RESUMEN
The physical processes causing energy exchange between the Sun's hot corona and its cool lower atmosphere remain poorly understood. The chromosphere and transition region (TR) form an interface region between the surface and the corona that is highly sensitive to the coronal heating mechanism. High-resolution observations with the Interface Region Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60 seconds) of intensity and velocity on small spatial scales (â²500 kilometers) at the footpoints of hot and dynamic coronal loops. The observations are consistent with numerical simulations of heating by beams of nonthermal electrons, which are generated in small impulsive (â²30 seconds) heating events called "coronal nanoflares." The accelerated electrons deposit a sizable fraction of their energy (â²10(25) erg) in the chromosphere and TR. Our analysis provides tight constraints on the properties of such electron beams and new diagnostics for their presence in the nonflaring corona.
RESUMEN
The solar atmosphere was traditionally represented with a simple one-dimensional model. Over the past few decades, this paradigm shifted for the chromosphere and corona that constitute the outer atmosphere, which is now considered a dynamic structured envelope. Recent observations by the Interface Region Imaging Spectrograph (IRIS) reveal that it is difficult to determine what is up and down, even in the cool 6000-kelvin photosphere just above the solar surface: This region hosts pockets of hot plasma transiently heated to almost 100,000 kelvin. The energy to heat and accelerate the plasma requires a considerable fraction of the energy from flares, the largest solar disruptions. These IRIS observations not only confirm that the photosphere is more complex than conventionally thought, but also provide insight into the energy conversion in the process of magnetic reconnection.
RESUMEN
As the interface between the Sun's photosphere and corona, the chromosphere and transition region play a key role in the formation and acceleration of the solar wind. Observations from the Interface Region Imaging Spectrograph reveal the prevalence of intermittent small-scale jets with speeds of 80 to 250 kilometers per second from the narrow bright network lanes of this interface region. These jets have lifetimes of 20 to 80 seconds and widths of ≤300 kilometers. They originate from small-scale bright regions, often preceded by footpoint brightenings and accompanied by transverse waves with amplitudes of ~20 kilometers per second. Many jets reach temperatures of at least ~10(5) kelvin and constitute an important element of the transition region structures. They are likely an intermittent but persistent source of mass and energy for the solar wind.
RESUMEN
The heating of the outer solar atmospheric layers, i.e., the transition region and corona, to high temperatures is a long-standing problem in solar (and stellar) physics. Solutions have been hampered by an incomplete understanding of the magnetically controlled structure of these regions. The high spatial and temporal resolution observations with the Interface Region Imaging Spectrograph (IRIS) at the solar limb reveal a plethora of short, low-lying loops or loop segments at transition-region temperatures that vary rapidly, on the time scales of minutes. We argue that the existence of these loops solves a long-standing observational mystery. At the same time, based on comparison with numerical models, this detection sheds light on a critical piece of the coronal heating puzzle.
RESUMEN
The solar chromosphere and transition region (TR) form an interface between the Sun's surface and its hot outer atmosphere. There, most of the nonthermal energy that powers the solar atmosphere is transformed into heat, although the detailed mechanism remains elusive. High-resolution (0.33-arc second) observations with NASA's Interface Region Imaging Spectrograph (IRIS) reveal a chromosphere and TR that are replete with twist or torsional motions on sub-arc second scales, occurring in active regions, quiet Sun regions, and coronal holes alike. We coordinated observations with the Swedish 1-meter Solar Telescope (SST) to quantify these twisting motions and their association with rapid heating to at least TR temperatures. This view of the interface region provides insight into what heats the low solar atmosphere.
RESUMEN
It is now apparent that there are at least two heating mechanisms in the Sun's outer atmosphere, or corona. Wave heating may be the prevalent mechanism in quiet solar periods and may contribute to heating the corona to 1,500,000 K (refs 1-3). The active corona needs additional heating to reach 2,000,000-4,000,000 K; this heat has been theoretically proposed to come from the reconnection and unravelling of magnetic 'braids'. Evidence favouring that process has been inferred, but has not been generally accepted because observations are sparse and, in general, the braided magnetic strands that are thought to have an angular width of about 0.2 arc seconds have not been resolved. Fine-scale braiding has been seen in the chromosphere but not, until now, in the corona. Here we report observations, at a resolution of 0.2 arc seconds, of magnetic braids in a coronal active region that are reconnecting, relaxing and dissipating sufficient energy to heat the structures to about 4,000,000 K. Although our 5-minute observations cannot unambiguously identify the field reconnection and subsequent relaxation as the dominant heating mechanism throughout active regions, the energy available from the observed field relaxation in our example is ample for the observed heating.
