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Russell A. Howard - One of the best experts on this subject based on the ideXlab platform.

  • White-light observations oF Features in the Zodiacal dust cloud From within the solar Corona
    2020
    Co-Authors: Russell A. Howard, Guillermo Stenborg, Brendan Gallagher, Phil Hess, Karl Battams
    Abstract:

    <p>The Parker Solar Probe (PSP) mission has completed Four solar encounters, observing the solar Corona From distances signiFicantly closer to the Sun than From previous missions (to 36 solar radii during the First three perihelia and to 28 solar radii during the Fourth). During these encounters, the Wide-Field Imager For Solar Probe (WISPR) onboard PSP has been observing the F-Corona/Zodiacal light - probing the dust environment in the solar Corona as PSP moves through the Corona. This allowed WISPR to Find 1) a gradual decrease oF the expected brightness oF the F-Corona For distances shorter than about 0.1 AU, 2) dust trails oF short-period asteroid/cometary objects (e.g., 3200 Pheathon and 2P/Encke) and 3) a changing rate oF dust impacts on the S/C throughout the encounter period. In this presentation, we will present these Findings, discuss their nature, and elaborate on the novelty oF these results. The authors acknowledge support From the NASA Parker Solar Probe program.</p>

  • Evidence For a Circumsolar Dust Ring Near Mercury’s Orbit
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Johnathan R. Stauffer, Russell A. Howard
    Abstract:

    To test a technique to be used on the white-light imager onboard the recently launched Parker Solar Probe mission, we perFormed a numerical diFFerentiation oF the brightness proFiles along the photometric axis oF the F-Corona models that are derived From STEREO Ahead Sun Earth Connection Heliospheric Investigation observations recorded with the HI-1 instrument between 2007 December and 2014 March. We Found a consistent pattern in the derivatives that can be observed From any S/C longitude between about 18° and 23° elongation with a maximum at about 21°. These Findings indicate the presence oF a circumsolar dust density enhancement that peaks at about 23° elongation. A straightForward integration oF the excess signal in the derivative space indicates that the brightness increase over the background F-Corona is on the order oF 1.5%–2.5%, which implies an excess dust density oF about 3%–5% at the center oF the ring. This study has also revealed (1) a large-scale azimuthal modulation oF the inner boundary oF the pattern, which is in clear association with Mercury's orbit; and (2) a localized modulation oF the inner boundary that is attributable to the dust trail oF Comet 2P/Encke, which occurs near ecliptic longitudes corresponding to the crossing oF Encke's and Mercury's orbital paths. Moreover, evidence oF dust near the S/C in two restricted ranges oF ecliptic longitudes has also been revealed by this technique, which is attributable to the dust trails oF (1) comet 73P/Schwassmann–Wachmann 3, and (2) 169P/NEAT.

  • Measuring the Flattening oF the Outer F-Corona Using STEREO-A/HI-1 Images
    The Astrophysical Journal, 2018
    Co-Authors: Johnathan R. Stauffer, Guillermo Stenborg, Russell A. Howard
    Abstract:

    The white-light FraunhoFer-Corona (F-Corona) arises From light scattered by the circumsolar dust. Using weekly minimum background models oF ST-A/HI-1 observations, we characterized the Flattening oF the F-Corona between 5° and 24° elongation by measuring the radii oF constant-intensity contours along, and at a 25° angle to, the photometric axis. The ratio oF these quantities (the pseudo-Flattening index ) is analogous to the deFinition oF the Flattening index (). Measurements oF the pseudo-Flattening in the north and south hemispheres reveal a periodic asymmetry in the appearance oF the F-Corona (attributable to changes in polar brightness due to the elevation oF the spacecraFt From the dust symmetry surFace), as well as a north/south asymmetry possibly introduced by the warped dust symmetry surFace. The north/south averaged pseudo-Flattening was used to inFer the Flattening For each weekly model. We Found that the inFerred Flattening index (1) varies periodically with spacecraFt position, reaching a maximum in the range 262° λ 290° due to a brightening along the photometric axis when the spacecraFt passes through the surFace oF maximum dust density, and a minimum at λ ≈ 200°, and (2) slightly varies as a Function oF time (at least partially due to the displacement oF the circumsolar dust with respect to the Sun). Comparison oF the Flattening index with previous works suggests a cubic dependence oF the Flattening index with log elongation For .

