Data-driven Simulations of Magnetic Field Evolution in Active Region 11429:Magneto-frictional Method Using PENCIL CODE

Coronal magnetic fields evolve quasi-statically over long timescales and dynamically over short timescales.As of now there exist no regular measurements of coronal magnetic fields,and therefore generating the coronal magnetic field evolution using observations of the magnetic field at the photosphere is a fundamental requirement to understanding the origin of transient phenomena from solar active regions(ARs).Using the magneto-friction(MF)approach,we aim to simulate the coronal field evolution in the solar AR 11429.The MF method is implemented in the open source PENCIL CODE along with a driver module to drive the initial field with different boundary conditions prescribed from observed vector magnetic fields at the photosphere.In order to work with vector potential and the observations,we prescribe three types of bottom boundary drivers with varying free-magnetic energy.The MF simulation reproduces the magnetic structure,which better matches the sigmoidal morphology exhibited by Atmospheric Imaging Assembly(AIA)images at the pre-eruptive time.We found that the already sheared field further driven by the sheared magnetic field will maintain and further build the highly sheared coronal magnetic configuration,as seen in AR 11429.Data-driven MF simulation is a viable tool to generate the coronal magnetic field evolution,capturing the formation of the twisted flux rope and its eruption.

On the error analyses of polarization measurements of the white-light coronagraph aboard ASO-S

The Advanced Space-based Solar Observatory(ASO-S) mission aims to explore the two most spectacular eruptions on the Sun: solar flares and coronal mass ejections(CMEs), and their magnetism.For the study of CMEs, the payload Lyman-alpha Solar Telescope(LST) has been proposed. It includes a traditional white-light coronagraph and a Lyman-alpha coronagraph which opens a new window to CME observations. Polarization measurements taken by white-light coronagraphs are crucial for deriving fundamental physical parameters of CMEs. To make such measurements, there are two options for a Stokes polarimeter which have been applied by existing white-light coronagraphs for space missions. One uses a single or triple linear polarizer, the other involves both a half-wave plate and a linear polarizer. We find that the former option is subject to less uncertainty in the derived Stokes vector propagating from detector noise.The latter option involves two plates which are prone to internal reflections and may have a reduced transmission factor. Therefore, the former option is adopted as our Stokes polarimeter scheme for LST. Based on the parameters of the intended linear polarizer(s) colorPol provided by CODIXX and the half-wave plate 2-APW-L2-012 C by Altechna, it is further shown that the imperfect maximum transmittance of the polarizer significantly increases the variance amplification of Stokes vector by at least about 50% when compared with the ideal case. The relative errors of Stokes vector caused by the imperfection of colorPol polarizer and the uncertainty due to the polarizer assembly in the telescope are estimated to be about 5%. Among the considered parameters, we find that the dominant error comes from the uncertainty in the maximum transmittance of the polarizer.

BESTP——An automated Bayesian modeling tool for asteroseismology

Asteroseismic observations are crucial to constrain stellar models with precision.Bayesian Estimation of STellar Parameters(BESTP)is a tool that utilizes Bayesian statistics and nested sampling Monte Carlo algorithm to search for the stellar models that best match a given set of classical and asteroseismic constraints from observations.The computation and evaluation of models are efficiently performed in an automated and multi-threaded way.To illustrate the capabilities of BESTP,we estimate fundamental stellar properties for the Sun and the red-giant star HD 222076.In both cases,we find models that are consistent with observations.We also evaluate the improvement in the precision of stellar parameters when the oscillation frequencies of individual modes are included as constraints,compared to the case when only the large frequency separation is included.For the solar case,the uncertainties of estimated masses,radii and ages are reduced by 0.7%,0.3%and 8%respectively.For HD 222076,they are reduced even more noticeably by 2%,0.5%and 4.7%respectively.We also note an improvement of 10%for the age of HD 222076 when the Gaia parallax is included as a constraint compared to the case when only the large separation is included as a constraint.

KuaFu Mission

The KuaFu mission-Space Storms,Aurora and Space Weather Explorer-is an"L1+Polar"triple satellite project composed of three spacecraft:KuaFu-A will be located at L1 and have instruments to observe solar EUV and FUV emissions,and white-light Coronal Mass Ejections(CMEs),and to measure radio waves,the local plasma and magnetic field,and high-energy particles.KuaFuB1 and KuaFu-B2 will bein polar orbits chosen to facilitate continuous 24 hours a day observation of the north polar Aurora Oval.The KuaFu mission is designed to observe the complete chain of disturbances from the solar atmosphere to geospace,including solar flares,CMEs,interplanetary clouds,shock waves,and their geo-effects,such as magnetospheric sub-storms and magnetic storms,and auroral activities.The mission may start at the next solar maximum(launch in about 2012),and with an initial mission lifetime of two to three years.KuaFu data will be used for the scientific study of space weather phenomena,and will be used for space weather monitoring and forecast purposes.The overall mission design,instrument complement,and incorporation of recent technologies will target new fundamental science,advance our understanding of the physical processes underlying space weather,and raise the standard of end-to-end monitoring of the Sun-Earth system.