Observations with the Goode Solar Telescope (GST) are presented here showing that the emergence of 1.91 × 1018 Mx of new magnetic flux occurred at the edge of a filamentary light bridge (LB). This ...emergence was accompanied by brightness enhancement of a photospheric overturning convection cell (OCC) at the endpoints of the emerging magnetic structure. We present an analysis of the origin and the dynamics of this event using high-resolution GST Fe i 1564.85 nm vector magnetic field data, TiO photospheric, and H chromospheric images. The emerged structure was 1.5 × 0.3 Mm in size at the peak of development and lasted for 17 minutes. Doppler observations showed presence of systematic upflows before the appearance of the magnetic field signal and downflows during the decay phase. Changes in the orientation of the associated transverse fields, determined from the differential angle, suggest the emergence of a twisted magnetic structure. A fan-shaped jet was observed to be spatially and temporally correlated with the endpoint of the OCC intruding into the LB. Our data suggest that the emerging fields may have reconnected with the magnetic fields in the vicinity of the LB, which could lead to the formation of the jet. Our observation is the first report of flux emergence within a granular LB with evidence in the evolution of vector magnetic field, as well as photosphere convection motions, and supports the idea that the impulsive jets above the LB are caused by magnetic reconnection.
Aims. Observations of the Sun with the Atacama Large Millimeter Array have now started, and the thermal infrared will regularly be accessible from the NSF’s Daniel K. Inouye Solar Telescope. ...Motivated by the prospect of these new data, and by recent flare observations in the mid infrared, we set out here to model and understand the source of the infrared continuum in flares, and to explore its diagnostic capability for the physical conditions in the flare atmosphere. Methods. We use the one-dimensional (1D) radiation hydrodynamics code RADYN to calculate mid-infrared continuum emission from model atmospheres undergoing sudden deposition of energy by non-thermal electrons. Results. We identify and characterise the main continuum thermal emission processes relevant to flare intensity enhancement in the mid- to far-infrared (2–200 μm) spectral range as free-free emission on neutrals and ions. We find that the infrared intensity evolution tracks the energy input to within a second, albeit with a lingering intensity enhancement, and provides a very direct indication of the evolution of the atmospheric ionisation. The prediction of highly impulsive emission means that, on these timescales, the atmospheric hydrodynamics need not be considered in analysing the mid-IR signatures.
ABSTRACT We report high-resolution observations at mid-infrared wavelengths of a minor solar flare, SOL2014-09-24T17:50 (C7.0), using Quantum Well Infrared Photodetector cameras at an auxiliary of ...the McMath-Pierce telescope. The flare emissions, the first simultaneous observations in two mid-infrared bands at 5.2 and with white-light and hard X-ray coverage, revealed impulsive time variability with increases on timescales of ∼4 s followed by exponential decay at ∼10 s in two bright regions separated by about . The brightest source is compact, unresolved spatially at the diffraction limit ( at ). We identify the IR sources as flare ribbons also seen in white-light emission at 6173 observed by SDO/HMI, with twin hard X-ray sources observed by Reuven Ramaty High Energy Solar Spectroscopic Imager, and with EUV sources (e.g., 94 ) observed by SDO/AIA. The two infrared points have nearly the same flux density (f , W m−2 Hz) and extrapolate to a level of about an order of magnitude below that observed in the visible band by HMI, but with a flux of more than two orders of magnitude above the free-free continuum from the hot (∼15 MK) coronal flare loop observed in the X-ray range. The observations suggest that the IR emission is optically thin; this constraint and others suggest major contributions from a density less than about cm−3. We tentatively interpret this emission mechanism as predominantly free-free emission in a highly ionized but cool and rather dense chromospheric region.
ABSTRACT Solar flares are powerful particle accelerators, and in the accepted standard flare model most of the flare energy is transported from a coronal energy-release region by accelerated ...electrons that stop collisionally in the chromosphere, heating and ionizing the plasma, producing a broad-band enhancement to the solar radiative output. We present a time-delay analysis of the infrared (IR) emission from two chromospheric sources in the flare SOL2014-09-24T17:50 taken at the McMath–Pierce telescope. By cross-correlating the intensity signals, measured with 1 s cadence, from the two spatially resolved IR sources we find a delay of $0.75\pm 0.07$ s at $8.2\,\mu$m, where the uncertainties are quantified by a Monte Carlo analysis. The sources correlate well in brightness but have a time lag larger than can be reasonably explained by the energy transport dominated by non-thermal electrons precipitating from a single acceleration site in the corona. If interpreted as a time-of-flight difference between electrons travelling to each footpoint, we estimate time delays between 0.14 and 0.42 s, for a reconnection site at the interior quasi-separatrix layer, or at the null-point of the spine-fan topology inferred for this event. We employed modelling of electron transport via time-dependent Fokker–Planck and radiative hydrodynamic simulations to evaluate other possible sources of time-delay in the generation of the IR emission, such as differing ionization time-scales under different chromospheric conditions. Our results demonstrate that they are also unable to account for this discrepancy. This flare appears to require energy transport by some means other than electron beams originating in the corona.
