32 research outputs found
A Compact Full-disk Solar Magnetograph based on miniaturization of GONG instrument
Designing compact instruments is the key for the scientific exploration by
smaller spacecrafts such as cubesats or by deep space missions. Such missions
require compact instrument designs to have minimal instrument mass. Here we
present a proof of concept for miniaturization of the Global Oscillation
Network Group GONG instrument. GONG instrument routinely obtains solar full
disk Doppler and magnetic field maps of the solar photosphere using Ni 676 nm
absorption line. A key concept for miniaturization of GONG optical design is to
replace the bulky Lyot filter with a narrow-band interference filter and reduce
the length of feed telescope. We present validation of the concept via
numerical modeling as well as by proof of concept observations.Comment: 13 pages, 6 figure
Velocities of an Erupting Filament
Solar filaments exist as stable structures for extended periods of time before many of them form the core of a coronal mass ejection (CME). We examine the properties of an erupting filament on 2017 May 29–30 with high-resolution He i 10830 Å and Hα spectra from the Dunn Solar Telescope, full-disk Dopplergrams of He i 10830 Å from the Chromospheric Telescope, and EUV and coronograph data from SDO and STEREO. Pre-eruption line-of-sight velocities from an inversion of He i with the HAZEL code exhibit coherent patches of 5 Mm extent that indicate counter-streaming and/or buoyant behavior. During the eruption, individual, aligned threads appear in the He i velocity maps. The distribution of velocities evolves from Gaussian to strongly asymmetric. The maximal optical depth of He i 10830 Å decreased from τ = 1.75 to 0.25, the temperature increased by 13 kK, and the average speed and width of the filament increased from 0 to 25 km s−1 and 10 to 20 Mm, respectively. All data sources agree that the filament rose with an exponential acceleration reaching 7.4 m s−2 that increased to a final velocity of 430 km s−1 at 22:24 UT; a CME was associated with this filament eruption. The properties during the eruption favor a kink/torus instability, which requires the existence of a flux rope. We conclude that full-disk chromospheric Dopplergrams can be used to trace the initial phase of on-disk filament eruptions in real time, which might potentially be useful for modeling the source of any subsequent CMEs
Magnetic Structure of an Erupting Filament
The full 3-D vector magnetic field of a solar filament prior to eruption is
presented. The filament was observed with the Facility Infrared
Spectropolarimeter at the Dunn Solar Telescope in the chromospheric He i line
at 10830 {\AA} on May 29 and 30, 2017. We inverted the spectropolarimetric
observations with the HAnle and ZEeman Light (HAZEL) code to obtain the
chromospheric magnetic field. A bimodal distribution of field strength was
found in or near the filament. The average field strength was 24 Gauss, but
prior to the eruption we find the 90th percentile of field strength was 435
Gauss for the observations on May 29. The field inclination was about 67 degree
from the solar vertical. The field azimuth made an angle of about 47 to 65
degree to the spine axis. The results suggest an inverse configuration
indicative of a flux rope topology. He i intensity threads were found to be
co-aligned with the magnetic field direction. The filament had a sinistral
configuration as expected for the southern hemisphere. The filament was stable
on May 29, 2017 and started to rise during two observations on May 30, before
erupting and causing a minor coronal mass ejection. There was no obvious change
of the magnetic topology during the eruption process. Such information on the
magnetic topology of erupting filaments could improve the prediction of the
geoeffectiveness of solar storms
LEMUR: Large European Module for Solar Ultraviolet Research
The solar outer atmosphere is an extremely dynamic environment characterized by the continuous interplay between the plasma and the magnetic field that generates and permeates it. Such interactions play a fundamental role in hugely diverse astrophysical systems, but occur at scales that cannot be studied outside the solar system. Understanding this complex system requires concerted, simultaneous solar observations from the visible to the vacuum ultraviolet (VUV) and soft X-rays, at high spatial resolution (between 0.1 and 0.3), at high temporal resolution (on the order of 10 s, i.e., the time scale of chromospheric dynamics), with a wide temperature coverage (0.01 MK to 20 MK, from the chromosphere to the flaring corona), and the capability of measuring magnetic fields through spectropolarimetry at visible and near-infrared wavelengths. Simultaneous spectroscopic measurements sampling the entire temperature range are particularly important. These requirements are fulfilled by the Japanese Solar-C mission (Plan B), composed of a spacecraft in a geosynchronous orbit with a payload providing a significant improvement of imaging and spectropolarimetric capabilities in the UV, visible, and near-infrared with respect to what is available today and foreseen in the near future. The Large European Module for solar Ultraviolet Research (LEMUR), described in this paper, is a large VUV telescope feeding a scientific payload of high-resolution imaging spectrographs and cameras. LEMUR consists of two major components: a VUV solar telescope with a 30 cm diameter mirror and a focal length of 3.6 m, and a focal-plane package composed of VUV spectrometers covering six carefully chosen wavelength ranges between 170 Angstrom and 1270 Angstrom. The LEMUR slit covers 280 on the Sun with 0.14 per pixel sampling. In addition, LEMUR is capable of measuring mass flows velocities (line shifts) down to 2 km s 1 or better. LEMUR has been proposed to ESA as the European contribution to the Solar C mission
Magneto-static modeling of the mixed plasma Beta solar atmosphere based on SUNRISE/IMaX data
TN acknowledges support by the U.K.’s Science and Technology Facilities Council and would like to thank the MPS for its hospitality during a visit in December 2014.Our aim is to model the 3D magnetic field structure of the upper solar atmosphere, including regions of non-negligible plasma beta. We use high-resolution photospheric magnetic field measurements from SUNRISE/IMaX as boundary condition for a magneto-static magnetic field model. The high resolution of IMaX allows us to resolve the interface region between photosphere and corona, but modelling this region is challenging for the following reasons. While the coronal magnetic field is thought to be force-free (the Lorentz-force vanishes), this is not the case in the mixed plasma β environment in the photosphere and lower chromosphere. In our model, pressure gradients and gravity forces are taken self-consistently into account and compensate the non-vanishing Lorentz-force. Above a certain height (about 2 Mm) the non-magnetic forces become very weak and consequently the magnetic field becomes almost force-free. Here we apply a linear approach, where the electric current density consists of a superposition of a field-line parallel current and a current perpendicular to the Sun’s gravity field. We illustrate the prospects and limitations of this approach and give an outlook for an extension towards a non-linear model.Publisher PDFPeer reviewe