J. C. Raymond

Towson University, Maryland, United States

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Publications (671)2020.82 Total impact

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    ABSTRACT: Plasma in the Sun's hot corona expands into the heliosphere as a supersonic and highly magnetized solar wind. This paper provides an overview of our current understanding of how the corona is heated and how the solar wind is accelerated. Recent models of magnetohydrodynamic turbulence have progressed to the point of successfully predicting many observed properties of this complex, multi-scale system. However, it is not clear whether the heating in open-field regions comes mainly from the dissipation of turbulent fluctuations that are launched from the solar surface, or whether the chaotic "magnetic carpet" in the low corona energizes the system via magnetic reconnection. To help pin down the physics, we also review some key observational results from ultraviolet spectroscopy of the collisionless outer corona.
    12/2014;
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    ABSTRACT: We investigate seven eruptive plasma observations by Hinode/XRT. Their corresponding EUV and/or white light CME features are visible in some events. Five events are observed in several passbands in X-rays, which allows the determination of the eruptive plasma temperature using a filter ratio method. We find that the isothermal temperatures vary from 1.6 to 10 MK. These temperatures are an average weighted toward higher temperature plasma. We determine the mass constraints of eruptive plasmas by assuming simplified geometrical structures of the plasma with isothermal plasma temperatures. This method provides an upper limit to the masses of the observed eruptive plasmas in X-ray passbands since any clumping causes the overestimation of the mass. For the other two events, we assume the temperatures are at the maximum temperature of the XRT temperature response function, which gives a lower limit of the masses. We find that the masses in XRT, ~3x10 13 - 5x10 14 g, are smaller in their upper limit than total masses obtained by LASCO, ~1x10 15 g. In addition, we estimate the radiative loss, thermal conduction, thermal, and kinetic energies of the eruptive plasma in X-rays. For four events, we find that the thermal conduction time scales are much shorter than the duration of eruption. This result implies that additional heating during the eruption may be required to explain the plasma observations in X-rays for the four events.
    11/2014;
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    ABSTRACT: Magnetic reconnection is believed to be the dominant energy release mechanism in solar flares. The standard flare model predicts both downward and upward outflow plasmas with speeds close to the coronal Alfv\'{e}n speed. Yet, spectroscopic observations of such outflows, especially the downflows, are extremely rare. With observations of the newly launched Interface Region Imaging Spectrograph (IRIS), we report the detection of greatly redshifted ($\sim$125 km s$^{-1}$ along line of sight) Fe {\sc{xxi}} 1354.08\AA{} emission line with a $\sim$100 km s$^{-1}$ nonthermal width at the reconnection site of a flare. The redshifted Fe {\sc{xxi}} feature coincides spatially with the loop-top X-Ray source observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We interpret this large redshift as the signature of downward-moving reconnection outflow/hot retracting loops. Imaging observations from both IRIS and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) also reveal the eruption and reconnection processes. Fast downward-propagating blobs along these loops are also found from cool emission lines (e.g., Si {\sc{iv}}, O {\sc{iv}}, C {\sc{ii}}, Mg {\sc{ii}}) and images of AIA and IRIS. Furthermore, the entire Fe {\sc{xxi}} line is blueshifted by $\sim$260 km s$^{-1}$ at the loop footpoints, where the cool lines mentioned above all exhibit obvious redshift, a result that is consistent with the scenario of chromospheric evaporation induced by downward-propagating nonthermal electrons from the reconnection site.
    11/2014;
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    ABSTRACT: Comet C/2002 S2, a member of the Kreutz family of Sungrazing comets, was discovered in white light images of the SOHO/LASCO coronagraph on 2002 September 18 and observed in \hi\, \lya\, emission by the SOHO/UVCS instrument at four different heights as it approached the Sun. The \hi\, \lya\, line profiles detected by UVCS are analyzed to determine the spectral parameters: line intensity, width and Doppler shift with respect to the coronal background. Two dimensional comet images of these parameters are reconstructed at the different heights. A novel aspect of the observations of this sungrazing comet data is that, whereas the emission from the most of the tail is blue--shifted, that along one edge of the tail is red--shifted. We attribute these shifts to a combination of solar wind speed and interaction with the magnetic field. In order to use the comet to probe the density, temperature and speed of the corona and solar wind through which it passes, as well as to determine the outgassing rate of the comet, we develop a Monte Carlo simulation of the \hi\, \lya\, emission of a comet moving through a coronal plasma. From the outgassing rate, we estimate a nucleus diameter of about 9 meters. This rate steadily increases as the comet approaches the Sun while the optical brightness decreases by more than a factor of ten and suddenly recovers. This indicates that the optical brightness is determined by the lifetimes of the grains, sodium atoms and molecules produced by the comet.
