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Sample records for photosphere

  1. Vorticity in the solar photosphere

    NASA Astrophysics Data System (ADS)

    Shelyag, S.; Keys, P.; Mathioudakis, M.; Keenan, F. P.

    2011-02-01

    Aims: We use magnetic and non-magnetic 3D numerical simulations of solar granulation and G-band radiative diagnostics from the resulting models to analyse the generation of small-scale vortex motions in the solar photosphere. Methods: Radiative MHD simulations of magnetoconvection are used to produce photospheric models. Our starting point is a non-magnetic model of solar convection, where we introduce a uniform magnetic field and follow the evolution of the field in the simulated photosphere. We find two different types of photospheric vortices, and provide a link between the vorticity generation and the presence of the intergranular magnetic field. A detailed analysis of the vorticity equation, combined with the G-band radiative diagnostics, allows us to identify the sources and observational signatures of photospheric vorticity in the simulated photosphere. Results: Two different types of photospheric vorticity, magnetic and non-magnetic, are generated in the domain. Non-magnetic vortices are generated by the baroclinic motions of the plasma in the photosphere, while magnetic vortices are produced by the magnetic tension in the intergranular magnetic flux concentrations. The two types of vortices have different shapes. We find that the vorticity is generated more efficiently in the magnetised model. Simulated G-band images show a direct connection between magnetic vortices and rotary motions of photospheric bright points, and suggest that there may be a connection between the magnetic bright point rotation and small-scale swirl motions observed higher in the atmosphere.

  2. Solar and stellar photospheric abundances

    NASA Astrophysics Data System (ADS)

    Allende Prieto, Carlos

    2016-07-01

    The determination of photospheric abundances in late-type stars from spectroscopic observations is a well-established field, built on solid theoretical foundations. Improving those foundations to refine the accuracy of the inferred abundances has proven challenging, but progress has been made. In parallel, developments on instrumentation, chiefly regarding multi-object spectroscopy, have been spectacular, and a number of projects are collecting large numbers of observations for stars across the Milky Way and nearby galaxies, promising important advances in our understanding of galaxy formation and evolution. After providing a brief description of the basic physics and input data involved in the analysis of stellar spectra, a review is made of the analysis steps, and the available tools to cope with large observational efforts. The paper closes with a quick overview of relevant ongoing and planned spectroscopic surveys, and highlights of recent research on photospheric abundances.

  3. Photospheric and coronal magnetic fields

    SciTech Connect

    Sheeley, N.R., Jr. )

    1991-01-01

    Research on small-scale and large-scale photospheric and coronal magnetic fields during 1987-1990 is reviewed, focusing on observational studies. Particular attention is given to the new techniques, which include the correlation tracking of granules, the use of highly Zeeman-sensitive infrared spectral lines and multiple lines to deduce small-scale field strength, the application of long integration times coupled with good seeing conditions to study weak fields, and the use of high-resolution CCD detectors together with computer image-processing techniques to obtain images with unsurpassed spatial resolution. Synoptic observations of large-scale fields during the sunspot cycle are also discussed. 101 refs.

  4. REGULAR VERSUS DIFFUSIVE PHOTOSPHERIC FLUX CANCELLATION

    SciTech Connect

    Litvinenko, Yuri E.

    2011-04-20

    Observations of photospheric flux cancellation on the Sun imply that cancellation can be a diffusive rather than regular process. A criterion is derived, which quantifies the parameter range in which diffusive photospheric cancellation should occur. Numerical estimates show that regular cancellation models should be expected to give a quantitatively accurate description of photospheric cancellation. The estimates rely on a recently suggested scaling for a turbulent magnetic diffusivity, which is consistent with the diffusivity measurements on spatial scales varying by almost two orders of magnitude. Application of the turbulent diffusivity to large-scale dispersal of the photospheric magnetic flux is discussed.

  5. PHOTOSPHERIC EMISSION FROM STRATIFIED JETS

    SciTech Connect

    Ito, Hirotaka; Nagataki, Shigehiro; Ono, Masaomi; Lee, Shiu-Hang; Mao, Jirong; Yamada, Shoichi; Pe'er, Asaf; Mizuta, Akira; Harikae, Seiji

    2013-11-01

    We explore photospheric emissions from stratified two-component jets, wherein a highly relativistic spine outflow is surrounded by a wider and less relativistic sheath outflow. Thermal photons are injected in regions of high optical depth and propagated until the photons escape at the photosphere. Because of the presence of shear in velocity (Lorentz factor) at the boundary of the spine and sheath region, a fraction of the injected photons are accelerated using a Fermi-like acceleration mechanism such that a high-energy power-law tail is formed in the resultant spectrum. We show, in particular, that if a velocity shear with a considerable variance in the bulk Lorentz factor is present, the high-energy part of observed gamma-ray bursts (GRBs) photon spectrum can be explained by this photon acceleration mechanism. We also show that the accelerated photons might also account for the origin of the extra-hard power-law component above the bump of the thermal-like peak seen in some peculiar bursts (e.g., GRB 090510, 090902B, 090926A). We demonstrate that time-integrated spectra can also reproduce the low-energy spectrum of GRBs consistently using a multi-temperature effect when time evolution of the outflow is considered. Last, we show that the empirical E{sub p}-L{sub p} relation can be explained by differences in the outflow properties of individual sources.

  6. Photospheric Emission from Stratified Jets

    NASA Astrophysics Data System (ADS)

    Ito, Hirotaka; Nagataki, Shigehiro; Ono, Masaomi; Lee, Shiu-Hang; Mao, Jirong; Yamada, Shoichi; Pe'er, Asaf; Mizuta, Akira; Harikae, Seiji

    2013-11-01

    We explore photospheric emissions from stratified two-component jets, wherein a highly relativistic spine outflow is surrounded by a wider and less relativistic sheath outflow. Thermal photons are injected in regions of high optical depth and propagated until the photons escape at the photosphere. Because of the presence of shear in velocity (Lorentz factor) at the boundary of the spine and sheath region, a fraction of the injected photons are accelerated using a Fermi-like acceleration mechanism such that a high-energy power-law tail is formed in the resultant spectrum. We show, in particular, that if a velocity shear with a considerable variance in the bulk Lorentz factor is present, the high-energy part of observed gamma-ray bursts (GRBs) photon spectrum can be explained by this photon acceleration mechanism. We also show that the accelerated photons might also account for the origin of the extra-hard power-law component above the bump of the thermal-like peak seen in some peculiar bursts (e.g., GRB 090510, 090902B, 090926A). We demonstrate that time-integrated spectra can also reproduce the low-energy spectrum of GRBs consistently using a multi-temperature effect when time evolution of the outflow is considered. Last, we show that the empirical E p-L p relation can be explained by differences in the outflow properties of individual sources.

  7. STOCHASTIC COUPLING OF SOLAR PHOTOSPHERE AND CORONA

    SciTech Connect

    Uritsky, Vadim M.; Ofman, Leon; Davila, Joseph M.; Coyner, Aaron J.

    2013-05-20

    The observed solar activity is believed to be driven by the dissipation of nonpotential magnetic energy injected into the corona by dynamic processes in the photosphere. The enormous range of scales involved in the interaction makes it difficult to track down the photospheric origin of each coronal dissipation event, especially in the presence of complex magnetic topologies. In this paper, we propose an ensemble-based approach for testing the photosphere-corona coupling in a quiet solar region as represented by intermittent activity in Solar and Heliospheric Observatory Michelson Doppler Imager and Solar TErrestrial RElations Observatory Extreme Ultraviolet Imager image sets. For properly adjusted detection thresholds corresponding to the same degree of intermittency in the photosphere and corona, the dynamics of the two solar regions is described by the same occurrence probability distributions of energy release events but significantly different geometric properties. We derive a set of scaling relations reconciling the two groups of results and enabling statistical description of coronal dynamics based on photospheric observations. Our analysis suggests that multiscale intermittent dissipation in the corona at spatial scales >3 Mm is controlled by turbulent photospheric convection. Complex topology of the photospheric network makes this coupling essentially nonlocal and non-deterministic. Our results are in an agreement with the Parker's coupling scenario in which random photospheric shuffling generates marginally stable magnetic discontinuities at the coronal level, but they are also consistent with an impulsive wave heating involving multiscale Alfvenic wave packets and/or magnetohydrodynamic turbulent cascade. A back-reaction on the photosphere due to coronal magnetic reconfiguration can be a contributing factor.

  8. CO isotopologue ratios in the solar photosphere

    NASA Astrophysics Data System (ADS)

    Lyons, James; Gharib-Nezhad, Ehsan; Ayres, Thomas

    2015-08-01

    Determination of the oxygen isotope ratios in the solar photosphere is essential to constraining the formation environment of the solar system. The solar CO fundamental and first-overtone bands were previously measured by the shuttle-borne ATMOS Fourier transform spectrometer (FTS), and with the National Solar Observatory FTS on the McMath-Pierce telescope at Kitt Peak. Analyzing the rovibrational bands from these photospheric spectra, a 3D convection model was employed to calculate ratios with improved uncertainties (16O/17O=2738±118 and 16O/18O =511±10 Ayres et al. 2013), which fall between the terrestrial values and those inferred from solar wind measurements by the Genesis spacecraft. However, differences in published CO dipole moment functions yielded a range of isotopic ratios spanning ~ 3 % in δ18O. Here we re-evaluate the CO dipole moment function in order to obtain more accurate isotope ratios for the photosphere. We used a new set of dipole moments from HITEMP which were accurately determined by both semi-empirical and ab initio methods. Preliminary values of isotope ratios using the new dipole moments are in better agreement with the inferred photosphere values from Genesis, showing that the solar photosphere is isotopically similar to primitive inclusions in meteorites, but different from the terrestrial planets by ~ 6 %. New spectral observations are needed to reduce uncertainties in photospheric C17O abundances.

  9. The dark component of the photospheric network

    NASA Technical Reports Server (NTRS)

    Schoolman, S. A.; Ramsey, H. E.

    1976-01-01

    We examine a high quality Zeeman-analyzed lambda-scan through Ca I 6103, using a 0.1 A filter. We find that filter shifts of 0.01 A produce substantial changes in the contrast seen in the photospheric network in the core of the line, implying that the Doppler velocity in the network is constant to within 0.25 km/sec or less. Relative line profiles constructed from the lambda-scan indicate that the bright network points have smaller equivalent widths than does the background photosphere and are systematically Doppler shifted toward the red. However, we also find numerous small dark points within the magnetic network which exhibit increased equivalent widths. We infer these to be due to magnetic flux tubes which are highly inclined through the photosphere.

  10. MAGNETOHYDRODYNAMICS OF THE WEAKLY IONIZED SOLAR PHOTOSPHERE

    SciTech Connect

    Cheung, Mark C. M.; Cameron, Robert H.

    2012-05-01

    We investigate the importance of ambipolar diffusion and Hall currents for high-resolution comprehensive ({sup r}ealistic{sup )} photospheric simulations. To do so, we extended the radiative magnetohydrodynamics code MURaM to use the generalized Ohm's law under the assumption of local thermodynamic equilibrium. We present test cases comparing analytical solutions with numerical simulations for validation of the code. Furthermore, we carried out a number of numerical experiments to investigate the impact of these neutral-ion effects in the photosphere. We find that, at the spatial resolutions currently used (5-20 km per grid point), the Hall currents and ambipolar diffusion begin to become significant-with flows of 100 m s{sup -1} in sunspot light bridges, and changes of a few percent in the thermodynamic structure of quiet-Sun magnetic features. The magnitude of the effects is expected to increase rapidly as smaller-scale variations are resolved by the simulations.

  11. Do evaporating black holes form photospheres?

    NASA Astrophysics Data System (ADS)

    MacGibbon, Jane H.; Carr, B. J.; Page, Don N.

    2008-09-01

    Several authors, most notably Heckler, have claimed that the observable Hawking emission from a microscopic black hole is significantly modified by the formation of a photosphere around the black hole due to QED or QCD interactions between the emitted particles. In this paper we analyze these claims and identify a number of physical and geometrical effects which invalidate these scenarios. We point out two key problems. First, the interacting particles must be causally connected to interact, and this condition is satisfied by only a small fraction of the emitted particles close to the black hole. Second, a scattered particle requires a distance ˜E/me2 for completing each bremsstrahlung interaction, with the consequence that it is improbable for there to be more than one complete bremsstrahlung interaction per particle near the black hole. These two effects have not been included in previous analyses. We conclude that the emitted particles do not interact sufficiently to form a QED photosphere. Similar arguments apply in the QCD case and prevent a QCD photosphere (chromosphere) from developing when the black hole temperature is much greater than ΛQCD, the threshold for QCD particle emission. Additional QCD phenomenological arguments rule out the development of a chromosphere around black hole temperatures of order ΛQCD. In all cases, the observational signatures of a cosmic or Galactic halo background of primordial black holes or an individual black hole remain essentially those of the standard Hawking model, with little change to the detection probability. We also consider the possibility, as proposed by Belyanin et al. and D. Cline et al., that plasma interactions between the emitted particles form a photosphere, and we conclude that this scenario too is not supported.

  12. Carrington Maps of the Upper Photosphere

    NASA Astrophysics Data System (ADS)

    Sheeley, , N. R., Jr.; Warren, H. P.

    2006-04-01

    We have used images of the Sun's disk, obtained in the 6767 Å continuum with the Michelson Doppler Interferometer (MDI) on the Solar and Heliospheric Observatory (SOHO), to make Carrington maps of the upper photosphere during the years 1996-2005. Each map is constructed from observations near the limb where the continuum radiation originates relatively high in the photosphere and faculae have their greatest visibility. Consequently, the Carrington maps resemble spectroheliograms in temperature-sensitive photospheric lines and show the global distribution of faculae and all but the smallest sunspots (which are obscured by overlying faculae). A time-lapse sequence of the combined east-limb and west-limb maps shows the emergence of active regions and the evolution of large-scale patterns of faculae with an average temporal resolution of 14 days during the sunspot cycle. Also, a longitudinally averaged butterfly diagram of these maps shows that in each hemisphere there is a facula-free zone separating the old-cycle polar field from trailing-polarity flux that is migrating poleward from the sunspot belts. These facula-free zones coincide with the neutral zones of the axisymmetric component of photospheric magnetic field and their arrival at the poles in 2001 marks the reversal of the polar fields. We think that this mapmaking technique can be applied to white-light images obtained daily at the Mount Wilson Observatory since 1905 and that the resulting Carrington maps will provide details about the polar-field reversal process during past sunspot cycles when high-quality magnetograms were unavailable.

  13. Photospheric Radius Expansion During Magnetar Bursts

    NASA Astrophysics Data System (ADS)

    Watts, Anna L.; Kouveliotou, Chryssa; van der Horst, Alexander J.; Göǧüş, Ersin; Kaneko, Yuki; van der Klis, Michiel; Wijers, Ralph A. M. J.; Harding, Alice K.; Baring, Matthew G.

    2010-08-01

    On 2008 August 24 the new magnetar SGR 0501+4516 (discovered by Swift) emitted a bright burst with a pronounced double-peaked structure in hard X-rays, reminiscent of the double-peaked temporal structure seen in some bright thermonuclear bursts on accreting neutron stars. In the latter case this is due to Photospheric Radius Expansion (PRE): when the flux reaches the Eddington limit, the photosphere expands and cools so that emission becomes softer and drops temporarily out of the X-ray band, re-appearing as the photosphere settles back down. We consider the factors necessary to generate double-peaked PRE events, and show that such a mechanism could plausibly operate in magnetar bursts despite the vastly different emission process. Identification of the magnetic Eddington limit in a magnetar would constrain magnetic field and distance and could, in principle, enable a measurement of gravitational redshift. It would also locate the emitting region at the neutron star surface, constraining the burst trigger mechanism. Conclusive confirmation of PRE events will require more detailed radiative models for bursts. However, for SGR 0501+4516 the predicted critical flux (using the magnetic field strength inferred from timing and the distance suggested by its probable location in the Perseus arm of our Galaxy) is consistent with that observed in the August 24 burst.

  14. Sub-photosphere to Solar Atmosphere Connection

    NASA Astrophysics Data System (ADS)

    Komm, Rudolf; De Moortel, Ineke; Fan, Yuhong; Ilonidis, Stathis; Steiner, Oskar

    2015-12-01

    Magnetic fields extend from the solar interior through the atmosphere. The formation and evolution of active regions can be studied by measuring subsurface flows with local helioseismology. The emergence of magnetic flux from the solar convection zone is associated with acoustic perturbation signatures. In near-surface layers, the average dynamics can be determined for emerging regions. MHD simulations of the emergence of a twisted flux tube show how magnetic twist and free energy are transported from the interior into the corona and the dynamic signatures associated with such transport in the photospheric and sub-photospheric layers. The subsurface twisted flux tube does not emerge into the corona as a whole in emerging active regions. Shear flows at the polarity inversion line and coherent vortical motions in the subsurface flux tubes are the major means by which twist is transported into the corona, leading to the formation of sigmoid-shaped coronal magnetic fields capable of driving solar eruptions. The transport of twist can be followed from the interior by using the kinetic helicity of subsurface flows as a proxy of magnetic helicity; this quantity holds great promise for improving the understanding of eruptive phenomena. Waves are not only vital for studying the link between the solar interior and the surface but for linking the photosphere with the corona as well. Acoustic waves that propagate from the surface into the magnetically structured, dynamic atmosphere undergo mode conversion and refraction. These effects enable atmospheric seismology to determine the topography of magnetic canopies in the solar atmosphere. Inclined magnetic fields lower the cut-off frequency so that low frequency waves can leak into the outer atmosphere. Recent high resolution, high cadence observations of waves and oscillations in the solar atmosphere, have lead to a renewed interest in the potential role of waves as a heating mechanism. In light of their potential contribution

  15. Spherical harmonic analysis of steady photospheric flows

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    1987-01-01

    A technique is presented in which full disk Doppler velocity measurements are analyzed using spherical harmonic functions to determine the characteristics of the spectrum of spherical harmonic modes and the nature of steady photospheric flows. Synthetic data are constructed in order to test the technique. In spite of the mode mixing due to the lack of information about the motions on the backside of the sun, solar rotation and differential rotation can be accurately measured and monitored for secular changes, and meridional circulations with small amplitudes can be measured. Furthermore, limb shift measurements can be accurately obtained, and supergranules can be fully resolved and separated from giant cells by their spatial characteristics.

  16. The source surface and photospheric magnetic field models

    NASA Technical Reports Server (NTRS)

    Saito, T.; Kozuka, Y.; Oki, T.; Akasofu, S.-I.

    1991-01-01

    It is possible to reproduce the configuration of the neutral line on the solar source surface by the axial dipole at the center of the sun and a few fictitious dipoles on the photosphere. An attempt is made to identify the nature of such fictitious dipoles in the photospheric magnetic fields. It is shown that large-scale photospheric dipole fields can be identified clearly at the locations indicated by the fictitious dipoles when the photospheric field is very simple. They are found to be active regions.

  17. Standing sausage waves in photospheric magnetic waveguides

    NASA Astrophysics Data System (ADS)

    Dorotovič, I.; Erdélyi, R.; Freij, N.; Karlovský, V.; Márquez, I.

    2014-03-01

    Aims: By focussing on the oscillations of the cross-sectional area and the total intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Methods: Capturing several high-resolution time series of magnetic waveguides and employing a wavelet analysis, in conjunction with empirical mode decomposition (EMD), makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as examples of MHD waveguides in the lower solar atmosphere. Results: The waveguides display a range of periods from 4 to 65 min. These structures display in-phase behaviour between the area and intensity, presenting mounting evidence for sausage modes within these waveguides. The detected periods point towards standing oscillations. Conclusions: The presence of fast and slow MHD sausage waves has been detected in three different magnetic waveguides in the solar photosphere. Furthermore, these oscillations are potentially standing harmonics supported in the waveguides that are sandwiched vertically between the temperature minimum in the lower solar atmosphere and the transition region. The relevance of standing harmonic oscillations is that their exploitation by means of solar magneto-seismology may allow insight into the sub-pixel resolution structure of photospheric MHD waveguides.

  18. Magnetic structure of sunspot under the photosphere

    NASA Astrophysics Data System (ADS)

    Kirichek, Elena A.; Solov'ev, Alexandr A.

    2010-11-01

    In recent years, the local helioseismology has become a highly effective tool for investigating subphotospheric layers of the Sun, which can yield fairly detailed distributions of the subphotospheric temperatures and large-scale plasma flows based on the spectra of the oscillations observed at the photospheric layers and the observed peculiarities of propagation of magnetoacoustic waves in this medium (Zhao et al. (2001), Kosovichev (2006)). Unfortunately, the effects of temperature and the magnetic field on the wave propagation speed have not yet been separated Kosovichev (2006), so that the structure of the sunspot magnetic field in deep layers, beneath the photosphere, remains a subject of purely theoretical analysis. In his analysis of some theoretical models of the subphotospheric layers of sunspots based on recent helioseismological data, Kosovichev (2006) concluded that Parker's (“spaghetti”) cluster model Parker (1979) is most appropriate. In this model, the magnetic flux in the sunspot umbra is concentrated into separate, strongly compressed, vertical magnetic flux tubes that are interspaced with plasma that is almost free of magnetic field; the plasma can move between these tubes.

  19. Properties of Photospheric Bright Points outside Sunspots

    NASA Astrophysics Data System (ADS)

    Qu, H. X.; Yang, Y. F.; Feng, S.; Wang, F.; Deng, H.; Ji, K. F.

    2015-09-01

    Photospheric bright points are tiny bright features located in intergranular lanes. They are widely believed as the foot points of magnetic flux tubes. In this paper, various properties of bright points outside NOAA 11598 sunspots are analyzed using the TiO-band data detected by the 1-m New Vacuum Solar Telescope of Yunnan Observatories, which is located at the Fuxian Solar Physics Observing Station, Yunnan Province. We divide the periphery of the sunspot into four annular regions based on the dilation technology of image morphology. Then, a Laplacian and morphological dilation algorithm is used to identify bright points, and a three-dimensional segment algorithm is applied to track the evolution of bright points. Finally, we detect the parameters of the bright points in the four annular regions, including the density, intensity, size, shape, and velocity. Statistical results show that the density, size, and velocity of photospheric bright points are obviously affected by the strong magnetic fields of sunspots, and their peak values are in the second region instead of the closest region of the sunspot. The bright points decrease their densities and sizes, but increase their velocities with the distance away from the sunspot center. Additionally, the maximum intensity contrast presents the decreasing trend. However, the bright point shapes are basically invariant, and independent of this distance.

  20. Reconnection brightenings in the quiet solar photosphere

    NASA Astrophysics Data System (ADS)

    Rouppe van der Voort, Luc H. M.; Rutten, Robert J.; Vissers, Gregal J. M.

    2016-08-01

    We describe a new quiet-Sun phenomenon which we call quiet-Sun Ellerman-like brightenings (QSEB). QSEBs are similar to Ellerman bombs (EB) in some respects but differ significantly in others. EBs are transient brightenings of the wings of the Balmer Hα line that mark strong-field photospheric reconnection in complex active regions. QSEBs are similar but smaller and less intense Balmer-wing brightenings that occur in quiet areas away from active regions. In the Hα wing, we measure typical lengths of less than 0.5 arcsec, widths of 0.23 arcsec, and lifetimes of less than a minute. We discovered them using high-quality Hα imaging spectrometry from the Swedish 1-m Solar Telescope (SST) and show that, in lesser-quality data, they cannot be distinguished from more ubiquitous facular brightenings, nor in the UV diagnostics currently available from space platforms. We add evidence from concurrent SST spectropolarimetry that QSEBs also mark photospheric reconnection events, but in quiet regions on the solar surface. The movies are available in electronic form at http://www.aanda.org

  1. Temporal filters for isolating steady photospheric flows

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.

    1988-01-01

    A variety of temporal filters are tested on artificial data with 60 and 75 s sampling intervals to determine their accuracy in separating the nearly-steady photospheric flows from the p-mode oscillations in Doppler velocity data. Longer temporal averages are better at reducing the residual signal due to p-modes but they introduce additional errors from the rotation of the supergranule pattern across the solar disk. Unweighted filters (boxcar averages) leave residual rms errors of about 6 m/s from the p-modes after 60 min of averaging. Weighted filters, with nearly Gaussian shapes, leave similar residual errors after only 20 min of averaging and introduce smaller errors from the rotation of the supergranule pattern. The best filters found are weighted filters that use data separated by 150 or 120 s so that the p-modes are sampled at opposite phases.

  2. The quiet-Sun photosphere and chromosphere.

    PubMed

    Rutten, Robert J

    2012-07-13

    The overall structure and the fine structure of the solar photosphere outside active regions are largely understood, except possibly the important roles of a turbulent near-surface dynamo at its bottom, internal gravity waves at its top and small-scale vorticity. Classical one-dimensional static radiation-escape modelling has been replaced by three-dimensional time-dependent magento-hydrodynamic simulations that come closer to reality. The solar chromosphere, in contrast, remains little understood, although its pivotal role in coronal mass and energy loading makes it a principal research area. Its fine structure defines its overall structure, so that hard-to-observe and hard-to-model small-scale dynamical processes are key to understanding. However, both chromospheric observation and chromospheric simulation presently mature towards the required sophistication. Open-field features seem of greater interest than easier-to-see closed-field features. PMID:22665896

  3. A MAGNETIC CALIBRATION OF PHOTOSPHERIC DOPPLER VELOCITIES

    SciTech Connect

    Welsch, Brian T.; Fisher, George H.; Sun, Xudong

    2013-03-10

    The zero point of measured photospheric Doppler shifts is uncertain for at least two reasons: instrumental variations (from, e.g., thermal drifts); and the convective blueshift, a known correlation between intensity and upflows. Accurate knowledge of the zero point is, however, useful for (1) improving estimates of the Poynting flux of magnetic energy across the photosphere, and (2) constraining processes underlying flux cancellation, the mutual apparent loss of magnetic flux in closely spaced, opposite-polarity magnetogram features. We present a method to absolutely calibrate line-of-sight (LOS) velocities in solar active regions (ARs) near disk center using three successive vector magnetograms and one Dopplergram coincident with the central magnetogram. It exploits the fact that Doppler shifts measured along polarity inversion lines (PILs) of the LOS magnetic field determine one component of the velocity perpendicular to the magnetic field, and optimizes consistency between changes in LOS flux near PILs and the transport of transverse magnetic flux by LOS velocities, assuming that ideal electric fields govern the magnetic evolution. Previous calibrations fitted the center-to-limb variation of Doppler velocities, but this approach cannot, by itself, account for residual convective shifts at the limb. We apply our method to vector magnetograms of AR 11158, observed by the Helioseismic and Magnetic Imager aboard the Solar Dynamics Observatory, and find clear evidence of offsets in the Doppler zero point in the range of 50-550 m s{sup -1}. In addition, we note that a simpler calibration can be determined from an LOS magnetogram and Dopplergram pair from the median Doppler velocity among all near-disk-center PIL pixels. We briefly discuss shortcomings in our initial implementation, and suggest ways to address these. In addition, as a step in our data reduction, we discuss the use of temporal continuity in the transverse magnetic field direction to correct apparently

  4. Measurements of Photospheric and Chromospheric Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Lagg, Andreas; Lites, Bruce; Harvey, Jack; Gosain, Sanjay; Centeno, Rebecca

    2015-12-01

    The Sun is replete with magnetic fields, with sunspots, pores and plage regions being their most prominent representatives on the solar surface. But even far away from these active regions, magnetic fields are ubiquitous. To a large extent, their importance for the thermodynamics in the solar photosphere is determined by the total magnetic flux. Whereas in low-flux quiet Sun regions, magnetic structures are shuffled around by the motion of granules, the high-flux areas like sunspots or pores effectively suppress convection, leading to a temperature decrease of up to 3000 K. The importance of magnetic fields to the conditions in higher atmospheric layers, the chromosphere and corona, is indisputable. Magnetic fields in both active and quiet regions are the main coupling agent between the outer layers of the solar atmosphere, and are therefore not only involved in the structuring of these layers, but also for the transport of energy from the solar surface through the corona to the interplanetary space. Consequently, inference of magnetic fields in the photosphere, and especially in the chromosphere, is crucial to deepen our understanding not only for solar phenomena such as chromospheric and coronal heating, flares or coronal mass ejections, but also for fundamental physical topics like dynamo theory or atomic physics. In this review, we present an overview of significant advances during the last decades in measurement techniques, analysis methods, and the availability of observatories, together with some selected results. We discuss the problems of determining magnetic fields at smallest spatial scales, connected with increasing demands on polarimetric sensitivity and temporal resolution, and highlight some promising future developments for their solution.

  5. Data Assimilation in the ADAPT Photospheric Flux Transport Model

    SciTech Connect

    Hickmann, Kyle S.; Godinez, Humberto C.; Henney, Carl J.; Arge, C. Nick

    2015-03-17

    Global maps of the solar photospheric magnetic flux are fundamental drivers for simulations of the corona and solar wind and therefore are important predictors of geoeffective events. However, observations of the solar photosphere are only made intermittently over approximately half of the solar surface. The Air Force Data Assimilative Photospheric Flux Transport (ADAPT) model uses localized ensemble Kalman filtering techniques to adjust a set of photospheric simulations to agree with the available observations. At the same time, this information is propagated to areas of the simulation that have not been observed. ADAPT implements a local ensemble transform Kalman filter (LETKF) to accomplish data assimilation, allowing the covariance structure of the flux-transport model to influence assimilation of photosphere observations while eliminating spurious correlations between ensemble members arising from a limited ensemble size. We give a detailed account of the implementation of the LETKF into ADAPT. Advantages of the LETKF scheme over previously implemented assimilation methods are highlighted.

  6. X-ray spectra from convective photospheres of neutron stars

    SciTech Connect

    Zavlin, V.E.; Pavlov, G.G. |; Shibanov, Yu.A.; Rogers, F.J.; Iglesias, C.A.

    1996-01-17

    We present first results of modeling convective photospheres of neutron stars. We show that in photospheres composed of the light elements convection arises only at relatively low effective temperatures ({le}3 - 5 x 10{sup 4} K), whereas in the case of iron composition it arises at T{sub eff}{le} 3 x 10{sup 5}K. Convection changes the depth dependence of the photosphere temperature and the shapes of the emergent spectra. Thus, it should be taken into account for the proper interpretation of EUV/soft-X-ray observations of the thermal radiation from neutron stars.

  7. Photospheric Temperature Variations near the Solar Limb

    NASA Astrophysics Data System (ADS)

    Fivian, Martin; Hudson, H. S.; Lin, R. P.; Zahid, H. J.

    2010-05-01

    We use observations from the solar aspect sensor of RHESSI to characterize the latitude dependence of the temperature of the photosphere near the solar limb. Previous observations had suggested the presence of a polar temperature excess as large as 1.5 K. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. This photometry is differential, i.e. relative to a mean limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1.73 arc sec square pixels, observing a narrow band (12nm FWHM) at 670 nm. Each image shows a chord crossing the disk at a different location as the spacecraft rotates and precesses around its average solar pointing. We fit an average limb-darkening function and reassemble the residuals into synoptic maps of differential intensity variations as a function of position angle. We further mask these images against SOHO/EIT 284A images in order to eliminate magnetic regions. The analysis establishes a limit on the quadrupole dependence of temperature (brightness) on position angle of order 0.04 K, with a comparable uncertainty.

  8. ALFVÉN WAVES IN SIMULATIONS OF SOLAR PHOTOSPHERIC VORTICES

    SciTech Connect

    Shelyag, S.; Cally, P. S.; Reid, A.; Mathioudakis, M.

    2013-10-10

    Using advanced numerical magneto-hydrodynamic simulations of the magnetized solar photosphere, including non-gray radiative transport and a non-ideal equation of state, we analyze plasma motions in photospheric magnetic vortices. We demonstrate that apparent vortex-like motions in photospheric magnetic field concentrations do not exhibit 'tornado'-like behavior or a 'bath-tub' effect. While at each time instance the velocity field lines in the upper layers of the solar photosphere show swirls, the test particles moving with the time-dependent velocity field do not demonstrate such structures. Instead, they move in a wave-like fashion with rapidly changing and oscillating velocity field, determined mainly by magnetic tension in the magnetized intergranular downflows. Using time-distance diagrams, we identify horizontal motions in the magnetic flux tubes as torsional Alfvén perturbations propagating along the nearly vertical magnetic field lines with local Alfvén speed.

  9. Poynting flux dominated jets challenged by their photospheric emission

    SciTech Connect

    Bégué, Damien

    2015-12-17

    One of the key open question for gamma-ray bursts (GRBs) jets, is the magnetization of the outflow. Here we consider the photospheric emission of Poynting flux dominated outflows, when the dynamics is mediated by magnetic reconnection. We show that thermal three-particle processes, responsible for the thermalization of the plasma, become inefficient far below the photosphere. Conservation of the total photon number above this radius, combined with Compton scattering below the photosphere enforces kinetic equilibrium between electrons and photons. This, in turn, leads to an increase in the observed photon temperature, which reaches ≳ 8 MeV (observed energy) when decoupling the plasma at the photosphere. This result is weakly dependent on the free model parameters. The predicted peak energy is more than an order of magnitude higher than the observed peak energy of most GRBs, which puts strong constraints on the magnetization of these outflows.

  10. Photospheric Magnetic Diffusion by Measuring Moments of Active Regions

    NASA Astrophysics Data System (ADS)

    Engell, Alexander; Longcope, D.

    2013-07-01

    Photospheric magnetic surface diffusion is an important constraint for the solar dynamo. The HMI Active Region Patches (HARPs) program automatically identify all magnetic regions above a certain flux. In our study we measure the moments of ARs that are no longer actively emerging and can thereby give us good statistical constraints on photospheric diffusion. We also present the diffusion properties as a function of latitude, flux density, and single polarity (leading or following) within each HARP.

  11. EVIDENCE FOR THE PHOTOSPHERIC EXCITATION OF INCOMPRESSIBLE CHROMOSPHERIC WAVES

    SciTech Connect

    Morton, R. J.; Verth, G.; Fedun, V.; Erdelyi, R.; Shelyag, S.

    2013-05-01

    Observing the excitation mechanisms of incompressible transverse waves is vital for determining how energy propagates through the lower solar atmosphere. We aim to show the connection between convectively driven photospheric flows and incompressible chromospheric waves. The observations presented here show the propagation of incompressible motion through the quiet lower solar atmosphere, from the photosphere to the chromosphere. We determine photospheric flow vectors to search for signatures of vortex motion and compare results to photospheric flows present in convective simulations. Further, we search for the chromospheric response to vortex motions. Evidence is presented that suggests incompressible waves can be excited by the vortex motions of a strong magnetic flux concentration in the photosphere. A chromospheric counterpart to the photospheric vortex motion is also observed, presenting itself as a quasi-periodic torsional motion. Fine-scale, fibril structures that emanate from the chromospheric counterpart support transverse waves that are driven by the observed torsional motion. A new technique for obtaining details of transverse waves from time-distance diagrams is presented and the properties of transverse waves (e.g., amplitudes and periods) excited by the chromospheric torsional motion are measured.

  12. Decorrelation Times of Photospheric Fields and Flows

    NASA Technical Reports Server (NTRS)

    Welsch, B. T.; Kusano, K.; Yamamoto, T. T.; Muglach, K.

    2012-01-01

    We use autocorrelation to investigate evolution in flow fields inferred by applying Fourier Local Correlation Tracking (FLCT) to a sequence of high-resolution (0.3 "), high-cadence (approx = 2 min) line-of-sight magnetograms of NOAA active region (AR) 10930 recorded by the Narrowband Filter Imager (NFI) of the Solar Optical Telescope (SOT) aboard the Hinode satellite over 12 - 13 December 2006. To baseline the timescales of flow evolution, we also autocorrelated the magnetograms, at several spatial binnings, to characterize the lifetimes of active region magnetic structures versus spatial scale. Autocorrelation of flow maps can be used to optimize tracking parameters, to understand tracking algorithms f susceptibility to noise, and to estimate flow lifetimes. Tracking parameters varied include: time interval Delta t between magnetogram pairs tracked, spatial binning applied to the magnetograms, and windowing parameter sigma used in FLCT. Flow structures vary over a range of spatial and temporal scales (including unresolved scales), so tracked flows represent a local average of the flow over a particular range of space and time. We define flow lifetime to be the flow decorrelation time, tau . For Delta t > tau, tracking results represent the average velocity over one or more flow lifetimes. We analyze lifetimes of flow components, divergences, and curls as functions of magnetic field strength and spatial scale. We find a significant trend of increasing lifetimes of flow components, divergences, and curls with field strength, consistent with Lorentz forces partially governing flows in the active photosphere, as well as strong trends of increasing flow lifetime and decreasing magnitudes with increases in both spatial scale and Delta t.

  13. DECORRELATION TIMES OF PHOTOSPHERIC FIELDS AND FLOWS

    SciTech Connect

    Welsch, B. T.; Kusano, K.; Yamamoto, T. T.; Muglach, K.

    2012-03-10

    We use autocorrelation to investigate evolution in flow fields inferred by applying Fourier local correlation tracking (FLCT) to a sequence of high-resolution (0.''3), high-cadence ({approx_equal} 2 minute) line-of-sight magnetograms of NOAA active region (AR) 10930 recorded by the narrowband filter imager of the Solar Optical Telescope aboard the Hinode satellite over 2006 December 12 and 13. To baseline the timescales of flow evolution, we also autocorrelated the magnetograms, at several spatial binnings, to characterize the lifetimes of active region magnetic structures versus spatial scale. Autocorrelation of flow maps can be used to optimize tracking parameters, to understand tracking algorithms' susceptibility to noise, and to estimate flow lifetimes. Tracking parameters varied include: time interval {Delta}t between magnetogram pairs tracked, spatial binning applied to the magnetograms, and windowing parameter {sigma} used in FLCT. Flow structures vary over a range of spatial and temporal scales (including unresolved scales), so tracked flows represent a local average of the flow over a particular range of space and time. We define flow lifetime to be the flow decorrelation time, {tau}. For {Delta}t > {tau}, tracking results represent the average velocity over one or more flow lifetimes. We analyze lifetimes of flow components, divergences, and curls as functions of magnetic field strength and spatial scale. We find a significant trend of increasing lifetimes of flow components, divergences, and curls with field strength, consistent with Lorentz forces partially governing flows in the active photosphere, as well as strong trends of increasing flow lifetime and decreasing magnitudes with increases in both spatial scale and {Delta}t.

  14. CONVECTION THEORY AND SUB-PHOTOSPHERIC STRATIFICATION

    SciTech Connect

    Arnett, David; Meakin, Casey; Young, Patrick A. E-mail: casey.meakin@gmail.co

    2010-02-20

    As a preliminary step toward a complete theoretical integration of three-dimensional compressible hydrodynamic simulations into stellar evolution, convection at the surface and sub-surface layers of the Sun is re-examined, from a restricted point of view, in the language of mixing-length theory (MLT). Requiring that MLT use a hydrodynamically realistic dissipation length gives a new constraint on solar models. While the stellar structure which results is similar to that obtained by Yale Rotational Evolution Code (Guenther et al.; Bahcall and Pinsonneault) and Garching models (Schlattl et al.), the theoretical picture differs. A new quantitative connection is made between macro-turbulence, micro-turbulence, and the convective velocity scale at the photosphere, which has finite values. The 'geometric parameter' in MLT is found to correspond more reasonably with the thickness of the superadiabatic region (SAR), as it must for consistency in MLT, and its integrated effect may correspond to that of the strong downward plumes which drive convection (Stein and Nordlund), and thus has a physical interpretation even in MLT. If we crudely require the thickness of the SAR to be consistent with the 'geometric factor' used in MLT, there is no longer a free parameter, at least in principle. Use of three-dimensional simulations of both adiabatic convection and stellar atmospheres will allow the determination of the dissipation length and the geometric parameter (i.e., the entropy jump) more realistically, and with no astronomical calibration. A physically realistic treatment of convection in stellar evolution will require substantial additional modifications beyond MLT, including nonlocal effects of kinetic energy flux, entrainment (the most dramatic difference from MLT found by Meakin and Arnett), rotation, and magnetic fields.

  15. New Observations of Subarcsecond Photospheric Bright Points

    NASA Technical Reports Server (NTRS)

    Berger, T. E.; Schrijver, C. J.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Scharmer, G.

    1995-01-01

    We have used an interference filter centered at 4305 A within the bandhead of the CH radical (the 'G band') and real-time image selection at the Swedish Vacuum Solar Telescope on La Palma to produce very high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 15-20 Sept. 1993 we observed active region NOAA 7581 from its appearance on the East limb to a near-disk-center position on 20 Sept. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measured FWHM distribution of the bright points in the image is lognormal with a modal value of 220 km (0.30 sec) and an average value of 250 km (0.35 sec). The smallest measured bright point diameter is 120 km (0.17 sec) and the largest is 600 km (O.69 sec). Approximately 60% of the measured bright points are circular (eccentricity approx. 1.0), the average eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged 'quiet-Sun' area in the image, the modal contrast is 29% and the maximum value is 75%; when referenced to an average intergranular lane brightness in the image, the distribution has a modal value of 61% and a maximum of 119%. The bin-averaged contrast of G-band bright points is constant across the entire measured size range. The measured area of the bright points, corrected for pixelation and selection effects, covers about 1.8% of the total image area. Large pores and micropores occupy an additional 2% of the image area, implying a total area fraction of magnetic proxy features in the image of 3.8%. We discuss the implications of this area fraction measurement in the context of

  16. New Observations of Subarcsecond Photospheric Bright Points

    NASA Technical Reports Server (NTRS)

    Berger, T. E.; Schrijver, C. J.; Shine, R. A.; Tarbell, T. D.; Title, A. M.; Scharmer, G.

    1995-01-01

    We have used an interference filter centered at 4305 A within the bandhead of the CH radical (the 'G band') and real-time image selection at the Swedish Vacuum Solar Telescope on La Palma to produce very high contrast images of subarcsecond photospheric bright points at all locations on the solar disk. During the 6 day period of 1993 September 15-20 we observed active region NOAA 7581 from its appearance on the East limb to a near-disk-center position on September 20. A total of 1804 bright points were selected for analysis from the disk center image using feature extraction image processing techniques. The measured Full Width at Half Maximum (FWHM) distribution of the bright points in the image is lognormal with a modal value of 220 km (0 sec .30) and an average value of 250 km (0 sec .35). The smallest measured bright point diameter is 120 km (0 sec .17) and the largest is 600 km (O sec .69). Approximately 60% of the measured bright points are circular (eccentricity approx. 1.0), the average eccentricity is 1.5, and the maximum eccentricity corresponding to filigree in the image is 6.5. The peak contrast of the measured bright points is normally distributed. The contrast distribution variance is much greater than the measurement accuracy, indicating a large spread in intrinsic bright-point contrast. When referenced to an averaged 'quiet-Sun' area in the image, the modal contrast is 29% and the maximum value is 75%; when referenced to an average intergranular lane brightness in the image, the distribution has a modal value of 61% and a maximum of 119%. The bin-averaged contrast of G-band bright points is constant across the entire measured size range. The measured area of the bright points, corrected for pixelation and selection effects, covers about 1.8% of the total image area. Large pores and micropores occupy an additional 2% of the image area, implying a total area fraction of magnetic proxy features in the image of 3.8%. We discuss the implications of this

  17. Photosphere-Chromosphere Connection as Derived from Nst Observations

    NASA Astrophysics Data System (ADS)

    Yurchyshyn, V.; Abramenko, V.; Goode, P. R.

    2010-12-01

    Largest ground-based new solar telescope (NST) of Big Bear Solar Observatory allows us to simultaneously observe photospheric granulation with luxurious filigree of bright points (BPs) and low/middle chromosphere in H- alpha spectral line. Excellent climate conditions of Big Bear Valley, augmented with an adaptive optics system and speckle-reconstruction applications produce diffraction limited images. Recent observations (July- August 2010) showed that BPs visible in the photosphere with the TiO filter (centered at a wavelength of 705.7 nm) are co-spatial with the BPs visible in the blue wind of H-alpha line. As evidenced from these data, the H-alpha BPs, in turn, are frequently at origin of small-scale chromospheric jets. These jets are visible at all scales down to the smallest resolved features. As long as photospheric BPs are co-spatial with the magnetic elements, one might conclude that photospheric magnetic fields are relevant to the chromospheric jet formation. NST Ha-0.13nm image acquired on June 28, 2010. The dark features are upward directed flows that have velocities up to 60km/sec seen against the background of photospheric granulation with inclusions of BPs. The corresponding movie shows reveals significant dynamics associated with these rosette like structures stemming from clusters of BPs.

  18. Data Assimilation in the ADAPT Photospheric Flux Transport Model

    DOE PAGESBeta

    Hickmann, Kyle S.; Godinez, Humberto C.; Henney, Carl J.; Arge, C. Nick

    2015-03-17

    Global maps of the solar photospheric magnetic flux are fundamental drivers for simulations of the corona and solar wind and therefore are important predictors of geoeffective events. However, observations of the solar photosphere are only made intermittently over approximately half of the solar surface. The Air Force Data Assimilative Photospheric Flux Transport (ADAPT) model uses localized ensemble Kalman filtering techniques to adjust a set of photospheric simulations to agree with the available observations. At the same time, this information is propagated to areas of the simulation that have not been observed. ADAPT implements a local ensemble transform Kalman filter (LETKF)more » to accomplish data assimilation, allowing the covariance structure of the flux-transport model to influence assimilation of photosphere observations while eliminating spurious correlations between ensemble members arising from a limited ensemble size. We give a detailed account of the implementation of the LETKF into ADAPT. Advantages of the LETKF scheme over previously implemented assimilation methods are highlighted.« less

  19. Computation of solar magnetic fields from photospheric observations

    NASA Technical Reports Server (NTRS)

    Hannakam, L.; Gary, G. A.; Teuber, D. L.

    1984-01-01

    The observational difficulties of obtaining the magnetic field distribution in the chromosphere and corona of the sun has led to methods of extending photospheric magnetic mesurements into the solar atmosphere by mathematical procedures. A new approach to this problem presented here is that a constant alpha force-free field can be uniquely determined from the tangential components of the measured photospheric flux alone. The vector magnetographs now provide measurements of both the solar photospheric tangential and the longitudinal magnetic field. This paper presents derivations for the computation of the solar magnetic field from these type of measurements. The fields considered are assumed to be a constant alpha force-free fields or equivalent, producing vanishing Lorentz forces. Consequently, magnetic field lines and currents are related by a constant and hence show an identical distribution. The magnetic field above simple solar regions are described from the solution of the field equations.

  20. Computation of solar magnetic fields from photospheric observations

    NASA Astrophysics Data System (ADS)

    Hannakam, L.; Gary, G. A.; Teuber, D. L.

    1984-09-01

    The observational difficulties of obtaining the magnetic field distribution in the chromosphere and corona of the sun has led to methods of extending photospheric magnetic mesurements into the solar atmosphere by mathematical procedures. A new approach to this problem presented here is that a constant alpha force-free field can be uniquely determined from the tangential components of the measured photospheric flux alone. The vector magnetographs now provide measurements of both the solar photospheric tangential and the longitudinal magnetic field. This paper presents derivations for the computation of the solar magnetic field from these type of measurements. The fields considered are assumed to be a constant alpha force-free fields or equivalent, producing vanishing Lorentz forces. Consequently, magnetic field lines and currents are related by a constant and hence show an identical distribution. The magnetic field above simple solar regions are described from the solution of the field equations.

  1. Energetic electrons and photospheric electric currents during solar flares

    NASA Astrophysics Data System (ADS)

    Musset, Sophie; Vilmer, Nicole; Bommier, Veronique

    2016-07-01

    It is currently admitted that solar flares are powered by magnetic energy previously stored in the coronal magnetic field. During magnetic reconnection processes, this energy is transferred to particle acceleration, plasma motion and plasma heating. Magnetic energy release is likely to occur on coronal currents sheets along regions of strong gradient of magnetic connectivity. These coronal current sheets can be traced by their footprints at the surface on the Sun, i.e. by photospheric current ribbons. We aim to study the relation between these current ribbons observed at the photospheric level, tracing the coronal current sheets, and the flare energetic electrons traced by their X-ray emissions. The photospheric magnetic field and vertical current density have been calculated from SDO/HMI spectropolarimetric data with the UNNOFIT inversion and Metcalf disambiguation codes, while the X-ray images and spectra have been reconstructed from RHESSI data. In a first case, the GOES X2.2 flare of February 15, 2011, a spatial correlation is observed between the photospheric current ribbons and the coronal X-ray emissions from energetic electrons. Moreover, a conjoint evolution of both the photospheric currents and the X-ray emission is observed during the course of the flare. Both results are interpreted as consequences of the magnetic reconnection in coronal current sheets, and propagation of the reconnection sites to new structures during the flare, leading to new X-ray emission and local increase of the photospheric currents (Musset et al., 2015). We shall discuss here similar results obtained for other X-class flares.

  2. Solar coronal and photospheric abundances from solar energetic particle measurements

    NASA Technical Reports Server (NTRS)

    Breneman, H. H.; Stone, E. C.

    1985-01-01

    Solar energetic particle (SEP) elemental abundance data from the cosmic ray subsystem (CRS) aboard the Voyager 1 and 2 spacecraft are used to derive unfractionated coronal and photospheric abundances for elements with Z = 6-30. It is found that the ionic charge-to-mass ratio (Q/M) is the principal organizing parameter for the fractionation of SEPs by acceleration and propagation processes and for flare-to-flare variability, making possible a single-parameter Q/M-dependent correction to the average SEP abundances to obtain unfractionated coronal abundances. A further correction based on first ionization potential allows the determination of unfractionated photospheric abundances.

  3. Solar Coronal and photospheric abundances from solar energetic particle measurements

    NASA Technical Reports Server (NTRS)

    Breneman, H.; Stone, E. C.

    1985-01-01

    Solar energetic particle (SEP) elemental abundance data from the cosmic ray subsystem (CRS) aboard the Voyager 1 and 2 spacecraft are used to derive unfractionated coronal and photospheric abundances for elements with 3 Z or = 30. It is found that the ionic charge-to-mass ratio (Q/M) is the principal organizing parameter for the fractionation of SEPs by acceleration and propagation processes and for flare-to-flare variability, making possible a single-parameter Q/M-dependent correction to the average SEP abundances to obtain unfractionated coronal abundances. A further correction based on first ionization potential allows the determination of unfractionated photospheric abundances.

  4. Solar coronal and photospheric abundances from solar energetic particle measurements

    NASA Technical Reports Server (NTRS)

    Breneman, H.; Stone, E. C.

    1985-01-01

    Solar energetic particle (SEP) elemental abundance data from the Cosmic Ray Subsystem (CRS) aboard the Voyager 1 and 2 spacecraft are used to derive unfractionated coronal and photospheric abundances for elements with 3 = or Z or = 30. The ionic charge-to-mass ratio (Q/M) is the principal organizing parameter for the fractionation of SEPs by acceleration and propagation processes and for flare-to-flare variability, making possible a single-parameter Q/M-dependent correction to the average SEP abundances to obtain unfractionated coronal abundances. A further correction based on first ionization potential allows the determination of unfractionated photospheric abundances.

  5. Imaging Radio Photospheres with the Jansky Very Large Array

    NASA Astrophysics Data System (ADS)

    Matthews, L. D.; Reid, M. J.; Menten, K. M.

    2015-08-01

    Using the Jansky Very Large Array (JVLA), we have imaged the radio photosphere of the long-period variable star W Hya at 45 GHz (˜ 7 mm) with a resolution of ˜ 40 mas. Our data reveal a non-spherical photospheric shape, consistent with earlier measurements. We also find evidence for an elongation along PA ≍ -5°, the orientation of which is consistent with the previously measured projected magnetic field direction and an extension in the 18 μm dust emission, both at larger scales.

  6. Solar Photosphere: The Limb Effect and Gravitational Redshift

    NASA Astrophysics Data System (ADS)

    Wöhl, H.; Murdin, P.

    2000-11-01

    The `limb effect' is the observational finding that many spectral absorption lines formed in the photosphere (FRAUNHOFER LINES) show a REDSHIFT of their mean wavelength when comparing limb observations with observations from the solar disk center. The magnitude of this effect is different for each spectral line and equals some 100 m s-1 when explained as a DOPPLER EFFECT....

  7. Reconnection in photospheric-chromospheric current sheet and coronal heating

    SciTech Connect

    Kumar, P.; Kumar, N.; Uddin, W.

    2011-02-15

    It has been observed by various ground and space based solar missions that magnetic reconnection occurs frequently in the photosphere-chromosphere region as well as in the solar corona. The purpose of this article is to examine the process of reconnection in thin current sheet formed between two oppositely directed magnetic flux tubes in photospheric-chromospheric region. Using the data of different atmospheric models for the solar photosphere and chromosphere, we have estimated the rate of magnetic reconnection in terms of Alfvenic Mach number, growth rate of tearing mode, island length scales, and energy dissipation rate necessary to heat the chromospheric plasma. It is found that magnetic Reynolds number for the current sheet in the chromosphere varies from 1.14 Multiplication-Sign 10{sup 3} to 7.14 Multiplication-Sign 10{sup 6} which indicates that the field lines in the photosphere and chromosphere reconnect with speed, that is, 0.00034 to 0.0297 times the Alfven speed. Frequency of the MHD waves generated in the chromosphere reconnection region is of the order of 100 Hz, so these high-frequency waves may be the sources of coronal heating and solar wind acceleration.

  8. Proper horizontal photospheric flows in a filament channel

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Roudier, T.; Mein, N.; Mein, P.; Malherbe, J. M.; Chandra, R.

    2014-04-01

    Context. An extended filament in the central part of the active region NOAA 11106 crossed the central meridian on Sept. 17, 2010 in the southern hemisphere. It has been observed in Hα with the THEMIS telescope in the Canary Islands and in 304 Å with the EUV imager (AIA) onboard the Solar Dynamic Observatory (SDO). Counterstreaming along the Hα threads and bright moving blobs (jets) along the 304 Å filament channel were observed during 10 h before the filament erupted at 17:03 UT. Aims: The aim of the paper is to understand the coupling between magnetic field and convection in filament channels and relate the horizontal photospheric motions to the activity of the filament. Methods: An analysis of the proper photospheric motions using SDO/HMI continuum images with the new version of the coherent structure tracking (CST) algorithm developed to track granules, as well as the large scale photospheric flows, was performed for three hours. Using corks, we derived the passive scalar points and produced a map of the cork distribution in the filament channel. Averaging the velocity vectors in the southern hemisphere in each latitude in steps of 3.5 arcsec, we defined a profile of the differential rotation. Results: Supergranules are clearly identified in the filament channel. Diverging flows inside the supergranules are similar in and out of the filament channel. Converging flows corresponding to the accumulation of corks are identified well around the Hα filament feet and at the edges of the EUV filament channel. At these convergence points, the horizontal photospheric velocity may reach 1 km s-1, but with a mean velocity of 0.35 km s-1. In some locations, horizontal flows crossing the channel are detected, indicating eventually large scale vorticity. Conclusions: The coupling between convection and magnetic field in the photosphere is relatively strong. The filament experienced the convection motions through its anchorage points with the photosphere, which are

  9. Turbulent convective flows in the solar photospheric plasma

    NASA Astrophysics Data System (ADS)

    Caroli, A.; Giannattasio, F.; Fanfoni, M.; Del Moro, D.; Consolini, G.; Berrilli, F.

    2015-10-01

    > The origin of the 22-year solar magnetic cycle lies below the photosphere where multiscale plasma motions, due to turbulent convection, produce magnetic fields. The most powerful intensity and velocity signals are associated with convection cells, called granules, with a scale of typically 1 Mm and a lifetime of a few minutes. Small-scale magnetic elements (SMEs), ubiquitous on the solar photosphere, are passively transported by associated plasma flows. This advection makes their traces very suitable for defining the convective regime of the photosphere. Therefore the solar photosphere offers an exceptional opportunity to investigate convective motions, associated with compressible, stratified, magnetic, rotating and large Rayleigh number stellar plasmas. The magnetograms used here come from a Hinode/SOT uninterrupted 25-hour sequence of spectropolarimetric images. The mean-square displacement of SMEs has been modelled with a power law with spectral index . We found for times up to and for times up to . An alternative way to investigate the advective-diffusive motion of SMEs is to look at the evolution of the two-dimensional probability distribution function (PDF) for the displacements. Although at very short time scales the PDFs are affected by pixel resolution, for times shorter than the PDFs seem to broaden symmetrically with time. In contrast, at longer times a multi-peaked feature of the PDFs emerges, which suggests the non-trivial nature of the diffusion-advection process of magnetic elements. A Voronoi distribution analysis shows that the observed small-scale distribution of SMEs involves the complex details of highly nonlinear small-scale interactions of turbulent convective flows detected in solar photospheric plasma.

  10. Rotating plasma jets in the photospheric intergranular lanes

    NASA Astrophysics Data System (ADS)

    Lemmerer, Birgit; Hanslmeier, Arnold; Muthsam, Herbert; Piantschitsch, Isabell; Zaqarashvili, Teimuraz

    2016-07-01

    High resolution simulations and observations of the solar photosphere reveal the population of small granular cells with diameters less than 600 km. However, the underlying mechanisms of their generation are still unclear. Simulations show that the majority of small granules may not result from fragmentation of larger granular cells but instead evolve and dissolve in the intergranular lanes. We study the dynamics of these granular cells in high resolution simulations. We found that the small granules show a jet-like behavior with strong horizontal and vertical vortex motions. A newly developed algorithm that tracks the evolution of the 3D plasma cells in the convection zone and lower photosphere shows strong vertical vorticity within the small granular cells. The rotating plasma jets, which are visible as small granules, may generate magnetized vortex flows and torsional Alfvén waves observed at upper layers and hence can play a distinct role in the energy supply to the chromosphere and corona.

  11. Gamma radiation and photospheric white-light flare continuum

    NASA Technical Reports Server (NTRS)

    Hudson, H. S.; Dwivedi, B. N.

    1982-01-01

    It is noted that recent gamma-ray observations of solar flares have provided a better means for estimating the heating of the solar atmosphere by energetic protons. This type of heating has been suggested as the explanation of the continuum emission of the white-light flare. The effects on the photosphere of high-energy particles capable of producing the intense gamma-ray emission observed in the flare of July 11, 1978, are analyzed. A simple energy-balance argument is used, and hydrogen ionization is taken into account. It is found that energy deposition increases with height for the inferred proton spectra and is not strongly dependent upon the assumed angle of incidence. At the top of the photosphere, the computed energy inputs fall in the range 10-100 ergs/cu cm-s.

  12. Detection of coherent structures in photospheric turbulent flows

    SciTech Connect

    Chian, Abraham C.-L.; Rempel, Erico L.; Aulanier, Guillaume; Schmieder, Brigitte; Shadden, Shawn C.; Welsch, Brian T.; Yeates, Anthony R. E-mail: rempel@ita.br

    2014-05-01

    We study coherent structures in solar photospheric flows in a plage in the vicinity of the active region AR 10930 using the horizontal velocity data derived from Hinode/Solar Optical Telescope magnetograms. Eulerian and Lagrangian coherent structures (LCSs) are detected by computing the Q-criterion and the finite-time Lyapunov exponents of the velocity field, respectively. Our analysis indicates that, on average, the deformation Eulerian coherent structures dominate over the vortical Eulerian coherent structures in the plage region. We demonstrate the correspondence of the network of high magnetic flux concentration to the attracting Lagrangian coherent structures (aLCSs) in the photospheric velocity based on both observations and numerical simulations. In addition, the computation of aLCS provides a measure of the local rate of contraction/expansion of the flow.

  13. The white light corona and photospheric magnetic fields

    NASA Technical Reports Server (NTRS)

    Mccabe, Marie K.

    1986-01-01

    Some results are presented from a continuing investigation of the coronal structure vs. the photospheric magnetic field relationship. Two approaches to the problem are considered. First, the individual coronal features recorded at each limb were located on a chart of the magnetic field measured with low spatial resolution, depicting the large scale or global field configuration. Second, the characteristics of neutral line segments, defined by the presence of H alpha line filament, with no associated coronal structure were investigated. Preliminary results are discussed.

  14. Study of Magnetic Structure in the Solar Photosphere and Chromosphere

    NASA Technical Reports Server (NTRS)

    Noyes, Robert W.; Avrett, Eugene; Nisenson, Peter; Uitenbroek, Han; vanBallegooijen, Adriaan

    1998-01-01

    This grant funded an observational and theoretical program to study the structure and dynamics of the solar photosphere and low chromosphere, and the spectral signatures that result. The overall goal is to learn about mechanisms that cause heating of the overlying atmosphere, and produce variability of solar emission in spectral regions important for astrophysics and space physics. The program exploited two new ground-based observational capabilities: one using the Swedish Solar Telescope on La Palma for very high angular resolution observations of the photospheric intensity field (granulation) and proxies of the magnetic field (G-band images); and the other using the Near Infrared Magnetograph at the McMath-Pierce Solar Facility to map the spatial variation and dynamic behavior of the solar temperature minimum region using infrared CO lines. We have interpreted these data using a variety of theoretical and modelling approaches, some developed especially for this project. Previous annual reports cover the work done up to 31 May 1997. This final report summarizes our work for the entire period, including the period of no-cost extension from 1 June 1997 through September 30 1997. In Section 2 we discuss observations and modelling of the photospheric flowfields and their consequences for heating of the overlying atmosphere, and in Section 3 we discuss imaging spectroscopy of the CO lines at 4.67 mu.

  15. Pixel Analysis and Plasma Dynamics Characterized by Photospheric Spectral Data

    NASA Astrophysics Data System (ADS)

    Rasca, Anthony P.; Chen, James; Pevtsov, Alexei A.

    2016-05-01

    Recent observations of the photosphere using high spatial and temporal resolutions show small dynamic features at the resolving limit during emerging flux events. However, line-of-sight (LOS) magnetogram pixels only contain the net uncanceled magnetic flux, which is expected to increase for fixed regions as resolution limits improve. A new pixel dynamics method uses spectrographic images to characterize photospheric absorption line profiles by variations in line displacement, width, asymmetry, and peakedness and is applied to quiet-sun regions, active regions with no eruption, and an active region with an ongoing eruption. Using Stokes I images from SOLIS/VSM on 2012 March 13, variations in line width and peakedness of Fe I 6301.5 Å are shown to have a strong spatial and temporal relationship with an M7.9 X-ray flare originating from NOAA 11429. This relationship is observed as a flattening in the line profile as the X-ray flare approaches peak intensity and was not present in area scans of a non-eruptive active region on 2011 April 14. These results are used to estimate dynamic plasma properties on sub-pixel scales and provide both spatial and temporal information of sub-pixel activity at the photosphere. The analysis can be extended to include the full Stokes parameters and study signatures of magnetic fields and coupled plasma properties.

  16. The photospheric filling factor of the active binary II Pegasi

    NASA Astrophysics Data System (ADS)

    Marino, G.; Rodonó, M.; Leto, G.; Cutispoto, G.

    1999-12-01

    UBV and JHK photometry of the active single-lined binary II Peg, we performed in 1995, is presented. A method to determine the fraction of the photosphere covered by spots (filling factor) and to check the accuracy of generally assumed values of photospheric parameters has been developed. The procedure is based on the comparison between multiband fluxes and low resolution synthetic spectra weighted on the base of the spot filling factor and scaled with the ratio between the star radius and distance (R/d), so that we can also estimate the R/d ratio. A chi 2 fit has been performed for II Peg observations close to the light maximum and minimum by assuming reliable values of the photospheric parameters. Although a unique solution cannot be reached, we found clear indication for a spot filling factor at light maximum >= 40%. We find that the same set of parameters that gives us the best fit solutions at light maximum also provides the best fit at light minimum. The resulting solutions are consistent with the observed amplitude of the photometric wave, and with the commonly accepted value of R, unspotted V magnitude and spectral classification for II Pegasi.

  17. The Conundrum of the Solar Pre-Flare Photospheric State.

    NASA Astrophysics Data System (ADS)

    Leka, KD; Barnes, Graham; Wagner, Eric

    2015-08-01

    Knowledge of the state of the solar photospheric magnetic field at a single instant in time does not appear sufficient to predict the size and timing of impending solar flares. Such knowledge may provide necessary conditions, such as the free magnetic energy needed for a flare to occur. Given the necessary conditions, it is often assumed that the evolution of the field, possibly by only a small amount, may trigger the onset of a flare. We present the results of a study using time series of photospheric vector field data from the Helioseismic and Magnetic Imager (HMI) on NASA's Solar Dynamics Observatory (SDO) to quantitatively parameterize both the state and evolution of solar active regions - their complexity, magnetic topology and energy - as related to solar flare events. We examine both extensive and intensive parameters and their temporal behavior, in the context of both large and small flaring episodes. Statistical tests based on nonparametric Discriminant Analysis are used to compare pre-flare epochs to a control group of flare-quiet epochs and active regions. Results regarding the type of photospheric signature examined and the efficacy of using the present state vs. temporal evolution to predict solar flares is quantified by standard skill scores.This work is made possible by contracts NASA NNH12CG10C and NOAA/SBIR WC-133R-13-CN-0079.

  18. Correlating chromospheric and photospheric activity of FK Com

    NASA Astrophysics Data System (ADS)

    Vida, Krisztián; Korhonen, Heidi; Ilyin, Ilya; Oláh, Katalin; Andersen, Michael; Hackman, Thomas

    2015-08-01

    Using photometric observations between 1987-­­2010 and Halpha measurements from 1997-­­2010 we study the connection between the chromospheric and photospheric behaviour of the active late­-type star FK Comae. The Halpha region shows a double­-peaked emission, possibly indicating a circumstellar disc. Prominence-­like structures are often detected which extend to more than a stellar radius, and are stable for weeks. The prominences are often, but not always, connected with dark photospheric spots. From lower resolution Halpha spectra we find that the changes in the chromosphere happen mainly on a time scale longer than a few hours, but shorter variations are also observed. The rotational modulation of the Halpha emission are typically anticorrelated with the light curves, but we did not find convincing evidence of a clear connection between the long­-term trends of the Halpha emission and the overall brightness variation of the star. In addition, the chromosphere of FK Com seems to be in an unusually quiet state in 2009—2010, although there are many spots in the photosphere since the overall brightness of the star is low.

  19. Tracing Helioseismic Waves from the Photosphere to the Corona

    NASA Astrophysics Data System (ADS)

    Zhao, Junwei; Felipe, Tobias; Chen, Ruizhu; Khomenko, Elena

    2016-05-01

    Can p-mode waves in sunspots propagate to the chromosphere and the corona? And what are their counterparts in different atmospheric heights? In order to study the connection between the photospheric p-mode waves and the waves observed above the photosphere, we use a helioseismic analysis technique, namely time-distance helioseismology, and analyze multi-height observations from different instruments. We find clear evidences that some p-mode waves in the photosphere, running penumbral waves in the chromosphere, and the periodic disturbances in the coronal fan structures are actually same magnetoacoustic waves that exhibit differently at the different atmospheric heights. The 6-mHz waves, with inclined wavefronts, propagate slantingly upward along magnetic field lines. The 3-mHz waves, forming backward-'C'-shape wavefronts, propagate mostly horizontally. Through numerical simulations, we demonstrate that these p-mode waves that can travel upward to the corona, possibly originate from sources located a few megameters beneath sunspots' surface.

  20. Quantitative spectroscopy of photospheric-phase type II supernovae

    NASA Astrophysics Data System (ADS)

    Dessart, L.; Hillier, D. J.

    2005-07-01

    We present first results on the quantitative spectroscopic analysis of the photospheric-phase of type II supernovae (SN). The analyses are based on the model atmosphere code, CMFGEN, of Hillier & Miller (1998) which solves the radiative transfer and statistical equilibrium equations in expanding outflows under the constraint of radiative equilibrium. A key asset of CMFGEN is its thorough treatment of line-blanketing due to metal species. From its applicability to hot star environments, the main modifications to the source code were to allow a linear velocity law, a power-law density distribution, an adaptive grid to handle the steep H recombination/ionization front occurring in some SN models, and a routine to compute the gray temperature structure in the presence of large velocities. In this first paper we demonstrate the ability of CMFGEN to reproduce, with a high level of accuracy, the UV and optical observations of a sample of well observed type II SN, i.e. SN1987A and SN1999em, at representative stages of their photospheric evolution. Two principal stages of SN are modeled that where hydrogen is fully ionized, and that in which H is only partially ionized. For models with an effective temperature below ~8000 K, hydrogen recombines and gives rise to a steep ionization front. The effect of varying the location of the outer grid radius on the spectral energy distribution (SED) is investigated. We find that going to 5-6 times the optically-thick base radius is optimal, since above that, the model becomes prohibitively large, while below this, significant differences appear because of the reduced line-blanketing (which persists even far above the photosphere) and the truncation of line-formation regions. To constrain the metallicity and the reddening of SN, the UV spectral region of early-time spectra is essential. We find that the density of the photosphere and effect of line blanketing decline as the spatial scale of the SN increases. The density distribution is

  1. The Effects of Transients on Photospheric and Chromospheric Power Distributions

    NASA Astrophysics Data System (ADS)

    Samanta, T.; Henriques, V. M. J.; Banerjee, D.; Krishna Prasad, S.; Mathioudakis, M.; Jess, D.; Pant, V.

    2016-09-01

    We have observed a quiet-Sun region with the Swedish 1 m Solar Telescope equipped with the CRISP Imaging SpectroPolarimeter. High-resolution, high-cadence, Hα line scanning images were taken to observe different layers of the solar atmosphere from the photosphere to upper chromosphere. We study the distribution of power in different period bands at different heights. Power maps of the upper photosphere and the lower chromosphere show suppressed power surrounding the magnetic-network elements, known as “magnetic shadows.” These also show enhanced power close to the photosphere, traditionally referred to as “power halos.” The interaction between acoustic waves and inclined magnetic fields is generally believed to be responsible for these two effects. In this study we explore whether small-scale transients can influence the distribution of power at different heights. We show that the presence of transients, like mottles, Rapid Blueshifted Excursions (RBEs), and Rapid Redshifted Excursions (RREs), can strongly influence the power maps. The short and finite lifetime of these events strongly affects all power maps, potentially influencing the observed power distribution. We show that Doppler-shifted transients like RBEs and RREs that occur ubiquitously can have a dominant effect on the formation of the power halos in the quiet Sun. For magnetic shadows, transients like mottles do not seem to have a significant effect on the power suppression around 3 minutes, and wave interaction may play a key role here. Our high-cadence observations reveal that flows, waves, and shocks manifest in the presence of magnetic fields to form a nonlinear magnetohydrodynamic system.

  2. North south asymmetry in the coronal and photospheric magnetic fields

    NASA Astrophysics Data System (ADS)

    Virtanen, I.; Mursula, K.

    2013-12-01

    Several recent studies have shown that the Heliospheric current sheet (HCS) is southward shifted during about three years in the solar declining phase (the so-called bashful ballerina phenomenon). We study the hemispherical asymmetry in the photospheric and coronal magnetic fields using Wilcox Solar Observatory (WSO) measurements of the photospheric magnetic field since 1976 and the potential field source surface (PFSS) model. Multipole analysis of the photospheric magnetic field shows that during the late declining phase of solar cycles since 1970s, bashful ballerina phenomenon is a consequence of g02 quadrupole term, signed oppositely to the dipole moment. Surges of new flux transport magnetic field from low latitudes to the poles, thus leading to a systematically varying contribution to the g02-term from different latitudes. In the case of a north-south asymmetric flux production this is seen as a quadrupole contribution traveling towards higher latitudes. When the quadrupole term is largest the main contribution comes from the polar latitudes. At least during the four recent solar cycles the g02-term arises because the magnitude of the southern polar field is larger than in the north in the declining phase of the cycle. Magnetic flux is transported polewards by the meridional flow and it is most likely that besides the north-south asymmetric production of the magnetic flux, also the asymmetric transportation may significantly contribute to the observed asymmetry of polar field intensities. The overall activity during solar cycle is not significantly different in the northern and southern hemispheres, but hemispheres tend to develop in a different phase.

  3. Periodic photospheric and chromospheric modulation in Alpha Orionis (Betelgeuse)

    NASA Technical Reports Server (NTRS)

    Dupree, A. K.; Baliunas, S. L.; Hartmann, L.; Nassiopoulos, G. E.; Guinan, E. F.; Sonneborn, G.

    1987-01-01

    The bright cool supergiant Alpha Orionis has been monitored spectroscopically and photometrically over the past three years (1984-1986) in the optical and the ultraviolet wavelength regions. A 420-day periodic modulation of the flux is observed in the optical and ultaviolet continua, and in the Mg II line emission cores. Periodic photospheric pulsations are the most likely explanation of these observations. This identification is based on the large amplitude of the variation, the correlation of the continuum and chromospheric fluxes, and the length of the observed period. Pulsation may heat and extend the atmosphere of Alpha Ori and initiate the mass flow from the star.