  • Characterization oF the White-light Brightness oF the F-Corona between 5° and 24° Elongation
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Russell A. Howard, Johnathan R. Stauffer
    Abstract:

    The white-light F-Corona arises From light scattered by circumsolar dust. Using weekly models oF the eastern side oF the F-Corona between 5° and 24° elongation, we analyzed the elongation and time dependence oF the brightness oF its photometric axis. The models were constructed From STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We Found that the brightness proFiles can be approximated by power laws, with the coeFFicients oF the models depending upon the observer's ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes oF the dust plane, nor is the behavior similar in the two halves oF the spacecraFt orbit delimited by the line oF nodes. The exponents range between −2.31 and −2.35, the Former occurring when the observer is at the nodes. The asymmetry observed in the behavior oF the proportionality constant is indicative oF the projected center oF the dust cloud being oFFset From the Sun's center by ~0.4 R ⊙. The coeFFicients exhibit a secular variation correlated with the location oF the barycenter oF the solar system. We also used the HI-1 Frames obtained during STEREO-A calibration rolls to model the 360° F-Corona. We Found that (1) its Flattening index () decreases From ~0.66 to ~0.46 with decreasing elongation and (2) the isophotes' shape can be approximated by a series oF superellipses, with the superellipse index n increasing (nonlinearly) with brightness (). Cubic extrapolation oF the results below 5° elongation points to a circular F-Corona below 1° elongation.

  • characterization oF the white light brightness oF the F Corona between 5 and 24 elongation
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Russell A. Howard, Johnathan R. Stauffer
    Abstract:

    The white-light F-Corona arises From light scattered by circumsolar dust. Using weekly models oF the eastern side oF the F-Corona between 5° and 24° elongation, we analyzed the elongation and time dependence oF the brightness oF its photometric axis. The models were constructed From STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We Found that the brightness proFiles can be approximated by power laws, with the coeFFicients oF the models depending upon the observer's ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes oF the dust plane, nor is the behavior similar in the two halves oF the spacecraFt orbit delimited by the line oF nodes. The exponents range between −2.31 and −2.35, the Former occurring when the observer is at the nodes. The asymmetry observed in the behavior oF the proportionality constant is indicative oF the projected center oF the dust cloud being oFFset From the Sun's center by ~0.4 R ⊙. The coeFFicients exhibit a secular variation correlated with the location oF the barycenter oF the solar system. We also used the HI-1 Frames obtained during STEREO-A calibration rolls to model the 360° F-Corona. We Found that (1) its Flattening index () decreases From ~0.66 to ~0.46 with decreasing elongation and (2) the isophotes' shape can be approximated by a series oF superellipses, with the superellipse index n increasing (nonlinearly) with brightness (). Cubic extrapolation oF the results below 5° elongation points to a circular F-Corona below 1° elongation.

Ingrid Mann - One of the best experts on this subject based on the ideXlab platform.

  • The inFluence oF the dust-Free zone on F-Corona brightness
    2021
    Co-Authors: Saliha Eren, Ingrid Mann
    Abstract:

    <p>This presentation is related to model calculations oF the circumsolar dust brightness that is seen in the F-Corona and inner Zodiacal light. We calculate the brightness integral that includes the size distribution oF the interplanetary dust, the spatial distribution, and the scattering properties. The scattering properties are estimated with Mie calculations oF spherical particles consisting oF astronomical silicate. We consider diFFerent size distributions oF the dust particles with sizes between 1 nanometre - 100 micrometre. It was recently discussed that the extension oF the dust-Free zone can be inFerred From the slope oF the F-Corona brightness seen in new observations received From the WISPR instrument on the NASA Parker Solar Probe (Stenborg et al., 2020). We, thereFore, investigate the inFluence oF the dust-Free zone on the brightness and compare it to the inFluence that the dust size distribution has.</p><p>ReFerences</p><p>1. G. Stenborg, R. A. Howard, P. Hess, B. Gallagher, PSP/WISPR observations oF dust density depletion near the Sun I. Remote observations to 8 Rsol From an observer between 0.13-0.35 AU, A&A, Forthcoming article, 2020. DOI: 10.1051/0004-6361/202039284</p>

  • Model Calculations oF the F-Corona and inner Zodiacal Light
    2020
    Co-Authors: Saliha Eren, Ingrid Mann
    Abstract:

    <p>The white-light FraunhoFer Corona (F-Corona) and inner Zodiacal light are generated by interplanetary (Zodiacal) dust particles that are located between Sun and observer. At visible wavelength the brightness comes From sunlight scattered at the dust particles. F-Corona and inner Zodiacal light were recently observed From STEREO (Stenborg et al. 2018) and Parker Solar Probe (Howard et al. 2019) spacecraFt which motivates our model calculations. We investigate the brightness by integration oF scattered light along the line oF sight oF observations. We include a three-dimensional distribution oF the Zodiacal dust that describes well the brightness oF the Zodiacal light at larger elongations, a dust size distribution derived From observations at 1AU and assume Mie scattering at silicate particles to describe the scattered light over a large size distribution From 1 nm to 100 µm. From our simulations, we calculate the Flattening index oF the F-Corona, which is the ratio oF the minor axis to the major axis Found For isophotes at diFFerent distances From the Sun, respectively elongations oF the line oF sight. Our results agree well with results From STEREO/SECCHI observational data where the Flattening index varies From 0.45° and 0.65° at elongations between 5° and 24°. To compare with Parker Solar Probe observations, we investigate how the brightness changes when the observer moves closer to the Sun. This brightness change is inFluenced by the dust number density along the line oF sight and by the changing scattering geometry.</p><p>-Stenborg G., Howard R. A., and StauFFer J. R., 2018: Characterization oF the White-light Brightness oF the F-Corona between 5° and 24° Elongation, Astrophys. J. 862: 168 (21pp).</p><p>-Howard, R.A. and 25 co-authors, 2019: Near-Sun observations oF an F-Corona decrease and K-Corona Fine structure, Nature 576, 232–236.</p>

  • The J- and K-Band Brightness oF the Solar F Corona Observed during the Solar Eclipse on 1998 February 26
    The Astrophysical Journal, 2002
    Co-Authors: R. Ohgaito, Ingrid Mann, R. M. Macqueen, J. R. Kuhn, Hiroshi Kimura
    Abstract:

    We analyze J- and K-band observations oF the 1998 solar eclipse and derive the F-Corona brightness in the K band between 3 and 7 R☉ From the center oF the Sun and in the J band out to 5 R☉. The FalloFF in the K-band brightness From 3 to 7 R☉ is Fitted with a radial power law with exponent -2.4 ± 0.1 at the solar equator and with exponent -2.9 at the solar pole. This slope is gentler than that derived From observations in 1983 but is steeper than that derived From observations For the 1991 eclipse. The radial proFiles agree well with models that explain the F Corona with weakly absorbing dust particles. Comparison oF the J- and K-band brightness at 3 R☉ From the center oF the Sun indicates a reddening oF the F Corona with respect to the solar spectrum. The reddening is, however, less pronounced compared to the F Corona observed during the 1983 total solar eclipse. This Fact may be attributed to a change in the composition oF dust near the Sun. As with the radial proFiles, the reddening in 1998 is better explained with models that assume weakly absorbing rather than strongly absorbing dust particles in the solar Corona. Similar to recent eclipse observations, we do not detect an excess emission Feature oF near-solar dust in the F Corona. We hence can reject the hypothesis that suggests a correlation between the detection oF an emission Feature and the solar activity cycle.

  • Observations OF The Solar Eclipse On February 26. 1998: Study OF The Solar F - Corona
    Plasma Astrophysics And Space Physics, 1999
    Co-Authors: Ingrid Mann, Hiroshi Kimura, R. M. Macqueen, J. R. Kuhn, H. Lin, D. Edmunds, J. Streete, P. L. Judge, P. Hillebrand, G. Tansey
    Abstract:

    The solar eclipse on February 26, 1998, was observed From an aircraFt operated by the Research Aviation Facility oF the National Center For Atmospheric Research. The observations cover the near inFrared spectral range and were made at an altitude oF almost 6 km above the PaciFic about 800 km southwest From Panama City. Aside From spectroscopic observations oF Coronal emission lines, the solar F-Corona was observed in the J and K-band over a Field oF view oF 7°. A preliminary view on the data shows no indication For the existence oF pronounced brightness Features in the solar F-Corona.