RESUMEN
The Sun's outer atmosphere, or corona, is heated to millions of degrees, considerably hotter than its surface or photosphere. Explanations for this enigma typically invoke the deposition in the corona of nonthermal energy generated by magnetoconvection. However, the coronal heating mechanism remains unknown. We used observations from the Solar Dynamics Observatory and the Hinode solar physics mission to reveal a ubiquitous coronal mass supply in which chromospheric plasma in fountainlike jets or spicules is accelerated upward into the corona, with much of the plasma heated to temperatures between ~0.02 and 0.1 million kelvin (MK) and a small but sufficient fraction to temperatures above 1 MK. These observations provide constraints on the coronal heating mechanism(s) and highlight the importance of the interface region between photosphere and corona.
RESUMEN
Alfvén waves have been invoked as a possible mechanism for the heating of the Sun's outer atmosphere, or corona, to millions of degrees and for the acceleration of the solar wind to hundreds of kilometers per second. However, Alfvén waves of sufficient strength have not been unambiguously observed in the solar atmosphere. We used images of high temporal and spatial resolution obtained with the Solar Optical Telescope onboard the Japanese Hinode satellite to reveal that the chromosphere, the region sandwiched between the solar surface and the corona, is permeated by Alfvén waves with strong amplitudes on the order of 10 to 25 kilometers per second and periods of 100 to 500 seconds. Estimates of the energy flux carried by these waves and comparisons with advanced radiative magnetohydrodynamic simulations indicate that such Alfvén waves are energetic enough to accelerate the solar wind and possibly to heat the quiet corona.
RESUMEN
Solar prominences are cool 10(4) kelvin plasma clouds supported in the surrounding 10(6) kelvin coronal plasma by as-yet-undetermined mechanisms. Observations from Hinode show fine-scale threadlike structures oscillating in the plane of the sky with periods of several minutes. We suggest that these represent Alfvén waves propagating on coronal magnetic field lines and that these may play a role in heating the corona.
RESUMEN
We observed fine-scale jetlike features, referred to as penumbral microjets, in chromospheres of sunspot penumbrae. The microjets were identified in image sequences of a sunspot taken through a Ca II H-line filter on the Solar Optical Telescope on board the Japanese solar physics satellite Hinode. The microjets' small width of 400 kilometers and short duration of less than 1 minute make them difficult to identify in existing observations. The microjets are possibly caused by magnetic reconnection in the complex magnetic configuration in penumbrae and have the potential to heat the corona above a sunspot.
RESUMEN
The penumbra of a sunspot is composed of numerous thin, radially extended, bright and dark filaments carrying outward gas flows (the Evershed flow). Using high-resolution images obtained by the Solar Optical Telescope aboard the solar physics satellite Hinode, we discovered a number of penumbral bright filaments revealing twisting motions about their axes. These twisting motions are observed only in penumbrae located in the direction perpendicular to the symmetry line connecting the sunspot center and the solar disk center, and the direction of the twist (that is, lateral motions of intensity fluctuation across filaments) is always from limb side to disk-center side. Thus, the twisting feature is not an actual twist or turn of filaments but a manifestation of dynamics of penumbral filaments with three-dimensional radiative transfer effects.
RESUMEN
The flight of the Solar Optical Universal Polarimeter on Spacelab-2 provided the opportunity for the collection of time sequences of diffraction-limited (0.5 are second) solar images with excellent pointing stability (0.003 are second) and with freedom from the distortion that plagues ground-based images. A series of white-light images of active region 4682 were obtained on 5 August 1985, and the area containing the sunspot has been analyzed. These data have been digitally processed to remove noise and to separate waves from low-velocity material motions. The results include (i) proper motion measurements of a radial outflow in the photospheric granulation pattern just outside the penumbra; (ii) discovery of occasional bright structures ("streakers") that appear to be ejected outward from the penumbra; (iii) broad dark "clouds" moving outward in the penumbra, in addition to the well-known bright penumbral grains moving inward; (iv) apparent extensions and contractions of penumbral filaments over the photosphere; and (v) observation of a faint bubble or looplike structure that seems to expand from two bright penumbral filaments into the photosphere.