  4. Chromospheric Polarization in the Photospheric Solar Oxygen Infrared Triplet

    NASA Astrophysics Data System (ADS)

    Del Pino Alemán, Tanausú; Trujillo Bueno, Javier

    2015-07-01

    We present multilevel radiative transfer modeling of the scattering polarization observed in the solar O i infrared triplet around 777 nm. We demonstrate that the scattering polarization pattern observed on the solar disk forms in the chromosphere, far above the photospheric region where the bulk of the emergent intensity profiles originate. We investigate the sensitivity of the polarization pattern to the thermal structure of the solar atmosphere and to the presence of weak magnetic fields (10-2-100 G) through the Hanle effect, showing that the scattering polarization signals of the oxygen infrared triplet encode information on the magnetism of the solar chromosphere.

  5. Spectral and polarization properties of photospheric emission from stratified jets

    SciTech Connect

    Ito, Hirotaka; Nagataki, Shigehiro; Matsumoto, Jin; Lee, Shiu-Hang; Tolstov, Alexey; Mao, Jirong; Dainotti, Maria; Mizuta, Akira

    2014-07-10

    We explore the spectral and polarization properties of photospheric emissions from stratified jets in which multiple components, separated by sharp velocity shear regions, are distributed in lateral directions. Propagation of thermal photons injected at a high optical depth region are calculated until they escape from the photosphere. It is found that the presence of the lateral structure within the jet leads to the nonthermal feature of the spectra and significant polarization signal in the resulting emission. The deviation from thermal spectra, as well as the polarization degree, tends to be enhanced as the velocity gradient in the shear region increases. In particular, we show that emissions from multicomponent jet can reproduce the typical observed spectra of gamma-ray bursts irrespective of the position of the observer when a velocity shear region is closely spaced in various lateral (θ) positions. The degree of polarization associated with the emission is significant (>few percent) at a wide range of observer angles and can be higher than 30%.

  6. Rossby rogons in atmosphere and in the solar photosphere

    NASA Astrophysics Data System (ADS)

    Misra, A. P.; Shukla, P. K.

    2012-12-01

    The generation of Rossby rogue waves (Rossby rogons), as well as the excitation of bright and dark Rossby envelpe solitons are demonstrated on the basis of the modulational instability (MI) of a coherent Rossby wave packet. The evolution of an amplitude-modulated Rossby wave packet is governed by a one-dimensional (1D) nonlinear Schrödinger equation (NLSE). The latter is used to study the amplitude modulation of Rossby wave packets for fluids in Earth's atmosphere and in the solar photosphere. It is found that an ampitude-modulated Rossby wave packet becomes stable (unstable) against quasi-stationary, long-wavelength (in comparision with the Rossby wavelength) perturbations, when the carrier Rossby wave number satisfies k2 < 1/2 or \\sqrt {2}+1 (k2 > 3 or 1/2). It is also shown that a Rossby rogon or a bright Rossby envelope soliton may be excited in the shallow-water approximation for the Rossby waves in solar photosphere. However, the excitation of small- or large-scale perturbations may be possible for magnetized plasmas in the ionosphereic E-layer.

  7. Modelling the influence of photospheric turbulence on solar flare statistics.

    PubMed

    Mendoza, M; Kaydul, A; de Arcangelis, L; Andrade, J S; Herrmann, H J

    2014-01-01

    Solar flares stem from the reconnection of twisted magnetic field lines in the solar photosphere. The energy and waiting time distributions of these events follow complex patterns that have been carefully considered in the past and that bear some resemblance with earthquakes and stockmarkets. Here we explore in detail the tangling motion of interacting flux tubes anchored in the plasma and the energy ejections resulting when they recombine. The mechanism for energy accumulation and release in the flow is reminiscent of self-organized criticality. From this model, we suggest the origin for two important and widely studied properties of solar flare statistics, including the time-energy correlations. We first propose that the scale-free energy distribution of solar flares is largely due to the twist exerted by the vorticity of the turbulent photosphere. Second, the long-range temporal and time-energy correlations appear to arise from the tube-tube interactions. The agreement with satellite measurements is encouraging. PMID:25247788

  8. THE BUILDUP OF A SCALE-FREE PHOTOSPHERIC MAGNETIC NETWORK

    SciTech Connect

    Thibault, K.; Charbonneau, P.; Crouch, A. D. E-mail: paulchar@astro.umontreal.ca-b

    2012-10-01

    We use a global Monte Carlo simulation of the formation of the solar photospheric magnetic network to investigate the origin of the scale invariance characterizing magnetic flux concentrations visible on high-resolution magnetograms. The simulations include spatially and temporally homogeneous injection of small-scale magnetic elements over the whole photosphere, as well as localized episodic injection associated with the emergence and decay of active regions. Network elements form in response to cumulative pairwise aggregation or cancellation of magnetic elements, undergoing a random walk on the sphere and advected on large spatial scales by differential rotation and a poleward meridional flow. The resulting size distribution of simulated network elements is in very good agreement with observational inferences. We find that the fractal index and size distribution of network elements are determined primarily by these post-emergence surface mechanisms, and carry little or no memory of the scales at which magnetic flux is injected in the simulation. Implications for models of dynamo action in the Sun are briefly discussed.

  9. Germanium and lead: Significant differences between meteoritic and photospheric abundances?

    NASA Technical Reports Server (NTRS)

    Meyer, J. P.; Grevesse, N.

    1985-01-01

    The order of the Galactic cosmic ray source (GCRS) composition in terms of first ionization potential (FIP) was examined. For most elements, the degree of volatility is (positively) correlated with the value of the FIP, so that it is not easy to distinguish a correlation of GCRS abundances anomalies with FIP from a correlation with volatility. Only a few permit to distinguish between the two kinds of ordering: if they are depleted relative to refractory metals, volatility must be relevant, if not, FIP is relevant. Among them Cu and Zn would seem to favor FIP. Among the best indicators are Ge and Pb. The abundance anomalies in GCRS are defined relative to a standard which, for the heavy elements concerned, is commonly taken as C1 Carbonaceous Chondrites. Photospheric abundances are more directly representative of the protosolar nebula, and hence of ordinary local galactic (LG) matter. The Ge and Pb reference abundance determinations in the Photosphere and in C1 meteorites are examined and their relevance to the problem with FIP vs. volatility in GCRs is discussed.

  10. Measuring Photospheric Rotational and Meridional Flows Using Magnetic Feature Tracking

    NASA Astrophysics Data System (ADS)

    Lamb, Derek

    2016-05-01

    Long-lived rotational and meridional flows are important ingredients of the solar cycle. Using magnetic field images to measure these flows on the solar surface has typically been performed by cross-correlating thin longitudinal strips or square patches across sufficiently long time gaps. Here, I use one month of SDO/HMI line-of-sight magnetic field observations, combined with the SWAMIS magnetic feature tracking algorithm to measure the motion of individual features in these magnetograms. By controlling for perturbations due to short-lived flows and due to false motions from feature interactions, I effectively isolate the long-lived flows traced by the magnetic features. This allows me to produce high-fidelity differential rotation measurements with well-characterized variances and covariances of the fit parameters. I also produce medium-fidelity measurements of the much weaker meridional flow that is broadly consistent with previous results, showing a peak flow of 16.7 m/s at 45 degrees latitude. This work shows that measuring the motions of individual features in photospheric magnetograms can produce high precision results in relatively short time spans, which suggests that high resolution non-longitudinally averaged photospheric velocity residual measurements could be produced to compare with coronal results, and to provide other diagnostics of the solar dynamo. This work has been partially supported by NASA Grants NNX11AP03G and NNX14AJ67G.

  11. Evolving Photospheric Flux Concentrations and Filament Dynamic Changes

    NASA Astrophysics Data System (ADS)

    Schmieder, B.; Aulanier, G.; Mein, P.; López Ariste, A.

    2006-11-01

    We analyze the role of weak photospheric flux concentrations that evolve in a filament channel, in the triggering of dynamic changes in the shape of a filament. The high polarimetric sensitivity of THEMIS allowed us to detect weak flux concentrations (few Gauss) associated with the filament development. The synoptic instruments (MDI, SOLIS) even if their sensitivity is much less than THEMIS were useful to follow any subsequent strengthening of these flux concentrations after their identification in the THEMIS magnetograms. We found that (1) the northern part of the filament develops an Hα barb at the same time that weak minority polarity elements develop near a plage; (2) a section in the southern part of the Hα filament gradually disappears and later reforms at the same time that several mixed-polarity magnetic elements appear, then subsequently cancel or spread away from each other. These changes correspond to increases in EUV emission, as observed by TRACE, EIT, and CDS. This suggests that the plasma is temporarily heated along the filament spine. An idealized sequence of force-free models of this filament channel, based on plasma-supporting magnetic dips occurring in the windings of a very weakly twisted flux tube, naturally explains the evolution of its southern part as being due to changes in the topology of the coronal magnetic field as the photospheric flux concentrations evolve.

  12. Simulations of Magnetohydrodynamic Waves Driven by Photospheric Motions

    NASA Astrophysics Data System (ADS)

    Mumford, Stuart

    2016-04-01

    This thesis investigates the properties of various modelled photospheric motions as generation mechanisms for magnetohydrodynamic (MHD) waves in the low solar atmosphere. The solar atmosphere is heated to million-degree temperatures, yet there is no fully understood heating mechanism which can provide the ≈ 300 W/m^2) required to keep the quiet corona at its observed temperatures. MHD waves are one mechanism by which this energy could be provided to the upper solar atmosphere, however, these waves need to be excited. The excitation of these waves, in or below the photosphere is a complex interaction between the plasma and the magnetic field embedded within it. This thesis studies a model of a small-scale magnetic flux tube based upon a magnetic bright point (MBP). These features are very common in the photosphere and have been observed to be affected by the plasma motions. The modelled flux tube has a foot point magnetic field strength of 120 mT and a FWHM of 90 km, and is embedded in a realistic, stratified solar atmosphere based upon the VALIIIc model. To better understand the excitation of MHD waves in this type of magnetic structures, a selection of velocity profiles are implemented to excite waves. Initially a study of five different driving profiles was performed. A uniform torsional driver as well as Archimedean and logarithmic spiral drivers which mimic observed torsional motions in the solar photosphere, along with vertical and horizontal drivers to mimic different motions caused by convection in the photosphere. The results are then analysed using a novel method for extracting the parallel, perpendicular and azimuthal components of the perturbations, which caters to both the linear and non-linear cases. Employing this method yields the identification of the wave modes excited in the numerical simulations and enables a comparison of excited modes via velocity perturbations and wave energy flux. The wave energy flux distribution is calculated, to enable

  13. The Evolution of Open Magnetic Flux Driven by Photospheric Dynamics

    NASA Technical Reports Server (NTRS)

    Linker, Jon A.; Lionello, Roberto; Mikic, Zoran; Titov, Viacheslav S.; Antiochos, Spiro K.

    2010-01-01

    The coronal magnetic field is of paramount importance in solar and heliospheric physics. Two profoundly different views of the coronal magnetic field have emerged. In quasi-steady models, the predominant source of open magnetic field is in coronal holes. In contrast, in the interchange model, the open magnetic flux is conserved, and the coronal magnetic field can only respond to the photospheric evolution via interchange reconnection. In this view the open magnetic flux diffuses through the closed, streamer belt fields, and substantial open flux is present in the streamer belt during solar minimum. However, Antiochos and co-workers, in the form of a conjecture, argued that truly isolated open flux cannot exist in a configuration with one heliospheric current sheet (HCS) - it will connect via narrow corridors to the polar coronal hole of the same polarity. This contradicts the requirements of the interchange model. We have performed an MHD simulation of the solar corona up to 20R solar to test both the interchange model and the Antiochos conjecture. We use a synoptic map for Carrington Rotation 1913 as the boundary condition for the model, with two small bipoles introduced into the region where a positive polarity extended coronal hole forms. We introduce flows at the photospheric boundary surface to see if open flux associated with the bipoles can be moved into the closed-field region. Interchange reconnection does occur in response to these motions. However, we find that the open magnetic flux cannot be simply injected into closed-field regions - the flux eventually closes down and disconnected flux is created. Flux either opens or closes, as required, to maintain topologically distinct open and closed field regions, with no indiscriminate mixing of the two. The early evolution conforms to the Antiochos conjecture in that a narrow corridor of open flux connects the portion of the coronal hole that is nearly detached by one of the bipoles. In the later evolution, a

  14. The Role of Scale and Model Bias in ADAPT's Photospheric Eatimation

    SciTech Connect

    Godinez Vazquez, Humberto C.; Hickmann, Kyle Scott; Arge, Charles Nicholas; Henney, Carl

    2015-05-20

    The Air Force Assimilative Photospheric flux Transport model (ADAPT), is a magnetic flux propagation based on Worden-Harvey (WH) model. ADAPT would be used to provide a global photospheric map of the Earth. A data assimilation method based on the Ensemble Kalman Filter (EnKF), a method of Monte Carlo approximation tied with Kalman filtering, is used in calculating the ADAPT models.

  15. Stellar magnetic fields: From the photosphere into the corona

    NASA Astrophysics Data System (ADS)

    Liefke, Carolin

    2007-10-01

    Simultaneous X-ray and optical observations of the active M dwarf CN Leo have shown variability in its magnetic flux (as measured through magnetically sensitive lines in the molecular FeH band) on different timescales: within a few days, within one night, and possibly even related to a flare event. We propose to extend these studies to a larger sample of stars and observe the two flare stars Proxima Cen and YZ CMi simultaneously with XMM-Newton and VLT/UVES in order to characterize the amplitudes and time scales of variations in their photospheric magnetic fields together with the behavior of chromospheric emission lines and coronal X-ray emission. This will enable us to trace activity-related changes in the stellar magnetic field through all layers of the stellar atmosphere.

  16. The center-to-limb. [in solar photosphere

    NASA Technical Reports Server (NTRS)

    1978-01-01

    Center-to-limb measurements of the Ca I 6573 intercombination line and the Ca II 7324 forbidden line are compared with synthetic profiles based on a simple representation of the non-LTE Ca-Ca(+) ionization equilibrium. The effects of photoionizations from low lying excited states of neutral calcium are found to reduce the sensitivity of the 6573 center-to-limb behavior as a thermal structure diagnostic. The synthetic center-to-limb behavior is also sensitive to uncertainties in the nonthermal broadening. Nevertheless, the measured center-to-limb behavior of 6573 favors a 'cool' photospheric model over hotter models based on the Ca II K wings. The non-LTE calcium abundance obtained from the disk center equivalent widths of 6573 and 7324 using the best fit model is A(Ca) = 2.1 plus or minus 0.2 x 10 to the -6th (by number relative to hydrogen).

  17. Small magnetic structures in the photosphere, radiative properties

    NASA Astrophysics Data System (ADS)

    Palacios, Judith; Domingo, Vicente; Cabello, Iballa; Bonet, José Antonio; Sánchez Almeida, Jorge

    The three dimensional structure of small magnetic field features in the photosphere, their dynamic behavior and their radiative properties are studied. We analyze data obtained in simultaneous observations made on Sept 29 and 30, 2007 with the HINODE spacecraft and the Swedish Solar Telescope (SST) in La Palma in different wavelengths, such as CaII (396.85 nm) and CN (388.35 nm) and other with Hinode data; and Gband (430.56 nm) with SST. Tha analysis is completed with high resolution Gband and Gcontinuum (436.39 nm) images from SST obtained on 2005 and 2006. Magnetograms have been obtained from both observatories. SST images have been processed with MOMFB code. Ribbon-like structures and "flowers" are studied in detail. Comparisons with solar atmospheric models are presented.

  18. Solar photospheric network properties and their cycle variation

    SciTech Connect

    Thibault, K.; Charbonneau, P.; Béland, M. E-mail: paulchar@astro.umontreal.ca-b

    2014-11-20

    We present a numerical simulation of the formation and evolution of the solar photospheric magnetic network over a full solar cycle. The model exhibits realistic behavior as it produces large, unipolar concentrations of flux in the polar caps, a power-law flux distribution with index –1.69, a flux replacement timescale of 19.3 hr, and supergranule diameters of 20 Mm. The polar behavior is especially telling of model accuracy, as it results from lower-latitude activity, and accumulates the residues of any potential modeling inaccuracy and oversimplification. In this case, the main oversimplification is the absence of a polar sink for the flux, causing an amount of polar cap unsigned flux larger than expected by almost one order of magnitude. Nonetheless, our simulated polar caps carry the proper signed flux and dipole moment, and also show a spatial distribution of flux in good qualitative agreement with recent high-latitude magnetographic observations by Hinode. After the last cycle emergence, the simulation is extended until the network has recovered its quiet Sun initial condition. This permits an estimate of the network relaxation time toward the baseline state characterizing extended periods of suppressed activity, such as the Maunder Grand Minimum. Our simulation results indicate a network relaxation time of 2.9 yr, setting 2011 October as the soonest the time after which the last solar activity minimum could have qualified as a Maunder-type Minimum. This suggests that photospheric magnetism did not reach its baseline state during the recent extended minimum between cycles 23 and 24.

  19. Mass and Energy Transfer Between the Solar Photosphere and Corona

    NASA Astrophysics Data System (ADS)

    Peter, H.

    2015-12-01

    The problem of chromospheric and coronal heating is also a problem of mass supply to the corona. On average we see redshifts at transition region temperatures of the order of 10 km/s. If interpreted as downflows, this would quickly empty the corona, and fresh material has to be transported into the corona. Several models have been proposed to understand this mass cycle between the different atmospheric layers. However, as of yet all these proposals have serious shortcomings. On the observational side open questions remain, too. With the new IRIS mission we can observe the transition region at unprecedented spatial and spectral resolution, but the observational results are still puzzling. In particular the finding that the spatial distribution of line widths and Doppler shifts do not change with increasing resolution is against physical intuition. This shows that even with IRIS we still have significant velocity gradients along the line-of-sight, indicating that shocks might play a significant role. Likewise the temporal evolution might be a key for our understanding of the mass cycle. It might well be that the filling and draining of hot plasma occurs on significantly different time scales, which might be part of the difficulty to arrive at a conclusive observational picture. Considering the progress made for the quiet Sun, it seems clear that the processes responsible for the mass exchange are not resolved (yet). Therefore one might wonder to what extent one could use larger and resolved individual events in more active parts of the Sun to understand the details of the mass transport. In particular a common understanding of reconnection events such as Ellerman bombs in the photosphere, explosive events in the transition region and the recently discovered IRIS bombs in-between might provide the key to better understand the mass cycle throughout the atmospheric layers from the photosphere to the corona.

  20. Study of small magnetic structures in the solar photosphere

    NASA Astrophysics Data System (ADS)

    Cabello, I.; Domingo, V.; Bonet, J. A.; Blanco Rodríguez, J.; Balmaceda, L. A.

    2013-05-01

    The study of small scale magnetic structures in the solar photosphere is of great relevance for the understanding of the global behaviour of the Sun. Because of the small spatial and temporal scales involved, the use of high resolution images and fast cadence is fundamental for their study. In order to obtain such images, sophisticated computational techniques that compensate for the atmospheric degradation and telescope aberration have been developed, improving in this way the spatial resolution. In this work, we use G-band images obtained with the 1 m-Swedish Solar Telescope located at La Palma (Canary Islands, Spain). The images have been restored with MOMFBD (Multi-Object Multi-Frame Blind Deconvolution), a technique that combines multiple images acquired in a short time interval. The resulting images have a resolution close to the diffraction limit of the telescope (0.1 arcsec) allowing the study of very small bright structures present in the inter-granular lanes in the solar photosphere, known as Bright Points. It is highlighted the great presence of magnetic structures in quiet Sun regions analyzed from different observational campaigns. The density of BPs in the quiet Sun shows a decrease as we approach the limb, with values of ≃q 1% at the centre (μ ≈ 1), and ≃q 0.2% at μ ≈ 0.3. We also present the discovery of small vortexes detected in the solar surface through the movement of BPs, with radii around 241 km and lifetimes longer than 5 minutes. Further analyses, comprising longer time series and information from different solar layers, are being performed aiming at a more in-depth knowledge of these phenomena.

  1. Brightness of the photosphere and faculae at the limb based on eclipse observations

    SciTech Connect

    Akimov, L.A.; Belkina, I.L.; Dyatel, N.P.

    1982-05-01

    The absolute distributions of integral and surface brightness of the photospheric continuum (lambdaroughly-equal5870 A) and in faculae at the very limb are obtained from slitless spectrograms of the total solar eclipse of July 10, 1972. Several possible reasons for the brightness increase toward the limb in the distribution of photospheric surface brightness are discussed. The faculae showed high contrasts, up to 1.76 at a height of 200 km from the limb. A comparison of the times of local contacts observed and calculated with allowance for lunar relief showed that the active regions are at about 300 km above the photosphere. A schematic model of a facula is proposed.

  2. Photospheric Emission from Collapsar Jets in 3D Relativistic Hydrodynamics

    NASA Astrophysics Data System (ADS)

    Ito, Hirotaka; Matsumoto, Jin; Nagataki, Shigehiro; Warren, Donald C.; Barkov, Maxim V.

    2015-12-01

    We explore the photospheric emission from a relativistic jet breaking out from a massive stellar envelope based on relativistic hydrodynamical simulations and post-process radiation transfer calculations in three dimensions. To investigate the impact of three-dimensional (3D) dynamics on the emission, two models of injection conditions are considered for the jet at the center of the progenitor star: one with periodic precession and another without precession. We show that structures developed within the jet due to the interaction with the stellar envelope, as well as due to the precession, have a significant imprint on the resulting emission. Particularly, we find that the signature of precession activity by the central engine is not smeared out and can be directly observed in the light curve as a periodic signal. We also show that non-thermal features, which can account for observations of gamma-ray bursts, are produced in the resulting spectra even though only thermal photons are injected initially and the effect of non-thermal particles is not considered.

  3. Seismic Ripple Anisotropy on the photosphere: observed, simulated, explained

    NASA Astrophysics Data System (ADS)

    Donea, Alina

    2016-05-01

    Based on observations of seismic ripples generated by solar flares, we performed simulations of different configurations/ morphologies of acoustic structures at the "epicenter" of the sunquake, The production of seismic waves is caused by spatially confined, high impacts into the solar photosphere, inflicted during the impulsive phase of solar flares.An interesting characteristic feature of the seismic response of most sunquakes is a considerable anisotropy in acoustic amplitude of the ripples from the vantage of the source, the acoustic emission is much stronger in some directions than others.We have produced a catalogue of simulations showing varying degrees of wave front anisotropy. Due to the large number of parameters that have potential for variation within the code, an innumerable number of cases have the capacity to be constructed. The governing limits of variation for each parameter will therefore be restricted to those of real life physical situations that have either been observed or strongly proposed. I will present the most conclusive cases of our work, which elucidate some of the unsolved clues about sunquakes and their ripples.

  4. Laboratory measurements of white dwarf photospheric spectral lines: Hβ

    DOE PAGESBeta

    Falcon, Ross Edward; Rochau, Gregory A.; Bailey, James E.; Gomez, Thomas; Montgomery, Michael Houston; Winget, Donald E.; Nagayama, Taisuke

    2015-06-18

    We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. We also present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, ne, and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer amore » continuous range of electron densities increasing from ne ~ 4 to ~30 × 1016 cm-3 throughout a 120-ns evolution of our plasma. Also, we observe n2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ~55 ns to become consistent with LTE. This also supports our electron-temperature determination of Te ~ 1.3 eV (~15,000 K) after this time. At ne≲ 1017 cm-3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ2) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. Lastly, this work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.« less

  5. Solar photospheric and coronal abundances from solar energetic particle measurements

    SciTech Connect

    Breneman, H.H.

    1985-01-01

    Observations of solar energetic particles (SEPs) from 22 solar flares in the 1977-1982 time period are reported. The observations were made by the cosmic ray subsystem on board the Voyager 1 and 2 spacecraft. SEP abundances were obtained for all elements with 3 less than or equal to Z less than or equal to 30 except Li, Be, B, F, Sc, V, Co and Cu, for which upper limits have been obtained. Statistically meaningful abundances of several rare elements (e.g., P, Cl, K, Ti, Mn) were determined for the first time, and the average abundances of the more abundant elements were determined with improved precision, typically a factor of three better than the best previous determinations. Previously reported results concerning the dependence of the fractionation of SEPs relative to photosphere on first ionization potential (FIP) have been confirmed and amplified upon with the new data. The monotonic Z dependence of the variation between flares noted by earlier studies was found to be interpretable as a fractionation, produced by acceleration of the particles from the corona and their propagation through interplanetary space, which is ordered by the ionic charge-to-mass ratio Q/M of the species making up the SEPs. It was found that Q/M is the primary organizing parameter of acceleration and propagation effects in SEPs, as evidenced by the dependence on Q/M of time, spatial and energy dependence within flares and of the abundance variability from flare to flare.

  6. Fingerprints of giant planets in the photospheres of Herbig stars

    NASA Astrophysics Data System (ADS)

    Kama, M.; Folsom, C. P.; Pinilla, P.

    2015-10-01

    Around 2% of all A stars have photospheres depleted in refractory elements. This is hypothesised to arise from gas being accreted more efficiently than dust, but the specific processes and the origin of the material - circum- or interstellar - are not known. The same depletion is seen in 30% of young, disk-hosting Herbig Ae/Be stars. We investigate whether the chemical peculiarity originates in a circumstellar disk. Using a sample of systems for which both the stellar abundances and the protoplanetary disk structure are known, we find that stars hosting warm, flaring group I disks typically have Fe, Mg and Si depletions of 0.5 dex compared to the solar-like abundances of stars hosting cold, flat group II disks. The volatile, C and O, abundances in both sets are identical. Group I disks are generally transitional, having radial cavities depleted in millimetre-sized dust grains, while those of group II are usually not. Thus we propose that the depletion of heavy elements emerges as Jupiter-like planets block the accretion of part of the dust, while gas continues to flow towards the central star. We calculate gas to dust ratios for the accreted material and find values consistent with models of disk clearing by planets. Our results suggest that giant planets of ~0.1 to 10 MJup are hiding in at least 30% of Herbig Ae/Be disks. Appendix A is available in electronic form at http://www.aanda.org

  7. Magnetic flux submergence in the photosphere: A target for DKIST

    NASA Astrophysics Data System (ADS)

    Martinez Pillet, Valentin

    2016-05-01

    While magnetic flux emergence is ubiquitous on the Sun and relatively well observed, the opposite process, flux submergence, is elusive. In the absence of large-scale submergence processes, it has always been assumed that submergence occurs at granular or smaller scales. Models that explain flux rope and filament formation near neutral lines, specifically need small-scale submergence. The same is true for dynamo models that propose the repair of the large-scale toroidal tubes after they have emerged to the surface. However, the detection of field lines being pulled back down into the solar photosphere has escaped clear detection. In this work, I demonstrate that DKIST capabilities are uniquely tailored to observe and characterize small-scale flux submergence, if it indeed happens on the Sun. By searching for transverse fields at small scales and studying their Doppler shifts, an understanding of the nature of flux submergence can be achieved. Such studies are particularly relevant near magnetic neutral lines where filaments are formed though poorly understood processes.

  8. Generation of magnetic structures on the solar photosphere

    SciTech Connect

    Gangadhara, R. T.; Krishan, V.; Bhowmick, A. K.; Chitre, S. M.

    2014-06-20

    The lower solar atmosphere is a partially ionized plasma consisting of electrons, ions, and neutral atoms. In this, which is essentially a three-fluid system, the Hall effect arises from the treatment of the electrons and ions as two separate fluids and the ambipolar diffusion arises from the inclusion of neutrals as the third fluid. The Hall effect and ambipolar diffusion have been shown to be operational in a region beginning from near the photosphere up to the chromosphere. In a partially ionized plasma, the magnetic induction is subjected to ambipolar diffusion and the Hall drift in addition to the usual resistive dissipation. These nonlinear effects create sharp magnetic structures which then submit themselves to various relaxation mechanisms. A first-principles derivation of these effects in a three-fluid system and an analytic solution to the magnetic induction equation in a stationary state are presented, which in the general case includes the Hall effect, ambipolar diffusion, and ohmic dissipation. The temporal evolution of the magnetic field is then investigated under the combined as well as the individual effects of the Hall drift and ambipolar diffusion to demonstrate the formation of steep magnetic structures and the resultant current sheet formation. These structures have just the right features for the release of magnetic energy into the solar atmosphere.

  9. The source of 5 minute period photospheric umbral oscillations

    NASA Technical Reports Server (NTRS)

    Penn, M. J.; Labonte, B. J.

    1993-01-01

    We observed the oscillations in the umbrae of two sunspots, using the MCCD imaging spectrograph at the Mees Solar Observatory on Haleakala, Maui. We perform four spatial analyses of the umbral velocity and find that (1) there is more power traveling toward the center of the umbrae than leaving the center of the umbrae (this provides a direct measure of the absorption of p-modes by the sunspot umbrae); (2) the umbral oscillations display power in the same spatial and temporal frequency band as the quiet-sun oscillations; (3) Fourier-Bessel analysis of one umbra shows no obvious resonant frequencies which might represent natural oscillation modes; and (4) the centers of the umbrae have less rms velocity at high spatial wavenumber than the edges of the umbrae. We conclude: (1) the photospheric umbral oscillations are driven by a source external to the sunspot, the global p-mode oscillations; (2) there are no resonant frequencies in the oscillations; and (3) the absorption of acoustic waves occurs inside the umbrae.

  10. Forecasting the Solar photospheric magnetic field using solar flux transport model and local ensemble Kalman filtering

    NASA Astrophysics Data System (ADS)

    Zhang, Y.

    2015-12-01

    Accurate forecasting the solar photospheric magnetic field distribution play an important role in the estimates of the inner boundary conditions of the coronal and solar wind model. Forecasting solar photospheric magnetic field using the solar flux transport (SFT) model can achieve an acceptable match to the actual field. The observations from ground-based or spacecraft instruments can be assimilated to update the modeled flux. The local ensemble Kalman filtering (LEnKF) method is utilized to improve forecasts and characterize their uncertainty by propagating the SFT model with different model parameters forward in time to control the evolution of the solar photospheric magnetic field. Optimal assimilation of measured data into the ensemble produces an improvement in the fit of the forecast to the actual field. Our approach offers a method to improve operational forecasting of the solar photospheric magnetic field. The LEnKF method also allows sensitivity analysis of the SFT model to noise and uncertainty within the physical representation.

  11. Forecasting the solar photospheric magnetic field using solar flux transport model and local ensemble Kalman filtering

    NASA Astrophysics Data System (ADS)

    Zhang, Ying; Du, Aimin; Feng, Xueshang

    2015-04-01

    Accurate forecasting the solar photospheric magnetic field distribution play an important role in the estimates of the inner boundary conditions of the coronal and solar wind model. Forecasting solar photospheric magnetic field using the solar flux transport (SFT) model can achieve an acceptable match to the actual field. The observations from ground-based or spacecraft instruments can be assimilated to update the modeled flux. The local ensemble Kalman filtering (LEnKF) method is utilized to improve forecasts and characterize their uncertainty by propagating the SFT model with different model parameters forward in time to control the evolution of the solar photospheric magnetic field. Optimal assimilation of measured data into the ensemble produces an improvement in the fit of the forecast to the actual field. Our approach offers a method to improve operational forecasting of the solar photospheric magnetic field. The LEnKF method also allows sensitivity analysis of the SFT model to noise and uncertainty within the physical representation.

  12. Alfvén Waves in Simulations of Solar Photospheric Vortices

    NASA Astrophysics Data System (ADS)

    Shelyag, S.; Cally, P. S.; Reid, A.; Mathioudakis, M.

    2013-10-01

    Using advanced numerical magneto-hydrodynamic simulations of the magnetized solar photosphere, including non-gray radiative transport and a non-ideal equation of state, we analyze plasma motions in photospheric magnetic vortices. We demonstrate that apparent vortex-like motions in photospheric magnetic field concentrations do not exhibit "tornado"-like behavior or a "bath-tub" effect. While at each time instance the velocity field lines in the upper layers of the solar photosphere show swirls, the test particles moving with the time-dependent velocity field do not demonstrate such structures. Instead, they move in a wave-like fashion with rapidly changing and oscillating velocity field, determined mainly by magnetic tension in the magnetized intergranular downflows. Using time-distance diagrams, we identify horizontal motions in the magnetic flux tubes as torsional Alfvén perturbations propagating along the nearly vertical magnetic field lines with local Alfvén speed.

  13. Study of magnetic notions in the solar photosphere and their implications for heating the solar atmosphere

    NASA Technical Reports Server (NTRS)

    Noyes, Robert W.

    1995-01-01

    This progress report covers the first year of NASA Grant NAGw-2545, a study of magnetic structure in the solar photosphere and chromosphere. We have made significant progress in three areas: (1) analysis of vorticity in photospheric convection, which probably affects solar atmospheric heating through the stresses it imposes on photospheric magnetic fields; (2) modelling of the horizontal motions of magnetic footpoints in the solar photosphere using an assumed relation between brightness and vertical motion as well as continuity of flow; and (3) observations and analysis of infrared CO lines formed near the solar temperature minimum, whose structure and dynamics also yield important clues to the nature of heating of the upper atmosphere. Each of these areas are summarized in this report, with copies of those papers prepared or published this year included.

  14. The Dependence of Coronal Loop Heating on the Characteristics of Slow Photospheric Motions

    NASA Astrophysics Data System (ADS)

    Ritchie, M. L.; Wilmot-Smith, A. L.; Hornig, G.

    2016-06-01

    The Parker hypothesis assumes that heating of coronal loops occurs due to reconnection, induced when photospheric motions braid field lines to the point of current sheet formation. In this contribution we address the question of how the nature of photospheric motions affects the heating of braided coronal loops. We design a series of boundary drivers and quantify their properties in terms of complexity and helicity injection. We examine a series of long-duration full resistive MHD simulations in which a simulated coronal loop, consisting of initially uniform field lines, is subject to these photospheric flows. Braiding of the loop is continually driven until differences in behavior induced by the drivers can be characterized. It is shown that heating is crucially dependent on the nature of the photospheric driver—coherent motions typically lead to fewer large energy release events, while more complex motions result in more frequent but less energetic heating events.

  15. Driving of the solar p-modes by radiative pumping in the upper photosphere

    NASA Technical Reports Server (NTRS)

    Fontenla, Juan M.; Emslie, A. G.; Moore, Ronald L.

    1989-01-01

    It is shown that one viable driver of the solar p-modes is radiative pumping in the upper photosphere where the opacity is dominated by the negative hydrogen ion. This new option is suggested by the similar magnitudes of two energy flows that have been evaluated by independent empirical methods. The similarity indicates that the p-modes are radiatively pumped in the upper photosphere and therefore provide the required nonradiative cooling.

  16. CONDITIONS FOR PHOTOSPHERICALLY DRIVEN ALFVENIC OSCILLATIONS TO HEAT THE SOLAR CHROMOSPHERE BY PEDERSEN CURRENT DISSIPATION

    SciTech Connect

    Goodman, Michael L.

    2011-07-01

    A magnetohydrodynamic model that includes a complete electrical conductivity tensor is used to estimate conditions for photospherically driven, linear, non-plane Alfvenic oscillations extending from the photosphere to the lower corona to drive a chromospheric heating rate due to Pedersen current dissipation that is comparable to the observed net chromospheric radiative loss of {approx}10{sup 7} erg cm{sup -2} s{sup -1}. The heating rates due to electron current dissipation in the photosphere and corona are also computed. The wave amplitudes are computed self-consistently as functions of an inhomogeneous background (BG) atmosphere. The effects of the conductivity tensor are resolved numerically using a resolution of 3.33 m. The oscillations drive a chromospheric heating flux F{sub Ch} {approx} 10{sup 7}-10{sup 8} erg cm{sup -2} s{sup -1} at frequencies {nu} {approx} 10{sup 2}-10{sup 3} mHz for BG magnetic field strengths B {approx}> 700 G and magnetic field perturbation amplitudes {approx}0.01-0.1 B. The total resistive heating flux increases with {nu}. Most heating occurs in the photosphere. Thermalization of Poynting flux in the photosphere due to electron current dissipation regulates the Poynting flux into the chromosphere, limiting F{sub Ch}. F{sub Ch} initially increases with {nu}, reaches a maximum, and then decreases with increasing {nu} due to increasing electron current dissipation in the photosphere. The resolution needed to resolve the oscillations increases from {approx}10 m in the photosphere to {approx}10 km in the upper chromosphere and is {proportional_to}{nu}{sup -1/2}. Estimates suggest that these oscillations are normal modes of photospheric flux tubes with diameters {approx}10-20 km, excited by magnetic reconnection in current sheets with thicknesses {approx}0.1 km.

  17. CxO (x=16,17,18) isotopologue ratios in the solar photosphere

    NASA Astrophysics Data System (ADS)

    Lyons, James; Gharib-Nezhad, Ehsan; Ayres, Thomas

    2015-11-01

    Determination of the oxygen isotope ratios in the solar photosphere is essential to constraining the formation environment of the solar system. The solar CO fundamental and first-overtone bands were previously measured by the shuttle-borne ATMOS Fourier transform spectrometer (FTS), and with the National Solar Observatory FTS on the McMath-Pierce telescope at Kitt Peak. Analyzing the rovibrational bands from these photospheric spectra, a 3D convection model was employed to calculate ratios with improved uncertainties (16O/17O=2738±118 and 16O/18O =511±10 Ayres et al. 2013), which fall between the terrestrial values and those inferred from solar wind measurements by the Genesis spacecraft. However, differences in published CO dipole moment functions yielded a range of isotopic ratios spanning ~ 3 % in δ18O. Here we re-evaluate the CO dipole moment function in order to obtain more accurate isotope ratios for the photosphere. We used a new set of dipole moments from HITEMP which were accurately determined by both semi-empirical and ab initio methods. Preliminary values of isotope ratios using the new dipole moments are in better agreement with the inferred photosphere values from Genesis, showing that the solar photosphere is isotopically similar to primitive inclusions in meteorites, but different from the terrestrial planets by ~ 6 %. New spectral observations are needed to reduce uncertainties in photospheric C17O abundances.

  18. Horizontal Flows in the Photosphere and Subphotosphere of Two Active Regions

    NASA Technical Reports Server (NTRS)

    Liu, Yang; Zhao, Junwei; Schuck, P. W.

    2012-01-01

    We compare horizontal flow fields in the photosphere and in the subphotosphere (a layer 0.5 megameters below the photosphere) in two solar active regions: AR11084 and AR11158. AR11084 is a mature, simple active region without significant flaring activity, and AR11158 is a multipolar, complex active region with magnetic flux emerging during the period studied. Flows in the photosphere are derived by applying the Differential Affine Velocity Estimator for Vector Magnetograms (DAVE4VM) on HMI-observed vector magnetic fields, and the subphotospheric flows are inferred by time-distance helioseismology using HMI-observed Dopplergrams. Similar flow patterns are found for both layers for AR11084: inward flows in the sunspot umbra and outward flows surrounding the sunspot. The boundary between the inward and outward flows, which is slightly different in the photosphere and the subphotosphere, is within the sunspot penumbra. The area having inward flows in the subphotosphere is larger than that in the photosphere. For AR11158, flows in these two layers show great similarities in some areas and significant differences in other areas. Both layers exhibit consistent outward flows in the areas surrounding sunspots. On the other hand, most well-documented flux-emergence-related flow features seen in the photosphere do not have counterparts in the subphotosphere. This implies that the horizontal flows caused by flux emergence do not extend deeply into the subsurface.

  19. DETERMINING THE MAGNETIZATION OF THE QUIET SUN PHOTOSPHERE FROM THE HANLE EFFECT AND SURFACE DYNAMO SIMULATIONS

    SciTech Connect

    Shchukina, Nataliya; Trujillo Bueno, Javier E-mail: jtb@iac.es

    2011-04-10

    The bulk of the quiet solar photosphere is thought to be significantly magnetized, due to the ubiquitous presence of a tangled magnetic field at subresolution scales with an average strength (B) {approx} 100 G. This conclusion was reached through detailed three-dimensional (3D) radiative transfer modeling of the Hanle effect in the Sr I 4607 A line, using the microturbulent field approximation and assuming that the shape of the probability density function of the magnetic field strength is exponential. Here, we relax both approximations by modeling the observed scattering polarization in terms of the Hanle effect produced by the magnetic field of a 3D photospheric model resulting from a (state-of-the-art) magneto-convection simulation with surface dynamo action. We show that the scattering polarization amplitudes observed in the Sr I 4607 A line can be explained only after enhancing the magnetic strength of the photospheric model by a sizable scaling factor, F {approx} 10, which implies (B) {approx} 130 G in the upper photosphere. We also argue that in order to explain both the Hanle depolarization of the Sr I 4607 A line and the Zeeman signals observed in Fe I lines, we need to introduce a height-dependent scaling factor, such that the ensuing (B) {approx} 160 G in the low photosphere and (B) {approx} 130 G in the upper photosphere.

  20. Photospheric Temperature Variations near the Solar Limb II

    NASA Astrophysics Data System (ADS)

    Fivian, Martin; Hudson, H. S.

    2013-07-01

    We use observations from the Solar Aspect Sensor (SAS) of RHESSI to characterize the latitude dependence of the temperature of the photosphere near the solar limb. Previous observations had suggested the presence of a polar temperature excess as large as 1.5 K. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. This photometry is differential, i.e. relative to a mean limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1.73 arc sec square pixels, observing a narrow band (12nm FWHM) at 670 nm. Each image shows a chord crossing the disk at a different location as the spacecraft rotates and precesses around its average solar pointing. We fit an average limb-darkening function and reassemble the residuals into synoptic maps of differential intensity variations as a function of position angle. We further mask these images against EUV images (SOHO/EIT 284A for older data and SDO/AIA for more recent data) in order to eliminate magnetic regions. We present results from our new analysis which shows significantly larger signals of latitude-dependent temperature variations than what has been presented earlier in our preliminary analysis and interpretation.Abstract (2,250 Maximum Characters): We use observations from the Solar Aspect Sensor (SAS) of RHESSI to characterize the latitude dependence of the temperature of the photosphere near the solar limb. Previous observations had suggested the presence of a polar temperature excess as large as 1.5 K. The RHESSI observations, made with a rotating telescope in space, have great advantages in the rejection of systematic errors in the very precise photometry required for such an observation. This photometry is differential, i.e. relative to a mean limb-darkening function. The data base consists of about 1,000 images per day from linear CCDs with 1

  1. Laboratory measurements of white dwarf photospheric spectral lines: Hβ

    SciTech Connect

    Falcon, Ross Edward; Rochau, Gregory A.; Bailey, James E.; Gomez, Thomas; Montgomery, Michael Houston; Winget, Donald E.; Nagayama, Taisuke

    2015-06-18

    We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. We also present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, ne, and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from ne ~ 4 to ~30 × 1016 cm-3 throughout a 120-ns evolution of our plasma. Also, we observe n2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ~55 ns to become consistent with LTE. This also supports our electron-temperature determination of Te ~ 1.3 eV (~15,000 K) after this time. At ne≲ 1017 cm-3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ2) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. Lastly, this work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.

  2. Distribution of electric currents in sunspots from photosphere to corona

    SciTech Connect

    Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo

    2014-09-20

    We present a study of two regular sunspots that exhibit nearly uniform twist from the photosphere to the corona. We derive the twist parameter in the corona and in the chromosphere by minimizing the difference between the extrapolated linear force-free field model field lines and the observed intensity structures in the extreme-ultraviolet images of the Sun. The chromospheric structures appear more twisted than the coronal structures by a factor of two. Further, we derive the vertical component of electric current density, j{sub z} , using vector magnetograms from the Hinode Solar Optical Telescope (SOT). The spatial distribution of j{sub z} has a zebra pattern of strong positive and negative values owing to the penumbral fibril structure resolved by Hinode/SOT. This zebra pattern is due to the derivative of the horizontal magnetic field across the thin fibrils; therefore, it is strong and masks weaker currents that might be present, for example, as a result of the twist of the sunspot. We decompose j{sub z} into the contribution due to the derivatives along and across the direction of the horizontal field, which follows the fibril orientation closely. The map of the tangential component has more distributed currents that are coherent with the chromospheric and coronal twisted structures. Moreover, it allows us to map and identify the direct and return currents in the sunspots. Finally, this decomposition of j{sub z} is general and can be applied to any vector magnetogram in order to better identify the weaker large-scale currents that are associated with coronal twisted/sheared structures.

  3. Unresolved Magnetic Flux Removal Process in the Photosphere

    NASA Astrophysics Data System (ADS)

    Kubo, Masahito; Chye Low, Boon; Lites, Bruce

    The mutual loss of magnetic flux due to the apparent collision of opposite-polarity magnetic elements is called "magnetic flux cancellation" as a descriptive term. The flux cancellation is essential to understand the dissipation of magnetic flux from the solar surface. An Ω-loop submerging below the surface or a U-loop rising through the photosphere is the usual idea to explain the magnetic flux cancellation. Magnetic reconnection may be crucial for the forma-tion of these loops, especially for the submerging -loop. In fact, chromospheric and coronal activities are often observed at the cancellation sites. We investigate the evolution of 5 cancel-lation events of the opposite-polarity magnetic elements at granular scales by using accurate spectropolarimetric measurements with the Solar Optical Telescope aboard Hinode. We find that the horizontal magnetic field, which is expected in both submerging Ω-loop model and emerging U-loop model, does not appear between the canceling magnetic elements in 4 of the 5 events. The approaching magnetic elements in these events are more concentrated rather than gradually diffused, and they have nearly vertical fields even while they are in contact each other. We thus imply that the actual flux cancellation is highly time dependent event near the solar surface at scales less than a pixel of Hinode/SOT (about 200 km). At the polarity inversion line formed by the canceling magnetic elements, highly asymmetric Stokes-V profiles are observed. We confirm that such asymmetric profile can be made by the sum of the profiles at the opposite-polarity magnetic elements next to the polarity inversion line. This means that the approaching bipolar flux tubes still keep their nature within the pixel where they come in contact with each other, and thus supports the unresolved flux removal process within the pixel at the polarity inversion line.

  4. Laboratory Measurements of White Dwarf Photospheric Spectral Lines. Hβ

    SciTech Connect

    Falcon, Ross Edward; Rochau, Gregory A.; Bailey, James E.; Gomez, Thomas; Montgomery, Michael Houston; Winget, Donald E; Nagayama, Taisuke

    2015-06-18

    We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf (WD) atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating WD photospheric conditions. We also present time-resolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, ne, and n = 2 level population, n2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from ne ~ 4 to ~30 × 1016 cm-3 throughout a 120-ns evolution of our plasma. Also, we observe n2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ~55 ns to become consistent with LTE. This also supports our electron-temperature determination of Te ~ 1.3 eV (~15,000 K) after this time. At ne≲ 1017 cm-3, we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ2) than the line profiles currently used in the WD astronomy community. The inferred conditions, however, are in good quantitative agreement. This work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.

  5. Distribution of Electric Currents in Sunspots from Photosphere to Corona

    NASA Astrophysics Data System (ADS)

    Gosain, Sanjay; Démoulin, Pascal; López Fuentes, Marcelo

    2014-09-01

    We present a study of two regular sunspots that exhibit nearly uniform twist from the photosphere to the corona. We derive the twist parameter in the corona and in the chromosphere by minimizing the difference between the extrapolated linear force-free field model field lines and the observed intensity structures in the extreme-ultraviolet images of the Sun. The chromospheric structures appear more twisted than the coronal structures by a factor of two. Further, we derive the vertical component of electric current density, jz , using vector magnetograms from the Hinode Solar Optical Telescope (SOT). The spatial distribution of jz has a zebra pattern of strong positive and negative values owing to the penumbral fibril structure resolved by Hinode/SOT. This zebra pattern is due to the derivative of the horizontal magnetic field across the thin fibrils; therefore, it is strong and masks weaker currents that might be present, for example, as a result of the twist of the sunspot. We decompose jz into the contribution due to the derivatives along and across the direction of the horizontal field, which follows the fibril orientation closely. The map of the tangential component has more distributed currents that are coherent with the chromospheric and coronal twisted structures. Moreover, it allows us to map and identify the direct and return currents in the sunspots. Finally, this decomposition of jz is general and can be applied to any vector magnetogram in order to better identify the weaker large-scale currents that are associated with coronal twisted/sheared structures.

  6. On the continuum intensity distribution of the solar photosphere

    NASA Astrophysics Data System (ADS)

    Wedemeyer-Böhm, S.; Rouppe van der Voort, L.

    2009-08-01

    Context: For many years, there seemed to be significant differences between the continuum intensity distributions derived from observations and simulations of the solar photosphere. Aims: In order to settle the discussion on these apparent discrepancies, we present a detailed comparison between simulations and seeing-free observations that takes into account the crucial influence of instrumental image degradation. Methods: We use a set of images of quiet Sun granulation taken in the blue, green and red continuum bands of the Broadband Filter Imager of the Solar Optical Telescope (SOT) onboard Hinode. The images are deconvolved with point spread functions (PSF) that account for non-ideal contributions due to instrumental stray-light and imperfections. In addition, synthetic intensity images are degraded with the corresponding PSFs. The results are compared with respect to spatial power spectra, intensity histograms, and the centre-to-limb variation of the intensity contrast. Results: The intensity distribution of SOT granulation images is broadest for the blue continuum at disc-centre and narrows towards the limb and for longer wavelengths. The distributions are relatively symmetric close to the limb but exhibit a growing asymmetry towards disc-centre. The intensity contrast, which is connected to the width of the distribution, is found to be (12.8 ± 0.5)%, (8.3 ± 0.4)%, and (6.2 ± 0.2)% at disc-centre for blue, green, and red continuum, respectively. Removing the influence of the PSF unveils much broader intensity distributions with a secondary component that is otherwise only visible as an asymmetry between the darker and brighter than average part of the distribution. The contrast values increase to (26.7 ± 1.3)%, (19.4 ± 1.4)%, and (16.6 ± 0.7)% for blue, green, and red continuum, respectively. The power spectral density of the images exhibits a pronounced peak at spatial scales characteristic for the granulation pattern and a steep decrease towards

  7. Creating and measuring white dwarf photospheres in a terrestrial laboratory

    NASA Astrophysics Data System (ADS)

    Falcon, Ross Edward

    2014-08-01

    As the ultimate fate of nearly all stars, including our Sun, white dwarfs (WDs) hold rich and informative histories in their observable light. To determine a fundamental parameter of WDs, mass, we perform the first measurement of the average gravitational redshift of an ensemble of WDs. We find a larger mean mass than that determined from the primary and expansive technique known as the spectroscopic method. The potential inaccuracy of this method has broad astrophysical implications, including for our understanding of Type 1a supernova progenitors and for constraining the age of the Universe. This motivates us to investigate the WD atmosphere models used with the spectroscopic method, particularly the input theoretical line profiles, by developing a new experimental platform to create plasmas at WD photospheric conditions (Te~1 eV, ne~1017 cm-3). Instead of observing WD spectra to infer the plasma conditions at the surface of the star, we set the conditions and measure the emergent spectra in the laboratory. X-rays from a z-pinch dynamic hohlraum generated at the Z Pulsed Power Facility at Sandia National Laboratories irradiate a gas cell to initiate formation of a large (120x20x10 mm or 24 cm3) plasma. We observe multiple Balmer lines from our plasma in emission and in absorption simultaneously along relatively long (~120 mm) lines of sight perpendicular to the heating radiation. Using a large, radiation-driven plasma aides us to achieve homogeneity along our observed lines of sight. With time-resolved spectroscopy we measure lines at a range of electron densities that spans an order of magnitude, and we do this within one pulsed power shot experiment. Observing our plasma in absorption not only provides the signal-to-noise to measure relative line shapes, it allows us to measure relative line strengths because the lines share the same lower level population. This constrains the theoretical reduction factors used to describe ionization potential depression or the

  8. Semiempirical photospheric models of a solar flare on May 28, 2012

    NASA Astrophysics Data System (ADS)

    Andriets, E. S.; Kondrashova, N. N.

    2015-02-01

    The variation of the photosphere physical state during the decay phase of SF/B6.8-class solar flare on May 28, 2012 in active region NOAA 11490 is studied. We used the data of the spectropolarimetric observations with the French-Italian solar telescope THEMIS (Tenerife, Spain). Semi-empirical model atmospheres are derived from the inversion with SIR (Stokes Inversion based on Response functions) code. The inversion was based on Stokes profiles of six photospheric lines. Each model atmosphere has a two-component structure: a magnetic flux tube and non-magnetic surroundings. The Harvard Smithsonian Reference Atmosphere (HSRA) has been adopted for the surroundings. The macroturbulent velocity and the filling factor were assumed to be constant with the depth. The optical depth dependences of the temperature, magnetic field strength, and line-of-sight velocity are obtained from inversion. According to the received model atmospheres, the parameters of the magnetic field and the thermodynamical parameters changed during the decay phase of the flare. The model atmospheres showed that the photosphere remained in a disturbed state during observations after the maximum of the flare. There are temporal changes in the temperature and the magnetic field strength optical depth dependences. The temperature enhancement in the upper photospheric layers is found in the flaring atmospheres relative to the quiet-Sun model. The downflows are found in the low and upper photosphere at the decay phase of the flare.

  9. Average photospheric poloidal and toroidal magnetic field components near solar minimum

    NASA Technical Reports Server (NTRS)

    Duvall, T. L., Jr.; Scherrer, P. H.; Svalgaard, L.; Wilcox, J. M.

    1979-01-01

    Average (over longitude and time) photospheric magnetic field components are derived from 3-min Stanford magnetograms made near the solar minimum of cycle 21. The average magnetograph signal is found to behave as the projection of a vector for measurements made across the disk. The poloidal field exhibits the familiar dipolar structure near the poles, with a measured signal in the line Fe I 5250 A of about 1 G. At low latitudes the poloidal field has the polarity of the poles, but is of reduced magnitude (about 0.1 G). A net photospheric toroidal field with a broad latitudinal extent is found. The polarity of the toroidal field is opposite in the northern and southern hemispheres and has the same sense as subsurface flux tubes giving rise to active regions of solar cycle 21. These observations are used to discuss large-scale electric currents crossing the photosphere and angular momentum loss to the solar wind.

  10. Ultra-High-Resolution Observations of MHD Waves in Photospheric Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Jess, D. B.; Verth, G.

    2016-02-01

    This chapter reviews the recent observations of waves and oscillations manifesting in fine-scale magnetic structures in the solar photosphere, which are often interpreted as the "building blocks' of the magnetic Sun. The authors found, through phase relationships between the various waveforms, that small-scale magnetic bright points (MBPs) in the photosphere demonstrated signatures of specific magnetoacoustic waves, in particular the sausage and kink modes. Modern magnetohydrodynamic (MHD) simulations of the lower solar atmosphere clearly show how torsional motions can easily be induced in magnetic elements in the photosphere through the processes of vortical motions and/or buffeting by neighboring granules. The authors detected significant power associated with high-frequency horizontal motions, and suggested that these cases may be especially important in the creation of a turbulent environment that efficiently promotes Alfvén wave dissipation.

  11. New measurements of photospheric magnetic fields in late-type stars and emerging trends

    NASA Technical Reports Server (NTRS)

    Saar, S. H.; Linsky, J. L.

    1986-01-01

    The magnetic fields of late-type stars are measured using the method of Saar et al. (1986). The method includes radiative transfer effects and compensation for line blending; the photospheric magnetic field parameters are derived by comparing observed and theoretical line profiles using an LTE code that includes line saturation and full Zeeman pattern. The preliminary mean active region magnetic field strengths (B) and surface area coverages for 20 stars are discussed. It is observed that there is a trend of increasing B towards the cooler dwarfs stars, and the linear correlation between B and the equipartition value of the magnetic field strength suggests that the photospheric gas pressure determines the photospheric magnetic field strengths. A tendency toward larger filling factors at larger stellar angular velocities is also detected.

  12. Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability by GLAST

    SciTech Connect

    Battelino, Milan; Ryde, Felix; Omodei, Nicola; Longo, Francesco

    2007-05-01

    The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is the determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration.

  13. Simulation of Prompt Emission from GRBs with a Photospheric Component and its Detectability By GLAST

    SciTech Connect

    Battelino, Milan; Ryde, Felix; Omodei, Nicola; Longo, Francesco; /U. Trieste /INFN, Trieste

    2011-11-29

    The prompt emission from gamma-ray bursts (GRBs) still requires a physical explanation. Studies of time-resolved GRB spectra, observed in the keV-MeV range, show that a hybrid model consisting of two components, a photospheric and a non-thermal component, in many cases fits bright, single-pulsed bursts as well as, and in some instances even better than, the Band function. With an energy coverage from 8 keV up to 300 GeV, GLAST will give us an unprecedented opportunity to further investigate the nature of the prompt emission. In particular, it will give us the possibility to determine whether a photospheric component is the determining feature of the spectrum or not. Here we present a short study of the ability of GLAST to detect such a photospheric component in the sub-MeV range for typical bursts, using simulation tools developed within the GLAST science collaboration.

  14. Relation between the Sunrise photospheric magnetic field and the Ca II H bright features

    NASA Astrophysics Data System (ADS)

    Jafarzadeh, Shahin; Hirzberger, J.; Feller, A.; Lagg, A.; Solanki, S. K.; Pietarila, A.; Danilovic, S.; Riethmueller, T.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knülker, M.; Martínez Pillet, V.; Schmidt, W.; Schüssler, M.; Title, A.

    Recent observations from the Sunrise balloon-borne solar telescope have enabled us to reach an unprecedented high spatial resolution on the solar surface with the near-ultraviolet photo-spheric and chromospheric images as well as the magnetograms. We use these high resolution observations to investigate the structure of the solar upper photosphere and lower chromosphere as well as their temporal evolutions. We study the relation between the inter-granular Ca II 397 nm bright structures in images obtained by the Sunrise Filter Imager (SuFI) and their corresponding photospheric vector magnetic field computed from the Imaging Magnetogram eXperiment (IMaX) observations. The targets under study are in a quiet Sun region and close to disc-centre.

  15. Penumbral-like Structures in the Solar Photosphere: the Role of Flux Emergence

    NASA Astrophysics Data System (ADS)

    Zuccarello, Francesca; Romano, Paolo; Cristaldi, Alice; Falco, Mariachiara; Guglielmino, Salvo L.

    Observations of the solar photosphere rarely show the appearance of so-called orphan penumbrae, filamentary structures very similar to a bundle of sunspot penumbral filaments, but not connected to any umbra. We report on the plasma flows and on the magnetic properties of such structures observed in different active regions using the Solar Optical Telescope on board the Hinode satellite. We also benefit from continuous observations acquired by the SDO satellite and from some high-resolution data acquired by the DOT telescope. We find that these structures can form in different ways: one seems to break off the penumbra of a nearby sunspot, others are formed through the emergence of new flux. Our analysis suggests that, for these latter features, the horizontal component of the emerging field can be trapped in the photosphere by the overlying fields and form a structure resembling penumbral filaments due to the combination of photospheric flux emergence and magneto-convection in inclined fields.

  16. IDENTIFICATION AND PROPERTIES OF THE PHOTOSPHERIC EMISSION IN GRB090902B

    SciTech Connect

    Ryde, F.; McGlynn, S.; Lundman, C.; Battelino, M.; Axelsson, M.; Larsson, S.; Larsson, J.; Zhang, B. B.; Zhang, B.; Pe'er, A.; Bissaldi, E.; McBreen, S.; Bregeon, J.; Briggs, M. S.; Guiriec, S.; Chiang, J.; De Palma, F.; Longo, F.; Omodei, N.; Petrosian, V.

    2010-02-01

    The Fermi Gamma-ray Space Telescope observed the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover the spectral range from 8 keV to >300 GeV. Here we show that the prompt burst spectrum is consistent with emission from the jet photosphere combined with nonthermal emission described by a single power law with photon index -1.9. The photosphere gives rise to a strong quasi-blackbody spectrum which is somewhat broader than a single Planck function and has a characteristic temperature of {approx}290 keV. We model the photospheric emission with a multicolor blackbody, and its shape indicates that the photospheric radius increases at higher latitudes. We derive the averaged photospheric radius R {sub ph} = (1.1 {+-} 0.3) x 10{sup 12} Y {sup 1/4} cm and the bulk Lorentz factor of the flow, which is found to vary by a factor of 2 and has a maximal value of {gamma} = 750 Y {sup 1/4}. Here, Y is the ratio between the total fireball energy and the energy emitted in the gamma rays. We find that during the first quarter of the prompt phase the photospheric emission dominates, which explains the delayed onset of the observed flux in the LAT compared to the GBM. We interpret the broadband emission as synchrotron emission at R {approx} 4 x 10{sup 15} cm. Our analysis emphasizes the importance of having high temporal resolution when performing spectral analysis on gamma-ray bursts, since there is strong spectral evolution.

  17. Identification and Properties of the Photospheric Emission in GRB090902B

    NASA Astrophysics Data System (ADS)

    Ryde, F.; Axelsson, M.; Zhang, B. B.; McGlynn, S.; Pe'er, A.; Lundman, C.; Larsson, S.; Battelino, M.; Zhang, B.; Bissaldi, E.; Bregeon, J.; Briggs, M. S.; Chiang, J.; de Palma, F.; Guiriec, S.; Larsson, J.; Longo, F.; McBreen, S.; Omodei, N.; Petrosian, V.; Preece, R.; van der Horst, A. J.

    2010-02-01

    The Fermi Gamma-ray Space Telescope observed the bright and long GRB090902B, lying at a redshift of z = 1.822. Together the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM) cover the spectral range from 8 keV to >300 GeV. Here we show that the prompt burst spectrum is consistent with emission from the jet photosphere combined with nonthermal emission described by a single power law with photon index -1.9. The photosphere gives rise to a strong quasi-blackbody spectrum which is somewhat broader than a single Planck function and has a characteristic temperature of ~290 keV. We model the photospheric emission with a multicolor blackbody, and its shape indicates that the photospheric radius increases at higher latitudes. We derive the averaged photospheric radius R ph = (1.1 ± 0.3) × 1012 Y 1/4 cm and the bulk Lorentz factor of the flow, which is found to vary by a factor of 2 and has a maximal value of Γ = 750 Y 1/4. Here, Y is the ratio between the total fireball energy and the energy emitted in the gamma rays. We find that during the first quarter of the prompt phase the photospheric emission dominates, which explains the delayed onset of the observed flux in the LAT compared to the GBM. We interpret the broadband emission as synchrotron emission at R ~ 4 × 1015 cm. Our analysis emphasizes the importance of having high temporal resolution when performing spectral analysis on gamma-ray bursts, since there is strong spectral evolution.

  18. CHEMI-IONIZATION IN SOLAR PHOTOSPHERE: INFLUENCE ON THE HYDROGEN ATOM EXCITED STATES POPULATION

    SciTech Connect

    Mihajlov, Anatolij A.; Ignjatovic, Ljubinko M.; Sreckovic, Vladimir A.; Dimitrijevic, Milan S. E-mail: mihajlov@ipb.ac.rs

    2011-03-15

    In this paper, the influence of chemi-ionization processes in H*(n {>=} 2) + H(1s) collisions, as well as the influence of inverse chemi-recombination processes on hydrogen atom excited-state populations in solar photosphere, are compared with the influence of concurrent electron-atom and electron-ion ionization and recombination processes. It has been found that the considered chemi-ionization/recombination processes dominate over the relevant concurrent processes in almost the whole solar photosphere. Thus, it is shown that these processes and their importance for the non-local thermodynamic equilibrium modeling of the solar atmosphere should be investigated further.

  19. Solar abundances from gamma-ray spectroscopy - Comparisons with energetic particle, photospheric, and coronal abundances

    NASA Technical Reports Server (NTRS)

    Murphy, R. J.; Ramaty, R.; Reames, D. V.; Kozlovsky, B.

    1991-01-01

    Accelerated particle and ambient gas abundances have been derived using solar flare gamma-ray spectroscopy. The results with photospheric and coronal abundances, as well as with solar energetic particle abundances. This is the first time that the composition of accelerated particles interacting in an astrophysical source has been compared with the composition of particles escaping from the source. The analysis shows that the derived composition of the accelerated particles is different from the composition of particles observed in large proton flares; rather, it resembles the composition observed in He-3-rich flares. The analysis also suggests an ambient gas composition which differs from the composition of both the photosphere and the corona.

  20. Analyses of the Photospheric Magnetic Dynamics in Solar Active Region 11117 Using an Advanced CESE-MHD Model

    NASA Astrophysics Data System (ADS)

    Jiang, Chaowei; Wu, Shi; Feng, Xueshang

    2016-05-01

    In this study, the photospheric vector magnetograms obtained by Helioseismic and Magnetic Imager on-board the Solar Dynamics Observatory are used as boundary conditions for a CESE-MHD model to investigate some photosphere characteristics around the time of a confined flare in solar active region NOAA AR 11117. We report our attempt of characterizing a more realistic solar atmosphere by including a plasma with temperature stratified from the photosphere to the corona in the CESE-MHD model. The resulted photospheric transverse flow is comparable to the apparent movements of the magnetic flux features that demonstrates shearing and rotations. We calculated the relevant parameters such as the magnetic energy flux and helicity flux, and with analysis of these parameters, we find that magnetic non-potentiality is transported across the photosphere into the corona in the simulated time interval, which might provide a favorable condition for producing the flare.

  1. OBSERVATIONAL EVIDENCE OF CHANGING PHOTOSPHERIC VECTOR MAGNETIC FIELDS ASSOCIATED WITH SOLAR FLARES

    SciTech Connect

    Su, J. T.; Jing, J.; Wang, H. M.; Mao, X. J.; Wang, X. F.; Zhang, H. Q.; Deng, Y. Y.; Guo, J.; Wang, G. P.

    2011-06-01

    Recent observations have provided evidence that the solar photospheric magnetic fields could have rapid and permanent changes in both longitudinal and transverse components associated with major flares. As a result, the Lorentz force (LF) acting on the solar photosphere and solar interior could be perturbed, and the change of LF is always nearly in the downward direction. However, these rapid and permanent changes have not been systematically investigated, yet, using vector magnetograms. In this paper, we analyze photospheric vector magnetograms covering five flares to study the evolution of photospheric magnetic fields. In particular, we investigate two-dimensional spatial distributions of the changing LF. Around the major flaring polarity inversion line, the net change of the LF is directed downward in an area of {approx}10{sup 19} cm{sup 2} for X-class flares. For all events, the white-light observations show that sunspots darken in this location after flares, and magnetic fields become more inclined, which is consistent with the ideas put forward by Hudson et al. and Fisher et al., and observations.

  2. Solar chromospheric spicules from the leakage of photospheric oscillations and flows.

    PubMed

    De Pontieu, Bart; Erdélyi, Robert; James, Stewart P

    2004-07-29

    Spicules are dynamic jets propelled upwards (at speeds of approximately 20 km s(-1)) from the solar 'surface' (photosphere) into the magnetized low atmosphere of the Sun. They carry a mass flux of 100 times that of the solar wind into the low solar corona. With diameters close to observational limits (< 500 km), spicules have been largely unexplained since their discovery in 1877: none of the existing models can account simultaneously for their ubiquity, evolution, energetics and recently discovered periodicity. Here we report a synthesis of modelling and high-spatial-resolution observations in which numerical simulations driven by observed photospheric velocities directly reproduce the observed occurrence and properties of individual spicules. Photospheric velocities are dominated by convective granulation (which has been considered before for spicule formation) and by p-modes (which are solar global resonant acoustic oscillations visible in the photosphere as quasi-sinusoidal velocity and intensity pulsations). We show that the previously ignored p-modes are crucial: on inclined magnetic flux tubes, the p-modes leak sufficient energy from the global resonant cavity into the chromosphere to power shocks that drive upward flows and form spicules. PMID:15282598

  3. Study of the Photospheric Magnetic Field and Coronal Emission from Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Aguilera, Jordan Armando Guerra

    2016-01-01

    Solar explosive phenomena (flares and Coronal Mass Ejections, CMEs) are examples of how the most dynamical processes within the heliosphere are interconnected and powered by the Sun. Solar flares originate in active regions (AR) -- areas of strong magnetic field on the solar surface. The electromagnetic (EM) energy released during flares, along with the often-seen CMEs, propagate through the heliosphere. In the Earth's vicinity, EM radiation and charged particles have the potential to produce unfavorable conditions for humans and technology in space. From many points of view (scientific, operational, economical) it is thus important to understand and try to predict when solar flares and associated eruptive phenomena will occur. This dissertation explores how to best leverage the available observational data to provide predictive information about the future flaring activity. This dissertation consists of two main components: 1) investigation of the photosphere-corona coupling by analyzing photospheric magnetic field and coronal data in search for signals or behaviors that precede eruptions; and 2) the combination of existing flare prediction methods in order to develop a novel ensemble prediction. For the first part, the data employed correspond to line-of-sight (LOS) magnetograms from the Helioseismic and Magnetic Imager (HMI) and EUV intensity maps from the Atmospheric Imaging Assembly (AIA), both instruments onboard NASA's Solar Dynamics Observatory (SDO) satellite. Photospheric magnetic field and coronal EUV emissions were characterized by measuring the power-law decay of their spatio-temporal spectra and the data statistical associations (auto- and cross-correlations). These measures, calculated with high spatio-temporal resolution, appeared to characterize the AR evolution, provide information about the state of the photospheric plasma, reveal insights into the photospheric conditions for flares, and expose the potential of combining coronal and photospheric

  4. The close circumstellar environment of Betelgeuse. IV. VLTI/PIONIER interferometric monitoring of the photosphere

    NASA Astrophysics Data System (ADS)

    Montargès, M.; Kervella, P.; Perrin, G.; Chiavassa, A.; Le Bouquin, J.-B.; Aurière, M.; López Ariste, A.; Mathias, P.; Ridgway, S. T.; Lacour, S.; Haubois, X.; Berger, J.-P.

    2016-04-01

    Context. The mass-loss mechanism of cool massive evolved stars is poorly understood. The proximity of Betelgeuse makes it an appealing target to study its atmosphere, map the shape of its envelope, and follow the structure of its wind from the photosphere out to the interstellar medium. Aims: A link is suspected between the powerful convective motions in Betelgeuse and its mass loss. We aim to constrain the spatial structure and temporal evolution of the convective pattern on the photosphere and to search for evidence of this link. Methods: We report new interferometric observations in the infrared H-band using the VLTI/PIONIER instrument. We monitored the photosphere of Betelgeuse between 2012 January and 2014 November to look for evolutions that may trigger the outflow. Results: Our interferometric observations at low spatial frequencies are compatible with the presence of a hot spot on the photosphere that has a characteristic width of one stellar radius. It appears to be superposed on the smaller scale convective pattern. In the higher spatial frequency domain, we observe a significant difference between the observations and the predictions of 3D hydrodynamical simulations. Conclusions: We bring new evidence for the presence of a convective pattern in the photosphere of red supergiants. The inferred hot spot is probably the top of a giant convection cell although an asymmetric extension of the star cannot be excluded by these interferometric observations alone. The properties of the observed surface features show a stronger contrast and inhomogeneity as predicted by 3D radiative hydrodynamical simulations. We propose that the large observed feature is modifying the signature of the convective pattern at the surface of the star in a way that simulations cannot reproduce. Based on observations made with ESO telescopes at Paranal Observatory, under ESO programs 288.D-5035(A), 090.D-0548(A), 092.D-0366(A), 092.D-0366(B) and 094.D-0869 (A).

  5. Hydraulic concentration of magnetic fields in the solar photosphere. II - Bernoulli effect

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1974-01-01

    The magnetic filaments in the solar photosphere are subject to vigorous kneading and massaging by the convective turbulence at, and beneath, the visible surface. It is shown that the Bernoulli effect of the consequent surging of fluid up and down along the filaments is a major factor in concentrating the magnetic pressure of the filament (the mean square field). The mean field is also increased if the phase velocity of the external massaging exceeds the Alfven speed within the filament. The net observational magnetic result of the surging, then, depends upon the response of the observing instrument, and whether it essentially observes the mean field, the rms field, or whether there are saturation effects. It is suggested that the chromospheric mottles (spicules) seen in H alpha are in fact the intense magnetic filaments that carry most of the magnetic flux across the photospheric boundary of the sun.

  6. Recovering Photospheric Velocities from Vector Magnetograms by using a Three-Dimensional, Fully Magnetohydrodynamic (MHD) Model

    NASA Technical Reports Server (NTRS)

    Wang, A. H.; Wu, S. T.; Liu, Yang; Hathaway, D.

    2008-01-01

    We introduce a numerical simulation method for recovering the photospheric velocity field from the vector magnetograms. The traditional method is local correlation tracking (LCT) which is based on measuring the relative displacements of features in blocks of pixels between successive white-light images or magnetograms. Within this method, there are a variety of implementations. One of recently developed implementations is induction local correlation tracking (ILCT) as described by Welsch et al. (2004). They employ the normal component of magnetic induction equation as a constraint to assure consistent solutions. Our numerical method uses the fully three-dimensional MHD equations to recover the photospheric velocity field with individual vector magnetograms. We compare our method to the ILCT method using NOAA AR8210 as an example. The differences and similarities are discussed in detail.

  7. PHOTOSPHERIC EMISSION AS THE DOMINANT RADIATION MECHANISM IN LONG-DURATION GAMMA-RAY BURSTS

    SciTech Connect

    Lazzati, Davide; Morsony, Brian J.; Margutti, Raffaella; Begelman, Mitchell C.

