Oblateness

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L Twigg - One of the best experts on this subject based on the ideXlab platform.

  • high precision measurements of the solar diameter and Oblateness by the solar disk sextant sds experiment
    Solar Physics, 2006
    Co-Authors: A Egidi, Susan Sofia, William S Heaps, B Caccin, W R Hoegy, L Twigg
    Abstract:

    We reduce and analyze, in a uniform way, all of the data obtained by the Solar Disk Sextant (SDS) experiment, concerning high-precision measurements of the solar radius and Oblateness, in the bandwidth 590 {–} 670 nm, made onboard stratospheric balloons during a series of flights carried out in 1992, 1994, 1995, and 1996. The measured radius value appears anti-correlated with the level of solar activity, ranging from about 959.5 to 959.7 arcsec. Its variation from year to year is outside the error range, which is mostly due to a systematic diurnal behavior, particularly evident in the 1996 flight. The Oblateness shows an analogous temporal behavior, ranging from about (4.3 to 10.3) × 10−6.

  • the solar diameter and Oblateness measured by the solar disk sextant on the 1992 september 30 balloon flight
    The Astrophysical Journal, 1994
    Co-Authors: Susan Sofia, William S Heaps, L Twigg
    Abstract:

    This paper reports the results of a balloon flight of the Solar Disk Sextant (SDS) on 1992 September 30. This was the first flight in which the SDS used a wedge assembly fabricated by molecular contact in order to eliminate the wedge angle variations observed in previous flights. The instrument performed as designed. The main results obtained are values of the solar diameter for a number of discrete heliocentric latitudes, and the solar Oblateness. The accuracy of the diameter values is better than 0.2 sec whereas the precision is approximately 1-2 mas. The equatorial solar diameter, at 1 AU, was 1919.06 sec +/- 0.12 sec, and the Oblateness epsilon = 8.63 +/- 0.88 x 10(exp -6).

J P Rozelot - One of the best experts on this subject based on the ideXlab platform.

  • Revisiting the Solar Oblateness: Is Relevant Astrophysics Possible?
    Solar Physics, 2013
    Co-Authors: J P Rozelot, Z. Fazel
    Abstract:

    The measurement of solar Oblateness has a rich history extending well back into the past. Until recently, its estimate has been actively disputed, as has its temporal dependence. Recent accurate observations of the solar shape gave cause for doubt, and so far only balloon flights or satellite experiments, such as those onboard SDO, seem to achieve the required sensitivity to measure the expected small deviations from sphericity. A shrinking or an expanding shape is ultimately linked to solar activity (likely not homologously with its change), as gravitational or magnetic fields, which are existing mechanisms for storing energy during a solar cycle, lead to distinct perturbations in the equilibrium solar-structure and changes in the diameter. It follows that a sensitive determination of the solar radius fluctuations might give information about the origin of the solar cycle. In periods of higher activity, the outer photospheric shape seems to become aspheric under the influence of higher-order multipole moments of the Sun, resulting both from the centrifugal force and the core rotation. An accurate determination of the shape of the Sun is thus one of the ways that we have now for peering into its interior, learning empirically about flows and motions there that would otherwise only be guessed at from theoretical considerations, developing more precise inferences, and ultimately building possible alternative gravitational theories.

  • History of solar Oblateness measurements and interpretation
    The European Physical Journal H, 2011
    Co-Authors: J P Rozelot, C Damiani
    Abstract:

    The story of the solar Oblateness begins in the pre-relativity days when an explanation of the observed advance of Mercury’s perihelion was searched for. Then, examination of historical records during the first decade of the twentieth century shows clearly a strong effort to measure the solar shape. Results show discrepancies, due on one hand, to the fact that physical statements in the solar case are still pending (for example does the solar core rotate rapidly? Is the Sun an oblique rotator? How does the magnetic field distort the outer shape?) and on the other hand, due to the difficulty in measuring a faint quantity, even when using the cutting edge of up-to-date techniques. We provide a new perspective on the controversy which followed measurements made in Princeton (USA) in the mid-1960s, highlighting the possibility to advocate alternative theories of gravitation. Since then, the accurate shape of the Sun has been actively debated, and so far, only satellite experiments seem to achieve the required sensitivity to measure the expected faint deviations to sphericity. In a close cooperation between experiments and theory, we point out how false ideas or inexact past measurements may contribute to the advancement of new physical concepts.

