Preliminary Studies of Solar Limb Brightening At 8mm

The solar limb brightening has also been earlier studied in various microwave frequencies [1-4] and also in Extreme Ultraviolet (EUV) region [5,6]. The observations of solar limb brightening have highly variations and sometimes they have given even contradictory results. Several authors have reported the absence of limb brightening (such as [7]) at 35 GHz. This study focuses on studying limb brightening at 8 mm. Many of these previous studies have made at 17 GHz [1,4]. Theoretical models [8] predict the solar brightening is caused by the temperature gradient of the solar atmosphere. We only want to study the limb brightening at the intermediate regions of the Sun. Spicules (or jets) and facula features have been assumed to be the major contributor for the limb brightening at high radio frequencies. Spicules are chromospheric features that their role is probably important in high radio frequencies. A single spicule can reach 3,000-10,000km altitude above the solar photosphere. Faculae are photospheric feature [1] such that their contribution is probably decreases at higher radio frequencies. Earlier studies with similar observing frequency have reported varying result: 3-10% [3], <1% [3] and <1.5% [2]. For this study, we only selected days with low-level of solar activity. Thus the solar activity does not affect to the observations and results. This is the major (lowlevel solar activity) difference to the previous studies on the same wavelength regimes.