  • The circumsolar dust complex and solar magnetic Field
    Earth Planets and Space, 1998
    Co-Authors: Alexander V. Krivov, Ingrid Mann, Hiroshi Kimura
    Abstract:

    New model calculations For the dynamical evolution oF dust particles at several solar radii around the Sun are presented. We choose a Fractal aggregate consisting oF either silicate or carbon as a representative oF dielectric and absorbing FluFFy particles. We take into account a large array oF Forces and eFFects acting on the dust particles—solar gravity, direct solar radiation pressure, Poynting-Robertson eFFect, sublimation, and the Lorentz Force, with a special emphasis given to the latter. The Lorentz Force was computed on the base oF modeled grain’s charges and a model oF the actual solar magnetic Field From 1976 to 1996. We have investigated the dynamics oF individual grains, obtained radial and vertical density proFiles oF diFFerent-sized particles, and used the computed dust density distributions to calculate the expected F-Corona brightness during the periods oF weak and strong magnetic Field. We have Found that the solar magnetic Field and its variations do not aFFect the dynamics and spatial distribution oF carbon aggregates, which are thought to produce the peak Features oF the near-inFrared F-Corona brightness that were sometimes observed. On the other hand, the variations oF the solar magnetic Field may alter the latitudinal distribution oF silicate aggregates. However, the eFFect is not strong enough to account For the observed temporal variations in the brightness. Thus we can rule out the correlation between the appearance or disappearance oF a peak Feature and the solar activity cycle.

Shadia Rifai Habbal - One of the best experts on this subject based on the ideXlab platform.

  • The Color and Brightness oF the F-Corona InFerred From the 2019 July 2 Total Solar Eclipse.
    arXiv: Solar and Stellar Astrophysics, 2021
    Co-Authors: Benjamin Boe, Shadia Rifai Habbal, Cooper Downs, Miloslav Druckmüller
    Abstract:

    Total solar eclipses (TSEs) provide a unique opportunity to quantiFy the properties oF the K-Corona (electrons), F-Corona (dust) and E-Corona (ions) continuously From the solar surFace out to a Few solar radii. We apply a novel inversion method to separate emission From the K- and F-Corona continua using unpolarized total brightness (tB) observations From Five 0.5 nm bandpasses acquired during the 2019 July 2 TSE between 529.5 nm and 788.4 nm. The wavelength dependence relative to the photosphere (i.e., color) oF the F-Corona itselF is used to inFer the tB oF the K- and F-Corona For each line-oF-sight. We compare our K-Corona emission results with the Mauna Loa Solar Observatory (MLSO) K-Cor polarized brightness (pB) observations From the day oF the eclipse, and the Forward modeled K-Corona intensity From the Predictive Science Inc. (PSI) Magnetohydrodynamic (MHD) model prediction. Our results are generally consistent with previous work and match both the MLSO data and PSI-MHD predictions quite well, supporting the validity oF our approach and oF the PSI-MHD model. However, we Find that the tB oF the F-Corona is higher than expected in the low Corona, perhaps indicating that the F-Corona is slightly polarized -- challenging the common assumption that the F-Corona is entirely unpolarized.

  • CME-induced Thermodynamic Changes in the Corona as InFerred From Fe xi and Fe xiv Emission Observations during the 2017 August 21 Total Solar Eclipse
    The Astrophysical Journal, 2020
    Co-Authors: Benjamin Boe, Shadia Rifai Habbal, Miloslav Druckmüller, Adalbert Ding, Jana Hoderova, Pavel Starha
    Abstract:

    We present the First remote sensing observations oF the impact From a Coronal Mass Ejection (CME) on the thermodynamic properties oF the solar Corona between 1 and 3 Rs. Measurements oF the Fe XI (789.2 nm) and Fe XIV (530.3 nm) emission were acquired with identical narrow-bandpass imagers at three observing sites during the 2017 August 21 Total Solar Eclipse. Additional continuum imagers were used to observe K+F Corona scattering, which is critical For the diagnostics presented here. The total distance between sites along the path oF totality was 1400 km, corresponding to a diFFerence oF 28 minutes between the times oF totality at the First and last site. These observations were used to measure the Fe XI and Fe XIV emission relative to continuum scattering, as well as the relative abundance oF Fe 10+ and Fe 13+ From the line ratio. The electron temperature (Te) was then computed via theoretical ionization abundance values. We Find that the range oF Te is 1.1-1.2 x10^6 K in Coronal holes and 1.2-1.4 x10^6 K in streamers. Statistically signiFicant changes oF Te occurred throughout much oF the Corona between the sites as a result oF serendipitous CME activity prior to the eclipse. These results underscore the unique advantage oF multi-site and multi-wavelength total solar eclipse observations For probing the dynamic and thermodynamic properties oF the Corona over an uninterrupted distance range From 1 to 3 Rs.

