Objectives:
Statistics of mass loading in quiescent prominences based on observations in H_alpha by solar spectrographs of the Ondrejov observatory, in EUV by SDO/AIA and in soft X-rays by XRT on Hinode.
Scientific background:
Absorption of the EUV coronal radiation in cool prominences is due to photoionization of hydrogen at wavelengths below 912 A, of neutral helium HeI below 504 A and ionized helium HeII below 228 A. Another mechanism that contributes to a lowering of the EUV brightness of the corona at the prominence location is called the coronal emissivity blocking. This mechanism is based on the fact that cool prominence plasma cannot emit any coronal radiation. Then the intensity of a coronal line, expressed as the integral along the line of sight, is lower at the prominence than in the surrounding corona. Both mechanisms were studied theoretically by Anzer & Heinzel (2005). They also developed models which provide optical thickness of the prominence at the head of the hydrogen Lyman continuum. For mass-loading computations the decrease of coronal intensity at the prominence loaction due to absorption has to be be known. Thus, it is important to estimate well a contribution of the emissivity blocking to the intensity decrease. It was shown in Anzer et al. (2007) that prominences are transparent in soft X-ray coronal radiation around and below 50 A and therefore it was suggested to use the X-ray data from XRT on Hinode for determining the emissivity blocking. The method for estimation of the optical thickness at the hydrogen Lyman continuum head was proposed and used in Heinzel et al. (2008). When a map of values of the optical thickness for whole the prominence is constructed then its mass can be calculated. We have recently improved the method and used it for prominences observed in H_alpha by one of the Ondrejov solar spectrographs during years 2007 and 2008. For each prominence we found corresponding EIT observation but it was a problem to find complementary X-ray observation as XRT, the only X-ray solar space telescope operating at these times, was observing in the partial-FOV mode at other place at the limb This fact and rather low spatial resolution and sensitivity of EIT caused that we have chosen only three prominence observations suitable for the study. Despite the problems with the data we came to reliable results and the method and the computer code were tested. From April 20 to end of June, 2011 we plan to observe quiescent prominences in H_alpha with two solar spectrographs at the Ondrejov observatory. Almost simultaneous EUV data will be obtained from AIA/SDO as this instrument is observing full-disk in several EUV channels similar to EIT but with much higher cadence (~10 s) and spatial resolution (~ 1 arcsec). Thus, we need each day, at least one quasi-simultaneous full-disk hight-quality X-ray observations. |
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