermont Technical College, Randolph Center, VT, USA
| | | | - John G Lyon
- Department of Physics and Astronomy, Dartmouth College, Hanover, NH, USA
| |
Collapse
|
7
|
Responses of the magnetotail plasma sheet to two interplanetary shocks: TC-1 observations. CHINESE SCIENCE BULLETIN-CHINESE 2009. [DOI: 10.1007/s11434-009-0345-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
|
8
|
Behravesh E, Emami K, Wu H, Gonda S. Comparison of genotoxic damage in monolayer cell cultures and three-dimensional tissue-like cell assemblies. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 2005; 35:260-7. [PMID: 15934204 DOI: 10.1016/j.asr.2005.01.066] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Assessing the biological risks associated with exposure to the high-energy charged particles encountered in space is essential for the success of long-term space exploration. Although prokaryotic and eukaryotic cell models developed in our laboratory and others have advanced our understanding of many aspects of genotoxicity, in vitro models are needed to assess the risk to humans from space radiation insults. Such models must be representative of the cellular interactions present in tissues and capable of quantifying genotoxic damage. Toward this overall goal, the objectives of this study were to examine the effect of the localized microenvironment of cells, cultured as either 2-dimensional (2D) monolayers or 3-dimensional (3D) aggregates, on the rate and type of genotoxic damage resulting from exposure to Fe-charged particles, a significant portion of space radiation. We used rodent transgenic cell lines containing 50-70 copies of a LacI transgene to provide the enhanced sensitivity required to quantify mutational frequency and type in the 1100-bp LacI target as well as assessment of DNA damage to the entire 45-kbp construct. Cultured cells were exposed to high energy Fe charged particles at Brookhaven National Laboratory's Alternating Gradient Synchrotron facility for a total dose ranging from 0.1 to 2 Gy and allowed to recover for 0-7 days, after which mutational type and frequency were evaluated. The mutational frequency was found to be higher in 3D samples than in 2D samples at all radiation doses. Mutational frequency also was higher at 7 days after irradiation than immediately after exposure. DNA sequencing of the mutant targets revealed that deletional mutations contributed an increasingly high percentage (up to 27%) of all mutations in cells as the dose was increased from 0.5 to 2 Gy. Several mutants also showed large and complex deletions in multiple locations within the LacI target. However, no differences in mutational type were found between the 2D and the 3D samples. These 3D tissue-like model systems can reduce the uncertainty involved in extrapolating risk between in vitro cellular and in vivo models.
Collapse
Affiliation(s)
- E Behravesh
- Division of Space and Life Sciences, Universities Space Research Association, Houston, TX 77058, USA.
| | | | | | | |
Collapse
|
9
|
Persinger MA. Geophysical variables and behavior: XCVIII. Ambient geomagnetic activity and experiences of "memories": interactions with sex and implications for receptive psi experiences. Percept Mot Skills 2002; 94:1271-82. [PMID: 12186249 DOI: 10.2466/pms.2002.94.3c.1271] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
During 96 nonsequential days over a 3-yr. period, a total of 53 men and 86 women were exposed only once for 30 min. to transcerebral, weak complex magnetic fields while they sat alone within a quiet chamber. They were asked to record the frequency of specific experiences after the exposure was completed. There was a significant interaction between sex and global geomagnetic activity for the incidence of experiences attributed to memories. Women reported more experiences attributed to "childhood memories" when geomagnetic activity was less than 20 nT, while men reported more of these experiences when the activity was more than 20 nT. Re-analyses of a database of "paranormal experiences" reported by 395 separate individuals over a 100-yr. period indicated that more men than women reported "precognitive experiences" on days the geomagnetic activity was above 20 nT while women reported such experiences if the geomagnetic activity was below 20 nT. These results suggest that these experiences, be they veridical or illusory, may be influenced by global geomagnetic activity that affect the neuroelectrical or neurochemical processes associated with memory consolidation or the attribution of the serial order of experiences during retrieval.
Collapse
Affiliation(s)
- M A Persinger
- Department of Psychology, Laurentian University, Sudbury, Ontario, Canada
| |
Collapse
|
10
|
PERSINGER MA. GEOPHYSICAL VARIABLES AND BEHAVIOR: XCVIII. AMBIENT GEOMAGNETIC ACTIVITY AND EXPERIENCES OF 'MEMORIES': INTERACTIONS WITH SEX AND IMPLICATIONS FOR RECEPTIVE PSI EXPERIENCES. Percept Mot Skills 2002. [DOI: 10.2466/pms.94.2.1271-1282] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
11
|
PERSINGER MA. GEOPHYSICAL VARIABLES AND BEHAVIOR: XCVIII. AMBIENT GEOMAGNETIC ACTIVITY AND EXPERIENCES OF 'MEMORIES': INTERACTIONS WITH SEX AND IMPLICATIONS FOR RECEPTIVE PSI EXPERIENCES. Percept Mot Skills 2002. [DOI: 10.2466/pms.94.3.1271-1282] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
12
|
Sitnov MI, Sharma AS, Papadopoulos K, Vassiliadis D. Modeling substorm dynamics of the magnetosphere: from self-organization and self-organized criticality to nonequilibrium phase transitions. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2002; 65:016116. [PMID: 11800745 DOI: 10.1103/physreve.65.016116] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/09/2001] [Revised: 07/12/2001] [Indexed: 05/23/2023]
Abstract
Earth's magnetosphere during substorms exhibits a number of characteristic features such as the signatures of low effective dimension, hysteresis, and power-law spectra of fluctuations on different scales. The largest substorm phenomena are in reasonable agreement with low-dimensional magnetospheric models and in particular those of inverse bifurcation. However, deviations from the low-dimensional picture are also quite considerable, making the nonequilibrium phase transition more appropriate as a dynamical analog of the substorm activity. On the other hand, the multiscale magnetospheric dynamics cannot be limited to the features of self-organized criticality (SOC), which is based on a class of mathematical analogs of sandpiles. Like real sandpiles, during substorms the magnetosphere demonstrates features, that are distinct from SOC and are closer to those of conventional phase transitions. While the multiscale substorm activity resembles second-order phase transitions, the largest substorm avalanches are shown to reveal the features of first-order nonequilibrium transitions including hysteresis phenomena and a global structure of the type of a temperature-pressure-density diagram. Moreover, this diagram allows one to find a critical exponent, that reflects the multiscale aspect of the substorm activity, different from the power-law frequency and scale spectra of autonomous systems, although quite consistent with second-order phase transitions. In contrast to SOC exponents, this exponent relates input and output parameters of the magnetosphere. Using an analogy to the dynamical Ising model in the mean-field approximation, we show the connection between the data-derived exponent of nonequilibrium transitions in the magnetosphere and the standard critical exponent beta of equilibrium second-order phase transitions.
Collapse
Affiliation(s)
- M I Sitnov
- Department of Astronomy, University of Maryland at College Park, College Park, Maryland 20742, USA
| | | | | | | |
Collapse
|