  • probing the solar surface the Oblateness and astrophysical consequences
    First Middle East-Africa Regional IAU Meeting, 2008
    Co-Authors: J P Rozelot, C Damiani, S Pireaux
    Abstract:

    Based on historical records, the Sun's dimensions are temporally dependent. Until the recent past, varying dimensions were keenly disputed. Recent accurate observations have removed the doubt, whether from direct limb observations or from helioseismology f-modes analysis. A shrinking or an expanding shape is ultimately linked to solar activity, as even a small variation in the solar radius causes variations in gravitational energy. Based on accurate space- and ground-based observations, we will argue that the Oblateness of the Sun is time dependent. Indeed, considering the first two shape coefficients, we can interpret such a temporal variation as a change in the relative importance of the hexadecapolar term, i.e., at the time of high activity, only the dipolar moment c 2 has a significant effect, but at the time of low activity, c 4 is predominant; this results in a decrease of the total value of the Oblateness. The combination of the two terms leads to a solar Oblateness varying along with solar activity. More studies are needed to get accurate measurements from space, which will provide us with the unique opportunity to study detailed changes of global solar properties.

  • the solar Oblateness and its relationship with the structure of the tachocline and of the sun s subsurface
    Astronomy and Astrophysics, 2000
    Co-Authors: S Godier, J P Rozelot
    Abstract:

    The solar Oblateness " was computed with a dynami- cal up-to-date solar model of mass and density, combined with a recent rotational model established from the helioseismic data, and including the effects of differential rotation with depth. To determine the theoretical value of the Oblateness " of the Sun, we integrated the extended differential equation governing the fluids in hydrostatic equilibrium and the Poisson equation for the gravitational potential. From this analysis, we deduced the profiles of ", as a function of the radius and of the latitude, from the core to the surface, for a Sun splitted into a series of con- centric shells. As each shell is affected by a potential distortion, mainly due to the rotation, and as the rotation rate depends on the radius and on the latitude, each shell of the Sun is affected by a different Oblateness. As a result of the integration of this function, we found " =8 :77:10 6 , that we compared to the Oblateness of a rigidly rotating sphere. To interprete the difference in Oblateness " of the studied layers within the Sun, we linked the profiles to the solar interior structures, specially to the tachocline and to the subsurface, that help us to understand why and how these regions are mainly governed by shear. In particular, we propose for these two layers a double structure, one where the magnetic field would be stored and one of shear. Finally, we compared our results of radial integrated oblate- ness with the latitudinal variation of the semidiameter from solar astrolabe observations.

Abdanour Irbah - One of the best experts on this subject based on the ideXlab platform.

  • On HMI solar Oblateness during solar cycle 24 and impact of the space environment on results
    Advances in Space Research, 2016
    Co-Authors: Mustapha Meftah, Alain Hauchecorne, R. I. Bush, Abdanour Irbah
    Abstract:

    Solar Oblateness is a fundamental parameter of the Sun, which provides indirect information on the inner rotation profile and on the distribution of matter. It also puts constraints on General Relativity. But this quantity is difficult to measure due to its very small value where the solar equator-to-pole radius difference is less than 10 milli-arcsecond (mas). Indeed, the measurements can be affected by magnetic activity and by instrumental effects linked to the space environment. The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) has produced accurate determinations of the solar Oblateness from 2010 to 2015. The HMI measurements of the solar shape are obtained during special roll maneuvers of the spacecraft by 11.25 degrees steps around the spacecraft to the Sun line. HMI roll maneuver has been repeated ten times after the commissioning phase from October 2010 to July 2015. From HMI data, we observed a slight anti-correlation between solar Oblateness and solar activity. From a new correction method, we found a mean solar equator-to-pole radius difference of 8.36 ± 0.49 mas (i.e. 6.06 ± 0.35 km at one σ ) at 617.3 nm during the period 2010-2015.

  • On solar Oblateness measurements during the current solar cycle 24
    2015
    Co-Authors: Alain Hauchecorne, Abdanour Irbah, Rock Bush
    Abstract:

    The rotation of the Sun on itself involves a flatness of the Polar Regions. The solar Oblateness results from the rotation of the whole solar interior and the distribution of its mass according to the depth. Thus, possible diagnostic of the internal rotation is provided by the solar Oblateness. The solar Oblateness also places constraints on general relativity. Indeed, the modern era of measurements of the solar Oblateness began in the 1960s with Dicke’s measurements, which were useful in understanding the perihelion precession of Mercury’s orbit, one of the classical tests of general relativity. Thus, for various reasons, it is necessary to better know the solar Oblateness value and to study its dependence with the solar activity. Based on measurements collected from various instruments over the past 50 years, the measured solar equator-to-pole radius difference converges towards 8 mas (near 5.8 km). Now, with space era, we felt it was possible to obtain very accurate measurements of the solar equator-to-pole radius difference and its evolution over time. Thus, we developed an original method to estimate the solar equator-to-pole radius difference from two solar space missions (Solar Dynamics Observatory and PICARD). When analysing the solar radius versus angle data, we observed an anti-correlation between the limb brightness and the radius determined from the inflection point. The apparent radius was smaller if an active region was near the limb. The bright active regions were confined to low latitudes and never occur at the poles. The exact cause of this anti-correlation needs still to be understood but it is clear that it may cause an artefact in the determination of the solar Oblateness leading to a negative bias, even if the more active regions were eliminated from the analysis. In this talk, we describe the method, and then present current results about solar Oblateness variations after five years of solar observations (from 2010 to 2015) and linkages between measurements and harsh space environment.

  • on the determination and constancy of the solar Oblateness
    Solar Physics, 2015
    Co-Authors: Mustapha Meftah, Abdanour Irbah, Alain Hauchecorne, T Corbard, S Turckchieze, Jeanfrancois Hochedez, P Boumier, Andre Chevalier, Steven Dewitte, S Mekaoui
    Abstract:

    The equator-to-pole radius difference (Δr=R eq−R pol) is a fundamental property of our star, and understanding it will enrich future solar and stellar dynamical models. The solar Oblateness (Δ⊙) corresponds to the excess ratio of the equatorial solar radius (R eq) to the polar radius (R pol), which is of great interest for those working in relativity and different areas of solar physics. Δr is known to be a rather small quantity, where a positive value of about 8 milli-arcseconds (mas) is suggested by previous measurements and predictions. The Picard space mission aimed to measure Δr with a precision better than 0.5 mas. The Solar Diameter Imager and Surface Mapper (SODISM) onboard Picard was a Ritchey–Chretien telescope that took images of the Sun at several wavelengths. The SODISM measurements of the solar shape were obtained during special roll maneuvers of the spacecraft by 30° steps. They have produced precise determinations of the solar Oblateness at 782.2 nm. After correcting measurements for optical distortion and for instrument temperature trend, we found a solar equator-to-pole radius difference at 782.2 nm of 7.9±0.3 mas (5.7±0.2 km) at one σ. This measurement has been repeated several times during the first year of the space-borne observations, and we have not observed any correlation between Oblateness and total solar irradiance variations.

  • new space value of the solar Oblateness obtained with picard
    The Astrophysical Journal, 2014
    Co-Authors: Abdanour Irbah, Alain Hauchecorne, Mustapha Meftah, Djelloul Djafer, T Corbard, Maxime Bocquier, Momar E Cisse
    Abstract:

    The PICARD spacecraft was launched on 2010 June 15 with the scientific objective of studying the geometry of the Sun. It is difficult to measure solar Oblateness because images are affected by optical distortion. Rolling the satellite, as done in previous space missions, determines the contribution of the telescope by assuming that the geometry of the Sun is constant during the observations. The optical response of the telescope is considered to be time-invariant during the roll operations. This is not the case for PICARD because an orbital signature is clearly observed in the solar radius computed from its images. We take this effect into account and provide the new space value of solar Oblateness from PICARD images recorded in the solar continuum at 535.7 nm on 2011 July 4-5. The equator-pole radius difference is 8.4 ± 0.5 mas, which corresponds to an absolute radius difference of 6.1 km. This coincides with the mean value of all solar Oblateness measurements obtained during the last two decades from the ground, balloons, and space. It is also consistent with values determined from models using helioseismology data.

  • the solar Oblateness measured on board the picard spacecraft and the solar disk sextant instrument
    American Geophysical Union Fall Meeting 2011, 2011
    Co-Authors: Gerard Thuillier, Susan Sofia, Abdanour Irbah, Alain Hauchecorne, Mustapha Meftah, Jeanfrancois Hochedez, Terry Girard, Jeanpierre Marcovici, Mireille Meissonnier, Ulysses J Sofia
    Abstract:

    The PICARD Spacecraft was launched on 15 June 2010. It carries four instruments. One of them, SODISM is an imaging telescope with a 2K x 2K CCD detector, dedicated to the measurement of the solar diameter and the limb shape. Although the data processing is still in a validation phase, we can already present some preliminary results concerning the solar Oblateness. These measurements are obtained during a special operation in which the spacecraft turns around the Sun direction. The rotation, made by 300 angular increments, allows us to determine the instrument optical distortion and the solar Oblateness. The method used to extract this information will be described. We shall present the preliminary results as a function of wavelength, and compare them with measurements obtained with the SDS instrument, and with the predictions from theoretical modeling.

