Brightness of the solar F-corona

Abstract

We discuss our present knowledge about the brightness of the solar F-corona in the wavelength range from the visible to the middle infrared. From the general trend of the observational data, the F-corona is regarded as the continuous extension of the zodiacal light at smaller elongation of the line of sight. A contribution of thermal emission from dust is indicated by the increasing F-coronal brightness in comparison to the solar spectrum towards longer wavelength. As compared with the F-coronal brightness, the polarization and color in the visible regime are not well determined due to the high sensitivity of these quantities to the observational accuracy. Aside from observational problems, our present interpretation of the F-coronal brightness is also limited due to ambiguities in the inversion of the line of sight integral. Nevertheless, the measurements and model calculations of the brightness can be used to deduce some physical properties of dust grains. We show that the hump of the near-infrared brightness at 4 solar radii, which was sometimes observed in the corona, is related rather to the physical properties of dust grains along the line of sight than to the existence of a dust ring as previously discussed. We also show that the appearance or disappearance of the near-infrared peak in the coronal brightness cannot be described in any periodic cycle for each wavelength range.

Visible light and ultraviolet observations of coronal structures: physical properties of an equatorial streamer and modelling of the F corona

“…In recent years, several authors have investigated the intensity of the F corona. For instance, Kimura & Mann (1998) discussed the emission of the interplanetary dust in the wavelength range from the visible to the mid-infrared and showed that the hump of the near-infrared brightness at 4 R , sometimes observed in corona, is related to the physical properties of dust grains along the LOS rather than to the existence of a spherical dust ring. The hypothesis of an axisymmetric model of the F corona from the analysis of its morphology and photometry was first proposed by Koutchmy & Lamy (1985); they studied the infrared observations of the dust grains and obtained an expression of the F-corona intensity as a function of the heliocentric distance, which is the most quoted at present.…”

Cosmic dust VIII

“…It might be worthwhile to recognize that near-infrared excess emission observed in the solar F-corona is a similar enigmatic phenomenon. The excess emission of the solar F-corona has been detected around 4 R from the Sun until 1983 in the H and J bands and until 1973 in the K and L bands, but its origin is still an open question (Kimura and Mann, 1998). Here we cannot help but wonder whether the hot dust populations could be replenished by the super-catastrophic disruption of sub-kilometer to kilometer sized planetesimals in the vicinity of the star (cf.…”

On the Use of Total Brightness Measurements for Tomography of the Solar Corona

“…It is thought that the F-corona emission is weakly polarized or unpolarized, while the electron-scattered K corona is known to be strongly polarized with the electric field vector oscillating in a plane parallel to the limb tangent (e.g., Billings 1966;Kimura & Mann 1998). Blackwell & Petford (1966a, 1966b used spectroscopic separation of the F and K components to show that the F corona is about 0.2% polarized at 10 R and 0.5% polarized at 15 R .…”

“…The F corona models have significant uncertainty, and the importance of this uncertainty increases at larger heights above the limb where the F corona increasingly dominates the unpolarized signal. The current state of knowledge of the F corona and its optical/IR properties, including polarization, is reviewed in Kimura & Mann (1998). There is more discussion of dust physics in Blackwell et al (1967a) and Mann et al (2004).…”