22 research outputs found
A Nonlinear Force-Free Magnetic Field Approximation Suitable for Fast Forward-Fitting to Coronal Loops. II. Numeric Code and Tests
No full textConvolutional Neural Networks for Predicting the Strength of the Near-Earth Magnetic Field Caused by Interplanetary Coronal Mass Ejections
No full textExamination of Separator Reconnection Rates in a Series of Adjacent Emerging/Existing Active Region Pairs
No full textNo abstract availabl
Automated Temperature and Emission Measure Analysis of Coronal Loops and Active Regions Observed with the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (SDO/AIA)
No full textRemote distributed pipeline processing of GONG helioseismic data: experience and lessons learned
No full textDesigning a New Coronal Magnetic Field Energy Diagnostic
No full textInternational audienceIn the solar corona, the free energy, i.e., the excess in magnetic energy over a ground-state potential field, forms the reservoir of energy that can be released during solar flares and coronal mass ejections. Such free energy provides a measure of the magnetic field nonpotentiality. Recent theoretical and observational studies indicate that the presence of nonpotential magnetic fields is imprinted into the structures of infrared, off-limb, coronal polarization. In this paper, we investigate the possibility of exploiting such observations for mapping and studying the accumulation and release of coronal free magnetic energy, with the goal of developing a new tool for identifying "hot spots" of coronal free energy such as those associated with twisted and/or sheared coronal magnetic fields. We applied forward modeling of infrared coronal polarimetry to three-dimensional models of nonpotential and potential magnetic fields. From these we defined a quantitative diagnostic of nonpotentiality that in the future could be calculated from a comparison of infrared, off-limb, coronal polarization observations from, e.g., the Coronal Multi-channel Polarimeter or the Daniel K. Inouye Solar Telescope, and the corresponding polarization signal forward-modeled from a potential field extrapolated from photospheric magnetograms. We considered the relative diagnostic potential of linear and circular polarization, and the sensitivities of these diagnostics to coronal density distributions and assumed boundary conditions of the potential field. Our work confirms the capacity of polarization measurements for diagnosing nonpotentiality and free energy in the solar corona
Luminous blue variable candidates in M31
No full text© 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. We study five luminous blue variable (LBV) candidates in the Andromeda galaxy and one more (MN112) in the Milky Way. We obtain the same-epoch near-infrared (NIR) and optical spectra on the 3.5-m telescope at the Apache Point Observatory and on the 6-m telescope of the SAO RAS. The candidates show typical LBV features in their spectra: broad and strong hydrogen lines, He i, Fe ii, and [Fe ii] lines. We estimate the temperatures, reddening, radii and luminosities of the stars using their spectral energy distributions. Bolometric luminosities of the candidates are similar to those of known LBV stars in the Andromeda galaxy. One candidate, J004341.84+411112.0, demonstrates photometric variability (about 0.27 mag in the V band), which allows us to classify it as an LBV. The star J004415.04+420156.2 shows characteristics typical of B[e] supergiants. The star J004411.36+413257.2 is classified as a Fe ii star. We confirm that the stars J004621.08+421308.2 and J004507.65+413740.8 are warm hypergiants. We obtain for the first time the NIR spectrum of the Galactic LBV candidate MN112. We use both optical and NIR spectra of MN112 for comparison with similar stars in M31 and notice identical spectra and the same temperature in J004341.84+411112.0. This allows us to confirm that MN112 is an LBV, which should show its brightness variability in longer time span observations
MHD Modeling of a Geoeffective Interplanetary Coronal Mass Ejection with the Magnetic Topology Informed by In Situ Observations
No full textVariations of the magnetic field within a solar coronal mass ejection (CME) in the heliosphere depend on the CME’s magnetic structure as it leaves the solar corona and its interplanetary evolution. To account for this evolution, we developed a new numerical model of the inner heliosphere that simulates the propagation of a CME through a realistic solar wind background and allows various CME magnetic topologies. To this end, we incorporate the Gibson–Low CME model within our global MHD model of the inner heliosphere, GAMERA-Helio. We apply the model to study the propagation of the geoeffective CME that erupted on 2010 April 3, aiming to reproduce the temporal variations of the magnetic field vector during the CME’s passage by Earth. Parameters of the Gibson–Low CME are informed by STEREO white-light observations near the Sun. The magnetic topology for this CME—the tethered flux rope—is informed by in situ magnetic field observations near Earth. We performed two simulations testing different CME propagation directions. For an in-ecliptic direction, the simulation shows a rotation of all three magnetic field components within the CME, as seen at Earth, similar to that observed. However, the magnitudes of the components, particularly at the back of the CME, are underestimated by the model. With a southward direction, suggested by coronal imaging observations, the B _x component lacks the observed change from negative to positive. In both cases, the model favors the east–west orientation of the flux rope, consistent with the orientation previously inferred from the images from STEREO/Heliospheric Imager
Global Solar Magnetic Field Evolution Over 4 Solar Cycles: Use of the McIntosh Archive
No full textThe McIntosh Archive consists of a set of hand-drawn solar Carrington maps created by Patrick McIntosh from 1964 to 2009. McIntosh used mainly Hα, He-I 10830 Å and photospheric magnetic measurements from both ground-based and NASA satellite observations. With these he traced polarity inversion lines (PILs), filaments, sunspots and plage and, later, coronal holes over a ~45-year period. This yielded a unique record of synoptic maps of features associated with the large-scale solar magnetic field over four complete solar cycles. We first discuss how these and similar maps have been used in the past to investigate long-term solar variability. Then we describe our work in preserving and digitizing this archive, developing a digital, searchable format, and creating a website and an archival repository at NOAA's National Centers for Environmental Information (NCEI). Next we show examples of how the data base can be utilized for scientific applications. Finally, we present some preliminary results on the solar-cycle evolution of the solar magnetic field, including the polar field reversal process, the evolution of active longitudes, and the role of differential solar rotation