Jagadish Singh - One of the best experts on this subject based on the ideXlab platform.

  • stability of triangular points in the elliptic restricted three body problem with Oblateness up to zonal harmonic j4 of both primaries
    European Physical Journal Plus, 2016
    Co-Authors: Jagadish Singh, Richard K Tyokyaa
    Abstract:

    In this paper, we study the locations and stability of triangular points in the elliptic restricted three-body problem when both primaries are taken as oblate spheroids with Oblateness up to J4. The positions of the triangular points are seen to be affected by Oblateness of the primaries and the eccentricity of their orbits. The triangular points are conditionally stable for $0 < \mu < \mu_{c}$ and unstable for $\mu_{c}\le \mu \le \frac{1}{2}$ , where $\mu_{c}$ is the critical mass parameter depending on the Oblateness coefficients $J_{2i}$ (i =1,2) and the eccentricity of the orbits. We further observe that both coefficients J2 and J4, semi-major axis and the eccentricity have destabilizing tendencies resulting in a decrease in the size of the region of stability with an increase in the parameters involved. Knowing that, in general, the triangular equilibrium points are stable for $0 < \mu < \mu_{c}$ , in particular systems (Alpha Centauri, $X_{1}$ Bootis, Sirius and Kruger 60) this does not hold and such points are unstable.

  • stability of triangular points in the relativistic r3bp when the bigger primary is an oblate spheroid
    Journal of Dynamical Systems and Geometric Theories, 2016
    Co-Authors: Nakone Bello, Jagadish Singh
    Abstract:

    AbstractIn this paper, we study the effect of Oblateness of the more massive primary in the relativistic R3BP. We observe that the locations of the triangular points and their stability are affected by the relativistic and Oblateness factors. It is also noticed that the Oblateness factor possesses destabilizing behavior. Therefore, the size of the region of stability decreases with increase in the value of the Oblateness factor.Further, a numerical study on the locations of the triangular points and the critical mass for the Earth-Moon , Jupiter and its Moons, Saturn and its Moons systems is given.

  • existence and linear stability of triangular points in the perturbed relativistic r3bp when the bigger primary is an oblate spheroid
    International Journal of Advanced Astronomy, 2016
    Co-Authors: Bello Nakone, Jagadish Singh
    Abstract:

    We study the effects of Oblateness and small perturbations in the Coriolis and centrifugal forces on the locations and stability of the triangular points in the relativistic R3BP. It is observed that the positions are affected by the Oblateness, relativistic, and a small perturbation in the centrifugal force, but are unaffected by that of Coriolis force. It is also seen that the relativistic terms, Oblateness, small perturbations in the centrifugal and Coriolis forces influence the critical mass ratio. It is also noticed that all the former three and the latter one possess destabilizing and stabilizing behavior respectively. However, the range of stability increases or decreases according to as p >0 or p<0 where p depends upon the relativistic, Oblateness and small perturbations in the Coriolis and centrifugal forces.

  • combined effect of Oblateness radiation and a circular cluster of material points on the stability of triangular liberation points in the r3bp
    Astrophysics and Space Science, 2014
    Co-Authors: Jagadish Singh, Joel John Taura
    Abstract:

    This paper studies the motion of an infinitesimal mass in the framework of the restricted three-body problem (R3BP) under the assumption that the primaries of the system are radiating-oblate spheroids, enclosed by a circular cluster of material points. It examines the effects of radiation and Oblateness up to J4 of the primaries and the potential created by the circular cluster, on the linear stability of the liberation locations of the infinitesimal mass. The liberation points are found to be stable for 0<μ<μc and unstable for \(\mu_{c}\le\mu\le\frac{1}{2}\), where μc is the critical mass value depending on terms which involve parameters that characterize the Oblateness, radiation forces and the circular cluster of material points. The Oblateness up to J4 of the primaries and the gravitational potential from the circular cluster of material points have stabilizing propensities, while the radiation of the primaries and the Oblateness up to J2 of the primaries have destabilizing tendencies. The combined effect of these perturbations on the stability of the triangular liberation points is that, it has stabilizing propensity.

