The solar radius in the EUV during the cycle XXIII
Centro de Rádio Astronomia e Astrofísica Mackenzie, R. da Consolação 896, 01302-907 São Paulo, SP, Brazil e-mail: firstname.lastname@example.org
2 Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brazil
Accepted: 27 September 2007
Aims.We aim to determine the solar transition region and coronal radius at EUV wavelengths and its time evolution during Solar Cycle XXIII.
Methods.We use daily 30.4 and 17.1 nm images obtained by the Extreme Ultraviolet Imager (EIT) aboard the SoHO satellite and derive the solar radius by fitting a circle to the limb brightness ring.
Results.The weighted mean of the temporal series gives and at 30.4 and 17.1 nm respectively. No significant correlation was found with the solar cycle at either of the two wavelengths.
Conclusions.Since the temperature formation of the 30.4 nm line is between (60–80) 103 K (Transition Region), the obtained result is greater than that derived from present optical atmospheric models. On the contrary, this height is compatible with radio models.
Key words: Sun: chromosphere / Sun: transition region / Sun: corona / Sun: UV radiation
© ESO, 2007