Soul observations of solar spicules in a coronal hole by TS Bastian et al. – European astronomer radio community

The solar spicules were discovered by the Jesuit priest Angelo Secchi In 1877. They are small plasma jets of a few hundred kilometers in diameter that are thrown at heights> 10 mm with speeds ranging from a few of km/s to> 100 km/s. Individually they have lives of a few minutes. They occur in the chromospheric network during the entire sun. Early estimates (1972 Beckers) He suggested that spicules carry a mass flow up 100 times that they required to replace the losses of the crown due to the solar wind. With the advent of modern high -resolution observations from space using Hinode Sot (optical), Iris (UV) and SDOA (EUV), together with advanced modeling, there has been a resurgence of interest in spicules and their possible role in the mass and energy budget of the solar atmosphere.

Observations in millimeter wavelengths (mm- $ \ Lambda $) are highly complementary to those of the O/UV/EUV bands. This is because the emission of the spicle is free of thermal electrons in LTE, the function of origin in mm- $ \ Lambda $ is Planckian and the approach of Rayleight-Jeans is valid. In contrast, the O/UV lines are formed in no lte. The observations of the sun in general and the spicules in particular at mm- $ \ Lambda $ were hindered by the lack of angular and temporal resolution. With the availability of soul, that has changed. Alma can obtain images of spicules with Arcsec resolution and can solve its kinematics with high cadence images.

Here, we briefly summarize the soul observations of the solar spicules in a polar coronal hole. The details can be found in the article recently published by Bastian et al. (2025) or the Arxiv reprint.

Figure 1. A comparison between the observations of soul and iris. Left: Spicules observed in 3 mm (lower part) and by the Iris Slit-Jaw Imress in the 2796å (upper part). Right: The same, but the lower part of the compound shows the emission of 1.25 mm. The white arc indicates the photosphary limb.

Soul observations

The soul observations of the solar spicules in the Northern Polar coronal hole were obtained on December 25, 2018 in the 3 mm band in a field of vision of approximately 60 “with a cadence of 2 s, and in the 1.25 mm band on a similar field of vision with a cadence of almost 2 min. The reason for the slow length of the 1.25 mm images is that the mosaic techniques are combined to combine the techniques of the mosaics for the techniques of the mosaics for They combine at the points of the cadence at the length of the length.

We measure the variation in the brightness temperature with height for a set of spicules in both mm- $ \ Lambda $ bands. If the temperature of the espicular plasma is known, the optical depth can be inferred depending on the height, from which the density of the column can be inferred and, therefore, the density of the number of electrons $ n_e $. We assume two schematic models for the variation in the temperature of the spicle with the height: a) that was isothermal; b) that the temperature increased linearly to the values ​​of the transition region. It is important to keep in mind that the inferred densities of mm- $ \ Lambda $ emission are remarkably insensitive to the plasma temperature, with $ n_e \ propth t_e^{1/4} $. Whatever its temperature, soul observations capture the density of the spicular material.

Figure 2: Infulted densities of the observations mm- $ \ Lambda $. Densities based on 1.25 mm measurements are shown in blue and those based on 3 mm measurements are shown in red. a) It is assumed that spicules are isothermal with a temperature of $ 1.5 \ times 10^4 $ K. b) It is supposed to have a temperature of $ 1.5 \ times 10^4 $ k at a height of 2 mm, linearly increasing to $ 10^5 $ k at a height of 15 mm. In both panels, the continuous green line represents the adjustment to the aggregate data of 1.25 and 3 mm. Data points are Alissandrakis et al. (2018) (full green circles), Beckers (1972) (purple squares), and Krall et al. (1976) (Orange diamonds). The boarding lines labeled such as “B68”, “B72” and “A76” are the densities resulting from spicular filling factors based on the model of Beckers (1968, 1972), and Athay (1976), respectively.

We find that the spicular densities derived from the double-band observations mm- $ \ Lambda $ are well compared with the inferred of the historical observations of O and UV. When the filling factor of the line of vision is taken into account, the variation of the density with the height is somewhat flatter (discontinuous lines in Figure 2). We also find that the flow of ascending mass due to spicules quickly falls with height, questioning if they play an important role in the massive budget of the solar crown and the solar wind. However, we cannot exclude the idea that electric currents or wave modes transported by spicules can play a role in the transport of energy to the solar crown.

Conclusions

Alma observations in mm- $ \ Lambda $ provide new ideas about a variety of solar phenomena, including solar spicules. Our results do not provide support to the idea that spicules provide a significant mass to the crown. However, additional work is needed: observations of multiple spicuations in a variety of environments (coronal holes, silent sun), as well as detailed quantitative comparisons with observations made in wavelengths or/UV/EUV.

Based on the recent article By TS Bastian, C. Alissandrakis, A. Imudes, M. Shimojo and SM White, soul observations of solar spicules in a polar coronal hole, APJ 980 60 (2025). DOI:10.3847/1538-4357/ADA445

References

Alissandrakis, C., et al. 2018, Solar Phys. 293, 20 DOI: 10.1007/S11207-018-1242-4

Anthay, RG, 1976 “The solar chromosphere and the crown: quiet sun”, vol. 53, DOI: 10.1007/978-94-010-1715-2

Bastian, TS, Alissandrakis, C., Imper 2025, APJ 980, 60DOI: 10.3847/1538-4357/ADA445.

Beckers, J. 1968 Soph, 3, 367, DOI: 10.1007/BF00171614

Beckers, J. 1972, ARA & A, 10, 73, DOI: 10.1146/ANNUREV.AA.10.090172.00045

KRALL, KR, BESSEY, RJ AND BECKERS, JM 1976, Soph, 46, 93, DOI: 10.1007/BF00157556