  • equilibrium points and stability in the restricted three body problem with Oblateness and variable masses
    Astrophysics and Space Science, 2012
    Co-Authors: Jagadish Singh, Oni Leke
    Abstract:

    The existence and stability of a test particle around the equilibrium points in the restricted three-body problem is generalized to include the effect of variations in Oblateness of the first primary, small perturbations ϵ and ϵ′ given in the Coriolis and centrifugal forces α and β respectively, and radiation pressure of the second primary; in the case when the primaries vary their masses with time in accordance with the combined Meshcherskii law. For the autonomized system, we use a numerical evidence to compute the positions of the collinear points L2κ, which exist for 0 1, provided the abscissae \(\xi<\frac{\nu(\kappa-1)}{\beta}\). In the case of the triangular points, it is seen that these points exist for ϵ′<κ<∞ and are affected by the Oblateness term, radiation pressure and the mass parameter. The linear stability of these equilibrium points is examined. It is seen that the collinear points L2κ are stable for very small κ and the involved parameters, while the out of plane equilibrium points are unstable. The conditional stability of the triangular points depends on all the system parameters. Further, it is seen in the case of the triangular points, that the stabilizing or destabilizing behavior of the Oblateness coefficient is controlled by κ, while those of the small perturbations depends on κ and whether these perturbations are positive or negative. However, the destabilizing behavior of the radiation pressure remains unaltered but grows weak or strong with increase or decrease in κ. This study reveals that Oblateness coefficient can exhibit a stabilizing tendency in a certain range of κ, as against the findings of the RTBP with constant masses. Interestingly, in the region of stable motion, these parameters are void for \(\kappa=\frac{4}{3}\). The decrease, increase or non existence in the region of stability of the triangular points depends on κ, Oblateness of the first primary, small perturbations and the radiation pressure of the second body, as it is seen that the increasing region of stability becomes decreasing, while the decreasing region becomes increasing due to the inclusion of Oblateness of the first primary.

Alain Hauchecorne - One of the best experts on this subject based on the ideXlab platform.

  • On HMI solar Oblateness during solar cycle 24 and impact of the space environment on results
    Advances in Space Research, 2016
    Co-Authors: Mustapha Meftah, Alain Hauchecorne, R. I. Bush, Abdanour Irbah
    Abstract:

    Solar Oblateness is a fundamental parameter of the Sun, which provides indirect information on the inner rotation profile and on the distribution of matter. It also puts constraints on General Relativity. But this quantity is difficult to measure due to its very small value where the solar equator-to-pole radius difference is less than 10 milli-arcsecond (mas). Indeed, the measurements can be affected by magnetic activity and by instrumental effects linked to the space environment. The Helioseismic and Magnetic Imager (HMI) instrument onboard the Solar Dynamics Observatory (SDO) has produced accurate determinations of the solar Oblateness from 2010 to 2015. The HMI measurements of the solar shape are obtained during special roll maneuvers of the spacecraft by 11.25 degrees steps around the spacecraft to the Sun line. HMI roll maneuver has been repeated ten times after the commissioning phase from October 2010 to July 2015. From HMI data, we observed a slight anti-correlation between solar Oblateness and solar activity. From a new correction method, we found a mean solar equator-to-pole radius difference of 8.36 ± 0.49 mas (i.e. 6.06 ± 0.35 km at one σ ) at 617.3 nm during the period 2010-2015.

  • On solar Oblateness measurements during the current solar cycle 24
    2015
    Co-Authors: Alain Hauchecorne, Abdanour Irbah, Rock Bush
    Abstract:

    The rotation of the Sun on itself involves a flatness of the Polar Regions. The solar Oblateness results from the rotation of the whole solar interior and the distribution of its mass according to the depth. Thus, possible diagnostic of the internal rotation is provided by the solar Oblateness. The solar Oblateness also places constraints on general relativity. Indeed, the modern era of measurements of the solar Oblateness began in the 1960s with Dicke’s measurements, which were useful in understanding the perihelion precession of Mercury’s orbit, one of the classical tests of general relativity. Thus, for various reasons, it is necessary to better know the solar Oblateness value and to study its dependence with the solar activity. Based on measurements collected from various instruments over the past 50 years, the measured solar equator-to-pole radius difference converges towards 8 mas (near 5.8 km). Now, with space era, we felt it was possible to obtain very accurate measurements of the solar equator-to-pole radius difference and its evolution over time. Thus, we developed an original method to estimate the solar equator-to-pole radius difference from two solar space missions (Solar Dynamics Observatory and PICARD). When analysing the solar radius versus angle data, we observed an anti-correlation between the limb brightness and the radius determined from the inflection point. The apparent radius was smaller if an active region was near the limb. The bright active regions were confined to low latitudes and never occur at the poles. The exact cause of this anti-correlation needs still to be understood but it is clear that it may cause an artefact in the determination of the solar Oblateness leading to a negative bias, even if the more active regions were eliminated from the analysis. In this talk, we describe the method, and then present current results about solar Oblateness variations after five years of solar observations (from 2010 to 2015) and linkages between measurements and harsh space environment.