    11/2014;
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    ABSTRACT: We obtained UV spectra of X-ray binary Scorpius X-1 in the 900-1200 A range with the Far Ultraviolet Spectroscopic Explorer over the full 0.79 day binary orbit. The strongest emission lines are the doublet of O VI at 1032,1038 A and the C III complex at 1175 A. The spectrum is affected by a multitude of narrow interstellar absorption lines, both atomic and molecular. Examination of line variability and Doppler tomograms suggests emission from both the neighborhood of the donor star and the accretion disk. Models of turbulence and Doppler broadened Keplerian disk lines Doppler shifted with the orbit of the neutron star added to narrow Gaussian emission lines with undetermined Doppler shift fit the data with consistent values of disk radius, inclination, and radial line brightness profile. The Doppler shift of the narrow component with the orbit suggests an association with the donor star. We test our line models with previously analyzed near UV spectra obtained with the Hubble Space Telescope Goddard High Resolution Spectrograph and archival spectra obtained with the HST Cosmic Origins Spectrograph.
    The Astrophysical Journal 07/2014; 793(1). · 6.73 Impact Factor
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    ABSTRACT: We report results from Spitzer observations of SNR 0509-68.7, also known as N103B, a young Type Ia supernova remnant in the Large Magellanic Cloud that shows interaction with a dense medium in its western hemisphere. Our images show that N103B has strong IR emission from warm dust in the post-shock environment. The post-shock gas density we derive, 45 cm$^{-3}$, is much higher than in other Type Ia remnants in the LMC, though a lack of spatial resolution may bias measurements towards regions of higher than average density. This density is similar to that in Kepler's SNR, a Type Ia interacting with a circumstellar medium. Optical images show H$\alpha$ emission along the entire periphery of the western portion of the shock, with [O III] and [S II] lines emitted from a few dense clumps of material where the shock has become radiative. The dust is silicate in nature, though standard silicate dust models fail to reproduce the "18 $\mu$m" silicate feature that peaks instead at 17.3 $\mu$m. We propose that the dense material is circumstellar material lost from the progenitor system, as with Kepler. If the CSM interpretation is correct, this remnant would become the second member, along with Kepler, of a class of Type Ia remnants characterized by interaction with a dense CSM hundreds of years post-explosion. A lack of N enhancement eliminates symbiotic AGB progenitors. The white dwarf companion must have been relatively unevolved at the time of the explosion.
    The Astrophysical Journal 06/2014; 790(2). · 6.73 Impact Factor
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    ABSTRACT: Extreme-ultraviolet images of Comet Lovejoy (C/2011 W3) from the Atmospheric Imaging Assembly show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of six between neighboring flux tubes over scales of a few thousand kilometers. These density structures imply variations in the Alfvén speed on a similar scale. They will drastically affect the propagation and dissipation of Alfvén waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves along the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use a magnetohydrodynamic model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfvén waves as the cometary ions isotropize.
    The Astrophysical Journal 06/2014; 788(2):152. · 6.73 Impact Factor
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    ABSTRACT: EUV images of Comet Lovejoy (C/2011 W3) from the AIA show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of 6 between neighboring flux tubes over scales of a few thousand km. These density structures imply variations in the Alfven speed on a similar scale. They will drastically affect the propagation and dissipation of Alfven waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves along the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use an MHD model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfven waves as the cometary ions isotropize.
    05/2014;
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    ABSTRACT: EUV images of Comet Lovejoy (C/2011 W3) from the AIA show striations related to the magnetic field structure in both open and closed magnetic regions. The brightness contrast implies coronal density contrasts of at least a factor of 6 between neighboring flux tubes over scales of a few thousand km. These density structures imply variations in the Alfven speed on a similar scale. They will drastically affect the propagation and dissipation of Alfven waves, and that should be taken into account in models of coronal heating and solar wind acceleration. In each striation, the cometary emission moves along the magnetic field and broadens with time. The speed and the rate of broadening are related to the parallel and perpendicular components of the velocities of the cometary neutrals when they become ionized. We use an MHD model of the coronal magnetic field and the theory of pickup ions to compare the measurements with theoretical predictions, in particular with the energy lost to Alfven waves as the cometary ions isotropize.
