30 research outputs found
Optical Alignment of the High-Precision UV Spectro-Polarimeter (CLASP2)
Chromospheric LAyer Spectro-Polarimeter (CLASP2) is our next sounding rocket experiment after the success of Chromospheric Lyman-Alpha Spectro-Polarimeter (CLASP1). CLASP2 is scheduled to launch in 2019, and aims to achieve high precision measurements of the linear and circular polarizations in the Mg II h & k lines near the 280 nm, whose line cores originate in the upper solar chromosphere. The CLASP2 spectro-polarimeter follows very successful design concept of the CLASP1 instrument with the minimal modification. A new grating was fabricated with the same radius of curvature as the CLASP1 grating, but with a different ruling density. This allows us to essentially reuse the CLASP1 mechanical structures and layout of the optics. However, because the observing wavelength of CLASP2 is twice longer than that of CLASP1, a magnifier optical system was newly added in front of the cameras to double the focal length of CLASP2 in order to maintain the same wavelength resolution as CLASP1 (0.01 nm). Meanwhile, a careful optical alignment of the specto-polarimeter is required to reach the 0.01 nm wavelength resolution. Therefore, we established an efficient alignment procedure for the CLASP2 spectro-polarimeter based on an experience of CLASP1. Here, we explain in detail the methods for achieving the optical alignment of the CLASP2 spectro-polarimeter and discuss our results by comparing with the performance requirements
Magnetic nulls and super-radial expansion in the solar corona
Magnetic fields in the sun's outer atmosphere -- the corona -- control both
solar-wind acceleration and the dynamics of solar eruptions. We present the
first clear observational evidence of coronal magnetic nulls in off-limb
linearly polarized observations of pseudostreamers, taken by the Coronal
Multichannel Polarimeter (CoMP) telescope. These nulls represent regions where
magnetic reconnection is likely to act as a catalyst for solar activity. CoMP
linear-polarization observations also provide an independent, coronal proxy for
magnetic expansion into the solar wind, a quantity often used to parameterize
and predict the solar wind speed at Earth. We introduce a new method for
explicitly calculating expansion factors from CoMP coronal linear-polarization
observations, which does not require photospheric extrapolations. We conclude
that linearly-polarized light is a powerful new diagnostic of critical coronal
magnetic topologies and the expanding magnetic flux tubes that channel the
solar wind
Creating Synthetic Coronal Observational Data From MHD Models: The Forward Technique
We present a generalized forward code for creating simulated corona) observables off the limb from numerical and analytical MHD models. This generalized forward model is capable of creating emission maps in various wavelengths for instruments such as SXT, EIT, EIS, and coronagraphs, as well as spectropolari metric images and line profiles. The inputs to our code can be analytic models (of which four come with the code) or 2.5D and 3D numerical datacubes. We present some examples of the observable data created with our code as well as its functional capabilities. This code is currently available for beta-testing (contact authors), with the ultimate goal of release as a SolarSoft packag
The SWAP Filter: A Simple Azimuthally Varying Radial Filter for Wide-Field EUV Solar Images
We present the SWAP Filter: an azimuthally varying, radial normalizing filter
specifically developed for EUV images of the solar corona, named for the Sun
Watcher with Active Pixels and Image Processing (SWAP) instrument on the
Project for On-Board Autonomy 2 spacecraft. We discuss the origins of our
technique, its implementation and key user-configurable parameters, and
highlight its effects on data via a series of examples. We discuss the filter's
strengths in a data environment in which wide field-of-view observations that
specifically target the low signal-to-noise middle corona are newly available
and expected to grow in the coming years.Comment: Contact D. B. Seaton for animations referenced in figure caption
Evidence for the Operation of the Hanle and Magneto-Optical Effects in the Scattering Polarization Signals Observed by CLASP2 Across the Mg II h and k Lines
Radiative transfer investigations of the solar Mg II h and k resonance lines
around 280~nm showed that, while their circular polarization (Stokes V) signals
arise from the Zeeman effect, the linear polarization profiles (Stokes Q and U)
are dominated by the scattering of anisotropic radiation and the Hanle and
magneto-optical (MO) effects. Using the unprecedented observations of the Mg II
and Mn I resonance lines obtained by the Chromospheric LAyer
Spectro-Polarimeter (CLASP2), here we investigate how the linear polarization
signals at different wavelengths (i.e., at the center, and at the near and far
wings of the k line) vary with the longitudinal component of the magnetic field
() at their approximate height of formation. The is estimated
from the V signals in the aforementioned spectral lines. Particular attention
is given to the following quantities that are expected to be influenced by the
presence of magnetic fields through the Hanle and MO effects: the sign of the U
signals, the total linear polarization amplitude () and its direction
() with respect to a reference direction. We find that at the center and
near wings of the line, the behavior of these quantities is significantly
different in the observed quiet and plage regions, and that both and
seem to depend on . These observational results are indicative of
the operation of the Hanle effectComment: 26 pages, 18 figures, accepted for publication in the Astrophysical
Journa