  • The long-term stability oF the visible F Corona at heights oF 3-6 R⊙
    Astronomy & Astrophysics, 2007
    Co-Authors: Huw Morgan, Shadia Rifai Habbal
    Abstract:

    Context. CMEs can eFFect the distribution oF dust grains in the Corona. The brightness oF the visible F Corona is expected thereFore to change as the Frequency oF CMEs varies with solar cycle. Aims. We search For a variation in the F Corona by comparing LASCO C2 observations From solar minimum and maximum. Methods. An established inversion method is used to calculate the visible F Corona brightness From LASCO C2 solar minimum observations made during 1996/10. Good agreement is Found with the F Corona brightness calculated From Skylab observations during 1973/05–1974/02 For heights oF 3–6 R� . The unpolarized brightness, which is dominated by the unpolarized F Corona brightness at these heights, is obtained by subtracting many pairs oF polarized brightness images From total brightness images and averaging over a solar rotation. We calculate the unpolarized brightness For both solar activity minimum and maximum. Results. The unpolarized brightness, and thereFore the F Corona, remain virtually unchanged between solar minimum and maximum at heights above 2.6 R� , despite the large change in the shape and activity oF the Corona. Using a simple density model, it is shown

  • The Depiction oF Coronal Structure in White-Light Images
    Solar Physics, 2006
    Co-Authors: Huw Morgan, Shadia Rifai Habbal, Richard Woo
    Abstract:

    The very steep decrease in density with heliocentric distance makes imaging oF Coronal density structures out to a Few solar radii challenging. The radial gradient in brightness can be reduced using numerous image processing techniques, thus quantitative data are manipulated to provide qualitative images. We introduce a new normalizing-radial-graded Filter (NRGF): a simple Filter For removing the radial gradient to reveal Coronal structure. Applied to polarized brightness observations oF the Corona, the NRGF produces images which are striking in their detail. Total-brightness, white-light images include contributions From the F Corona, stray light, and other instrumental contributions which need to be removed as eFFectively as possible to properly reveal the electron Corona structure. A new procedure For subtracting this background From LASCO C2 white-light, total-brightness images is introduced. The background is created From the unpolarized component oF total-brightness images and is Found to be remarkably time-invariant, remaining virtually unchanged over the solar cycle. By direct comparison with polarized-brightness data, we show that the new background-subtracting procedure is superior in depicting Coronal structure accurately, particularly when used in conjunction with the NRGF. The eFFectiveness oF the procedures is demonstrated on a series oF LASCO C2 observations oF a Coronal mass ejection (CME).

  • The Depiction oF Coronal Structure in White Light Images
    Solar Physics, 2006
    Co-Authors: Huw Morgan, Shadia Rifai Habbal, Richard Woo
    Abstract:

    The very sharp decrease oF density with heliocentric distance makes imaging oF Coronal density structures out to a Few solar radii challenging. The radial gradient in brightness can be reduced using numerous image processing techniques, thus quantitative data are manipulated to provide qualitative images. Introduced in this study is a new normalizing radial graded Filter (NRGF), a simple Filter For removing the radial gradient to reveal Coronal structure. Applied to polarized brightness observations oF the Corona, the NRGF produces images which are striking in their detail. Total brightness white light images include contributions From the F Corona, stray light and other instrumental contributions which need to be removed as eFFectively as possible to properly reveal the electron Corona structure. A new procedure For subtracting this background From LASCO C2 white light total brightness images is introduced. The background is created From the unpolarized component oF total brightness images and is Found to be remarkably time-invariant, remaining virtually unchanged over the solar cycle. By direct comparison with polarized brightness data, we show that the new background subtracting procedure is superior in depicting Coronal structure accurately, particularly when used in conjunction with the NRGF. The eFFectiveness oF the procedures is demonstrated on a series oF LASCO C2 observations oF a Coronal mass ejection (CME).

Johnathan R. Stauffer - One of the best experts on this subject based on the ideXlab platform.