    04/2014;
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    ABSTRACT: We report on spectra of two positions in the XA region of the Cygnus Loop supernova remnant obtained with the InfraRed Spectrograph on the Spitzer Space Telescope. The spectra span the 10-35 micron wavelength range, which contains a number of collisionally excited forbidden lines. These data are supplemented by optical spectra obtained at the Whipple Observatory and an archival UV spectrum from the International Ultraviolet Explorer. Coverage from the UV through the IR provides tests of shock wave models and tight constraints on model parameters. Only lines from high ionization species are detected in the spectrum of a filament on the edge of the remnant. The filament traces a 180 km/s shock that has just begun to cool, and the oxygen to neon abundance ratio lies in the normal range found for Galactic H II regions. Lines from both high and low ionization species are detected in the spectrum of the cusp of a shock-cloud interaction, which lies within the remnant boundary. The spectrum of the cusp region is matched by a shock of about 150 km/s that has cooled and begun to recombine. The post-shock region has a swept-up column density of about 1.3E18 cm^-2, and the gas has reached a temperature of 7000 to 8000 K. The spectrum of the Cusp indicates that roughly half of the refractory silicon and iron atoms have been liberated from the grains. Dust emission is not detected at either position.
    03/2014; 787(1).
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    ABSTRACT: We have detected emission in C IV λλ1548,1551 from C atoms sputtered from dust in the gas behind a shock wave in the Cygnus Loop using COS on HST. The intensity agrees approximately with predictions from model calculations that match the Spitzer 24 μm and the X-ray intensity profiles. Thus these observations confirm the overall picture of dust destruction in SNR shocks and the sputtering rates assumed. However, the CIV intensity 10" behind the shock is too high compared to the intensities at the shock and 25" behind it. Projection effects and a complex geometry are probably responsible for the discrepancy.
    01/2014;
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    ABSTRACT: We present an observational study using high-resolution echelle spectroscopy of collisionless shocks in the Cygnus Loop supernova remnant. Measured H alpha line profiles constrain pre-shock heating processes resulting in narrow component broadening, cosmic-ray acceleration, and electron-proton equilibration. The shocks produce faint H alpha emission line profiles, which are characterized by narrow and broad components. The narrow component is representative of the pre-shock conditions, while the broad component is produced after charge transfer between neutrals entering the shock and protons in the post-shock gas, thus reflecting the properties of the post-shock gas. We observe a diffuse H alpha region extending about 2.5 arcmin ahead of the shock with line width about 29 km/s, while the H alpha profile of the shock itself consists of a broader than expected narrow (36 km/s) and a broad (250 km/s) component. The observed diffuse emission arises in a photoionization precursor heated to about 18,000 K by He I and He II emission from the shock, with additional narrow component broadening originating from a thin cosmic-ray precursor. Broad to narrow component intensity ratios of about 1.0 imply full electron-proton temperature equilibration (equal ion and electron temperatures) in the post-shock region. Broad component line widths indicate shock velocities of about 400 km/s. Combining the shock velocities with proper motions suggests the distance to the Cygnus Loop is about 890 pc, significantly greater than the generally accepted upper limit of 637 pc. This work is supported in part by the NSF REU and DOD ASSURE programs under NSF grant no. 1262851 and by the Smithsonian Institution. This work was partially supported by the grant HST-60-12885 to the Smithsonian Institution.
    The Astrophysical Journal 01/2014; 791(1). · 6.73 Impact Factor
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    ABSTRACT: The Cygnus Loop supernova remnant serves as an excellent laboratory for the study of radiative and non-radiative shocks with speeds in the 150-450 km s-1 range. We present results on shock-excited emission and dust destruction based on Spitzer Space Telescope observations of two well-studied regions in the remnant, (i) a non-radiative shock filament along the NE limb, and (ii) the XA region, characterized by emission from bright radiative shocks.
