TY - JOUR
T1 - Ubiquitous hundred-Gauss magnetic fields in solar spicules
AU - Kriginsky, M.
AU - Oliver, R.
AU - Freij, N.
AU - Kuridze, D.
AU - Asensio Ramos, A.
AU - Antolin, P.
N1 - Funding Information:
Acknowledgements. MK and RO acknowledge support from the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER funds through project AYA2017-85465-P. They are also grateful for the travel support received from the International Space Science Institute (Bern, Switzerland) as well as for discussions with members of the ISSI team on “Observed multi-scale variability of coronal loops as a probe of coronal heating”, led by C. Froment and P. Antolin. PA acknowledges funding from his STFC Ernest Rutherford Fellowship (No. ST/R004285/2). This research has made use of SunPy v1.1, an open-source and free community-developed solar data analysis Python package (The SunPy Community 2020). The Swedish 1-m Solar Telescope is operated on the island of La Palma by the Institute for Solar Physics of Stockholm University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias. The Institute for Solar Physics is supported by a grant for research infrastructures of national importance from the Swedish Research Council (registration number 2017-00625). D.K. has received funding from the Sêr Cymru II scheme, part-funded by the European Regional Development Fund through the Welsh Government and from the Georgian Shota Rustaveli National Science Foundation project FR17 323. AAR acknowledges support from the Spanish Ministry of Economy and Competitiveness (MINECO) and FEDER funds through project PGC2018-102108-B-I00. And last but not least, we thank the anonymous referee for very useful comments.
Publisher Copyright:
© ESO 2020.
PY - 2020/10/7
Y1 - 2020/10/7
N2 - Aims. We aim to study the magnetic field in solar spicules using high-resolution spectropolarimetric observations in the CaII 8542 Å line obtained with the Swedish 1-m Solar Telescope. Methods. The equations that result from the application of the weak field approximation (WFA) to the radiative transfer equations were used to infer the line-of-sight (LOS) component of the magnetic field (BLOS). Two restrictive conditions were imposed on the Stokes I and V profiles at each pixel before they could be used in a Bayesian inversion to compute its BLOS. Results. The LOS magnetic field component was inferred in six data sets totalling 448 spectral scans in the CaII 8542 Å line and containing both active region and quiet Sun areas, with values of hundreds of Gauss being abundantly inferred. There seems to be no difference, from a statistical point of view, between the magnetic field strength of spicules in the quiet Sun or near an active region. On the other hand, the BLOS distributions present smaller values on the disc than off-limb, a fact that can be explained by the effect of superposition on the chromosphere of on-disc structures. We show that on-disc pixels in which the BLOS is determined are possibly associated with spicular structures because these pixels are co-spatial with the magnetic field concentrations at the network boundaries and the sign of their BLOS agrees with that of the underlying photosphere. We find that spicules in the vicinity of a sunspot have a magnetic field polarity (i.e. north or south) equal to that of the sunspot. This paper also contains an analysis of the effect of off-limb overlapping structures on the observed Stokes I and V parameters and the BLOS obtained from the WFA. It is found that this value is equal to or smaller than the largest LOS magnetic field components of the two structures. In addition, using random BLOS, Doppler velocities, and line intensities of these two structures leads in ≃ 50% of the cases to Stokes I and V parameters that are unsuitable to be used with the WFA. Conclusions. Our results present a scarcity of LOS magnetic field components smaller than some 50 G, which must not be taken as evidence against the existence of these magnetic field strengths in spicules. This fact possibly arises as the consequence of signal superposition and noise in the data. We also suggest that the failure of previous works to infer the strong magnetic fields in spicules detected here is their coarser spatial and/or temporal resolution.
AB - Aims. We aim to study the magnetic field in solar spicules using high-resolution spectropolarimetric observations in the CaII 8542 Å line obtained with the Swedish 1-m Solar Telescope. Methods. The equations that result from the application of the weak field approximation (WFA) to the radiative transfer equations were used to infer the line-of-sight (LOS) component of the magnetic field (BLOS). Two restrictive conditions were imposed on the Stokes I and V profiles at each pixel before they could be used in a Bayesian inversion to compute its BLOS. Results. The LOS magnetic field component was inferred in six data sets totalling 448 spectral scans in the CaII 8542 Å line and containing both active region and quiet Sun areas, with values of hundreds of Gauss being abundantly inferred. There seems to be no difference, from a statistical point of view, between the magnetic field strength of spicules in the quiet Sun or near an active region. On the other hand, the BLOS distributions present smaller values on the disc than off-limb, a fact that can be explained by the effect of superposition on the chromosphere of on-disc structures. We show that on-disc pixels in which the BLOS is determined are possibly associated with spicular structures because these pixels are co-spatial with the magnetic field concentrations at the network boundaries and the sign of their BLOS agrees with that of the underlying photosphere. We find that spicules in the vicinity of a sunspot have a magnetic field polarity (i.e. north or south) equal to that of the sunspot. This paper also contains an analysis of the effect of off-limb overlapping structures on the observed Stokes I and V parameters and the BLOS obtained from the WFA. It is found that this value is equal to or smaller than the largest LOS magnetic field components of the two structures. In addition, using random BLOS, Doppler velocities, and line intensities of these two structures leads in ≃ 50% of the cases to Stokes I and V parameters that are unsuitable to be used with the WFA. Conclusions. Our results present a scarcity of LOS magnetic field components smaller than some 50 G, which must not be taken as evidence against the existence of these magnetic field strengths in spicules. This fact possibly arises as the consequence of signal superposition and noise in the data. We also suggest that the failure of previous works to infer the strong magnetic fields in spicules detected here is their coarser spatial and/or temporal resolution.
KW - Sun: chromosphere
KW - Sun: magnetic fields
UR - http://www.scopus.com/inward/record.url?scp=85093927315&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/202038546
DO - 10.1051/0004-6361/202038546
M3 - Article
AN - SCOPUS:85093927315
SN - 0004-6361
VL - 642
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A61
ER -