Figure 2. ALMA Band 3 (3 mm) observations at a later time on the day do not reveal the filament structure. The Band 3 temperatures are capped at 8,000 K to improve Tb variations within the filament. The cyan contours show the filament in the AIA 304 Å images. (da Silva Santos et al. 2022).
The kinetic temperature level and optical thickness of the filament can not be concurrently inferred from single-band ALMA observations, however it needs imaging at different mm wavelengths and the typically employed presumption of isothermal conditions (e.g. Heinzel et al. 2015). Assuming that the typical residential or commercial properties of the filament did not considerably alter in between the time the data were taken in both bands, the observed mean brightness temperatures at 1.25 mm and 3 mm are not suitable with an isothermal design but suggest that Band 6 most likely probes the coolest filament threads, whereas Band 3 senses warmer filament plasma or potentially the outer shell that separates it from the corona if the optical thickness is big. Simultaneous observations in both bands would be required to even more investigate these findings; nevertheless, this is not currently possible due to instrumental overheads.
Conclusions.
ALMA continuum observations can be used to measure temporal variations in temperature level in filament fine-scale structures. In the absence of appropriate models in the literature to which our data can be compared, our results underline the need for follow-up radiative transfer modeling of the mm continuum and the Mg resonance lines to constrain the thermodynamics of AR filaments.
* Based on the recent article: da Silva Santos, J. M., White, S. M., Reardon, K., Cauzzi, G., Stanislav, G., Heinzel, P. & & Leenaarts, J., Subarcsecond imaging of a solar active area filament with ALMA and IRIS, 2022, Front. Astron.
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Chen, P., Xu, A., & & Ding, M., 2020, Res. Astron. Astrophys, 20, 166.
Gunár et al., 2016, Astrophys. J., 833, 141.
Heinzel at al., 2015, Sol. Phys., 290, 1981.
Heinzel et al., 2022, Astrophys. J. Lett., 927, L29.
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Rodger, A.S., Labrosse, N.: 2017, Sol. Phys., 292, 130.
Filaments (or prominences) are “clouds” of cool (<< 104 K) product suspended in the solar corona by approximately 10s of megameters above the photosphere, and they can be broadly divided into quiescent filaments and active area (AR) filaments. Both of these structures have been observed for a long time, particularly in recent years by NASAs IRIS telescope, there are open questions on the magnetic geography of filaments and the formation of their dark threads (e.g., Chen et al. 2020).. AR filaments had not yet been observed at mm wavelengths due to the fact that their comparatively little spatial scales (few arcseconds) might not be dealt with. In da Silva Santos et al. 2022, we provide brightness temperature maps of an AR filament taken with Band 6 (1.25 mm or 240 GHz) at 0.6 arcsec spatial resolution. ALMA and IRIS capture the dramatic time advancement of an AR filament. We find dark/cool extended features in the ALMA Band 6 (1.25 mm) maps with brightness temperature level values usually within ~ 4000-5000 K, however they can be as low as ~ 3000 K in some circumstances, hence considerably listed below the regional background level (~ 6000 K). Those structures partially accompany the filament body seen in the AIA 304 Å channel and the blue and red peaks of the Mg II resonance lines penetrated by IRIS. However, there are significant brightness variations across the filament spinal column and in time (Fig. 1). In da Silva Santos et al. 2022, we present brightness temperature level maps of an AR filament taken with Band 6 (1.25 mm or 240 GHz) at 0.6 arcsec spatial resolution. The lower spatial resolution of Band 3 relative to Band 6 (by a factor of ~ 2) partially describes the lower contrast, however the filament threads with normal sizes of a few arcseconds should be fixed in the Band 3 maps. ALMA Band 3 (3 mm) observations at a later time on the day do not reveal the filament structure. The kinetic temperature level and optical density of the filament can not be at the same time presumed from single-band ALMA observations, but it requires imaging at different mm wavelengths and the typically utilized assumption of isothermal conditions (e.g. Heinzel et al. 2015). Assuming that the typical homes of the filament did not considerably alter between the time the data were taken in both bands, the observed mean brightness temperatures at 1.25 mm and 3 mm are not compatible with an isothermal model however suggest that Band 6 likely probes the coolest filament threads, whereas Band 3 senses warmer filament plasma or possibly the outermost shell that separates it from the corona if the optical thickness is big. Time development of an AR filament observed by SDO/AIA, IRIS, and ALMA Band 6 in April 2019 near the disk. The dashed rectangular shapes show the area covered by the IRIS raster scan. The cyan contours show Tb (1.25 mm) = 5,000 K. (da Silva Santos et al. 2022). Clustering analysis reveals that brightness temperature level worths lower than 5000 K at 1.25 mm correspond with areas of low incorporated intensity in the Mg II h and k lines where the lines are weak, the central reversals are shallow, and the peak asymmetry and Doppler shifts are little. Together, these multi-wavelength observations can be utilized to set restrictions on the filament speed, density, and temperature gradients. ALMA temperatures in various bands are not consistent with isothermal conditions. ALMA Band 3 maps obtained after the Band 6 observations on the exact same day do not show the very same high-contrast dark threads still noticeable in the AIA 304 passband at that time (Fig. 2). The lower spatial resolution of Band 3 relative to Band 6 (by an aspect of ~ 2) partly describes the lower contrast, but the filament threads with typical sizes of a couple of arcseconds need to be resolved in the Band 3 maps. This is interesting in that the contrast was anticipated to increase at lower frequencies, as revealed by previous low-resolution (>> 20 arcsec) observations of quiescent filaments.