    2013-03-10

    We present the results of a set of numerical simulations of long-duration gamma-ray burst jets associated with massive, compact stellar progenitors. The simulations extend to large radii and allow us to locate the region in which the peak frequency of the advected radiation is set before the radiation is released at the photosphere. Light curves and spectra are calculated for different viewing angles as well as different progenitor structures and jet properties. We find that the radiation released at the photosphere of matter-dominated jets is able to reproduce the observed Amati and energy-Lorentz factor correlations. Our simulations also predict a correlation between the burst energy and the radiative efficiency of the prompt phase, consistent with observations.

  8. Solar atmospheric dynamics. II - Nonlinear models of the photospheric and chromospheric oscillations

    NASA Technical Reports Server (NTRS)

    Leibacher, J.; Gouttebroze, P.; Stein, R. F.

    1982-01-01

    The one-dimensional, nonlinear dynamics of the solar atmosphere is investigated, and models of the observed photospheric (300 s) and chromospheric (200 s) oscillations are described. These are resonances of acoustic wave cavities formed by the variation of the temperature and ionization between the subphotospheric, hydrogen convection zone and the chromosphere-corona transition region. The dependence of the oscillations upon the excitation and boundary conditions leads to the conclusion that for the observed amplitudes, the modes are independently excited and, as trapped modes, transport little if any mechanical flux. In the upper photosphere and lower chromosphere, where the two modes have comparable energy density, interference between them leads to apparent vertical phase delays which might be interpreted as evidence of an energy flux.

  9. Photospheric abundances of oxygen, neon, and argon derived from the XUV spectrum of an impulsive flare

    SciTech Connect

    Feldman, U.; Widing, K.G. )

    1990-11-01

    Relative elemental abundances of O, Ne, Na, Mg, Ar, and Ca are determined from detailed analysis of XUV spectra emitted by an impulsive flare. The electron density measured from three diagnostic line ratios is 2-3 x 10 to the 12th/cu cm. It was found that the relative abundances in the flare are similar to values obtained from or proposed for photospheric material. The ratios of O/Mg, Ne/Mg, and Ar/Mg are about four times higher in the impulsive flare than the values typically observed in the average corona. It is suggested that electric fields above the photosphere may be responsible for the order of magnitude variations between the abundances of the group of elements with high first ionization potentials (FIP) and the group with low FIP. 18 refs.

  10. Investigation of photospheric temperature gradient variations using limb darkening measurements and simulations

    NASA Astrophysics Data System (ADS)

    Criscuoli, Serena; Foukal, Peter V.

    2016-05-01

    The temperature stratifications of magnetic elements and unmagnetized plasma are different, so that changes of the facular and network filling factor over the cycle modify the average temperature gradient in the photosphere.Such variations have been suggested to explain irradiance measurements obtained by the SIM spectrometers in he visible and infrared spectral ranges. On the other hand, limb darkening measurements show no dependence upon activity level. We investigate the sensitivity of limb darkening to changes in network area filling factor using a 3-D MHD model of the magnetized photosphere. We find that the expected limb darkening change due to the measured 11- yr variation in filling factor lies outside the formal 99% confidence limit of the limb darkening measurements. This poses important constraints for observational validation of 3D-MHD simulations.

  11. Distance determinations using type II supernovae and the expanding photosphere method

    NASA Astrophysics Data System (ADS)

    Dessart, L.; Hillier, D. J.

    2005-08-01

    Due to their high intrinsic brightness, caused by the disruption of the progenitor envelope by the shock-wave initiated at the bounce of the collapsing core, hydrogen-rich (type II) supernovae (SN) can be used as lighthouses to constrain distances in the Universe using variants of the Baade-Wesselink method. Based on a large set of CMFGEN models (Hillier & Miller 1998) covering the photospheric phase of type II SN, we study the various concepts entering one such technique, the Expanding Photosphere Method (EPM). We compute correction factors ξ needed to approximate the synthetic Spectral Energy Distribution (SED) with that of a blackbody at temperature T. Our ξ, although similar, are systematically greater, by ~0.1, than the values obtained by Eastman et al. (1996) and translate into a systematic enhancement of 10-20% in EPM-distances. We find that line emission and absorption, not directly linked to color temperature variations, can considerably alter the synthetic magnitude: in particular, line-blanketing attributable to Fe ii and Ti ii is the principal cause for above-unity correction factors in the B and V bands in hydrogen-recombining models. Following the dominance of electron-scattering opacity in type II SN outflows, the blackbody SED arising at the thermalization depth is diluted, by a factor of approximately 0.2 to 0.4 for fully- or partially-ionized models, but rising to unity as hydrogen recombines for effective temperatures below 9000 K. For a given effective temperature, models with a larger spatial scale, or lower density exponent, have a larger electron-scattering optical depth at the photosphere and consequently suffer enhanced dilution. We also find that when lines are present in the emergent spectrum, the photospheric radius in the corresponding wavelength range can be enhanced by a factor of 2-3 compared to the case when only continuum opacity is considered. Lines can thus nullify the uniqueness of the photosphere radius and invalidate the

  12. Turbulent transport of Small-scale magnetic flux elements on Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Agrawal, Piyush; Rempel, Matthias; Bellot Rubio, Luis; Rast, Mark

    2016-05-01

    We study the transport of small-scale magnetic elements on the solar photosphere using both observations and simulations. Observational data was obtained from Hinode - Solar Optical Telescope (SOT/SP) instrument and simulations from MURaM code. The magnetic flux elements were tracked in both data sets and statistics were obtained. We compute the probability density of the Eulerian distances traveled by the flux elements along Lagrangian trajectories. For a two-dimensional random walk process this distribution should be Rayleigh. Preliminary results show that the measured probability distribution in both the observed and simulated data approximates a random walk, on time scale close to the lifetime of granules, but deviates from it for longer times. This implies that diffusion may not be an appropriate framework for transport in the solar photosphere. We explore the roles of flux cancelation and element trapping in producing this result. Work is ongoing.

  13. The emergence of different polarity photospheric flux as the cause of CMEs and interplanetary shocks

    NASA Technical Reports Server (NTRS)

    Bravo, S.

    1995-01-01

    Here we discuss the effect that the emergence of flux with a polarity opposed to that previously established in a certain photospheric region. can have on the magnetic structure of the solar atmosphere. We show that such a flux emergence may lead to the ejection of coronal material into the interplanetary medium (a CME) and also to a rapid change in the velocity of the solar wind from the region, which may eventually lead to the formation of an interplanetary shock.

  14. 22 year cycle in the imbalance of the photospheric magnetic fluxes

    NASA Astrophysics Data System (ADS)

    Vernova, Elena; Baranov, Dmitrii; Tyasto, Marta

    The manifestation of the 22 year solar magnetic cycle in the imbalance of positive and negative photospheric magnetic fluxes is studied. For the analysis we use synoptic maps of the photospheric magnetic field of Kitt Peak Observatory (1976 - 2003) and John Wilcox Observatory in Stanford (1976 - 2012). We consider strong magnetic fields for the heliolatitudes in the interval from +40° to -40°. It is shown that the sign of the imbalance between positive and negative fluxes remains constant during 11 years from one inversion of the Sun’s global magnetic field to the next one and always coincides with the sign of the polar field in the Northern hemisphere. Thus, the imbalance between the magnetic fluxes of different polarities changes according to the 22 year cycle. The sign of the imbalance is determined both by the phase of the solar cycle (before or after the inversion) and by the parity of the solar cycle. The imbalance of positive and negative magnetic fluxes can be observed not only for the strong fields in the sunspot zone. The mean magnetic field of the Sun (Sun as a star), which is determined by the net flux of the background fields, changes according to the same pattern as the imbalance of the strong fields. The regular changes of the imbalance of the photospheric magnetic fields are reflected also in the parameters of heliosphere. We show the connection of the imbalance with the quadrupole component of the photospheric magnetic field and with the imbalance of the interplanetary magnetic field (the difference between the numbers of the days with positive and negative polarities of the interplanetary magnetic field near Earth).

  15. GENERATION OF MAGNETOHYDRODYNAMIC WAVES IN LOW SOLAR ATMOSPHERIC FLUX TUBES BY PHOTOSPHERIC MOTIONS

    SciTech Connect

    Mumford, S. J.; Fedun, V.; Erdélyi, R.

    2015-01-20

    Recent ground- and space-based observations reveal the presence of small-scale motions between convection cells in the solar photosphere. In these regions, small-scale magnetic flux tubes are generated via the interaction of granulation motion and the background magnetic field. This paper studies the effects of these motions on magnetohydrodynamic (MHD) wave excitation from broadband photospheric drivers. Numerical experiments of linear MHD wave propagation in a magnetic flux tube embedded in a realistic gravitationally stratified solar atmosphere between the photosphere and the low choromosphere (above β = 1) are performed. Horizontal and vertical velocity field drivers mimic granular buffeting and solar global oscillations. A uniform torsional driver as well as Archimedean and logarithmic spiral drivers mimic observed torsional motions in the solar photosphere. The results are analyzed using a novel method for extracting the parallel, perpendicular, and azimuthal components of the perturbations, which caters to both the linear and non-linear cases. Employing this method yields the identification of the wave modes excited in the numerical simulations and enables a comparison of excited modes via velocity perturbations and wave energy flux. The wave energy flux distribution is calculated to enable the quantification of the relative strengths of excited modes. The torsional drivers primarily excite Alfvén modes (≈60% of the total flux) with small contributions from the slow kink mode, and, for the logarithmic spiral driver, small amounts of slow sausage mode. The horizontal and vertical drivers primarily excite slow kink or fast sausage modes, respectively, with small variations dependent upon flux surface radius.

  16. Generation of Magnetohydrodynamic Waves in Low Solar Atmospheric Flux Tubes by Photospheric Motions

    NASA Astrophysics Data System (ADS)

    Mumford, S. J.; Fedun, V.; Erdélyi, R.

    2015-01-01

    Recent ground- and space-based observations reveal the presence of small-scale motions between convection cells in the solar photosphere. In these regions, small-scale magnetic flux tubes are generated via the interaction of granulation motion and the background magnetic field. This paper studies the effects of these motions on magnetohydrodynamic (MHD) wave excitation from broadband photospheric drivers. Numerical experiments of linear MHD wave propagation in a magnetic flux tube embedded in a realistic gravitationally stratified solar atmosphere between the photosphere and the low choromosphere (above β = 1) are performed. Horizontal and vertical velocity field drivers mimic granular buffeting and solar global oscillations. A uniform torsional driver as well as Archimedean and logarithmic spiral drivers mimic observed torsional motions in the solar photosphere. The results are analyzed using a novel method for extracting the parallel, perpendicular, and azimuthal components of the perturbations, which caters to both the linear and non-linear cases. Employing this method yields the identification of the wave modes excited in the numerical simulations and enables a comparison of excited modes via velocity perturbations and wave energy flux. The wave energy flux distribution is calculated to enable the quantification of the relative strengths of excited modes. The torsional drivers primarily excite Alfvén modes (≈60% of the total flux) with small contributions from the slow kink mode, and, for the logarithmic spiral driver, small amounts of slow sausage mode. The horizontal and vertical drivers primarily excite slow kink or fast sausage modes, respectively, with small variations dependent upon flux surface radius.

  17. Photospheric and chromospheric active regions on three single-lined RS CVn binaries

    NASA Astrophysics Data System (ADS)

    Biazzo, K.; Frasca, A.; Catalano, S.; Marilli, E.

    2006-02-01

    A monitoring of three active RS CVn binaries has been performed with medium resolution spectroscopy with the aim of investigating the behavior of chromospheric and photospheric inhomogeneities. Surface temperature, as recovered from line-depth ratios (LDRs), allowed us to map the photospheric spots, while the Hα emission has been used as an indicator of chromospheric inhomogeneities. We have found that the rotational modulation of the Hα emission is always in anti-phase with the temperature wave, i.e. at the time of our observations active regions at chromospheric and photospheric levels are closely spatially associated in these active stars. The residual Hα profiles, obtained as the difference between the observed spectra and non-active templates, are well reproduced by a two Gaussian fitting. The broad emission component, responsible for the wide emission wings in near all the spectra, is often blue-shifted with respect to the center of the stellar disk. The narrow Hα emission displays a phase-dependent variation in all stars and is anti-correlated with the photospheric diagnostics, while the broad one displays no or little rotational modulation. We suggest that the broad emission component is mainly related to physical phenomena, like micro-flaring or strong chromospheric velocity fields, occurring all over the star disk, while the central narrow emission is more affected by chromospheric plages. We have also detected a modulation of the intensity of the He I D3 line with the star rotation, suggesting surface features also in the upper chromosphere of these stars.

  18. Coronal structures deduced from photospheric magnetic field and He I lambda 10830 observations

    NASA Technical Reports Server (NTRS)

    Harvey, Karen L.

    1995-01-01

    The National Solar Observatory synoptic program provides an extensive and unique data base of high-resolution full-disk observations of the line-of-sight photospheric magnetic fields and of the He I lambda 10830 equivalent width. These data have been taken nearly daily for more than 21 years since 1974 and provide the opportunity to investigate the behavior of the magnetic fields in the photosphere and those inferred for the corona spanning on the time scales of a day to that of a solar cycle. The intensity of structures observed in He I lambda 10830 are strongly modulated by overlying coronal radiation; areas with low coronal emission are generally brighter in He I lambda 10830, while areas with high coronal emission are darker. For this reason, He I lambda 10830 was selected in the mid-1970's as way to identify and monitor coronal holes, magnetic fields with an open configuration, and the sources of high-speed solar wind streams. The He I lambda 10830 spectroheliograms also show a wide variety of other structures from small-scale, short-lived dark points (less than 30 arc-sec, hours) to the large-scale, long-lived two 'ribbon' flare events that follow the filament eruptions (1000 arc-sec, days). Such structures provide clues about the connections and changes in the large-scale coronal magnetic fields that are rooted in concentrations of magnetic network and active regions in the photosphere. In this paper, what observations of the photospheric magnetic field and He I lambda 10830 can tell us about the short- and long-term evolution of the coronal magnetic fields will be discussed, focussing on the quiet Sun and coronal holes. These data and what we infer from them will be compared with direct observations of the coronal structure from the Yohkoh Soft X-ray Telescope.

  19. North south asymmetry in the photospheric and coronal magnetic fields observed by different instruments

    NASA Astrophysics Data System (ADS)

    Virtanen, Ilpo; Mursula, Kalevi

    2015-04-01

    Several recent studies have shown that the solar and heliospheric magnetic fields are north-south asymmetric. The southward shift of the Heliospheric current sheet (HCS) (the so-called bashful ballerina phenomenon) is a persistent pattern, which occurs typically for about three years during the late declining phase of solar cycle. We study here the hemispherical asymmetry in the photospheric and coronal magnetic fields using Wilcox Solar Observatory (WSO), Mount Wilson, Kitt Peak, Solis, SOHO/MDI and SDO/HMI measurements of the photospheric magnetic field since the 1970s and the potential field source surface (PFSS) model.Multipole analysis of the photospheric magnetic field has shown that the bashful ballerina phenomenon is a consequence of g20 quadrupole term, which is oppositely signed to the dipole moment. We find that, at least during the four recent solar cycles, the g20 reflects the larger magnitude of the southern polar field during a few years in the declining phase of the cycle. Although the overall magnetic activity during the full solar cycle is not very different in the two hemispheres, the temporal distribution of activity is different, contributing to the asymmetry. The used data sets are in general in a good agreement with each other, but there are some significant deviations, especially in WSO data. Also, the data from Kitt Peak 512 channel magnetograph is known to suffer from zero level errors.We also note that the lowest harmonic coefficients do not scale with the overall magnitude in photospheric synoptic magnetic maps. Scaling factors based on histogram techniques can be as large as 10 (from Wilcox to HMI), but the corresponding difference in dipole strength is typically less than two. This is because the polar field has a dominant contribution to the dipole and quadrupole components. This should be noted, e.g., when using synoptic maps as input for coronal models.

  20. Photospheric and coronal abundances of solar-type stars with planets: the case of τ Bootis

    NASA Astrophysics Data System (ADS)

    Maggio, Antonio; Sanz-Forcada, Jorge; Scelsi, Luigi

    2010-03-01

    We present the results of a study of coronal and photospheric abundances in τ Bootis, a middle-aged solar analogue, well known for the presence of a close-in Jovian mass planet. We employ the results of this study, based on high-resolution optical and X-ray spectra, to address the issue of abundance stratification vs. First Ionization Potential (FIP) in the outer stellar atmospheres of solar-type stars with and without planets.

  1. A LIGHT CURVE ANALYSIS OF CLASSICAL NOVAE: FREE-FREE EMISSION VERSUS PHOTOSPHERIC EMISSION

    SciTech Connect

    Hachisu, Izumi; Kato, Mariko E-mail: mariko@educ.cc.keio.ac.jp

    2015-01-10

    We analyzed light curves of seven relatively slower novae, PW Vul, V705 Cas, GQ Mus, RR Pic, V5558 Sgr, HR Del, and V723 Cas, based on an optically thick wind theory of nova outbursts. For fast novae, free-free emission dominates the spectrum in optical bands rather than photospheric emission, and nova optical light curves follow the universal decline law. Faster novae blow stronger winds with larger mass-loss rates. Because the brightness of free-free emission depends directly on the wind mass-loss rate, faster novae show brighter optical maxima. In slower novae, however, we must take into account photospheric emission because of their lower wind mass-loss rates. We calculated three model light curves of free-free emission, photospheric emission, and their sum for various white dwarf (WD) masses with various chemical compositions of their envelopes and fitted reasonably with observational data of optical, near-IR (NIR), and UV bands. From light curve fittings of the seven novae, we estimated their absolute magnitudes, distances, and WD masses. In PW Vul and V705 Cas, free-free emission still dominates the spectrum in the optical and NIR bands. In the very slow novae, RR Pic, V5558 Sgr, HR Del, and V723 Cas, photospheric emission dominates the spectrum rather than free-free emission, which makes a deviation from the universal decline law. We have confirmed that the absolute brightnesses of our model light curves are consistent with the distance moduli of four classical novae with known distances (GK Per, V603 Aql, RR Pic, and DQ Her). We also discussed the reason why the very slow novae are about ∼1 mag brighter than the proposed maximum magnitude versus rate of decline relation.

  2. MAGNETIC AND DYNAMICAL PHOTOSPHERIC DISTURBANCES OBSERVED DURING AN M3.2 SOLAR FLARE

    SciTech Connect

    Kuckein, C.; Collados, M.; Sainz, R. Manso

    2015-02-01

    This Letter reports on a set of full-Stokes spectropolarimetric observations in the near-infrared He i 10830 Å spectral region covering the pre-flare, flare, and post-flare phases of an M3.2 class solar flare. The flare originated on 2013 May 17 and belonged to active region NOAA 11748. We detected strong He i 10830 Å emission in the flare. The red component of the He i triplet peaks at an intensity ratio to the continuum of about 1.86. During the flare, He i Stokes V is substantially larger and appears reversed compared to the usually larger Si i Stokes V profile. The photospheric Si i inversions of the four Stokes profiles reveal the following: (1) the magnetic field strength in the photosphere decreases or is even absent during the flare phase, as compared to the pre-flare phase. However, this decrease is not permanent. After the flare, the magnetic field recovers its pre-flare configuration in a short time (i.e., 30 minutes after the flare). (2) In the photosphere, the line of sight velocities show a regular granular up- and downflow pattern before the flare erupts. During the flare, upflows (blueshifts) dominate the area where the flare is produced. Evaporation rates of ∼10{sup −3} and ∼10{sup −4} g cm{sup −2} s{sup −1} have been derived in the deep and high photosphere, respectively, capable of increasing the chromospheric density by a factor of two in about 400 s.

  3. SUPERNOVA RESONANCE-SCATTERING LINE PROFILES IN THE ABSENCE OF A PHOTOSPHERE

    SciTech Connect

    Friesen, Brian; Baron, E.; Branch, David; Chen Bin; Parrent, Jerod T.; Thomas, R. C.

    2012-11-15

    In supernova (SN) spectroscopy relatively little attention has been given to the properties of optically thick spectral lines in epochs following the photosphere's recession. Most treatments and analyses of post-photospheric optical spectra of SNe assume that forbidden-line emission comprises most if not all spectral features. However, evidence exists that suggests that some spectra exhibit line profiles formed via optically thick resonance-scattering even months or years after the SN explosion. To explore this possibility, we present a geometrical approach to SN spectrum formation based on the 'Elementary Supernova' model, wherein we investigate the characteristics of resonance-scattering in optically thick lines while replacing the photosphere with a transparent central core emitting non-blackbody continuum radiation, akin to the optical continuum provided by decaying {sup 56}Co formed during the explosion. We develop the mathematical framework necessary for solving the radiative transfer equation under these conditions and calculate spectra for both isolated and blended lines. Our comparisons with analogous results from the Elementary Supernova code SYNOW reveal several marked differences in line formation. Most notably, resonance lines in these conditions form P Cygni-like profiles, but the emission peaks and absorption troughs shift redward and blueward, respectively, from the line's rest wavelength by a significant amount, despite the spherically symmetric distribution of the line optical depth in the ejecta. These properties and others that we find in this work could lead to misidentification of lines or misattribution of properties of line-forming material at post-photospheric times in SN optical spectra.

  4. GRB 110721A: PHOTOSPHERE 'DEATH LINE' AND THE PHYSICAL ORIGIN OF THE GRB BAND FUNCTION

    SciTech Connect

    Zhang Bing; Lu Ruijing; Liang Enwei; Wu Xuefeng

    2012-10-20

    The prompt emission spectra of gamma-ray bursts (GRBs) usually have a dominant component that is well described by a phenomenological Band function. The physical origin of this spectral component is debated. Although the traditional interpretation is synchrotron radiation of non-thermal electrons accelerated in internal shocks or magnetic dissipation regions, the growing trend within the community is to interpret this component as modified thermal emission from a dissipative photosphere of a GRB fireball. We analyze the time-dependent spectrum of GRB 110721A detected by the Fermi Gamma-Ray Burst Monitor and Large Area Telescope, and pay special attention to the rapid evolution of the peak energy E{sub p} . We define a 'death line' of thermally dominated dissipative photospheric emission in the E{sub p} -L plane, and show that E{sub p} of GRB 110721A at the earliest epoch has a very high E{sub p} {approx} 15 MeV that is beyond the 'death line'. Together with the finding that an additional 'shoulder' component exists in this burst that is consistent with a photospheric origin, we suggest that at least for some bursts, the Band component is not from a dissipative photosphere, but must invoke a non-thermal origin (e.g., synchrotron or inverse Compton) in the optically thin region of a GRB outflow. We also suggest that the rapid hard-to-soft spectral evolution is consistent with the quick discharge of magnetic energy in a magnetically dominated outflow in the optically thin region.

  5. PENUMBRAL-LIKE FILAMENTS IN THE SOLAR PHOTOSPHERE AS A MANIFESTATION OF FLUX EMERGENCE

    SciTech Connect

    Guglielmino, Salvo L.; Zuccarello, Francesca; Romano, Paolo

    2014-05-10

    Rare observations of the solar photosphere show the appearance of orphan penumbrae, filamentary structures very similar to a bundle of sunspot penumbral filaments not connected to any umbra. Lim et al. found an orphan penumbra in active region NOAA 11391 near a mature sunspot. We analyze a different data set to study the same structure using the Solar Optical Telescope on board the Hinode satellite. Spectropolarimetric measurements along the Fe I 630.2 nm pair, complemented by G-band and Ca II H filtergrams, show the evolution of this penumbral-like structure and reveal that an emerging flux region is its ancestor. We find new evidence for the interaction between the emerging flux and the pre-existing field that leads to a brightening observed near the base of the chromosphere. Our analysis suggests that as a result of the combination of photospheric flux emergence and magneto-convection in inclined fields the horizontal component of the emerging field can be trapped in the photosphere by the overlying fields and form a structure resembling penumbral filaments.

  6. THE PHOTOSPHERIC ENERGY AND HELICITY BUDGETS OF THE FLUX-INJECTION HYPOTHESIS

    SciTech Connect

    Schuck, P. W.

    2010-05-01

    The flux-injection hypothesis for driving coronal mass ejections (CMEs) requires the transport of substantial magnetic energy and helicity flux through the photosphere concomitant with the eruption. Under the magnetohydrodynamics approximation, these fluxes are produced by twisting magnetic field and/or flux emergence in the photosphere. A CME trajectory, observed 2000 September 12 and fitted with a flux-rope model, constrains energy and helicity budgets for testing the flux-injection hypothesis. Optimal velocity profiles for several driving scenarios are estimated by minimizing the photospheric plasma velocities for a cylindrically symmetric flux-rope magnetic field subject to the flux budgets required by the flux-rope model. Ideal flux injection, involving only flux emergence, requires hypersonic upflows in excess of the solar escape velocity 617 km s{sup -1} over an area of 6 x 10{sup 8} km{sup 2} to satisfy the energy and helicity budgets of the flux-rope model. These estimates are compared with magnetic field and Doppler measurements from Solar and Heliospheric Observatory/Michelson Doppler Imager on 2000 September 12 at the footpoints of the CME. The observed Doppler signatures are insufficient to account for the required energy and helicity budgets of the flux-injection hypothesis.

  7. Numerical Investigations of Capabilities and Limits of Photospheric Data Driven Magnetic Flux Emergence

    NASA Astrophysics Data System (ADS)

    Linton, Mark; Leake, James; Schuck, Peter W.

    2016-05-01

    The magnetic field of the solar atmosphere is the primary driver of solar activity. Understanding the magnetic state of the solar atmosphere is therefore of key importance to predicting solaractivity. One promising means of studying the magnetic atmosphere is to dynamically build up and evolve this atmosphere from the time evolution of the magnetic field at the photosphere, where it can be measured with current solar vector magnetograms at high temporal and spatial resolution.We report here on a series of numerical experiments investigating the capabilities and limits of magnetohydrodynamical simulations of such a process, where a magnetic corona is dynamically built up and evolved from a time series of synthetic photospheric data. These synthetic data are composed of photospheric slices taken from self consistent convection zone to corona simulations of flux emergence. The driven coronae are then quantitatively compared against the coronae of the original simulations. We investigate and report on the fidelity of these driven simulations, both as a function of the emergence timescale of the magnetic flux, and as a function of the driving cadence of the input data.This work was supported by the Chief of Naval Research and the NASA Living with a Star and Heliophysics Supporting Research programs.

  8. New Measurements of the Radio Photosphere of Mira Based on Data from the JVLA and ALMA

    NASA Astrophysics Data System (ADS)

    Matthews, L. D.; Reid, M. J.; Menten, K. M.

    2015-07-01

    We present new measurements of the millimeter wavelength continuum emission from the long period variable Mira (o Ceti) at frequencies of 46, 96, and 229 GHz (λ ≈ 7, 3, and 1 mm) based on observations obtained with the Jansky Very Large Array (JVLA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities are consistent with a radio photosphere model derived from previous observations, where flux density {S}ν \\propto {ν }1.86. The stellar disk is resolved, and the measurements indicate a decrease in the size of the radio photosphere at higher frequencies, as expected if the opacity decreases at shorter wavelengths. The shape of the radio photosphere is found to be slightly elongated, with a flattening of ∼10%–20%. The data also reveal evidence for brightness non-uniformities on the surface of Mira at radio wavelengths. Mira’s hot companion, Mira B was detected at all three observed wavelengths, and we measure a radius for its radio-emitting surface of ≈ 2.0× {10}13 cm. The data presented here highlight the power of the JVLA and ALMA for the study of the atmospheres of evolved stars.

  9. Velocity and Temperature Response Functions of 77 Near-Infrared (800 - 1400 nm) Photospheric Lines - I

    NASA Astrophysics Data System (ADS)

    Penza, V.; Berrilli, F.

    2012-04-01

    We present a new list of solar photospheric lines in the near-infrared (NIR) region obtained by synthesis under local thermodynamic equilibrium (LTE) approximation. We give novel velocity and temperature response functions (RFs) for 77 lines over the spectral range 800 - 1400 nm. Using these RFs, we are able to obtain for each line the core formation height and the range of atmospheric layers where thermodynamic perturbations are dominant. Moreover, by using the depth-integrated RFs, we give an indication of the dependence on the wavelength of the RFs and quantify their sensitivity to thermodynamic variations. The NIR region represents a significant source of interest for spectroscopic and polarimetric studies. Indeed, at these wavelengths we explore the deeper photospheric layers, and the Zeeman splitting is larger than in the visible range. Several research fields in solar astrophysics ( e.g., photospheric and chromospheric dynamics, magnetoconvection in active regions, and interaction between solar plasma and magnetic field) should benefit from using this new line list. Moreover, various new NIR instruments are planned for future space missions or next generation ground-based solar telescopes, such as the European Solar Telescope (EST) or the Advanced Technology Solar Telescope (ATST).

  10. Photospheric and Coronal Observations of Abrupt Magnetic Restructuring in Two Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Petrie, Gordon

    2016-05-01

    For two major X-class flares observed by the Solar Dynamics Observatory (SDO) and the Solar TErrestrial RElations Observatory Ahead (STEREO-A) spacecraft when they were close to quadrature, we compare major, abrupt changes in the photospheric magnetic vector field to changes in the observed coronal magnetic structure during the two flares. The Lorentz force changes in strong photospheric fields within active regions are estimated from time series of SDO Helioseismic and Magnetic Imager (HMI) vector magnetograms. These show that the major changes occurred in each case near the main neutral line of the region and in two neighboring twisted opposite-polarity sunspots. In each case the horizontal parallel field strengthened significantly near the neutral line while the azimuthal field in the sunspots decreased, suggesting that a flux rope joining the two sunspots collapsed across the neutral line with reduced magnetic pressure because of a reduced field twist component. At the same time, the coronal extreme ultraviolet (EUV) loop structure was observed by the Atmospheric Imaging Assembly (AIA) onboard SDO and the Extreme Ultraviolet Imager (EUVI) on STEREO-A to decrease significantly in height during each eruption, discontinuous changes signifying ejection of magnetized plasma, and outward-propagating continuous but abrupt changes consistent with loop contraction. An asymmetry in the observed EUV loop changes during one of the flares matches an asymmetry in the photospheric magnetic changes associated with that flare. The observations are discussed in terms of the well-known tether-cutting and breakout flare initiation models.

  11. Different Modes of Turbulence in the Active Regions of the Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Kozak, L. V.; Kostik, R. I.; Cheremnykh, O. K.

    In work the range of different methods for the analysis of characteristics of turbulent processes in the active regions of the solar photosphere has been used. The changes of fluctuations distribution function and its moments were analyzed, spectral analysis was carried out.It was found out from the observations of active region carried out with the 70-cm vacuum tower telescope VTT in Isanie (Tenerife Island, Spain) that the turbulent processes in the sun photosphere are characterized by two different spectra of turbulence. The first one of them is well known Kolmohorov spectrum, which describes the plasma with zero mean magnetic field. The second one is the Kraichnan spectrum with a different from zero mean magnetic field. Transition from one spectrum type to another one occurs at scale of 3 Mm.We have to note that the scale 3 Mm corresponds to one of mesogranulation and testifies about non-zero mean magnetic fields for the consideration of regions exceeding the granulation in active regions of the photosphere. Besides, this clears the possibility of appearance of selforganizing magnetic plasma structures such as spots, active regions and complexes of activity.

  12. Penumbral-like Filaments in the Solar Photosphere as a Manifestation of Flux Emergence

    NASA Astrophysics Data System (ADS)

    Guglielmino, Salvo L.; Zuccarello, Francesca; Romano, Paolo

    2014-05-01

    Rare observations of the solar photosphere show the appearance of orphan penumbrae, filamentary structures very similar to a bundle of sunspot penumbral filaments not connected to any umbra. Lim et al. found an orphan penumbra in active region NOAA 11391 near a mature sunspot. We analyze a different data set to study the same structure using the Solar Optical Telescope on board the Hinode satellite. Spectropolarimetric measurements along the Fe I 630.2 nm pair, complemented by G-band and Ca II H filtergrams, show the evolution of this penumbral-like structure and reveal that an emerging flux region is its ancestor. We find new evidence for the interaction between the emerging flux and the pre-existing field that leads to a brightening observed near the base of the chromosphere. Our analysis suggests that as a result of the combination of photospheric flux emergence and magneto-convection in inclined fields the horizontal component of the emerging field can be trapped in the photosphere by the overlying fields and form a structure resembling penumbral filaments.

  13. Photospheric Abundances of Polar Jets on the Sun Observed by Hinode

    NASA Astrophysics Data System (ADS)

    Lee, Kyoung-Sun; Brooks, David H.; Imada, Shinsuke

    2015-08-01

    Many jets are detected at X-ray wavelengths in the Sun's polar regions, and the ejected plasma along the jets has been suggested to contribute mass to the fast solar wind. From in situ measurements in the magnetosphere, it has been found that the fast solar wind has photospheric abundances while the slow solar wind has coronal abundances. Therefore, we investigated the abundances of polar jets to determine whether they are the same as that of the fast solar wind. For this study, we selected 22 jets in the polar region observed by Hinode/EUV Imaging Spectroscopy (EIS) and X-ray Telescope (XRT) simultaneously on 2007 November 1-3. We calculated the First Ionization Potential (FIP) bias factor from the ratio of the intensity between high (S) and low (Si, Fe) FIP elements using the EIS spectra. The values of the FIP bias factors for the polar jets are around 0.7-1.9, and 75% of the values are in the range of 0.7-1.5, which indicates that they have photospheric abundances similar to the fast solar wind. The results are consistent with the reconnection jet model where photospheric plasma emerges and is rapidly ejected into the fast wind.

  14. Photospheric and Coronal Observations of Abrupt Magnetic Restructuring in Two Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Petrie, G. J. D.

    2016-03-01

    For two major X-class flares observed by the Solar Dynamics Observatory (SDO) and the Solar TErrestrial RElations Observatory Ahead (STEREO-A) spacecraft when they were close to quadrature, we compare major, abrupt changes in the photospheric magnetic vector field to changes in the observed coronal magnetic structure during the two flares. The Lorentz force changes in strong photospheric fields within active regions are estimated from time series of SDO Helioseismic and Magnetic Imager (HMI) vector magnetograms. These show that the major changes occurred in each case near the main neutral line of the region and in two neighboring twisted opposite-polarity sunspots. In each case the horizontal parallel field strengthened significantly near the neutral line while the azimuthal field in the sunspots decreased, suggesting that a flux rope joining the two sunspots collapsed across the neutral line with reduced magnetic pressure because of a reduced field twist component. At the same time, the coronal extreme ultraviolet (EUV) loop structure was observed by the Atmospheric Imaging Assembly (AIA) onboard SDO and the Extreme Ultraviolet Imager (EUVI) on STEREO-A to decrease significantly in height during each eruption, discontinuous changes signifying ejection of magnetized plasma, and outward-propagating continuous but abrupt changes consistent with loop contraction. An asymmetry in the observed EUV loop changes during one of the flares matches an asymmetry in the photospheric magnetic changes associated with that flare. The observations are discussed in terms of the well-known tether-cutting and breakout flare initiation models.

  15. Magnetic and Velocity Field of Sunspots in the Photosphere and Upper Chromosphere

    NASA Astrophysics Data System (ADS)

    Joshi, Jayant

    2014-03-01

    Sunspots, the dark blemishes on the solar surface have been widely studied for the past 400 years. Sunspots are the most readily identifiable manifestation of magnetic field concentrations on the solar surface. Interaction of the sunspot magnetic field with the plasma makes them one of the most interesting objects for research in solar physics. This thesis presents a study of the photospheric and upper chromospheric velocity and magnetic field structure of sunspots by analyzing spectro-polarimetric observations. These observations comprise different spectral lines obtained with two ground based telescopes and a space borne telescope. The lower brightness of sunspots on the solar surface is due to the presence of strong magnetic fields (up to 4 kG in the umbra), which makes the overturning convection inefficient. Convection is the main heat transport mechanism in the quiet Sun. The Penumbra, the annular part around the umbra has a brightness of about 75% of that in the quiet Sun. At the same time it has an average magnetic field strength of around 1.5 kG. The brightness of penumbrae has been an enigma for solar physicists for a long time. Theoretical models like the gappy penumbra model and the convective roll model as well as magnetohydrodynamic (MHD) simulations suggest that the heat transport in penumbrae is based on the presence of overturning convection. Direct observational evidence for the presence of convective flows in penumbral filaments was missing so far. In Chapter 3 we present observations of a penumbra in the C i 5380 Å spectral line formed in the deep photosphere. These high spatial resolution observations (0. '' 14) are obtained with the Swedish 1-m Solar Telescope (SST). Doppler map clearly shows the presence of several dark downflow lanes at the edges of the penumbral filaments which surround the bright upflows at the center of the filaments, supporting overturning convection as a mechanism of heat transport in penumbrae. Chapter 4 analyses the

  16. Statistical study of photospheric bright points in an active region and quiet Sun

    NASA Astrophysics Data System (ADS)

    Feng, Song; Deng, Linhua; Yang, Yunfei; Ji, Kaifan

    2013-11-01

    The statistical properties of photospheric bright points (PBPs) in active regions (ARs) and the quiet Sun (QS) are investigated using two data sets obtained with the Dutch Open Telescope. Data for AR NOAA 10642 (July 12, 2004) and the QS (October 19, 2005) near the disk center are analyzed. For extracting PBPs, an automatic algorithm, employing Laplacian and morphological dilation (LMD) technique, is developed. The statistical properties of PBPs such as size distribution, contrast between maximum of PBPs and mean photospheric intensity, area coverage, number coverage and geometric shape are quantified. We then use goodness-of-fit to evaluate the fit of the size distribution of PBPs in the two regions. Finally, the Kolmogorov-Smirnov test is used to analyze the statistical difference in the AR and the QS. The following results are obtained: (1) the size distributions (probability density function) of PBPs in the two regions follow a lognormal distribution, moreover they are from the same size distribution; (2) the number coverage and the area coverage in the AR are about twice larger than those in the QS, respectively; (3) the geometrical shape of PBPs is quantified by the ratio of the length of major axis to the length of minor axis by the center of gravity. The ratio of about 50 % PBPs is less than 1.5, and their geometrical shapes are exactly alike in the two regions; (4) the ratio of maximum intensity of PBPs to their corresponding mean photospheric intensity is larger in the AR than in the QS. The results suggest that size and shape of PBPs in the AR and the QS are just the same, but the brightness of PBPs in the AR is different from that in the QS.

  17. Zeeman-tomography of the solar photosphere. Three-dimensional surface structures retrieved from Hinode observations

    NASA Astrophysics Data System (ADS)

    Carroll, T. A.; Kopf, M.

    2008-04-01

    Aims:The thermodynamic and magnetic field structure of the solar photosphere is analyzed by means of a novel 3-dimensional spectropolarimetric inversion and reconstruction technique. Methods: On the basis of high-resolution, mixed-polarity magnetoconvection simulations, we used an artificial neural network (ANN) model to approximate the nonlinear inverse mapping between synthesized Stokes spectra and the underlying stratification of atmospheric parameters like temperature, line-of-sight (LOS) velocity and LOS magnetic field. This approach not only allows us to incorporate more reliable physics into the inversion process, it also enables the inversion on an absolute geometrical height scale, which allows the subsequent combination of individual line-of-sight stratifications to obtain a complete 3-dimensional reconstruction (tomography) of the observed area. Results: The magnetoconvection simulation data, as well as the ANN inversion, have been properly processed to be applicable to spectropolarimetric observations from the Hinode satellite. For the first time, we show 3-dimensional tomographic reconstructions (temperature, LOS velocity, and LOS magnetic field) of a quiet sun region observed by Hinode. The reconstructed area covers a field of approximately 12 000 × 12 000 km and a height range of 510 km in the photosphere. An enormous variety of small and large scale structures can be identified in the 3-D reconstructions. The low-flux region (B_mag = 20 G) we analyzed exhibits a number of tube-like magnetic structures with field strengths of several hundred Gauss. Most of these structures rapidly loose their strength with height and only a few larger structures can retain a higher field strength to the upper layers of the photosphere.

  18. Study of FK Comae Berenices. VII. Correlating photospheric and chromospheric activity

    NASA Astrophysics Data System (ADS)

    Vida, K.; Korhonen, H.; Ilyin, I. V.; Oláh, K.; Andersen, M. I.; Hackman, T.

    2015-08-01

    Aims: We study the connection between the chromospheric and photospheric behaviour of the active late-type star FK Comae. Methods: We use spot temperature modelling, light curve inversion based on narrow- and wide-band photometric measurements, Hα observations from 1997-2010, and Doppler maps from 2004-2010 to compare the behaviour of chromospheric and photospheric features. Results: Investigating low-resolution Hα spectra, we find that the changes in the chromosphere seem to happen mainly on a time scale longer than a few hours, but shorter variations are also observed. According to the Hα measurements, prominences are often found in the chromosphere that reach to more than a stellar radius and are stable for weeks, and they seem to be often, but not always connected to dark photospheric spots. The rotational modulation of the Hα emission typically seems to be anticorrelated with the light curve, but we did not find convincing evidence of a clear connection in the long-term trends of the Hα emission and the brightness of the star. In addition, FK Com seems to be in an unusually quiet state in 2009-2010 with very little chromospheric activity and low spot contrast, which might indicate the long-term decrease in activity. Based on the observations obtained at the Nordic Optical Telescope, Observatorio Roque de los Muchachos, La Palma, Canary Islands, Spain; Kitt Peak National Observatory, USA.Figures 12, 13, and Appendix A are available in electronic form at http://www.aanda.orgNew data are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/580/A64

  19. Observations of photospheric magnetic fields and shear flows in flaring active regions

    NASA Technical Reports Server (NTRS)

    Tarbell, T.; Ferguson, S.; Frank, Z.; Title, A.; Topka, K.

    1988-01-01

    Horizontal flows in the photosphere and subsurface convection zone move the footpoints of coronal magnetic field lines. Magnetic energy to power flares can be stored in the corona if the flows drive the fields far from the potential configuration. Videodisk movies were shown with 0.5 to 1 arcsecond resolution of the following simultaneous observations: green continuum, longitudinal magnetogram, Fe I 5576 A line center (mid-photosphere), H alpha wings, and H alpha line center. The movies show a 90 x 90 arcsecond field of view of an active region at S29, W11. When viewed at speeds of a few thousand times real-time, the photospheric movies clearly show the active region fields being distorted by a remarkable combination of systematic flows and small eruptions of new flux. Magnetic bipoles are emerging over a large area, and the polarities are systematically flowing apart. The horizontal flows were mapped in detail from the continuum movies, and these may be used to predict the future evolution of the region. The horizontal flows are not discernable in H alpha. The H alpha movies strongly suggest reconnection processes in the fibrils joining opposite polarities. When viewed in combination with the magnetic movies, the cause for this evolution is apparent: opposite polarity fields collide and partially cancel, and the fibrils reconnect above the surface. This type of reconnection, driven by subphotospheric flows, complicates the chromospheric and coronal fields, causing visible braiding and twisting of the fibrils. Some of the transient emission events in the fibrils and adjacent plage may also be related.

  20. North-South Asymmetric Solar Cycle Evolution: Signatures in the Photosphere and Consequences in the Corona

    NASA Astrophysics Data System (ADS)

    Virtanen, I. I.; Mursula, K.

    2014-02-01

    The heliospheric current sheet is the continuum of the coronal magnetic equator that divides the heliospheric magnetic field into two sectors (polarities). Several recent studies have shown that the heliospheric current sheet is southward shifted during approximately 3 years in the solar declining phase (the so-called bashful ballerina phenomenon). In this article we study the hemispherical asymmetry in the photospheric and coronal magnetic fields using Wilcox Solar Observatory measurements of the photospheric magnetic field since 1976 as well as the potential field source surface model. Multipole analysis of the photospheric magnetic field shows that during the late declining phase of solar cycles since the 1970s, the "bashful ballerina phenomenon" is a consequence of the g^{0}_{2} quadrupole term, signed oppositely to the dipole moment. Surges of new flux transport magnetic field from low latitudes to the poles, thus leading to a systematically varying contribution to the g^{0}_{2}-term from different latitudes. In the case of a north-south asymmetric flux production, this is seen as a quadrupole contribution traveling toward higher latitudes. When the quadrupole term is largest, the main contribution comes from the polar latitudes. At least during the four recent solar cycles, the g^{0}_{2}-term arises because the magnitude of the southern polar field is larger than the magnitude found in the north in the declining phase of the cycle. In the heliosphere this hemispheric asymmetry of the coronal fields is seen as a southward shift of the heliospheric current sheet by about 2°.

  1. PHOTOSPHERIC PROPERTIES OF WARM EUV LOOPS AND HOT X-RAY LOOPS

    SciTech Connect

    Kano, R.; Ueda, K.; Tsuneta, S.

    2014-02-20

    We investigate the photospheric properties (vector magnetic fields and horizontal velocity) of a well-developed active region, NOAA AR 10978, using the Hinode Solar Optical Telescope specifically to determine what gives rise to the temperature difference between ''warm loops'' (1-2 MK), which are coronal loops observed in EUV wavelengths, and ''hot loops'' (>3 MK), coronal loops observed in X-rays. We found that outside sunspots, the magnetic filling factor in the solar network varies with location and is anti-correlated with the horizontal random velocity. If we accept that the observed magnetic features consist of unresolved magnetic flux tubes, this anti-correlation can be explained by the ensemble average of flux-tube motion driven by small-scale random flows. The observed data are consistent with a flux tube width of ∼77 km and horizontal flow at ∼2.6 km s{sup –1} with a spatial scale of ∼120 km. We also found that outside sunspots, there is no significant difference between warm and hot loops either in the magnetic properties (except for the inclination) or in the horizontal random velocity at their footpoints, which are identified with the Hinode X-Ray Telescope and the Transition Region and Coronal Explorer. The energy flux injected into the coronal loops by the observed photospheric motion of the magnetic fields is estimated to be 2 × 10{sup 6} erg s{sup –1} cm{sup –2}, which is the same for both warm and hot loops. This suggests that coronal properties (e.g., loop length) play a more important role in giving rise to temperature differences of active-region coronal loops than photospheric parameters.

  2. ON THERMALIZATION IN GAMMA-RAY BURST JETS AND THE PEAK ENERGIES OF PHOTOSPHERIC SPECTRA

    SciTech Connect

    Vurm, Indrek; Piran, Tsvi; Lyubarsky, Yuri

    2013-02-20

    The low-energy spectral slopes of the prompt emission of most gamma-ray bursts (GRBs) are difficult to reconcile with radiatively efficient optically thin emission models irrespective of the radiation mechanism. An alternative is to ascribe the radiation around the spectral peak to a thermalization process occurring well inside the Thomson photosphere. This quasi-thermal spectrum can evolve into the observed non-thermal shape by additional energy release at moderate to small Thomson optical depths, which can readily give rise to the hard spectral tail. The position of the spectral peak is determined by the temperature and Lorentz factor of the flow in the thermalization zone, where the total number of photons carried by the jet is established. To reach thermalization, dissipation alone is not sufficient and photon generation requires an efficient emission/absorption process in addition to scattering. We perform a systematic study of all relevant photon production mechanisms searching for possible conditions in which thermalization can take place. We find that a significant fraction of the available energy should be dissipated at intermediate radii, {approx}10{sup 10} to a few Multiplication-Sign 10{sup 11} cm, and the flow there should be relatively slow: the bulk Lorentz factor could not exceed a few tens for all but the most luminous bursts with the highest E {sub pk} values. The least restrictive constraint for successful thermalization, {Gamma} {approx}< 20, is obtained if synchrotron emission acts as the photon source. This requires, however, a non-thermal acceleration deep below the Thomson photosphere transferring a significant fraction of the flow energy to relativistic electrons with Lorentz factors between 10 and 100. Other processes require bulk flow Lorentz factors of order of a few for typical bursts. We examine the implications of these results to different GRB photospheric emission models.

  3. North-south asymmetric solar cycle evolution: Signatures in the photosphere and consequences in the corona

    SciTech Connect

    Virtanen, I. I.; Mursula, K.

    2014-02-01

    The heliospheric current sheet is the continuum of the coronal magnetic equator that divides the heliospheric magnetic field into two sectors (polarities). Several recent studies have shown that the heliospheric current sheet is southward shifted during approximately 3 years in the solar declining phase (the so-called bashful ballerina phenomenon). In this article we study the hemispherical asymmetry in the photospheric and coronal magnetic fields using Wilcox Solar Observatory measurements of the photospheric magnetic field since 1976 as well as the potential field source surface model. Multipole analysis of the photospheric magnetic field shows that during the late declining phase of solar cycles since the 1970s, the 'bashful ballerina phenomenon' is a consequence of the g{sub 2}{sup 0} quadrupole term, signed oppositely to the dipole moment. Surges of new flux transport magnetic field from low latitudes to the poles, thus leading to a systematically varying contribution to the g{sub 2}{sup 0}-term from different latitudes. In the case of a north-south asymmetric flux production, this is seen as a quadrupole contribution traveling toward higher latitudes. When the quadrupole term is largest, the main contribution comes from the polar latitudes. At least during the four recent solar cycles, the g{sub 2}{sup 0}-term arises because the magnitude of the southern polar field is larger than the magnitude found in the north in the declining phase of the cycle. In the heliosphere this hemispheric asymmetry of the coronal fields is seen as a southward shift of the heliospheric current sheet by about 2°.

  4. Spectrum of Small-scale Plasma Fluctuations In The Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Kyzyurov, Yu.

    Due to progress in high-resolution observations of process in the solar atmosphere we can obtain a better understanding of different phenomena on the Sun. In particular, data of the observations provide us with important information about turbulent veloc- ity field in the photoosphere. Detailed study of the velocity field and plasma density inhomogenieties is essential for investigation of the contribution of solar photosphere to the stochastic component of the magnetic field of the Sun. In this report the for- mation of plasma irregularities (with scales smaller than 1 Mm) by turbulent mixing of weakly ionized gas in the solar atmosphere is discussed. The consideration of the process takes a background plasma density gradient and a uniform magnetic field into account. It is supposed that plasma density is a passive scalar field and is submerged in turbulent motions of incompressible non-ionized gas. The relation between plasma density fluctuations and the random velocity field of neutral gas is derived from the 3-fluid equations. Restricting the consideration to the inertial range of scales of tur- bulence, an analytic expression for the spectrum of plasma fluctuations is obtained. This expression predicts power-law dependence for the spectrum of plasma irregular- ities in the photosphere in general as well as some possible departures in details of the spectrum from a simple power law with a constant power index. The rms level of rela- tive plasma-density fluctuations is estimated. Under the usual conditions for the quiet photosphere the level of the relative plasma fluctuations is less than or about 10% for wave numbers corresponding to the inertial range of turbulence.

  5. Photospheric Properties of Warm EUV Loops and Hot X-Ray Loops

    NASA Astrophysics Data System (ADS)

    Kano, R.; Ueda, K.; Tsuneta, S.

    2014-02-01

    We investigate the photospheric properties (vector magnetic fields and horizontal velocity) of a well-developed active region, NOAA AR 10978, using the Hinode Solar Optical Telescope specifically to determine what gives rise to the temperature difference between "warm loops" (1-2 MK), which are coronal loops observed in EUV wavelengths, and "hot loops" (>3 MK), coronal loops observed in X-rays. We found that outside sunspots, the magnetic filling factor in the solar network varies with location and is anti-correlated with the horizontal random velocity. If we accept that the observed magnetic features consist of unresolved magnetic flux tubes, this anti-correlation can be explained by the ensemble average of flux-tube motion driven by small-scale random flows. The observed data are consistent with a flux tube width of ~77 km and horizontal flow at ~2.6 km s-1 with a spatial scale of ~120 km. We also found that outside sunspots, there is no significant difference between warm and hot loops either in the magnetic properties (except for the inclination) or in the horizontal random velocity at their footpoints, which are identified with the Hinode X-Ray Telescope and the Transition Region and Coronal Explorer. The energy flux injected into the coronal loops by the observed photospheric motion of the magnetic fields is estimated to be 2 × 106 erg s-1 cm-2, which is the same for both warm and hot loops. This suggests that coronal properties (e.g., loop length) play a more important role in giving rise to temperature differences of active-region coronal loops than photospheric parameters.

  6. Reorganization of Photospheric Magnetic Fields in Active Regions During Energetic Flares

    NASA Astrophysics Data System (ADS)

    Santos, J. C.; Wrasse, C. M.

    2016-04-01

    The reorganization of the photospheric magnetic field may be important for flaring activity. In this work we use the time evolution of the magnetic power spectra to identify for which length scales the reorganization of the active region magnetic field is most closely related to energetic flares. Our results show that the reorganization occurs mainly for length scales larger than 12.6 Mm and may start much before the time of the flare, but the time evolution of magnetic power spectra does not show regular patterns. An analysis of the dissipation spectra suggests that the dissipation takes place at all spatial scales, including small wavenumbers in which more energy is available.

  7. The stability of solar coronal loops with realistic photospheric boundary conditions

    NASA Technical Reports Server (NTRS)

    Van Hoven, G.; Ma, S. S.; Einaudi, G.

    1981-01-01

    Finite-length effects are the primary influence for the MHD stability of coronal loops. This paper gives a new physical description of the photospheric boundary conditions, and the first complete and uniformly convergent initial-perturbation set. A general energy-principle (or variational) stability analysis is then developed. The results of this calculation show that large classes of cylindrical-symmetry perturbations, those with separable contributions to the energy integral, are completely stable. Comparisons are also made with other more restrictive formulations of this problem.

  8. Temporal Evolution of Magnetic Field and Intensity Properties of Photospheric Pores

    NASA Astrophysics Data System (ADS)

    Dorotovič, I.; Rybanský, M.; Sobotka, M.; Lorenc, M.; Barandas, M.; Fonseca, J. M.

    2016-04-01

    We describe conditions of pore formation in relation to the configuration and intensity of magnetic field, using observations of the SDO/HMI instrument, which observes the photosphere in the visible continuum and simultaneously the magnetic field with a spatial resolution of better than 1''. An area with a diameter of 35'' containing 6 pores during the period from October 10, 2013, 22:01:30 UT to October 11, 2013, 20:01:30 UT is selected from the HMI full-disk images. We analyze the temporal evolution of the area and brightness of the pores (time step 15 minutes), their statistics, and in parallel a time-sequence of the line-of-sight magnetic field intensity and its correlation with the area and brightness. We find that the pores become visible when their intensity decreases below 0.85 of the photospheric surrounding intensity and the magnetic field increases to 650 G in the HMI measurements. We determine the mean synodical rotational speed of the pores to be 14.44°/24 hours, which is 1° more than the tabular value. Positions of maximum magnetic field precede the positions of the pores in the direction of rotation for the positive polarity and lag behind it for the negative polarity.

  9. MONTE CARLO SIMULATIONS OF THE PHOTOSPHERIC EMISSION IN GAMMA-RAY BURSTS

    SciTech Connect

    Begue, D.; Siutsou, I. A.; Vereshchagin, G. V.

    2013-04-20

    We studied the decoupling of photons from ultra-relativistic spherically symmetric outflows expanding with constant velocity by means of Monte Carlo simulations. For outflows with finite widths we confirm the existence of two regimes: photon-thick and photon-thin, introduced recently by Ruffini et al. (RSV). The probability density function of the last scattering of photons is shown to be very different in these two cases. We also obtained spectra as well as light curves. In the photon-thick case, the time-integrated spectrum is much broader than the Planck function and its shape is well described by the fuzzy photosphere approximation introduced by RSV. In the photon-thin case, we confirm the crucial role of photon diffusion, hence the probability density of decoupling has a maximum near the diffusion radius well below the photosphere. The time-integrated spectrum of the photon-thin case has a Band shape that is produced when the outflow is optically thick and its peak is formed at the diffusion radius.

  10. The energy flux of MHD wave modes excited by realistic photospheric drivers

    NASA Astrophysics Data System (ADS)

    Fedun, Viktor; Von Fay-Siebenburgen, Erdélyi Robert; Mumford, Stuart

    The mechanism(s) responsible for solar coronal heating are still an unresolved and challenging task. In the framework of 3D numerical modelling of MHD wave excitation and propagation in the strongly stratified solar atmosphere we analyse the mode coupling and estimate the wave energy partition which can be supplied to the upper layers of the solar atmosphere by locally decomposed slow, fast and Alfven modes. These waves are excited by a number of realistic photospheric drivers which are mimicking the random granular buffeting, the coherent global solar oscillations and swirly motion observed in e.g. magnetic bright points. Based on a self-similar approach, a realistic magnetic flux tubes configuration is constructed and implemented in the VALIIIC model of the solar atmosphere. A novel method for decomposing the velocity perturbations into parallel, perpendicular and azimuthal components in 3D geometry is developed using field lines to trace a volume of constant energy flux. This method is used to identify the excited wave modes propagating upwards from the photosphere and to compute the percentage energy contribution of each mode. We have found, that for all cases where torsional motion is present, the main contribution to the flux (60%) is by Alfven wave. In the case of the vertical driver it is found to mainly excite the fast- and slow-sausage modes and a horizontal driver primarily excites the slow kink mode.

  11. Tracking Back the Solar Wind to Its Photospheric Footpoints from Wind Observations - A Statistical Study

    NASA Astrophysics Data System (ADS)

    Huang, Chong; Yan, Yihua; Li, Gang; Deng, Yuanyong; Tan, Baolin

    2014-08-01

    It is of great importance to track the solar wind back to its photospheric source region and identify the related current sheets; this will provide key information for investigating the origin and predictions of the solar wind. We report a statistical study relating the photospheric footpoint motion and in-situ observation of current sheets in the solar wind. We used the potential force-free source-surface (PFSS) model and the daily synoptic charts to trace the solar wind back from 1 AU, as observed by the Wind spacecraft, to the solar surface. As the footpoints move along the solar surface we obtain a time series of the jump times between different points. These jumps can be within a cell and between adjacent cells. We obtained the distribution of the jump times and the distribution for a subset of the jump times in which only jumps between adjacent cells were counted. For both cases, the distributions clearly show two populations. These distributions are compared with the distribution of in-situ current sheets reported in an earlier work of Miao, Peng, and Li ( Ann. Geophys. 29, 237, 2011). Its implications on the origin of the current sheets are discussed.

  12. IUE observations of a hot DAO white dwarf: Implications for diffusion theory and photospheric stratification

    NASA Technical Reports Server (NTRS)

    Holberg, J. B.; Sion, E. M.; Liebert, J.; Vauclair, Gerard

    1988-01-01

    Observations of the DAO white dwarf PG1210+533, including the first high dispersion spectrum of a hybrid H-He object of this nature were obtained by IUE. In contrast with hot DAs in the 50,000 K temperature range, PG1210+533 shows no narrow interstellar-like metal lines, in spite of an optically observed He/H abundance of 0.1. This lack of metal makes accretion from the ISM an unlikely source for the He in the PG1210+533 photosphere. A significant discovery in the high dispersion spectrum is the existence of a sharp, non-LTE like, core seen in the He II 1640 line. Such features are detected in DO white dwarfs. A small aperture SWP low dispersion observation reveals the Lyman alpha profile of PG1210+533 to be surprisingly weak and narrow. Fits of this profile using pure H models yielded a T(eff) = 56,000 K. Fits of the Balmer H gamma profile however, yield T(eff) = 42,300 K and log g = 8.5 + or - 0.5 for the same models. It is unlikely that homogeneously mixed H-He atmospheres can resolve the inconsistency between the Lyman alpha and H gamma features in this star. Stratified models involving thin H photospheres may be necessary to explain these results.

  13. PHOTOSPHERIC SIGNATURES OF GRANULAR-SCALE FLUX EMERGENCE AND CANCELLATION AT THE PENUMBRAL BOUNDARY

    SciTech Connect

    Lim, Eun-Kyung; Yurchyshyn, Vasyl; Abramenko, Valentyna; Ahn, Kwangsu; Cao Wenda; Goode, Philip

    2011-10-20

    We studied flux emergence events of sub-granular scale in a solar active region. The New Solar Telescope (NST) of the Big Bear Solar Observatory made it possible to clearly observe the photospheric signature of flux emergence with very high spatial (0.''11 at 7057 A) and temporal (15 s) resolution. From TiO observations with the pixel scale of 0.''0375, we found several elongated granule-like features (GLFs) stretching from the penumbral filaments of a sunspot at a relatively high speed of over 4 km s{sup -1}. After a slender arched darkening appeared at the tip of a penumbral filament, a bright point (BP) developed and quickly moved away from the filament, forming and stretching a GLF. The size of a GLF was approximately 0.''5 wide and 3'' long. The moving BP encountered nearby structures after several minutes of stretching, and the well-defined elongated shape of the GLF faded away. Magnetograms from the Solar Dynamics Observatory/Helioseismic and Magnetic Imager and NST/InfraRed Imaging Magnetograph revealed that those GLFs are photospheric indicators of small-scale flux emergence, and their disappearance is related to magnetic cancellation. From two well-observed events, we describe detailed development of the sub-structures of GLFs and different cancellation processes that each of the two GLFs underwent.

  14. A quantitative study relating observed shear in photospheric magnetic fields to repeated flaring

    NASA Astrophysics Data System (ADS)

    Hagyard, M. J.; Teuber, D.; West, E. A.; Smith, J. B.

    1984-03-01

    In this paper a quantitative evaluation of the shear in the magnetic field along the neutral line in an active region during an epoch of flare activity is presented. Shear is defined as the angular difference in the photosphere between the potential magnetic field, which fits the boundary conditions imposed by the observed line-of-sight field, and the observed magnetic field. For the active region studied, this angular difference (shear) is non-uniform along the neutral line with maxima occurring at the locations of repeated flare onsets. It is suggested that continued magnetic evolution causes the field's maximum shear to exceed a critical value of shear, resulting in a flare around the site of maximum shear. Evidently, the field at the site of the flare must relax to a state of shear somewhat below the critical value (but still far from potential), with subsequent evolution returning the field to the critical threshold. This inference is drawn because several flares occured at sites of maximum photospheric shear which were persistent in location.

  15. A quantitative study relating observed shear in photospheric magnetic fields to repeated flaring

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Teuber, D.; West, E. A.; Smith, J. B.

    1984-01-01

    In this paper a quantitative evaluation of the shear in the magnetic field along the neutral line in an active region during an epoch of flare activity is presented. Shear is defined as the angular difference in the photosphere between the potential magnetic field, which fits the boundary conditions imposed by the observed line-of-sight field, and the observed magnetic field. For the active region studied, this angular difference (shear) is non-uniform along the neutral line with maxima occurring at the locations of repeated flare onsets. It is suggested that continued magnetic evolution causes the field's maximum shear to exceed a critical value of shear, resulting in a flare around the site of maximum shear. Evidently, the field at the site of the flare must relax to a state of shear somewhat below the critical value (but still far from potential), with subsequent evolution returning the field to the critical threshold. This inference is drawn because several flares occured at sites of maximum photospheric shear which were persistent in location.

  16. Determining the solar-flare photospheric scale height from SMM gamma-ray measurements

    NASA Technical Reports Server (NTRS)

    Lingenfelter, Richard E.

    1991-01-01

    A connected series of Monte Carlo programs was developed to make systematic calculations of the energy, temporal and angular dependences of the gamma-ray line and neutron emission resulting from such accelerated ion interactions. Comparing the results of these calculations with the Solar Maximum Mission/Gamma Ray Spectrometer (SMM/GRS) measurements of gamma-ray line and neutron fluxes, the total number and energy spectrum of the flare-accelerated ions trapped on magnetic loops at the Sun were determined and the angular distribution, pitch angle scattering, and mirroring of the ions on loop fields were constrained. Comparing the calculations with measurements of the time dependence of the neutron capture line emission, a determination of the He-3/H ratio in the photosphere was also made. The diagnostic capabilities of the SMM/GRS measurements were extended by developing a new technique to directly determine the effective photospheric scale height in solar flares from the neutron capture gamma-ray line measurements, and critically test current atmospheric models in the flare region.

  17. Photospheric and Coronal Observations of Abrupt Magnetic Restructuring in Flaring Active Regions

    NASA Astrophysics Data System (ADS)

    Petrie, G. J. D.

    2015-12-01

    The Lorentz force changes associated with strong photospheric fields in large structures within active regions can be estimated from time series of Solar Dynamics Observatory (SDO) Helioseismic and Magnetic Imager (HMI) vector magnetograms. The major, most organized changes tend to occur close to the centers of flaring regions, near the main neutral line and/or in twisted sunspots. Fields close to the neutral line tend to collapse downward and inward, consistent with compression rather than rotation of the vector field. In sunspots the twist (or azimuthal component around the sunspot axis) tends to decrease. In a limited number of cases particularly well-observed by the Atmospheric Imaging Assembly (AIA) on SDO and the Extreme Ultraviolet Imager (EUVI) on the Solar TErrestrial RElations Observatory (STEREO), the evolution of the photospheric magnetic vector field can be related to changes in coronal magnetic structure to provide a coherent description of the magnetic changes during the different phases of a flare. This work was supported by NASA grant NNX14AE05G.

  18. Photospheric Vertical Current Density and Overlying Atmospheric Activity in an Emerging Flux Region

    NASA Astrophysics Data System (ADS)

    Georgoulis, M. K.; Rust, D. M.; Bernasconi, P. N.; Schmieder, B.

    2002-05-01

    Using high-resolution vector magnetograms obtained by the balloon-borne Flare Genesis Experiment (FGE), we construct maps of the vertical current density in the emerging flux region NOAA 8844. The vertical current density has been decomposed into components that are field-aligned and perpendicular to the magnetic field, thus allowing a straightforward identification of force-free areas, as well as of areas where the force-free approximation breaks down. Small-scale chromospheric activity, such as H α Ellerman bombs and Ultraviolet bright points in 1600 Åshow a remarkable correlation with areas of strong current density. Simultaneous data of overlying coronal loops, observed by TRACE in the Extreme Ultraviolet (171 Åand 195 Å), have been carefully co-aligned with the FGE photospheric maps. We find that the footpoints of the TRACE loops always coincide with strong vertical currents and enhancements of the current helicity density. We also investigate whether the force-free approximation is valid on the photosphere during various evolutionary stages of the active region.

  19. Observations of the longitudinal magnetic field in the transition region and photosphere of a sunspot

    NASA Technical Reports Server (NTRS)

    Henze, W., Jr.; Tandberg-Hanssen, E.; Hagyard, M. J.; West, E. A.; Woodgate, B. E.; Shine, R. A.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; West, E. A.

    1982-01-01

    The Ultraviolet Spectrometer and Polarimeter on the Solar Maximum Mission spacraft has observed for the first time the longitudinal component of the magnetic field by means of the Zeeman effect in the transition region above a sunspot. The data presented here were obtained on three days in one sunspot, have spatial resolutions of 10 arcsec and 3 arcsec, and yield maximum field strengths greater than 1000 G above the umbrae in the spot. The method of analysis, including a line-width calibration feature used during some of the observations, is described in some detail in an appendix; the line width is required for the determination of the longitudinal magnetic field from the observed circular polarization. The transition region data for one day are compared with photospheric magnetograms from the Marshall Space Flight Center. Vertical gradients of the magnetic field are compared from the two sets of data; the maximum gradients of 0.41 to 0.62 G/km occur above the umbra and agree with or are smaller than values observed previously in the photosphere and low chromosphere.

  20. Rotation of the photospheric magnetic fields: A north-south asymmetry

    NASA Technical Reports Server (NTRS)

    Antonucci, E.; Hoeksema, J. T.; Scherrer, P. H.

    1989-01-01

    During most of solar cycle 21 the large-scale photospheric field rotated more rapidly in the Northern Hemisphere than in the southern. The large-scale northern field rotated with a 26.9 day period (synodic), was centered at 15 degress N, and covered a latitude zone about 24 degrees wide. The large-scale southern field rotated with a periodicity of 28.1 days, was centered at 26 degrees S, and covered a latitude zone about 32 degrees wide. Our analysis showed rotational power at only a few discrete latitudes and frequencies in each hemisphere. The center of each peak lies near the sunspot differential rotation curve. The largest scale field contributes to the configuration of the coronal and interplanetary magnetic field (IMF). The strength of the first harmonic of the northern field suggests that this structure may be related to the 4-sector pattern observed in the IMF polarity. The southern field had much lower power at the first harmonic of the solar rotation rate and so would contribute only to a 2-sector structure in the IMF. These results were discovered in Fourier analysis of photospheric synoptic charts obtained at the Wilcox Solar Observatory from 1976 to 1986 and confirmed in higher resolution maps from the National Solar Observatory. Mt. Wilson magnetic field measurements from solar cycle 20 show a similar north-south asymmetry.

  1. Photospheric Vector Magnetic Field Evolution of NOAA Active Region 11504 and the Ensuing CME

    NASA Astrophysics Data System (ADS)

    James, Alexander; Green, Lucie; Valori, Gherardo; van Driel-Gesztelyi, Lidia; Baker, Deborah; Brooks, David; Palmerio, Erika

    2016-05-01

    Coronal mass ejections (CMEs) are eruptions of billions of tonnes of plasma from the Sun that drive the most severe space weather effects we observe. In order to be able to produce forecasts of space weather with lead times of the order of days, accurate predictions of the occurrence of CMEs must be developed. The eruptive active-region studied in this work (NOAA 11504) is complex, featuring fragmentation of penumbral magnetic field in the days prior to eruption, as well as rotation of the leading sunspot. SDO/HMI vector photospheric magnetic field measurements are utilised alongside SDO/AIA multi-wavelength extreme ultra-violet (EUV) observations to study the dynamics of the photospheric and coronal structures, as well as Hinode/EIS spectroscopic measurements, including elemental composition data. The EUV data show flare ribbons as well as coronal dimmings, which are used to infer the orientation of the erupting flux rope. This flux rope orientation is then compared to in situ measurements of the flux rope. The vector magnetic field data is used to determine the possible contributions the field fragmentation and sunspot rotation may have made to the formation of the flux rope and the triggering of the CME.

  2. Towards a coherent view of mass loss in Betelgeuse from the photosphere to the interstellar medium

    NASA Astrophysics Data System (ADS)

    Montarges, Miguel; Kervella, Pierre; Perrin, Guy

    2013-06-01

    Massive evolved stars contribute to the chemical enrichment of the interstellar medium (ISM), the Galaxy and ultimately the Universe through their mass loss. From the photosphere to the ISM, large convective motions, low surface gravity and high brightness combine to trigger an intense stellar wind. The released material evolves chemically as the distance from the star increases, and eventually forms dust particles. The involved physical and chemical processes are central to apprehend the cosmic impact of massive evolved stars, but they are poorly understood: the surface convection remains essentially uncharacterized, as the composition of the wind, and the role of the magnetic field is unknown. Betelgeuse is the closest red supergiant and therefore it stands out as the best candidate to obtain detailed observations of the close circumstellar environment of a massive evolved star. We are currently running a high angular resolution observations program to obtain a multi-wavelength and multi-epoch characterisation of this star. Using the IOTA interferometer, Haubois et al. reconstructed an image of the photosphere of the star. Within 1 to 100 stellar radii, the VLT and VLTI allowed us to probe the compact molecular envelope of Betelgeuse (the MOLsphere) in the near-infrared, and the extended dusty envelope in the thermal infrared domain. They were recently completed with HST/STIS observations of the chromosphere in the UV, whose location is surprisingly coincident with the MOLsphere. We will present a brief review of our recent results and of our ongoing work on Betelgeuse.

  3. Identifying and Tracking Solar Photospheric Bright Points Based on Three-dimensional Segmentation Technology

    NASA Astrophysics Data System (ADS)

    Xiong, J. P.; Zhang, A. L.; Ji, K. F.; Feng, S.; Deng, H.; Yang, Y. F.

    2016-01-01

    Photospheric bright points (PBPs) are tiny and short-lived phenomena which can be seen within dark inter-granular lanes. In this paper, we develop a new method to identify and track the PBPs in the three-dimensional data cube. Different from the previous way such as Detection-Before-Tracking, this method is based on the Tracking-While-Detection. Using this method, the whole lifetime of a PBP can be accurately measured while this PBP is possibly separated into several with Laplacian and morphological dilation (LMD) method due to its weak intensity sometimes. With consideration of the G-band PBPs observed by Hinode/SOT (Solar Optical Telescope) for more than two hours, we find that the isolated PBPs have an average lifetime of 3 minutes, and the longest one is up to 27 minutes, which are greater than the values detected by the previous LMD method. Furthermore, we also find that the mean intensity of PBPs is 1.02 times of the mean photospheric intensity, which is less than the values detected by LMD method, and the intensity of PBPs presents a period of oscillation with 2-3 minutes during the whole lifetime.

  4. An experimental platform for creating white dwarf photospheres in the laboratory: Preliminary results

    NASA Astrophysics Data System (ADS)

    Montgomery, M. H.; Falcon, Ross E.; Rochau, G. A.; Bailey, J. E.; Gomez, T. A.; Carlson, A. L.; Bliss, D. E.; Nagayama, T.; Stein, M.; Winget, D. E.

