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Astron. Astrophys. 363, 279-288 (2000)

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6. Conclusions

  1. There are 3 classes of INBPs

    1. those that show excess emission and are associated with enhanced IN magnetic fields [FORMULA] 4 Mx cm-2 (these constitute 60% in our study),

    2. those that show equal excess emission but are associated with bipoles with flux densities generally [FORMULA] 4 Mx cm-2 (these constitute 25% in our study), and

    3. those that show weak emission (probably unresolved emission) and seemingly associated with fields [FORMULA] 4 Mx cm-2 which is below the noise level set by us for our magnetic scans (these constitute 15% in our study). These are probably the unresolved background fields.

  2. In particular, this study suggests that cases of magnetic bipole merging have been discounted in other studies (Nindos & Zirin, 1998; Lites et al., 1999) since these bright points are associated typically with relatively small (and temporally diminishing) net field values. When these cases are also included, it is found that the correlation between bright points and co-located magnetic elements in the data reported here is as high as 85%.

  3. Although we have established a spatial correspondence in the locations of the INBPs and IN magnetic elements, we have not been able to obtain a correlation between the brightness of the INBPs and the corresponding IN magnetic elements (if this exists on the sun) because of the scatter caused by the 3-min. oscillations.

  4. The results of the present study establish the association of K2V bright points with magnetic elements and, so, confirm the findings of Sivaraman & Livingston (1982) and Nindos & Zirin (1998). The mean field of the IN magnetic elements associated with the INBPs from our measurements is 7.2 Mx cm-2 above the noise level. Our observations are with limited spatial resolution as we have averaged the brightness and magnetic field values over a 2 [FORMULA] 2 pixel area. If the INBPs and IN magnetic elements are sub-arc-sec structures in reality then the flux density of the IN elements as per our measurements could be several hundred Mx cm-2. Such fields would then become dynamically important since the IN elements would serve as sites where the 3-minute waves can be excited (Kalkofen, 1996). Fields of this strength have been measured by Keller et al. (1994) and Lin (1995). Note that one should normally observe significantly more IN magnetic elements than INBPs since INBPs, due to their brightening process (3-minute pulse), could be "dark" at the time the spectroheliogram is recorded. The apparent lack of IN magnetic elements is probably due to the averaging process of the smaller sub-arc-sec unresolved magnetic flux tubes.

  5. We have identified instances of short fibril (loop) structures connecting adjacent INBPs from the excellent K spectroheliogram close to the limb obtained by Bruce Gillespie. This is a direct visual evidence of the INBPs' association with the IN magnetic elements.

  6. We are aware that the data we have analysed are not an ideal set of observations to settle this question - association of INBPs with IN magnetic elements (or otherwise) indisputably. But this is the best that can be done with the best facilities that are currently available. What is needed?

    1. spectroheliogram time sequence at high cadence (every 5 sec or so) with a narrow spectral band pass as we have used and under excellent seeing conditions, and

    2. magnetic scans with better S/N ratio at high cadence and simultaneous with the spectroheliograms.

  7. With these data

    1. the effect of the 3-min. oscillations can be effectively eliminated,

    2. the trajectories of the INBPs and the associated IN magnetic elements can be monitored to see whether they follow identical patterns. Zhang et al. (1998a) have done this for many IN magnetic elements using the BBSO data,

    3. the oscillation period of the NBPs (low brightness) can be determined. This would tell us the effect, if any, due to magnetic field coalescing.

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© European Southern Observatory (ESO) 2000

Online publication: December 5, 2000
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