RESUMEN
The characteristics and performance of a Ranicon photon-counting system combined with digital tape recording are described. The most important features are a bialkali photocathode response over 256 x 256 digital pixels, with ~100 x 100 resolvable pixels at 50% MTF, a dead time of 16 microsec/count, a maximum recordable count rate of 14,400/sec, and a background of <1 count/digital pixel/h. A video cassette recorder serves for the digital recording which retains the temporal sequence of the registered photons. Astronomical applications will include low light level quantitative imaging and speckle imaging.
RESUMEN
A 100-mA analog birefringent element has been built from a polarizing wide field solid Michelson interferometer. The analog element behaves on-axis identically to a crystal element but has the field characteristics of a wide field Michelson. It is demonstrated that by proper choice of glasses for the arms of the Michelson the wide field condition can hold over a large spectral and large temperature range. Most important, proper choice of arm materials allows minimization of the wavelength sensitivity to temperature. A reduction of a factor of 10(2)-10(3) compared to birefringent crystals can be achieved.
RESUMEN
The field of view characteristics of wide field birefringent (WFB) elements are compared with those of the Fabry-Perot (F.P.), Michelson (MI), and wide field Michelson (WFM) interferometers. Throughput gains of 50 to 300 or more with respect to the F.P. or MI are demonstrated. Further, it is shown that by proper choice of material WFB elements can have angular characteristics identical with WFM interferometers. The properties of misaligned and mismatched half-length WFB elements are calculated. It is shown that properly misadjusted WFB elements can exhibit throughput gains with respect to properly adjusted systems. Finally, a catalog of fringe patterns for WFB elements of different materials and differing angular misadjustment is presented.
RESUMEN
A design for a birefringent filter is proposed in which alternate polarizers are partial polarizers. Calculated performance characteristics of alternate partial polarizer filters (APP) are compared with those of Lyot and contrast element Lyot filters. These calculations show that the APP design has significant advantages in both transmission and profile shape. Using pulse techniques, partial polarizer systems are shown to be a natural evolution from the standard Lyot and contrast element Lyot systems. The APP filter using achromatic waveplates discussed in earlier papers of this series has been used to construct a universal alternate partial polarizer filter. This filter has a measured full width at half-maximum (FWHM) of 0.09 A at 5500 A and a transmission in polarized light of 38%. It is tunable from 4500 A to 8500 A. The measured characteristics of the filter agree well with theoretical predictions.
RESUMEN
By use of Jones' matrix techniques, nine-element achromatic waveplates are developed. These combination plates are achromatic to within 1 degrees throughout the visible (3,500-10,000 A). In addition, a two-section general retarder rotator is demonstrated. The retardation of the combination is twice the complement of the angle between the halves, while the rotation is equal to the angle between the halves. For a 90 degrees retardation, the dual five-element combination is also achromatic to within 1 degrees throughout the visible.
RESUMEN
The properties of nontunable and tunable Lyot wide field elements are examined when the components of the elements deviate from their proper values. Special emphasis is put on determining what variations cause light to be transmitted at the transmission minima. The analysis shows that the nine- and ten-element plastic waveplates described in Paper 2 of this series can be used to make a Lyot filter that is tunable from 3500 A to 10,000 A.
RESUMEN
The design and operating characteristics of several recently fabricated solid-spaced Fabry-Perot interference filters having bandwidths from 0.3 A to 8 A in the 1-5-microm ir wavelength range are discussed. The 10(4) achievable resolving power of these devices, particularly at the higher wavelengths, represents several orders of magnitude improvement over conventional ir filters, and the implications of this very high resolution along with the tilt-tuning properties of narrow-band filters are discussed in relation to atmospheric remote sensing.
RESUMEN
We describe a semiautomatic procedure for the reduction of high-dispersion echelle spectra recorded with an image tube. The spectra are traced with a computer-controlled microdensitometer that scans along the curved spectral orders. The curvature of each order is calculated approximately by a FORTRAN program from known grating and distortion parameters. A typical spectrum includes 25 orders (covering 1500 A) and is traced with a slit 0.012 A wide. To produce an atlas of intensity vs wavelength and to determine the equivalent widths of 300 lines currently require a day. We discuss the reduction procedures and time requirements in detail.