  • on the determination and constancy of the solar Oblateness
    Solar Physics, 2015
    Co-Authors: Mustapha Meftah, Abdanour Irbah, Alain Hauchecorne, T Corbard, S Turckchieze, Jeanfrancois Hochedez, P Boumier, Andre Chevalier, Steven Dewitte, S Mekaoui
    Abstract:

    The equator-to-pole radius difference (Δr=R eq−R pol) is a fundamental property of our star, and understanding it will enrich future solar and stellar dynamical models. The solar Oblateness (Δ⊙) corresponds to the excess ratio of the equatorial solar radius (R eq) to the polar radius (R pol), which is of great interest for those working in relativity and different areas of solar physics. Δr is known to be a rather small quantity, where a positive value of about 8 milli-arcseconds (mas) is suggested by previous measurements and predictions. The Picard space mission aimed to measure Δr with a precision better than 0.5 mas. The Solar Diameter Imager and Surface Mapper (SODISM) onboard Picard was a Ritchey–Chretien telescope that took images of the Sun at several wavelengths. The SODISM measurements of the solar shape were obtained during special roll maneuvers of the spacecraft by 30° steps. They have produced precise determinations of the solar Oblateness at 782.2 nm. After correcting measurements for optical distortion and for instrument temperature trend, we found a solar equator-to-pole radius difference at 782.2 nm of 7.9±0.3 mas (5.7±0.2 km) at one σ. This measurement has been repeated several times during the first year of the space-borne observations, and we have not observed any correlation between Oblateness and total solar irradiance variations.

  • new space value of the solar Oblateness obtained with picard
    The Astrophysical Journal, 2014
    Co-Authors: Abdanour Irbah, Alain Hauchecorne, Mustapha Meftah, Djelloul Djafer, T Corbard, Maxime Bocquier, Momar E Cisse
    Abstract:

    The PICARD spacecraft was launched on 2010 June 15 with the scientific objective of studying the geometry of the Sun. It is difficult to measure solar Oblateness because images are affected by optical distortion. Rolling the satellite, as done in previous space missions, determines the contribution of the telescope by assuming that the geometry of the Sun is constant during the observations. The optical response of the telescope is considered to be time-invariant during the roll operations. This is not the case for PICARD because an orbital signature is clearly observed in the solar radius computed from its images. We take this effect into account and provide the new space value of solar Oblateness from PICARD images recorded in the solar continuum at 535.7 nm on 2011 July 4-5. The equator-pole radius difference is 8.4 ± 0.5 mas, which corresponds to an absolute radius difference of 6.1 km. This coincides with the mean value of all solar Oblateness measurements obtained during the last two decades from the ground, balloons, and space. It is also consistent with values determined from models using helioseismology data.

  • the solar Oblateness measured on board the picard spacecraft and the solar disk sextant instrument
    American Geophysical Union Fall Meeting 2011, 2011
    Co-Authors: Gerard Thuillier, Susan Sofia, Abdanour Irbah, Alain Hauchecorne, Mustapha Meftah, Jeanfrancois Hochedez, Terry Girard, Jeanpierre Marcovici, Mireille Meissonnier, Ulysses J Sofia
    Abstract:

    The PICARD Spacecraft was launched on 15 June 2010. It carries four instruments. One of them, SODISM is an imaging telescope with a 2K x 2K CCD detector, dedicated to the measurement of the solar diameter and the limb shape. Although the data processing is still in a validation phase, we can already present some preliminary results concerning the solar Oblateness. These measurements are obtained during a special operation in which the spacecraft turns around the Sun direction. The rotation, made by 300 angular increments, allows us to determine the instrument optical distortion and the solar Oblateness. The method used to extract this information will be described. We shall present the preliminary results as a function of wavelength, and compare them with measurements obtained with the SDS instrument, and with the predictions from theoretical modeling.