Abstract
We present observations of NOAA AR 11159, obtained on 2011 February 14 in the 4.7
μ
m band of carbon monoxide (CO) and coordinated with spectroscopic imaging of three atomic lines (Na
i
5896 ...Å, Fe
i
7090 Å, and Ca
ii
8542 Å) which sample heights from the mid-photosphere to the chromosphere. Phase-difference spectra between the observed spectral lines instead indicate that the CO lines form at
z
≈ 530−650 km in the quiet Sun. During the two hours of observations, seven long-lived cooling events (“cold bubbles”) were observed in CO in the region surrounding a large pore, but were not visible in the three atomic lines. These events show self-similar temporal evolution with time scales consistent with the chemical formation rate of CO at
z
≈ 1000 km. Due to the lack of such features in the surrounding quiet Sun, we hypothesize that the magnetic canopy field surrounding the pore, which suppresses the upward propagation of acoustic waves into the chromosphere and the subsequent formation of shocks, depresses the rate of acoustic heating and allows CO to condense and cool the atmosphere at those heights. These “cold bubbles” may be a source of the chromospheric CO that produces the unexpectedly high (
z
≈ 1000 km) limb extensions seen in the stronger CO lines, and may provide a unique opportunity to study this enigmatic component of the solar atmosphere in spatially resolved observations.
Solar flares are powerful particle accelerators, and in the accepted standard flare model most of the flare energy is transported from a coronal energy-release region by accelerated electrons which ...stop collisionally in the chromosphere, heating and ionising the plasma, producing a broadband enhancement to the solar radiative output. We present a time-delay analysis of the infrared emission from two chromospheric sources in the flare SOL2014-09-24T17:50 taken at the McMath-Pierce telescope. By cross-correlating the intensity signals, measured with 1s cadence, from the two spatially resolved infrared sources we find a delay of 0.75 \(\pm\) 0.07 s at 8.2 \(\mu\)m, where the uncertainties are quantified by a Monte Carlo analysis. The sources correlate well in brightness but have a time lag larger than can be reasonably explained by the energy transport dominated by non-thermal electrons precipitating from a single acceleration site in the corona. If interpreted as a time-of-flight difference between electrons traveling to each footpoint, we estimate time delays between 0.14 s and 0.42 s, for a reconnection site at the interior quasi-separatrix layer or at the null-point of the spine-fan topology inferred for this event. We employed modelling of electron transport via time-dependent Fokker-Planck and radiative hydrodynamic simulations to evaluate other possible sources of time-delay in the generation of the IR emission, such as differing ionisation timescales under different chromospheric conditions. Our results demonstrate that they are also unable to account for this discrepancy. This flare appears to require energy transport by some means other than electron beams originating in the corona.
CYRA (CrYogenic solar spectrogRAph) is a facility instrument of the 1.6-meter Goode Solar Telescope (GST) at the Big Bear Solar Observatory (BBSO). CYRA focuses on the study of the near-infrared ...solar spectrum between 1 and 5 microns, a under explored region which is not only a fertile ground for photospheric magnetic diagnostics, but also allows a unique window into the chromosphere lying atop the photosphere. CYRA is the first ever fully cryogenic spectrograph in any solar observatory with its two predecessors, on the McMath-Pierce and Mees Telescopes, being based on warm optics except for the detectors and order sorting filters. CYRA is used to probe magnetic fields in various solar features and the quiet photosphere. CYRA measurements will allow new and better 3D extrapolations of the solar magnetic field and will provide more accurate boundary conditions for solar activity models. Superior spectral resolution of 150,000 and better allows enhanced observations of the chromosphere in the carbon monoxide (CO) spectral bands and will yield a better understanding of energy transport in the solar atmosphere. CYRA is divided into two optical sub-systems: The Fore-Optics Module and the Spectrograph. The Spectrograph is the heart of the instrument and contains the IR detector, grating, slits, filters, and imaging optics all in a cryogenically cooled Dewar (cryostat). The detector a 2048 by 2048 pixel HAWAII 2 array produced by Teledyne Scientific & Imaging, LLC. The interior of the cryostat and the readout electronics are maintained at 90 Kelvin by helium refrigerant based cryo-coolers, while the IR array is cooled to 30 Kelvin. The Fore-Optics Module de-rotates and stabilizes the solar image, provides scanning capabilities, and transfers the GST image to the Spectrograph. CYRA has been installed and is undergoing its commissioning phase.
PDF
