Abstract
Spectroscopic studies of the solar corona, using the high spatial and spectral resolution 25-cm coronagraph at the Norikura Solar Observatory for equatorial off-limb observations, indicated that the variation of radiance and line width with height is different for different temperature lines. The line width of the forbidden red emission line [Fe x] 6374 Å was found to increase with height, and that of the green emission line [Fe xiv] 5303 Å decreased with height. This had been interpreted in terms of the interaction between different temperature plasmas but needed to be confirmed. Further observations were made on several days during 2004, in two emission lines simultaneously covering the mid-latitude and polar regions to investigate the existence of the observed variation in other parts of the solar corona. In this study, we have analysed several raster scans that cover mid- and high-latitude regions of the off-limb corona in all four bright emission lines [Fe x] 6374 Å, [Fe xi] 7892 Å, [Fe xiii] 10747 Å, and [Fe xiv] 5303 Å. We find that the FWHM of the red line increases with height and that of the green line decreases with height, similar to the observations in the equatorial regions. The line widths are higher in the polar regions for all of the observed emission lines except the green line. Higher values of FWHM in polar regions may imply higher non-thermal velocities, which could be further linked to a non-thermal source powering the solar-wind acceleration, but the reason for the behaviour of the green emission line remains to be explored.
Similar content being viewed by others
References
Akiyama, S., Doschek, G.A., Mariska, J.T.: 2005, Nonthermal velocities in different temperature regions of the solar lower transition region. Astrophys. J. 623, 540 – 550. doi: 10.1086/428638 .
Banerjee, D., Pérez-Suárez, D., Doyle, J.G.: 2009, Signatures of Alfvén waves in the polar coronal holes as seen by EIS/Hinode. Astron. Astrophys. 501, L15 – L18. doi: 10.1051/0004-6361/200912242 .
Banerjee, D., Teriaca, L., Doyle, J.G., Wilhelm, K.: 1998, Broadening of SI viii lines observed in the solar polar coronal holes. Astron. Astrophys. 339, 208 – 214.
Bemporad, A., Abbo, L.: 2012, Spectroscopic signature of Alfvén waves damping in a polar coronal hole up to 0.4 solar radii. Astrophys. J. 751, 110. doi: 10.1088/0004-637X/751/2/110 .
Contesse, L., Koutchmy, S., Viladrich, C.: 2004, Analysis of non-thermal velocities in the solar corona. Ann. Geophys. 22, 3055 – 3062. doi: 10.5194/angeo-22-3055-2004 .
Doyle, J.G., Banerjee, D., Perez, M.E.: 1998, Coronal line-width variations. Solar Phys. 181, 91 – 101. ADS: 1998SoPh..181...91D , doi: 10.1023/A:1005019931323 .
Hahn, M., Landi, E., Savin, D.W.: 2012, Evidence of wave damping at low heights in a polar coronal hole. Astrophys. J. 753, 36. doi: 10.1088/0004-637X/753/1/36 .
Harrison, R.A., Hood, A.W., Pike, C.D.: 2002, Off-limb EUV line profiles and the search for wave activity in the low corona. Astron. Astrophys. 392, 319 – 327. doi: 10.1051/0004-6361:20021189 .
Hassler, D.M., Moran, T.G.: 1994, Broadening of the FeX (6374 Å) profiles above the limb in a coronal hole. Space Sci. Rev. 70, 373 – 377. doi: 10.1007/BF00777895 .
Hassler, D.M., Rottman, G.J., Shoub, E.C., Holzer, T.E.: 1990, Line broadening of MG X 609 and 625 A coronal emission lines observed above the solar limb. Astrophys. J. Lett. 348, L77 – L80. doi: 10.1086/185635 .
Mierla, M., Schwenn, R., Teriaca, L., Stenborg, G., Podlipnik, B.: 2008, Analysis of the Fe X and Fe XIV line width in the solar corona using LASCO-C1 spectral data. Astron. Astrophys. 480, 509 – 514. doi: 10.1051/0004-6361:20078329 .
O’Shea, E., Banerjee, D., Doyle, J.G.: 2005, On the widths and ratios of Mg X 609.79 and 624.94 Å lines in polar off-limb regions. Astron. Astrophys. 436, L35 – L38. doi: 10.1051/0004-6361:200500120 .
O’Shea, E., Banerjee, D., Poedts, S.: 2003, Variation of coronal line widths on and off the disk. Astron. Astrophys. 400, 1065 – 1070. doi: 10.1051/0004-6361:20030060 .
Pekünlü, E.R., Bozkurt, Z., Afsar, M., Soydugan, E., Soydugan, F.: 2002, Alfvén waves in the inner polar coronal hole. Mon. Not. Roy. Astron. Soc. 336, 1195 – 1200. doi: 10.1046/j.1365-8711.2002.05849.x .