  • Evidence For a Circumsolar Dust Ring Near Mercury’s Orbit
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Johnathan R. Stauffer, Russell A. Howard
    Abstract:

    To test a technique to be used on the white-light imager onboard the recently launched Parker Solar Probe mission, we perFormed a numerical diFFerentiation oF the brightness proFiles along the photometric axis oF the F-Corona models that are derived From STEREO Ahead Sun Earth Connection Heliospheric Investigation observations recorded with the HI-1 instrument between 2007 December and 2014 March. We Found a consistent pattern in the derivatives that can be observed From any S/C longitude between about 18° and 23° elongation with a maximum at about 21°. These Findings indicate the presence oF a circumsolar dust density enhancement that peaks at about 23° elongation. A straightForward integration oF the excess signal in the derivative space indicates that the brightness increase over the background F-Corona is on the order oF 1.5%–2.5%, which implies an excess dust density oF about 3%–5% at the center oF the ring. This study has also revealed (1) a large-scale azimuthal modulation oF the inner boundary oF the pattern, which is in clear association with Mercury's orbit; and (2) a localized modulation oF the inner boundary that is attributable to the dust trail oF Comet 2P/Encke, which occurs near ecliptic longitudes corresponding to the crossing oF Encke's and Mercury's orbital paths. Moreover, evidence oF dust near the S/C in two restricted ranges oF ecliptic longitudes has also been revealed by this technique, which is attributable to the dust trails oF (1) comet 73P/Schwassmann–Wachmann 3, and (2) 169P/NEAT.

  • Measuring the Flattening oF the Outer F-Corona Using STEREO-A/HI-1 Images
    The Astrophysical Journal, 2018
    Co-Authors: Johnathan R. Stauffer, Guillermo Stenborg, Russell A. Howard
    Abstract:

    The white-light FraunhoFer-Corona (F-Corona) arises From light scattered by the circumsolar dust. Using weekly minimum background models oF ST-A/HI-1 observations, we characterized the Flattening oF the F-Corona between 5° and 24° elongation by measuring the radii oF constant-intensity contours along, and at a 25° angle to, the photometric axis. The ratio oF these quantities (the pseudo-Flattening index ) is analogous to the deFinition oF the Flattening index (). Measurements oF the pseudo-Flattening in the north and south hemispheres reveal a periodic asymmetry in the appearance oF the F-Corona (attributable to changes in polar brightness due to the elevation oF the spacecraFt From the dust symmetry surFace), as well as a north/south asymmetry possibly introduced by the warped dust symmetry surFace. The north/south averaged pseudo-Flattening was used to inFer the Flattening For each weekly model. We Found that the inFerred Flattening index (1) varies periodically with spacecraFt position, reaching a maximum in the range 262° λ 290° due to a brightening along the photometric axis when the spacecraFt passes through the surFace oF maximum dust density, and a minimum at λ ≈ 200°, and (2) slightly varies as a Function oF time (at least partially due to the displacement oF the circumsolar dust with respect to the Sun). Comparison oF the Flattening index with previous works suggests a cubic dependence oF the Flattening index with log elongation For .

  • Characterization oF the White-light Brightness oF the F-Corona between 5° and 24° Elongation
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Russell A. Howard, Johnathan R. Stauffer
    Abstract:

    The white-light F-Corona arises From light scattered by circumsolar dust. Using weekly models oF the eastern side oF the F-Corona between 5° and 24° elongation, we analyzed the elongation and time dependence oF the brightness oF its photometric axis. The models were constructed From STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We Found that the brightness proFiles can be approximated by power laws, with the coeFFicients oF the models depending upon the observer's ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes oF the dust plane, nor is the behavior similar in the two halves oF the spacecraFt orbit delimited by the line oF nodes. The exponents range between −2.31 and −2.35, the Former occurring when the observer is at the nodes. The asymmetry observed in the behavior oF the proportionality constant is indicative oF the projected center oF the dust cloud being oFFset From the Sun's center by ~0.4 R ⊙. The coeFFicients exhibit a secular variation correlated with the location oF the barycenter oF the solar system. We also used the HI-1 Frames obtained during STEREO-A calibration rolls to model the 360° F-Corona. We Found that (1) its Flattening index () decreases From ~0.66 to ~0.46 with decreasing elongation and (2) the isophotes' shape can be approximated by a series oF superellipses, with the superellipse index n increasing (nonlinearly) with brightness (). Cubic extrapolation oF the results below 5° elongation points to a circular F-Corona below 1° elongation.

