686 research outputs found

    Estimate of solar radius from f-mode frequencies

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    Frequency and rotational splittings of the solar f-modes are estimated from the GONG data. Contrary to earlier observations the frequencies of f-modes are found to be close to the theoretically computed values for a standard solar model. The f-mode being essentially a surface mode is a valuable diagnostic probe of the properties of the solar surface, and also provides an independent measure of solar radius. The estimated solar radius is found to be about 0.03% less than what is traditionally used in construction of standard solar models. If this decrease in solar radius is confirmed then the current solar models as well as inversion results will need to be revised. The rotational splittings of the f-modes yield an independent measure of the rotation rate near the solar surface, which is compared with other measurements.Comment: 5 pages, A&A-TeX, 5 figure

    The discrepancy between solar abundances and helioseismology

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    There have been recent downward revisions of the solar photospheric abundances of Oxygen and other heavy elements. These revised abundances along with OPAL opacities are not consistent with seismic constraints. In this work we show that the recently released OP opacity tables cannot resolve this discrepancy either. While the revision in opacities does not seem to resolve this conflict, an upward revision of Neon abundance in solar photosphere offers a possible solution to this problem.Comment: To appear in ApJ Letter

    Constraining solar abundances using helioseismology

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    Recent analyses of solar photospheric abundances suggest that the oxygen abundance in the solar atmosphere needs to be revised downwards. In this study we investigate the consequence of this revision on helioseismic analyses of the depth of the solar convection zone and the helium abundance in the solar envelope and find no significant effect. We also find that the revised abundances along with the current OPAL opacity tables are not consistent with seismic data. A significant upward revision of the opacity tables is required to make solar models with lower oxygen abundance consistent with seismic observations.Comment: To appear in ApJ Letters. 12 pages (that include 4 figures

    Does the Sun shrink with increasing magnetic activity?

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    It has been demonstrated that frequencies of f-modes can be used to estimate the solar radius to a good accuracy. These frequencies have been used to study temporal variations in the solar radius with conflicting results. The variation in f-mode frequencies is more complicated than what is assumed in these studies. If a careful analysis is performed then it turns out that there is no evidence for any variation in the solar radius.Comment: To appear in Astrophys.

    Solar internal rotation rate and the latitudinal variation of the tachocline

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    A new set of accurately measured frequencies of solar oscillations are used to infer the rotation rate inside the Sun, as a function of radial distance as well as latitude. We have adopted a regularized least squares technique with iterative refinement for both 1.5D inversion using the splitting coefficients and 2D inversion using individual m splittings. The inferred rotation rate agrees well with earlier estimates showing a shear layer just below the surface and another one around the base of the convection zone. The tachocline or the transition layer where the rotation rate changes from differential rotation in the convection zone to almost latitudinally independent rotation rate in the radiative interior is studied in detail. No compelling evidence for any latitudinal variation in position and width of tachocline is found though it appears that the tachocline probably shifts to slightly larger radial distance at higher latitudes and possibly becomes thicker also. However, these variations are within the estimated errors and more accurate data would be needed to make a definitive statement about latitudinal variations.Comment: 15 pages, MNRAS-TeX, 15 figure

    Temporal variations of the rotation rate in the solar interior

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    The temporal variations of the rotation rate in the solar interior are studied using frequency splittings from Global Oscillations Network Group (GONG) data obtained during the period 1995-99. We find alternating latitudinal bands of faster and slower rotation which appear to move towards the equator with time - similar to the torsional oscillations seen at the solar surface. This flow pattern appears to persist to a depth of about 0.1R_sun and in this region its magnitude is well correlated with solar activity indices. We do not find any periodic or systematic changes in the rotation rate near the base of the convection zone.Comment: To appear in Ap

    Solar Rotation Rate During the Cycle 24 Minimum in Activity

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    The minimum of solar cycle 24 is significantly different from most other minima in terms of its duration as well as its abnormally low levels of activity. Using available helioseismic data that cover epochs from the minimum of cycle 23 to now, we study the differences in the nature of the solar rotation between the minima of cycles 23 and 24. We find that there are significant differences between the rotation rates during the two minima. There are differences in the zonal-flow pattern too. We find that the band of fast rotating region close to the equator bifurcated around 2005 and recombined by 2008. This behavior is different from that during the cycle 23 minimum. By auto-correlating the zonal-flow pattern with a time shift, we find that in terms of solar dynamics, solar cycle 23 lasted for a period of 11.7 years, consistent with the result of Howe et al. (2009). The autocorrelation coefficient also confirms that the zonal-flow pattern penetrates through the convection zone.Comment: Accepted for publication in Ap

    On the magnetic field required for driving the observed angular-velocity variations in the solar convection zone

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    A putative temporally varying circulation-free magnetic-field configuration is inferred in an equatorial segment of the solar convection zone from the helioseismologically inferred angular-velocity variation, assuming that the predominant dynamics is angular acceleration produced by the azimuthal Maxwell stress exerted by a field whose surface values are consistent with photospheric line-of-sight measurements.Comment: to appear in MNRA

    Large scale flows in the solar interior: Effect of asymmetry in peak profiles

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    Ring diagram analysis can be used to study large scale velocity fields in the outer part of the solar convection zone. All previous works assume that the peak profiles in the solar oscillation power spectrum are symmetric. However, it has now been demonstrated that the peaks are not symmetric. In this work we study how the explicit use of asymmetric peak profiles in ring-diagram analysis influences the estimated velocity fields. We find that the use of asymmetric profiles leads to significant improvement in the fits, but the estimated velocity fields are not substantially different from those obtained using a symmetric profile to fit the peaks. The resulting velocity fields are compared with those obtained by other investigators.Comment: To appear in Ap
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