    2015-12-01

    We present the current status of the White Dwarf Photosphere Experiment at the Z Pulsed Power Facility at Sandia National Laboratories. This experiment has evolved into a unique platform for simultaneously measuring emission, absorption, and back-lighter continua spectra of plasmas with white dwarf (WD) photospheric compositions and conditions (Te∼1 eV, ne∼1016-1018e/cm3); our current experiments involve line profile measurements of hydrogen-corresponding to the most common surface composition in white dwarf stars, with future experiments planned for helium, carbon, and oxygen. These profiles will test line broadening theories used in white dwarf model atmospheres to infer the fundamental parameters (e.g., effective temperature and mass) of thousands of WDs. This experiment uses the large amount of x-rays generated from a z-pinch dynamic hohlraum to radiatively drive plasma formation in a gas cell. We reach significantly higher densities than the landmark study of Wiese et al. (1972), thereby putting competing line broadening theories to the test in a regime where their predictions strongly diverge. The simultaneous measurement of emission, absorption, and back-lighter continua in macroscopic plasmas represents a significant advance relative to hydrogen line profile experiments of the past.

  5. On the relationship between photospheric footpoint motions and coronal heating in solar active regions

    SciTech Connect

    Van Ballegooijen, A. A.; Asgari-Targhi, M.; Berger, M. A.

    2014-05-20

    Coronal heating theories can be classified as either direct current (DC) or alternating current (AC) mechanisms, depending on whether the coronal magnetic field responds quasi-statically or dynamically to the photospheric footpoint motions. In this paper we investigate whether photospheric footpoint motions with velocities of 1-2 km s{sup –1} can heat the corona in active regions, and whether the corona responds quasi-statically or dynamically to such motions (DC versus AC heating). We construct three-dimensional magnetohydrodynamic models for the Alfvén waves and quasi-static perturbations generated within a coronal loop. We find that in models where the effects of the lower atmosphere are neglected, the corona responds quasi-statically to the footpoint motions (DC heating), but the energy flux into the corona is too low compared to observational requirements. In more realistic models that include the lower atmosphere, the corona responds more dynamically to the footpoint motions (AC heating) and the predicted heating rates due to Alfvén wave turbulence are sufficient to explain the observed hot loops. The higher heating rates are due to the amplification of Alfvén waves in the lower atmosphere. We conclude that magnetic braiding is a highly dynamic process.

  6. Photospheric electric current and transition region brightness within an active region

    NASA Technical Reports Server (NTRS)

    Deloach, A. C.; Hagyard, M. J.; Rabin, D.; Moore, R. L.; Smith, B. J., Jr.; West, E. A.; Tandberg-Hanssen, E.

    1984-01-01

    Distributions of vertical electrical current density J(z) calculated from vector measurements of the photospheric magnetic field are compared with ultraviolet spectroheliograms to investigate whether resistive heating is an important source of enhanced emission in the transition region. The photospheric magnetic fields in Active Region 2372 were measured on April 6 and 7, 1980 with the Marshall Space Flight Center vector magnetograph; ultraviolet wavelength spectroheliograms (L-alpha and N V 1239 A) were obtained with the UV Spectrometer and Polarimeter experiment aboard the Solar Maximum Mission satellite. Spatial registration of the J(z) (5 arcsec resolution) and UV (3 arcsec resolution) maps indicates that the maximum current density is cospatial with a minor but persistent UV enhancement, but there is little detected current associated with other nearby bright areas. It is concluded that, although resistive heating may be important in the transition region, the currents responsible for the heating are largely unresolved in the present measurements and have no simple correlation with the residual current measured on 5-arcsec scales.

  7. A New Technique for the Photospheric Driving of Non-potential Solar Coronal Magnetic Field Simulations

    NASA Astrophysics Data System (ADS)

    Weinzierl, Marion; Yeates, Anthony R.; Mackay, Duncan H.; Henney, Carl J.; Arge, C. Nick

    2016-05-01

    In this paper, we develop a new technique for driving global non-potential simulations of the Sun’s coronal magnetic field solely from sequences of radial magnetic maps of the solar photosphere. A primary challenge to driving such global simulations is that the required horizontal electric field cannot be uniquely determined from such maps. We show that an “inductive” electric field solution similar to that used by previous authors successfully reproduces specific features of the coronal field evolution in both single and multiple bipole simulations. For these cases, the true solution is known because the electric field was generated from a surface flux-transport model. The match for these cases is further improved by including the non-inductive electric field contribution from surface differential rotation. Then, using this reconstruction method for the electric field, we show that a coronal non-potential simulation can be successfully driven from a sequence of ADAPT maps of the photospheric radial field, without including additional physical observations which are not routinely available.

  8. Photon and neutrino spectra of time-dependent photospheric models of gamma-ray bursts

    SciTech Connect

    Asano, K.; Mészáros, P. E-mail: nnp@astro.psu.edu

    2013-09-01

    Thermal photons from the photosphere may be the primary source of the observed prompt emission of gamma-ray bursts (GRBs). In order to produce the observed non-thermal spectra, some kind of dissipation mechanism near the photosphere is required. In this paper we numerically simulate the evolution of the photon spectrum in a relativistically expanding shell with a time-dependent numerical code. We consider two basic models. One is a leptonic model, where a dissipation mechanism heats the thermal electrons maintaining their high temperature. The other model involves a cascade process induced by pp(pn)-collisions which produce high-energy electrons, modify the thermal spectrum, and emit neutrinos. The qualitative properties of the photon spectra are mainly determined by the optical depth at which the dissipation mechanism sets in. Too large optical depths lead to a broad and curved spectrum contradicting the observations, while for optical depths smaller than unity the spectral hardness becomes softer than observed. A significant shift of the spectral peak energy to higher energies due to a large energy injection can lead to an overly broad spectral shape. We show ideal parameter ranges for which these models are able to reproduce the observed spectra. For the pn-collision model, the neutrino fluence in the 10–100 GeV range is well above the atmospheric neutrino fluence, but its detection is challenging for presently available detectors.

  9. An automated classification approach to ranking photospheric proxies of magnetic energy build-up

    NASA Astrophysics Data System (ADS)

    Al-Ghraibah, A.; Boucheron, L. E.; McAteer, R. T. J.

    2015-07-01

    Aims: We study the photospheric magnetic field of ~2000 active regions over solar cycle 23 to search for parameters that may be indicative of energy build-up and its subsequent release as a solar flare in the corona. Methods: We extract three sets of parameters: (1) snapshots in space and time: total flux, magnetic gradients, and neutral lines; (2) evolution in time: flux evolution; and (3) structures at multiple size scales: wavelet analysis. This work combines standard pattern recognition and classification techniques via a relevance vector machine to determine (i.e., classify) whether a region is expected to flare (≥C1.0 according to GOES). We consider classification performance using all 38 extracted features and several feature subsets. Classification performance is quantified using both the true positive rate (the proportion of flares correctly predicted) and the true negative rate (the proportion of non-flares correctly classified). Additionally, we compute the true skill score which provides an equal weighting to true positive rate and true negative rate and the Heidke skill score to allow comparison to other flare forecasting work. Results: We obtain a true skill score of ~0.5 for any predictive time window in the range 2 to 24 h, with a true positive rate of ~0.8 and a true negative rate of ~0.7. These values do not appear to depend on the predictive time window, although the Heidke skill score (<0.5) does. Features relating to snapshots of the distribution of magnetic gradients show the best predictive ability over all predictive time windows. Other gradient-related features and the instantaneous power at various wavelet scales also feature in the top five (of 38) ranked features in predictive power. It has always been clear that while the photospheric magnetic field governs the coronal non-potentiality (and hence likelihood of producing a solar flare), photospheric magnetic field information alone is not sufficient to determine this in a unique manner

  10. The role of photospheric magnetic fields in the variation of solar oscillation eigenfrequencies

    NASA Technical Reports Server (NTRS)

    Rosenthal, C. S.

    1995-01-01

    The frequencies of solar oscillations have been found to be higher at the peak of the solar cycle, their variation being consistent with that expected from a change in the solar structure confined to the Sun's outer layers. In this work, a technique is introduced for estimating the effect of the highly inhomogeneous photospheric magnetic field on solar oscillation eigenfrequencies, and its results are compared with the solar data. It is found that the observed steep rise in frequency shift at low frequency and the leveling of or decline at high frequency are well reproduced by the model. The correct order of magnitude for the frequency changes is also reproduced, at least at low frequency. The model implies a particular functional form for the variation of the frequency changes with order and degree, and it is suggested that future advances in observation and theory will therefore allow this model to be confirmed or refuted.

  11. MAGNETICALLY AND BARYONICALLY DOMINATED PHOTOSPHERIC GAMMA-RAY BURST MODEL FITS TO FERMI-LAT OBSERVATIONS

    SciTech Connect

    Veres, Peter; Meszaros, Peter; Zhang, Bin-Bin

    2013-02-10

    We consider gamma-ray burst models where the radiation is dominated by a photospheric region providing the MeV Band spectrum, and an external shock region responsible for the GeV radiation via inverse Compton scattering. We parameterize the initial dynamics through an acceleration law {Gamma}{proportional_to}r {sup {mu}}, with {mu} between 1/3 and 1 to represent the range between an extreme magnetically dominated and a baryonically dominated regime, depending also on the magnetic field configuration. We compare these models to several bright Fermi-LAT bursts, and show that both the time-integrated and the time-resolved spectra, where available, can be well described by these models. We discuss the parameters which result from these fits, and discuss the relative merits and shortcomings of the two models.

  12. Photospheric subrotations, differential rotation and zonal wind bands - A reverse pirouette

    NASA Technical Reports Server (NTRS)

    Schatten, K. H.; Mayr, H. G.; Levine, R. H.

    1981-01-01

    It is noted that on the sun the core is assumed to be rotating with a period of about 12 days while the overlying 'mantle' convection zone has a solid body component of about 27 days. It is proposed that this phenomenon could simply be understood as a 'reverse pirouette'. It is noted that while previously proposed models provide solutions of valid equations and computer analyses, they lack a simple physical picture to explain the phenomenon. In the model proposed here, the solar oblateness is conventionally providing added heat input at the poles. The result is the large scale transport of material toward the equator, causing subrotation. The model is thus seen as facilitating an understanding of the formation of a slowly rotating convection zone above the more rapidly rotating core. The latitudinal photospheric differential rotation is interpreted as a 'second order' effect associated with the horizontal transport of momentum.

  13. Contribution functions for Zeeman-split lines, and line formation in photospheric faculae

    NASA Technical Reports Server (NTRS)

    Vanballegooijen, A. A.

    1985-01-01

    The transfer of polarized light in an inhomogeneous stellar atmosphere, and the formation of magnetically sensitive spectral lines, are discussed. A new method for the solution of the transfer equations is proposed. The method gives a natural definition of the contribution functions for Stokes' parameters, i.e., functions describing the contributions from different parts along the line-of-sight (LOS). The formalism includes all magneto-optical effects, and allows for an arbitrary variation of magnetic field, velocity field, temperature, density, etc., along the LOS. The formation of FeI lambda 5250.2 in photospheric faculae is described. A potential-field model of a facular element is presented, and spectra profiles and contribution functions are computed for the Stokes parameters I, Q, and V.

  14. The spontaneous concentration of magnetic field in the photosphere of the sun

    NASA Technical Reports Server (NTRS)

    Parker, E. N.

    1981-01-01

    The basic physics of magnetic flux tubes in the solar photosphere is reviewed, with areas still open to conjecture pointed out. The question of the concentration of individual small flux tubes to levels of 1-2 kilogauss, when the average solar surface magnetic field is on the order of 10 gauss, by processes of twisting and the formation of flux ropes made up of tubes wound around each other is considered together with the effects of turbulence on the flux tube. Mechanisms for tube compression by the evacuation of the gas contained within a flux tube are then examined, and the possibility of field concentration through the cooling of the gas within the tube in a superadiabatic process is suggested. Attention is then given to possible mechanisms serving to maintain the concentration of flux tubes far below the surface of the sun which gives rise to sunspots and pores as the flux tree emerges through the surface.

  15. Turbulent magnetic energy spectrum and the cancellation function of solar photospheric magnetic fields

    NASA Astrophysics Data System (ADS)

    Marschalkó, G.; Petrovay, K.; Petrovay, K.

    2013-11-01

    A simple analytical relation of form α=2κ-1 between the magnetic energy spectral exponent α of the turbulent magnetic field in the solar photosphere and its magnetic flux cancellation exponent κ, valid under certain restrictive assumptions, is tested and extended outside its range of validity in a series of Monte Carlo simulations. In these numerical tests artificial ``magnetograms'' are constructed in 1D and 2D by superposing a discrete set of Fourier modes of the magnetic field distribution with amplitudes following a power law spectrum and measuring the cancellation function on these simulated magnetograms. Our results confirm the validity of the analytical relation and extend it to the domain α<-1 where κ-> 0 as α-> -∞. The observationally derived upper limit of 0.38 on κ implies α<-0.24 in the granular size range, apparently at odds with a small scale dynamo driven in the inertial range.

  16. TRANSVERSE COMPONENT OF THE MAGNETIC FIELD IN THE SOLAR PHOTOSPHERE OBSERVED BY SUNRISE

    SciTech Connect

    Danilovic, S.; Beeck, B.; Pietarila, A.; Schuessler, M.; Solanki, S. K.; Barthol, P.; Gandorfer, A.; MartInez Pillet, V.; Bonet, J. A.; Domingo, V.; Berkefeld, T.; Schmidt, W.; Knoelker, M.; Title, A. M.

    2010-11-10

    We present the first observations of the transverse component of a photospheric magnetic field acquired by the imaging magnetograph SUNRISE/IMaX. Using an automated detection method, we obtain statistical properties of 4536 features with significant linear polarization signal. We obtain a rate of occurrence of 7 x 10{sup -4} s{sup -1} arcsec{sup -2}, which is 1-2 orders of magnitude larger than the values reported by previous studies. We show that these features have no characteristic size or lifetime. They appear preferentially at granule boundaries with most of them being caught in downflow lanes at some point. Only a small percentage are entirely and constantly embedded in upflows (16%) or downflows (8%).

  17. Transverse Component of the Magnetic Field in the Solar Photosphere Observed by SUNRISE

    NASA Astrophysics Data System (ADS)

    Danilovic, S.; Beeck, B.; Pietarila, A.; Schüssler, M.; Solanki, S. K.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta, J. C.; Domingo, V.; Barthol, P.; Berkefeld, T.; Gandorfer, A.; Knölker, M.; Schmidt, W.; Title, A. M.

    2010-11-01

    We present the first observations of the transverse component of a photospheric magnetic field acquired by the imaging magnetograph SUNRISE/IMaX. Using an automated detection method, we obtain statistical properties of 4536 features with significant linear polarization signal. We obtain a rate of occurrence of 7 × 10-4 s-1 arcsec-2, which is 1-2 orders of magnitude larger than the values reported by previous studies. We show that these features have no characteristic size or lifetime. They appear preferentially at granule boundaries with most of them being caught in downflow lanes at some point. Only a small percentage are entirely and constantly embedded in upflows (16%) or downflows (8%).

  18. Photospheric motions from an observational point of view: HINODE and SDO satellite observations

    NASA Astrophysics Data System (ADS)

    Roudier, T.

    2011-12-01

    Thanks to the Solar Optical Telescope onboard HINODE, we mainly aim at the understanding of temporal evolution and spatial characterization of solar granular and supergranular features and their relation with magnetic field. We study the photospheric motions and the network magnetic field interactions using the Tree of Fragmenting Granules (TFGs). The mutual interactions of the TFGs tend to expulse corks outside of them on 3h-4h and concentrate the corks on supergranular scale in approximatively 6h-8h to form the magnetic network. Then, the long living families contribute to form the magnetic network. The measurement of the horizontal velocities by the proper motion of granules over the full Sun with SDO data, allow us to determine, for the first time, the solar differential rotation directly at the central meridian. During the starting phase of the solar cycle 24, the solar differential rotation seems to show some modification which must be confirmed.

  19. Creating 3-dimensional Models of the Photosphere using the SIR Code

    NASA Astrophysics Data System (ADS)

    Thonhofer, S.; Utz, D.; Jurčák, J.; Pauritsch, J.; Hanslmeier, A.; Lemmerer, B.

    A high-resolution 3-dimensional model of the photospheric magnetic field is essential for the investigation of magnetic features such as sunspots, pores or smaller elements like single flux tubes seen as magnetic bright points. The SIR code is an advanced inversion code that retrieves physical quantities, e.g. magnetic field, from Stokes profiles. Based on this code, we developed a program for automated inversion of Hinode SOT/SP data and for storing these results in 3-dimensional data cubes in the form of fits files. We obtained models of the temperature, magnetic field strength, magnetic field angles and LOS-velocity in a region of the quiet sun. We will give a first discussion of those parameters in regards of small scale magnetic fields and what we can obtain and learn in the future.

  20. Non-WKB Alfven Wave Reflection from the Solar Photosphere to the Distant Heliosphere

    NASA Astrophysics Data System (ADS)

    Cranmer, S. R.; van Ballegooijen, A.

    2003-12-01

    Magnetohydrodynamic (MHD) turbulence has been considered for several decades as a possibly substantial heat source for the solar chromosphere, corona, and heliosphere. However, it is still not well understood how the turbulent fluctuations are generated and how they evolve in frequency and wavenumber. Although the dominant population of Alfvén waves near the Sun must be propagating outwards, one also needs waves propagating inwards in order to ``seed'' a turbulent cascade. As a part of an ongoing study of various aspects of solar MHD turbulence, we present a model of linear, non-WKB reflection of Alfvén waves that propagate in both directions along an open magnetic flux tube. Our work differs from previous models in the following ways. (1) The background plasma density, magnetic field, and flow velocity are constrained empirically from below the photosphere to distances past 1 AU. The successive merging of flux tubes on granular and supergranular scales is described using a two-dimensional magnetostatic model of a magnetic network element in the stratified solar atmosphere. (2) The amplitudes of horizontal wave motions are specified only at the photosphere, based on previous analyses of G-band bright point motions. Everywhere else in the model the amplitudes of outward and inward propagating waves are computed self-consistently. We compare the resulting wave properties with observed nonthermal motions in the chromosphere and corona, radio scintillation measurements, and in-situ fluctuation spectra. Quantities such as the MHD turbulent heating rate and the non-WKB wave pressure are computed, and the need for other sources of inward waves (e.g., nonlinear reflection or scattering off density inhomogeneities) will also be discussed. This work is supported by the National Aeronautics and Space Administration under grants NAG5-11913 and NAG5-12865 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA

  1. Magnetic Upflow Events in the Quiet-Sun Photosphere. I. Observations

    NASA Astrophysics Data System (ADS)

    Jafarzadeh, S.; Rouppe van der Voort, L.; de la Cruz Rodríguez, J.

    2015-09-01

    Rapid magnetic upflows in the quiet-Sun photosphere were recently uncovered from both Sunrise/IMaX and Hinode/SOT observations. Here, we study magnetic upflow events (MUEs) from high-quality, high- (spatial, temporal, and spectral) resolution, and full Stokes observations in four photospheric magnetically sensitive Fe i lines centered at 5250.21, 6173.34, 6301.51, and 6302.50 Å acquired with the Swedish Solar Telescope (SST)/CRISP. We detect MUEs by subtracting in-line Stokes V signals from those in the far blue wing whose signal-to-noise ratio (S/N) ≥slant 7. We find a larger number of MUEs at any given time (2.0× {10}-2 arcsec-2), larger by one to two orders of magnitude, than previously reported. The MUEs appear to fall into four classes presenting different shapes of Stokes V profiles with (I) asymmetric double lobes, (II) single lobes, (III) double-humped (two same-polarity lobes), and (IV) three lobes (an extra blueshifted bump in addition to double lobes), of which less than half are single-lobed. We also find that MUEs are almost equally distributed in network and internetwork areas and they appear in the interior or at the edge of granules in both regions. Distributions of physical properties, except for horizontal velocity, of the MUEs (namely, Stokes V signal, size, line-of-sight velocity, and lifetime) are almost identical for the different spectral lines in our data. A bisector analysis of our spectrally resolved observations shows that these events host modest upflows and do not show a direct indication of the presence of supersonic upflows reported earlier. Our findings reveal that the numbers, types (classes), and properties determined for MUEs can strongly depend on the detection techniques used and the properties of the employed data, namely, S/Ns, resolutions, and wavelengths.

  2. Photospheric and coronal magnetic fields in six magnetographs. I. Consistent evolution of the bashful ballerina

    NASA Astrophysics Data System (ADS)

    Virtanen, Ilpo; Mursula, Kalevi

    2016-06-01

    Aims: We study the long-term evolution of photospheric and coronal magnetic fields and the heliospheric current sheet (HCS), especially its north-south asymmetry. Special attention is paid to the reliability of the six data sets used in this study and to the consistency of the results based on these data sets. Methods: We use synoptic maps constructed from Wilcox Solar Observatory (WSO), Mount Wilson Observatory (MWO), Kitt Peak (KP), SOLIS, SOHO/MDI, and SDO/HMI measurements of the photospheric field and the potential field source surface (PFSS) model. Results: The six data sets depict a fairly similar long-term evolution of magnetic fields and the heliospheric current sheet, including polarity reversals and hemispheric asymmetry. However, there are time intervals of several years long, when first KP measurements in the 1970s and 1980s, and later WSO measurements in the 1990s and early 2000s, significantly deviate from the other simultaneous data sets, reflecting likely errors at these times. All of the six magnetographs agree on the southward shift of the heliospheric current sheet (the so-called bashful ballerina phenomenon) in the declining to minimum phase of the solar cycle during a few years of the five included cycles. We show that during solar cycles 20-22, the southward shift of the HCS is mainly due to the axial quadrupole term, reflecting the stronger magnetic field intensity at the southern pole during these times. During cycle 23 the asymmetry is less persistent and mainly due to higher harmonics than the quadrupole term. Currently, in the early declining phase of cycle 24, the HCS is also shifted southward and is mainly due to the axial quadrupole as for most earlier cycles. This further emphasizes the special character of the global solar field during cycle 23.

  3. Three-dimensional temperature mapping of solar photospheric fine structure using Ca ii H filtergrams

    NASA Astrophysics Data System (ADS)

    Henriques, V. M. J.

    2012-12-01

    Context. The wings of the Ca ii H and K lines provide excellent photospheric temperature diagnostics. At the Swedish 1-m Solar Telescope (SST), the blue wing of Ca ii H is scanned with a narrowband interference filter mounted on a rotation stage. This provides up to 0farcs10 spatial resolution filtergrams at high cadence that are concurrent with other diagnostics at longer wavelengths. Aims: The aim is to develop observational techniques that provide photospheric temperature stratification at the highest spatial resolution possible and use them to compare simulations and observations at different heights. Methods: We use filtergrams in the Ca ii H blue wing that were obtained with a tiltable interference filter at the SST. Synthetic observations are produced from three-dimensional (3D) hydro and magneto-hydrodynamic numerical simulations and degraded to match the observations. The temperature structure obtained from applying the method to the synthetic data is compared with the known structure in the simulated atmospheres and with observations of an active region. Cross-correlation techniques using restored non-simultaneous continuum images are used to reduce high-altitude, small-scale seeing signal introduced from the non-simultaneity of the frames when differentiating data. Results: Temperature extraction using high-resolution filtergrams in the Ca ii H blue wing works reasonably well when tested with simulated 3D atmospheres. The cross-correlation technique successfully compensates for the problem of small-scale seeing differences and provides a measure of the spurious signal from this source in differentiated data. Synthesized data from the simulated atmospheres (including pores) match well the observations morphologically at different observed heights and in vertical temperature gradients.

  4. The Solar Photospheric Oxygen Abundance and the Role of 3D Model Atmospheres

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Steffen, M.; Ludwig, H.-G.

    2008-09-01

    The solar oxygen abundance has undergone a major downward revision in the last decade, reputedly as a result of employing 3D hydrodynamical simulations to model the inhomogeneous structure of the solar photosphere. The very low oxygen abundance advocated by Asplund et al. 2004, A(O)=8.66, together with the downward revision of the abundances of other key elements, has created serious problems for solar models to explain the helioseismic measurements. In an effort to contribute to the dispute of whether the Sun has "solar" or "sub-solar" abundances, we have re-derived its photospheric abundance of oxygen, nitrogen, and other elements, independently of previous analyses. We applied a state-of-the art 3D (CO5BOLD) hydrodynamical simulation of the solar granulation as well as different 1D model atmospheres for the line by line spectroscopic abundance determinations. The analysis is based on both standard disk-center and full-disk spectral atlases; for oxygen we acquired in addition spectra at different heliocentric angles. The derived abundances are the result of equivalent width and/or line profile fitting of the available atomic lines. Our recommended oxygen abundance is A(O)=8.76+- 0.07, 0.1 dex higher than the value of Asplund et al. (2004). Our current estimate of the overall solar metallicity is 0.014< Z<0.016. Questions we discuss include: (i) Is the general downward revision of the solar abundances a 3D effect? (ii) How large are the abundance corrections due to horizontal inhomogeneities? (iii) What is the main reason for the differences between the abundances obtained in our study and those derived by Apslund and coworkers? (iv) How large are the uncertainties in the observed solar spectra? (v) What is the reason why the two forbidden oxygen lines, [OI] lambda 630 nm and [OI] lambda 636.3 nm, give significantly different answers for the solar oxygen abundance?

  5. An optical spectroscopic study of T Tauri stars. I. Photospheric properties

    SciTech Connect

    Herczeg, Gregory J.; Hillenbrand, Lynne A.

    2014-05-10

    Estimates of the mass and age of young stars from their location in the H-R diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux-calibrated optical spectra to measure accurate spectral types and extinctions of 281 nearby T Tauri stars (TTSs). The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars, many of which are well known and can serve as benchmarks. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are one to two subclasses later than literature spectral types for the original members of the TW Hya Association (TWA) and are discrepant with literature values for some well-known members of the Taurus Molecular Cloud. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than near-IR measurements, likely the result of methodological differences and the presence of near-IR excesses in most CTTSs. As an illustration of the impact of accretion, spectral type, and extinction uncertainties on the H-R diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15%-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to

  6. CHARACTERIZING THE STELLAR PHOTOSPHERES AND NEAR-INFRARED EXCESSES IN ACCRETING T TAURI SYSTEMS

    SciTech Connect

    McClure, M. K.; Calvet, N.; Hartmann, L.; Ingleby, L.; Espaillat, C.; Hernandez, J.; Luhman, K. L.; D'Alessio, P.; Sargent, B. E-mail: ncalvet@umich.edu E-mail: lingleby@umich.edu E-mail: hernandj@cida.ve E-mail: p.dalessio@astrosmo.unam.mx

    2013-05-20

    Using NASA Infrared Telescope Facility SpeX data from 0.8 to 4.5 {mu}m, we determine self-consistently the stellar properties and excess emission above the photosphere for a sample of classical T Tauri stars (CTTS) in the Taurus molecular cloud with varying degrees of accretion. This process uses a combination of techniques from the recent literature as well as observations of weak-line T Tauri stars to account for the differences in surface gravity and chromospheric activity between the T Tauri stars and dwarfs, which are typically used as photospheric templates for CTTS. Our improved veiling and extinction estimates for our targets allow us to extract flux-calibrated spectra of the excess in the near-infrared. We find that we are able to produce an acceptable parametric fit to the near-infrared excesses using a combination of up to three blackbodies. In half of our sample, two blackbodies at temperatures of 8000 K and 1600 K suffice. These temperatures and the corresponding solid angles are consistent with emission from the accretion shock on the stellar surface and the inner dust sublimation rim of the disk, respectively. In contrast, the other half requires three blackbodies at 8000, 1800, and 800 K, to describe the excess. We interpret the combined two cooler blackbodies as the dust sublimation wall with either a contribution from the disk surface beyond the wall or curvature of the wall itself, neither of which should have single-temperature blackbody emission. In these fits, we find no evidence of a contribution from optically thick gas inside the inner dust rim.

  7. The photosphere-corona Interface: enrichement of the corona in low FIP elements and helium shells

    NASA Astrophysics Data System (ADS)

    Bazin, C.; Koutchmy, S.; Lamy, P.; Veselovski, I.

    2014-12-01

    Slitless consecutive spectra were obtained during the contacts of the last total solar eclipses (2008, 2009, 2010, 2012, et 2013). They allowed to show that the overabundance of low First Ionisation Potential (FIP) elements (Fe II, Ti II, Ba II) in the corona comes from the low layers of the solar atmosphere, just near and above the temperature minimum region of the high photosphere. All spectra are recorded with a fast CCD/CMOS camera, with an equivalent radial resolution of 60 milliarcseconds, or 45 km in the solar atmosphere, above a solar edge not affected by the parasitic light like it is outside of total eclipse conditions. Many emission lines of low FIP elements appear in regions situated between 200 to 600 km above the solar limb defined by the true continuum measured between the lines. This continuum appears at these altitudes where the beta of the plasma is near 1. The He I 4713 Å and He II 4686 Å (Paschen alpha line) shells appear at the height of 800 km above the solar edge and higher. The light curve I = f(h) of each ion is located at a particuliar altitude in the solar atmosphere. The scale height corresponds to a density variation, which allows to evaluate the temperature thanks to the hydrostatic equilibrium assumption. Moreover, with ionised Titanium lines taken as markers, we show a similarity between the photosphere-corona interface and the prominence-corona interface. We discuss the role of the magnetic field and the ambipolar diffusion for supplying the corona in mass, without taking into account the role of spicules. The photo-ionisation of the helium lines by the EUV coronal lines is illustrated thanks to an extract of SDO/AIA coronal stacked image simultaneously obtained.

  8. Photospheric magnitude diagrams for type II supernovat: A promising tool to compute distances

    SciTech Connect

    Rodríguez, Ósmar; Clocchiatti, Alejandro; Hamuy, Mario

    2014-12-01

    We develop an empirical color-based standardization for Type II supernovae (SNe II), equivalent to the classical surface brightness method given in Wesselink. We calibrate this standardization using SNe II with host galaxy distances measured using Cepheids, and a well-constrained shock breakout epoch and extinction due to the host galaxy. We estimate the reddening with an analysis of the B – V versus V – I color-color curves, similar to that of Natali et al. With four SNe II meeting the above requirements, we build a photospheric magnitude versus color diagram (similar to an H-R diagram) with a dispersion of 0.29 mag. We also show that when using time since shock breakout instead of color as the independent variable, the same standardization gives a dispersion of 0.09 mag. Moreover, we show that the above time-based standardization corresponds to the generalization of the standardized candle method of Hamuy and Pinto for various epochs throughout the photospheric phase. To test the new tool, we construct Hubble diagrams for different subsamples of 50 low-redshift (cz < 10{sup 4} km s{sup –1}) SNe II. For 13 SNe within the Hubble flow (cz {sub CMB} > 3000 km s{sup –1}) and with a well-constrained shock breakout epoch we obtain values of 68-69 km s{sup –1} Mpc{sup –1} for the Hubble constant and a mean intrinsic scatter of 0.12 mag or 6% in relative distances.

  9. NONLINEAR PROPAGATION OF ALFVEN WAVES DRIVEN BY OBSERVED PHOTOSPHERIC MOTIONS: APPLICATION TO THE CORONAL HEATING AND SPICULE FORMATION

    SciTech Connect

    Matsumoto, Takuma; Shibata, Kazunari

    2010-02-20

    We have performed MHD simulations of Alfven wave propagation along an open flux tube in the solar atmosphere. In our numerical model, Alfven waves are generated by the photospheric granular motion. As the wave generator, we used a derived temporal spectrum of the photospheric granular motion from G-band movies of Hinode/Solar Optical Telescope. It is shown that the total energy flux at the corona becomes larger and the transition region's height becomes higher in the case when we use the observed spectrum rather than the white/pink noise spectrum as the wave generator. This difference can be explained by the Alfven wave resonance between the photosphere and the transition region. After performing Fourier analysis on our numerical results, we have found that the region between the photosphere and the transition region becomes an Alfven wave resonant cavity. We have confirmed that there are at least three resonant frequencies, 1, 3, and 5 mHz, in our numerical model. Alfven wave resonance is one of the most effective mechanisms to explain the dynamics of the spicules and the sufficient energy flux to heat the corona.

  10. The flows of He-3 ions from the region of acceleration downwards to the photosphere

    NASA Astrophysics Data System (ADS)

    Troitskaia, Evgenia; Arkhangelskaja, Irene; Arkhangelsky, Andrey; Lishnevskii, Andrey

    We have studied the powerful solar event of January 20, 2005 by nuclear-physics methods. We based on gamma-emission data of AVS-F apparatus from SONG-D detector onboard CORONAS-F satellite. By the statistical modeling method, proposed in MSU SINP, we calculated the temporal profile of 2.223-MeV line. The calculations were performed under assumptions of Bessel type of accelerated particles energy spectrum, different (3) He content in the region of nuclear reactions to occur, and several density models of the solar atmosphere. The 4.44- and 6.13-MeV gamma-lines temporal profiles were also used. A comparison of the results of modeling with observational 2.223 MeV data reveals the numerical values of all mentioned parameters. The method gives the possibility to detect not only the time-averaged 2.223-MeV gamma-emission parameters over the whole flare, but also their evolution with the time of flare. Particularly, the comparison reveals an increase of the ratio of (3) He/ (1) H concentrations during the flare from 2×10 (-5) at the rise phase of the gamma-ray flux up to 2×10 (-4) at the decay one. The (3) He/ (1) H concentration ratio, averaged over whole time of 2.223-MeV gamma-emission, is equal to (1.40±0.15)×10(-4) . The enlarged ratio of (3) He/ (1) H in the region of nuclear reactions to occur and the increase of this ratio with the time may be understood by the supposition of the gradual accumulation of (3) He in the photosphere and low chromosphere. In this case we can assume that the increased (3) He content in the area of neutron interactions with the medium may be due to the predominant acceleration of (3) He ions in the corona. Then the ions slow down and propagate in the solar atmosphere, downward to the lower chromosphere and photosphere, where they can be accumulated. Several authors proposed different mechanisms of (3) He enrichment. For example, it was suggested that ion-acoustic turbulence could be responsible for this process (L. G. Kocharov et al

  11. Modelling the photosphere of active stars for planet detection and characterization

    NASA Astrophysics Data System (ADS)

    Herrero, Enrique; Ribas, Ignasi; Jordi, Carme; Morales, Juan Carlos; Perger, Manuel; Rosich, Albert

    2016-02-01

    Context. Stellar activity patterns are responsible for jitter effects that are observed at different timescales and amplitudes in the measurements obtained from photometric and spectroscopic time series observations. These effects are currently in the focus of many exoplanet search projects, since the lack of a well-defined characterization and correction strategy hampers the detection of the signals associated with small exoplanets. Aims: Accurate simulations of the stellar photosphere based on the most recent available models for main-sequence stars can provide synthetic photometric and spectroscopic time series data. These may help to investigate the relation between activity jitter and stellar parameters when considering different active region patterns. Moreover, jitters can be analysed at different wavelength scales (defined by the passbands of given instruments or space missions) to design strategies to remove or minimize them. Methods: We present the StarSim tool, which is based on a model for a spotted rotating photosphere built from the integration of the spectral contribution of a fine grid of surface elements. The model includes all significant effects affecting the flux intensities and the wavelength of spectral features produced by active regions and planets. The resulting synthetic time series data generated with this simulator were used to characterize the effects of activity jitter in extrasolar planet measurements from photometric and spectroscopic observations. Results: Several cases of synthetic data series for Sun-like stars are presented to illustrate the capabilities of the methodology. A specific application for characterizing and modelling the spectral signature of active regions is considered, showing that the chromatic effects of faculae are dominant for low-temperature contrasts of spots. Synthetic multi-band photometry and radial velocity time series are modelled for HD 189733 by adopting the known system parameters and fitting for the

  12. Mass loss from evolved massive stars: self-consistent modeling of the wind and photosphere

    NASA Astrophysics Data System (ADS)

    Groh, J. H.

    2007-03-01

    This work analyzes the mass loss phenomenon in evolved massive stars through self-consistent modeling of the wind and photosphere of such stars, using the radiative transfer code CMFGEN. In the first part, fundamental physical parameters of Wolf-Rayet stars of spectral types WN3-w (WR 46 e WR 152) and WN6-s (WR 136) were obtained. The results clearly indicate that hydrogen is present on the surface of those stars in a considerable fraction, defying current evolutionary models. For both WN subtypes, significant difference between the physical parameters obtained here and in previous works were noticed. The 20-year evolution of the luminous blue variable (LBV) AG Carinae was analyzed in detail in the second part of this work. The results indicate unexpected changes in the current paradigm of massive star evolution during the S Dor cycle. In this work, the high rotational velocity obtained during the hot phases, and the transition between the bistability regimes of line-driven winds were detected for the first time in LBVs. Those results need to be considered in future analysis of such massive stars. This Thesis also presents a pioneering study about the impact of the time variability effects on the analysis of the winds of LBVs. The results achieved here are valid for the whole LBV class, and show that the mass-loss rates derived from Hα and radio free-free emission are affected by time-dependent effects. The mass-loss rate evolution during the S Dor cycle, derived using time-dependent models, implies that LBV eruptions begin well before the maximum in the visual lightcurve during this phase. The analysis of the full S Dor cycle of AG Car rule out that the S Dor variability is caused exclusively by an expanding pseudo-photosphere. The AG Car hydrostatic radius was found to vary by a factor of six between cool and hot phases, while the bolometric luminosity is 50% higher during the hot phase. Both results provide observational contraints for the physical mechanism

  13. Spectroscopic Detection of a Stellar-like Photosphere in an Accreting Protostar

    NASA Technical Reports Server (NTRS)

    Greene, Thomas P.; Lada, Charles J.; DeVincenzi, Donald L. (Technical Monitor)

    2002-01-01

    We present high-resolution (R is approximately equal to 18,000), high signal-to-noise 2 micron spectra of two luminous, X-ray flaring Class I protostars in the rho Ophiuchi cloud acquired with the NIRSPEC (near infrared spectrograph) of the Keck II telescope. We present the first spectrum of a highly veiled, strongly accreting protostar which shows photospheric absorption features and demonstrates the stellar nature of its central core. We find the spectrum of the luminous (L (sub bol) = 10 solar luminosity) protostellar source, YLW 15, to be stellar-like with numerous atomic and molecular absorption features, indicative of a K5 IV/V spectral type and a continuum veiling r(sub k) = 3.0. Its derived stellar luminosity (3 stellar luminosity) and stellar radius (3.1 solar radius) are consistent with those of a 0.5 solar mass pre-main-sequence star. However, 70% of its bolometric luminosity is due to mass accretion, whose rate we estimate to be 1.7 x 10(exp -6) solar masses yr(exp -1). We determine that excess infrared emission produced by the circumstellar accretion disk, the inner infalling envelope, and accretion shocks at the surface of the stellar core of YLW 15 all contribute significantly to its near-IR (infrared) continuum veiling. Its rotational velocity v sin i = 50 km s(exp -1) is comparable to those of flat-spectrum protostars but considerably higher than those of classical T Tauri stars in the rho Oph cloud. The protostar may be magnetically coupled to its circumstellar disk at a radius of 2 - 3 R(sub *). It is also plausible that this protostar can shed over half its angular momentum and evolve into a more slowly rotating classical T Tauri star by remaining coupled to its circumstellar disk (at increasing radius) as its accretion rate drops by an order of magnitude during the rapid transition between the Class I and Class II phases of evolution. The spectrum of WL 6 does not show any photospheric absorption features, and we estimate that its continuum

  14. Using Beta Cen to Probe the Photosphere-wind Connection in B Stars

    NASA Technical Reports Server (NTRS)

    Miller, Nathan A.

    2005-01-01

    In this project we began by identifying the large number of emission lines visible in the XMM-Newton RGS spectra of Beta Cen. A comprehensive analysis of the temperature structure of the hot gas was carried out by simultaneously fitting the data from all the instruments on the spacecraft. This resulted in a measured temperature range of 0.1-0.6 keV. In more detailed analysis, three characteristic plasma temperatures were found: 0.1, 0.2, and 0.6 keV. The research carried out at UW-Eau Claire primarily focused on two aspects of the data: the analysis of the forbidden line to intercombination line ratio for He-like ions and the time variability of the overall X-ray flux as detected in the direct X-ray images of the star. The analysis of the lines from He-like ions indicate that the Ne IX lines are formed no farther than about 4 stellar radii from the star's photosphere, while the N VI lines are formed within 11 stellar radii of the photosphere. X-ray flux variability would be particularly interesting for this star because it is a known Beta Cep-type variable as seen in optical light: similar variation in the X-ray region would forge an interesting link between the two wavebands. Initial analysis of the X-ray flux was complicated by spikes in the count rates early in the observation. Detailed analysis of the spectral characteristics these count rate anomalies indicated that these flares were probably not intrinsic to the star, rather they were contaminations of the data due to the passage of the satellite through soft proton clouds in the Earth's magnetosphere. An analysis of the light curve of the uncontaminated portions of the light curve did not reveal any variation on the known optical period of variation for this star, and a general search for periodic variability also did not find any significant periods of variation.

  15. ON THE DOPPLER SHIFT AND ASYMMETRY OF STOKES PROFILES OF PHOTOSPHERIC Fe I AND CHROMOSPHERIC Mg I LINES

    SciTech Connect

    Na Deng; Choudhary, Debi Prasad; Balasubramaniam, K. S. E-mail: debiprasad.choudhary@csun.ed

    2010-08-10

    We analyzed the full Stokes spectra using simultaneous measurements of the photospheric (Fe I 630.15 and 630.25 nm) and chromospheric (Mg I b {sub 2} 517.27 nm) lines. The data were obtained with the High Altitude Observatory/National Solar Observatory (HAO/NSO) advanced Stokes polarimeter, about a near disk center sunspot region, NOAA AR 9661. We compare the characteristics of the Stokes profiles in terms of Doppler shifts and asymmetries among the three spectral lines, helping us to better understand the chromospheric lines and the magnetic and flow fields in different magnetic regions. The main results are: (1) for the penumbral area observed by the photospheric Fe I lines, Doppler velocities derived from Stokes I ({nu} {sub i}) are very close to those derived from linear polarization profiles ({nu}{sub lp}) but significantly different from those derived from Stokes V profiles ({nu}{sub zc}), thus providing direct and strong evidence that the penumbral Evershed flows are magnetized and mainly carried by the horizontal magnetic component; (2) the rudimentary inverse Evershed effect observed by the Mg I b {sub 2} line provides qualitative evidence on its formation height that is around or just above the temperature minimum region; (3) {nu}{sub zc} and {nu}{sub lp} in the penumbrae and {nu}{sub zc} in the pores generally approach their {nu} {sub i} observed by the chromospheric Mg I line, which is not the case for the photospheric Fe I lines; (4) the outer penumbrae and pores show similar Stokes V asymmetry behavior that tend to change from positive values in the photosphere (Fe I lines) to negative values in the low chromosphere (Mg I line); (5) the Stokes V profiles in plage regions are highly asymmetric in the photosphere and more symmetric in the low chromosphere; and (6) strong redshifts and large asymmetries are found around the magnetic polarity inversion line within the common penumbra of the {delta} spot. We offer explanations or speculations to the

  16. X-ray flares in GRBs: general considerations and photospheric origin

    NASA Astrophysics Data System (ADS)

    Beniamini, Paz; Kumar, Pawan

    2016-03-01

    Observations of X-ray flares from Gamma Ray Bursts imply strong constraints on possible physical models. We provide a general discussion of these. In particular, we show that in order to account for the relatively flat and weak optical flux during the X-ray flares, the size of the emitting region should be ≲3 × 1014cm. The bolometric luminosity of flares also strongly constrain the energy budget, and are inconsistent with late time activity of a central engine powered by the spin-down of a magnetar. We provide a simple toy model according to which flares are produced by an outflow of modest Lorentz factor (a few tens instead of hundreds) that is launched more or less simultaneously with the highly relativistic jet which produced the prompt gamma-ray emission. The `slower moving outflow produces the flare as it reaches its photosphere. If the X-ray flare jets are structured, the existence of such a component may naturally resolve the observational challenges imposed by flares, outlined in this work.

  17. Chromospheric and photospheric evolution of an extremely active solar region in solar cycle 19

    NASA Technical Reports Server (NTRS)

    Mckenna-Lawlor, S. M. P.

    1981-01-01

    a comprehensive investigation was made of phenomena attending the disk passage, July 7 to 21, 1959, of active solar center HAO-59Q. At the photospheric level that comprised an aggregate of groups of sunspots of which one group, Mt. Wilson 14284, showed all the attributes deemed typical of solar regions associated with the production of major flares. A special characteristic of 59Q was its capability to eject dark material. Part of this material remained trapped in the strong magnetic fields above group 14284 where it formed a system of interrelated arches, the legs of which passed through components of the bright chromospheric network of the plage and were rooted in various underlying umbrae. Two apparently diffeent kinds of flare were identified in 59Q; namely, prominence flares (which comprised brightenings within part of the suspended dark prominence) and plage flares (which comprised brightenings within part of the chromospheric network). Prominence flares were of three varieties described as 'impact', 'stationary' and 'moving' prominence flares. Plage flares were accompanied in 3 percent of cases by Type III bursts. These latter radio events indicate the associated passage through the corona of energetic electrons in the approximate energy range 10 to 100 keV. At least 87.5 percent, and probably all, impulsive brightenings in 59Q began directly above minor spots, many of which satellites to major umbrae. Stationary and moving prominence flares were individually triggered at sites beneath which magnetic changes occurred within intervals which included each flare's flash phase.

  18. Polarity Reversal of the Solar Photospheric Magnetic Field During Activity Cycle 24

    NASA Astrophysics Data System (ADS)

    Sun, Xudong; Hoeksema, Jon Todd; Liu, Yang; Zhao, Junwei

    2014-06-01

    The large-scale solar magnetic field reverses its polarity during the maximum phase of each activity cycle. As observed on the photosphere, active region (AR) magnetic flux migrates poleward in narrow, sheared streams resulted from large-scale flows and diffusion. A small net flux of the trailing sunspot polarity eventually aggregates at high latitudes, manifesting the poloidal field of the next cycle. We characterize this process for the ongoing cycle 24 based on four years' line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI). The axial dipole component reversed sign in early 2012, but the poleward flux migration was grossly out of phase in the two hemispheres. As a proxy, the northern polar field (taken as mean above 70 degrees latitude) switched from negative to positive in late 2012, whereas the southern remained positive as of March 2014. Three factors that are in line with the surface flux transport model may have contributed. First, AR emergence started and peaked earlier in the north. Second, several ARs with small or inverse tilt angles (w.r.t. the Joy's law) emerged in the south in late 2010. Third, meridional flow speed inferred from helioseismology varied greatly prior to 2013; slower streams (compared to a three-year mean at the same latitude) appeared earlier in the north. We correlate HMI with the long-running Wilcox Solar Observatory (WSO) dataset, and compare the current cycle with the previous three.

  19. Chromospheric and photospheric evolution of an extremely active solar region in solar cycle 19

    SciTech Connect

    Mckenna-Lawlor, S.M.P.

    1981-08-01

    a comprehensive investigation was made of phenomena attending the disk passage, July 7 to 21, 1959, of active solar center HAO-59Q. At the photospheric level that comprised an aggregate of groups of sunspots of which one group, Mt. Wilson 14284, showed all the attributes deemed typical of solar regions associated with the production of major flares. A special characteristic of 59Q was its capability to eject dark material. Part of this material remained trapped in the strong magnetic fields above group 14284 where it formed a system of interrelated arches, the legs of which passed through components of the bright chromospheric network of the plage and were rooted in various underlying umbrae. Two apparently diffeent kinds of flare were identified in 59Q namely, prominence flares (which comprised brightenings within part of the suspended dark prominence) and plage flares (which comprised brightenings within part of the chromospheric network). Prominence flares were of three varieties described as 'impact', 'stationary' and 'moving' prominence flares. Plage flares were accompanied in 3 percent of cases by Type III bursts. These latter radio events indicate the associated passage through the corona of energetic electrons in the approximate energy range 10 to 100 keV. At least 87.5 percent, and probably all, impulsive brightenings in 59Q began directly above minor spots, many of which satellites to major umbrae. Stationary and moving prominence flares were individually triggered at sites beneath which magnetic changes occurred within intervals which included each flare's flash phase.

  20. Measurements of magnetic fluxes and field strengths in the photospheric network

    NASA Technical Reports Server (NTRS)

    Tarbell, T. D.; Title, A. M.

    1977-01-01

    Digital pictures of an active-region network cell are presented in five quantities measured simultaneously: continuum intensity, line-center intensity, equivalent width, magnetogram signal, and magnetic-field strength. These maps are derived from computer analysis of circularly polarized line profiles of Fe I 5250.2-A; spectral and spatial resolution are 1/40 A and 1.5 arcsec, respectively. Measured Zeeman splittings show the existence of strong magnetic fields (1000-1800 G) at nearly all points with a magnetogram signal exceeding 125 G. The mean and rms deviation of the field strengths change by less than 20% over a factor-of-four range of fluxes. From the significant disparity between measured fluxes and field strengths, it is concluded that large flux patches (up to 4 arcsec across) consist of closely-packed unresolved filaments. The smallest filaments must be less than 0.7 arcsec in diameter. The dark component of the photospheric network, which appears to contain sizable transverse fields, is also observed.

  1. Milne-Eddington inversion for unresolved magnetic structures in the quiet Sun photosphere

    NASA Astrophysics Data System (ADS)

    Bommier, Véronique

    2016-06-01

    This paper is first devoted to present our method for modeling unresolved magnetic structures in the Milne-Eddington inversion of spectropolarimetric data. The related definitions and other approaches and different used inversion algorithms are recalled for comparison. In a second part, we apply our method to quiet Sun data outside active regions. We obtain the quiet Sun photospheric magnetic field as composed of unresolved opening and connected magnetic flux tubes, which form a loop carpet of field lines. We then analyze the spatial correlation, which we also observed for the magnetic field vector, in terms of flux tube diameter, distance, and field strength. We find that different observations with the Zurich imaging polarimeter and THEMIS polarimeter mounted on the THEMIS telescope give very close results, and we add results also very close derived from HINODE/Solar Optical Telescope/spectropolarimeter observations analyzed with the same method. We obtain a mean flux tube diameter of 30 km, a mean flux tube distance of 230 km, and a mean flux tube magnetic field of 1.3 kG.

  2. SIMULTANEOUS OBSERVATION OF SOLAR OSCILLATIONS ASSOCIATED WITH CORONAL LOOPS FROM THE PHOTOSPHERE TO THE CORONA

    SciTech Connect

    Su, J. T.; Liu, S.; Zhang, Y. Z.; Zhao, H.; Xu, H. Q.; Xie, W. B.; Liu, Y.

    2013-01-01

    The solar oscillations along one coronal loop in AR 11504 are observed simultaneously in white light emission and Doppler velocity by SDO/HMI, and in UV and EUV emissions by SDO/AIA. The technique of the time-distance diagram is used to detect the propagating oscillations of the emission intensities along the loop. We find that although all the oscillation signals were intercorrelated, the low chromospheric oscillation correlated more closely to the oscillations of the transition region and corona than to those of the photosphere. Situated above the sunspot, the oscillation periods were {approx}3 minutes in the UV/EUV emissions; however, moving away from the sunspot and into the quiet Sun, the periods became longer, e.g., up to {approx}5 minutes or more. In addition, along another loop we observe both the high-speed outflows and oscillations, which roughly had a one-to-one corresponding relationship. This indicates that the solar periodic oscillations may modulate the magnetic reconnections between the loops of the high and low altitudes that drive the high-speed outflows along the loop.

  3. Markov Properties of the Magnetic Field in the Quiet Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Gorobets, A. Y.; Borrero, J. M.; Berdyugina, S.

    2016-07-01

    The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we study the temporal stochasticity of the magnetic field on the solar surface without relying on either the concept of magnetic feature or on the subjective assumptions about their identification and interaction. The analysis is applied to observations of the magnetic field of the quiet solar photosphere carried out with the Imaging Magnetograph eXperiment (IMaX) instrument on board the stratospheric balloon, Sunrise. We show that the joint probability distribution functions of the longitudinal ({B}\\parallel ) and transverse ({B}\\perp ) components of the magnetic field, as well as of the magnetic pressure ({B}2={B}\\perp 2+{B}\\parallel 2), verify the necessary and sufficient condition for the Markov chains. Therefore, we establish that the magnetic field as seen by IMaX with a resolution of 0.″15–0.″18 and 33 s cadence, which can be considered as a memoryless temporal fluctuating quantity.

  4. Dynamic Power Spectral Analysis of Solar Measurements from Photospheric, Chromospheric, and Coronal Sources

    NASA Technical Reports Server (NTRS)

    Bouwer, S. D.; Pap, J.; Donnelly, R. F.

    1990-01-01

    An important aspect in the power spectral analysis of solar variability is the quasistationary and quasiperiodic nature of solar periodicities. In other words, the frequency, phase, and amplitude of solar periodicities vary on time scales ranging from active region lifetimes to solar cycle time scales. Here, researchers employ a dynamic, or running, power spectral density analysis to determine many periodicities and their time-varying nature in the projected area of active sunspot groups (S sub act). The Solar Maximum Mission/Active Cavity Radiometer Irradiance Monitor (SMM/ACRIM) total solar irradiance (S), the Nimbus-7 MgII center-to-wing ratio (R (MgII sub c/w)), the Ottawa 10.7 cm flux (F sub 10.7), and the GOES background x ray flux (X sub b) for the maximum, descending, and minimum portions of solar cycle 21 (i.e., 1980 to 1986) are used. The technique dramatically illustrates several previously unrecognized periodicities. For example, a relatively stable period at about 51 days has been found in those indices which are related to emerging magnetic fields. The majority of solar periodicities, particularly around 27, 150 and 300 days, are quasiperiodic because they vary in amplitude and frequency throughout the solar cycle. Finally, it is shown that there are clear differences between the power spectral densities of solar measurements from photospheric, chromospheric, and coronal sources.

  5. MAGNETIC NONPOTENTIALITY IN PHOTOSPHERIC ACTIVE REGIONS AS A PREDICTOR OF SOLAR FLARES

    SciTech Connect

    Yang Xiao; Lin Ganghua; Zhang Hongqi; Mao Xinjie

    2013-09-10

    Based on several magnetic nonpotentiality parameters obtained from the vector photospheric active region magnetograms obtained with the Solar Magnetic Field Telescope at the Huairou Solar Observing Station over two solar cycles, a machine learning model has been constructed to predict the occurrence of flares in the corresponding active region within a certain time window. The Support Vector Classifier, a widely used general classifier, is applied to build and test the prediction models. Several classical verification measures are adopted to assess the quality of the predictions. We investigate different flare levels within various time windows, and thus it is possible to estimate the rough classes and erupting times of flares for particular active regions. Several combinations of predictors have been tested in the experiments. The True Skill Statistics are higher than 0.36 in 97% of cases and the Heidke Skill Scores range from 0.23 to 0.48. The predictors derived from longitudinal magnetic fields do perform well, however, they are less sensitive in predicting large flares. Employing the nonpotentiality predictors from vector fields improves the performance of predicting large flares of magnitude {>=}M5.0 and {>=}X1.0.

  6. FIRST SIMULTANEOUS DETECTION OF MOVING MAGNETIC FEATURES IN PHOTOSPHERIC INTENSITY AND MAGNETIC FIELD DATA

    SciTech Connect

    Lim, Eun-Kyung; Yurchyshyn, Vasyl; Goode, Philip

    2012-07-01

    The formation and the temporal evolution of a bipolar moving magnetic feature (MMF) was studied with high-spatial and temporal resolution. The photometric properties were observed with the New Solar Telescope at Big Bear Solar Observatory using a broadband TiO filter (705.7 nm), while the magnetic field was analyzed using the spectropolarimetric data obtained by Hinode. For the first time, we observed a bipolar MMF simultaneously in intensity images and magnetic field data, and studied the details of its structure. The vector magnetic field and the Doppler velocity of the MMF were also studied. A bipolar MMF with its positive polarity closer to the negative penumbra formed, accompanied by a bright, filamentary structure in the TiO data connecting the MMF and a dark penumbral filament. A fast downflow ({<=}2 km s{sup -1}) was detected at the positive polarity. The vector magnetic field obtained from the full Stokes inversion revealed that a bipolar MMF has a U-shaped magnetic field configuration. Our observations provide a clear intensity counterpart of the observed MMF in the photosphere, and strong evidence of the connection between the MMF and the penumbral filament as a serpentine field.

  7. Using Beta Cen to Probe the Photosphere-Wind Connection to B Stars

    NASA Technical Reports Server (NTRS)

    MacFarlane, Joseph J.

    2005-01-01

    The goal of the project was to probe the connection between the photospheric pulsations and the X-ray production in the stellar winds of B stars. The B1 III star Beta Centauri is a Beta Cephei variable with a high X-ray count rate, and was observed by XMM. Analysis of XMM X-ray spectra showed characteristic plasma temperatures of 0.1, 0.2 and 0.6 keV. Analysis of He-like forbidden-to-intercombination lines was performed to determine the dominant locations of the X-ray emission. At Prism, work focused on developing and upgrading spectral models to calculate forbidden-to-intercombination line ratios using more detailed atomic models than the simple models typically used in the analysis of X-ray spectral lines, thereby allowing us to assess the effects of a broader variety of populating and depopulating channels for energy levels contributing to the observed X-ray line emission. Based on Ne IX lines, the source location was determined to be no farther than 4 stellar radii. Examination of the time variability of the XMM data for Beta Cen showed no significant correlation with the known optical pulsation period for the star, and also did not find any significant periods of variation at X-ray wavelengths.

  8. Probing pulsation physics by resolving dynamical structure in the photosphere of V652 Herculis

    NASA Astrophysics Data System (ADS)

    Jeffery, Simon

    2015-08-01

    The extrem helium star V652 Herculis is pulsating in a fundamental radial model with a period of 0.1 d. Amongst many other unique properties, the radial motion of the surface can be cleanly divided into an intense acceleration phase followed by a near ballistic phase. The major question was whether the accelaration phase is shocked. In addition, the transparency of the hydrogen-deficient atmosphere means that layers of the atmosphere are observed which are deeper than is normal in hydrogen-rich stars. New observations have been able to resolve the vertical motion of the photosphere as a function of optical depth, and hence have mapped the outward passage of minimum radius. New hydrodynamic models for the pulsation are being developed, and these are coupled to a formal radiative transfer solution in order to model the dynamical spectrum directly. We will present the latest models for the pulsations in V652 Her, compare these with our Subaru high-resolution observations, and endeavour to extract new information about the overall and internal properties of V652 Her - the born-again rocket star.

  9. Diagnosis of Flow and Magnetic Fields Using Simultaneous Spectro-Polarimetry of Photospheric Fe I and Chromospheric Mg I lines

    NASA Astrophysics Data System (ADS)

    Deng, N.; Choudhary, D. P.; Balasubramaniam, K. S.

    2012-08-01

    We present a study of active region (AR) NOAA 9661 using simultaneous spectro-polarimetric observations of photospheric Fe I (630.25 and 630.15 nm) and chromospheric Mg I b2 (517.27 nm) lines obtained with the HAO/NSO Advanced Stokes Polarimeter (ASP). SIR (Stokes Inversion based on Response function) code was applied to the Stokes spectra of Fe I line pair and Mg I line, thus providing magnetic field vectors at the photosphere and low chromosphere. We quantitatively compared the magnetic field at the two heights and obtained reasonable results. Doppler velocities were extracted from both Stokes I and V profiles of the three spectral lines, which reveal strong red shifts in the penumbra near the magnetic neutral line.

  10. RESPONSE OF THE PHOTOSPHERIC MAGNETIC FIELD TO THE X2.2 FLARE ON 2011 FEBRUARY 15

    SciTech Connect

    Wang Shuo; Liu Chang; Liu Rui; Deng Na; Wang Haimin; Liu Yang

    2012-02-15

    It is well known that the long-term evolution of the photospheric magnetic field plays an important role in building up free energy to power solar eruptions. Observations, despite being controversial, have also revealed a rapid and permanent variation of the photospheric magnetic field in response to the coronal magnetic field restructuring during the eruption. The Helioseismic and Magnetic Imager instrument (HMI) on board the newly launched Solar Dynamics Observatory produces seeing-free full-disk vector magnetograms at consistently high resolution and high cadence, which finally makes possible an unambiguous and comprehensive study of this important back-reaction process. In this study, we present a near disk-center, GOES-class X2.2 flare, which occurred in NOAA AR 11158 on 2011 February 15. Using the magnetic field measurements made by HMI, we obtained the first solid evidence of a rapid (in about 30 minutes) and irreversible enhancement in the horizontal magnetic field at the flaring magnetic polarity inversion line (PIL) by a magnitude of {approx}30%. It is also shown that the photospheric field becomes more sheared and more inclined. This field evolution is unequivocally associated with the flare occurrence in this sigmoidal active region, with the enhancement area located in between the two chromospheric flare ribbons and the initial conjugate hard X-ray footpoints. These results strongly corroborate our previous conjecture that the photospheric magnetic field near the PIL must become more horizontal after eruptions, which could be related to the newly formed low-lying fields resulting from the tether-cutting reconnection.

  11. PHOTOSPHERIC FLOW FIELD RELATED TO THE EVOLUTION OF THE SUN'S POLAR MAGNETIC PATCHES OBSERVED BY HINODE SOLAR OPTICAL TELESCOPE

    SciTech Connect

    Kaithakkal, Anjali John; Suematsu, Y.; Kubo, M.; Iida, Y.; Tsuneta, S.; Shiota, D.

    2015-02-01

    We investigated the role of photospheric plasma motions in the formation and evolution of polar magnetic patches using time-sequence observations with high spatial resolution. The observations were obtained with the spectropolarimeter on board the Hinode satellite. From the statistical analysis using 75 magnetic patches, we found that they are surrounded by strong converging, supergranulation associated flows during their apparent lifetime and that the converging flow around the patch boundary is better observed in the Doppler velocity profile in the deeper photosphere. Based on our analysis, we suggest that the like-polarity magnetic fragments in the polar region are advected and clustered by photospheric converging flows, thereby resulting in the formation of polar magnetic patches. Our observations show that, in addition to direct cancellation, magnetic patches decay by fragmentation followed by unipolar disappearance or unipolar disappearance without fragmentation. It is possible that the magnetic patches of existing polarity fragment or diffuse away into smaller elements and eventually cancel out with opposite polarity fragments that reach the polar region around the solar cycle maximum. This could be one of the possible mechanisms by which the existing polarity decays during the reversal of the polar magnetic field.

  12. Objective Image-Quality Assessment for High-Resolution Photospheric Images by Median Filter-Gradient Similarity

    NASA Astrophysics Data System (ADS)

    Deng, Hui; Zhang, Dandan; Wang, Tianyu; Ji, Kaifan; Wang, Feng; Liu, Zhong; Xiang, Yongyuan; Jin, Zhenyu; Cao, Wenda

    2015-05-01

    All next-generation ground-based and space-based solar telescopes require a good quality-assessment metric to evaluate their imaging performance. In this paper, a new image quality metric, the median filter-gradient similarity (MFGS) is proposed for photospheric images. MFGS is a no-reference/blind objective image-quality metric (IQM) by a measurement result between 0 and 1 and has been performed on short-exposure photospheric images captured by the New Vacuum Solar Telescope (NVST) of the Fuxian Solar Observatory and by the Solar Optical Telescope (SOT) onboard the Hinode satellite, respectively. The results show that (1) the measured value of the MFGS changes monotonically from 1 to 0 with degradation of image quality; (2) there exists a linear correlation between the measured values of the MFGS and the root-mean-square contrast (RMS-contrast) of the granulation; (3) the MFGS is less affected by the image contents than the granular RMS-contrast. Overall, the MFGS is a good alternative for the quality assessment of photospheric images.

  13. SUDDEN PHOTOSPHERIC MOTION AND SUNSPOT ROTATION ASSOCIATED WITH THE X2.2 FLARE ON 2011 FEBRUARY 15

    SciTech Connect

    Wang, Shuo; Liu, Chang; Deng, Na; Wang, Haimin

    2014-02-20

    The Helioseismic and Magnetic Imager provides 45 s cadence intensity images and 720 s cadence vector magnetograms. These unprecedented high-cadence and high-resolution data give us a unique opportunity to study the change of photospheric flows and sunspot rotations associated with flares. By using the differential affine velocity estimator method and the Fourier local correlation tracking method separately, we calculate velocity and vorticity of photospheric flows in the flaring NOAA AR 11158, and investigate their temporal evolution around the X2.2 flare on 2011 February 15. It is found that the shear flow around the flaring magnetic polarity inversion line exhibits a sudden decrease, and both of the two main sunspots undergo a sudden change in rotational motion during the impulsive phase of the flare. These results are discussed in the context of the Lorentz-force change that was proposed by Hudson et al. and Fisher et al. This mechanism can explain the connections between the rapid and irreversible photospheric vector magnetic field change and the observed short-term motions associated with the flare. In particular, the torque provided by the horizontal Lorentz force change agrees with what is required for the measured angular acceleration.

  14. ABRUPT CHANGES OF THE PHOTOSPHERIC MAGNETIC FIELD IN ACTIVE REGIONS AND THE IMPULSIVE PHASE OF SOLAR FLARES

    SciTech Connect

    Cliver, E. W.; Petrie, G. J. D.; Ling, A. G.

    2012-09-10

    We compared time profiles of changes of the unsigned photospheric magnetic flux in active regions with those of their associated soft X-ray (SXR) bursts for a sample of 75 {>=} M5 flares well observed by Global Oscillation Network Group longitudinal magnetographs. Sixty-six of these events had stepwise changes in the spatially integrated unsigned flux during the SXR flares. In superposed epoch plots for these 66 events, there is a sharp increase in the unsigned magnetic flux coincident with the onset of the flare impulsive phase while the end of the stepwise change corresponds to the time of peak SXR emission. We substantiated this result with a histogram-based comparison of the timing of flux steps (onset, midpoint of step, and end) for representative points in the flaring regions with their associated SXR event time markers (flare onset, onset of impulsive phase, time of peak logarithmic derivative, maximum). On an individual event basis, the principal part of the stepwise magnetic flux change occurred during the main rise phase of the SXR burst (impulsive phase onset to SXR peak) for {approx}60% of the 66 cases. We find a close timing agreement between magnetic flux steps and >100 keV emission for the three largest hard X-ray (>100 keV) bursts in our sample. These results identify the abrupt changes in photospheric magnetic fields as an impulsive phase phenomenon and indicate that the coronal magnetic field changes that drive flares are rapidly transmitted to the photosphere.

  15. Understanding Solar Eruptions with SDO/HMI Measuring Photospheric Flows, Testing Models, and Steps Towards Forecasting Solar Eruptions

    NASA Technical Reports Server (NTRS)

    Schuck, Peter W.; Linton, Mark; Muglach, Karin; Welsch, Brian; Hageman, Jacob

    2010-01-01

    The imminent launch of Solar Dynamics Observatory (SDO) will carry the first full-disk imaging vector magnetograph, the Helioseismic and Magnetic Imager (HMI), into an inclined geosynchronous orbit. This magnetograph will provide nearly continuous measurements of photospheric vector magnetic fields at cadences of 90 seconds to 12 minutes with I" resolution, precise pointing, and unfettered by atmospheric seeing. The enormous data stream of 1.5 Terabytes per day from SDO will provide an unprecedented opportunity to understand the mysteries of solar eruptions. These ground-breaking observations will permit the application of a new technique, the differential affine velocity estimator for vector magnetograms (DAVE4VM), to measure photospheric plasma flows in active regions. These measurements will permit, for the first time, accurate assessments of the coronal free energy available for driving CMEs and flares. The details of photospheric plasma flows, particularly along magnetic neutral-lines, are critical to testing models for initiating coronal mass ejections (CMEs) and flares. Assimilating flows and fields into state-of-the art 3D MHD simulations that model the highly stratified solar atmosphere from the convection zone to the corona represents the next step towards achieving NASA's Living with a Star forecasting goals of predicting "when a solar eruption leading to a CME will occur." This talk will describe these major science and predictive advances that will be delivered by SDO /HMI.

  16. ON THE FORCE-FREE NATURE OF PHOTOSPHERIC SUNSPOT MAGNETIC FIELDS AS OBSERVED FROM HINODE (SOT/SP)

    SciTech Connect

    Tiwari, Sanjiv Kumar

    2012-01-01

    A magnetic field is force-free if there is no interaction between it and the plasma in the surrounding atmosphere, i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. The computation of various magnetic parameters, such as magnetic energy (using the virial theorem), gradient of twist of sunspot magnetic fields (computed from the force-free parameter {alpha}), and any kind of extrapolation, heavily hinges on the force-free approximation of the photospheric sunspot magnetic fields. Thus, it is of vital importance to inspect the force-free behavior of sunspot magnetic fields. The force-free nature of sunspot magnetic fields has been examined earlier by some researchers, ending with incoherent results. Accurate photospheric vector field measurements with high spatial resolution are required to inspect the force-free nature of sunspots. For this purpose, we use several vector magnetograms of high spatial resolution obtained from the Solar Optical Telescope/Spectro-Polarimeter on board Hinode. Both the necessary and sufficient conditions for force-free nature are examined by checking the global and local nature of equilibrium magnetic forces over sunspots. We find that sunspot magnetic fields are not very far from the force-free configuration, although they are not completely force-free on the photosphere. The umbral and inner penumbral fields are more force-free than the middle and outer penumbral fields. During their evolution, sunspot magnetic fields are found to maintain their proximity to force-free field behavior. Although a dependence of net Lorentz force components is seen on the evolutionary stages of the sunspots, we do not find a systematic relationship between the nature of sunspot magnetic fields and the associated flare activity. Further, we examine whether the fields at the photosphere follow linear or nonlinear force-free conditions. After examining this in various complex and simple sunspots, we conclude that

  17. Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

    NASA Astrophysics Data System (ADS)

    Beck, C.; Fabbian, D.; Moreno-Insertis, F.; Puschmann, K. G.; Rezaei, R.

    2013-09-01

    Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to check that no excessive thermodynamic fluctuations arise as a consequence of the partially incomplete treatment of radiative transfer causing radiative damping that is too modest. Aims: We investigate the realism of the thermodynamics in recent state-of-the-art 3D convection simulations of the solar atmosphere carried out with the Stagger code. Methods: We compared the characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565 nm) and one Si i line at 1082.7 nm in solar disc-centre observations of different spatial resolution with spectra synthesized from 3D convection simulations. The observations were taken with ground-based (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI), POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all at the Vacuum Tower Telescope on Tenerife) and space-based instruments (Hinode/Spectropolarimeter). We degraded the synthetic spectra to the spatial resolution of the observations, based on the distribution of the continuum intensity Ic. We estimated the spectral degradation to be applied to the simulation results by comparing atlas spectra with averaged observed spectra. In addition to deriving a set of line parameters directly from the intensity profiles, we used the SIR (Stokes Inversion based on Response functions) code to invert the spectra. Results: The spatial degradation kernels yield a similar generic spatial stray-light contamination of about 30% for all instruments. The spectral stray light inside the different spectrometers is found to be between 2% and 20%. Most of the line parameters from the observational data are matched by the degraded

  18. Evolution and dynamics of orphan penumbrae in the solar photosphere: Analysis from multi-instrument observations

    SciTech Connect

    Zuccarello, Francesca; Guglielmino, Salvo L.; Romano, Paolo

    2014-05-20

    We investigate the dynamics and magnetic properties of orphan penumbrae observed in the solar photosphere to understand the formation process of such structures. We observed two orphan penumbrae in active region NOAA 11089 during a coordinated observing campaign carried out in 2010 July, involving the Hinode/Solar Optical Telescope (SOT) and Dutch Open Telescope (DOT), benefiting also from continuous observations acquired by the SDO satellite. We follow their evolution during about three days. The two structures form in different ways: one seems to break off the penumbra of a nearby sunspot, the other is formed through the emergence of new flux. Then they fragment while evolving. The SDO Helioseismic and Magnetic Imager measurements indicate the presence of strong line-of-sight motions in the regions occupied by these orphan penumbrae, lasting for several hours and decreasing with time. This is confirmed by SOT spectro-polarimetric measurements of the Fe I 630.2 nm pair. The latter also show that Stokes parameters exhibit significant asymmetries in the orphan penumbral regions, typical of an uncombed filamentary structure. The orphan penumbrae lie above polarity inversion lines, where peculiar plasma motions take place with velocities larger than ±3 km s{sup –1}. The vector magnetic field in these regions is highly inclined, with the average magnetic field strength decreasing with time. The DOT observations in the Hα line and SDO Atmospheric Imaging Assembly measurements in the He II 30.4 nm line indicate that there is no counterpart for the orphan penumbrae at midchromospheric heights or above. Our findings suggest that in at least one of the features investigated the emerging flux may be trapped in the low atmospheric layers by the overlying pre-existing fields, forming these filamentary structures.