  • characterization oF the white light brightness oF the F Corona between 5 and 24 elongation
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Russell A. Howard, Johnathan R. Stauffer
    Abstract:

    The white-light F-Corona arises From light scattered by circumsolar dust. Using weekly models oF the eastern side oF the F-Corona between 5° and 24° elongation, we analyzed the elongation and time dependence oF the brightness oF its photometric axis. The models were constructed From STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We Found that the brightness proFiles can be approximated by power laws, with the coeFFicients oF the models depending upon the observer's ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes oF the dust plane, nor is the behavior similar in the two halves oF the spacecraFt orbit delimited by the line oF nodes. The exponents range between −2.31 and −2.35, the Former occurring when the observer is at the nodes. The asymmetry observed in the behavior oF the proportionality constant is indicative oF the projected center oF the dust cloud being oFFset From the Sun's center by ~0.4 R ⊙. The coeFFicients exhibit a secular variation correlated with the location oF the barycenter oF the solar system. We also used the HI-1 Frames obtained during STEREO-A calibration rolls to model the 360° F-Corona. We Found that (1) its Flattening index () decreases From ~0.66 to ~0.46 with decreasing elongation and (2) the isophotes' shape can be approximated by a series oF superellipses, with the superellipse index n increasing (nonlinearly) with brightness (). Cubic extrapolation oF the results below 5° elongation points to a circular F-Corona below 1° elongation.

Guillermo Stenborg - One of the best experts on this subject based on the ideXlab platform.

  • White-light observations oF Features in the Zodiacal dust cloud From within the solar Corona
    2020
    Co-Authors: Russell A. Howard, Guillermo Stenborg, Brendan Gallagher, Phil Hess, Karl Battams
    Abstract:

    <p>The Parker Solar Probe (PSP) mission has completed Four solar encounters, observing the solar Corona From distances signiFicantly closer to the Sun than From previous missions (to 36 solar radii during the First three perihelia and to 28 solar radii during the Fourth). During these encounters, the Wide-Field Imager For Solar Probe (WISPR) onboard PSP has been observing the F-Corona/Zodiacal light - probing the dust environment in the solar Corona as PSP moves through the Corona. This allowed WISPR to Find 1) a gradual decrease oF the expected brightness oF the F-Corona For distances shorter than about 0.1 AU, 2) dust trails oF short-period asteroid/cometary objects (e.g., 3200 Pheathon and 2P/Encke) and 3) a changing rate oF dust impacts on the S/C throughout the encounter period. In this presentation, we will present these Findings, discuss their nature, and elaborate on the novelty oF these results. The authors acknowledge support From the NASA Parker Solar Probe program.</p>

  • Evidence For a Circumsolar Dust Ring Near Mercury’s Orbit
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Johnathan R. Stauffer, Russell A. Howard
    Abstract:

    To test a technique to be used on the white-light imager onboard the recently launched Parker Solar Probe mission, we perFormed a numerical diFFerentiation oF the brightness proFiles along the photometric axis oF the F-Corona models that are derived From STEREO Ahead Sun Earth Connection Heliospheric Investigation observations recorded with the HI-1 instrument between 2007 December and 2014 March. We Found a consistent pattern in the derivatives that can be observed From any S/C longitude between about 18° and 23° elongation with a maximum at about 21°. These Findings indicate the presence oF a circumsolar dust density enhancement that peaks at about 23° elongation. A straightForward integration oF the excess signal in the derivative space indicates that the brightness increase over the background F-Corona is on the order oF 1.5%–2.5%, which implies an excess dust density oF about 3%–5% at the center oF the ring. This study has also revealed (1) a large-scale azimuthal modulation oF the inner boundary oF the pattern, which is in clear association with Mercury's orbit; and (2) a localized modulation oF the inner boundary that is attributable to the dust trail oF Comet 2P/Encke, which occurs near ecliptic longitudes corresponding to the crossing oF Encke's and Mercury's orbital paths. Moreover, evidence oF dust near the S/C in two restricted ranges oF ecliptic longitudes has also been revealed by this technique, which is attributable to the dust trails oF (1) comet 73P/Schwassmann–Wachmann 3, and (2) 169P/NEAT.