Raju, K.P., Chandrasekhar, T., Ashok, N.M.: 2011, Analysis of coronal green line profiles: Evidence of excess blueshifts. Astrophys. J. 736, 164. doi: 10.1088/0004-637X/736/2/164 .
Seely, J.F., Feldman, U., Schühle, U., Wilhelm, K., Curdt, W., Lemaire, P.: 1997, Turbulent velocities and ion temperatures in the solar corona obtained from SUMER line widths. Astrophys. J. Lett. 484, L87. doi: 10.1086/310769 .
Singh, J., Sakurai, T., Ichimoto, K. 2006, Do the line widths of coronal emission lines increase with height above the limb? Astrophys. J. 639, 475 – 483. doi: 10.1086/499200 .
Singh, J., Ichimoto, K., Imai, H., Sakurai, T., Takeda, A.: 1999, Spectroscopic studies of the solar corona I. Spatial variations in line parameters of green and red coronal lines. Pub. Astron. Soc. Japan 51, 269 – 276.
Singh, J., Sakurai, T., Ichimoto, K., Suematsu, Y., Takeda, A.: 2002a, Spectroscopic studies of the solar corona II. Properties of green and red emission lines in open and closed coronal structures. Pub. Astron. Soc. Japan 54, 793 – 806.
Singh, J., Sakurai, T., Ichimoto, K., Takeda, A.: 2002b, Spectroscopic studies of the solar corona III. Density diagnostics using the infrared lines of Fe xiii. Pub. Astron. Soc. Japan 54, 807 – 816.
Singh, J., Sakurai, T., Ichimoto, K., Muneer, S.: 2003a, Spectroscopic studies of the solar corona – V. Physical properties of coronal structures. Solar Phys. 212, 343 – 359. ADS: 2003SoPh..212..343S , doi: 10.1023/A:1022948520902 .
Singh, J., Ichimoto, K., Sakurai, T., Muneer, S.: 2003b, Spectroscopic studies of the solar corona. IV. Physical properties of coronal structure. Astrophys. J. 585, 516 – 523. doi: 10.1086/346000 .
Singh, J., Sakurai, T., Ichimoto, K., Watanabe, T.: 2004, Complex variations in the line-intensity ratio of coronal emission lines with height above the limb. Astrophys. J. Lett. 617, L81 – L84. doi: 10.1086/427078 .
Singh, J., Sakurai, T., Ichimoto, K., Muneer, S., Raveendran, A.V.: 2006, Spectroscopic studies of solar corona VIII. Temperature and non-thermal variations in steady coronal structures. Solar Phys. 236, 245 – 262. ADS: 2006SoPh..236..245S , doi: 10.1007/s11207-006-0104-7 .
Singh, J., Hasan, S.S., Gupta, G.R., Nagaraju, K., Banerjee, D.: 2011, Spectroscopic observation of oscillations in the corona during the total solar eclipse of 22 July 2009. Solar Phys. 270, 213 – 233. ADS: 2011SoPh..270..213S , doi: 10.1007/s11207-011-9732-7 .
Tripathi, D., Mason, H.E., Dwivedi, B.N., del Zanna, G., Young, P.R.: 2009, Active region loops: Hinode/Extreme-Ultraviolet Imaging Spectrometer observations. Astrophys. J. 694, 1256 – 1265. doi: 10.1088/0004-637X/694/2/1256 .
Wilhelm, K., Dwivedi, B.N., Teriaca, L.: 2004, On the widths of the Mg x lines near 60 nm in the corona. Astron. Astrophys. 415, 1133 – 1139. doi: 10.1051/0004-6361:20034234 .
Wilhelm, K., Curdt, W., Marsch, E., Schühle, U., Lemaire, P., Gabriel, A., Vial, J.-C., Grewing, M., Huber, M.C.E., Jordan, S.D., Poland, A.I., Thomas, R.J., Kühne, M., Timothy, J.G., Hassler, D.M., Siegmund, O.H.W.: 1995, SUMER – Solar Ultraviolet Measurements of Emitted Radiation. Solar Phys. 162, 189 – 231. ADS: 1995SoPh..162..189W , doi: 10.1007/BF00733430 .
Wilhelm, K., Fludra, A., Teriaca, L., Harrison, R.A., Dwivedi, B.N., Pike, C.D.: 2005, The widths of vacuum-ultraviolet spectral lines in the equatorial solar corona observed with CDS and SUMER. Astron. Astrophys. 435, 733 – 741. doi: 10.1051/0004-6361:20042460 .
Acknowledgements
The authors thank the referee for useful comments. J. Singh thanks the National Astronomical Observatory of Japan (NAOJ) for providing the financial grant enabling a trip to Norikura Solar Observatory to make the observations. He also thanks the team at the observatory for their help during the observations.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Prasad, S.K., Singh, J. & Banerjee, D. Variation of Emission Line Width in Mid- and High-Latitude Corona. Sol Phys 282, 427–442 (2013). https://doi.org/10.1007/s11207-012-0160-0
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s11207-012-0160-0