  19. CHROMOSPHERIC RAPID BLUESHIFTED EXCURSIONS OBSERVED WITH IBIS AND THEIR ASSOCIATION WITH PHOTOSPHERIC MAGNETIC FIELD EVOLUTION

    SciTech Connect

    Deng, Na; Chen, Xin; Liu, Chang; Jing, Ju; Wang, Shuo; Wang, Haimin; Tritschler, Alexandra; Reardon, Kevin P.; Lamb, Derek A.; Deforest, Craig E.; Denker, Carsten; Liu, Rui

    2015-02-01

    Chromospheric rapid blueshifted excursions (RBEs) are suggested to be the disk counterparts of type II spicules at the limb and believed to contribute to the coronal heating process. Previous identification of RBEs was mainly based on feature detection using Dopplergrams. In this paper, we study RBEs on 2011 October 21 in a very quiet region at the disk center, which were observed with the high-cadence imaging spectroscopy of the Ca II 8542 Å line from the Interferometric Bidimensional Spectrometer (IBIS). By using an automatic spectral analysis algorithm, a total of 98 RBEs are identified during an 11 minute period. Most of these RBEs have either a round or elongated shape, with an average area of 1.2 arcsec{sup 2}. The detailed temporal evolution of spectra from IBIS makes possible a quantitative determination of the velocity (∼16 km s{sup –1}) and acceleration (∼400 m s{sup –2}) of Ca II 8542 RBEs, and reveals an additional deceleration (∼–160 m s{sup –2}) phase that usually follows the initial acceleration. In addition, we also investigate the association of RBEs with the concomitant photospheric magnetic field evolution, using coordinated high-resolution and high-sensitivity magnetograms made by Hinode. Clear examples are found where RBEs appear to be associated with the preceding magnetic flux emergence and/or the subsequent flux cancellation. However, further analysis with the aid of the Southwest Automatic Magnetic Identification Suite does not yield a significant statistical association between these RBEs and magnetic field evolution. We discuss the implications of our results in the context of understanding the driving mechanism of RBEs.

  20. The expanding photosphere method applied to SN 1992am AT cz = 14 600 km/s

    NASA Technical Reports Server (NTRS)

    Schmidt, Brian P.; Kirshner, Robert P.; Eastman, Ronald G.; Hamuy, Mario; Phillips, Mark M.; Suntzeff, Nicholas B.; Maza, Jose; Filippenko, Alexei V.; Ho, Luis C.; Matheson, Thomas

    1994-01-01

    We present photometry and spectroscopy of Supernova (SN) 1992am for five months following its discovery by the Calan Cerro-Tololo Inter-American Observatory (CTIO) SN search. These data show SN 1992am to be type II-P, displaying hydrogen in its spectrum and the typical shoulder in its light curve. The photometric data and the distance from our own analysis are used to construct the supernova's bolometric light curve. Using the bolometric light curve, we estimate SN 1992am ejected approximately 0.30 solar mass of Ni-56, an amount four times larger than that of other well studied SNe II. SN 1992am's; host galaxy lies at a redshift of cz = 14 600 km s(exp -1), making it one of the most distant SNe II discovered, and an important application of the Expanding Photsphere Method. Since z = 0.05 is large enough for redshift-dependent effects to matter, we develop the technique to derive luminosity distances with the Expanding Photosphere Method at any redshift, and apply this method to SN 1992am. The derived distance, D = 180(sub -25) (sup +30) Mpc, is independent of all other rungs in the extragalactic distance ladder. The redshift of SN 1992am's host galaxy is sufficiently large that uncertainties due to perturbations in the smooth Hubble flow should be smaller than 10%. The Hubble ratio derived from the distance and redshift of this single object is H(sub 0) = 81(sub -15) (sup +17) km s(exp -1) Mpc(exp -1). In the future, with more of these distant objects, we hope to establish an independent and statistically robust estimate of H(sub 0) based solely on type II supernovae.

  1. Creation of the CMB spectrum: precise analytic solutions for the blackbody photosphere

    SciTech Connect

    Khatri, Rishi; Sunyaev, Rashid A. E-mail: sunyaev@mpa-Garching.mpg.de

    2012-06-01

    The blackbody spectrum of CMB was created in the blackbody photosphere at redshifts z∼>2 × 10{sup 6}. At these early times, the Universe was dense and hot enough that complete thermal equilibrium between baryonic matter (electrons and ions) and photons could be established on time scales much shorter than the age of the Universe. Any perturbation away from the blackbody spectrum was suppressed exponentially. New physics, for example annihilation and decay of dark matter, can add energy and photons to CMB at redshifts z∼>10{sup 5} and result in a Bose-Einstein spectrum with a non-zero chemical potential (μ). Precise evolution of the CMB spectrum around the critical redshift of z ≅ 2 × 10{sup 6} is required in order to calculate the μ-type spectral distortion and constrain the underlying new physics. Although numerical calculation of important processes involved (double Compton process, comptonization and bremsstrahlung) is not difficult with present day computers, analytic solutions are much faster and easier to calculate and provide valuable physical insights. We provide precise (better than 1%) analytic solutions for the decay of μ, created at an earlier epoch, including all three processes, double Compton, Compton scattering on thermal electrons and bremsstrahlung in the limit of small distortions. This is a significant improvement over the existing solutions with accuracy ∼ 10% or worse. We also give a census of important sources of energy injection into CMB in standard cosmology. In particular, calculations of distortions from electron-positron annihilation and primordial nucleosynthesis illustrate in a dramatic way the strength of the equilibrium restoring processes in the early Universe. Finally, we point out the triple degeneracy in standard cosmology, i.e., the μ and y distortions from adiabatic cooling of baryons and electrons, Silk damping and annihilation of thermally produced WIMP dark matter are of similar order of magnitude ( ∼ 10{sup

  2. Thermohaline mixing and the photospheric composition of low-mass giant stars

    NASA Astrophysics Data System (ADS)

    Wachlin, F. C.; Miller Bertolami, M. M.; Althaus, L. G.

    2011-09-01

    Aims: By means of numerical simulations and different recipes, we test the efficiency of thermohaline mixing as a process to alter the surface abundances in low-mass giant stars. Methods: We compute full evolutionary sequences of red giant branch stars close to the luminosity bump by including state-of-the-art composition transport prescriptions for the thermohaline mixing regimes. In particular, we adopt a self-consistent double-diffusive convection theory that allows handling both instabilities that arise when thermal and composition gradients compete against each other and a very recent empirically motivated and parameter-free asymptotic scaling law for thermohaline composition transport. Results: In agreement with previous works, we find that, during the red giant stage, a thermohaline instability sets in shortly after the hydrogen burning shell (HBS) encounters the chemical discontinuity left behind by the first dredge-up. We also find that the thermohaline unstable region, which initially appears on the exterior wing of the HBS, is unable to reach the outer convective envelope, with the consequence that no mixing of elements occurs that produces a noncanonical modification of the stellar surface abundances. Also in agreement with previous works, we find that artificially increasing the mixing efficiency of thermohaline regions makes it possible to connect both unstable regions, thus affecting the photospheric composition. However, we find that to reproduce the observed abundances of red giant branch stars close to the luminosity bump, thermohaline mixing efficiency has to be artificially increased by about four orders of magnitude from what is predicted by recent 3D numerical simulations of thermohaline convection close to astrophysical environments. From this we conclude that the chemical abundance anomalies of red giant stars cannot be explained on the basis of thermohaline mixing alone.

  3. Evolution and Dynamics of Orphan Penumbrae in the Solar Photosphere: Analysis from Multi-instrument Observations

    NASA Astrophysics Data System (ADS)

    Zuccarello, Francesca; Guglielmino, Salvo L.; Romano, Paolo

    2014-05-01

    We investigate the dynamics and magnetic properties of orphan penumbrae observed in the solar photosphere to understand the formation process of such structures. We observed two orphan penumbrae in active region NOAA 11089 during a coordinated observing campaign carried out in 2010 July, involving the Hinode/Solar Optical Telescope (SOT) and Dutch Open Telescope (DOT), benefiting also from continuous observations acquired by the SDO satellite. We follow their evolution during about three days. The two structures form in different ways: one seems to break off the penumbra of a nearby sunspot, the other is formed through the emergence of new flux. Then they fragment while evolving. The SDO Helioseismic and Magnetic Imager measurements indicate the presence of strong line-of-sight motions in the regions occupied by these orphan penumbrae, lasting for several hours and decreasing with time. This is confirmed by SOT spectro-polarimetric measurements of the Fe I 630.2 nm pair. The latter also show that Stokes parameters exhibit significant asymmetries in the orphan penumbral regions, typical of an uncombed filamentary structure. The orphan penumbrae lie above polarity inversion lines, where peculiar plasma motions take place with velocities larger than ±3 km s-1. The vector magnetic field in these regions is highly inclined, with the average magnetic field strength decreasing with time. The DOT observations in the Hα line and SDO Atmospheric Imaging Assembly measurements in the He II 30.4 nm line indicate that there is no counterpart for the orphan penumbrae at midchromospheric heights or above. Our findings suggest that in at least one of the features investigated the emerging flux may be trapped in the low atmospheric layers by the overlying pre-existing fields, forming these filamentary structures.

  4. ELLERMAN BOMBS AT HIGH RESOLUTION. I. MORPHOLOGICAL EVIDENCE FOR PHOTOSPHERIC RECONNECTION

    SciTech Connect

    Watanabe, Hiroko; Kitai, Reizaburo; Vissers, Gregal; Rouppe van der Voort, Luc; Rutten, Robert J.

    2011-07-20

    High-resolution imaging-spectroscopy movies of solar active region NOAA 10998 obtained with the Crisp Imaging Spectropolarimeter at the Swedish 1-m Solar Telescope show very bright, rapidly flickering, flame-like features that appear intermittently in the wings of the Balmer H{alpha} line in a region with moat flows and likely some flux emergence. They show up at regular H{alpha} blue-wing bright points that outline the magnetic network, but flare upward with much larger brightness and distinct 'jet' morphology seen from aside in the limbward view of these movies. We classify these features as Ellerman bombs and present a morphological study of their appearance at the unprecedented spatial, temporal, and spectral resolution of these observations. The bombs appear along the magnetic network with footpoint extents up to 900 km. They show apparent travel away from the spot along the pre-existing network at speeds of about 1 km s{sup -1}. The bombs flare repetitively with much rapid variation at timescales of seconds only, in the form of upward jet-shaped brightness features. These reach heights of 600-1200 km and tend to show blueshifts; some show bi-directional Doppler signature and some seem accompanied with an H{alpha} surge. They are not seen in the core of H{alpha} due to shielding by overlying chromospheric fibrils. The network where they originate has normal properties. The morphology of these jets strongly supports deep-seated photospheric reconnection of emergent or moat-driven magnetic flux with pre-existing strong vertical network fields as the mechanism underlying the Ellerman bomb phenomenon.

  5. PHOTOSPHERIC FLUX CANCELLATION AND THE BUILD-UP OF SIGMOIDAL FLUX ROPES ON THE SUN

    SciTech Connect

    Savcheva, A. S.; Van Ballegooijen, A. A.; DeLuca, E. E.; Green, L. M.

    2012-11-10

    In this study we explore the scenario of photospheric flux cancellation being the primary formation mechanism of sigmoidal flux ropes in decaying active regions. We analyze magnetogram and X-ray observations together with data-driven non-linear force-free field (NLFFF) models of observed sigmoidal regions to test this idea. We measure the total and canceled fluxes in the regions from MDI magnetograms, as well as the axial and poloidal flux content of the modeled NLFFF flux ropes for three sigmoids-2007 February, 2007 December, and 2010 February. We infer that the sum of the poloidal and axial flux in the flux ropes for most models amounts to about 60%-70% of the canceled flux and 30%-50% of the total flux in the regions. The flux measurements and the analysis of the magnetic field structure show that the sigmoids first develop a strong axial field manifested as a sheared arcade and then, as flux cancellation proceeds, form long S-shaped field lines that contribute to the poloidal flux. In addition, the dips in the S-shaped field lines are located at the sites of flux cancellation that have been identified from the MDI magnetograms. We find that the line-of-sight-integrated free energy is also concentrated at these locations for all three regions, which can be liberated in the process of eruption. Flare-associated brightenings and flare loops coincide with the location of the X-line topology that develops at the site of most vigorous flux cancellation.

  6. Measuring Magnetic Oscillations in the Solar Photosphere: Coordinated Observations with MDI, ASP and MWO

    NASA Astrophysics Data System (ADS)

    Norton, A. A.; Ulrich, R. K.

    2000-03-01

    A comprehensive observing effort was undertaken to simultaneously obtain full Stokes profiles as well as longitudinal magnetogram maps of a positive plage region on 8 December, 1998 with the Michelson Doppler Imager, the Advanced Stokes Polarimeter and Mt. Wilson Observatory magnetograph. We compare 1.2'' spatially-averaged signals of velocities as well as filter magnetograph longitudinal flux signals with Stokes determined fluctuations in filling factor, field inclination, magnetic flux and field strength. The velocity signals are in excellent agreement. Michelson Doppler Imager magnetic flux correlates best with fluctuations in the Advanced Stokes Polarimeter filling factor, not inclination angle or field strength. A correlated flux and filling factor change in the absence of a field strength fluctuation can be understood in terms of internally unperturbed flux tubes being buffeted by external pressure fluctuations. The 12.5'' square aperture spatially averaged Mt. Wilson magnetograph signals are compared with Michelson Doppler Imager signals from the corresponding observing area. Velocity signals are in superb agreement. Magnetic signals exhibit similar oscillatory behavior. Lack of Advanced Stokes Polarimeter data for this time excludes interpretation of magnetic fluctuations as due to filling factor or field inclination angle. Mt. Wilson Observatory simultaneous sampling of the nickel and sodium spectral line profiles with several wing pairs allowed inter-comparison of signals from different heights of formation. Slight phase shifts and large propagation speeds for the velocity signals are indicative of modified standing waves. Phase speeds associated with magnetic signals are characteristic of photospheric Alfvén speeds for plage fields. The phase speed increase with height agrees with the altitude dependence of the Alfvén speed. The observed fluctuations and phases are interpreted as a superposition of signatures from the horizontal component of the

  7. SN 2012ec: mass of the progenitor from PESSTO follow-up of the photospheric phase

    NASA Astrophysics Data System (ADS)

    Barbarino, C.; Dall'Ora, M.; Botticella, M. T.; Della Valle, M.; Zampieri, L.; Maund, J. R.; Pumo, M. L.; Jerkstrand, A.; Benetti, S.; Elias-Rosa, N.; Fraser, M.; Gal-Yam, A.; Hamuy, M.; Inserra, C.; Knapic, C.; LaCluyze, A. P.; Molinaro, M.; Ochner, P.; Pastorello, A.; Pignata, G.; Reichart, D. E.; Ries, C.; Riffeser, A.; Schmidt, B.; Schmidt, M.; Smareglia, R.; Smartt, S. J.; Smith, K.; Sollerman, J.; Sullivan, M.; Tomasella, L.; Turatto, M.; Valenti, S.; Yaron, O.; Young, D.

    2015-04-01

    We present the results of a photometric and spectroscopic monitoring campaign of SN 2012ec, which exploded in the spiral galaxy NGC 1084, during the photospheric phase. The photometric light curve exhibits a plateau with luminosity L = 0.9 × 1042 erg s-1 and duration ˜90 d, which is somewhat shorter than standard Type II-P supernovae (SNe). We estimate the nickel mass M(56Ni) = 0.040 ± 0.015 M⊙ from the luminosity at the beginning of the radioactive tail of the light curve. The explosion parameters of SN 2012ec were estimated from the comparison of the bolometric light curve and the observed temperature and velocity evolution of the ejecta with predictions from hydrodynamical models. We derived an envelope mass of 12.6 M⊙, an initial progenitor radius of 1.6 × 1013 cm and an explosion energy of 1.2 foe. These estimates agree with an independent study of the progenitor star identified in pre-explosion images, for which an initial mass of M = 14-22 M⊙ was determined. We have applied the same analysis to two other Type II-P SNe (SNe 2012aw and 2012A), and carried out a comparison with the properties of SN 2012ec derived in this paper. We find a reasonable agreement between the masses of the progenitors obtained from pre-explosion images and masses derived from hydrodynamical models. We estimate the distance to SN 2012ec with the standardized candle method (SCM) and compare it with other estimates based on other primary and secondary indicators. SNe 2012A, 2012aw and 2012ec all follow the standard relations for the SCM for the use of Type II-P SNe as distance indicators.

  8. ``Ultimate'' information content in solar and stellar spectra. Photospheric line asymmetries and wavelength shifts

    NASA Astrophysics Data System (ADS)

    Dravins, Dainis

    2008-12-01

    Context: Spectral-line asymmetries (displayed as bisectors) and wavelength shifts are signatures of the hydrodynamics in solar and stellar atmospheres. Theory may precisely predict idealized lines, but accuracies in real observed spectra are limited by blends, few suitable lines, imprecise laboratory wavelengths, and instrumental imperfections. Aims: We extract bisectors and shifts until the “ultimate” accuracy limits in highest-quality solar and stellar spectra, so as to understand the various limits set by (i) stellar physics (number of relevant spectral lines, effects of blends, rotational line broadening); by (ii) observational techniques (spectral resolution, photometric noise); and by (iii) limitations in laboratory data. Methods: Several spectral atlases of the Sun and bright solar-type stars were examined for those thousands of “unblended” lines with the most accurate laboratory wavelengths, yielding bisectors and shifts as averages over groups of similar lines. Representative data were obtained as averages over groups of similar lines, thus minimizing the effects of photometric noise and of random blends. Results: For the solar-disk center and integrated sunlight, the bisector shapes and shifts were extracted for previously little-studied species (Fe II, Ti I, Ti II, Cr II, Ca I, C I), using recently determined and very accurate laboratory wavelengths. In Procyon and other F-type stars, a sharp blueward bend in the bisector near the spectral continuum is confirmed, revealing line saturation and damping wings in upward-moving photospheric granules. Accuracy limits are discussed: “astrophysical” noise due to few measurable lines, finite instrumental resolution, superposed telluric absorption, inaccurate laboratory wavelengths, and calibration noise in spectrometers, together limiting absolute lineshift studies to ≈50-100 m s-1. Conclusions: Spectroscopy with resolutions λ/Δλ ≈ 300 000 and accurate wavelength calibration will enable

  9. An Overview of Alfven Wave Generation, Reflection, and Damping from the Solar Photosphere to the Distant Heliosphere

    NASA Astrophysics Data System (ADS)

    Cranmer, S. R.; van Ballegooijen, A. A.

    2004-05-01

    The continually evolving convection below the solar photosphere gives rise to a wide spectrum of magnetohydrodynamic (MHD) fluctuations in the magnetic atmosphere and solar wind. The propagation of waves through the solar atmosphere has been studied for more than a half century, and the mainly incompressible Alfven mode has been believed to be dominant in regions that are open to the heliosphere. As a part of an ongoing study of various aspects of solar MHD waves and turbulence, we present a comprehensive model of the radially evolving properties of Alfvenic fluctuations in a representative open magnetic region. This work differs from previous models in the following ways. (1) The background plasma density, magnetic field, and flow velocity are constrained empirically from below the photosphere to distances past 1 AU. The successive merging of flux tubes on granular and supergranular scales is described using a two-dimensional magnetostatic model of a magnetic network element. (2) The frequency power spectrum of horizontal motions is specified only at the photosphere, based on prior analyses of G-band bright points. Everywhere else in the model the amplitudes of outward and inward propagating waves are computed with no free parameters. We compare the resulting wave properties with observed nonthermal motions in the chromosphere and corona, radio scintillation measurements, and in-situ fluctuation spectra. This work is supported by NASA under grants NAG5-11913, NAG5-12865, and NAG5-10996 to the Smithsonian Astrophysical Observatory, by Agenzia Spaziale Italiana, and by the Swiss contribution to the ESA PRODEX program.

  10. Analysis of sudden variations in photospheric magnetic fields during a large flare and their influences in the solar atmosphere

    NASA Astrophysics Data System (ADS)

    Kumar, Brajesh; Raja Bayanna, Ankala; Venkatakrishnan, Parameswaran; Kuchandy Mathew, Shibu

    2016-08-01

    The solar active region NOAA 11719 produced a large two-ribbon flare on 2013 April 11. We have investigated sudden variations in the photospheric magnetic fields in this active region during the flare by employing magnetograms obtained in the spectral line Fe I 6173 Å acquired by the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) spacecraft. The analysis of the line-of-sight magnetograms from HMI show sudden and persistent magnetic field changes at different locations of the active region before the onset of the flare and during the flare. The vector magnetic field observations available from HMI also show coincident variations in the total magnetic field strength and its inclination angle at these locations. Using the simultaneous Dopplergrams obtained from HMI, we observe perturbations in the photospheric Doppler signals following the sudden changes in the magnetic fields in the aforementioned locations. The power spectrum analysis of these velocity signals shows enhanced acoustic power in these affected locations during the flare as compared to the pre-flare condition. Accompanying these observations, we have also used nearly simultaneous chromospheric observations obtained in the spectral line Hα 6562.8 Å by the Global Oscillation Network Group (GONG) to study the evolution of flare-ribbons and intensity oscillations in this active region. The Hα intensity oscillations also show enhanced oscillatory power during the flare in the aforementioned locations. These results indicate that the transient Lorentz force associated with sudden changes in the magnetic fields could drive localized photospheric and chromospheric oscillations, like the flare-induced oscillations in the solar atmosphere.

  11. THE ABRUPT CHANGES IN THE PHOTOSPHERIC MAGNETIC AND LORENTZ FORCE VECTORS DURING SIX MAJOR NEUTRAL-LINE FLARES

    SciTech Connect

    Petrie, G. J. D.

    2012-11-01

    We analyze the spatial and temporal variations of the abrupt photospheric magnetic changes associated with six major flares using 12 minute, 0.''5 pixel{sup -1} vector magnetograms from NASA's Helioseismic and Magnetic Imager instrument on the Solar Dynamics Observatory satellite. The six major flares occurred near the main magnetic neutral lines of four active regions, NOAA 11158, 11166, 11283, and 11429. During all six flares the neutral-line field vectors became stronger and more horizontal, in each case almost entirely due to strengthening of the horizontal field components parallel to the neutral line. In all six cases the neutral-line pre-flare fields were more vertical than the reference potential fields, and collapsed abruptly and permanently closer to potential-field tilt angles during every flare, implying that the relaxation of magnetic stress associated with non-potential tilt angles plays a major role during major flares. The shear angle with respect to the reference potential field did not show such a pattern, demonstrating that flare processes do not generally relieve magnetic stresses associated with photospheric magnetic shear. The horizontal fields became significantly and permanently more aligned with the neutral line during the four largest flares, suggesting that the collapsing field is on average more aligned with the neutral line than the pre-flare neutral-line field. The vertical Lorentz force had a large, abrupt, permanent downward change during each of the flares, consistent with loop collapse. The horizontal Lorentz force changes acted mostly parallel to the neutral line in opposite directions on each side, a signature of the fields contracting during the flare, pulling the two sides of the neutral line toward each other. The greater effect of the flares on field tilt than on shear may be explained by photospheric line-tying.

  12. SIMULATION OF MAGNETOHYDRODYNAMIC SHOCK WAVE GENERATION, PROPAGATION, AND HEATING IN THE PHOTOSPHERE AND CHROMOSPHERE USING A COMPLETE ELECTRICAL CONDUCTIVITY TENSOR

    SciTech Connect

    Goodman, Michael L.; Kazeminezhad, Farzad E-mail: fkazemin@earthlink.ne

    2010-01-01

    An electrical conductivity tensor is used in a 1.5D magnetohydrodynamic (MHD) simulation to describe how MHD shock waves may form, propagate, and heat the photosphere and chromosphere by compression and resistive dissipation. The spatial resolution is 1 km. A train of six shock waves is generated by a sinusoidal magnetic field driver in the photosphere with a period T = 30 s, mean of 500 G, and variation of 250 G. The duration of the simulation is 200 s. Waves generated in the photosphere evolve into shock waves at a height z approx 375 km above the photosphere. The transition of the atmosphere from weakly to strongly magnetized with increasing height causes the Pedersen resistivity eta{sub P} to increase to approx2000 times the Spitzer resistivity. This transition occurs over a height range of a few hundred kilometers near the temperature minimum of the initial state at z approx 500 km. The initial state is a model atmosphere derived by Fontenla et al., plus a background magnetic field. The increase in eta{sub P} is associated with an increase in the resistive heating rate Q. Shock layer thicknesses are approx10-20 km. They are nonzero due to the presence of resistive dissipation, so magnetization-induced resistivity plays a role in determining shock structure, and hence the compressive heating rate Q{sub c} . At t = 200 s the solution has the following properties. Within shock layers, Q{sub maximum} approx 1.4-7 erg cm{sup -3} s{sup -1}, and Q{sub c,maximum} approx 10-10{sup 3} Q{sub maximum}. Between shock waves, and at some points within shock layers, Q{sub c} < 0, indicating cooling by rarefaction. The integrals of Q and Q{sub c} over the shock wave train are F approx 4.6 x 10{sup 6} erg cm{sup -2} s{sup -1} and F{sub c} approx 1.24 x 10{sup 9} erg cm{sup -2} s{sup -1}. A method based on the thermal, mechanical, and electromagnetic energy conservation equations is presented for checking the accuracy of the numerical solution, and gaining insight into energy

  13. Photospheric Fluorescence and Resonance Scattering: Non Classical Diagnostics and the Future of X-ray Stellar Spectroscopy

    NASA Technical Reports Server (NTRS)

    Drake, Jeremy

    1998-01-01

    High resolution AXAF and XMM observations of stellar coronae will yield a wealth of X-ray plasma line diagnostics that will provide a giant leap forward in our understanding of coronal densities, abundance anomalies and emission measure distributions. Unfortunately, there is one very basic unanswered question in the physics of active stellar coronae that the usual plasma diagnostics cannot address directly: What are the spatial characteristics of stellar coronae-the scale height and filling factor? What do other stellar coronae actually look like? I will discuss two novel diagnostics of coronal geometry and their application to future X-ray spectra: photospheric fluorescence and resonance line optical depths.

  14. The type IIP supernova 2012aw in M95: Hydrodynamical modeling of the photospheric phase from accurate spectrophotometric monitoring

    SciTech Connect

    Dall'Ora, M.; Botticella, M. T.; Della Valle, M.; Pumo, M. L.; Zampieri, L.; Tomasella, L.; Cappellaro, E.; Benetti, S.; Pignata, G.; Bufano, F.; Bayless, A. J.; Pritchard, T. A.; Taubenberger, S.; Benitez, S.; Kotak, R.; Inserra, C.; Fraser, M.; Elias-Rosa, N.; Haislip, J. B.; Harutyunyan, A.; and others

    2014-06-01

    We present an extensive optical and near-infrared photometric and spectroscopic campaign of the Type IIP supernova SN 2012aw. The data set densely covers the evolution of SN 2012aw shortly after the explosion through the end of the photospheric phase, with two additional photometric observations collected during the nebular phase, to fit the radioactive tail and estimate the {sup 56}Ni mass. Also included in our analysis is the previously published Swift UV data, therefore providing a complete view of the ultraviolet-optical-infrared evolution of the photospheric phase. On the basis of our data set, we estimate all the relevant physical parameters of SN 2012aw with our radiation-hydrodynamics code: envelope mass M {sub env} ∼ 20 M {sub ☉}, progenitor radius R ∼ 3 × 10{sup 13} cm (∼430 R {sub ☉}), explosion energy E ∼ 1.5 foe, and initial {sup 56}Ni mass ∼0.06 M {sub ☉}. These mass and radius values are reasonably well supported by independent evolutionary models of the progenitor, and may suggest a progenitor mass higher than the observational limit of 16.5 ± 1.5 M {sub ☉} of the Type IIP events.

  15. Impulsive solar X-ray bursts. III - Polarization, directivity, and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

    NASA Technical Reports Server (NTRS)

    Langer, S. H.; Petrosian, V.

    1977-01-01

    The paper presents the spectrum, directivity, and state of polarization of the bremsstrahlung radiation expected from a beam of high-energy electrons spiraling along radial magnetic field lines toward the photosphere. A Monte Carlo method is then described for evaluation of the spectrum, directivity, and polarization of X-rays diffusely reflected from stellar photospheres. The accuracy of the technique is evaluated through comparison with analytic results. The calculated characteristics of the incident X-rays are used to evaluate the spectrum, directivity, and polarization of the reflected and total X-ray fluxes. The results are compared with observations.

  16. The dependence of coronal hole size on large scale magnetic field strength. [using a mathematical model of the photosphere

    NASA Technical Reports Server (NTRS)

    Suess, S. T.; Steinolfson, R. S.

    1980-01-01

    The importance of mathematical models of the coronal structure for studies of coronal energetics, to simulate global flows of the solar wind, and to obtain reliable solar terrestrial predictions is discussed. Previous coronal models, including an example of a coronal MHD flow model, are reviewed. The development of a coronal model which is a logical extension of earlier models and which allows a closer relationship to the photospheric magnetic field as it is observed daily is described. The calculations are outlined. The assumptions of the model are: axisymmetric flow with no rotation, resulting in two dimensional flow in a meridional plane; zero viscosity and infinite electrical conductivity; polytropic, single fluid flow; and no momentum addition.

  17. Reproducing the Photospheric Magnetic Field Evolution during the Rise of Cycle 24 with Flux Transport by Supergranules

    NASA Technical Reports Server (NTRS)

    Hathaway, David; Upton, Lisa

    2012-01-01

    We simulate the transport of magnetic flux in the Sun s photosphere by an evolving pattern of cellular horizontal flows (supergranules). Characteristics of the simulated flow pattern can match observed characteristics including the velocity power spectrum, cell lifetimes, and cell motions in longitude and latitude. Simulations using an average, and north-south symmetric, meridional motion of the cellular pattern produce polar magnetic fields that are too weak in the North and too strong in the South. Simulations using cellular patterns with meridional motions that evolve with the observed changes in strength and north-south asymmetry will be analyzed to see if they reproduce the polar field evolution observed during the rise of Cycle 24.

  18. Reproducing the Photospheric Magnetic Field Evolution During the Rise of Cycle 24 with Flux Transport by Supergranules

    NASA Technical Reports Server (NTRS)

    Hathaway, David H.; Upton, Lisa

    2012-01-01

    We simulate the transport of magnetic flux in the Sun s photosphere by an evolving pattern of cellular horizontal flows (supergranules). Characteristics of the simulated flow pattern match observed characteristics including the velocity power spectrum, cell lifetimes, and cell pattern motion in longitude and latitude. Simulations using an average, and north-south symmetric, meridional motion of the cellular pattern produce polar magnetic fields that are too weak in the North and too strong in the South. Simulations using cellular patterns with meridional motions that evolve with the observed changes in strength and north-south asymmetry will be analyzed to see if they reproduce the polar field evolution observed during the rise of Cycle 24.

  19. Sub-photospheric, radiation-mediated shocks in gamma-ray bursts: Multiple shock emission and the band spectrum

    SciTech Connect

    Keren, Shai; Levinson, Amir

    2014-07-10

    We compute the time-integrated, thermal emission produced by a series of radiation-mediated shocks that emerge from the photosphere of a gamma-ray burst outflow. We show that for a sufficiently broad distribution of shock strengths, the overall shape of the time-integrated spectral energy distribution below the peak is a power law, νE{sub ν}∝ν{sup α}, with a slope of 1 < α < 2. A substructure in the spectral energy distribution (SED) can also be produced in this model for certain choices of the shock train distribution. In particular, we demonstrate that our model can reproduce the double-peak SED observed in some bursts, in events where a strong shock is followed by a sequence of sufficiently weaker ones.

  20. A comparison of photospheric electric current and ultraviolet and X-ray emission in a solar active region

    NASA Technical Reports Server (NTRS)

    Haisch, B. M.; Bruner, M. E.; Hagyard, M. J.; Bonnet, R. M.

    1986-01-01

    This paper presents an extensive set of coordinated observations of a solar active region, taking into account spectroheliograms obtained with the aid of the Solar Maximum Mission (SMM) Ultraviolet Spectrometer Polarimeter (UVSP) instrument, SMM soft X-ray polychromator (XRP) raster maps, and high spatial resolution ultraviolet images of the sun in Lyman-alpha and in the 1600 A continuum. These data span together the upper solar atmosphere from the temperature minimum to the corona. The data are compared to maps of the inferred photospheric electric current derived from the Marshall Space Flight Center (MSFC) vector magnetograph observations. Some empirical correlation is found between regions of inferred electric current density and the brightest features in the ultraviolet continuum and to a lesser extent those seen in Lyman-alpha within an active region.

  1. NON-THERMAL RESPONSE OF THE CORONA TO THE MAGNETIC FLUX DISPERSAL IN THE PHOTOSPHERE OF A DECAYING ACTIVE REGION

    SciTech Connect

    Harra, L. K.; Abramenko, V. I.

    2012-11-10

    We analyzed Solar Dynamics Observatory line-of-sight magnetograms for a decaying NOAA active region (AR) 11451 along with co-temporal Extreme-Ultraviolet Imaging Spectrometer (EIS) data from the Hinode spacecraft. The photosphere was studied via time variations of the turbulent magnetic diffusivity coefficient, {eta}(t), and the magnetic power spectrum index, {alpha}, through analysis of magnetogram data from the Helioseismic and Magnetic Imager (HMI). These measure the intensity of the random motions of magnetic elements and the state of turbulence of the magnetic field, respectively. The time changes of the non-thermal energy release in the corona was explored via histogram analysis of the non-thermal velocity, v {sub nt}, in order to highlight the largest values at each time, which may indicate an increase in energy release in the corona. We used the 10% upper range of the histogram of v {sub nt} (which we called V {sup upp} {sub nt}) of the coronal spectral line of Fe XII 195 A. A 2 day time interval was analyzed from HMI data, along with the EIS data for the same field of view. Our main findings are the following. (1) The magnetic turbulent diffusion coefficient, {eta}(t), precedes the upper range of the v {sub nt} with the time lag of approximately 2 hr and the cross-correlation coefficient of 0.76. (2) The power-law index, {alpha}, of the magnetic power spectrum precedes V {sup upp} {sub nt} with a time lag of approximately 3 hr and the cross-correlation coefficient of 0.5. The data show that the magnetic flux dispersal in the photosphere is relevant to non-thermal energy release dynamics in the above corona. The results are consistent with the nanoflare mechanism of the coronal heating, due to the time lags being consistent with the process of heating and cooling the loops heated by nanoflares.

  2. Impulsive solar X-ray bursts. 3: Polarization and directivity of bremsstrahlung radiation from a beam of electrons directed toward the photosphere

    NASA Technical Reports Server (NTRS)

    Langer, S. H.; Petrosian, V.

    1976-01-01

    The spectrum, directivity and state of polarization is presented of the bremsstrahlung radiation expected from a beam of high energy electrons spiraling along radial magnetic field lines toward the photosphere. The results are used for calculation of the characteristics of the reflected plus direct flux.

  3. The magnetic field of active region 11158 during the 2011 February 12-17 flares: Differences between photospheric extrapolation and coronal forward-fitting methods

    SciTech Connect

    Aschwanden, Markus J.; Sun, Xudong; Liu, Yang E-mail: xudongs@stanford.edu

    2014-04-10

    We developed a coronal nonlinear force-free field (COR-NLFFF) forward-fitting code that fits an approximate nonlinear force-free field (NLFFF) solution to the observed geometry of automatically traced coronal loops. In contrast to photospheric NLFFF codes, which calculate a magnetic field solution from the constraints of the transverse photospheric field, this new code uses coronal constraints instead, and this way provides important information on systematic errors of each magnetic field calculation method, as well as on the non-force-freeness in the lower chromosphere. In this study we applied the COR-NLFFF code to NOAA Active Region 11158, during the time interval of 2011 February 12-17, which includes an X2.2 GOES-class flare plus 35 M- and C-class flares. We calculated the free magnetic energy with a 6 minute cadence over 5 days. We find good agreement between the two types of codes for the total nonpotential E{sub N} and potential energy E{sub P} but find up to a factor of 4 discrepancy in the free energy E {sub free} = E{sub N} – E{sub P} and up to a factor of 10 discrepancy in the decrease of the free energy ΔE {sub free} during flares. The coronal NLFFF code exhibits a larger time variability and yields a decrease of free energy during the flare that is sufficient to satisfy the flare energy budget, while the photospheric NLFFF code shows much less time variability and an order of magnitude less free-energy decrease during flares. The discrepancy may partly be due to the preprocessing of photospheric vector data but more likely is due to the non-force-freeness in the lower chromosphere. We conclude that the coronal field cannot be correctly calculated on the basis of photospheric data alone and requires additional information on coronal loop geometries.

  4. Rotational modulation of the photospheric and chromospheric activity in the young, single K2-dwarf PW And

    NASA Astrophysics Data System (ADS)

    López-Santiago, J.; Montes, D.; Fernández-Figueroa, M. J.; Ramsey, L. W.

    2003-12-01

    High resolution echelle spectra of PW And (HD 1405) have been taken during eight observing runs from 1999 to 2002. The detailed analysis of the spectra allow us to determine its spectral type (K2V), mean heliocentric radial velocity (Vhel = -11.15 km s-1) rotational velocity (vsin i = 22.6 km s-1), and equivalent width of the lithium line lambda 6707.8 Å (EW(Li I) = 273 mÅ). The kinematic (Galactic Velocity (U,V,W)) confirms its membership in the Local Association moving group, in agreement with the age (30 to 80 Myrs) inferred from the color magnitude diagram and the lithium equivalent width. Photospheric activity (presence of cool spots that disturb the profiles of the photospheric lines) has been detected as changes in the bisectors of the cross correlation function (CCF) resulting of cross-correlate the spectra of PW And with the spectrum of a non-active star of similar spectral type. These variations of the CCF bisectors are related to the variations in the measured radial velocities and are modulated with a period similar to the photometric period of the star. At the same time, chromospheric activity has been analyzed, using the spectral subtraction technique and simultaneous spectroscopic observations of the Hα , Hβ , Na I D1 and D2, He I D3, Mg I b triplet, Ca II H&K, and Ca II infrared triplet lines. A flare was observed during the last observing run of 2001, showing an enhancement in the observed chromospheric lines. A less powerful flare was observed on 2002 August 23. The variations of the chromospheric activity indicators seem to be related to the photospheric activity. A correlation between radial velocity, changes in the CCF bisectors and equivalent width of different chromospheric lines is observed with a different behaviour between epochs 1999, 2001 and 2002. Based on observations made with the 2.2 m telescope of the German-Spanish Astronomical Centre, Calar Alto (Almería, Spain), operated by the Max-Planck-Institute for Astronomy, Heidelberg

  5. Photospheric Magnetic Field Properties of Flaring vs. Flare-Quiet Active Regions I: Data, General Approach, and Statistical Results

    NASA Astrophysics Data System (ADS)

    Leka, K. D.; Barnes, G.

    2003-05-01

    Photospheric vector magnetic field data from the U. Hawai`i Imaging Vector Magnetograph are examined for pre-event signatures unique to solar energetic phenomena. Parameters are constructed from B(x,y) to describe (for example) the distributions of the field, spatial gradients of the field, vertical current, current helicity, ''twist'' parameter α and magnetic shear angles. A quantitative statistical approach employing discriminant analysis and Hotelling's T2-test is applied to the magnitude and temporal evolution of parameters from 24 flare-event and flare-quiet epochs from seven active regions. We demonstrate that (1) when requiring a flare-unique signature, numerous candidate parameters are nullified by considering flare-quiet epochs, (2) a more robust method exists for estimating error rates than conventional ''truth tables'', (3) flaring and flare-quiet populations do not necessarily have low error rates for classification even when statistically distinguishable, and that (4) simultaneous consideration of a large number of variables is required to produce acceptable error rates. That is, when the parameters are considered individually, they show little ability to differentiate between the two populations; multi-variable combinations can discriminate the populations and/or result in perfect classification tables. In lieu of constructing a single all-variable discriminant function to quantify the flare-predictive power of the parameters considered, we devise a method whereby all permutations of the four-variable discriminant functions are ranked by Hotelling's T2. We present those parameters (e.g. the temporal increase of the kurtosis of the spatial distribution of the vertical current density) which consistently appear in the best combinations, indicating that they may play an important role in defining a pre-event photospheric state. While no single combination is clearly the best discriminator, we demonstrate here the requisite approach: include flare

  6. UNRESOLVED MIXED POLARITY MAGNETIC FIELDS AT FLUX CANCELLATION SITE IN SOLAR PHOTOSPHERE AT 0.''3 SPATIAL RESOLUTION

    SciTech Connect

    Kubo, Masahito; Low, Boon Chye; Lites, Bruce W

    2014-09-20

    This is a follow-up investigation of a magnetic flux cancellation event at a polarity inversion line (PIL) on the Sun observed with the spectropolarimeter on board Hinode. Anomalous circular polarization (Stokes V) profiles are observed in the photosphere along the PIL at the cancellation sites. Kubo et al. previously reported that the theoretically expected horizontal fields between the canceling opposite-polarity magnetic elements in this event are not detected at granular scales. We show that the observed anomalous Stokes V profiles are reproduced successfully by adding the nearly symmetric Stokes V profiles observed at pixels immediately adjacent to the PIL. This result suggests that these observed anomalous Stokes V profiles are not indications of a flux removal process, but are the result of either a mixture of unresolved, opposite-polarity magnetic elements or the unresolved width of the PIL, at an estimated resolution element of about 0.''3. The hitherto undetected flux removal process accounting for the larger-scale disappearance of magnetic flux during the observing period is likely to also fall below resolution.

  7. Photospheric models of solar active regions and the network based on the Mg II h and k line wings

    NASA Technical Reports Server (NTRS)

    Morrison, N. D.; Linsky, J. L.

    1978-01-01

    From a comparison between observed and computed wings of the Mg II resonance lines, distributions of temperature versus mass column density for solar photospheric layers in plages and in the chromospheric network are derived. The theoretical profiles are computed assuming partial coherent scattering. In the active regions, temperatures exceed those in the quiet sun by up to 200 K near the temperature minimum and up to 400 K in deeper layers. In the observed network structure, the temperature is enhanced by 200 K at the temperature minimum but is the same as that in the quiet sun at greater depths. The difference in the slope of the temperature distribution between the network and plages is real, but may refer only to long elements of the network rather than to the brightest portions. Adjacent to the network is a region in which the temperatures are similar to those in the quiet sun, except immediately below the temperature minimum, where the temperatures are depressed by 150 K.

  8. A Computational Analysis of the Expanding Photosphere Method and the Distances to Type II-P Supernovae

    NASA Astrophysics Data System (ADS)

    Mitchell, Robert C.; Didier, Brian

    2015-01-01

    We present the results of research into the Expanding Photosphere Method (EPM) and its use in determining the distance to a supernova and the epoch in which the explosion occurred. This research was part of a six-week summer program pairing faculty with undergraduate students, computationally determining the distance and explosion epoch through the EPM's assumption of blackbody luminosity with empirically-derived correction factors. This method was applied to a sampling of supernovae with data sets covering different post-explosion time periods. We compare our distance and explosion epoch calculations to those determined by other means, demonstrate which types of data sets can be more reliably applied to the EPM, and describe the uncertainties involved. Although it is inconclusive for now as to how effective the EPM is as an indicator of the explosion epoch, this research provides further evidence of its effectiveness as an indicator of distance, provided the data set is large enough and covers earlier post-explosion phases of the supernova.

  9. The Effects of Magnetic Field Morphology on the Determination of Oxygen and Iron Abundances in the Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Moore, Christopher S.; Uitenbroek, Han; Rempel, Matthias; Criscuoli, Serena; Rast, Mark

    2016-01-01

    The solar chemical abundance (or a scaled version of it) is implemented in numerous astrophysical analyses. Thus, an accurate and precise estimation of the solar elemental abundance is crucial in astrophysics.We have explored the impact of magnetic fields on the determination of the solar photospheric oxygen andiron abundances using 3D radiation-magnetohydrodynamic (MHD) simulations of convection. Specifically, weexamined differences in abundance deduced from three classes of atmospheres simulated with the MURaM code: apure hydrodynamic (HD) simulation, an MHD simulation with a local dynamo magnetic field that has saturated withan unsigned vertical field strength of 80 G at the optical depth unity surface, and an MHD simulation with an initially imposed vertical mean field of 80 G. We use differential equivalent width analysis for diagnosing abundances derived from five oxygen and four iron spectral lines of differing wavelength, oscillator strength, excitation potential, and Lande g-factor, and find that the morphology of the magnetic field is important to the outcome of abundance determinations. The largest deduced abundance differences are found in the vertical mean field simulations and small scale unresolved field resulting from the local dynamo has a smaller impact on abundance determinations.

  10. The Effects of Magnetic Field Morphology on the Determination of Oxygen and Iron Abundances in the Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Moore, Christopher S.; Uitenbroek, Han; Rempel, Matthias; Criscuoli, Serena; Rast, Mark P.

    2015-02-01

    We have explored the impact of magnetic fields on the determination of the solar photospheric oxygen and iron abundances using three-dimensional radiation-magnetohydrodynamic (MHD) simulations of convection. Specifically, we examined differences in abundance deduced from three classes of atmospheres simulated with the MURaM code: a pure hydrodynamic (HD) simulation, an MHD simulation with a local dynamo magnetic field that has saturated with an unsigned vertical field strength of 80 G at τ = 1, and an MHD simulation with an initially imposed vertical mean field of 80 G. We use differential equivalent width analysis for diagnosing abundances derived from five oxygen and four iron lines of differing wavelength, oscillator strength, excitation potential, and Landé g-factor, and find that the morphology of the magnetic field is important to the outcome of abundance determinations. The largest deduced abundance differences are found in the vertical mean field simulations, where the O I and Fe I abundance corrections compared to the pure HD case are ~+0.011 dex and +0.065 dex respectively. Small scale unresolved field resulting from the local dynamo has a smaller impact on abundance determinations, with corrections of -0.0001 dex and +0.0044 dex in the magnetized compared to the pure HD simulations. While the overall influence of magnetic field on abundance estimates is found to be small, we stress that such estimates are sensitive not only to the magnitude of magnetic field but also to its morphology.

  11. Signature of Temporary Burning Front Stalling from a Non-Photospheric Radius Expansion Double-Peaked Burst

    NASA Technical Reports Server (NTRS)

    Bhattacharyya, Sudip; Strohmayer, Tod E.

    2006-01-01

    Non-photospheric-radius-expansion(non-PRE) double-peaked bursts may be explained in terms of spreading (and temporary stalling) of thermonuclear flames on the neutron star surface, as we argued in a previous study of a burst assuming polar ignition. Here we analyze Rossi X-ray Timing Explorer (RXTE) Proportional Counter Array (PCA) data of such a burst (but with a considerably different intensity profile from the previous one) from the low mass X-ray binary (LMXB) system 4U 1636-536, and show that this model can qualitatively explain the observed burst profile and spectral evolution, if we assume an off-polar, but high-latitude ignition, and burning front stalling at a higher latitude compared to that for the previous burst. The off-polar ignition can account for the millisecond period brightness oscillations detected from this burst. This is the first time oscillations have been seen from such a burst. Our model can qualitatively explain the oscillation amplitude measured during the first (weaker) peak, and the absence of oscillations during the second peak. The higher latitude front stalling facilitates the first clear detection of a signature of this stalling, which is the primary result of this work, and may be useful for understanding thermonuclear flame spreading on neutron stars.

  12. Predicting the near-Sun and Interplanetary Magnetic Field of CMEs using photospheric magnetograms and coronagraph images

    NASA Astrophysics Data System (ADS)

    Patsourakos, Spiros; Georgoulis, Manolis

    2016-04-01

    Earth-directed Coronal Mass Ejections (CMEs) containing a strong southward magnetic-field component upon arrival at 1 AU statistically account for the most powerful geomagnetic storms. Unfortunately, though, we currently lack routine diagnostics of the magnetic field of CMEs and its evolution in the inner heliosphere and the interplanetary (IP) medium. We hereby present a simple, yet powerful and easy-to-implement, method to deduce the near-Sun and IP magnetic field entrained in CMEs, by using photospheric magnetograms of the solar source regions and multi-viewpoint coronagraph images of the corresponding CMEs. The method relies on the principle of magnetic-helicity conservation in low plasma-beta, flux-rope CMEs and a power-law prescription of the radial evolution of the CME magnetic field in the IP medium. We outline a parametric study based on the observed statistics of input parameters to calculate a matrix of magnetic-field solutions for 10000 synthetic CMEs. The robustness and possible limitations / ramifications of the method are deduced by a comparison with the distributions of the predicted CME-ICME magnetic fields at 0.3 and 1 AU using actual Messenger and ACE published observations.

  13. THE INCOMPATIBILITY OF RAPID ROTATION WITH NARROW PHOTOSPHERIC X-RAY LINES IN EXO 0748-676

    SciTech Connect

    Lin Jinrong; Chakrabarty, Deepto; Oezel, Feryal; Psaltis, Dimitrios E-mail: deepto@mit.ed E-mail: dpsaltis@email.arizona.ed

    2010-11-10

    X-ray observations of EXO 0748-676 during thermonuclear bursts revealed a set of narrow ({Delta}{lambda}/{lambda} = 0.018) absorption lines that potentially originate from the stellar photosphere. The identification of these lines with particular atomic transitions led to the measurement of the surface gravitational redshift of the neutron star and to constraints on its mass and radius. However, the recent detection of 552 Hz oscillations at 15% rms amplitude revealed the spin frequency of the neutron star and brought into question the consistency of such a rapid spin with the narrow width of the absorption lines. Here, we calculate the amplitudes of burst oscillations and the width of absorption lines emerging from the surface of a rapidly rotating neutron star for a wide range of model parameters. We show that no combination of neutron star and geometric parameters can simultaneously reproduce the narrowness of the absorption lines, the high amplitude of the oscillations, and the observed flux at the time the oscillations were detected. We, therefore, conclude that the observed absorption lines are unlikely to originate from the surface of this neutron star.

  14. SMM observations of K-alpha radiation from fluorescence of photospheric iron by solar flare X-rays

    NASA Technical Reports Server (NTRS)

    Parmar, A. N.; Culhane, J. L.; Rapley, C. G.; Wolfson, C. J.; Acton, L. W.; Phillips, K. J. H.; Dennis, B. R.

    1984-01-01

    High-resolution Fe K-alpha spectra near 1.94 A observed during solar flares with the Bent Crystal Spectrometer on the Solar Maximum Mission are presented. The evidence for two possible excitation mechanisms, electron impact and fluorescence, is examined. It is found that the fluorescence mechanism satisfactorily describes the results, while the observations do not support electron collisional excitation of the Fe K-alpha transitions in low ionization stages (II-XII) of iron. Using Bai's model of the fluorescent excitation process, the photospheric iron abundance relative to that of hydrogen is estimated to be 5-6 x 10 to the -5th. The mean height of the soft X-ray source producing the K-alpha fluorescence is calculated on the basis of this model for about 40 large flares. The solar K-alpha lines are found to be about 25 percent wider than those measured in the laboratory. Weak line features observed at wavelengths shorter than that of the K-alpha lines are discussed.

  15. Simultaneous soft and hard X-ray spectroscopy of AM Herculis with EXOSAT: Discovery of photospheric absorption features

    NASA Technical Reports Server (NTRS)

    Paerels, Frits; Heise, John; Teeseling, Andre Van

    1994-01-01

    We present 0.1-10 keV spectroscopic observations of AM Herculis obtained with the Transmission Grating Spectrometers and Medium Energy experiments on EXOSAT, taken when the object was in its 'reversed X-ray mode.' The observation covers over six binary orbits without interruption, enabling us to analyze the phase and intensity dependence of both the hard and the soft spectrum simultaneously. We resolve the optically thick soft X-ray spectrum, and find definite evidence for time- and phase-dependent photospheric absorption structure arising in the white dwarf atmosphere. We present a simple empirical analysis of the combined soft and hard X-ray spectra, to examine whether the effect of a better determination of the column density of neutral absorbing material, afforded by our data, would solve the problem of the large relative soft X-ray overluminosity previously observed in AM Her. We find that a single absorbing column fits the entire spectrum, and that the column densities implied are indeed substantially lower than previously estimated. However, during half the binary orbit we still determine a strong lower limit to the soft-to-hard luminosity ratio of L(sub soft)/L(sub hard) is greater than or approximately equal to 10, in conflict with the simple radiative shock models for the accretion region. We argue that this indicates the need to reexamine the luminosity problem using explicit models for the emission spectrum based on a full solution of the atmospheric radiative transfer problem.

  16. Photospheric Stratification of a Central Umbral Dot Using Stokes Profiles Recorded by Hinode: A Different Single-Case Study

    NASA Astrophysics Data System (ADS)

    Hamedivafa, H.

    2013-09-01

    We aim to study the physical nature of a central umbral dot (UD) close to disk center by analyzing full-Stokes spectra of the two Fe i lines at 630 nm recorded by the spectropolarimeter on Hinode. Thermal and magnetic properties of the UD were directly inferred from Stokes profiles. Then, we applied the inversion code SIR to retrieve a single-component magnetic model atmosphere that recovers the observed full-Stokes profiles. The inversion results and direct inferences from the iron line pair are consistent. The studied UD does not show any signatures of upflows, but tends to show downflows. At the deeper-half of the photosphere (log τ>-1.0), the UD exhibits rapid changes in temperature with respect to its surroundings. The UD has a large magnetic field strength of about 3000 G without significant reduction at its center. Magnetic field lines are more vertical and twisted in the UD area than in the magnetic field of its surroundings. To explain the observational findings, we propose that the UD perturbs the funnel magnetic field of the umbra, making a tilt-ankle-knee configuration. A new interesting inference, deduced from the blending spectral lines in the observed wavelength interval, is that the shape and surface span of the UD in normalized intensity filtergrams computed at the core of the blending lines differ from the UD area seen in continuum intensity and in the filtergrams computed at the core of the iron line pair.

  17. Impulsive solar X-ray bursts. 4: Polarization, directivity and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

    NASA Technical Reports Server (NTRS)

    Langer, S. H.; Petrosian, V.

    1976-01-01

    A Monte Carlo method is described for evaluation of the spectrum, directivity and polarization of X-rays diffusely reflected from stellar photospheres. the accuracy of the technique is evaluated through comparison with analytic results. Using the characteristics of the incident X-rays of the model for solar X-ray flares, the spectrum, directivity and polarization of the reflected and the total X-ray fluxes are evaluated. The results are compared with observations.

  18. Photospheric, circumstellar, and interstellar features of HE, C, N. O, and Si in the HST spectra of four hot white dwarf stars

    NASA Technical Reports Server (NTRS)

    Shipman, Harry L.; Provencal, Judi; Roby, Scott W.; Barstow, Martin; Bond, Howard; Bruhweiler, Fred; Finley, David; Fontaine, Gilles; Holberg, Jay; Nousek, John

    1995-01-01

    This paper reports on the observations of four hot white dwarf stars with the spectrographs on the Hubble Space Telescope (HST). The higher resolving power and higher signal/noise, in comparison with IUE, reveals a very rich phenomomenology, including photospheric features from heavy elements, circumstellar features, and the first direct detection of accretion onto the white dwarf component of a binary system. Specific results include the following: Our observations of the ultrahot degenerate H1504+65 confirm that it has a photosphere which is depleted in both H and He, and reveals features of C IV and O VI. The spectrum fits previously published models extremely well. The intermediate-temperature DO star PG 1034+001 has an ultraviolet spectrum showing complex profiles of the well-known resonance doublets of C IV, N v, and Si IV. The O V 1371 line shows a clear separation into a photospheric and a circumstellar component, and it is likely that the same two components can explain the other lines as well. The cooler DA star GD 394 has an extensive system of heavy-element features, but their radial velocity is such that it is highly unlikely that they are formed in the stellar photosphere. Time-resolved spectra of the accreting white dwarf in the V 471 Tau binary system are briefly presented here; they do show the presence of C IV, Si IV, and He II. However, the C IV and He II lines are in emission, rather than in aborption as had been expected.

  19. Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL

    NASA Astrophysics Data System (ADS)

    Khouri, T.; Maercker, M.; Waters, L. B. F. M.; Vlemmings, W. H. T.; Kervella, P.; de Koter, A.; Ginski, C.; De Beck, E.; Decin, L.; Min, M.; Dominik, C.; O'Gorman, E.; Schmid, H.-M.; Lombaert, R.; Lagadec, E.

    2016-06-01

    Context. On the asymptotic giant branch (AGB) low- and intermediate-mass stars eject a large fraction of their envelope, but the mechanism driving these outflows is still poorly understood. For oxygen-rich AGB stars, the wind is thought to be driven by radiation pressure caused by scattering of radiation off dust grains. Aims: We study the photosphere, the warm molecular layer, and the inner wind of the close-by oxygen-rich AGB star R Doradus. We focus on investigating the spatial distribution of the dust grains that scatter light and whether these grains can be responsible for driving the outflow of this star. Methods: We use high-angular-resolution images obtained with SPHERE/ZIMPOL to study R Dor and its inner envelope in a novel way. We present observations in filters V, cntHα, and cnt820 and investigate the surface brightness distribution of the star and of the polarised light produced in the inner envelope. Thanks to second-epoch observations in cntHα, we are able to see variability on the stellar photosphere. We study the polarised-light data using a continuum-radiative-transfer code that accounts for direction-dependent scattering of photons off dust grains. Results: We find that in the first epoch the surface brightness of R Dor is asymmetric in V and cntHα, the filters where molecular opacity is stronger, while in cnt820 the surface brightness is closer to being axisymmetric. The second-epoch observations in cntHα show that the morphology of R Dor has changed completely in a timespan of 48 days to a more axisymmetric and compact configuration. This variable morphology is probably linked to changes in the opacity provided by TiO molecules in the extended atmosphere. The observations show polarised light coming from a region around the central star. The inner radius of the region from where polarised light is seen varies only by a small amount with azimuth. The value of the polarised intensity, however, varies by between a factor of 2.3 and 3.7 with

  20. The energy of waves in the photosphere and lower chromosphere. IV. Inversion results of Ca II H spectra

    NASA Astrophysics Data System (ADS)

    Beck, C.; Rezaei, R.; Puschmann, K. G.

    2013-05-01

    Context. Most semi-empirical static one-dimensional (1D) models of the solar atmosphere in the magnetically quiet Sun (QS) predict an increase in temperature at chromospheric layers. Numerical simulations of the solar chromosphere with a variable degree of sophistication, i.e. from 1D to three-dimensional (3D) simulations; assuming local thermal equilibrium (LTE) or non-LTE (NLTE), on the other hand, only yielded an increase in the brightness temperature without any stationary increase in the gas temperature. Aims: We investigate the thermal structure in the solar chromosphere as derived from an LTE inversion of observed Ca ii H spectra in QS and active regions (ARs). Methods: We applied an inversion strategy based on the SIR (Stokes inversion by response functions) code to Ca ii H spectra to obtain 1D temperature stratifications. We investigated the temperature stratifications on differences between magnetic and field-free regions in the QS, and on differences between QS and ARs. We determined the energy content of individual calcium bright grains (BGs) as specific candidates of chromospheric heating events. We compared observed with synthetic NLTE spectra to estimate the significance of the LTE inversion results. Results: The fluctuations of observed intensities yield a variable temperature structure with spatio-temporal rms fluctuations below 100 K in the photosphere and between 200 and 300 K in the QS chromosphere. The average temperature stratification in the QS does not exhibit a clear chromospheric temperature rise, unlike the AR case. We find a characteristic energy content of about 7 × 1018 J for BGs that repeat with a cadence of about 160 s. The precursors of BGs have a vertical extent of about 200 km and a horizontal extent of about 1 Mm. The comparison of observed with synthetic NLTE profiles partly confirms the results of the LTE inversion that the solar chromosphere in the QS oscillates between an atmosphere in radiative equilibrium and one with a

  1. SIMULTANEOUS OBSERVATIONS OF A LARGE-SCALE WAVE EVENT IN THE SOLAR ATMOSPHERE: FROM PHOTOSPHERE TO CORONA

    SciTech Connect

    Shen, Yuandeng; Liu, Yu

    2012-06-20

    For the first time, we report a large-scale wave that was observed simultaneously in the photosphere, chromosphere, transition region, and low corona layers of the solar atmosphere. Using the high temporal and high spatial resolution observations taken by the Solar Magnetic Activity Research Telescope at Hida Observatory and the Atmospheric Imaging Assembly (AIA) on board Solar Dynamic Observatory, we find that the wave evolved synchronously at different heights of the solar atmosphere, and it propagated at a speed of 605 km s{sup -1} and showed a significant deceleration (-424 m s{sup -2}) in the extreme-ultraviolet (EUV) observations. During the initial stage, the wave speed in the EUV observations was 1000 km s{sup -1}, similar to those measured from the AIA 1700 A (967 km s{sup -1}) and 1600 A (893 km s{sup -1}) observations. The wave was reflected by a remote region with open fields, and a slower wave-like feature at a speed of 220 km s{sup -1} was also identified following the primary fast wave. In addition, a type-II radio burst was observed to be associated with the wave. We conclude that this wave should be a fast magnetosonic shock wave, which was first driven by the associated coronal mass ejection and then propagated freely in the corona. As the shock wave propagated, its legs swept the solar surface and thereby resulted in the wave signatures observed in the lower layers of the solar atmosphere. The slower wave-like structure following the primary wave was probably caused by the reconfiguration of the low coronal magnetic fields, as predicted in the field-line stretching model.

  2. Modeling the Rossiter-McLaughlin Effect: Impact of the Convective Center-to-limb Variations in the Stellar Photosphere

    NASA Astrophysics Data System (ADS)

    Cegla, H. M.; Oshagh, M.; Watson, C. A.; Figueira, P.; Santos, N. C.; Shelyag, S.

    2016-03-01

    Observations of the Rossiter-McLaughlin (RM) effect provide information on star-planet alignments, which can inform planetary migration and evolution theories. Here, we go beyond the classical RM modeling and explore the impact of a convective blueshift that varies across the stellar disk and non-Gaussian stellar photospheric profiles. We simulated an aligned hot Jupiter with a four-day orbit about a Sun-like star and injected center-to-limb velocity (and profile shape) variations based on radiative 3D magnetohydrodynamic simulations of solar surface convection. The residuals between our modeling and classical RM modeling were dependent on the intrinsic profile width and v sin i; the amplitude of the residuals increased with increasing v sin i and with decreasing intrinsic profile width. For slowly rotating stars the center-to-limb convective variation dominated the residuals (with amplitudes of 10 s of cm s-1 to ˜1 m s-1) however, for faster rotating stars the dominant residual signature was due a non-Gaussian intrinsic profile (with amplitudes from 0.5 to 9 m s-1). When the impact factor was 0, neglecting to account for the convective center-to-limb variation led to an uncertainty in the obliquity of ˜10°-20°, even though the true v sin i was known. Additionally, neglecting to properly model an asymmetric intrinsic profile had a greater impact for more rapidly rotating stars (e.g., v sin i = 6 km s-1) and caused systematic errors on the order of ˜20° in the measured obliquities. Hence, neglecting the impact of stellar surface convection may bias star-planet alignment measurements and consequently theories on planetary migration and evolution.

  3. The forbidden 1082 nm line of sulphur:. the photospheric abundance of sulphur in the Sun and 3D effects

    NASA Astrophysics Data System (ADS)

    Caffau, E.; Ludwig, H.-G.

    2007-05-01

    Context: Sulphur is an element which is formed in the α-process and is easily measured in the gaseous phase in external galaxies. Since it does not form dust, it is the preferred indicator for α-elements, rather than Si or Mg, for which dust corrections are necessary. The measurement of the sulphur abundance in stars is not an easy task, relying mainly on high excitation lines with non-negligible deviations from LTE. The 1082 nm sulphur forbidden transition is less sensitive to departures from LTE and is less dependent on temperature uncertainties than other sulphur lines usually employed as abundance indicators. Therefore it should provide a more robust abundance diagnostics. Aims: To derive the solar photospheric abundance of sulphur from the 1082 nm [SI] line and to investigate 3D effects present in G- and F-type atmospheres at solar and lower metallicity. Methods: High-resolution, high signal-to-noise solar intensity and flux spectra were used to measure the sulphur abundance from the [SI] 1082 nm line. CO^5BOLD hydrodynamical model atmospheres were applied to predict 3D abundance corrections for the [SI] line. Results: The solar sulphur abundance is derived to be 7.15± (0.01)_stat ± (0.05)_sys, where the statistical uncertainty represents the scatter in the determination using four different solar spectra and the systematic uncertainty is due to the modelling of the blending lines. Sulphur abundances obtained from this line are insensitive to the micro-turbulence. 3D abundance corrections, found from strictly differential comparisons between 1D and 3D models, are negligible in the Sun, but become sizable for more metal-poor dwarfs.

  4. Brown dwarf photospheres are patchy: A Hubble space telescope near-infrared spectroscopic survey finds frequent low-level variability

    SciTech Connect

    Buenzli, Esther; Apai, Dániel; Radigan, Jacqueline; Reid, I. Neill; Flateau, Davin

    2014-02-20

    Condensate clouds strongly impact the spectra of brown dwarfs and exoplanets. Recent discoveries of variable L/T transition dwarfs argued for patchy clouds in at least some ultracool atmospheres. This study aims to measure the frequency and level of spectral variability in brown dwarfs and to search for correlations with spectral type. We used Hubble Space Telescope/Wide Field Camera 3 to obtain spectroscopic time series for 22 brown dwarfs of spectral types ranging from L5 to T6 at 1.1-1.7 μm for ≈40 minutes per object. Using Bayesian analysis, we find six brown dwarfs with confident (p > 95%) variability in the relative flux in at least one wavelength region at sub-percent precision, and five brown dwarfs with tentative (p > 68%) variability. We derive a minimum variability fraction f{sub min}=27{sub −7}{sup +11}% over all covered spectral types. The fraction of variables is equal within errors for mid-L, late-L, and mid-T spectral types; for early-T dwarfs we do not find any confident variable but the sample is too small to derive meaningful limits. For some objects, the variability occurs primarily in the flux peak in the J or H band, others are variable throughout the spectrum or only in specific absorption regions. Four sources may have broadband peak-to-peak amplitudes exceeding 1%. Our measurements are not sensitive to very long periods, inclinations near pole-on and rotationally symmetric heterogeneity. The detection statistics are consistent with most brown dwarf photospheres being patchy. While multiple-percent near-infrared variability may be rare and confined to the L/T transition, low-level heterogeneities are a frequent characteristic of brown dwarf atmospheres.

  5. Compton backscattered and primary X-rays from solar flares: angle dependent Green's function correction for photospheric albedo

    NASA Astrophysics Data System (ADS)

    Kontar, E. P.; MacKinnon, A. L.; Schwartz, R. A.; Brown, J. C.

    2006-02-01

    The observed hard X-ray (HXR) flux spectrum I(ɛ) from solar flares is a combination of primary bremsstrahlung photons I_P(ɛ) with a spectrally modified component from photospheric Compton backscatter of downward primary emission. The latter can be significant, distorting or hiding the true features of the primary spectrum which are key diagnostics for acceleration and propagation of high energy electrons and of their energy budget. For the first time in solar physics, we use a Green's function approach to the backscatter spectral deconvolution problem, constructing a Green's matrix including photoelectric absorption. This approach allows spectrum-independent extraction of the primary spectrum for several HXR flares observed by the Ramaty High Energy Solar Spectroscopic Imager (RHESSI). We show that the observed and primary spectra differ very substantially for flares with hard spectra close to the disk centre. We show in particular that the energy dependent photon spectral index γ (ɛ)=-d log I/d log ɛ is very different for I_P(ɛ) and for I(ɛ) and that inferred mean source electron spectra F(E) differ greatly. Even for a forward fitting of a parametric F(E) to the data, a clear low-energy cutoff required to fit I(ɛ) essentially disappears when the fit is to I_P(ɛ) - i.e. when albedo correction is included. The self-consistent correction for backscattered photons is thus shown to be crucial in determining the energy spectra of flare accelerated electrons, and hence their total number and energy.

  6. Photosphere emission in the X-ray flares of swift gamma-ray bursts and implications for the fireball properties

    SciTech Connect

    Peng, Fang-Kun; Liang, En-Wei; Xi, Shao-Qiang; Lu, Rui-Jing; Zhang, Bing; Wang, Xiang-Yu; Hou, Shu-Jin; Zhang, Jin E-mail: xywang@nju.edu.cn

    2014-11-10

    X-ray flares of gamma-ray bursts (GRBs) are usually observed in the soft X-ray range and the spectral coverage is limited. In this paper, we present an analysis of 32 GRB X-ray flares that are simultaneously observed by both Burst Alert Telescope and X-Ray Telescope on board the Swift mission, so that a joint spectral analysis with a wider spectral coverage is possible. Our results show that the joint spectra of 19 flares are fitted with the absorbed single power law or the Band function models. More interestingly, the joint spectra of the other 13 X-ray flares are fitted with the absorbed single power-law model plus a blackbody component. Phenomenally, the observed spectra of these 13 flares are analogous to several GRBs with a thermal component, but only with a much lower temperature of kT = 1 ∼ 3 keV. Assuming that the thermal emission is the photosphere emission of the GRB fireball, we derive the fireball properties of the 13 flares that have redshift measurements, such as the bulk Lorentz factor Γ{sub ph} of the outflow. The derived Γ{sub ph} range from 50 to 150 and a relation of Γ{sub ph} to the thermal emission luminosity is found. It is consistent with the Γ{sub 0} – L {sub iso} relations that are derived for the prompt gamma-ray emission. We discuss the physical implications of these results within the content of jet composition and the radiation mechanism of GRBs and X-ray flares.

  7. THE EFFECTS OF MAGNETIC FIELD MORPHOLOGY ON THE DETERMINATION OF OXYGEN AND IRON ABUNDANCES IN THE SOLAR PHOTOSPHERE

    SciTech Connect

    Moore, Christopher S.; Uitenbroek, Han; Criscuoli, Serena; Rempel, Matthias; Rast, Mark P.

    2015-02-01

    We have explored the impact of magnetic fields on the determination of the solar photospheric oxygen and iron abundances using three-dimensional radiation-magnetohydrodynamic (MHD) simulations of convection. Specifically, we examined differences in abundance deduced from three classes of atmospheres simulated with the MURaM code: a pure hydrodynamic (HD) simulation, an MHD simulation with a local dynamo magnetic field that has saturated with an unsigned vertical field strength of 80 G at τ = 1, and an MHD simulation with an initially imposed vertical mean field of 80 G. We use differential equivalent width analysis for diagnosing abundances derived from five oxygen and four iron lines of differing wavelength, oscillator strength, excitation potential, and Landé g-factor, and find that the morphology of the magnetic field is important to the outcome of abundance determinations. The largest deduced abundance differences are found in the vertical mean field simulations, where the O I and Fe I abundance corrections compared to the pure HD case are ∼+0.011 dex and +0.065 dex respectively. Small scale unresolved field resulting from the local dynamo has a smaller impact on abundance determinations, with corrections of –0.0001 dex and +0.0044 dex in the magnetized compared to the pure HD simulations. While the overall influence of magnetic field on abundance estimates is found to be small, we stress that such estimates are sensitive not only to the magnitude of magnetic field but also to its morphology.

  8. Coronal structures in extreme ultraviolet and soft X-rays, and their relation to the photospheric magnetic flux

    NASA Astrophysics Data System (ADS)

    Benevolenskaya, E. E.

    2002-10-01

    The EIT/SOHO data in four EUV lines (1996-2001 yrs) and soft X-ray YOHKOH data (1991-2001 yrs) were analyzed in the form of coronal synoptic maps. Two types of the bright structures have been detected. The structures of the first type migrate equatorward as the solar cycle progresses. They are related to complexes of sunspot activity and display a "butterfly"-type distribution. The structures of the second type migrate polarward and are associated with footpoints of giant coronal loops in EUV, which magnetically couple the polar regions and the following parts of the active complexes. These structures of coronal activity are also pronounced in the soft X-ray maps. However, the whole structure of the giant polar loops is visible in X-rays, and reveal connections to the mid-latitude coronal structures. These structures appear during the rising phase of the solar cycle and its maximum, and show quasiperiodic impulsive variations with 1-1.5-year period. For the low- and mid-latitude structures we have studied the relationship between the soft X-ray intensity and the photospheric magnetic flux and found that it can be represented by the power law. However, the power index is higher for the period of the declining phase and minimum of solar activity than for its rising phase and maximum. This indicates that coronal heating has different characteristics at different phases of the solar cycle, and depends not only on the magnetic flux, but probably also on structural properties of the magnetic field.

  9. Photospheric magnetic fields

    NASA Technical Reports Server (NTRS)

    Howard, R.

    1972-01-01

    Knowledge on the nature of magnetic fields on the solar surface is reviewed. At least a large part of the magnetic flux in the solar surface is confined to small bundles of lines of force within which the field strength is of the order of 500 gauss. Magnetic fields are closely associated with all types of solar activity. Magnetic flux appears at the surface at the clearly defined birth or regeneration of activity of an active region. As the region ages, the magnetic flux migrates to form large-scale patterns and the polar fields. Some manifestations of the large-scale distribution are discussed.

  10. Photospheric Magnetic Field Properties of Flaring vs. Flare-Quiet Active Regions II: A Magnetic Charge Topology Model and Statistical Results

    NASA Astrophysics Data System (ADS)

    Barnes, G.; Leka, K. D.; Longcope, D. W.