    12/2013;
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    ABSTRACT: The magnetic field plays a pivotal role in many fields of Astrophysics. This is especially true for the physics of the solar atmosphere. Measuring the magnetic field in the upper solar atmosphere is crucial to understand the nature of the underlying physical processes that drive the violent dynamics of the solar corona—that can also affect life on Earth. SolmeX, a fully equipped solar space observatory for remote-sensing observations, will provide the first comprehensive measurements of the strength and direction of the magnetic field in the upper solar atmosphere. The mission consists of two spacecraft, one carrying the instruments, and another one in formation flight at a distance of about 200 m carrying the occulter to provide an artificial total solar eclipse. This will ensure high-quality coronagraphic observations above the solar limb. SolmeX integrates two spectro-polarimetric coronagraphs for off-limb observations, one in the EUV and one in the IR, and three instruments for observations on the disk. The latter comprises one imaging polarimeter in the EUV for coronal studies, a spectro-polarimeter in the EUV to investigate the low corona, and an imaging spectro-polarimeter in the UV for chromospheric studies. SOHO and other existing missions have investigated the emission of the upper atmosphere in detail (not considering polarization), and as this will be the case also for missions planned for the near future. Therefore it is timely that SolmeX provides the final piece of the observational quest by measuring the magnetic field in the upper atmosphere through polarimetric observations.
    European Solar Physics Meeting (ESPM-13); 12/2013
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    ABSTRACT: Phosphorus ((31)P), which is essential for life, is thought to be synthesized in massive stars and dispersed into interstellar space when these stars explode as supernovae (SNe). Here, we report on near-infrared spectroscopic observations of the young SN remnant Cassiopeia A, which show that the abundance ratio of phosphorus to the major nucleosynthetic product iron ((56)Fe) in SN material is up to 100 times the average ratio of the Milky Way, confirming that phosphorus is produced in SNe. The observed range is compatible with predictions from SN nucleosynthetic models but not with the scenario in which the chemical elements in the inner SN layers are completely mixed by hydrodynamic instabilities during the explosion.
    Science 12/2013; 342(6164):1346-1348. · 31.20 Impact Factor
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    ABSTRACT: Major solar eruptive events (SEEs), consisting of both a large flare and a near simultaneous large fast coronal mass ejection (CME), are the most powerful explosions and also the most powerful and energetic particle accelerators in the solar system, producing solar energetic particles (SEPs) up to tens of GeV for ions and hundreds of MeV for electrons. The intense fluxes of escaping SEPs are a major hazard for humans in space and for spacecraft. Furthermore, the solar plasma ejected at high speed in the fast CME completely restructures the interplanetary medium (IPM) - major SEEs therefore produce the most extreme space weather in geospace, the interplanetary medium, and at other planets. Thus, understanding the flare/CME energy release process(es) and the related particle acceleration processes are major goals in Heliophysics. To make the next major breakthroughs, we propose a new mission concept, SEE 2020, a single spacecraft with a complement of advanced new instruments that focus directly on the coronal energy release and particle acceleration sites, and provide the detailed diagnostics of the magnetic fields, plasmas, mass motions, and energetic particles required to understand the fundamental physical processes involved.
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    ABSTRACT: The magnetic field plays a pivotal role in many fields of Astrophysics. This is especially true for the physics of the solar atmosphere. Measuring the magnetic field in the upper solar atmosphere is crucial to understand the nature of the underlying physical processes that drive the violent dynamics of the solar corona—that can also affect life on Earth. SolmeX, a fully equipped solar space observatory for remote-sensing observations, will provide the first comprehensive measurements of the strength and direction of the magnetic field in the upper solar atmosphere. The mission consists of two spacecraft, one carrying the instruments, and another one in formation flight at a distance of about 200 m carrying the occulter to provide an artificial total solar eclipse. This will ensure high-quality coronagraphic observations above the solar limb. SolmeX integrates two spectro-polarimetric coronagraphs for off-limb observations, one in the EUV and one in the IR, and three instruments for observations on the disk. The latter comprises one imaging polarimeter in the EUV for coronal studies, a spectro-polarimeter in the EUV to investigate the low corona, and an imaging spectro-polarimeter in the UV for chromospheric studies. SOHO and other existing missions have investigated the emission of the upper atmosphere in detail (not considering polarization), and as this will be the case also for missions planned for the near future. Therefore it is timely that SolmeX provides the final piece of the observational quest by measuring the magnetic field in the upper atmosphere through polarimetric observations.