  • Measuring the Flattening oF the Outer F-Corona Using STEREO-A/HI-1 Images
    The Astrophysical Journal, 2018
    Co-Authors: Johnathan R. Stauffer, Guillermo Stenborg, Russell A. Howard
    Abstract:

    The white-light FraunhoFer-Corona (F-Corona) arises From light scattered by the circumsolar dust. Using weekly minimum background models oF ST-A/HI-1 observations, we characterized the Flattening oF the F-Corona between 5° and 24° elongation by measuring the radii oF constant-intensity contours along, and at a 25° angle to, the photometric axis. The ratio oF these quantities (the pseudo-Flattening index ) is analogous to the deFinition oF the Flattening index (). Measurements oF the pseudo-Flattening in the north and south hemispheres reveal a periodic asymmetry in the appearance oF the F-Corona (attributable to changes in polar brightness due to the elevation oF the spacecraFt From the dust symmetry surFace), as well as a north/south asymmetry possibly introduced by the warped dust symmetry surFace. The north/south averaged pseudo-Flattening was used to inFer the Flattening For each weekly model. We Found that the inFerred Flattening index (1) varies periodically with spacecraFt position, reaching a maximum in the range 262° λ 290° due to a brightening along the photometric axis when the spacecraFt passes through the surFace oF maximum dust density, and a minimum at λ ≈ 200°, and (2) slightly varies as a Function oF time (at least partially due to the displacement oF the circumsolar dust with respect to the Sun). Comparison oF the Flattening index with previous works suggests a cubic dependence oF the Flattening index with log elongation For .

  • Characterization oF the White-light Brightness oF the F-Corona between 5° and 24° Elongation
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Russell A. Howard, Johnathan R. Stauffer
    Abstract:

    The white-light F-Corona arises From light scattered by circumsolar dust. Using weekly models oF the eastern side oF the F-Corona between 5° and 24° elongation, we analyzed the elongation and time dependence oF the brightness oF its photometric axis. The models were constructed From STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We Found that the brightness proFiles can be approximated by power laws, with the coeFFicients oF the models depending upon the observer's ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes oF the dust plane, nor is the behavior similar in the two halves oF the spacecraFt orbit delimited by the line oF nodes. The exponents range between −2.31 and −2.35, the Former occurring when the observer is at the nodes. The asymmetry observed in the behavior oF the proportionality constant is indicative oF the projected center oF the dust cloud being oFFset From the Sun's center by ~0.4 R ⊙. The coeFFicients exhibit a secular variation correlated with the location oF the barycenter oF the solar system. We also used the HI-1 Frames obtained during STEREO-A calibration rolls to model the 360° F-Corona. We Found that (1) its Flattening index () decreases From ~0.66 to ~0.46 with decreasing elongation and (2) the isophotes' shape can be approximated by a series oF superellipses, with the superellipse index n increasing (nonlinearly) with brightness (). Cubic extrapolation oF the results below 5° elongation points to a circular F-Corona below 1° elongation.

  • characterization oF the white light brightness oF the F Corona between 5 and 24 elongation
    The Astrophysical Journal, 2018
    Co-Authors: Guillermo Stenborg, Russell A. Howard, Johnathan R. Stauffer
    Abstract:

    The white-light F-Corona arises From light scattered by circumsolar dust. Using weekly models oF the eastern side oF the F-Corona between 5° and 24° elongation, we analyzed the elongation and time dependence oF the brightness oF its photometric axis. The models were constructed From STEREO-A SECCHI/HI-1 images taken between 2007 December and 2014 March. We Found that the brightness proFiles can be approximated by power laws, with the coeFFicients oF the models depending upon the observer's ecliptic longitude. Their variation is not symmetric with respect to the orbital nodes oF the dust plane, nor is the behavior similar in the two halves oF the spacecraFt orbit delimited by the line oF nodes. The exponents range between −2.31 and −2.35, the Former occurring when the observer is at the nodes. The asymmetry observed in the behavior oF the proportionality constant is indicative oF the projected center oF the dust cloud being oFFset From the Sun's center by ~0.4 R ⊙. The coeFFicients exhibit a secular variation correlated with the location oF the barycenter oF the solar system. We also used the HI-1 Frames obtained during STEREO-A calibration rolls to model the 360° F-Corona. We Found that (1) its Flattening index () decreases From ~0.66 to ~0.46 with decreasing elongation and (2) the isophotes' shape can be approximated by a series oF superellipses, with the superellipse index n increasing (nonlinearly) with brightness (). Cubic extrapolation oF the results below 5° elongation points to a circular F-Corona below 1° elongation.