    2003-05-01

    The complexity of the coronal magnetic field extrapolated from a Magnetic Charge Topology (MCT) model, is examined for pre-event signatures unique to solar energetic phenomena. Although extensive use has been made of quantities measured at the photosphere, it is important to consider the magnetic field in the corona, where (for example) the hard X-ray signatures of energy release in solar flares are observed. By quantifying the inferred coronal magnetic topology we are no longer limited to considering solely the magnetic state of the photosphere. MCT is applied to temporally sampled photospheric magnetic data from the U. Hawai`i Imaging Vector Magnetograph, for 24 flare-event and flare-quiet epochs from seven active regions. We outline the methodology employed for automating the application of MCT to large data sets of complex active regions: partitioning the observed Bz at the photosphere, assigning a charge to each partition, and using this charge distribution to extrapolate the field in the corona. From the resulting field we compute the connectivity matrix ψ ij, the location of null points and the intersection of separatrix surfaces, i.e. separator field lines. Parameters are constructed to describe, for example, the magnetic connectivities, the magnetic flux in those connections, and the number of separators. Examining particular events results in no obvious trends in the magnitude and temporal evolution of the parameters just prior to flare events. Thus, we employ the same quantitative statistical approach outlined in Leka and Barnes [this session], i.e. applying discriminant analysis and Hotelling's T2-test, and ranking all four-variable discriminant functions as a proxy for a single all-variable discriminant function. We present those parameters which consistently appear in the best combinations, indicating that they may play an important role in defining a pre-event coronal state. This work was performed under Air Force Office of Scientific Research

  11. NONLINEAR FORCE-FREE FIELD EXTRAPOLATION OF A CORONAL MAGNETIC FLUX ROPE SUPPORTING A LARGE-SCALE SOLAR FILAMENT FROM A PHOTOSPHERIC VECTOR MAGNETOGRAM

    SciTech Connect

    Jiang, Chaowei; Wu, S. T.; Hu, Qiang; Feng, Xueshang E-mail: wus@uah.edu E-mail: fengx@spaceweather.ac.cn

    2014-05-10

    Solar filaments are commonly thought to be supported in magnetic dips, in particular, in those of magnetic flux ropes (FRs). In this Letter, based on the observed photospheric vector magnetogram, we implement a nonlinear force-free field (NLFFF) extrapolation of a coronal magnetic FR that supports a large-scale intermediate filament between an active region and a weak polarity region. This result is a first, in the sense that current NLFFF extrapolations including the presence of FRs are limited to relatively small-scale filaments that are close to sunspots and along main polarity inversion lines (PILs) with strong transverse field and magnetic shear, and the existence of an FR is usually predictable. In contrast, the present filament lies along the weak-field region (photospheric field strength ≲ 100 G), where the PIL is very fragmented due to small parasitic polarities on both sides of the PIL and the transverse field has a low signal-to-noise ratio. Thus, extrapolating a large-scale FR in such a case represents a far more difficult challenge. We demonstrate that our CESE-MHD-NLFFF code is sufficient for the challenge. The numerically reproduced magnetic dips of the extrapolated FR match observations of the filament and its barbs very well, which strongly supports the FR-dip model for filaments. The filament is stably sustained because the FR is weakly twisted and strongly confined by the overlying closed arcades.

  12. Nonlinear Force-free Field Extrapolation of a Coronal Magnetic Flux Rope Supporting a Large-scale Solar Filament from a Photospheric Vector Magnetogram

    NASA Astrophysics Data System (ADS)

    Jiang, Chaowei; Wu, S. T.; Feng, Xueshang; Hu, Qiang

    2014-05-01

    Solar filaments are commonly thought to be supported in magnetic dips, in particular, in those of magnetic flux ropes (FRs). In this Letter, based on the observed photospheric vector magnetogram, we implement a nonlinear force-free field (NLFFF) extrapolation of a coronal magnetic FR that supports a large-scale intermediate filament between an active region and a weak polarity region. This result is a first, in the sense that current NLFFF extrapolations including the presence of FRs are limited to relatively small-scale filaments that are close to sunspots and along main polarity inversion lines (PILs) with strong transverse field and magnetic shear, and the existence of an FR is usually predictable. In contrast, the present filament lies along the weak-field region (photospheric field strength <~ 100 G), where the PIL is very fragmented due to small parasitic polarities on both sides of the PIL and the transverse field has a low signal-to-noise ratio. Thus, extrapolating a large-scale FR in such a case represents a far more difficult challenge. We demonstrate that our CESE-MHD-NLFFF code is sufficient for the challenge. The numerically reproduced magnetic dips of the extrapolated FR match observations of the filament and its barbs very well, which strongly supports the FR-dip model for filaments. The filament is stably sustained because the FR is weakly twisted and strongly confined by the overlying closed arcades.

  13. The photospheric solar oxygen project. IV. 3D-NLTE investigation of the 777 nm triplet lines

    NASA Astrophysics Data System (ADS)

    Steffen, M.; Prakapavičius, D.; Caffau, E.; Ludwig, H.-G.; Bonifacio, P.; Cayrel, R.; Kučinskas, A.; Livingston, W. C.

    2015-11-01

    Context. The solar photospheric oxygen abundance is still widely debated. Adopting the solar chemical composition based on the "low" oxygen abundance, as determined with the use of three-dimensional (3D) hydrodynamical model atmospheres, results in a well-known mismatch between theoretical solar models and helioseismic measurements that is so far unresolved. Aims: We carry out an independent redetermination of the solar oxygen abundance by investigating the center-to-limb variation of the O i IR triplet lines at 777 nm in different sets of spectra. Methods: The high-resolution and high signal-to-noise solar center-to-limb spectra are analyzed with the help of detailed synthetic line profiles based on 3D hydrodynamical CO5BOLD model atmospheres and 3D non-LTE line formation calculations with NLTE3D. The idea is to exploit the information contained in the observations at different limb angles to simultaneously derive the oxygen abundance, A(O), and the scaling factor SH that describes the cross-sections for inelastic collisions with neutral hydrogen relative to the classical Drawin formula. Using the same codes and methods, we compare our 3D results with those obtained from the semi-empirical Holweger-Müller model atmosphere as well as from different one-dimensional (1D) reference models. Results: With the CO5BOLD 3D solar model, the best fit of the center-to-limb variation of the triplet lines is obtained when the collisions by neutral hydrogen atoms are assumed to be efficient, i.e., when the scaling factor SH is between 1.2 and 1.8, depending on the choice of the observed spectrum and the triplet component used in the analysis. The line profile fits achieved with standard 1D model atmospheres (with fixed microturbulence, independent of disk position μ) are clearly of inferior quality compared to the 3D case, and give the best match to the observations when ignoring collisions with neutral hydrogen (SH = 0). The results derived with the Holweger-Müller model are

  14. How Dusty Is Alpha Centauri? Excess or Non-excess over the Infrared Photospheres of Main-sequence Stars

    NASA Technical Reports Server (NTRS)

    Wiegert, J.; Liseau, R.; Thebault, P.; Olofsson, G.; Mora, A.; Bryden, G.; Marshall, J. P.; Eiroa, C.; Montesinos, B.; Ardila, D.; Augereau, J. C.; Aran, A. Bayo; Danchi, W. C.; del Burgo, C.; Ertel, S.; Fridlund, M. C. W.; Hajigholi, M.; Krivov, A. V.; Pilbratt, G. L.; Roberge, A.; White, G. J.; Wolf, S.

    2014-01-01

    Context. Debris discs around main-sequence stars indicate the presence of larger rocky bodies. The components of the nearby, solar-type binary Centauri have metallicities that are higher than solar, which is thought to promote giant planet formation. Aims. We aim to determine the level of emission from debris around the stars in the Cen system. This requires knowledge of their photospheres.Having already detected the temperature minimum, Tmin, of CenA at far-infrared wavelengths, we here attempt to do the same for the moreactive companion Cen B. Using the Cen stars as templates, we study the possible eects that Tmin may have on the detectability of unresolveddust discs around other stars. Methods.We used Herschel-PACS, Herschel-SPIRE, and APEX-LABOCA photometry to determine the stellar spectral energy distributions in thefar infrared and submillimetre. In addition, we used APEX-SHeFI observations for spectral line mapping to study the complex background around Cen seen in the photometric images. Models of stellar atmospheres and of particulate discs, based on particle simulations and in conjunctionwith radiative transfer calculations, were used to estimate the amount of debris around these stars. Results. For solar-type stars more distant than Cen, a fractional dust luminosity fd LdustLstar 2 107 could account for SEDs that do not exhibit the Tmin eect. This is comparable to estimates of fd for the Edgeworth-Kuiper belt of the solar system. In contrast to the far infrared,slight excesses at the 2:5 level are observed at 24 m for both CenA and B, which, if interpreted as due to zodiacal-type dust emission, wouldcorrespond to fd (13) 105, i.e. some 102 times that of the local zodiacal cloud. Assuming simple power-law size distributions of the dustgrains, dynamical disc modelling leads to rough mass estimates of the putative Zodi belts around the Cen stars, viz.4106 M$ of 4 to 1000 msize grains, distributed according to n(a) a3:5. Similarly, for filled-in Tmin

  15. EVIDENCE FOR A PHOTOSPHERIC COMPONENT IN THE PROMPT EMISSION OF THE SHORT GRB 120323A AND ITS EFFECTS ON THE GRB HARDNESS-LUMINOSITY RELATION

    SciTech Connect

    Guiriec, S.; McEnery, J.; Gehrels, N.; Daigne, F.; Hascoeet, R.; Mochkovitch, R.; Vianello, G.; Ryde, F.; Kouveliotou, C.; Foley, S.; McGlynn, S.; Gruber, D.

    2013-06-10

    The short GRB 120323A had the highest flux ever detected with the Gamma-Ray Burst Monitor on board the Fermi Gamma-Ray Space Telescope. Here we study its remarkable spectral properties and their evolution using two spectral models: (1) a single emission component scenario, where the spectrum is modeled by the empirical Band function (a broken power law), and (2) a two-component scenario, where thermal (a Planck-like function) emission is observed simultaneously with a non-thermal component (a Band function). We find that the latter model fits the integrated burst spectrum significantly better than the former, and that their respective spectral parameters are dramatically different: when fit with a Band function only, the E{sub peak} of the event is unusually soft for a short gamma-ray burst (GRB; 70 keV compared to an average of 300 keV), while adding a thermal component leads to more typical short GRB values (E{sub peak} {approx} 300 keV). Our time-resolved spectral analysis produces similar results. We argue here that the two-component model is the preferred interpretation for GRB 120323A based on (1) the values and evolution of the Band function parameters of the two component scenario, which are more typical for a short GRB, and (2) the appearance in the data of a significant hardness-intensity correlation, commonly found in GRBs, when we employee two-component model fits; the correlation is non-existent in the Band-only fits. GRB 110721A, a long burst with an intense photospheric emission, exhibits the exact same behavior. We conclude that GRB 120323A has a strong photospheric emission contribution, observed for the first time in a short GRB. Magnetic dissipation models are difficult to reconcile with these results, which instead favor photospheric thermal emission and fast cooling synchrotron radiation from internal shocks. Finally, we derive a possibly universal hardness-luminosity relation in the source frame using a larger set of GRBs (L{sub i}{sup Band

  16. One- and multi-component models of the upper photosphere based on molecular spectra. I - The violet system of CN /0, 0/

    NASA Technical Reports Server (NTRS)

    Mount, G. H.; Linsky, J. L.; Shine, R. A.

    1973-01-01

    Spectroheliograms taken in the CN (0, 0) violet band near 3883 A show very small scale network and cell structures with high contrast. The bandhead itself, which is a broad feature due to overlap of several CN lines, allows the diagnostic simplicity of a continuum since motions, magnetic fields, and broadening mechanisms are unimportant. We have obtained spectroheliograms in the bandhead and center-to-limb photoelectric spectra of CN (0, 0) at Kitt Peak National Observatory. From the photoelectric spectra and a detailed analysis of the formation of the CN (0, 0) spectrum we derive a best-fit one-component upper photospheric model differing from that of the HSRA and recommend a change in solar carbon abundance from the HSRA value.

  17. The photosphere and chromosphere of the RS Canum Venaticorum star, II Pegasi. II. A multi-wavelength campaign in August/September 1992

    NASA Astrophysics Data System (ADS)

    Byrne, P. B.; Abdul Aziz, H.; Amado, P. J.; Arevalo, M. J.; Avgoloupis, S.; Doyle, J. G.; Eibe, M. T.; Elliott, K. H.; Jeffries, R. D.; Lanzafame, A. C.; Lazaro, C.; Murphy, H. M.; Neff, J. E.; Panov, K. P.; Sarro, L. M.; Seiradakis, J. H.; Spencer, R. E.

    1998-02-01

    We describe multi-wavelength, simultaneous observations of the RS CVn star, II Pegasi, most of which were obtained during the first three weeks of September 1992. These observations were made using optical and infra-red broad-band photometry, ultraviolet and optical spectroscopy and microwave monitoring. We have detected photospheric spots and chromospheric flares, as well as deriving a description of mean conditions in the quiet chromosphere. One of the flares, observed in optical photometry and ultraviolet spectroscopy is one of the most energetic ever observed on this star. We demonstrate that in its ``quiescent'' state II Peg is continually variable in most of its chromospheric emissions, as well as in its coronal output.

  18. Improved Co I log(gf) & hfs data and Abundance Determinations in the Photospheres of the Sun & Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, James E.; Sneden, Chris; Cowan, John J.

    2016-01-01

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co I) from hollow cathode lamp spectra recorded with a 1m Fourier transform spectrometer (FTS) and a high resolution echelle spectrometer are reported. Radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate log(gf)s for the 898 lines. Selected published hyperfine structure (hfs) constants for levels of neutral Co are used to generate complete hfs component patterns for 195 transitions of Co I. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log eps(Co) = 4.955 ± 0.007 (sigma = 0.059) based on 82 Co I lines and log eps(Co) = 2.785 ± 0.008 (sigma = 0.065) based on 66 Co I lines respectively. A Saha balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co II, and good agreement is found with the Co I result in this metal-poor ([Fe I /H] = -2.32, [Fe II /H] = -2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies. These new Co I data are part of a continuing effort to explore the limits of 1D/LTE photospheric models in metal-poor stars and to determine the relative abundance of Fe-group elements at low metallicity. This work is supported in part by NASA grant NNX10AN93G (J.E.L.), by NSF grant AST-1211055 (J.E.L.), and by NSF grant AST-1211585 (C.S.).

  19. Improved log(gf) Values Of Selected Lines In Mn I And Mn II For Studies Of Non-equilibrium Effects In Stellar Photospheres

    NASA Astrophysics Data System (ADS)

    Den Hartog, Elizabeth; Lawler, J. E.; Sobeck, J.; Sneden, C.; Cowan, J. J.; Asplund, M.

    2010-01-01

    The work presents transition probabilities with very low uncertainties for a selected set of multiplets of Mn I and Mn II. Multiplets are chosen which are accessible to ground-based observation, are relatively unblended and unsaturated in stellar spectra and which are amenable to accurate branching fraction determination. These lab measurements provide a foundation for studies of non-LTE and 3-dimensional effects in stellar photospheres. We report on new radiative lifetime measurements for 22 levels of Mn I from the e8D, z6P, z6D, z4F, e8S and e6S multiplets and 3 levels of Mn II from the z5P multiplet using time-resolved laser-induced fluorescence on a slow atomic beam. New branching fractions for transitions from these levels, measured using a Fourier-transform spectrometer, are also reported. When combined, these measurements yield transition probabilities for 47 transitions of Mn I and 12 transitions of Mn II. Comparisons are made to data from the literature and to simple Russell-Saunders or LS theory. Final recommended values, which are weighted averages of all available modern measurements and in some cases LS theory, are given for the transition probabilities. These recommended log(gf) values are accurate to +/- 0.02 dex with high ( 2 sigma) confidence. The companion paper applies these new lab results to studies of departures from both LTE in Mn I and Saha equilibrium between Mn I and Mn II on a variety of stellar photospheres. This research is supported in part by NASA Grant NNX08AQ09G and NSF Grant AST-0907732.

  20. The EUV photosphere- corona interface from eclipses to study the origin of low- FIP elements and the root of the basis of the chromosphere

    NASA Astrophysics Data System (ADS)

    Bazin, Cyrille; Veselovsky, Igor; Vial, Jean-Claude; Tavabi, Ehsan; Serge, Koutchmy

    We use the full occultation of the Sun by the Moon to study the upper solar atmosphere with flash spectra free of any parasitic light from the disc. A radial resolution of 40 km is obtained from unique images in many emission lines seen as crescents of the low atmosphere. The natural motion of the lunar limb probes the photosphere - corona interface where the solar magnetic field emerges. High cadence CCD slitless flash spectra obtained before and after the eclipse totality (in 2008, 2009, 2010, 2012, and 2013) show that the over-abundance of the low First Ionisation Potential elements (low FIP) like FeII, TiII, BaII, etc. comes from the interface layers close to the temperature minimum. For the 1st time, the solar edge is defined by considering the “true” continuum analysed outside of faint emission lines at heights ranging from 0.2 to 0.6 Mm. We also measure the helium shells of He I 4713Å and of He II 4686Å (Paschen alpha, optically thin high FIP lines), starting at the height of 0.8 Mm. Enhancements of the high FIP lines (H beta, He I and He II) are found at altitudes lower than 0.8 Mm above the limb from new 2013 spectra. The extensions of the helium shells are compared in equatorial and Polar Regions. The widths of the lines are evaluated for the 1st time. The light curves I = f(h) corresponding to low FIP ions are measured for different positions of the low solar atmosphere. The scale heights correspond to radial density gradients allowing temperature evaluations in case of the hydrostatic assumptions. We also demonstrate some density gradient analogies between the photosphere- corona and the prominence-corona interface using the Ti II lines as a marker. The effect of the magnetic field emergence for supplying mass to the corona through low FIP elements is discussed. A simultaneously obtained 193 SDO/AIA processed image is used to discuss what the coronal extensions are.

  1. Improved V II Log(gf) Values, Hyperfine Structure Constants, and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J.

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ɛ(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = -2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  2. Improved Co I log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, J. E.; Sneden, C.; Cowan, J. J.

    2015-09-01

    New emission branching fraction measurements for 898 lines of the first spectrum of cobalt (Co i) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer on Kitt Peak, AZ and a high-resolution echelle spectrometer. Published radiative lifetimes from laser induced fluorescence measurements are combined with the branching fractions to determine accurate absolute atomic transition probabilities for the 898 lines. Hyperfine structure (hfs) constants for levels of neutral Co in the literature are surveyed and selected values are used to generate complete hfs component patterns for 195 transitions of Co i. These new laboratory data are applied to determine the Co abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(Co) = 4.955 ± 0.007 (σ = 0.059) based on 82 Co i lines and log ɛ(Co) = 2.785 ± 0.008 (σ = 0.065) based on 66 Co i lines, respectively. A Saha or ionization balance test on the photosphere of HD 84937 is performed using 16 UV lines of Co ii, and good agreement is found with the Co i result in this metal-poor ([Fe i/H] = -2.32, [Fe ii/H] = -2.32) dwarf star. The resulting value of [Co/Fe] = +0.14 supports a rise of Co/Fe at low metallicity that has been suggested in other studies.

  3. Applying the expanding photosphere and standardized candle methods to Type II-Plateau supernovae at cosmologically significant redshifts . The distance to SN 2013eq

    NASA Astrophysics Data System (ADS)

    Gall, E. E. E.; Kotak, R.; Leibundgut, B.; Taubenberger, S.; Hillebrandt, W.; Kromer, M.

    2016-08-01

    Based on optical imaging and spectroscopy of the Type II-Plateau SN 2013eq, we present a comparative study of commonly used distance determination methods based on Type II supernovae. The occurrence of SN 2013eq in the Hubble flow (z = 0.041 ± 0.001) prompted us to investigate the implications of the difference between "angular" and "luminosity" distances within the framework of the expanding photosphere method (EPM) that relies upon a relation between flux and angular size to yield a distance. Following a re-derivation of the basic equations of the EPM for SNe at non-negligible redshifts, we conclude that the EPM results in an angular distance. The observed flux should be converted into the SN rest frame and the angular size, θ, has to be corrected by a factor of (1 + z)2. Alternatively, the EPM angular distance can be converted to a luminosity distance by implementing a modification of the angular size. For SN 2013eq, we find EPM luminosity distances of DL = 151 ± 18 Mpc and DL = 164 ± 20 Mpc by making use of different sets of dilution factors taken from the literature. Application of the standardized candle method for Type II-P SNe results in an independent luminosity distance estimate (DL = 168 ± 16 Mpc) that is consistent with the EPM estimate. Spectra of SN 2013eq are available in the Weizmann Interactive Supernova data REPository (WISeREP): http://wiserep.weizmann.ac.il

  4. IMPROVED V II log(gf) VALUES, HYPERFINE STRUCTURE CONSTANTS, AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Wood, M. P.; Lawler, J. E.; Den Hartog, E. A.; Sneden, C.; Cowan, J. J. E-mail: jelawler@wisc.edu E-mail: chris@verdi.as.utexas.edu

    2014-10-01

    New experimental absolute atomic transition probabilities are reported for 203 lines of V II. Branching fractions are measured from spectra recorded using a Fourier transform spectrometer and an echelle spectrometer. The branching fractions are normalized with radiative lifetime measurements to determine the new transition probabilities. Generally good agreement is found between this work and previously reported V II transition probabilities. Two spectrometers, independent radiometric calibration methods, and independent data analysis routines enable a reduction in systematic uncertainties, in particular those due to optical depth errors. In addition, new hyperfine structure constants are measured for selected levels by least squares fitting line profiles in the FTS spectra. The new V II data are applied to high resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to determine new, more accurate V abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. Very good agreement is found between our new solar photospheric V abundance, log ε(V) = 3.95 from 15 V II lines, and the solar-system meteoritic value. In HD 84937, we derive [V/H] = –2.08 from 68 lines, leading to a value of [V/Fe] = 0.24.

  5. FIRST SYNOPTIC MAPS OF PHOTOSPHERIC VECTOR MAGNETIC FIELD FROM SOLIS/VSM: NON-RADIAL MAGNETIC FIELDS AND HEMISPHERIC PATTERN OF HELICITY

    SciTech Connect

    Gosain, S.; Pevtsov, A. A.; Rudenko, G. V.; Anfinogentov, S. A.

    2013-07-20

    We use daily full-disk vector magnetograms from Vector Spectromagnetograph on Synoptic Optical Long-term Investigations of the Sun system to synthesize the first Carrington maps of the photospheric vector magnetic field. We describe these maps and make a comparison of the observed radial field with the radial field estimate from line-of-sight magnetograms. Furthermore, we employ these maps to study the hemispheric pattern of current helicity density, H{sub c} , during the rising phase of solar cycle 24. The longitudinal average over the 23 consecutive solar rotations shows a clear signature of the hemispheric helicity rule, i.e., H{sub c} is predominantly negative in the north and positive in the south. Although our data include the early phase of cycle 24, there appears to be no evidence for a possible (systematic) reversal of the hemispheric helicity rule at the beginning of the cycle as predicted by some dynamo models. Furthermore, we compute the hemispheric pattern in active region latitudes (-30 Degree-Sign {<=} {theta} {<=} 30 Degree-Sign ) separately for weak (100 G < |B{sub r} | < 500 G) and strong (|B{sub r} | > 1000 G) radial magnetic fields. We find that while the current helicity of strong fields follows the well-known hemispheric rule (i.e., {theta} {center_dot} H{sub c} < 0), H{sub c} of weak fields exhibits an inverse hemispheric behavior (i.e., {theta} {center_dot} H{sub c} > 0), albeit with large statistical scatter. We discuss two plausible scenarios to explain the opposite hemispheric trend of helicity in weak and strong field regions.

  6. The energy of waves in the photosphere and lower chromosphere. III. Inversion setup for Ca II H spectra in local thermal equilibrium

    NASA Astrophysics Data System (ADS)

    Beck, C.; Rezaei, R.; Puschmann, K. G.

    2013-01-01

    Context. The Ca II H line is one of the strongest lines in the solar spectrum, and it provides continuous information on the solar atmosphere from the photosphere to the lower chromosphere. Aims: We describe an inversion approach that reproduces observed Ca II H spectra by assuming local thermal equilibrium (LTE). Methods: We developed an inversion strategy based on the SIR code that reproduces Ca II H spectra in the LTE approximation. The approach uses a two-step procedure with an archive of pre-calculated spectra to fit the line core and a subsequent iterative modification to improve the fit mainly in the line wing. Simultaneous spectra in the 630 nm range can optionally be used to fix the continuum temperature. The method retrieves one-dimensional (1D) temperature stratifications while neglecting lateral radiative transport. Line-of-sight velocities are included post facto with an empirical approach. Results: An archive of about 300 000 pre-calculated spectra is more than sufficient to reproduce the line core of observed Ca II H spectra both in the quiet Sun and in active regions. The subsequent iterative adjustment of the thermodynamical stratification matches observed and best-fit spectra to a level of about 0.5% of Ic in the line wing and about 1% of Ic in the line core. Conclusions: The successful application of the LTE inversion strategy suggests that inversion schemes based on pre-calculated spectra allow a reliable and relatively fast retrieval of solar properties from observed chromospheric spectra. The approach can be easily extended to a 1D non-LTE (NLTE) case by a simple exchange of the pre-calculated archive spectra. Using synthetic NLTE spectra from numerical three-dimensional (3D) simulations instead will finally allow one to extend the approach from the static 1D-case to dynamical atmosphere models, including the complete 3D radiative transport. The animation is available in electronic form at http://www.aanda.org

  7. Investigation of Solar Wind Source Regions by Using Ulysses/SWICS/SWOOPS Composition Data and a Potential Field Source Surface Model to map in situ Measurements back onto the Photosphere

    NASA Astrophysics Data System (ADS)

    Peleikis, T.; Kruse, M. A., II; Berger, L.; Drews, C.; Wimmer-Schweingruber, R. F.; McComas, D. J.; Gloeckler, G.

    2014-12-01

    The fast solar wind most likely originates from coronal holes, primarily the polar coronal holes, as evidently shown by Ulysses/SWICS observations of the solar wind at high heliographic latitudes. The source of the slow solar wind, on the other hand, remains elusive and is still under debate. In order to analyze the transition between different solar wind regimes, we use Ulysses/SWICS/SWOOPS/VHM solar wind and solar wind composition data to investigate solar wind dwell (transition from fast to slow wind) and compression regions (transition from slow to fast wind). Because the solar wind dwells are dynamically pulled apart, thus magnifying the transition region, we can observe the nature of the transition with increased accuracy and, in the near future, will provide limits on models of the origin of the slow solar wind. We map the composition data provided by SWICS back onto the source surface of the sun. Utilizing a Potential Field Source Surface (PFSS) model we trace the corresponding magnetic field lines from the source surface down to the photosphere, which provides a direct link between the composition measurements of Ulysses/SWICS and its source on the Sun's photosphere. In addition ot that, we will trace the field lines to several height layers between the photosphere and source surface so that we will be able to create a height profile of the solar wind source regions. Finally, we will calculate the distance from the determined source locations to the borders of the open field line regions in order to look for correlations between solar wind speed, charge state composition and source location. Here we will show results of our back-mapping analysis and preliminary implications for the solar wind source regions.

  8. Polar Faculae Are Faculae Of Old Age, Ascending To Photosphere From Sun's Upper Magnetic Toroid Levels, And Then Descending Near Equator by 105 Km, In Their Circulatory Motion, To Depths Slightly Below That of Lower Magnetic Toroid, And Then Ascending Again To Photosphere At Lat. 0c ¡A~50¢ª, N. And S.KEITH L. MCDONALD, P. O. Box 2433, Salt Lake City, UT

    NASA Astrophysics Data System (ADS)

    McDonald, K. L.

    2004-11-01

    We present arguments that Sun's polar magnetic fields, near 1 gauss strength, ascend to photosphere in polar facular increments, in accord with Fig. 1, 1 thru secular meridional circulation of both 3,600 + 25 gauss mag. toroids (as obs. at upper level) of each hemisphere, reversing polarities every 11 yr. Having been submerged to just below lower mag. toroid and traveling slightly faster there in circulatory mer. motions of Sun, which drive toroids, incipient polar faculae do not ascend with toroid at 0c = 40¢ª, but continue to higher latitudes ¡A~ 50¢ª, and now having aged by as much as one solar cycle plus ¢« 3 yr., they begin their appearance at photosphere. Ascent to photosphere requires greater travel time the greater is their lat. of vertical ascent, owing to reduced mer. circulation velocity with inc. in lat. above 40¢ª (Confer sketch of fluid motions, Fig. 1.1) Thus, polar faculae reaching photosphere at 63¢ª, where surface density increases strongly and reaches an almost constant value at 0c = 70¢ª, and that possibly extends over whole polar cap when near polar facular max., would be expected to have been formed at 40¢ª or at lesser lat. as faculae in previous sunspot cycle and would thus possess a significantly reduced observed lifetime compared to faculae in photosphere newly found below 40¢ª. Sheeley2 has counted numbers of n., s. polar faculae for period 1935-1963, 1964-1975. He finds a min. value corresponding to sunspot max. years, and conversely, so that their numbers are approx. 180¢ª out of phase with time variation of sunspot numbers for whole disk. Faculae and plages have property of being any bright regions of Sun¡¯s photosphere, seen most easily near Sun¡¯s limb and occurring most often in neighborhood of sunspots, their incandescence resulting from slow collapse of their individual engulfing mag. fields; violent turbulent eddies excise portions of toroids, including their mag. fields and transport them laterally into

  9. IMPROVED log(gf) VALUES FOR LINES OF Ti I AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937 (ACCURATE TRANSITION PROBABILITIES FOR Ti I)

    SciTech Connect

    Lawler, J. E.; Guzman, A.; Wood, M. P.; Sneden, C.; Cowan, J. J. E-mail: adrianaguzman2014@u.northwestern.edu E-mail: chris@verdi.as.utexas.edu

    2013-04-01

    New atomic transition probability measurements for 948 lines of Ti I are reported. Branching fractions from Fourier transform spectra and from spectra recorded using a 3 m echelle spectrometer are combined with published radiative lifetimes from laser-induced fluorescence measurements to determine these transition probabilities. Generally good agreement is found in comparisons to the NIST Atomic Spectra Database. The new Ti I data are applied to re-determine the Ti abundance in the photospheres of the Sun and metal-poor star HD 84937 using many lines covering a range of wavelength and excitation potential to explore possible non-local thermal equilibrium effects. The variation of relative Ti/Fe abundance with metallicity in metal-poor stars observed in earlier studies is supported in this study.

  10. Determination of solar flare accelerated ion angular distributions from SMM gamma ray and neutron measurements and determination of the He-3/H ratio in the solar photosphere from SMM gamma ray measurements

    NASA Technical Reports Server (NTRS)

    Lingenfelter, Richard E.

    1989-01-01

    Comparisons of Solar Maximum Mission (SMM) observations of gamma-ray line and neutron emission with theoretical calculation of their expected production by flare accelerated ion interactions in the solar atmosphere have led to significant advances in the understanding of solar flare particle acceleration and interaction, as well as the flare process itself. These comparisons have enabled the determination of, not only the total number and energy spectrum of accelerated ions trapped at the sun, but also the ion angular distribution as they interact in the solar atmosphere. The Monte Carlo program was modified to include in the calculations of ion trajectories the effects of both mirroring in converging magnetic fields and of pitch angle scattering. Comparing the results of these calculations with the SMM observations, not only the angular distribution of the interacting ions can be determined, but also the initial angular distribution of the ions at acceleration. The reliable determination of the solar photospheric He-3 abundance is of great importance for understanding nucleosynthesis in the early universe and its implications for cosmology, as well as for the study of the evolution of the sun. It is also essential for the determinations of the spectrum and total number of flare accelerated ions from the SMM/GRS gamma-ray line measurements. Systematic Monte Carlo calculations of the time dependence were made as a function of the He-3 abundance and other variables. A new series of calculations were compared for the time-dependent flux of 2.223 MeV neutron capture line emission and the ratio of the time-integrated flux in the 2.223 MeV line to that in the 4.1 to 6.4 MeV nuclear deexcitation band.

  11. The Frontier between Small-scale Bipoles and Ephemeral Regions in the Solar Photosphere: Emergence and Decay of an Intermediate-scale Bipole Observed with SUNRISE/IMaX

    NASA Astrophysics Data System (ADS)

    Guglielmino, S. L.; Martínez Pillet, V.; Bonet, J. A.; del Toro Iniesta, J. Carlos; Bellot Rubio, L. R.; Solanki, S. K.; Schmidt, W.; Gandorfer, A.; Barthol, P.; Knölker, M.

    2012-02-01

    We report on the photospheric evolution of an intermediate-scale (≈4 Mm footpoint separation) magnetic bipole, from emergence to decay, observed in the quiet Sun at high spatial (0farcs3) and temporal (33 s) resolution. The observations were acquired by the Imaging Magnetograph Experiment imaging magnetograph during the first science flight of the SUNRISE balloon-borne solar observatory. The bipole flux content is 6 × 1017 Mx, representing a structure bridging the gap between granular scale bipoles and the smaller ephemeral regions. Footpoints separate at a speed of 3.5 km s-1 and reach a maximum distance of 4.5 Mm before the field dissolves. The evolution of the bipole is revealed to be very dynamic: we found a proper motion of the bipole axis and detected a change of the azimuth angle of 90° in 300 s, which may indicate the presence of some writhe in the emerging structure. The overall morphology and behavior are in agreement with previous analyses of bipolar structures emerging at the granular scale, but we also found several similarities with emerging flux structures at larger scales. The flux growth rate is 2.6 × 1015 Mx s-1, while the mean decay rate is one order of magnitude smaller. We describe in some detail the decay phase of the bipole footpoints that includes break up into smaller structures, and interaction with preexisting fields leading to cancellation, but it appears to be dominated by an as-yet unidentified diffusive process that removes most of the flux with an exponential flux decay curve. The diffusion constant (8 × 102 km2 s-1) associated with this decay is similar to the values used to describe the large-scale diffusion in flux transport models.

  12. Coronal magnetic fields produced by photospheric shear

    NASA Technical Reports Server (NTRS)

    Sturrock, P. A.; Yang, W.-H.

    1987-01-01

    The magneto-frictional method is used for computing force free fields to examine the evolution of the magnetic field of a line dipole, when there is relative shearing motion between the two polarities. It found that the energy of the sheared field can be arbitrarily large compared with the potential field. It is also found that it is possible to fit the magnetic energy, as a function of shear, by a simple functional form.

  13. Vorticity and divergence in the solar photosphere

    NASA Technical Reports Server (NTRS)

    Wang, YI; Noyes, Robert W.; Tarbell, Theodore D.; Title, Alan M.

    1995-01-01

    We have studied an outstanding sequence of continuum images of the solar granulation from Pic du Midi Observatory. We have calculated the horizontal vector flow field using a correlation tracking algorithm, and from this determined three scalar field: the vertical component of the curl; the horizontal divergence; and the horizontal flow speed. The divergence field has substantially longer coherence time and more power than does the curl field. Statistically, curl is better correlated with regions of negative divergence - that is, the vertical vorticity is higher in downflow regions, suggesting excess vorticity in intergranular lanes. The average value of the divergence is largest (i.e., outflow is largest) where the horizontal speed is large; we associate these regions with exploding granules. A numerical simulation of general convection also shows similar statistical differences between curl and divergence. Some individual small bright points in the granulation pattern show large local vorticities.

  14. Photospheric Line Equivalent Widths in Calcium K Faculae

    NASA Astrophysics Data System (ADS)

    Walton, S. R.; Preminger, D. G.; Chapman, G. A.; Cookson, A. M.

    2003-05-01

    We have recently shown (Preminger, Walton, and Chapman 2002) that the total solar irradiance S can be modeled by a linear combination of photometric quantities which measure the fractional brightness change in the continuum and in the Ca II K line. We concluded that the change in S on solar cycle time scales is caused by variations in spectral lines, not in the continuum. In order to further test this conclusion, we have begun comparing our photometric Ca II K images with line equivalent width maps made in Fe I 6302.5. Bright features in our K images are well correlated with areas of lower equivalent width. We are beginning to quantitatively measure this correlation and will present further results at the meeting. This research has been supported by NSF grant ATM-9912132.

  15. Near-equatorial magnetic field of the photosphere

    NASA Astrophysics Data System (ADS)

    Vernova, Elena; Tyasto, Marta; Baranov, Dmitrii

    2016-04-01

    The heliolatitude distribution of magnetic field groups of different strength was studied on the basis of the synoptic maps of NSO Kitt Peak (1976-2003). The analysis of the synoptic maps averaged over 3 solar cycles allowed to distinguish four typical groups of magnetic fields: B = 0 - 5 G; B = 5 - 15 G; B = 15 - 50 G and B > 50 G. It is shown that there exists a definite relation between the strength of the magnetic field and its latitudinal localization. The time-dependence is studied for different groups of magnetic fields. The fields of different polarity are considered separately for the North and the South solar hemispheres. A special attention is given to the weakest magnetic fields (B = 0 - 5 G) which are localized near the equator (latitudes ± 5°) and in the interval 40° - 60° in each of the hemispheres. For the near-equatorial region the weakest fields in the North and the South hemispheres change synchronously and are approximately in anti-phase with the Wolf numbers. On the contrary the stronger fields (B = 5 - 10 G and higher) change in the phase with the solar cycle. Thus the magnetic field strength of the 5 G value represents the threshold below which the time-course of the magnetic field is in anti-phase with the solar cycle, while above 5 G it changes in the phase with the solar cycle. It should be noted that in the near-equatorial region the fields of the same sign in the North and the South hemispheres change almost synchronously, while the relation between the fields of the opposite signs in one hemisphere is much less pronounced. This relation differs sharply from the case of strong magnetic fields in the sunspot zone where a strong correlation is observed for the magnetic fields of opposite sign within the same hemisphere. The obtained results allow to conclude that the weak magnetic fields of the near-equatorial region of the Sun are not just the "wings" of the magnetic field distribution of the sunspot zone, but represent a separate phenomenon.

  16. Dynamical behaviour of photospheric bright points during merging

    NASA Astrophysics Data System (ADS)

    Criscuoli, S.; Stangalini, M.; Ermolli, I.; Zuccarello, F.; Cristaldi, A.; Falco, M.; Guglielmino, S.; Giorgi, F.

    2014-12-01

    We investigate the merging of bright points observed at high spatial and temporal resolution with CRISP/SST in a quiet region region. We analyze the MHD perturbations excited during the merging, their role in the energy budget of the magnetic structure and the potential role that they can play in heating the upper layers of the Sun's atmosphere.

  17. Tracing the sub-photospheric layers of optically thick winds

    NASA Astrophysics Data System (ADS)

    Graefener, G.

    2013-06-01

    Towards the end of their evolution hot massive stars develop strong stellar winds and appear as emission line stars, such as WR stars or LBVs. The quanitative description of the mass loss in these important pre-SN phases is hampered by unkowns such as wind clumping and porosity, and by an incomplete theoretical understanding of optically thick stellar winds. Even the stellar radii in these phases are badly undestood as they are often variable (LBVs), or deviate from theoretical expectations (WR stars). Here we present a new semi-empirical method that helps to tackle these problems. By analysing a large sample of Galactic WR stars we gain information about deep wind layers near the sonic point which are otherwise not directly observable. We find evidence that these layers are clumped, with clumping factors comparable to the ones observed in the winds of WR stars. Moreover, density and temperature near the sonic point seem to follow a relation which is ubiqitous for optically thick winds, and which may be responsible for the peculiar radius properties of these objects.

  18. Unavoidable CMB Spectral Features and Blackbody Photosphere of Our Universe

    NASA Astrophysics Data System (ADS)

    Sunyaev, Rashid A.; Khatri, Rishi

    2015-01-01

    Spectral features in the CMB energy spectrum contain a wealth of information about the physical processes in the early Universe, z ≲ 2 × 106. The CMB spectral distortions are complementary to all other probes of cosmology. In fact, most of the information contained in the CMB spectrum is inaccessible by any other means. This review outlines the main physics behind the spectral features in the CMB throughout the history of the Universe, concentrating on the distortions which are inevitable and must be present at a level observable by the next generation of proposed CMB experiments. The spectral distortions considered here include spectral features from cosmological recombination, resonant scattering of CMB by metals during reionization which allows us to measure their abundances, y-type distortions during and after reionization and μ-type and i-type (intermediate between μ and y) distortions created at redshifts z ≳ 1.5 × 104.

  19. Study of environment and photosphere of 51 Oph

    NASA Astrophysics Data System (ADS)

    Jamialahmadi, N.; Berio, Ph.; Lopez, B.; Meilland, A.; Stee, Ph.

    2015-01-01

    The main objective of this work is to improve our understanding of young fast-rotating stars evolving from the Herbig Ae/Be class to the Vega-like one. We observed with the VEGA instrument on CHARA one object so-called 51 Oph that is probably in such an evolutionary phase, allowing us to measure a mean stellar radius for the first time for this star and to show that the Hα emission was produced in a Keplerian rotating disc. However, additional observations are needed to improve our (u,v) plan coverage in order to measure the flattening of this close-to-critically rotating star and to probe the inner region of its circumstellar gaseous disc. These studies will help to disentangle the gas and dust emission around this late young star and will finally improve our understanding of the planet formation conditions in the inner regions of protoplanetary discs.

  20. Analysis of Photospheric Convection Cells with SDO/HMI

    NASA Technical Reports Server (NTRS)

    Williams, Peter E.; Pesnell, William Dean

    2010-01-01

    Supergranulation is a component of solar convection that assists in the outward transportation of internal energy. Supergranule cells are approximately 35 Mm across, have lifetimes on the order of a day and have divergent horizontal velocities of around 300 m/s, a factor of 10 higher than their central radial components. While they have been observed using Doppler methods for around half a century, their existence is also observed in other datasets such as magnetograms and Ca II K images. These datasets clearly show the influence of supergranulation on solar magnetism and how the local field is organized by the flows of supergranule cells. The Heliospheric and Magnetic Imager (HMI) aboard SDO is making fresh observations of convection phenomena at a higher cadence and a higher resolution that should make granular features visible. Granulation and supergranulation characteristics can now be compared within the same datasets, which may lead to further understanding of any mutual influences. The temporal and spatial enhancements of HMI will also reduce the noise level within studies of convection so that more detailed studies of their characteristics may be made. We present analyses of SDO/HMI Dopplergrams that provide new estimates of convection cell sizes, lifetimes, and velocity flows, as well as the rotation rates of the convection patterns across the solar disk. We make comparisons with previous data produced by MDI, as well as from data simulations.

  1. Connecting Photospheric Magnetic Fields and Transition Temperature Plasma Emission

    NASA Astrophysics Data System (ADS)

    Schmit, Donald

    2016-05-01

    The connectivity of quiet sun magnetic fields is not well understood. One observational obstacle to probe this question has been the sparse spectral observations spanning the transition temperatures (3×104 K< T < 1×105K) between the chromosphere and corona. The Si IV lines observed by IRIS provide a rich dataset to address the structure of the cool quiet sun. We use over 900 deep exposures from IRIS to map the correlation between transition-temperature emission structures and magnetic field concentrations. Ultimately, our aim is to discern the topology and energetic equilibrium of the magnetic structures that span the quiet sun. We use both a potential field model and a snapshot of the Bifrost 3D MHD simulation to interpret our emission data. In a broad sense, we find there is a clear correlation between magnetic fields and strong Si IV emission. However, more pointed statistics suggest that the relationship is quite complex. We do not find evidence for cool loops longer than 3 Mm in length, but we see ubiquitous, smooth emission nearly everywhere in the quiet sun. Emission voids on scales larger than 8 Mm cannot be well explained by their proximity to magnetic fields. This evidence suggests that weak-field transition-temperature loops contribute significantly to quiet sun transition-temperature emission measure, and evolutionary effects likely play a role in structuring the magnetic atmosphere.

  2. Photospheric imaging of the RS CVn system HR 1099

    NASA Technical Reports Server (NTRS)

    Donati, J.-F.; Brown, S. F.; Semel, M.; Rees, D. E.; Dempsey, R. C.; Matthews, J. M.; Henry, G. W.; Hall, D. S.

    1992-01-01

    Spectropolarimetric, spectroscopic, and photometric observations of the RS CVn binary system HR 1099 = V711 Tau (K1IV+G5V) were made from Oct. 1988 to Jan. 1991. From Doppler imaging of the unpolarized spectra and the corresponding data, two maximum entropy images of the temperature distribution of the active K1 subgiant at epochs 1988.9 and 1990.9 were derived. Zeeman-Doppler imaging of the circularly polarized spectra has led to the first magnetic maps of a star other than the sun. The fragmentary observations made at epoch 1989.6 suggest that the star's magnetic field lines were emerging radially and/or poloidally from an equatorial warm region at that time, quite likely one of these reconstructed in the 1988.9 temperature image.

  3. GRB110721A: AN EXTREME PEAK ENERGY AND SIGNATURES OF THE PHOTOSPHERE

    SciTech Connect

    Axelsson, M.; Baldini, L.; Bellazzini, R.; Bregeon, J.; Barbiellini, G.; Baring, M. G.; Brigida, M.; Bruel, P.; Caliandro, G. A.; Caraveo, P. A.; Cecchi, C.; D'Ammando, F.; Chaves, R. C. G.; Conrad, J.; Cutini, S. E-mail: moretti@particle.kth.se E-mail: josefin.larsson@astro.su.se; and others

    2012-10-01

    GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The burst consisted of one major emission episode which lasted for {approx}24.5 s (in the GBM) and had a peak flux of (5.7 {+-} 0.2) Multiplication-Sign 10{sup -5} erg s{sup -1} cm{sup -2}. The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum. The peak energy of the Band component was initially 15 {+-} 2 MeV, which is the highest value ever detected in a GRB. This measurement was made possible by combining GBM/BGO data with LAT Low Energy events to achieve continuous 10-100 MeV coverage. The peak energy later decreased as a power law in time with an index of -1.89 {+-} 0.10. The temperature of the blackbody component also decreased, starting from {approx}80 keV, and the decay showed a significant break after {approx}2 s. The spectrum provides strong constraints on the standard synchrotron model, indicating that alternative mechanisms may give rise to the emission at these energies.

  4. On the Properties of Slow MHD Sausage Waves within Small-scale Photospheric Magnetic Structures

    NASA Astrophysics Data System (ADS)

    Freij, N.; Dorotovič, I.; Morton, R. J.; Ruderman, M. S.; Karlovský, V.; Erdélyi, R.

    2016-01-01

    The presence of magnetoacoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magnetoacoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope and Rapid Oscillations in the Solar Atmosphere instruments, we captured two series of high-resolution intensity images with short cadences of two isolated magnetic pores. Combining wavelet analysis and empirical mode decomposition (EMD), we determined characteristic periods within the cross-sectional (i.e., area) and intensity time series. Then, by applying the theory of linear magnetohydrodynamics (MHD), we identified the mode of these oscillations within the MHD framework. Several oscillations have been detected within these two magnetic pores. Their periods range from 3 to 20 minutes. Combining wavelet analysis and EMD enables us to confidently find the phase difference between the area and intensity oscillations. From these observed features, we concluded that the detected oscillations can be classified as slow sausage MHD waves. Furthermore, we determined several key properties of these oscillations such as the radial velocity perturbation, the magnetic field perturbation, and the vertical wavenumber using SMS. The estimated range of the related wavenumbers reveals that these oscillations are trapped within these magnetic structures. Our results suggest that the detected oscillations are standing harmonics, and this allows us to estimate the expansion factor of the waveguides by employing SMS. The calculated expansion factor ranges from 4 to 12.

  5. Solar photospheric and coronal abundances from solar energetic particle measurements. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Breneman, H.

    1985-01-01

    Observations of solar energetic particles (SEP) from 22 solar flares in the 1977 to 1982 time period are reported. SEP abundances were obtained for all elements with 3 approximately less than Z approximately less than 30 except Li, Be, B, F, Sc, v, Co and Cu for which upper limits were obtained. Statistically meaningful abundances of several rare elements (P, Cl, K, Ti, and Mn) were determined for the first time, and the average abundance of the more abundant elements were determined with improved precision.

  6. GRB110721A: An Extreme Peak Energy and Signatures of the Photosphere

    NASA Technical Reports Server (NTRS)

    Axelsson, M.; Baldini, L.; Barbiellini, G.; Baring, M. G.; Bellazzini, R.; Bregeon, J.; Brigida, M.; Bruel, P.; Buehler, R.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Cecchi, C.; Chaves, R. C. G.; Chekhtman, A.; Chiang, J.; Claus, R.; Conrad, J.; Cutini, S.; Ferrara, E. C.; Gehrels, N.; Guiriec, S.; McEnery, J. E.; Fishman, G.; Wilson-Hodge, C.

    2012-01-01

    GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments, the Large Area Telescope (LAT) and the Gamma-ray Burst Monitor (GBM). The burst consisted of one major emission episode which lasted for approximately 24.5 s (in the GBM) and had a peak flux of (5.7 +/- 0.2) 10(exp -5) erg s(exp -1) cm(exp -2). The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum. The peak energy of the Band component was initially 15 +/- 2 MeV, which is the highest value ever detected in a GRB. This measurement was made possible by combining GBM/BGO data with LAT Low Energy events to achieve continuous 10-100 MeV coverage. The peak energy later decreased as a power law in time with an index of -1.89 +/- 0.10. The temperature of the blackbody component also decreased, starting from approximately 80 keV, and the decay showed a significant break after approximately 2s. The spectrum provides strong constraints on the standard synchrotron model, indicating that alternative mechanisms may give rise to the emission at these energies.

  7. Do Quasi-Regular Structures Really Exist in the Solar Photosphere? I. Observational Evidence

    NASA Astrophysics Data System (ADS)

    Getling, A. V.

    2006-12-01

    Two series of solar-granulation images - the La Palma series of 5 June 1993 and the SOHO MDI series of 17 - 18 January 1997 - are analysed both qualitatively and quantitatively. New evidence is presented for the existence of long-lived, quasi-regular structures (first reported by Getling and Brandt, Astron. Astrophys. 382, L5 (paper I), 2002), which no longer appear unusual in images averaged over 1 - 2-hour time intervals. Such structures appear as families of light and dark concentric rings or families of light and dark parallel strips (“ridges” and “trenches” in the brightness distributions). In some cases, rings are combined with radial “spokes” and can thus form “web” patterns. The characteristic width of a ridge or trench is somewhat larger than the typical size of granules. Running-average movies constructed from the series of images are used to seek such structures. An algorithm is developed to obtain, for automatically selected centres, the radial distributions of the azimuthally averaged intensity, which highlight the concentric-ring patterns. We also present a time-averaged granulation image processed with a software package intended for the detection of geological structures in aerospace images. A technique of running-average-based correlations between the brightness variations at various points of the granular field is developed and indications are found for a dynamical link between the emergence and sinking of hot and cool parcels of the solar plasma. In particular, such a correlation analysis confirms our suggestion that granules - overheated blobs - may repeatedly emerge on the solar surface. Based on our study, the critical remarks by Rast ( Astron. Astrophys. 392, L13, 2002) on the original paper by Getling and Brandt (paper I) can be dismissed.

  8. The photospheric temperatures and composition of very hot He-rich white dwarfs

    NASA Technical Reports Server (NTRS)

    Barstow, M. A.; Holberg, J. B.

    1990-01-01

    Results are reported from a detailed analysis of Exosat observations of six hot He-rich white dwarfs belonging to, or related to, the spectroscopic subclass of PG1159 stars. These objects are thought to evolve directly from O VI type planetary nebulae nuclei and provide an important link in models of white dwarf evolution. When the Exosat data are compared with the predictions of an extensive grid of He-rich model atmospheres, it is possible to obtain temperature estimates for these stars that are much better constrained than previous attempts.

  9. Generation of a North/South Magnetic Field Component from Variations in the Photospheric Magnetic Field

    NASA Astrophysics Data System (ADS)

    Ulrich, Roger K.; Tran, Tham

    2016-04-01

    We address the problem of calculating the transverse magnetic field in the solar wind outside of the hypothetical sphere that is called the source surface where the solar wind originates. This calculation must overcome a widely used fundamental assumption about the source surface - the field is normally required to be purely radial at the source surface. Our model rests on the fact that a change in the radial field strength at the source surface is a change in the field line density. Surrounding field lines must move laterally to accommodate this field line density change. As the outward wind velocity drags field lines past the source surface, this lateral component of motion produces a tilt, implying there is a transverse component to the field. An analytic method of calculating the lateral translation speed of the field lines is developed. We apply the technique to an interval of approximately two Carrington rotations at the beginning of 2011 using 2-h averages of data from the Helioseismic Magnetic Imager instrument onboard the Solar Dynamics Observatory spacecraft. We find that the value of the transverse magnetic field is dominated on a global scale by the effects of high-latitude concentrations of field lines that are buffeted by supergranular motions.

  10. Synoptic Solar Cycle 24 in Corona, Chromosphere, and Photosphere Seen by the Solar Dynamics Observatory

    NASA Astrophysics Data System (ADS)

    Benevolenskaya, E.; Slater, G.; Lemen, J.

    2014-09-01

    The Solar Dynamics Observatory provides multiwavelength imagery from extreme ultraviolet (EUV) to visible light as well as magnetic-field measurements. These data enable us to study the nature of solar activity in different regions of the Sun, from the interior to the corona. For solar-cycle studies, synoptic maps provide a useful way to represent global activity and evolution by extracting a central meridian band from sequences of full-disk images over a full solar Carrington rotation (≈ 27.3 days). We present the global evolution during Solar Cycle 24 from 20 May 2010 to 31 August 2013 (CR 2097 - CR 2140), using synoptic maps constructed from full-disk, line-of-sight magnetic-field imagery and EUV imagery (171 Å, 193 Å, 211 Å, 304 Å, and 335 Å). The synoptic maps have a resolution of 0.1 degree in longitude and steps of 0.001 in sine of latitude. We studied the axisymmetric and non-axisymmetric structures of solar activity using these synoptic maps. To visualize the axisymmetric development of Cycle 24, we generated time-latitude (also called butterfly) images of the solar cycle in all of the wavelengths, by averaging each synoptic map over all longitudes, thus compressing it to a single vertical strip, and then assembling these strips in time order. From these time-latitude images we observe that during the ascending phase of Cycle 24 there is a very good relationship between the integrated magnetic flux and the EUV intensity inside the zone of sunspot activities. We observe a North-South asymmetry of the EUV intensity in high-latitudes. The North-South asymmetry of the emerging magnetic flux developed and resulted in a consequential asymmetry in the timing of the polar magnetic-field reversals.

  11. Five-minute oscillations and the fine structure of the solar photosphere. I.

    NASA Astrophysics Data System (ADS)

    Kostyk, R. I.; Shchukina, N. G.

    The authors analyze the spatial relationship between the solar granulation and the local five-minute velocity and intensity oscillations observed in the Fe I λ532.4185 nm line. The spectral granulation images were recorded with high spatial and temporal resolution (<0.5 arcsec and 9.3 s) at the German Vacuum Tower Telescope. In the temperature minimum region, where the line is formed, the most energetic intensity oscillations occur mainly over dark intergranular lanes. Strong velocity oscillations are observed over granules and intergranules, their amplitude increasing with the granulation brightness contrast. The space-averaged intensity oscillation power is concentrated at higher frequencies compared to the power of velocity oscillations.

  12. Five-minute oscillations and the fine structure of the solar photosphere. I.

    NASA Astrophysics Data System (ADS)

    Kostyk, R. I.; Shchukina, N. G.

    1999-02-01

    The authors analyse the spatial relationship between the solar granulation and the local five-minute oscillations of velocity and intensity observed in the Fe I λ532.4185 nm line. The time series of CCD spectral images of solar granulation taken at the Germany Vacuum Tower Telescope (VTT) were recorded with high spatial (<0.5 arcsec) and temporal (9.3 s) resolution. In the temperature minimum region, where the line is formed, the most energetic intensity oscillations are shown to occur mainly over dark intergranular lanes, while strong velocity oscillations are observed over granules and intergranules. The amplitude of the latter oscillations increases with the granulation brightness contrast. The spatially averaged power of intensity oscillations is concentrated at higher frequencies compared to the power of velocity oscillations.

  13. Ca II H sunspot tomography from the photosphere to the chromosphere

    NASA Astrophysics Data System (ADS)

    Henriques, V. M. J.; Kiselman, D.

    2013-09-01

    Aims: We aim at gaining insight into the thermal properties of different small-scale structures related to sunspots. Methods: We use filtergrams in the Ca ii H filter at the Swedish 1-m Solar Telescope to study the relationship between fine structure at different heights in a sunspot. Results: The methods for destretching and aligning the different image data work well. The magnetic spine structure in the outer parts of the sunspot penumbra is found to be associated with higher intensities in the Ca ii H wing passbands but with less steep vertical temperature gradients. Dark lanes in a light bridge behave very similarly to dark cores in penumbral filaments. Fibril structures are seen in the line-core images over the umbra and penumbra. Conclusions: The observations add support to the idea that penumbral filaments, light bridges, and umbral dots are caused by similar processes of overturning convection. Observations in the Ca ii H & K wings are a promising observable, complementing others, for testing simulation results for sunspots at high spatial resolution.

  14. Speckle interferometric techniques applied to the observation of the solar photosphere

    NASA Astrophysics Data System (ADS)

    Aime, C.; Ricort, G.

    1980-01-01

    Speckle interferometric techniques are used to study the solar granulation. Calibration of the effects of atmospheric turbulence is performed by using either the difference in behavior between redundant and non redundant apertures in presence of atmospheric turbulence, or by analysing moon-limb blurring during a solar eclipse, or by using the changes in seeing conditions during speckle-interferometric measurements. These techniques require a theoretical knowledge of the effects of atmospheric turbulence on the modulation transfer function (M.T.F.) of the image as it is impractical to use an unresolved star near the sun as a reference source during day time observations. The agreement between the experimental M.T.F. obtained with an unresolved star and the theoretical form deduced from Korff's log-normal assumptions is extended to day time conditions.

  15. Trend of photospheric helicity flux in active regions generating halo CMEs

    NASA Astrophysics Data System (ADS)

    Smyrli, Aimilia; Zuccarello, Francesco; Zuccarello, Francesca; Romano, Paolo; Guglielmino, Salvatore Luigi; Spadaro, Daniele; Hood, Alan; Mackay, Duncan

    Coronal Mass Ejections (CMEs) are very energetic events initiated in the solar atmosphere, re-sulting in the expulsion of magnetized plasma clouds that propagate into interplanetary space. It has been proposed that CMEs can play an important role in shedding magnetic helicity, avoiding its endless accumulation in the corona. We therefore investigated the behavior of magnetic helicity accumulation in sites where the initiation of CMEs occurred, in order to de-termine whether and how changes in magnetic helicity accumulation are temporally correlated with CME occurrence. After identifying the active regions (AR) where the CMEs were ini-tiated by means of a double cross-check based on the flaring-eruptive activity and the use of SOHO/EIT difference images, we used MDI magnetograms to calculate magnetic flux evolu-tion, magnetic helicity injection rate and magnetic helicity injection in 10 active regions that gave rise to 12 halo CMEs observed during the period February 2000 -June 2003. No unique behavior in magnetic helicity injection accompanying halo CME occurrence is found. In fact, in some cases there is an abrupt change in helicity injection timely correlated with the CME event, while in some others no significant variation is recorded. However, our analysis show that the most significant changes in magnetic flux and magnetic helicity injection are associated with impulsive CMEs rather than gradual CMEs. Moreover, the most significant changes in mag-netic helicity are observed when X-class flares or eruptive filaments occur, while the occurrence of flares of class C or M seems not to affect significantly the magnetic helicity accumulation.

  16. Centre-to-limb properties of small, photospheric quiet-Sun jets

    NASA Astrophysics Data System (ADS)

    Rubio da Costa, F.; Solanki, S. K.; Danilovic, S.; Hizberger, J.; Martínez-Pillet, V.

    2015-02-01

    Context. Strongly Doppler-shifted Stokes V profiles have been detected in the quiet Sun with the IMaX instrument on-board the SUNRISE stratospheric balloon-borne telescope. High velocities are required to produce such signals, hence these events have been interpreted as jets, although other sources are also possible. Aims: We aim to characterize the variation of the main properties of these events (occurrence rate, lifetime, size, and velocities) with their position on the solar disk between disk centre and the solar limb. Methods: These events were identified in SUNRISE/IMaX data according to the same objective criteria at all available positions on the solar disk. Their properties were determined using standard techniques. Results: Our study yielded a number of new insights into this phenomenon. Most importantly, the number density of these events is independent of the heliocentric angle, meaning that the investigated supersonic flows are nearly isotropically distributed. Size and lifetime are also nearly independent of the heliocentric angle, while their intensity contrast increases towards the solar limb. The Stokes V jets are associated with upflow velocities deduced from Stokes I, which are stronger towards the limb. Their intensity decreases with time, while their line-of-sight velocity does not display a clear temporal evolution. Their association with linear polarization signals decreases towards the limb. Conclusions: The density of events appears to be independent of heliocentric angle, establishing that they are directed nearly randomly. If these events are jets triggered by magnetic reconnection between emerging magnetic flux and the ambient field, then our results suggest that there is no preferred geometry for the reconnection process.

  17. Solution to the discrepancy between the seismic and photospheric solar radius

    NASA Astrophysics Data System (ADS)

    Haberreiter, M.; Kosovichev, A. G.; Schmutz, W.

    2009-04-01

    Two methods are usually used to observationally determine the solar radius: One is the observation of the intensity profile at the limb, the other one uses f-mode frequencies to derive a 'seismic' solar radius which is then corrected to optical depth unity. The two methods are inconsistent and lead to a difference in the solar radius of approx. 0.3 Mm. Based on radiative transfer calculations we show that this discrepancy can be explained by the difference between the height at disk center where tau500=1 and the inflection point of the intensity profile on the limb. We calculate the intensity profile of the limb for the MDI continuum and the continuum at 5000 A for two atmosphere structures and compare the position of the inflection points with the radius at optical depth unity. The calculated difference between the 'seismic' radius and the inflection point is 0.347 Mm with respect to optical depth unity and 0.333 Mm with respect to the Rossland mean opacity. We conclude that the standard solar radius in evolutionary models has to be lowered by 0.333 Mm and is 695.66 Mm. This correction reconciles inflection point measurements and the seismic radius within the uncertainty. This finding is very important for the analysis of the solar diameter measurements with the SODISM instrument on PICARD.

  18. Study of Magnetic Motions in the Solar Photosphere and their Implications for Heating the Solar Atmosphere

    NASA Technical Reports Server (NTRS)

    Noyes, Robert W.

    1997-01-01

    We continued our program of CO observations with the McMath-Pierce facility at Kitt Peak National Solar Observatory. Uitenbroek has developed a two-and three dimensional radiative transfer code that now includes chemical equilibrium calculations. This code allows us to compute a CO spectrum from for instance a snapshot of a solar granulation simulation (e.g. Stein & Nordlund 1989, Apj 342, L95) and compare these theoretical spectra with our spatially resolved CO spectroscopy. Van Ballegooijen and Uitenbroek have started calculations of two-dimensional fluxtube models that account consistently for hydrogen ionization in the calculation of the electron density. To this end we solve radiative transfer for hydrogen (bound-bound and bound-free transitions) in the two-dimensional models, including the effect of partial frequency redistribution (PRD) in the Lyman (alpha) and (beta) lines. From our internally consistent models we will calculate emergent spectra and the way these vary with location of some well-known spectral diagnostics and compare our results with observed line profiles. We can readily compare theoretical CO profiles from out models with our spatially resolved CO observations. Also we can compare with spatially resolved Ca II (ground based) and Mg II (we have observations done with the UVSP/SMM instrument), and Lyman (alpha) observations that should be available from SUMER/SOHO.

  19. Photospheric Activity in Selected Be STARS: lambda Eri and gamma Cas

    NASA Technical Reports Server (NTRS)

    Smith, Myron A.

    1994-01-01

    Recent observations of rapid variations in optical He I lines, X-rays, and FUV wavelengths in the prototypical classical Be stars lambda Eri and star gamma Cas hint that the violent processes occur on the surfaces of these stars almost all the time. We suggest that of these phenomena show greater similarities with magnetic flaring than any other process through to occur on stars.

  20. Generation of coronal electric currents due to convective motions on the photosphere

    NASA Technical Reports Server (NTRS)

    Sakurai, T.; Levine, R. H.

    1981-01-01

    Generation of electric currents in a magnetized plasma overlying a dense convective layer is studied, assuming that the magnetic field perturbation is small and satisfies the force-free equation. Currents are produced by rotational motions on the boundary in the case of a uniform equilibrium field. In a simple two-dimensional bipolar configuration, however, both irrotational and incompressible motions give rise to currents, and the current density has a peak at the magnetic neutral line. Scaling laws for the current density as well as for the stored magnetic energy are derived, and the possibility of heating the solar corona through the dissipation of coronal currents generated in this way is discussed.

  1. Stokes profile analysis and vector magnetic fields. I - Inversion of photospheric lines

    NASA Astrophysics Data System (ADS)

    Skumanich, A.; Lites, B. W.

    1987-11-01

    The authors consider improvements to the Auer, Heasley, and House method for the analytic inversion of Stokes profiles via nonlinear least squares. In the application of this method to actual sunspot observations, the authors have found that its simplifications often yield erroneous solutions or nonconvergent behavior. By including damping wings and magneto-optical birefringence and by decoupling the intensity profile from the three-vector polarization profile in the analysis, the authors develop a more robust inversion method that provides a more reliable and accurate estimate of sunspot vector magnetic fields without significant loss of economy.

  2. Relation between photospheric flow fields and the magnetic field distribution on the solar surface

    SciTech Connect

    Simon, G.W.; Title, A.M.; Topka, K.P.; Tarbell, T.D.; Shine, R.A.

    1988-04-01

    Using the technique of local correlation tracking on a 28 minute time sequence of white-light images of solar granulation, the horizontal flow field on the solar surface is measured. The time series was obtained by the Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 (Space Shuttle flight 51-F) and is free from atmospheric blurring and distortion. The SOUP flow fields have been compared with carefully aligned magnetograms taken over a nine hour period at the Big Bear Solar Observatory before, during, and after the SOUP images. The flow field and the magnetic field agree in considerable detail: vectors which define the flow of the white-light intensity pattern (granulation) point toward magnetic field regions, magnetic fields surround flow cells, and magnetic features move along the flow arrows. The projected locations of free particles (corks) in the measured flow field congregate at the same locations where the magnetic field is observed. 31 references.

  3. Analysis of time dependent phenomena observed with the LPSP OSO-8 instrument. [solar chromosphere and photosphere

    NASA Technical Reports Server (NTRS)

    Leibacher, J. W.

    1979-01-01

    Data obtained by the Laboratoire de Physique Stellaire et Planetaire's ultraviolet spectrometer onboard the OSO-8 spacecraft were analyzed in an effort to dynamically model the solar chromosphere as an aid in enhancing knowledge of the dynamical processes themselves and of spectral line formation in the dynamic chromosphere. Repeated spectral scans of strong, optically thick resonance lines formed in the solar chromosphere were examined for indications of oscillatory velocities and intensities among other indications of velocity which were studied, the blue peak is reasonably well defined, and the position of a parabolic filter fitted by the least squares method was used to define it. Observed chromospheric oscillation periods are discussed as well as the variations in altitude of the emitting region which result primarily from the motion up and down during the oscillation.

  4. HEMISPHERIC ASYMMETRIES OF SOLAR PHOTOSPHERIC MAGNETISM: RADIATIVE, PARTICULATE, AND HELIOSPHERIC IMPACTS

    SciTech Connect

    McIntosh, Scott W.; Burkepile, Joan; Miesch, Mark; Markel, Robert S.; Sitongia, Leonard; Leamon, Robert J.; Gurman, Joseph B.; Olive, Jean-Philippe; Cirtain, Jonathan W.; Hathaway, David H.

    2013-03-10

    Among many other measurable quantities, the summer of 2009 saw a considerable low in the radiative output of the Sun that was temporally coincident with the largest cosmic-ray flux ever measured at 1 AU. Combining measurements and observations made by the Solar and Heliospheric Observatory (SOHO) and Solar Dynamics Observatory (SDO) spacecraft we begin to explore the complexities of the descending phase of solar cycle 23, through the 2009 minimum into the ascending phase of solar cycle 24. A hemispheric asymmetry in magnetic activity is clearly observed and its evolution monitored and the resulting (prolonged) magnetic imbalance must have had a considerable impact on the structure and energetics of the heliosphere. While we cannot uniquely tie the variance and scale of the surface magnetism to the dwindling radiative and particulate output of the star, or the increased cosmic-ray flux through the 2009 minimum, the timing of the decline and rapid recovery in early 2010 would appear to inextricably link them. These observations support a picture where the Sun's hemispheres are significantly out of phase with each other. Studying historical sunspot records with this picture in mind shows that the northern hemisphere has been leading since the middle of the last century and that the hemispheric ''dominance'' has changed twice in the past 130 years. The observations presented give clear cause for concern, especially with respect to our present understanding of the processes that produce the surface magnetism in the (hidden) solar interior-hemispheric asymmetry is the normal state-the strong symmetry shown in 1996 was abnormal. Further, these observations show that the mechanism(s) which create and transport the magnetic flux are slowly changing with time and, it appears, with only loose coupling across the equator such that those asymmetries can persist for a considerable time. As the current asymmetry persists and the basal energetics of the system continue to dwindle we anticipate new radiative and particulate lows coupled with increased cosmic-ray fluxes heading into the next solar minimum.

  5. OBSERVATION OF HIGH-SPEED OUTFLOWS IN CORONAL LOOPS ASSOCIATED WITH PHOTOSPHERIC MAGNETIC FIELD EVOLUTION

    SciTech Connect

    Su, J. T.; Liu, S.; Mao, X. J.; Liu, Y.; Shen, Y. D.

    2012-11-20

    Using SDO/AIA instruments, we provide an EUV observation of two adjacent loop strands (Loops 1 and 2) with one side of their footpoints rooted in the boundaries of active region (AR) NOAA 11158 and the other side in the quiet-Sun regions. The AR footpoints of Loop 1 were located in monopolar magnetic areas and those of Loop 2 in mixed polar areas (SDO/HMI magnetograms). There were no apparent outflows found in Loop 1 in 10 hr of observations, whereas in Loop 2, the outflows were detected throughout the whole observation with an average speed of 120-150 km s{sup -1}. We find clear evidence of magnetic reconnections occurring in the AR footpoints of Loop 2 (the opposite magnetic polarities came close and then a part of them disappeared) and magnetic flux dispersal in the quiet-Sun footpoints (a patch of positive polarities decayed with time). Furthermore, with Hinode/SOT observations, there were no significant Ca II H brightenings detected at the loop footpoints of Loop 2 at the chromospheric heights in response to those of the AIA 171 A and 304 A channels when four strong outflow events took place in the loops, which seem to differ from the conclusions of previous studies. In other studies, the rapid coronal outflows along the coronal loops were found to originate from the chromosphere through transient events (e.g., type II spicules).

  6. Inferring the Magnetic Structure of a Sunspot from Decomposition of Photospheric Vertical Current Density into Twist and Shear Components

    NASA Astrophysics Data System (ADS)

    Venkatakrishnan, P.

    2015-12-01

    The electric current density, derived from the curl of the vector magnetic field, can be decomposed into the so-called twist and shear components. We examined this decomposition for 2 highly flare productive active regions undergoing magnetic flux emergence, viz. AR 10930 observed by SOT aboard Hinode and AR 11158 observed by HMI aboard SDO. We found the following common evolutionary behaviour in both the cases: 1. The percentage of variation of the spatially averaged value of the ratio of the shear current density to the twist current density is much smaller than the percentage of variation of the twist current throughout the evolution. 2. The average ratio was negative in sign, viz. the shear current density was opposite in sign to the twist current density in most of the pixels. 3. The magnitude of the average ratio increased with increase of pixel size. The above 3 results were examined for two extreme kinds of magnetic structure: a) a monolithic continuous didtribution of magnetic flux and b) an intermittent cluster of magnetic fibrils separated by field free regions. We arrive at the conclusion that the above mentioned observations tend to favor the monolithic model of sunspot magnetic field over the fibril model, although a fibril structure at deeper layers cannot be ruled out. Observations of vector magnetic fields of sunspots using the infrared FeI line around 1560 nm could perhaps resolve this issue.

  7. The photosphere and chromosphere of the RS Canum Venaticorum star, II Pegasi I. Spots and chromospheric emission in 1991.

    NASA Astrophysics Data System (ADS)

    Byrne, P. B.; Panagi, P. M.; Lanzafame, A. C.; Avgoloupis, S.; Huenemoerder, D. P.; Kilkenny, D.; Marang, F.; Panov, K. P.; Roberts, G.; Seiradakis, J. H.; van Wyk, F.