    Experimental Astronomy 11/2013; · 2.97 Impact Factor
  • E. Landi, M. P. Miralles, J. C. Raymond, H. Hara
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    ABSTRACT: We analyze coordinated observations from the EUV Imaging Spectrometer (EIS) and X-Ray Telescope (XRT) on board Hinode of an X-ray Plasma Ejection (XPE) that occurred during the coronal mass ejection (CME) event of 2008 April 9. The XPE was trailing the CME core from behind, following the same trajectory, and could be identified both in EIS and XRT observations. Using the EIS spectrometer, we have determined the XPE plasma parameters, measuring the electron density, thermal distribution, and elemental composition. We have found that the XPE composition and electron density were very similar to those of the pre-event active region plasma. The XPE temperature was higher, and its thermal distribution peaked at around 3 MK also, typical flare lines were absent from EIS spectra, indicating that any XPE component with temperatures in excess of 5 MK was likely either faint or absent. We used XRT data to investigate the presence of hotter plasma components in the XPE that could have gone undetected by EIS and found that—if at all present—these components have small emission measure values and their temperature is in the 8-12.5 MK range. The very hot plasma found in earlier XPE observations obtained by Yohkoh seems to be largely absent in this CME, although plasma ionization timescales may lead to non-equilibrium ionization effects that could make bright lines from ions formed in a 10 MK plasma not detectable by EIS. Our results supersede the XPE findings of Landi et al., who studied the same event with older response functions for the XRT Al-poly filter; the differences in the results stress the importance of using accurate filter response functions.
    The Astrophysical Journal 11/2013; 778(1):29-. · 6.73 Impact Factor
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    ABSTRACT: Dust grains are sputtered away in the hot gas behind shock fronts in supernova remnants, gradually enriching the gas phase with refractory elements. We have measured emission in C IV $\lambda$1550 from C atoms sputtered from dust in the gas behind a non-radiative shock wave in the northern Cygnus Loop. Overall, the intensity observed behind the shock agrees approximately with predictions from model calculations that match the Spitzer 24 micron and the X-ray intensity profiles. Thus these observations confirm the overall picture of dust destruction in SNR shocks and the sputtering rates used in models. However, there is a discrepancy in that the CIV intensity 10" behind the shock is too high compared to the intensities at the shock and 25" behind it. Variations in the density, hydrogen neutral fraction and the dust properties over parsec scales in the pre-shock medium limit our ability to test dust destruction models in detail.
    The Astrophysical Journal 10/2013; 778(2). · 6.73 Impact Factor

Publication Stats

7k Citations
2,020.82 Total Impact Points

Institutions

  • 2014
    • Towson University
      • Department of Physics, Astronomy and Geosciences
      Maryland, United States
    • New Mexico State University
      • Department of Physics
      Las Cruces, New Mexico, United States
  • 1970–2014
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
  • 2013
    • Chinese Academy of Sciences
      • Graduate School
      Peping, Beijing, China
    • Max Planck Institute for Solar System Research
      Göttingen, Lower Saxony, Germany
    • The University of Tokyo
      • Department of Astronomy
      Edo, Tōkyō, Japan
  • 2012
    • Elmhurst College
      Elmhurst, Illinois, United States
  • 2011
    • Northeastern University
      Boston, Massachusetts, United States
    • China University of Petroleum
      Ch’ang-p’ing-ch’ü, Beijing, China
  • 2010
    • United States Naval Observatory
      Washington, Maine, United States
    • Hiroshima University
      Hirosima, Hiroshima, Japan
  • 2008
    • University of Michigan
      • Department of Astronomy
      Ann Arbor, Michigan, United States
    • University of Groningen
      • Kapteyn Astronomical Institute
      Groningen, Groningen, Netherlands
    • Pennsylvania State University
      • Department of Astronomy and Astrophysics
      University Park, Maryland, United States
  • 2004–2007
    • Idenix Pharmaceuticals, Inc.
      Cambridge, Massachusetts, United States
    • Middlebury College
      • Department of Physics
      Middlebury, Indiana, United States
  • 1996–2007
    • University of Florence
      • Dipartimento di Fisica e Astronomia
      Florens, Tuscany, Italy
  • 2006
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, ENG, United Kingdom
  • 2003
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 2000
    • Rutgers, The State University of New Jersey
      • Department Physics and Astronomy
      New Brunswick, New Jersey, United States
  • 1999
    • Johns Hopkins University
      • Department of Physics and Astronomy
      Baltimore, MD, United States
    • University of Maryland, College Park
      • Department of Astronomy
      Maryland, United States
  • 1997
    • University of Oregon
      Eugene, Oregon, United States
    • European Space Agency
      Lutetia Parisorum, Île-de-France, France
  • 1993
    • Lawrence Livermore National Laboratory
      Livermore, California, United States
    • University of Colorado
      Denver, Colorado, United States
  • 1988
    • European Southern Observatory
      Arching, Bavaria, Germany