    1995-07-01

    We report on high-resolution spectroscopy of the RSCVn binary IIPeg, along with contemporaneous UBV(RI)_KC_ photometry, including partly simultaneous U-band flare monitoring, during the third quarter of 1991. The spectroscopy was taken at two epochs separated by more than 6(1)/(2) weeks or seven rotations of IIPeg. At the first epoch we have observed the three chromospheric lines, Hα, Hβ and HeID_3_, over a single rotation and at the second epoch we observed almost the entire visible region, for a substantial fraction of one rotation, including Hα-Hɛ and CaIIH. Our photometric results show that there was an unusually complicated spot distribution at this epoch, with at least three centres of activity discernable. We demonstrate, for the first time on a spotted late-type star, that these centres of spot activity have significantly different mean temperatures from one another. Furthermore, our derived spot temperatures are markedly lower than those previously derived from such multicolour photometry and more similar to those derived spectroscopically. Using multiple repeat exposures on each spectral line within each night, we are confident that we have derived a mean, non-flaring spectrum at each observational phase. Furthermore, the line flux variations at the two epochs repeat very well, suggesting that the mean global chromospheric structures are stable on a 1(1)/(2) months time scale. We discuss the implications of the mean spectra for the non-flaring atmosphere of IIPeg and conclude that, in the region of formation of the Hα line, velocity fields are required to account for the line profile. These results suggest upward motions of the deep chromosphere with a less dramatic downflow in the high chromosphere. We examine the variation of the chromospheric line fluxes as a function of spot visibility and conclude that there is only a very loose spatial correlation of chromsopheric heating with spots. The motions suggested from the Hα profile variations appear to be spot-associated.

  8. Doing Away with Occupation Probability: A New Way to Model Continuum Lowering at White Dwarf Photosphere Conditions

    NASA Astrophysics Data System (ADS)

    Gomez, Thomas A.; Winget, Donald E.; Montgomery, Michael H.; Kilcrease, Dave; Nagayama, Taisuke

    2016-01-01

    White dwarfs are interesting for a number of applications including studying equations of state, stellar pulsations, and determining the age of the universe.These interesting applications require accurate determination of surface conditions: temperatures and surface gravity (or mass).The most common technique to estimate the temperature and gravity is to find the model spectrun that best fits the observed spectra of a star (known as the spectroscopic method); however, this model rests on our ability to accurately model the hydrogen spectrum at high densities.There are currently disagreements between the spectroscopic method and other techniques to determine mass.We seek to resolve this issue by exploring the continuum lowering (or disappearance of states) of the hydrogen atom.The current formalism, called "occupation probability," defines some criteria for the isolated atom's bound state to be ionized, then extrapolates the continuous spectrum to the same energy threshold.The two are then combined to create the final cross-section.I introduce a new way of calculating the atomic spectrum by doing some averaging of the plasma interaction potential energy (previously used in the physics community) and directly integrating the Schrodinger equation.This technique is a major improvement over the Taylor expansion used to describe the ion-emitter interaction and removes the need of the occupation probability and treats continuum states and discrete states on the same footing in the spectrum calculation.The resulting energy spectrum is in fact many discrete states that when averaged over the electric field distribution in the plasma appears to be a continuum.In the low density limit, the two methods are in agreement, but show some differences at high densities (above 10$^{17} e/cc$) including line shifts near the ``continuum'' edge.

  9. Comparison of Synoptic Maps of Solar Soft X-Ray Features, Photospheric Magnetic Fields, and Helium 1083 NM

    NASA Astrophysics Data System (ADS)

    Harvey, J.; Slater, G.; Nitta, N.; Shibata, K.; Tsuneta, S.; Sakurai, T.; Hara, H.

    1994-12-01

    We studied the wealth of structural features visible in Yohkoh/SXT and NSO/KP synoptic maps of the Sun that cover Carrington rotations 1847 through 1879. In order to do this comparison, various methods to reduce soft X-ray maps to simple structural elements were explored. In the end, the best way of comparing the various data sets turned out to be to filter the X-ray maps to emphasize high-spatial frequencies and then to either simply blink the various images or to make colorized composite maps that distinctively assign different colors to various quantities. Among the results are: 1. Active regions exhibit normal or "anemone" (fountain-like) X-ray loop structure tendency depending on whether the surrounding large-scale unipolarity of the magnetic field is small or large. 2. There is a systematic twist of the coronal loops around magnetic concentrations in the southern hemisphere and vice-versa in the north. The sense is the same as one would expect from the action of differential rotation. 3. Dark lanes in the X-ray images are centered over large-scale polarity patterns of one sign or the other. 4. The X-ray loops at the boundaries between large-scale opposite polarity patterns are frequently strongly sheared. The presence or absence of a filament in these locations may be related in a complicated way to the amount of shear. 5. At the resolution of the synoptic maps, the footpoints of X-ray loops are almost always rooted in locally strong magnetic concentrations and also in extra-dark 1083 nm elements.

  10. White-light movies of the solar photosphere from the SOUP instrument on Spacelab. [Solar Optical Universal Polarimeter

    NASA Technical Reports Server (NTRS)

    Title, A. M.; Tarbell, T. D.; Acton, L; Duncan, D.; Simon, G. W.

    1986-01-01

    Initial results are presented on solar granulation, pores and sunspots from the white-light films obtained by the Solar Optical Universal Polarimeter (SOUP) instrument in Spacelab 2. Several hours of movies were taken at various disk and limb positions in quiet and active regions. The images are diffraction-limited at 0.5 arcsec resolution and are, of course, free of atmospheric seeing and distortion. Properties of the granulation in magnetic and nonmagnetic regions are compared and are found to differ significantly in size, rate of intensity variation, and lifetime. In quiet sun, on the order of fifty-percent of the area has at least one 'exploding granule' occurring in it during a 25-min period. Local correlation tracking has detected several types of transverse flows, including systematic outflow from the penumbral boundary of a spot, motion of penumbral filaments, and cellular flow patterns of supergranular and mesogranular size. Feature tracking has shown that, in the quiet sun, the average granule fragment has a velocity of about one kilometer/second.

  11. Relation between Intensity Contrast and Magnetic Field for Active and Quiet Regions Observed on the Solar Photosphere

    NASA Astrophysics Data System (ADS)

    Whitney, Taylor; Criscuoli, Serena; Norton, Aimee Ann

    2016-05-01

    Current solar modeling techniques assume that active and quiet regions can be considered in the same manner. However, recent results from numerical simulations and high-spatial resolution observations indicate that radiative properties of small magnetic elements depend on whether they are located in plages, network, or quiet areas. These studies have been carried out typically at, or close to, disk center. In this study, data from the Helioseismic Magnetic Imager (HMI) are used to investigate the differences between magnetic elements located in Network/Quiet and Active Regions (AR) observed at different positions over the solar disk.

  12. Numerical experiments on the evolution in coronal magnetic configurations including a filament in response to the change in the photosphere

    NASA Astrophysics Data System (ADS)

    Wang, Hong-Juan; Liu, Si-Qing; Gong, Jian-Cun; Lin, Jun

    2015-03-01

    We investigate equilibrium height of a flux rope, and its internal equilibrium in a realistic plasma environment by carrying out numerical simulations of the evolution of systems including a current-carrying flux rope. We find that the equilibrium height of a flux rope is approximately described by a power-law function of the relative strength of the background field. Our simulations indicate that the flux rope can escape more easily from a weaker background field. This further confirms that a catastrophe in the magnetic configuration of interest can be triggered by a decrease in strength of the background field. Our results show that it takes some time to reach internal equilibrium depending on the initial state of the flux rope. The plasma flow inside the flux rope due to the adjustment for the internal equilibrium of the flux rope remains small and does not last very long when the initial state of the flux rope commences from the stable branch of the theoretical equilibrium curve. This work also confirms the influence of the initial radius of the flux rope in its evolution; the results indicate that a flux rope with a larger initial radius erupts more easily. In addition, by using a realistic plasma environment and a much higher resolution in our simulations, we notice some different characteristics compared to previous studies in Forbes. Supported by the National Natural Science Foundation of China.

  13. Shocks produced by impulsively driven reconnection. [during solar flares or emergence of magnetic flux from photosphere into corona

    NASA Technical Reports Server (NTRS)

    Forbes, T. G.

    1988-01-01

    Shock waves produced by impulsively driven reconnection are investigated by carrying out numerical experiments using two-dimensional magnetohydrodynamics. The results of the numerical experiments imply that there are three different categories of shocks associated with impulsively driven reconnection: (1) fast-mode, blast waves which rapidly propagate away from the reconnection site; (2) slow-mode, Petschek shocks which are attached to the reconnection site; and (3) fast-mode, termination shocks which terminate the plasma jets flowing out from the reconnection site.

  14. A Minimum Energy Fit Method to Reconstruct Photospheric Velocity and Magnetic Diffusivity in Active Regions from Observed Magnetograms and Dopplergrams

    NASA Astrophysics Data System (ADS)

    Tremblay, Benoit; Vincent, Alain

    2015-02-01

    We introduce MEF-R, a generalization of the minimum energy fit (MEF; Longcope, Astrophys. J. 612, 1181, 2004) to a non-ideal (resistive) gas. The new technique requires both vector magnetograms and Doppler velocities as input fields. However, in the case of active regions observed only with the Michelson-Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) such as AR 9077, we have only access to line-of-sight magnetograms. We reconstruct two-dimensional maps of the magnetic diffusivity η( x, y) together with velocity components v x ( x, y), v y ( x, y), and v z ( x, y) under the linear force-free magnetic field approximation. Computed maps for v z ( x, y) very well match the Doppler velocities v r ( x, y). We find the average value < η>≈108 m2 s-1 with a standard deviation of ≈ 1010 m2 s-1. Such high values of η( x, y) are to be expected at some places since our magnetic diffusivity is actually eddy-diffusivity. Inside AR 9077, the maps of η( x, y) do not resemble closely the maps from classical models of the magnetic diffusivity, but they are closer to η as a function of temperature than to η as a function of electric current density.

  15. Comparison of physical properties of quiet and active regions through the analysis of magnetohydrodynamic simulations of the solar photosphere

    SciTech Connect

    Criscuoli, S.

    2013-11-20

    Recent observations have shown that the photometric and dynamic properties of granulation and small-scale magnetic features depend on the amount of magnetic flux of the region they are embedded in. We analyze results from numerical hydrodynamic and magnetohydrodynamic simulations characterized by different amounts of average magnetic flux and find qualitatively the same differences as those reported from observations. We show that these different physical properties result from the inhibition of convection induced by the presence of the magnetic field, which changes the temperature stratification of both quiet and magnetic regions. Our results are relevant for solar irradiance variations studies, as such differences are still not properly taken into account in irradiance reconstruction models.

  16. Is There Evidence for X-Ray Emitting Plasma Very Close to the Photospheres of O Stars?

    NASA Technical Reports Server (NTRS)

    Leutenegger, Maurice A.

    2008-01-01

    Aims. We reexamine the implications of the recent HESS observations of the blazar 1ES0229+200 for constraining the extragalactic mid-infrared background radiation. Methods. We examine the effect of gamma-ray absorption by the extragalactic infrared radiation on predicted intrinsic spectra for this blazar and compare our results with the observational data. Results. We find agreement with our previous results on the shape of the infrared spectral energy distribution, contrary to the recent assertion of the HESS group. Our analysis indicates that 1ES0229+200 has a very hard intrinsic spectrum with a spectral index between 1.1 +/- 0.3 and 1.5 +/- 0.3 in the energy range between approx.0.5 TeV and approx.15 TeV. Conclusions. Under the assumptions that (1) the models of Stecker et al. (2006, ApJ, 648, 774) as derived from numerous detailed infrared observations are reasonable, and (2) spectral indexes in the range 1 < gamma < 1.5 are obtainable from relativistic shock acceleration under the astrophysical conditions extant in blazar flares (Stecker et al. 2007, ApJ, 667, L29), the fits to the observations of 1ES0229+200 using our previous infrared spectral energy distributions are consistent with both the infrared and gamma-ray observations. Our analysis presents evidence indicating that the energy spectrum of relativistic particles in 1ES0229+200 is produced by relativistic shock acceleration, producing an intrinsic -ray spectrum with index 1 < gamma < 1.5 and with no evidence of a peak in the spectral energy distribution up to energies approx.15 TeV.

  17. Characterizing and modeling magnetic flux transport in the sun's photosphere and determining its impact on the sunspot cycle

    NASA Astrophysics Data System (ADS)

    Upton, Lisa A.

    The characterization and modeling of magnetic flux transport within the surface layers of the Sun are vital to explaining the sunspot cycle. The Sun's polar fields at solar cycle minimum are the seeds of the next solar cycle: weak polar fields produce weak cycles. Magnetic flux transport is key to the buildup of the polar fields and the subsequent magnetic reversals that are essential to modulating the sunspot cycle. The primary goals of this dissertation are threefold: 1. Make precise measurements of the Sun's axisymmetric flows (i.e., differential rotation and meridional flow). 2. Create a realistic surface flux transport model that reproduces the magnetic field evolution at the surface by incorporating the observed flows. 3. Investigate the role of flux transport in modulating the polar fields, and thereby the solar activity cycle. This work has been done in collaboration with Dr. David H. Hathaway of NASA Marshall Space Flight Center. In Chapter 1, I provide an introduction to the Sun as a star. I begin with a discussion on stellar structure and evolution. I then discuss the techniques and instruments that have been used to study the Sun. I conclude Chapter 1 with a section on magnetic activity cycles on the Sun and in other stars. Magnetic flux on the Sun is transported by supergranular flows and the axisymmetric flows of differential rotation (DR) and meridional flow (MF). In Chapter 2, I introduce these flows. I then show a derivation of the Surface Flux Transport equation starting from Maxwell's equations and Ohm's Law. I conclude this chapter with an introduction to prior Surface Flux Transport models. In Chapter 3, I discuss a cross-correlation technique that we have used on magnetograms (maps of the magnetic field strengths over the surface of the Sun) to characterize the DR and MF and their variations from 1996 to present. Results show that while variability in DR is negligible, the MF varies in two fundamental ways: over the course of a solar cycle and from one cycle to the next. The MF is faster at solar cycle minimum and slower at maximum. Furthermore, the MF speeds that preceded the Solar Cycle 23/24 minimum were ˜ 20% faster than the MF speeds that preceded the prior minimum. This faster MF may have led to weaker polar field strengths and thus the subsequent extended solar minimum and an unusually weak Cycle 24. To understand the impact flux transport on the evolution of the polar fields, I have conducted experiments using a surface magnetic flux transport model, introduced in Chapter 4, that we have developed. This model advects the magnetic flux emerging in active regions (sunspots) using detailed observations of the near-surface flows that transport the magnetic elements. These flows include the axisymmetric differential rotation and meridional flow and the non-axisymmetric cellular convective flows (supergranules), all of which vary in time in the model as indicated by direct observations. At each time step, magnetic maps of the entire Sun are created. These maps are used to create plots of the Sun's axial dipole moment, a measure of the polar field. Also in Chapter 4, I illustrate how this model is used to create a baseline. In this regime, the model assimilates (i.e. continually adds in data weighted by its noise level) magnetic data from magnetograms at all available latitudes. This ensures that it accurately represents the magnetic fields observed on the surface of the Sun. This baseline is used to illustrate the difference in the timing of the polar field reversals based on four different definitions of polar fields. Advantages and disadvantages of each of these definitions are discussed. In Chapter 5, I discuss how the model is used in a predictive or simulation regime. I have tested the predictability of this model using a baseline map as an initial condition, but with daily sunspot area data used to give the sources of new magnetic flux. I found that the strength of the polar fields at cycle minimum and the polar field reversals at cycle maximum can be reliably predicted up to 3 years in advance. I have included a prediction for the Cycle 24 polar field reversal. In Chapter 6, I use the predictive model in three simulations to determine the impact of MF variations on the sunspot cycle. (Abstract shortened by UMI.)

  18. Abundances of r-PROCESS Elements in the Photosphere of Red Supergiant Star PMMR23 in Small Magellanic Cloud

    NASA Astrophysics Data System (ADS)

    Vasil'Eva, S. V.; Gopka, V. F.; Yushchenko, A. V.; Andryevsky, S. M.

    Detailed analysis of chemical abundances determined from high-resolution CCD-spectrogram of supergiant star PMMR23 (K5 I) in SMC is presented. The observation were obtained at 3.6 meter ESO La Silla telescope by Hill (1997). Spectral resolving power is near R=30.000. The wavelength coverage is 5050-7200 A. The abundances of iron and 15 r-, s-processes elements are found. The abundances of Cu, Zr, Mo, Ru, Pr, Sm, Gd, Dy, Er are found for the first time. The abundances of elements with atomic numbers less than 55 are deficient with respect to the Sun. The mean underabundance is near 0.7 dex. The abundances of barium and lanthanides are near solar values. The overabundances of these elements with respect to iron are in the range from 0.4 tp 0.9 dex. The abundances of heavy lanthanides are higher than the abundances of light lanthanides. The abundance pattern of PMMR23 can be fitted by scaled solar r-process distribution. The atmosphere of PMMR23 is enriched by r-process elements.

  19. Parallelization of the SIR code for the investigation of small-scale features in the solar photosphere

    NASA Astrophysics Data System (ADS)

    Thonhofer, Stefan; Rubio, Luis R. Bellot; Utz, Dominik; Hanslmeier, Arnold; Jurçák, Jan

    2015-10-01

    Magnetic fields are one of the most important drivers of the highly dynamic processes that occur in the lower solar atmosphere. They span a broad range of sizes, from large- and intermediate-scale structures such as sunspots, pores and magnetic knots, down to the smallest magnetic elements observable with current telescopes. On small scales, magnetic flux tubes are often visible as Magnetic Bright Points (MBPs). Apart from simple V/I magnetograms, the most common method to deduce their magnetic properties is the inversion of spectropolarimetric data. Here we employ the SIR code for that purpose. SIR is a well-established tool that can derive not only the magnetic field vector and other atmospheric parameters (e.g., temperature, line-of-sight velocity), but also their stratifications with height, effectively producing 3-dimensional models of the lower solar atmosphere. In order to enhance the runtime performance and the usability of SIR we parallelized the existing code and standardized the input and output formats. This and other improvements make it feasible to invert extensive high-resolution data sets within a reasonable amount of computing time. An evaluation of the speedup of the parallel SIR code shows a substantial improvement in runtime.

  20. The discovery of Ni V in the photospheres of the hot DA white dwarfs RE 2214-492 and G191-B2B

    NASA Technical Reports Server (NTRS)

    Holberg, J. B.; Hubeny, I.; Barstow, M. A.; Lanz, T.; Sion, E. M.; Tweedy, R. W.

    1994-01-01

    We have co-added six recently obtained International Ultraviolet Explorer (IUE) echelle spectra of the hot DA white dwarf RE 2214-492 and 10 existing archive spectra of the well-known hot DA, G191-B2B. We find that both stars contain numerous weak features due to Ni V. Nickel is thus the second iron-group element to be found in the spectra of the very hottest DA white dwarfs. In addition to Ni V, we also observe Al III in both stars and present evidence for the possible presence of Ni IV and Fe IV in RE 2214-492. The presence of Ni and Al, together with previously reported elements, will contribute significantly to both the EUV opacity and to the apparent complexity of the UV spectra of these stars. Using Non-Local Thermodynamic Equilibrium (NLTE) model atmospheres we estimate the Ni abundances in RE 2214-492 the G191-B2B to be log(Ni/H) = -5.5 +/- 0.3 and -6.0 +/- 0.3, respectively.

  1. Improved V I Log(gf) Values and Abundance Determinations in the Photospheres of the Sun and Metal-poor Star HD 84937

    NASA Astrophysics Data System (ADS)

    Lawler, J. E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T.; Sneden, C.; Cowan, J. J.

    2014-12-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ɛ(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V I lines and log ɛ(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V I lines, respectively, using the Holweger-Müller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.

  2. IMPROVED Ni I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Wood, M. P.; Lawler, J. E.; Sneden, C.; Cowan, J. J. E-mail: jelawler@wisc.edu E-mail: cowan@nhn.ou.edu

    2014-04-01

    Atomic transition probability measurements for 371 Ni I lines in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer and a new echelle spectrograph are combined with published radiative lifetimes to determine these transition probabilities. Generally good agreement is found in comparisons to previously reported Ni I transition probability measurements. Use of the new echelle spectrograph, independent radiometric calibration methods, and independent data analysis routines enable a reduction of systematic errors and overall improvement in transition probability uncertainty over previous measurements. The new Ni I data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ni abundances. Lines covering a wide range of wavelength and excitation potential are used to search for non-LTE effects.

  3. IMPROVED Ti II log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Wood, M. P.; Lawler, J. E.; Sneden, C.; Cowan, J. J. E-mail: jelawler@wisc.edu E-mail: cowan@nhn.ou.edu

    2013-10-01

    Atomic transition probability measurements for 364 lines of Ti II in the UV through near-IR are reported. Branching fractions from data recorded using a Fourier transform spectrometer (FTS) and a new echelle spectrometer are combined with published radiative lifetimes to determine these transition probabilities. The new results are in generally good agreement with previously reported FTS measurements. Use of the new echelle spectrometer, independent radiometric calibration methods, and independent data analysis routines enables a reduction of systematic errors and overall improvement in transition probability accuracy over previous measurements. The new Ti II data are applied to high-resolution visible and UV spectra of the Sun and metal-poor star HD 84937 to derive new, more accurate Ti abundances. Lines covering a range of wavelength and excitation potential are used to search for non-LTE effects. The Ti abundances derived using Ti II for these two stars match those derived using Ti I and support the relative Ti/Fe abundance ratio versus metallicity seen in previous studies.

  4. IS THE SUN LIGHTER THAN THE EARTH? ISOTOPIC CO IN THE PHOTOSPHERE, VIEWED THROUGH THE LENS OF THREE-DIMENSIONAL SPECTRUM SYNTHESIS

    SciTech Connect

    Ayres, Thomas R.; Lyons, J. R.; Ludwig, H.-G.; Caffau, E.; Wedemeyer-Boehm, S.

    2013-03-01

    We consider the formation of solar infrared (2-6 {mu}m) rovibrational bands of carbon monoxide (CO) in CO5BOLD 3D convection models, with the aim of refining abundances of the heavy isotopes of carbon ({sup 13}C) and oxygen ({sup 18}O, {sup 17}O), to compare with direct capture measurements of solar wind light ions by the Genesis Discovery Mission. We find that previous, mainly 1D, analyses were systematically biased toward lower isotopic ratios (e.g., R {sub 23} {identical_to} {sup 12}C/{sup 13}C), suggesting an isotopically 'heavy' Sun contrary to accepted fractionation processes that were thought to have operated in the primitive solar nebula. The new 3D ratios for {sup 13}C and {sup 18}O are R {sub 23} = 91.4 {+-} 1.3 (R {sub Circled-Plus} = 89.2) and R {sub 68} = 511 {+-} 10 (R {sub Circled-Plus} = 499), where the uncertainties are 1{sigma} and 'optimistic'. We also obtained R {sub 67} = 2738 {+-} 118 (R {sub Circled-Plus} = 2632), but we caution that the observed {sup 12}C{sup 17}O features are extremely weak. The new solar ratios for the oxygen isotopes fall between the terrestrial values and those reported by Genesis (R {sub 68} = 530, R {sub 67} = 2798), although including both within 2{sigma} error flags, and go in the direction favoring recent theories for the oxygen isotope composition of Ca-Al inclusions in primitive meteorites. While not a major focus of this work, we derive an oxygen abundance, {epsilon}{sub O} {approx} 603 {+-} 9 ppm (relative to hydrogen; log {epsilon} {approx} 8.78 on the H = 12 scale). The fact that the Sun is likely lighter than the Earth, isotopically speaking, removes the necessity of invoking exotic fractionation processes during the early construction of the inner solar system.

  5. Relations between the photospheric magnetic field and the emission from the outer atmospheres of cool stars. II - The C IV 1550 A doublet

    NASA Technical Reports Server (NTRS)

    Schrijver, C. J.

    1990-01-01

    Solar and stellar data are used to determine the relationship between C IV 1548 + 1551 A and magnetic flux densities. C IV SMM-UVSP spectroheliograms of solar quiet regions and plages are analyzed. Typical distribution functions of C IV flux densities over both quiet and active solar regions are presented. The C IV emission is shown to be dependent on magnetic flux density.

  6. IMPROVED V I log(gf) VALUES AND ABUNDANCE DETERMINATIONS IN THE PHOTOSPHERES OF THE SUN AND METAL-POOR STAR HD 84937

    SciTech Connect

    Lawler, J. E.; Wood, M. P.; Den Hartog, E. A.; Feigenson, T.; Sneden, C.; Cowan, J. J. E-mail: mpwood@wisc.edu E-mail: tfeigenson@wisc.edu E-mail: cowan@nhn.ou.edu

    2015-01-01

    New emission branching fraction measurements for 836 lines of the first spectrum of vanadium (V I) are determined from hollow cathode lamp spectra recorded with the National Solar Observatory 1 m Fourier transform spectrometer (FTS) and a high-resolution echelle spectrometer. The branching fractions are combined with recently published radiative lifetimes from laser-induced fluorescence measurements to determine accurate absolute atomic transition probabilities for the 836 lines. The FTS data are also used to extract new hyperfine structure A coefficients for 26 levels of neutral vanadium. These new laboratory data are applied to determine the V abundance in the Sun and metal-poor star HD 84937, yielding log ε(V) = 3.956 ± 0.004 (σ = 0.037) based on 93 V I lines and log ε(V) = 1.89 ± 0.03 (σ = 0.07) based on nine V I lines, respectively, using the Holweger-Müller 1D model. These new V I abundance values for the Sun and HD 84937 agree well with our earlier determinations based upon V II.

  7. Is the Sun Lighter than the Earth? Isotopic CO in the Photosphere, Viewed through the Lens of Three-dimensional Spectrum Synthesis

    NASA Astrophysics Data System (ADS)

    Ayres, Thomas R.; Lyons, J. R.; Ludwig, H.-G.; Caffau, E.; Wedemeyer-Böhm, S.

    2013-03-01

    We consider the formation of solar infrared (2-6 μm) rovibrational bands of carbon monoxide (CO) in CO5BOLD 3D convection models, with the aim of refining abundances of the heavy isotopes of carbon (13C) and oxygen (18O, 17O), to compare with direct capture measurements of solar wind light ions by the Genesis Discovery Mission. We find that previous, mainly 1D, analyses were systematically biased toward lower isotopic ratios (e.g., R 23 ≡ 12C/13C), suggesting an isotopically "heavy" Sun contrary to accepted fractionation processes that were thought to have operated in the primitive solar nebula. The new 3D ratios for 13C and 18O are R 23 = 91.4 ± 1.3 (R ⊕ = 89.2) and R 68 = 511 ± 10 (R ⊕ = 499), where the uncertainties are 1σ and "optimistic." We also obtained R 67 = 2738 ± 118 (R ⊕ = 2632), but we caution that the observed 12C17O features are extremely weak. The new solar ratios for the oxygen isotopes fall between the terrestrial values and those reported by Genesis (R 68 = 530, R 67 = 2798), although including both within 2σ error flags, and go in the direction favoring recent theories for the oxygen isotope composition of Ca-Al inclusions in primitive meteorites. While not a major focus of this work, we derive an oxygen abundance, epsilonO ~ 603 ± 9 ppm (relative to hydrogen; log epsilon ~ 8.78 on the H = 12 scale). The fact that the Sun is likely lighter than the Earth, isotopically speaking, removes the necessity of invoking exotic fractionation processes during the early construction of the inner solar system.

  8. Variations over time in latitudinal distribution of the large-scale magnetic fields in the solar atmosphere at heights from the photosphere to the source surface

    NASA Astrophysics Data System (ADS)

    Akhtemov, Z. S.; Andreyeva, O. A.; Rudenko, G. V.; Stepanian, N. N.; Fainshtein, V. G.

    2015-02-01

    Calculations of magnetic field in the solar atmosphere and the "potential field-source surface" model have been used to study time variations in several parameters of the large-scale magnetic field at various heights during the last four solar cycles. At ten heights from the solar surface (R = Ro) to the source surface (R = 2.5Ro), we have constructed synoptic charts (SC) of the radial component Br of the estimated magnetic field. For these SC, we have identified 10-degree latitudinal zones. Within these zones, we found values of Sp (positive Br values averaged within the latitudinal zone over latitude and longitude), Sm (averaged modulus of negative Br values) and S + fields (a part of the latitudinal zone area (in %) occupied by positive Br values). At lower latitudes, cyclic variations in the Sp + Sm parameter are demonstrated to be similar (but not in detail) to time variations in Wolf numbers. Latitudes of 55° and higher exhibited virtually no cyclic peculiarities of time variations in this parameter. The authors believe that this indicates the diverse nature of the large-scale magnetic field in the near-equatorial and polar regions of the solar atmosphere. At R = 2.5Ro, Sp + Sm cyclic variations are almost invisible at all latitudes and only slightly apparent near the equator. The analysis of S + fields variations revealed that at low latitudes at R = 2.5Ro during solar cycles 21, 22 and ascending phase of cycle 23 there were almost no mixed-polarity periods. However, beginning from the maximum of cycle 23, in the near-equatorial region the mixed polarity was observed until the end of the long solar activity minimum. An assumption has been made that this might have been one of the forerunners and manifestations of the prolonged minimum between cycles 23 and 24. It has been found that during solar activity minima poleward there appears motion of magnetic fields with polarity opposite to that of the field at the pole. We have estimated the velocity of such a latitudinal movement of fields. The magnetic field at R = R⊙ during the maximum of cycle 24 is shown to be significantly less than that during the maximum of cycle 23; in a range 55°-75° this difference is as much as one order of magnitude. We have verified the conclusion drawn in our previous studies that in solar cycles 21-23 the polar-field reversal started and ended earlier at large heights than on the solar surface. Peculiarities of the magnetic-field reversal in solar cycle 24 have been revealed.

  9. Relations between the photospheric magnetic field and the emission from the outer atmospheres of cool stars. I - The solar Ca II K line core emission

    NASA Technical Reports Server (NTRS)

    Schrijver, C. J.; Cote, J.; Zwaan, C.; Saar, S. H.

    1989-01-01

    Observations of a solar active region complex and its surroundings are used to establish a quantitative relation between the Ca II K line core intensity and magnetic flux density. The Ca II K line core intensity is transformed to a Ca II H + K line core flux density to facilitate a comparison of solar and stellar data. A new absolute calibration for the Mount Wilson Ca II H + K fluxes for G-type dwarfs is derived. The minimum Ca II K flux, found in the centers of supergranulation cells in quiet regions on the sun, is identical to the minimum flux that is observed for solar-type stars. An expression is presented for the nonlinear trend between the Ca II H + K line core excess flux density and the absolute value of the magnetic flux density. Models that explain the nonlinearity of the mean trend and the large intrinsic scatter about it are discussed. The solar data define a relation that is similar to the relation between stellar hemisphere-average magnetic flux densities and Ca II H + K excess flux densities.

  10. Spatial distribution of large-scale solar magnetic fields and their relation to the interplanetary magnetic field

    NASA Technical Reports Server (NTRS)

    Levine, R. H.

    1979-01-01

    The spatial organization of the observed photospheric magnetic field as well as its relation to the polarity of the IMF have been studied using high resolution magnetograms from the Kitt Peak National Observatory. Systematic patterns in the large scale field are due to contributions from both concentrated flux and more diffuse flux. The polarity of the photospheric field, determined on various spatial scales, correlates with the polarity of the IMF. Analyses based on several spatial scales in the photosphere suggest that new flux in the interplanetary medium is often due to relatively small photospheric features which appear in the photosphere up to one month before they are manifest at the earth.

  11. On the presence of electric currents in the solar atmosphere. I - A theoretical framework

    NASA Technical Reports Server (NTRS)

    Hagyard, M.; Low, B. C.; Tandberg-Hanssen, E.

    1981-01-01

    The general magnetic field above the solar photosphere is divided by an elementary analysis based on Ampere's law into two parts: a potential field due to electric currents below the photosphere and a field produced by electric currents above the photosphere combined with the induced mirror currents. The latter, by symmetry, has a set of field lines lying in the plane taken to be the photosphere which may be constructed from given vector magnetograph measurements. These field lines also represent all the information on the electric currents above the photosphere that a magnetograph can provide. Theoretical illustrations are given, and implications for data analysis are discussed.

  12. Solar sources of the interplanetary magnetic field and solar wind

    NASA Technical Reports Server (NTRS)

    Levine, R. H.; Altschuler, M. D.; Harvey, J. W.

    1977-01-01

    Open magnetic field lines, those which extend from the solar photosphere to interplanetary space, are traced in the current-free (potential field) approximation using measured photospheric fields as a boundary condition. It is found that (1) only a relatively small fraction of the photospheric area connects via open field lines to the interplanetary magnetic field; (2) those photospheric areas which do contribute open field lines lie beneath coronal holes and within the boundaries of the holes as projected onto the photosphere or else between loop systems of an active region; (3) the interplanetary magnetic field in the plane of the sun's equator, essentially the field in the ecliptic plane, may connect to photospheric regions of high latitude; and (4) the fastest solar wind streams are correlated with those magnetic flux tubes which expand least in cross-sectional area over the distance between the photosphere and the coronal height where the solar wind begins.

  13. The Convection of Close Red Supergiant Stars Observed With Near-Infrared Interferometry

    NASA Astrophysics Data System (ADS)

    Montargès, M.; Kervella, P.; Perrin, G.; Chiavassa, A.; Aurière, M.

    2015-12-01

    Our team has obtained observations of the photosphere of the two closest red supergiant stars Betelgeuse (α Ori) and Antares (α Sco) using near infrared interferometry. We have been monitoring the photosphere of Betelgeuse with the VLTI/PIONIER instrument for three years. On Antares, we obtained an unprecedented sampling of the visibility function. These data allow us to probe the convective photosphere of massive evolved stars.

  14. IRIS Launch, Deploy and Beauty Pass Animation

    NASA Video Gallery

    Understanding the interface between the photosphere and corona remains a fundamental challenge in solar and heliospheric science. The Interface Region Imaging Spectrograph (IRIS) mission opens a wi...

  15. Magnetic diffusion and flare energy buildup

    NASA Technical Reports Server (NTRS)

    Wu, S. T.; Yin, C. L.; Yang, W.-H.

    1992-01-01

    Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear 2D force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field and photospheric velocity field are used, it is found that 3-4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal magnetic energy, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.

  16. The Role of Magnetic Reconnection in Solar Activity

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro; DeVore, C. R.

    2008-01-01

    The central challenge in solar/heliospheric physics is to understand how the emergence and transport of magnetic flux at the photosphere drives the structure and dynamics that we observe in the corona and heliosphere. This presentation focuses on the role of magnetic reconnection in determining solar/heliospheric activity. We demonstrate that two generic properties of the photospheric magnetic and velocity fields are responsible for the ubiquitous reconnection in the corona. First, the photospheric velocities are complex, which leads to the injection of energy and helicity into the coronal magnetic fields and to the efficient, formation of small-scale structure. Second, the flux distribution at the photosphere is multi-polar, which implies that topological discontinuities and, consequently, current sheets, must be present in the coronal magnetic field. We: present numerical simulations showing that photospherically-driven reconnection is responsible for the heating and dynamics of coronal plasma, and for the topology of the coronal/heliospheric magnetic field.

  17. Transparency parameters from relativistically expanding outflows

    SciTech Connect

    Bégué, D.; Iyyani, S.

    2014-09-01

    In many gamma-ray bursts a distinct blackbody spectral component is present, which is attributed to the emission from the photosphere of a relativistically expanding plasma. The properties of this component (temperature and flux) can be linked to the properties of the outflow and have been presented in the case where there is no sub-photospheric dissipation and the photosphere is in coasting phase. First, we present the derivation of the properties of the outflow for finite winds, including when the photosphere is in the accelerating phase. Second, we study the effect of localized sub-photospheric dissipation on the estimation of the parameters. Finally, we apply our results to GRB 090902B. We find that during the first epoch of this burst the photosphere is most likely to be in the accelerating phase, leading to smaller values of the Lorentz factor than the ones previously estimated. For the second epoch, we find that the photosphere is likely to be in the coasting phase.

  18. The high-resolution spectrum of the pulsating, pre-white dwarf star PG 1159-035 (GW VIR)

    NASA Technical Reports Server (NTRS)

    Liebert, James; Wesemael, F.; Husfeld, D.; Wehrse, R.; Starrfield, S. G.

    1989-01-01

    High-resolution and low-resolution UV spectra and a high-resolution optical spectrum were obtained for PG 1159-035, revealing apparent photospheric absorption features with defined cores from N V 1240 A, N IV 1270 A, O V 1371 A, and C IV 1550 A. The photospheric velocity derived using all of these lines except for C IV is about +35 km/s. Equivalent-width measurements determined for all of the features may provide a tighter constraint on the photospheric temperature in a detailed model atmosphere analysis treating the CNO ions.

  19. An essay on sunspots and solar flares

    NASA Astrophysics Data System (ADS)

    Akasofu, S.-I.

    1984-11-01

    The author reviews some of the recent findings on large-scale magnetic fields and sunspots. Then, instead of relying on the hypothetical flux tube beneath the photosphere, he considers an amplification process of the observed large-scale fields by a dynamo process on the basis of the observed and possible photospheric shear flows. Thus, the photosphere is considered as an active medium, rather than the passive medium through which the hypothetical flux tube merely penetrates. Specifically, the author considers the dynamo process associated with vortex motions which can supply the power needed for the formation of sunspots from the observed weak field and the power needed for solar flares.

  20. Siphon flows in isolated magnetic flux tubes

    NASA Technical Reports Server (NTRS)

    Thomas, John H.

    1988-01-01

    The paper considers steady siphon flows in isolated thin magnetic flux tubes surrounded by field-free gas, with plasma beta greater than or equal to 1, appropriate for conditions in the solar photosphere. The cross-sectional area of the flux tube varies along the tube in response to pressure changes induced by the siphon flow. Consideration is also given to steady isothermal siphon flows in arched magnetic flux tubes in a stratified atmosphere. Applications of the results to intense magnetic flux tubes in the solar photosphere and to the photospheric Evershed flow in a sunspot penumbra are addressed.

  1. Diffusion in the chromosphere and the composition of the solar corona and energetic particles

    NASA Technical Reports Server (NTRS)

    Vauclair, S.; Meyer, J. P.

    1985-01-01

    Composition observations, in the solar photosphere, and in the upper transition region (TR) and corona imply a change of composition of the solar atmosphere somewhere between the photosphere and the upper TR. Heavy elements with first ionization potential (FIP) 9 eV (high-FIP element) are approx. 4 times less abundant in the TR and corona than in the photosphere, as compared to both hydrogen and heavy elements with lower low-FIP elements. A separation is suggested between neutral and ionized elements in a region where the high-FIP elements are mostly neutral, and the low-FIP elements ionized. This occurs in the chromosphere at altitudes above 600 km and below 2000 km above Photosphere. Whether the diffusion processes can explain the observed change in composition is investigated.

  2. Ultraviolet Spectrometer and Polarimeter (UVSP) software development and hardware tests for the solar maximum mission

    NASA Technical Reports Server (NTRS)

    1984-01-01

    An analysis of UVSP wavelength drive hardware, problems, and recovery procedures; radiative power loss from solar plasmas; and correlations between observed UV brightness and inferred photospheric currents are given.

  3. Solar abundances from gamma-ray spectroscopy

    NASA Technical Reports Server (NTRS)

    Ramaty, R.

    1989-01-01

    Determinations of solar abundances from gamma-ray line observations are reviewed. The principal results are: (1) in flare loops, at atmospheric heights betwen the transition region and the upper photosphere, the Mg/O ratio is higher by about a factor of 3 than in the photosphere, while the C/O ratio is essentially photospheric; (2) in the same region, the Ne/O ratio is higher by about a factor of 3 than the Ne/O ratio in the corona; (3) the photospheric He-3/H ratio is less than 0.000035. These results, combined with other data, suggest abundance variations in the solar atmosphere, possibly resulting from charge and mass dependent transport.

  4. Simulation of the magnetic structure of the inner heliosphere by means of non-spherical source surface

    NASA Technical Reports Server (NTRS)

    Levine, R. H.; Schulz, M.; Frazier, E. N.

    1981-01-01

    A new method for mapping the Sun's magnetic field B from the photosphere through the corona and interplanetary space is presented. The method entails the derivation of B from a scalar potential within a current-free annular volume bounded inside by photosphere and outside by a prescribed nonspherical source surface to which B is made (as nearly as possible) perpendicular. As usual we obtain the potential for the part of B that arises from currents inside the Sun by fitting an expansion to the observed line-of-sight component of B at the photosphere. A second least-squares fit is introduced to obtain the part of B that arises from currents outside the source surface. Comparisons are made between this model and observed coronal and interplanetary structures. There is evidence that observation data underestimate the strength of photospheric polar magnetic fields.

  5. Quasi-thermal models

    NASA Technical Reports Server (NTRS)

    Delareza, Ramiro

    1987-01-01

    Non-local thermodynamics equilibrium (LTE) effects in the photosphere; recent research on the chromosphere of the M and C stars; and elementary shock-waves and pulsation theories and their applications to Mira long-period variables are discussed.

  6. Solar cycle variation of large-scale coronal structures

    NASA Technical Reports Server (NTRS)

    Antonucci, E.; Duvall, T. L.

    1974-01-01

    A green line intensity variation is associated with the interplanetary and photospheric magnetic sector structure. This effect depends on the solar cycle and occurs with the same amplitude in the latitude range 60 deg N - 60 deg S. Extended longitudinal coronal structures are suggested, which indicate the existence of closed magnetic field lines over the neutral line, separating adjacent regions of opposite polarities on the photospheric surface.

  7. Multiwavelength spectropolarimetric observations of an Ellerman bomb

    NASA Astrophysics Data System (ADS)

    Rezaei, R.; Beck, C.

    2015-10-01

    Context. Ellerman bombs (EBs) are enhanced emission in the wings of the Hα line in the solar spectrum. Aims: We study the structure of an EB in the photosphere and chromosphere. Methods: We analyze simultaneous observations of four chromospheric lines (Hα, Ca ii H, Ca ii IR 854 nm, and He i 1083 nm) as well as two photospheric lines (Fe i 630 and Si i 1082.7 nm) along with high-cadence 160 and 170 nm ultraviolet (UV) continuum filtergrams. Full Stokes data from the Helioseismic and Magnetic Imager (HMI) are used to trace the temporal evolution of the magnetic structure. Results: We identify the EB by excess emission in the wings of the Hα line, a brightening in the UV continuum, and large emission peaks in the core of the two Ca ii lines. The EB shows a blueshift in all chromospheric lines, while no shifts are observed in the photospheric lines. The blueshift in the chromospheric layer causes very asymmetric emission peaks in the Ca ii H line. The photospheric Si i spectral line shows a shallower line depth at the location of the EB. The UV continuum maps show that the EB was substantially brighter than its surroundings for about 30 min. The continuum contrast of the EB from 170 nm to 1080 nm shows a power-law dependency on the wavelength. The temperature enhancement amounts to 130 K in the low photosphere and 400 K at the temperature minimum level. This temperature excess is also seen in an LTE inversion of the Ca ii spectra. The total thermal and radiative energy content of the EB is about 1020 J and 1018 J in the photosphere and chromosphere, respectively. The HMI data hints at a photospheric magnetic flux cancellation as the driver of the EB. Conclusions: Ellerman bombs release the energy in a height range of several pressure scale heights around the temperature minimum such that they affect both the photosphere and the lower chromosphere.

  8. Explorations of electric current system in solar active regions. I - Empirical inferences of the current flows

    NASA Technical Reports Server (NTRS)

    Ding, Y. J.; Hong, Q. F.; Hagyard, M. J.; Deloach, A. C.; Liu, X. P.

    1987-01-01

    Techniques to identify sources of electric current systems and their channels of flow in solar active regions are explored. Measured photospheric vector magnetic fields together with high-resolution white-light and H-alpha filtergrams provide the data base to derive the current systems in the photosphere and chromosphere. As an example, the techniques are then applied to infer current systems in AR 2372 in early April 1980.

  9. The impact of surface dynamo magnetic fields on the solar iron abundance

    NASA Astrophysics Data System (ADS)

    Shchukina, N.; Trujillo Bueno, J.

    2015-07-01

    Most chemical abundance determinations ignore that the solar photosphere is significantly magnetized by the ubiquitous presence of a small-scale magnetic field. A recent investigation has suggested that there should be a significant impact on the derived iron abundance, owing to the magnetically induced changes on the photospheric temperature and density structure (indirect effect). The three-dimensional (3D) photospheric models used in that investigation have non-zero net magnetic flux values and stem from magneto-convection simulations without small-scale dynamo action. Here we address the same problem by instead using 3D models of the quiet solar photosphere that result from a state-of-the-art magneto-convection simulation with small-scale dynamo action, where the net magnetic flux is zero. One of these 3D models has negligible magnetization, while the other is characterized by a mean field strength of 160 Gauss in the low photosphere. With such 3D models we carried out spectral synthesis for a large set of Fe i lines to derive abundance corrections, taking the above-mentioned indirect effect and the Zeeman broadening of the intensity profiles (direct effect) into account. We conclude that if the magnetism of the quiet solar photosphere is mainly produced by a small-scale dynamo, then its impact on the determination of the solar iron abundance is negligible. Table 1 is available in electronic form at http://www.aanda.org

  10. Multiscale Dynamics of Solar Magnetic Structures

    NASA Technical Reports Server (NTRS)

    Uritsky, Vadim M.; Davila, Joseph M.

    2012-01-01

    Multiscale topological complexity of the solar magnetic field is among the primary factors controlling energy release in the corona, including associated processes in the photospheric and chromospheric boundaries.We present a new approach for analyzing multiscale behavior of the photospheric magnetic flux underlying these dynamics as depicted by a sequence of high-resolution solar magnetograms. The approach involves two basic processing steps: (1) identification of timing and location of magnetic flux origin and demise events (as defined by DeForest et al.) by tracking spatiotemporal evolution of unipolar and bipolar photospheric regions, and (2) analysis of collective behavior of the detected magnetic events using a generalized version of the Grassberger-Procaccia correlation integral algorithm. The scale-free nature of the developed algorithms makes it possible to characterize the dynamics of the photospheric network across a wide range of distances and relaxation times. Three types of photospheric conditions are considered to test the method: a quiet photosphere, a solar active region (NOAA 10365) in a quiescent non-flaring state, and the same active region during a period of M-class flares. The results obtained show (1) the presence of a topologically complex asymmetrically fragmented magnetic network in the quiet photosphere driven by meso- and supergranulation, (2) the formation of non-potential magnetic structures with complex polarity separation lines inside the active region, and (3) statistical signatures of canceling bipolar magnetic structures coinciding with flaring activity in the active region. Each of these effects can represent an unstable magnetic configuration acting as an energy source for coronal dissipation and heating.

  11. MULTISCALE DYNAMICS OF SOLAR MAGNETIC STRUCTURES

    SciTech Connect

    Uritsky, Vadim M.; Davila, Joseph M.

    2012-03-20

    Multiscale topological complexity of the solar magnetic field is among the primary factors controlling energy release in the corona, including associated processes in the photospheric and chromospheric boundaries. We present a new approach for analyzing multiscale behavior of the photospheric magnetic flux underlying these dynamics as depicted by a sequence of high-resolution solar magnetograms. The approach involves two basic processing steps: (1) identification of timing and location of magnetic flux origin and demise events (as defined by DeForest et al.) by tracking spatiotemporal evolution of unipolar and bipolar photospheric regions, and (2) analysis of collective behavior of the detected magnetic events using a generalized version of the Grassberger-Procaccia correlation integral algorithm. The scale-free nature of the developed algorithms makes it possible to characterize the dynamics of the photospheric network across a wide range of distances and relaxation times. Three types of photospheric conditions are considered to test the method: a quiet photosphere, a solar active region (NOAA 10365) in a quiescent non-flaring state, and the same active region during a period of M-class flares. The results obtained show (1) the presence of a topologically complex asymmetrically fragmented magnetic network in the quiet photosphere driven by meso- and supergranulation, (2) the formation of non-potential magnetic structures with complex polarity separation lines inside the active region, and (3) statistical signatures of canceling bipolar magnetic structures coinciding with flaring activity in the active region. Each of these effects can represent an unstable magnetic configuration acting as an energy source for coronal dissipation and heating.

  12. Origin and evolution of ices around massive young stars

    NASA Astrophysics Data System (ADS)

    Krijger, Johannes Mattheus

    2002-10-01

    The thesis Structure and dynamics of the solar chromosphere of J.M. Krijger is a study on the behavior of the solar chromosphere, the thin layer just above the solar surface (photosphere) visible in purple red light during a total solar eclipse. The most important result of this thesis is that the chromosphere is filled with acoustic and internal gravity waves that travel upward until they collide with a canopy of expanding magnetic field. The photosphere is the layer of which we see the light with the naked eye. Through this layer poke large and small magnetic tubes. Above the photosphere and the chromosphere sits the hot solar corona of a few million degrees. With observations of among others the space satellite TRACE (Transition Region and Coronal Explorer) J.M. Krijger shows that the photosphere is dominated by flows of the ambient gas that dictate the magnetic field where to go. The possible heating of the chromosphere is an important unsolved problem in solar physics. The chromosphere forms the transition region between the very hot corona, dominated by magnetic fields, and the photosphere where gasflows drag the magnetic field along. In this transition region the magnetic field, which in the photosphere is still trapped in individual tubes, expands to a canopy above which the magnetic field fills the entire space. In this thesis it is shown that the chromosphere is dominated by upward propagating acoustic waves and a magnetic canopy that changes the dynamics of the oscillations. Finally J.M. Krijger shows that the network of magnetic field in the chromosphere is formed by magnetic tubes that are swepped together by flows in the photosphere.

  13. No first ionization potential fractionation in the active stars AR Piscium and AY Ceti

    NASA Astrophysics Data System (ADS)

    Sanz-Forcada, J.; Affer, L.; Micela, G.

    2009-10-01

    Context: The comparison of coronal and photospheric abundances in cool stars is an essential question to resolve. In the Sun an enhancement of the elements with low first ionization potential (FIP) is observed in the corona with respect to the photosphere. Stars with high levels of activity seem to show a depletion of elements with low FIP when compared to solar standard values; however, the few cases of active stars in which photospheric values are available for comparison lead to confusing results, and an enlargement of the sample is mandatory for solving this longstanding problem. Aims: We calculate in this paper the photospheric and coronal abundances of two well known active binary systems, AR Psc and AY Cet, to get further insight into the complications of coronal abundances. Methods: Coronal abundances of 9 elements were calculated by means of the reconstruction of a detailed emission measure distribution, using a line-based method that considers the lines from different elements separately. Photospheric abundances of 8 elements were calculated using high-resolution optical spectra of the stars. Results: The results once again show a lack of any FIP-related effect in the coronal abundances of the stars. The presence of metal abundance depletion (MAD) or inverse FIP effects in some stars could stem from a mistaken comparison to solar photospheric values or from a deficient calculation of photospheric abundances in fast-rotating stars. Conclusions: The lack of FIP fractionation seems to confirm that Alfvén waves combined with pondermotive forces are dominant in the corona of active stars. Tables 2 and 3 are only available in electronic form at http://www.aanda.org

  14. UTILIZATION OF MULTIPLE MEASUREMENTS FOR GLOBAL THREE-DIMENSIONAL MAGNETOHYDRODYNAMIC SIMULATIONS

    SciTech Connect

    Wang, A. H.; Wu, S. T.; Tandberg-Hanssen, E.; Hill, Frank

    2011-05-01

    Magnetic field measurements, line of sight (LOS) and/or vector magnetograms, have been used in a variety of solar physics studies. Currently, the global transverse velocity measurements near the photosphere from the Global Oscillation Network Group (GONG) are available. We have utilized these multiple observational data, for the first time, to present a data-driven global three-dimensional and resistive magnetohydrodynamic (MHD) simulation, and to investigate the energy transport across the photosphere to the corona. The measurements of the LOS magnetic field and transverse velocity reflect the effects of convective zone dynamics and provide information from the sub-photosphere to the corona. In order to self-consistently include the observables on the lower boundary as the inputs to drive the model, a set of time-dependent boundary conditions is derived by using the method of characteristics. We selected GONG's global transverse velocity measurements of synoptic chart CR2009 near the photosphere and SOLIS full-resolution LOS magnetic field maps of synoptic chart CR2009 on the photosphere to simulate the equilibrium state and compute the energy transport across the photosphere. To show the advantage of using both observed magnetic field and transverse velocity data, we have studied two cases: (1) with the inputs of the LOS magnetic field and transverse velocity measurements, and (2) with the input of the LOS magnetic field and without the input of transverse velocity measurements. For these two cases, the simulation results presented here are a three-dimensional coronal magnetic field configuration, density distributions on the photosphere and at 1.5 solar radii, and the solar wind in the corona. The deduced physical characteristics are the total current helicity and the synthetic emission. By comparing all the physical parameters of case 1 and case 2 and their synthetic emission images with the EIT image, we find that using both the measured magnetic field and the

  15. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Technical Reports Server (NTRS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-01-01

    The helicity condensation model has been proposed by Antiochos (2013) to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the system. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of, for example, a bipolar active region. The calculations demonstrate that, contrary to common belief, coronal loops having opposite helicity do not reconnect, whereas loops having the same sense of helicity do reconnect. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  16. Intermittent Emission of High-Frequency Waves by Magnetic Reconnection Between Canopy Field and Small-Scale Horizontal Field

    NASA Astrophysics Data System (ADS)

    Isobe, H.

    2007-12-01

    The energy source of coronal heating and solar wind acceleration is the interaction of magnetic field and thermal convection in the photosphere. Magnetoconvection has complicated bifurcation structure, and the mode, spectra and power of the waves generated in the photosphere depend on the nature of magnetoconvection in the photosphere. In order to study the relation between magnetoconvection and coronal heating/solar wind acceleration, we performed three-dimensional magnetohydrodynamic simulation of a domain that includes from upper convection zone to the corona. We first ran the simulation without magnetic field until convection developed to quasi-steady state, and then imposed a vertical and uniform magnetic field. We found that, in addition to the well-known fact that vertical magnetic field is swept into the downflow region, small scale horizontal fields as strong as 800G intermittently emerge in the photosphere. Even though the initial magnetic field is vertical and uniform, magnetic field in the convection zone become turbulent, and occasionally a bundle of strong magnetic flux is driven by the upward convection flow and emerges in the photosphere. Such horizontal fields undergo magnetic reconnection with pre-existing magnetic field in the chromosphere (so called "canopy" field), and then emit high-frequency (>0.05mHz) waves into the corona. We discuss the possible role of these processes in heating, acceleration and turbulence of the corona and the solar wind.

  17. Magnetic coupling of the active chromosphere to the solar interior.

    NASA Technical Reports Server (NTRS)

    Foukal, P.

    1972-01-01

    Evidence is summarized to show that the configuration of e lines which governs the appearance of H-alpha fine structure in active regions is set mainly by motions in the subphotosphere where these lines are anchored. It is shown that H-alpha fine structure is directly coupled to a layer probably more than 5000 km below the photosphere, and little distortion of the strong fields is expected in the ines. The shorter rotation period of active regions observed by Howard and others (compared to the photospheric gas) reted as a result ofthis direct coupling of the strong field to a more rapidly rotating solar interior. The effects of dragging such a field through a photosphere of finite resistivity are briefly considered for features of various observed cross-sections.

  18. MORPHOLOGY AND DYNAMICS OF SOLAR PROMINENCES FROM 3D MHD SIMULATIONS

    SciTech Connect

    Terradas, J.; Soler, R.; Oliver, R.; Ballester, J. L.; Luna, M.

    2015-01-20

    In this paper we present a numerical study of the time evolution of solar prominences embedded in sheared magnetic arcades. The prominence is represented by a density enhancement in a background-stratified atmosphere and is connected to the photosphere through the magnetic field. By solving the ideal magnetohydrodynamic equations in three dimensions, we study the dynamics for a range of parameters representative of real prominences. Depending on the parameters considered, we find prominences that are suspended above the photosphere, i.e., detached prominences, but also configurations resembling curtain or hedgerow prominences whose material continuously connects to the photosphere. The plasma-β is an important parameter that determines the shape of the structure. In many cases magnetic Rayleigh-Taylor instabilities and oscillatory phenomena develop. Fingers and plumes are generated, affecting the whole prominence body and producing vertical structures in an essentially horizontal magnetic field. However, magnetic shear is able to reduce or even to suppress this instability.

  19. A multiwavelength campaign of active stars with intermediate rotation rates

    NASA Technical Reports Server (NTRS)

    Dempsey, Robert C.; Neff, James E.; ONeal, Douglas; Olah, Katalin

    1995-01-01

    Near-to-simultaneous ultraviolet and visual spectroscopy of two moderate nu(sin i) RS CVn systems, V815 Herculis (nu(sin i) = 27 km s(exp -1)) and LM Pegasi (nu(sin i) = 24 km s(exp -1)), are presented along with contemporaneous UBV (RI)(sub c) - band photometry. These data were used to probe inhomogeneities in the chromospheres and photospheres, and the possible relationship between them. Both systems show evidence for rotationally modulated chromospheric emission, generally varying in antiphase to the photospheric brightness. A weak flare was observed at Mg II for V815 Her. In the case of IM Peg, we use photometry and spectra to estimate temperatures, sizes, and locations of photospheric spots. Further constraints on the spot temperature is provided by TiO observations. For IM Peg, the anticorrelation between chromospheric emission and brightness is discussed in the context of a possible solar-like spot cycle.

  20. UV Spectra, Bombs, and the Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Judge, Philip G.

    2015-08-01

    A recent analysis of UV data from the Interface Region Imaging Spectrograph (IRIS) reports plasma “bombs” with temperatures near 8 × 104 K within the solar photosphere. This is a curious result, first because most bomb plasma pressures p (the largest reported case exceeds 103 dyn cm-2) fall well below photospheric pressures (\\gt 7× {10}3), and second, UV radiation cannot easily escape from the photosphere. In the present paper the IRIS data is independently analyzed. I find that the bombs arise from plasma originally at pressures between ≤ 80 and 800 dyne cm-2 before explosion, i.e., between ≥ 850 and 550 km above {τ }500=1. This places the phenomenon’s origin in the low-mid chromosphere or above. I suggest that bomb spectra are more compatible with Alfvénic turbulence than with bi-directional reconnection jets.

  1. Transverse oscillations and stability of prominences in a magnetic field dip

    NASA Astrophysics Data System (ADS)

    Kolotkov, D. Y.; Nisticò, G.; Nakariakov, V. M.

    2016-05-01

    Aims: We developed an analytical model of the global transverse oscillations and mechanical stability of a quiescent prominence in the magnetised environment with a magnetic field dip that accounts for the mirror current effect. Methods: The model is based on the interaction of line currents through the Lorentz force. Within this concept the prominence is treated as a straight current-carrying wire, and the magnetic dip is provided by two photospheric current sources. Results: Properties of both vertical and horizontal oscillations are determined by the value of the prominence current, its density and height above the photosphere, and the parameters of the magnetic dip. The prominence can be stable in both horizontal and vertical directions simultaneously when the prominence current dominates in the system and its height is less than the half-distance between the photospheric sources.

  2. Vertical gradients of sunspot magnetic fields

    NASA Astrophysics Data System (ADS)

    Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen, E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate, B. E.

    1983-04-01

    The results of a Solar Maximum Mission (SMM) guest investigation to determine the vertical gradients of sunspot magnetic fields for the first time from coordinated observations of photospheric and transition-region fields are described. Descriptions are given of both the photospheric vector field of a sunspot, derived from observations using the NASA Marshall Space Flight Center vector magnetograph, and of the line-of-sight component in the transition region, obtained from the SMM Ultraviolet Spectrometer and Polarimeter instrument. On the basis of these data, vertical gradients of the line-of-sight magnetic field component are calculated using three methods. It is found that the vertical gradient of Bz is lower than values from previous studies and that the transition-region field occurs at a height of approximately 4000-6000 km above the photosphere.

  3. Vertical gradients of sunspot magnetic fields

    NASA Technical Reports Server (NTRS)

    Hagyard, M. J.; Teuber, D.; West, E. A.; Tandberg-Hanssen, E.; Henze, W., Jr.; Beckers, J. M.; Bruner, M.; Hyder, C. L.; Woodgate, B. E.

    1983-01-01

    The results of a Solar Maximum Mission (SMM) guest investigation to determine the vertical gradients of sunspot magnetic fields for the first time from coordinated observations of photospheric and transition-region fields are described. Descriptions are given of both the photospheric vector field of a sunspot, derived from observations using the NASA Marshall Space Flight Center vector magnetograph, and of the line-of-sight component in the transition region, obtained from the SMM Ultraviolet Spectrometer and Polarimeter instrument. On the basis of these data, vertical gradients of the line-of-sight magnetic field component are calculated using three methods. It is found that the vertical gradient of Bz is lower than values from previous studies and that the transition-region field occurs at a height of approximately 4000-6000 km above the photosphere.

  4. Numerical simulation of flare energy build-up and release via Joule dissipation. [solar MHD model

    NASA Technical Reports Server (NTRS)

    Wu, S. T.; Bao, J. J.; Wang, J. F.

    1986-01-01

    A new numerical MHD model is developed to study the evolution of an active region due to photospheric converging motion, which leads to magnetic-energy buildup in the form of electric current. Because this new MHD model has incorporated finite conductivity, the energy conversion occurs from magnetic mode to thermal mode through Joule dissipation. In order to test the causality relationship between the occurrence of flare and photospheric motion, a multiple-pole configuration with neutral point is used. Using these results it is found that in addition to the converging motion, the initial magnetic-field configuration and the redistribution of the magnetic flux at photospheric level enhance the possibility for the development of a flare.

  5. The magnetic field of the BY Draconis flare star EQ Virginis

    NASA Technical Reports Server (NTRS)

    Saar, . H.; Linsky, J. L.; Beckers, J. M.

    1986-01-01

    High resolution, high S/N-ratio line profiles of the BY Draconis-type flare star EQ Vir obtained with the MMT are presently subjected to a novel Zeeman analysis procedure which includes radiative transfer effects and compensation for blends. A mean field of 2500 + or - 300 G covering 80 + or 15 percent of EQ Vir is determined. This constitutes the first positive detection of a magnetic field in a BY Draconis-type flare star, confirming that magnetic fields are present on these stars. The value of 2500 G obtained for the photospheric field strength is similar to the value derived by assuming equipartition of magnetic and thermal energy densities in the photosphere and scaling from the solar network fields, suggesting that equipartition may determine the mean field strength in the nonspotted portion of the flare star photosphere.

  6. Exploring the water and carbon monoxide shell around Betelgeuse with VLTI/AMBER

    NASA Astrophysics Data System (ADS)

    Montargès, M.; Kervella, P.; Perrin, G.; Ohnaka, K.

    2013-05-01

    We present the results of the analysis of our recent interferometric observations of Betelgeuse, using the AMBER instrument of the VLTI. Using the medium spectral resolution mode (R ~ 1500) we detected the presence of the water vapour and carbon monoxide (CO) molecules in the H and K bands. We also derived the photospheric angular diameter in the continuum. By analysing the depth of the molecular lines and the interferometric visibilities, we derived the column densities of the molecules, as well as the temperature and the size of the corresponding regions in the atmosphere of Betelgeuse (the MOLsphere) using a single shell model around the photosphere. Our results confirm the findings by Perrin et al. (2004) and Ohnaka et al. (2011) that the H2O and CO molecules are distributed around Betelgeuse in a MOLsphere extending to approximately 1.3 times the star's photospheric radius.

  7. A hillock and cloud model for faculae

    NASA Technical Reports Server (NTRS)

    Schatten, Kenneth H.; Mayr, Hans G.; Omidvar, Kazem; Maier, Eugene

    1986-01-01

    A hillock model is used here to explain facular contrasts, allowing faculae to emit more energy than the surrounding unmagnetized photosphere. For downflows, horizontal motions converge near the photosphere and many fibril flux tubes are drawn together to form a large dark area, the sunspot. For upflows, the motions diverge near the photosphere and fibril flux tubes are dispersed over a larger area associated with faculae. The upflows transport material and energy, resulting in hotter than normal temperatures, which in turn cause the gas to expand compared with its surroundings. Buoyancy thus causes a 'network' of patchy hillocks, clouds, or geysers to form which allows the sun to reradiate the energy deficit associated with sunspots by locally increasing the effective surface area of the sun beyond that of a sphere. The consequences of this model for the physical form of the facular manifestation, the appearance of faculae from earth, and the 'energy balance' in active regions are addressed.

  8. Formation and eruption of solar prominences

    NASA Technical Reports Server (NTRS)

    Van Ballegooijen, A. A.; Martens, P. C. H.

    1989-01-01

    A model for the magnetic field associated with solar prominences is considered. It is shown that flux cancellation at the neutral line of a sheared magnetic arcade leads to the formation of helical field lines which are capable, in principle, of supporting prominence plasma. A numerical method for the computation of force-free, canceling magnetic structures is presented. Starting from an initial potential field we prescribe the motions of magnetic footpoints at the photosphere, with reconnection occurring only at the neutral line. As more and more flux cancels, magnetic flux is transferred from the arcade field to the helical field. Results for a particular model of the photospheric motions are presented. The magnetic structure is found to be stable: the arcade field keeps the helical field tied down at the photosphere. The axis of the helical field moves to larger and larger height, suggestive of prominence eruption. These results suggest that prominence eruptions may be trigered by flux cancellation.

  9. An optical emission-line phase of the extreme carbon star IRC +30219

    NASA Technical Reports Server (NTRS)

    Cohen, M.

    1980-01-01

    Optical spectroscopic monitoring of the extreme carbon star IRC +30219 has revealed striking changes between 1977 and 1980. The stellar photosphere was barely visible in early 1979. There was an emission line spectrum consisting of H, forbidden O I, forbidden O II, forbidden N I, forbidden N II, forbidden S II, and He I. It is likely that these lines arose in a shocked region where recent stellar mass loss encountered the extensive circumstellar envelope. By late 1979, this emission-line spectrum had vanished, and the photosphere had reappeared. The weakening of the photospheric features in early 1979 was caused by increased attenuation of starlight and overlying thermal emission, both due to recently condensed hot dust grains.

  10. Amplitudes of MHD Waves in Sunspots

    NASA Astrophysics Data System (ADS)

    Norton, Aimee Ann; Cally, Paul; Baldner, Charles; Kleint, Lucia; Tarbell, Theodore D.; De Pontieu, Bart; Scherrer, Philip H.; Rajaguru, Paul

    2016-05-01

    The conversion of p-modes into MHD waves by strong magnetic fields occurs mainly in the sub-photospheric layers. The photospheric signatures of MHD waves are weak due to low amplitudes at the beta=1 equipartion level where mode-conversion occurs. We report on small amplitude oscillations observed in the photosphere with Hinode SOT/SP in which we analyze time series for sunspots ARs 12186 (11.10.2014) and 12434 (17.10.2015). No significant magnetic field oscillations are recovered in the umbra or penumbra in the ME inversion. However, periodicities in the inclination angle are found at the umbral/penumbral boundary with 5 minute periods. Upward propagating waves are indicated in the intensity signals correlated between HMI and AIA at different heights. We compare SP results with the oscillations observed in HMI data. Simultaneous IRIS data shows transition region brightening above the umbral core.

  11. Sunspot observations from the SOUP instrument on Spacelab 2

    NASA Technical Reports Server (NTRS)

    Shine, R. A.; Title, A. M.; Tarbell, T. D.; Acton, L.; Duncan, D.; Ferguson, S. H.; Finch, M.; Frank, Z.; Kelly, G.; Lindgren, R.

    1987-01-01

    A series of white light images obtained by the SOUP instrument on Spacelab 2 of active region 4682 on August 5, 1985 were analyzed in the area containing sunspots. Although the umbra of the spot is underexposed, the film is well exposed in the penumbral regions. These data were digitally processed to remove noise and to separate p-mode oscillations from low velocity material motions. The results of this preliminary investigation include: (1) proper motion measurements of a radial outflow in the photospheric granulation pattern just outside the penumbra; (2) discovery of occasional bright structures (streakers) that appear to be ejected outward from the penumbra; (3) broad dark clouds moving outward in the penumbra in addition to the well known bright penumbral grains moving inward; (4) apparent extensions and contractions of penumbral filaments over the photosphere; and (5) observation of a faint bubble or loop-like structure which seems to expand from two bright penumbral filaments into the photosphere.

  12. HIGHEST RESOLUTION OBSERVATIONS OF THE QUIETEST SUN

    SciTech Connect

    Goode, Philip R.; Yurchyshyn, Vasyl; Cao, Wenda; Abramenko, Valentyna; Andic, Aleksandra; Ahn, Kwangsu; Chae, Jongchul

    2010-05-01

    Highest resolution observations made with the new 1.6 m aperture solar telescope in Big Bear Solar Observatory during this time of historic inactivity on the Sun reveal new insights into the small-scale dynamics of the Sun's photosphere. The telescope's unprecedented resolution enabled us to observe that the smallest scale photospheric magnetic field seems to come in isolated points in the dark intergranular lanes, rather than the predicted continuous sheets confined to the lanes, and the unexpected longevity of the bright points implies a deeper anchoring than predicted. Further, we demonstrated for the first time that the photospheric plasma motion and magnetic fields are in equipartition over a wide dynamic range, and both cascade energy to ever-smaller scales according to classical Kolmogorov turbulence theory. Finally, we discovered tiny jet-like features originating in the dark lanes that surround the ubiquitous granules that characterize the solar surface.

  13. THERMAL RADIATION FROM GAMMA-RAY BURST JETS

    SciTech Connect

    Mizuta, Akira; Nagataki, Shigehiro; Aoi, Junichi

    2011-05-01

    In this study, the light curves and spectrum of the photospheric thermal radiation from ultrarelativistic gamma-ray burst (GRB) jets are calculated using two-dimensional relativistic hydrodynamic simulations of jets from a collapsar. As the jet advances, the density around the head of the jet decreases, and its Lorentz factor reaches as high as 200 at the photosphere and 400 inside the photosphere. For an on-axis observer, the photosphere appears concave due to the low density and high beaming factor of the jet. The luminosity varies because of the abrupt change in the position of the photosphere due to the internal structure of the jet. Comparing our results with GRB 090902B, the flux level of the thermal-like component is similar to our model, although the peak energy appears slightly higher (but still within a factor of two). From the comparison, we estimate that the bulk Lorentz factor of GRB 090902B is {Gamma} {approx} 2.4 x 10{sup 2}(r/10{sup 12} cm), where r is the radius of the photosphere. The spectrum for an on-axis observer is harder than that for an off-axis observer. There is a time lag of a few seconds for high energy bands in the light curve. This may be the reason for the delayed onset of GeV emission seen in GRB 080916C. The spectrum below the peak energy is a power law and the index is 2.3-2.6, which is softer than that of a single temperature Planck distribution but still harder than that of the typical value of the observed spectrum.

  14. Radial dependence of line profile variability in seven O9-B0.5 stars

    NASA Astrophysics Data System (ADS)

    Martins, F.; Marcolino, W.; Hillier, D. J.; Donati, J.-F.; Bouret, J.-C.

    2015-02-01

    Context. Massive stars show a variety of spectral variabilities: discrete absorption components in UV P-Cygni profiles, optical line profile variability, X-ray variability, and radial velocity modulations. Aims: Our goal is to study the spectral variability of single OB stars to better understand the relation between photospheric and wind variability. For that, we rely on high spectral resolution and on high signal-to-noise ratio optical spectra collected with the spectrograph NARVAL on the Télescope Bernard Lyot at Pic du Midi. Methods: We investigated the variability of twelve spectral lines by means of the temporal variance spectrum. The selected lines probe the radial structure of the atmosphere from the photosphere to the outer wind. We also performed a spectroscopic analysis with atmosphere models to derive the stellar and wind properties and to constrain the formation region of the selected lines. Results: We show that variability is observed in the wind lines of all bright giants and supergiants on a daily timescale. Lines formed in the photosphere are sometimes variable, sometimes not. The dwarf stars do not show any sign of variability. If variability is observed on a daily timescale, it can also (but not always) be observed on hourly timescales, albeit with lower amplitude. There is a very clear correlation between amplitude of the variability and fraction of the line formed in the wind. Strong anti-correlations between the different parts of the temporal variance spectrum are observed. Conclusions: Our results indicate that variability is stronger in lines formed in the wind. A link between photospheric and wind variability is not obvious from our study, since wind variability is observed regardless of the level of photospheric variability. Different photospheric lines also show different degrees of variability. Appendices are available in electronic form at http://www.aanda.org

  15. Period-colour and amplitude-colour relations in classical Cepheid variables - III. The Large Magellanic Cloud Cepheid models

    NASA Astrophysics Data System (ADS)

    Kanbur, Shashi M.; Ngeow, Chow-Choong

    2006-06-01

    Period-colour (PC) and amplitude-colour (AC) relations are studied for the Large Magellanic Cloud (LMC) Cepheids under the theoretical framework of the hydrogen ionization front (HIF)-photosphere interaction. LMC models are constructed with pulsation codes that include turbulent convection, and the properties of these models are studied at maximum, mean and minimum light. As with Galactic models, at maximum light the photosphere is located next to the HIF for the LMC models. However, very different behaviour is found at minimum light. The long-period (P > 10 d) LMC models imply that the photosphere is disengaged from the HIF at minimum light, similar to the Galactic models, but there are some indications that the photosphere is located near the HIF for the short-period (P < 10 d) LMC models. We also use the updated LMC data to derive empirical PC and AC relations at these phases. Our numerical models are broadly consistent with our theory and the observed data, though we discuss some caveats in the paper. We apply the idea of the HIF-photosphere interaction to explain recent suggestions that the LMC period-luminosity (PL) and PC relations are non-linear with a break at a period close to 10 d. Our empirical LMC PC and PL relations are also found to be non-linear with the F-test. Our explanation relies on the properties of the Saha ionization equation, the HIF-photosphere interaction and the way this interaction changes with the phase of pulsation and metallicity to produce the observed changes in the LMC PC and PL relations.

  16. First observation of bald patches in a filament channel and at a barb endpoint

    NASA Astrophysics Data System (ADS)

    López Ariste, A.; Aulanier, G.; Schmieder, B.; Sainz Dalda, A.

    2006-09-01

    The 3D magnetic field topology of solar filaments/prominences is strongly debated, because it is not directly measureable in the corona. Among various prominence models, several are consistent with many observations, but their related topologies are very different. We conduct observations to address this paradigm. We measure the photospheric vector magnetic field in several small flux concentrations surrounding a filament observed far from disc center. Our objective is to test for the presence/absence of magnetic dips around/below the filament body/barb, which is a strong constraint on prominence models, and that is still untested by observations. Our observations are performed with the THEMIS/MTR instrument. The four Stokes parameters are extracted, from which the vector magnetic fields are calculated using a PCA inversion. The resulting vector fields are then deprojected onto the photospheric plane. The 180° ambiguity is then solved by selecting the only solution that matches filament chirality rules. Considering the weakness of the resulting magnetic fields, a careful analysis of the inversion procedure and its error bars was performed, to avoid over-interpretation of noisy or ambiguous Stokes profiles. Thanks to the simultaneous multi-wavelength THEMIS observations, the vector field maps are coaligned with the Hα image of the filament. By definition, photospheric dips are identifiable where the horizontal component of the magnetic field points from a negative toward a positive polarity. Among six bipolar regions analyzed in the filament channel, four at least display photospheric magnetic dips, i.e. bald patches. For barbs, the topology of the endpoint is that of a bald patch located next to a parasitic polarity, not of an arcade pointing within the polarity. The observed magnetic field topology in the photosphere tends to support models of prominence based on magnetic dips located within weakly twisted flux tubes. Their underlying and lateral extensions form

  17. Total solar irradiance measurements by ERB/Nimbus-7 - A review of nine years

    NASA Technical Reports Server (NTRS)

    Hickey, John R.; Alton, Bradley M.; Kyle, H. Lee; Hoyt, Douglas

    1988-01-01

    The total solar irradiance measurements made by the cavity sensor of the Earth Radiation Budget experiment on the Nimbus-7 spacecraft have detected the sunspot-blocking effect, established the downward trend of the declining solar cycle, and appear to be confirming an upturn in irradiance at the outset of the new cycle. Studies of the measurements' frequency spectra have advanced the interest in helioseismology or mode analysis, and studies of photospheric activity have advanced through the modeling of the sunspot blocking and photospheric brightening vs measured irradiance.

  18. Investigation of the shell stars omicron and theta Per, and of the eclipsing binary beta Lyr

    NASA Technical Reports Server (NTRS)

    Plavec, M.

    1975-01-01

    All three stars showed rather complicated spectra, which require a very detailed spectroscopic analysis. The far UV spectrum of Beta Lyrae is clearly peculiar, with a multitude of emission lines not observed on any other star so far scanned with Copernicus. This made this star at once the most interesting and also, in a sense, easier to study. The other two stars display a spectrum rich in absorption lines, some of them being fairly broad (as expected for photospheric lines of rapidly rotating objects), some sharp. The later were clearly non-photospheric lines. An attempt was made to distinguish the circumstellar from the interstellar components.

  19. Numerical Simulations of Nanoflares: PDFs of Released Energy, Waiting Times and Quiet- Sun Magnetic Field Elements

    NASA Astrophysics Data System (ADS)

    Egidi, A.; Viticchie`, B.; Berrilli, F.; Del Moro, D.

    2007-12-01

    A numerical model for nanoflares is proposed to describe probability density functions (PDF) and waiting time statistics of the emitted magnetic energy and to guess PDF of quiet-Sun magnetic field strength. In the simulation, footpoints of reconnecting magnetic loops are advected by photospheric flows computed via a n-body algorithm. The model simulates a system whose behavior is characterized by small scale (i.e., granulation) flows that interact to develop large organization scales (i.e., mesogranulation). Such spatio-temporal correlated flows, incessantly supply , remove and convey the passive magnetic footpoints onto the photospheric surface, triggering reconnections and magnetic field reconfigurations.

  20. Magnetic probing of the solar interior

    NASA Technical Reports Server (NTRS)

    Benton, E. R.; Estes, R. H.

    1985-01-01

    The magnetic field patterns in the region beneath the solar photosphere is determined. An approximate method for downward extrapolation of line of sight magnetic field measurements taken at the solar photosphere was developed. It utilizes the mean field theory of electromagnetism in a form thought to be appropriate for the solar convection zone. A way to test that theory is proposed. The straightforward application of the lowest order theory with the complete model fit to these data does not indicate the existence of any reasonable depth at which flux conservation is achieved.

  1. Backscatter of hard X-rays in the solar atmosphere. [Calculating the reflectance of solar x ray emission

    NASA Technical Reports Server (NTRS)

    Bai, T.; Ramaty, R.

    1977-01-01

    The solar photosphere backscatters a substantial fraction of the hard X rays from solar flares incident upon it. This reflection was studied using a Monte Carlo simulation which takes into account Compton scattering and photo-electric absorption. Both isotropic and anisotropic X ray sources are considered. The bremsstrahlung from an anisotropic distribution of electrons are evaluated. By taking the reflection into account, the inconsistency is removed between recent observational data regarding the center-to-limb variation of solar X ray emission and the predictions of models in which accelerated electrons are moving down toward the photosphere.

  2. Solar abundances and 3D model atmospheres

    NASA Astrophysics Data System (ADS)

    Ludwig, Hans-Günter; Caffau, Elisabetta; Steffen, Matthias; Bonifacio, Piercarlo; Freytag, Bernd; Cayrel, Roger

    2010-03-01

    We present solar photospheric abundances for 12 elements from optical and near-infrared spectroscopy. The abundance analysis was conducted employing 3D hydrodynamical (CO5BOLD) as well as standard 1D hydrostatic model atmospheres. We compare our results to others with emphasis on discrepancies and still lingering problems, in particular exemplified by the pivotal abundance of oxygen. We argue that the thermal structure of the lower solar photosphere is very well represented by our 3D model. We obtain an excellent match of the observed center-to-limb variation of the line-blanketed continuum intensity, also at wavelengths shortward of the Balmer jump.

  3. NEW RARE EARTH ELEMENT ABUNDANCE DISTRIBUTIONS FOR THE SUN AND FIVE r-PROCESS-RICH VERY METAL-POOR STARS

    SciTech Connect

    Sneden, Christopher; Lawler, James E.; Den Hartog, Elizabeth A.; Cowan, John J.; Ivans, Inese I. E-mail: jelawler@wisc.edu E-mail: cowan@nhn.ou.edu

    2009-05-15

    We have derived new abundances of the rare earth elements Pr, Dy, Tm, Yb, and Lu for the solar photosphere and for five very metal-poor, neutron-capture r-process-rich giant stars. The photospheric values for all five elements are in good agreement with meteoritic abundances. For the low-metallicity sample, these abundances have been combined with new Ce abundances from a companion paper, and reconsideration of a few other elements in individual stars, to produce internally consistent Ba, rare earth, and Hf (56 {<=} Z {<=} 72) element distributions. These have been used in a critical comparison between stellar and solar r-process abundance mixes.

  4. Elemental composition of solar energetic particles in 1977 and 1978

    NASA Technical Reports Server (NTRS)

    Cook, W. R.; Stone, E. C.; Vogt, R. E.; Trainor, J. H.; Webber, W. R.

    1979-01-01

    The elemental composition of energetic nuclei from seven major solar flare events were measured wit the cosmic ray detector systems aboard the Voyager 1 and 2 spacecraft. The energetic nuclei abundances differ significantly from those of photospheric material. They are enhanced relative to the photonsphere by a factor which is the ratio of abundance of an energetic nuclei species (relative to oxygen) over the corresponding abundance of photospheric material. This factor is common to all events and has a nonmonochromatic characteristic dependence on nuclear charge. This factor is roughly ordered by first ionization potential into two groups of elements, metallics and volatiles.

  5. Heating of the corona by magnetic singularities

    NASA Technical Reports Server (NTRS)

    Antiochos, Spiro K.

    1990-01-01

    Theoretical models of current-sheet formation and magnetic heating in the solar corona are examined analytically. The role of photospheric connectivity in determining the topology of the coronal magnetic field and its equilibrium properties is explored; nonequilibrium models of current-sheet formation (assuming an initially well connected field) are described; and particular attention is given to models with discontinuous connectivity, where magnetic singularities arise from smooth footpoint motions. It is shown that current sheets arise from connectivities in which the photospheric flux structure is complex, with three or more polarity regions and a magnetic null point within the corona.

  6. Atmospheric structure and mass loss in Miras

    NASA Astrophysics Data System (ADS)

    Hinkle, Kenneth H.; Lebzelter, Thomas; Straniero, Oscar

    2016-07-01

    The cool molecular region of late-type stellar atmospheres, the ‘MOLsphere’ located between the photosphere and expanding circumstellar shell, is explored by using time series of near-IR spectra of one large amplitude AGB (Mira) variable. The ∼⃒1400 K MOLsphere of the Mira R Cas is shown to undergo large amplitude velocity changes that are aperiodic with time scales many times longer than the photospheric pulsation. The mass of the MOLsphere is ∼⃒3×10‑5 M⊙. Initial analysis suggests that MOLsphere is thin compared to the stellar radius.

  7. Origin of the warped heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Wilcox, J. M.; Hoeksema, J. T.; Scherrer, P. H.

    1980-08-01

    The warped heliospheric current sheet for early 1976 is calculated from the observed photospheric magnetic field by a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity for early 1976 obtained at several locations in the heliosphere by Helios 1, Helios 2, Pioneer 11, and at the earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large-scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field and that 'ballerina skirt' effects may add small scale ripples.

  8. The origin of the warped heliospheric current sheet

    NASA Astrophysics Data System (ADS)

    Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.

    1980-03-01

    The warped heliospheric current sheet in early 1976 was calculated from the observed photospheric magnetic field using a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity in early 1976 obtained at several locations in the heliosphere at Helios 1, Helios 2, Pioneer 11 and Earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field, and that "ballerina skirt" effects may add small scale ripples.

  9. The origin of the warped heliospheric current sheet

    NASA Technical Reports Server (NTRS)

    Wilcox, J. M.; Scherrer, P. H.; Hoeksema, J. T.

    1980-01-01

    The warped heliospheric current sheet in early 1976 was calculated from the observed photospheric magnetic field using a potential field method. Comparisons with measurements of the interplanetary magnetic field polarity in early 1976 obtained at several locations in the heliosphere at Helios 1, Helios 2, Pioneer 11 and Earth show a rather detailed agreement between the computed current sheet and the observations. It appears that the large scale structure of the warped heliospheric current sheet is determined by the structure of the photospheric magnetic field, and that "ballerina skirt" effects may add small scale ripples.

  10. Comments on Magnetic Reconnection Models of Canceling Magnetic Features on the Sun

    NASA Astrophysics Data System (ADS)

    Litvinenko, Yuri E.

    2015-06-01

    Data analysis and theoretical arguments support magnetic reconnection in a chromospheric current sheet as the mechanism of the observed photospheric magnetic flux cancellation on the Sun. Flux pile-up reconnection in a Sweet-Parker current sheet can explain the observed properties of canceling mag-netic features, including the speeds of canceling magnetic fragments, the magnetic uxes in the fragments, and the flux cancellation rates, inferred from the data. It is discussed how more realistic chromospheric reconnection models can be developed by relaxing the assumptions of a negligible current sheet curvature and a constant height of the reconnection site above the photosphere.

  11. On the effects of magnetic field line topology on the energy propagation in the solar corona

    NASA Astrophysics Data System (ADS)

    Candelaresi, Simon

    2016-05-01

    Using the MHD approximation, we study the propagation of energy from photospheric footpoint motions into the corona. Our model consists of a magnetic carpet with closed and open magnetic field lines. Magnetic null points are present close at the surface. The applied photospheric driver twists the field into a topologically non-trivial configuration which leads to reconnection and a change in field line topology. Prior to this event, the energy propagation into the corona is largely inhibited due to closed field lines. After such events the energy is free to propagate into the corona.

  12. Solar corona top heating

    NASA Astrophysics Data System (ADS)

    Molotkov, I. A.; Ryabova, N. A.

    2016-05-01

    The solar magnetic field fragmentation into thin magnetic tubes above the photosphere makes it possible to transform and factorize MHD equations analytically and to obtain explicit expressions for Alfvén and magnetosonic fields. A physical model that enables an explanation of the effect of strong heating of the solar chromosphere and corona has been proposed. This model makes it possible to estimate analytically a powerful Alfvén disturbance entering the chromosphere due to convective motions of the photosphere and a thermal release due to a three-wave interaction within the chromosphere.

  13. ON THE PROPAGATION OF p-MODES INTO THE SOLAR CHROMOSPHERE

    SciTech Connect

    De Wijn, A. G.; McIntosh, S. W.; De Pontieu, B.

    2009-09-10

    We employ tomographic observations of a small region of plage to study the propagation of waves from the solar photosphere to the chromosphere using a Fourier phase-difference analysis. Our results show the expected vertical propagation for waves with periods of 3 minutes. Waves with 5 minute periods, i.e., above the acoustic cutoff period, are found to propagate only at the periphery of the plage, and only in the direction in which the field can be reasonably expected to expand. We conclude that field inclination is critically important in the leakage of p-mode oscillations from the photosphere into the chromosphere.

  14. The quiet sun

    NASA Technical Reports Server (NTRS)

    Gibson, E. G.

    1973-01-01

    An up-to-date textbook of solar physics is presented. The solar structure and processes, and the interior are described along with the photosphere, the chromosphere, and the corona. The strongest Fraunhofer lines, visible coronal lines, and coronal UV, XUV, and X-ray lines are listed.

  15. Helium emission features in the D3 line in the lower and middle solar chromosphere.

    NASA Astrophysics Data System (ADS)

    Akimov, L. A.; Belkina, I. L.; Dyatel, N. P.

    The height distribution of the surface brightness of the chromosphere obtained from cinematographic eclipse observations is analyzed. It is shown that the two-peak character of the distribution with a maximum near the photosphere is real for the active chromosphere. A qualitative explanation of this phenomenon is proposed.

  16. A Driving Mechanism for Flux-Rope Coronal Mass Ejections

    NASA Astrophysics Data System (ADS)

    Krall, J.; Chen, J.

    2001-05-01

    Numerous quantitative comparisons[1-4] of observational data to a flux-rope model of coronal mass ejections (CMEs) show that flux-rope CMEs are common events with specific geometrical and dynamical properties. In the model, a CME corresponds to a flux rope with foot points that remain anchored in the photosphere as it erupts. Comparisons of model results for various drive mechanisms[5] to observed CMEs show that flux injection (an increase in poloidal flux) provides the best match. With flux-injection, the CME is driven during and after the onset of eruption. Thus, acceleration time-scales are on the order of hours in agreement with observed CMEs, many or which are neither ``quasi-static'' nor ``impulsive.'' This contrasts with the photospheric-shearing paradigm in which there is a loss of equilibrium resulting in a characteristic velocity profile that does not match the observations in detail. Photospheric signatures of eruption are also studied; the model predicts no significant ``twisting up'' of the magnetic field at the photosphere during flux injection. [1] Chen, J. et al., 1997, ApJ, 490, L191 [2] Wood, B.E. et al., 1998, ApJ, 512, 484. [3] Chen, J. et al., 2000, ApJ, 533, 481 [4] Krall, J. et al., 2001, ApJ, submitted [5] Krall, J. et al., 2000, ApJ, 539, 964 Work supported by ONR.

  17. VizieR Online Data Catalog: T Tauri star population in Lupus (Galli+, 2015)

    NASA Astrophysics Data System (ADS)

    Galli, P. A. B.; Bertout, C.; Teixeira, R.; Ducourant, C.

    2015-11-01

    The newly derived individual parallaxes from our previous kinematic study of the Lupus association have been used in this paper to determine the photospheric luminosities and refine the masses and ages of the TTS population in this SFR. We investigated the mass and age distributions of CTTSs and WTTSs in the Lupus association. (1 data file).

  18. Elemental composition of solar energetic particles. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Cook, W. R., III

    1981-01-01

    The Low Energy Telescopes on the Voyager spacecraft are used to measure the elemental composition (2 or = Z or = 28) and energy spectra (5 to 15 MeV/nucleon) of solar energetic particles (SEPs) in seven large flare events. Four flare events are selected which have SEP abundance ratios approximately independent of energy/nucleon. The abundances for these events are compared from flare to flare and are compared to solar abundances from other sources: spectroscopy of the photosphere and corona, and solar wind measurements. The four flare average SEP composition is significantly different from the solar composition determined by photospheric spectroscopy. The average SEP composition is in agreement with solar wind abundance results and with a number of recent coronal abundance measurements. The evidence for a common depletion of oxygen in SEPs, the corona and the solar wind relative to the photosphere suggest that the SEPs originate in the corona and that both the SEPs and solar wind sample a coronal composition which is significantly and persistently different from that of the photosphere.

  19. Report on carbon and nitrogen abundance studies

    NASA Technical Reports Server (NTRS)

    Boehm-Vitense, Erika

    1991-01-01

    The aim of the proposal was to determine the nitrogen to carbon abundance ratios from transition layer lines in stars with different T(sub eff) and luminosities. The equations which give the surface emission line fluxes and the measured ratio of the NV to CIV emission line fluxes are presented and explained. The abundance results are compared with those of photospheric abundance studies for stars in common with the photospheric investigations. The results show that the analyses are at least as accurate as the photospheric determinations. These studies can be extended to F and early G stars for which photospheric abundance determinations for giants are hard to do because molecular bands become too weak. The abundance determination in the context of stellar evolution is addressed. The N/C abundance ratio increases steeply at the point of evolution for which the convection zone reaches deepest. Looking at the evolution of the rotation velocities v sin i, a steep decrease in v sin i is related to the increasing depth of the convection zone. It is concluded that the decrease in v sin i for T(sub eff) less than or approximately = 5800 K is most probably due to the rearrangement of the angular momentum in the stars due to deep convective mixing. It appears that the convection zone is rotating with nearly depth independent angular momentum. Other research results and ongoing projects are discussed.

  20. Nonlinear force-free field modeling of the solar magnetic carpet and comparison with SDO/HMI and Sunrise/IMAX observations

    SciTech Connect

    Chitta, L. P.; Kariyappa, R.; Van Ballegooijen, A. A.; DeLuca, E. E.; Solanki, S. K.

    2014-10-01

    In the quiet solar photosphere, the mixed polarity fields form a magnetic carpet that continuously evolves due to dynamical interaction between the convective motions and magnetic field. This interplay is a viable source to heat the solar atmosphere. In this work, we used the line-of-sight (LOS) magnetograms obtained from the Helioseismic and Magnetic Imager on the Solar Dynamics Observatory, and the Imaging Magnetograph eXperiment instrument on the Sunrise balloon-borne observatory, as time-dependent lower boundary conditions, to study the evolution of the coronal magnetic field. We use a magneto-frictional relaxation method, including hyperdiffusion, to produce a time series of three-dimensional nonlinear force-free fields from a sequence of photospheric LOS magnetograms. Vertical flows are added up to a height of 0.7 Mm in the modeling to simulate the non-force-freeness at the photosphere-chromosphere layers. Among the derived quantities, we study the spatial and temporal variations of the energy dissipation rate and energy flux. Our results show that the energy deposited in the solar atmosphere is concentrated within 2 Mm of the photosphere and there is not sufficient energy flux at the base of the corona to cover radiative and conductive losses. Possible reasons and implications are discussed. Better observational constraints of the magnetic field in the chromosphere are crucial to understand the role of the magnetic carpet in coronal heating.

  1. Observational evidence for buffeting-induced kink waves in solar magnetic elements

    NASA Astrophysics Data System (ADS)

    Stangalini, M.; Consolini, G.; Berrilli, F.; De Michelis, P.; Tozzi, R.

    2014-09-01

    The role of diffuse photospheric magnetic elements in the energy budget of the upper layers of the Sun's atmosphere has been the recent subject of many studies. This was made possible by the availability of high temporal and spatial resolution observations of the solar photosphere, allowing large numbers of magnetic elements to be tracked to study their dynamics. In this work we exploit a long temporal series of seeing-free magnetograms of the solar photosphere to study the effect of the turbulent convection on the excitation of kink oscillations in magnetic elements. We make use of the empirical mode decomposition technique in order to study the transverse oscillations of several magnetic flux tubes. This technique permits analysis of non-stationary time series like those associated to the horizontal velocities of these flux tubes, which are continuously advected and dispersed by granular flows. Our primary findings reveal the excitation of low frequency modes of kink oscillations, which are subharmonics of a fundamental mode with a 7.6 ± 0.2 min periodicity. These results constitute observational proof of the excitation of kink waves by the buffeting of the convection cells in the solar photosphere, and they are discussed in light of their possible role in the energy budget of the upper Sun's atmosphere.

  2. An Improved Optical Spectrum and New Model Fits of the Likely Brown Dwarf GD 165B

    NASA Technical Reports Server (NTRS)

    Kirkpatrick, J.; Allard, F.; Bida, T.; Zuckerman, B.; Becklin, E.; Chabrier, G.; Baraffe, I.

    1999-01-01

    Long thought by some researchers to be an oddity, GD 165B has instead proven to be the first example of a class of very cool objects (the L dwarfs) which, due to dust formation in their photosphere, lack the dominant bands of TiO seen in warmer M dwarfs.

  3. Magnetic Helicity and the Solar Dynamo

    NASA Technical Reports Server (NTRS)

    Canfield, Richard C.

    1997-01-01

    The objective of this investigation is to open a new window into the solar dynamo, convection, and magnetic reconnection through measurement of the helicity density of magnetic fields in the photosphere and tracing of large-scale patterns of magnetic helicity in the corona.

  4. Back-reaction on the Solar Surface Associated with Coronal Magnetic Restructuring in Solar Eruptions

    NASA Astrophysics Data System (ADS)

    Wang, Haimin; Liu, C.

    2010-05-01

    Solar eruptions have been understood as the result of magnetic reconnection in solar corona, therefore most models of flares and coronal mass ejections assume that photospheric magnetic fields are anchored and do not have rapid, irreversible changes associated with the eruptions. Recently, we note the work by Hudson, Fisher and Welsch (2008, ASP, 383, 221), who quantitatively assessed the back reaction on the photosphere and solar interior by the coronal field evolution required to release flare energy, and made the prediction that after flares, the photospheric magnetic fields turn to a more horizontal state. Here we summarize our studies of several papers and a few new events that describe changes of magnetic fields associated with flares. For the events that vector magnetograms are available, we indeed find a rapid increase of transverse magnetic fields near the polarity inversion line associated with large flares. For the other events that only line-of-sight magnetograms are present, we always observe that limb-ward flux increases while disk-ward flux decreases rapidly and irreversibly associated with flares, which also indirectly supports the theory of Hudson, Fisher and Welsch. Finally, we discuss the possible relationship between the rapid changes of photospheric magnetic fields and the excitation of seismic waves, the so-called sunquakes (Kosovichev and Zharkova, 1998, Nature, 393, 317).

  5. Next space solar observatory SOLAR-C: mission instruments and science objectives

    NASA Astrophysics Data System (ADS)

    Katsukawa, Y.; Watanabe, T.; Hara, H.; Ichimoto, K.; Kubo, M.; Kusano, K.; Sakao, T.; Shimizu, T.; Suematsu, Y.; Tsuneta, S.

    2012-12-01

    SOLAR-C, the fourth space solar mission in Japan, is under study with a launch target of fiscal year 2018. A key concept of the mission is to view the photosphere, chromosphere, and corona as one system coupled by magnetic fields along with resolving the size scale of fundamental physical processes connecting these atmospheric layers. It is especially important to study magnetic structure in the chromosphere as an interface layer between the photosphere and the corona. The SOLAR-C satellite is equipped with three telescopes, the Solar UV-Visible-IR Telescope (SUVIT), the EUV/FUV High Throughput Spectroscopic Telescope (EUVS/LEMUR), and the X-ray Imaging Telescope (XIT). Observations with SUVIT of photospheric and chromospheric magnetic fields make it possible to infer three dimensional magnetic structure extending from the photosphere to the chromosphere and corona.This helps to identify magnetic structures causing magnetic reconnection, and clarify how waves are propagated, reflected, and dissipated. Phenomena indicative of or byproducts of magnetic reconnection, such as flows and shocks, are to be captured by SUVIT and by spectroscopic observations using EUVS/LEMUR, while XIT observes rapid changes in temperature distribution of plasma heated by shock waves.

  6. The topological description of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Berger, Mitchell A.

    1986-01-01

    Determining the structure and behavior of solar coronal magnetic fields is a central problem in solar physics. At the photosphere, the field is believed to be strongly localized into discrete flux tubes. After providing a rigorous definition of field topology, how the topology of a finite collection of flux tubes may be classified is discussed.

  7. The evolution of line-tied coronal arcades including a converging footpoint motion

    NASA Technical Reports Server (NTRS)

    Inhester, B.; Birn, J.; Hesse, M.

    1992-01-01

    It has been demonstrated in the past that single, 2D coronal arcades are very unlikely driven unstable by a simple shear of the photospheric footpoints of the magnetic field lines. By means of 2D, time-dependent MHD simulations, evidence is presented that a resistive instability can result if in addition to the footpoint shear a slow motion of the footpoints toward the photospheric neutral line is included. The photospheric footpoint velocity in this model is nonsingular and the shear dominates everywhere. Starting from a planar potential field geometry for the arcade, it is found that after some time a current sheet is formed which is unstable with respect to the tearing instability. The time of its onset scales with the logarithm of the magnetic diffusivity assumed in the calculation. In its nonlinear phase, a quasi-stationary situation arises in the vicinity of the x-line with an almost constant reconnection rate. The height of the x-line above the photosphere and the distance of the separatrix footpoints remain almost constant in this phase, while the helical flux tube, formed above the neutral line, continuously grows in size.

  8. Optical Spectropolarimetry and Asphericity of the Type Ic SN 2007gr

    NASA Astrophysics Data System (ADS)

    Tanaka, Masaomi; Kawabata, Koji S.; Maeda, Keiichi; Hattori, Takashi; Nomoto, Ken'ichi

    2008-12-01

    We present an optical spectropolarimetric observation of the Type Ic supernova (SN) 2007gr made with the Subaru Telescope at 21 days after maximum brightness (~37 days after the explosion). Nonzero polarization as high as ~3% is observed at the absorption feature of the Ca II IR triplet. The polarization of the continuum light is ~0.5% if we estimate the interstellar polarization (ISP) component by assuming that the continuum polarization has a single polarization angle. This suggests that the axis ratio of the SN photosphere projected on the sky differs from unity by ~10%. The polarization angle at the Ca II absorption is almost aligned with that of the continuum light. These features may be understood in the context of a model in which a bipolar explosion with an oblate photosphere is being viewed from a slightly off-axis direction and explosively synthesized Ca near the polar region obscures the light that originates around the minor axis of the SN photosphere. Given the uncertainty in the ISP, however, the polarization data could also be interpreted with a model with an almost spherically symmetric photosphere and a clumpy Ca II distribution. Based on data collected at the Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  9. The OVI Issue

    NASA Astrophysics Data System (ADS)

    Barstow, M. A.; Boyce, D. D.; Welsh, B. Y.; Lallement, R.; Barstow, J. K.

    2009-08-01

    We report the results of a search for O VI absorption in the spectra of ~100 hot DA white dwarfs observed by the FUSE satellite. We have carried out a detailed analysis of the radial velocities of interstellar and (where present) stellar absorption lines for the entire sample of stars. In many cases, the velocity differences between the interstellar and photospheric components are below the resolution of the FUSE spectrographs. However, in a significant number of cases the interstellar and photospheric contributions can be separated. Within this group, for those stars where O VI is positively detected, it is possible to unambiguously determine the nature of the O VI component (interstellar or photospheric). In the majority of stars where we find O VI absorption lines, the material is clearly associated with the stellar photosphere and not the interstellar medium. There are a number of lines-of-sight where the gas is interstellar in nature. Mostly these stars are located beyond the boundaries of the local cavity or are at high galactic latitude. Hence, it appears that the Local Bubble contains little hot gas. That component responsible for the O VI absorption may reside at the interface between the cavity and surrounding medium or in that medium itself and is also associated with the soft X-ray background.

  10. Observations of sunspot umbral velocity oscillations.

    NASA Technical Reports Server (NTRS)

    Bhatnagar, A.; Livingston, W. C.; Harvey, J. W.

    1972-01-01

    Review of sunspot umbral velocity measurements obtained free from any cross talk introduced by photospheric and penumbral scattered light by using lines formed only in the sunspot umbrae and showing no Zeeman effect. The maximum peak-to-peak amplitude of the umbral oscillatory velocity component is found to be of the order of 0.5 km per sec.

  11. Imaging and Processing Images of the Solar Corona

    NASA Astrophysics Data System (ADS)

    Espenak, Fred

    Of all astronomical phenomena visible to the naked eye, none is as spectacular, or as fleeting, as a total eclipse of the Sun. For a few brief minutes, the Moon blocks the Sun's blindingly bright photosphere to reveal the ethereal solar corona. This gossamer halo, forming the outer atmosphere of the Sun, can only be seen in the eerie twilight brought on by totality.

  12. The impact of surface dynamo magnetic fields on the chemical abundance determination

    NASA Astrophysics Data System (ADS)

    Shchukina, Nataliya G.; Sukhorukov, Andrii V.; Bueno, Javier Trujillo

    2015-10-01

    The solar abundances of Fe and of the CNO elements play an important role in addressing a number of important issues such as the formation, structure, and evolution of the Sun and the solar system, the origin of the chemical elements, and the evolution of stars and galaxies. Despite the large number of papers published on this issue, debates about the solar abundances of these elements continue. The aim of the present investigation is to quantify the impact of photospheric magnetic fields on the determination of the solar chemical abundances. To this end, we used two 3D snapshot models of the quiet solar photosphere with a different magnetization taken from recent magneto-convection simulations with small-scale dynamo action. Using such 3D models we have carried out spectral synthesis for a large set of Fei, Ci, Ni, and Oi lines, in order to derive abundance corrections caused by the magnetic, Zeeman broadening of the intensity profiles and the magnetically induced changes of the photospheric temperature structure. We find that if the magnetism of the quiet solar photosphere is mainly produced by a small-scale dynamo, then its impact on the determination of the abundances of iron, carbon, nitrogen and oxygen is negligible.

  13. Doppler observations of solar rotation

    NASA Technical Reports Server (NTRS)

    Scherrer, P. H.; Wilcox, J. M.

    1980-01-01

    Daily observations of the photospheric equatorial rotation rate using the Doppler effect are made at the Stanford Solar Observatory. These observations show no variations in the rotation rate that exceed the observational error of about 1%. The average rotation rate is indistinguishable from that of sunspots and large-scale magnetic field structures.

  14. Doppler observations of solar rotation

    NASA Technical Reports Server (NTRS)

    Scherrer, P. H.

    1980-01-01

    Daily observations of the photospheric equatorial rotation rate using the Doppler effect mode at the Sanford Solar Observatory are presented. These observations show no variations in the rotation rate that exceed the observational error of about one percent. The average rotation rate is indistinguishable from that of sunspots and large scale magnetic field structures.

  15. Total Solar Irradiance Variability: A Review

    NASA Technical Reports Server (NTRS)

    Pap, Judit M.

    1996-01-01

    Observations of total solar irradiance from space within the last two decaades convinced the skeptics that total irradiance varies over a wide range of periodicities: from minutes to the 11-year solar activity cycle. Analyses based on these space-borne observations have demonstrated that the irradiance variations are directly related to changes at the photosphere and the solar interior.

  16. Dynamics of the solar granulation. IX. A global approach

    NASA Astrophysics Data System (ADS)

    Nesis, A.; Hammer, R.; Roth, M.; Schleicher, H.

    2006-06-01

    Based on a series of spectrograms taken with the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide (Tenerife), we study the temporal evolution of granular dynamics and energy transport in the photospheric layers. We consider the ensemble of the granules cut by the spectrograph slit, modulated by wave motion, as a complex system. We describe this ensemble by the rms of the fluctuations of the observables along the slit: continuum intensity I, gas velocity v measured from line center Doppler shifts with respect to the mean profile, and line width w. The history of the rms of the observables v and w reflects the dynamical change of the system over the 20 min observation time. We find a burst-like change for both observables. However, the cross-correlation between I and v remains virtually constant, with the exception of two gaps. Using six lines of different strength we measure the rms of v in the deep photospheric layers. On the basis of this v variation we derive an upper limit of the kinetic energy flux as a function of height in the photosphere for different times during the observation. The shape of the variation with height is constant over time. A limit for the convective enthalpy flux is calculated using the temperature variations of our earlier models. Its shape remains the same over time. Taken together, these results quantify the different roles that the lower and higher photospheric layers play in the energetics of convective overshoot.

  17. The evolution of coronal magnetic fields

    NASA Technical Reports Server (NTRS)

    Priest, E. R.; Forbes, T. G.

    1990-01-01

    Slow photospheric motions can produce flow speeds in the corona which are fast enough to violate quasi-static evolution. Therefore, high-speed flows observed in the corona are not necessarily due to a loss of equilibrium or stability. This paper presents an example where the flow speed increases indefinitely with height while the coronal magnetic energy increases quadratically with time.

  18. Multi-Satellite Attitude Prediction program/Orbiting Solar Observatory-8 (MSAP/OSO-8) operating guide

    NASA Technical Reports Server (NTRS)

    Tate, V. H.; Wyckoff, D. C.; Decicco, J. M.

    1976-01-01

    The sun's lower corona and chromosphere and their interaction in the X-ray and ultraviolet (UV) spectral regions were investigated to better understand the transport of energy from the photosphere to the corona. The interaction between the solar electromagnetic and particle radiation and the earth's environment was studied and the background component of cosmic X-rays was discussed.

  19. Motions and oscillations in a filament preceding its eruption

    NASA Astrophysics Data System (ADS)

    Mashnich, G. P.; Bashkirtsev, V. S.

    2016-02-01

    The Doppler motions in a filament and the underlying photosphere over the several days before its eruption are analyzed. A large filament in the northern hemisphere near the central meridian observed from August 31-September 2, 2014 erupted on September 2, 2014. The filament lost the bulk of its mass as a result of its eruption, and the process of its reconstruction had begun a day later. Observations of this filament in a spectral range encompassing the Hβ λ 486.1 nm (chromospheric) and Fe I λ 485.9 nm (photospheric) lines were carried out on the Horizontal Solar Telescope of the Sayan Solar Observatory on August 31-September 2, 2014. Analysis of the Doppler motions in and beneath the filament yielded the following results. Strong rotational motions were present in the filament over a prolonged period (the entire three days of observations). The coincidence of the steady-state motions of the photosphere and filament was disrupted at the moment of destabilization of the filament by the emergence of new magnetic flux. Short-period (about five-minute) photospheric oscillationswith a train-like character arose in filament from time to time several hours before the eruption. Large segments underwent nearly vertical oscillations in the initial phase of the ascent of the filament.

  20. Spectral analysis of A and F dwarf members of the open cluster M6: preliminary results

    NASA Astrophysics Data System (ADS)

    Kılıçoǧlu, T.; Monier, R.; Fossati, L.

    2010-12-01

    We present the first abundance analysis of CD-32 13109 (NGC 6405 47), member of the M6 open cluster. The photospheric abundances of 14 chemical elements were determined by comparing synthetic spectra and observed spectra of the star. Findings show that this star should be an Am star.

  1. Abundances from solar-flare gamma-ray line spectroscopy

    NASA Technical Reports Server (NTRS)

    Murphy, R. J.; Ramaty, R.; Forrest, D. J.; Kozlovsky, B.

    1985-01-01

    Elemental abundances of the ambient gas at the site of gamma ray line production inthe solar atmosphere are deduced using gamma ray line observations from a solar flare. The resultant abundances are different from local galactic abundances which are thought to be similar to photospheric abundances.

  2. On the magnetic field required for driving the observed angular-velocity variations in the solar convection zone

    NASA Astrophysics Data System (ADS)

    Antia, H. M.; Chitre, S. M.; Gough, D. O.

    2013-01-01

    A putative temporally varying circulation-free magnetic-field configuration is inferred in an equatorial segment of the solar convection zone from the helioseismologically inferred angular-velocity variation, assuming that the predominant dynamics is an angular acceleration produced by the azimuthal Maxwell stress exerted by a field whose surface values are consistent with photospheric line-of-sight measurements.

  3. Elemental abundances of mercury-manganese stars and the population 2 type star HD 109995

    NASA Technical Reports Server (NTRS)

    Adelman, S. J.

    1985-01-01

    Ultraviolet and optical data for the Hg Mn stars Coronae Borealis and Cancri is being combined with data for the field horizontal branch population II star HD 109995 in order to derive the element abundances in their photospheres. Data collected by IUE is being utilized.

  4. Modelling extended chromospheres

    NASA Technical Reports Server (NTRS)

    Linsky, J. L.

    1986-01-01

    Attention is given to the concept that the warm, partially ionized plasma (presently called chromosphere) associated with such stars as Alpha Boo and Rho Per extends outwards at least several photospheric radii. Calculations are presented for the Mg II K line in light of two input model atmospheres. Specific predictions are deduced from the results obtained by each of the two models.

  5. EFFECT OF SOLAR CHROMOSPHERIC NEUTRALS ON EQUILIBRIUM FIELD STRUCTURES

    SciTech Connect

    Arber, T. D.; Botha, G. J. J.; Brady, C. S. E-mail: G.J.J.Botha@warwick.ac.u

    2009-11-10

    Solar coronal equilibrium fields are often constructed by nonlinear force-free field (NLFFF) extrapolation from photospheric magnetograms. It is well known that the photospheric field is not force-free and the correct lower boundary for NLFFF construction ought to be the top of the chromosphere. To compensate for this, pre-filtering algorithms are often applied to the photospheric data to remove the non-force-free components. Such pre-filtering models, while physically constrained, do not address the mechanisms that may be responsible for the field becoming force-free. The chromospheric field can change through, for example, field expansion due to gravitational stratification, reconnection, or flux emergence. In this paper, we study and quantify the effect of the chromospheric neutrals on equilibrium field structures. It is shown that, depending on the degree to which the photospheric field is not force-free, the chromosphere will change the structure of the equilibrium field. This is quantified to give an estimate of the change in alpha profiles one might expect due to neutrals in the chromosphere. Simple scaling of the decay time of non-force-free components of the magnetic field due to chromospheric neutrals is also derived. This is used to quantify the rate at which, or equivalent at which height, the chromosphere is expected to become force-free.

  6. PROPERTIES OF UMBRAL DOTS AS MEASURED FROM THE NEW SOLAR TELESCOPE DATA AND MHD SIMULATIONS

    SciTech Connect

    Kilcik, A.; Yurchyshyn, V. B.; Abramenko, V.; Goode, P. R.; Cao, W.; Rempel, M.; Kitai, R.; Watanabe, H.

    2012-02-01

    We studied bright umbral dots (UDs) detected in a moderate size sunspot and compared their statistical properties to recent MHD models. The study is based on high-resolution data recorded by the New Solar Telescope at the Big Bear Solar Observatory and three-dimensional (3D) MHD simulations of sunspots. Observed UDs, living longer than 150 s, were detected and tracked in a 46 minute long data set, using an automatic detection code. A total of 1553 (620) UDs were detected in the photospheric (low chromospheric) data. Our main findings are (1) none of the analyzed UDs is precisely circular, (2) the diameter-intensity relationship only holds in bright umbral areas, and (3) UD velocities are inversely related to their lifetime. While nearly all photospheric UDs can be identified in the low chromospheric images, some small closely spaced UDs appear in the low chromosphere as a single cluster. Slow-moving and long-living UDs seem to exist in both the low chromosphere and photosphere, while fast-moving and short-living UDs are mainly detected in the photospheric images. Comparison to the 3D MHD simulations showed that both types of UDs display, on average, very similar statistical characteristics. However, (1) the average number of observed UDs per unit area is smaller than that of the model UDs, and (2) on average, the diameter of model UDs is slightly larger than that of observed ones.

  7. ABRUPT LONGITUDINAL MAGNETIC FIELD CHANGES AND ULTRAVIOLET EMISSIONS ACCOMPANYING SOLAR FLARES

    SciTech Connect

    Johnstone, B. M.; Petrie, G. J. D.; Sudol, J. J.

    2012-11-20

    We have used Transition Region and Coronal Explorer 1600 A images and Global Oscillation Network Group (GONG) magnetograms to compare ultraviolet (UV) emissions from the chromosphere to longitudinal magnetic field changes in the photosphere during four X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred across more than 10 pixels in the GONG magnetograms for each flare. These magnetic changes lagged the GOES flare start times in all cases, showing that they were consequences and not causes of the flares. Ultraviolet emissions were spatially coincident with the field changes. The UV emissions tended to lag the GOES start times for the flares and led the changes in the magnetic field in all pixels except one. The UV emissions led the photospheric field changes by 4 minutes on average with the longest lead being 9 minutes; however, the UV emissions continued for tens of minutes, and more than an hour in some cases, after the field changes were complete. The observations are consistent with the picture in which an Alfven wave from the field reconnection site in the corona propagates field changes outward in all directions near the onset of the impulsive phase, including downward through the chromosphere and into the photosphere, causing the photospheric field changes, whereas the chromosphere emits in the UV in the form of flare kernels, ribbons, and sequential chromospheric brightenings during all phases of the flare.

  8. The Abundances of Some Heavy Elements in the Atmosphere of γ Tauri

    NASA Astrophysics Data System (ADS)

    Yushchenko, A. V.; Gopka, V. F.

    Comparison of synthetic spectrum of the γ Tauri photosphere and high quality spectral atlases of this star permit us to identify absorption lines of rubidium, indium, disprosium, erbium, osmium in the observed spectra. The abundances of these elements in the atmosphere of γ Tauri with respect to their abundances in the solar atmosphere were determined by the method of spectrum synthesis.

  9. Possible in situ tests of the evolution of elemental and isotopic abundances in the solar convection zone

    NASA Astrophysics Data System (ADS)

    Turcotte, S.; Wimmer-Schweingruber, R. F.

    2002-12-01

    Helioseismology has shown that the chemical composition of the Sun has changed over its lifetime. The surface abundance of helium and heavy elements is believed to have decreased by up to 10% in relation to their initial values. However, this reduction is too small to be tested by direct observations of the photospheric chemical composition. Here we compare the predicted variations in the solar photospheric composition with precise measurements of abundances in meteorites and the solar wind composition. Although elemental composition ratios can vary by roughly a percent (e.g., for Ca/Mg and Ca/Fe) over the Sun's lifetime, their measurements are rife with uncertainties related to uncertainties in the interpretation of meteoritic measurements, photospheric determinations, and the complex fractionation processes occurring between the upper photosphere and lower chromosphere and the corona. On the other hand, isotopic ratios can be measured much more accurately and are not expected to be affected as much by extrasolar processes, although more work is required to quantify their effect. As the isotopic ratios evolve in the Sun proportionally to the mass ratios of the isotopes, light elements yield the highest variations in isotopic ratios. They are predicted to reach as high as 0.6% for 18O/16O and are only slightly lower in the cases of 26Mg/24Mg and 30Si/28Si. Such a value should be well within the sensitivity of new missions such as Genesis.

  10. Liquid Water Oceans in Ice Giants

    NASA Technical Reports Server (NTRS)

    Wiktorowicz, Sloane J.; Ingersoll, Andrew P.

    2007-01-01

    Aptly named, ice giants such as Uranus and Neptune contain significant amounts of water. While this water cannot be present near the cloud tops, it must be abundant in the deep interior. We investigate the likelihood of a liquid water ocean existing in the hydrogen-rich region between the cloud tops and deep interior. Starting from an assumed temperature at a given upper tropospheric pressure (the photosphere), we follow a moist adiabat downward. The mixing ratio of water to hydrogen in the gas phase is small in the photosphere and increases with depth. The mixing ratio in the condensed phase is near unity in the photosphere and decreases with depth; this gives two possible outcomes. If at some pressure level the mixing ratio of water in the gas phase is equal to that in the deep interior, then that level is the cloud base. The gas below the cloud base has constant mixing ratio. Alternately, if the mixing ratio of water in the condensed phase reaches that in the deep interior, then the surface of a liquid ocean will occur. Below this ocean surface, the mixing ratio of water will be constant. A cloud base occurs when the photospheric temperature is high. For a family of ice giants with different photospheric temperatures, the cooler ice giants will have warmer cloud bases. For an ice giant with a cool enough photospheric temperature, the cloud base will exist at the critical temperature. For still cooler ice giants, ocean surfaces will result. A high mixing ratio of water in the deep interior favors a liquid ocean. We find that Neptune is both too warm (photospheric temperature too high) and too dry (mixing ratio of water in the deep interior too low) for liquid oceans to exist at present. To have a liquid ocean, Neptune s deep interior water to gas ratio would have to be higher than current models allow, and the density at 19 kbar would have to be approx. equal to 0.8 g/cu cm. Such a high density is inconsistent with gravitational data obtained during the Voyager

  11. Solar Magnetic Tracking. IV. The Death of Magnetic Features

    NASA Astrophysics Data System (ADS)

    Lamb, D. A.; Howard, T. A.; DeForest, C. E.; Parnell, C. E.; Welsch, B. T.

    2013-09-01

    The removal of magnetic flux from the quiet-Sun photosphere is important for maintaining the statistical steady state of the magnetic field there, for determining the magnetic flux budget of the Sun, and for estimating the rate of energy injected into the upper solar atmosphere. Magnetic feature death is a measurable proxy for the removal of detectable flux, either by cancellation (submerging or rising loops, or reconnection in the photosphere) or by dispersal of flux. We used the SWAMIS feature tracking code to understand how nearly 2 × 104 magnetic features die in an hour-long sequence of Hinode/SOT/NFI magnetograms of a region of the quiet Sun. Of the feature deaths that remove visible magnetic flux from the photosphere, the vast majority do so by a process that merely disperses the previously detected flux so that it is too small and too weak to be detected, rather than completely eliminating it. The behavior of the ensemble average of these dispersals is not consistent with a model of simple planar diffusion, suggesting that the dispersal is constrained by the evolving photospheric velocity field. We introduce the concept of the partial lifetime of magnetic features, and show that the partial lifetime due to Cancellation of magnetic flux, 22 hr, is three times slower than previous measurements of the flux turnover time. This indicates that prior feature-based estimates of the flux replacement time may be too short, in contrast with the tendency for this quantity to decrease as resolution and instrumentation have improved. This suggests that dispersal of flux to smaller scales is more important for the replacement of magnetic fields in the quiet Sun than observed bipolar cancellation. We conclude that processes on spatial scales smaller than those visible to Hinode dominate the processes of flux emergence and cancellation, and therefore also the quantity of magnetic flux that threads the photosphere.

  12. RECONSTRUCTING THE LOCAL TWIST OF CORONAL MAGNETIC FIELDS AND THE THREE-DIMENSIONAL SHAPE OF THE FIELD LINES FROM CORONAL LOOPS IN EXTREME-ULTRAVIOLET AND X-RAY IMAGES

    SciTech Connect

    Malanushenko, A.; Longcope, D. W.; McKenzie, D. E.

    2009-12-20

    Nonlinear force-free fields are the most general case of force-free fields, but the hardest to model as well. There are numerous methods of computing such fields by extrapolating vector magnetograms from the photosphere, but very few attempts have so far made quantitative use of coronal morphology. We present a method to make such quantitative use of X-ray and EUV images of coronal loops. Each individual loop is fit to a field line of a linear force-free field, allowing the estimation of the field line's twist, three-dimensional geometry, and the field strength along it. We assess the validity of such a reconstruction since the actual corona is probably not a linear force-free field, and that the superposition of linear force-free fields is generally not itself a force-free field. To do so, we perform a series of tests on nonlinear force-free fields, described in Low and Lou. For model loops we project field lines onto the photosphere. We compare several results of the method with the original field, in particular the three-dimensional loop shapes, local twist (coronal alpha), distribution of twist in the model photosphere, and strength of the magnetic field. We find that (1) for these trial fields, the method reconstructs twist with a mean absolute deviation of at most 15% of the range of photospheric twist, (2) heights of the loops are reconstructed with a mean absolute deviation of at most 5% of the range of trial heights, and (3) the magnitude of non-potential contribution to a photospheric field is reconstructed with a mean absolute deviation of at most 10% of the maximal value.

  13. Analysis of the flux and polarization spectra of the type Ia supernova SN 2001el: Exploring the geometry of the high-velocity Ejecta

    SciTech Connect

    Kasen, Daniel; Nugent, Peter; Wang, Lifan; Howell, D.A.; Wheeler, J. Craig; Hoeflich, Peter; Baade, Dietrich; Baron, E.; Hauschildt, P.H.

    2003-01-15

    SN 2001el is the first normal Type Ia supernova to show a strong, intrinsic polarization signal. In addition, during the epochs prior to maximum light, the CaII IR triplet absorption is seen distinctly and separately at both normal photospheric velocities and at very high velocities. The unusual, high-velocity triplet absorption is highly polarized, with a different polarization angle than the rest of the spectrum. The unique observation allows us to construct a relatively detailed picture of the layered geometrical structure of the supernova ejecta: in our interpretation, the ejecta layers near the photosphere (v approximately 10,000 km/s) obey a near axial symmetry, while a detached, high-velocity structure (v approximately 18,000-25,000 $ km/s) of CaII line opacity deviates from the photospheric axisymmetry. By partially obscuring the underlying photosphere, the high-velocity structure causes a more incomplete cancellation of the polarization of the photospheric light, and so gives rise to the polarization peak of the high-velocity IR triplet feature. In an effort to constrain the ejecta geometry, we develop a technique for calculating 3-D synthetic polarization spectra and use it to generate polarization profiles for several parameterized configurations. In particular, we examine the case where the inner ejecta layers are ellipsoidal and the outer, high-velocity structure is one of four possibilities: a spherical shell, an ellipsoidal shell, a clumped shell, or a toroid. The synthetic spectra rule out the clearly discriminated if observations are obtained from several different lines of sight. Thus, assuming the high velocity structure observed for SN 2001el is a consistent feature of at least known subset of type Ia supernovae, future observations and analyses such as these may allow one to put strong constraints on the ejecta geometry and hence on supernova progenitors and explosion mechanisms.

  14. Semianalytic continuum spectra of Type 2 supernovae

    NASA Technical Reports Server (NTRS)

    Montes, Marcos J.; Wagoner, Robert V.

    1995-01-01

    We extend the approximate radiative transfer analysis of Hershkowitz, Linder, & Wagoner (1986) to a more general class of supernova model atmospheres, using a simple fit to the effective continuum opacity produced by lines (Wagoner, Perez, & Vasu 1991). At the low densities considered, the populations of the excited states of hydrogen are governed mainly by photoionization and recombination, and scattering dominates absorptive opacity. We match the asymptotic expressions for the spectral energy density J(sub nu) at the photosphere, whose location at each frequency is determined by a first-order calculation of the deviation of J(sub nu) from the Planck function B(sub nu). The emergent spectral luminosity then assumes the form L(sub nu) = 4 pi(squared)r(squared)(sub *) zeta(squared)B(sub nu)(T(sub p)), where T(sub p)(nu) is the photospheric temperature zeta is the dilution factor, and r(sub *) is a fiducial radius (ultimately taken to be the photospheric radius r(sub p)(nu)). The atmosphere is characterized by an effective temperature T(sub e) (varies as L(sup 1/4)r(sup -1/2)(sub *)) and hydrogen density n(sub H) = dependence of zeta on frequency nu and the parameters T(sub p), r(sub p), and alpha. The resulting understanding of the dependence of the spectral luminosity on observable parameters which characterize the relevant physical conditions will be of particular use in assessing the reliability of the expanding photosphere method of distance determination. This is particularly important at cosmological distances, where no information about the progenitor star will be available. This technique can also be applied to other low-density photosphere.

  15. Fields and Flares: Understanding the Complex Magnetic Topologies of Solar Active Regions

    NASA Astrophysics Data System (ADS)

    Murray, Sophie A.

    2013-01-01

    Sunspots are regions of decreased brightness on the visible surface of the Sun (photosphere) that are associated with strong magnetic fields. They have been found to be locations associated with solar flares, which occur when energy stored in sunspot magnetic fields is suddenly released. The processes involved in flaring and the link between sunspot magnetic fields and flares is still not fully understood, and this thesis aims to gain a better understanding of these topics. The magnetic field evolution of a number of sunspot regions is examined using high spatial resolution data from the Hinode spacecraft. The research presented in this thesis gives insight into both photospheric and coronal magnetic field evolution of flaring regions. Significant increases in vertical field strength, current density, and field inclination angle towards the vertical are observed in the photosphere just hours before a flare occurs, which is on much shorter timescales than previously studied. First observations of spatial changes in field inclination across a magnetic neutral line (generally believed to be a typical source region of flares) are also discovered. 3D magnetic field extrapolation methods are used to study the coronal magnetic field, using the photospheric magnetic field data as a boundary condition. Magnetic energy and free magnetic energy are observed to increase significantly a few hours before a flare, and decrease afterwards, which is a similar trend to the photospheric field parameter changes observed. Evidence of partial Taylor relaxation is also detected after a flare, as predicted by several previous studies. The results outlined in this thesis show that this particular field of research is vital in furthering our understanding of the magnetic nature of sunspots and its link to flare processes.

  16. Water Vapor on Betelgeuse as Revealed by TEXES High-Resolution 12 μm Spectra

    NASA Astrophysics Data System (ADS)

    Ryde, N.; Harper, G. M.; Richter, M. J.; Greathouse, T. K.; Lacy, J. H.

    2006-02-01

    The outer atmosphere of the M supergiant Betelgeuse is puzzling. Published observations of different kinds have shed light on different aspects of the atmosphere, but no unified picture has emerged. They have shown, for example, evidence of a water envelope (MOLsphere) that in some studies is found to be optically thick in the mid-infrared. In this paper, we present high-resolution, mid-infrared spectra of Betelgeuse recorded with the TEXES spectrograph. The spectra clearly show absorption features of water vapor and OH. We show that a spectrum based on a spherical, hydrostatic model photosphere with Teff=3600 K, an effective temperature often assumed for Betelgeuse, fails to model the observed lines. Furthermore, we show that published MOLsphere scenarios are unable to explain our data. However, we are able to model the observed spectrum reasonably well by adopting a cooler outer photospheric structure corresponding to Tmod=3250 K. The success of this model may indicate that the observed mid-infrared lines are formed in cool photospheric surface regions. Given the uncertainties of the temperature structure and the likely presence of inhomogeneities, we cannot rule out the possibility that our spectrum could be mostly photospheric, albeit nonclassical. Our data put new, strong constraints on atmospheric models of Betelgeuse, and we conclude that continued investigation requires consideration of nonclassical model photospheres, as well as possible effects of a MOLsphere. We show that the mid-infrared water vapor features have great diagnostic value for the environments of K and M (super)giant star atmospheres.

  17. MAGNETIC FIELDS OF AN ACTIVE REGION FILAMENT FROM FULL STOKES ANALYSIS OF Si I 1082.7 nm AND He I 1083.0 nm

    SciTech Connect

    Xu, Z.; Liu, Y.

    2012-04-20

    Vector magnetic fields of an active region filament in the photosphere and upper chromosphere are obtained from spectro-polarimetric observations recorded with the Tenerife Infrared Polarimeter (TIP II) at the German Vacuum Tower Telescope. We apply Milne-Eddington inversions on full Stokes vectors of the photospheric Si I 1082.7 nm and the upper chromospheric He I triplet at 1083.0 nm to obtain the magnetic field vector and velocity maps in two atmosphere layers. We find that (1) a complete filament was already present in H{alpha} at the beginning of the TIP II data acquisition. Only a partially formed one, composed of multiple small threads, was present in He I. (2) The AR filament comprises two sections. One shows strong magnetic field intensities, about 600-800 G in the upper chromosphere and 800-1000 G in the photosphere. The other exhibits only comparatively weak magnetic field strengths in both layers. (3) The Stokes V signal is indicative of a dip in the magnetic field strength close to the chromospheric PIL. (4) In the chromosphere, consistent upflows are found along the PIL flanked by downflows. (5) The transversal magnetic field is nearly parallel to the PIL in the photosphere and inclined by 20 Degree-Sign -30 Degree-Sign in the chromosphere. (6) The chromospheric magnetic field around the filament is found to be in normal configuration, while the photospheric field presents a concave magnetic topology. The observations are consistent with the emergence of a flux rope with a subsequent formation of a filament.

  18. Evolution of the Granular Dynamics and Energy Transport

    NASA Astrophysics Data System (ADS)

    Nesis, A.; Hammer, R.; Schleicher, H.

    2003-05-01

    Based on series of excellent spectrograms taken at the German Vacuum Tower Telescope (VTT) at the Observatorio del Teide (Tenerife), we study the temporal evolution of the granular dynamics and the energy transport in the photospheric layers. We consider the ensemble of the granules cut by the spectrograph slit as a complex system. We describe this ensemble by the rms of the fluctuations of the granular observables along the slit: continuum intensity I, Doppler velocity v, and line width w. The history of the rms of the observables v and w reflects the dynamical change of the system over the 20 minutes observation time. We find for both observables a quasi-periodical change. However, the history of the cross-correlation between I and v remains virtually constant, with the exception of two gaps. We measure the rms of v in the deep photospheric layers for six lines of different strength included in the spectrograms. Using a model velocity variation based on our previous publications, we assign photospheric heights to the velocity measurements. These heights agree with those calculated by other means. On the basis of this v variation we calculate the kinetic energy flux as a function of the height in the photosphere for different times during the observation. The form of the variation with height turns out to be constant in time. The convective energy flux, finally, is calculated from the measured velocity and the temperature variations of our earlier models. Again we find practically the same variation form over the time of the observation. Taken together, these results quantify the different roles that the lower and higher photospheric layers play for the energetics of the convective overshoot at the upper boundary of the superadiabatic region of the Sun. A.N. acknowledges travel support from the German science foundation DFG.

  19. THE ROLE OF TORSIONAL ALFVEN WAVES IN CORONAL HEATING

    SciTech Connect

    Antolin, P.; Shibata, K. E-mail: shibata@kwasan.kyoto-u.ac.j

    2010-03-20

    In the context of coronal heating, among the zoo of magnetohydrodynamic (MHD) waves that exist in the solar atmosphere, Alfven waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption, or turbulent cascade in order to heat the plasma. Furthermore, their incompressibility makes their detection in the solar atmosphere very difficult. New observations with polarimetric, spectroscopic, and imaging instruments such as those on board the Japanese satellite Hinode, or the Crisp spectropolarimeter of the Swedish Solar Telescope or the Coronal Multi-channel Polarimeter, are bringing strong evidence for the existence of energetic Alfven waves in the solar corona. In order to assess the role of Alfven waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfven wave heating through the mode conversion mechanism. Using a 1.5 dimensional MHD code, we carry out a parameter survey varying the magnetic flux tube geometry (length and expansion), the photospheric magnetic field, the photospheric velocity amplitudes, and the nature of the waves (monochromatic or white-noise spectrum). The regimes under which Alfven wave heating produces hot and stable coronae are found to be rather narrow. Independently of the photospheric wave amplitude and magnetic field, a corona can be produced and maintained only for long (>80 Mm) and thick (area ratio between the photosphere and corona >500) loops. Above a critical value of the photospheric velocity amplitude (generally a few km s{sup -1}) the corona can no longer be maintained over extended periods of time and collapses due to the large momentum of the waves. These results establish several

  20. Far-Infrared and Millimeter Continuum Studies of K-Giants: Alpha Boo and Alpha Tau

    NASA Technical Reports Server (NTRS)

    Cohen, Martin; Carbon, Duane F.; Welch, William J.; Lim, Tanya; Forster, James R.; Goorvitch, David; Thigpen, William (Technical Monitor)

    2002-01-01

    We have imaged two normal, non-coronal, infrared-bright K-giants, alpha Boo and alpha Tau, in the 1.4-millimeter and 2.8-millimeter continuum using BIMA. These stars have been used as important absolute calibrators for several infrared satellites. Our goals are: (1) to probe the structure of their upper photospheres; (2) to establish whether these stars radiate as simple photospheres or possess long-wavelength chromospheres; and (3) to make a connection between millimeter-wave and far-infrared absolute flux calibrations. To accomplish these goals we also present ISO Long Wavelength Spectrometer (LWS) measurements of both these K-giants. The far-infrared and millimeter continuum radiation is produced in the vicinity of the temperature minimum in a Boo and a Tau, offering a direct test of the model photospheres and chromospheres for these two cool giants. We find that current photospheric models predict fluxes in reasonable agreement with those observed for those wavelengths which sample the upper photosphere, namely less than or equal to 170 micrometers in alpha Tau and less than or equal to 125 micrometers in alpha Boo. It is possible that alpha Tau is still radiative as far as 0.9 - 1.4 millimeters. We detect chromospheric radiation from both stars by 2.8 millimeters (by 1.4 millimeters in alpha Boo), and are able to establish useful bounds on the location of the temperature minimum. An attempt to interpret the chromospheric fluxes using the two-component "bifurcation model" proposed by Wiedemann et al. (1994) appears to lead to a significant contradiction.

  1. On the Dynamics of Small-Scale Solar Magnetic Elements

    NASA Technical Reports Server (NTRS)

    Berger, T. E.; Title, A. M.

    1996-01-01

    We report on the dynamics of the small-scale solar magnetic field, based on analysis of very high resolution images of the solar photosphere obtained at the Swedish Vacuum Solar Telescope. The data sets are movies from 1 to 4 hr in length, taken in several wavelength bands with a typical time between frames of 20 s. The primary method of tracking small-scale magnetic elements is with very high contrast images of photospheric bright points, taken through a 12 A bandpass filter centered at 4305 A in the Fraunhofer 'G band.' Previous studies have established that such bright points are unambiguously associated with sites of small-scale magnetic flux in the photosphere, although the details of the mechanism responsible for the brightening of the flux elements remain uncertain. The G band bright points move in the intergranular lanes at speeds from 0.5 to 5 km/s. The motions appear to be constrained to the intergranular lanes and are primarily driven by the evolution of the local granular convection flow field. Continual fragmentation and merging of flux is the fundamental evolutionary mode of small-scale magnetic structures in the solar photosphere. Rotation and folding of chains or groups of bright points are also observed. The timescale for magnetic flux evolution in active region plage is on the order of the correlation time of granulation (typically 6-8 minutes), but significant morphological changes can occur on timescales as short as 100 S. Smaller fragments are occasionally seen to fade beyond observable contrast. The concept of a stable, isolated subarcsecond magnetic 'flux tube' in the solar photosphere is inconsistent with the observations presented here.

  2. Comparing ADAPT-WSA Model Predictions With EUV And Solar Wind Observations

    NASA Astrophysics Data System (ADS)

    Arge, Charles; Henney, C. J.; Shurkin, K.; Toussaint, W.; Koller, J.; Harvey, J. W.

    2011-05-01

    Global estimates of the solar photospheric magnetic field distribution are critical for space weather forecasting. These global maps are the essential data input for accurate modeling of the corona and solar wind, which is vital for gaining the basic understanding necessary to improve forecasting models needed for Air Force operations. We are now testing the global photospheric field maps generated by the Air Force Data Assimilative Photospheric flux Transport (ADAPT) model as input to the WSA coronal and solar wind model. ADAPT incorporates the Los Alamos National Laboratory data assimilation methodology with a modified version of the Worden and Harvey photospheric magnetic flux transport model. The ADAPT maps provide a more instantaneous snapshot of the global photospheric field distribution compared to traditional synoptic maps. In this presentation, we make a detailed comparison of WSA coronal and solar wind model output with STEREO EUVI disk observations and in situ plasma observations from the STEREO and ACE spacecraft. The current orbital configuration of the two STEREO spacecraft is such that they provide a nearly instantaneous global snapshot of the Sun's coronal hole distribution. In addition, the STEREO observations along with those from the ACE spacecraft provide three widely spaced ecliptic locations at 1 AU to sample the solar wind plasma. In combination, these differing observations from multiple spacecraft provide a unique and highly sensitive test of the ability of the WSA model to capture the global coronal hole and solar wind structure. This is done using both ADAPT and standard updated photospheric field maps as input to the model.

  3. Numerical Simulations of Helicity Condensation in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-05-01

    The helicity condensation model has been proposed by Antiochos to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences are observed to form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the corona. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of a bipolar active region, for example. The calculations demonstrate that, contrary to common belief, opposite helicity twists do not lead to significant reconnection in such a coronal system, whereas twists with the same sense of helicity do produce substantial reconnection. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  4. Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms

    NASA Astrophysics Data System (ADS)

    Tadesse, T.; Wiegelmann, T.; Inhester, B.; MacNeice, P.; Pevtsov, A.; Sun, X.

    2013-02-01

    Context. The magnetic field configuration is essential for understanding solar explosive phenomena, such as flares and coronal mass ejections. To overcome the unavailability of coronal magnetic field measurements, photospheric magnetic field vector data can be used to reconstruct the coronal field. Two complications of this approach are that the measured photospheric magnetic field is not force-free and that one has to apply a preprocessing routine to achieve boundary conditions suitable for the force-free modeling. Furthermore the nonlinear force-free extrapolation code should take uncertainties into account in the photospheric field data. They occur due to noise, incomplete inversions, or azimuth ambiguity-removing techniques. Aims: Extrapolation codes in Cartesian geometry for modeling the magnetic field in the corona do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. Here we apply a method for nonlinear force-free coronal magnetic field modeling and preprocessing of photospheric vector magnetograms in spherical geometry using the optimization procedure to full disk vector magnetograms. We compare the analysis of the photospheric magnetic field and subsequent force-free modeling based on full-disk vector maps from Helioseismic and Magnetic Imager (HMI) onboard the solar dynamics observatory (SDO) and Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS). Methods: We used HMI and VSM photospheric magnetic field measurements to model the force-free coronal field above multiple solar active regions, assuming magnetic forces to dominate. We solved the nonlinear force-free field equations by minimizing a functional in spherical coordinates over a full disk and excluding the poles. After searching for the optimum modeling parameters for the particular data sets, we compared the resulting nonlinear force-free model fields. We compared

  5. Constraints on Solar Coronal Abundances from MESSENGER X-ray Solar Monitor Data

    NASA Astrophysics Data System (ADS)

    Nittler, L.; Starr, R. D.; Schlemm, C., III; McNutt, R. L.; Solomon, S. C.

    2010-12-01

    The chemical composition of the solar corona is fractionated from that of the photosphere, with elements having low first-ionization-potential (FIP <~10 eV) enriched relative to higher-FIP elements. However, the absolute normalization of coronal abundances relative to photospheric ones as well as possible time variation in coronal abundances (e.g., during flares) is a matter of longstanding controversy. Moreover, the effects of a recent downward revision in photospheric C, N, and especially O abundances on coronal composition have not yet been extensively studied. The shape of the soft X-ray spectrum emitted from the coronal plasma depends strongly on chemical composition both through emission lines and free-bound emission contributions to the continuum. The MESSENGER spacecraft, en route to orbit Mercury, includes a Si-PIN detector to monitor the solar X-ray spectrum (~1.5 to 8 keV) as part of an experiment to determine planetary surface composition via X-ray fluorescence. A pinhole and thin Be window in front of the PIN attenuate much of the flux below 2 keV, providing a high dynamic range in measuring the highly variable solar spectrum. The energy resolution of the solar monitor (~600 eV) is not sufficient to resolve individual solar lines but does allow line complexes of Ca and Fe to be distinguished from continuum during flares. In preparation for analysis of X-ray data from Mercury’s surface, we have begun a systematic effort to fit theoretical solar spectra to MESSENGER solar monitor data, using the CHIANTI 5.2 code and assuming isothermal plasma. The key fitting parameters are the plasma temperature, emission measure, and level of fractionation for low-FIP elements. Preliminary fitting of some 1400 individual spectra (300-450 s integration) from ~200 B-level and above solar flares during June-August 2010 reveals two interesting results: (1) The best fits are obtained for plasma with low-FIP elements enriched by a factor of ~2 relative to photospheric

  6. Neon and Oxygen Abundances and Abundance Ratio in the Solar Corona

    NASA Astrophysics Data System (ADS)

    Landi, E.; Testa, P.

    2015-02-01

    In this work we determine the Ne/O abundance ratio from Solar and Heliospheric Observatory (SOHO)/Solar Ultraviolet Measurement of Emitted Radiation (SUMER) off-disk observations of quiescent streamers over the 1996-2008 period. We find that the Ne/O ratio is approximately constant over solar cycle 23 from 1996 to 2005, at a value of 0.099 ± 0.017 this value is lower than the transition region determinations from the quiet Sun used to infer the neon photospheric abundance from the oxygen photospheric abundance. Also, the Ne/O ratio we determined from SUMER is in excellent agreement with in situ determinations from ACE/SWICS. In 2005-2008, the Ne/O abundance ratio increased with time and reached 0.25 ± 0.05, following the same trend found in the slowest wind analyzed by ACE/SWICS. Further, we measure the absolute abundance in the corona for both oxygen and neon from the data set of 1996 November 22, obtaining A o = 8.99 ± 0.04 and A Ne = 7.92 ± 0.03, and we find that both elements are affected by the first ionization potential (FIP) effect, with oxygen being enhanced by a factor of 1.4-2.1 over its photospheric abundance, and neon being changed by a factor of 0.75-1.20. We conclude that the Ne/O ratio is not constant in the solar atmosphere, both in time and at different heights, and that it cannot be reliably used to infer the neon abundance in the photosphere. Also, we argue that the FIP effect was less effective during the minimum of solar cycle 24, and that the Ne/O = 0.25 ± 0.05 value measured at that time is closer to the true photospheric value, leading to a neon photospheric abundance larger than assumed by ≈40%. We discuss the implications of these results for the solar abundance problem, for the FIP effect, and for the identification of the source regions of the solar wind.

  7. Multi-wavelength analysis from tomography study on solar chromosphere

    SciTech Connect

    Mumpuni, Emanuel Sungging; Herdiwijaya, Dhani; Djamal, Mitra

    2015-04-16

    The Sun as the most important star for scientific laboratory in astrophysics as well as encompassing all living aspect on Earth, still holds scientific mystery. As the established model that the Sun’s energy fueled by the nuclear reaction, along with transport process to the typical Solar surface on around 6000-K temperature, many aspects still left as an open questions, such as how the chromosphere responded to the photospheric dynamics. In this preliminary work, we try to analyze the Solar chromosphere respond to the Photospheric dynamics using tomography study implementing multi-wavelength analysis observation obtained from Dutch Open Telescope. Using the Hydrogen-alpha Doppler signal as the primary diagnostic tool, we try to investigate the inter-relation between the magnetic and gas pressure dynamics that occur in the chromosphere.

  8. Spatial distribution and statistical properties of small-scale convective vortex-like motions in a quiet-Sun region

    NASA Astrophysics Data System (ADS)

    Vargas Domínguez, S.; Palacios, J.; Balmaceda, L.; Cabello, I.; Domingo, V.

    2011-09-01

    High-resolution observations of a quiet-Sun internetwork region taken with the Solar 1-m Swedish Telescope in La Palma are analysed. We determine the location of small-scale vortex motions in the solar photospheric region by computing the horizontal proper motions of small-scale structures on time-series of images. These plasma convectively driven swirl motions are associated to (1) downdrafts (that have been commonly explained as corresponding to sites where the plasma is cooled down and hence returned to the interior below the visible photospheric level) and (2) horizontal velocity vectors converging on a central point. The sink cores are proved to be the final destination of passive floats tracing plasma flows towards the centre of each vortex. We establish the occurrence of these events to be 1.4 × 10-3 and 1.6 × 10-3 vortices Mm-2 min-1, respectively, for the two time-series analysed here.

  9. Wave energy in white dwarf atmospheres. I - Magnetohydrodynamic energy spectra for homogeneous DB and layered DA stars

    NASA Technical Reports Server (NTRS)

    Musielak, Zdzislaw E.

    1987-01-01

    The radiative damping of acoustic and MHD waves that propagate through white dwarf photospheric layers is studied, and other damping processes that may be important for the propagation of the MHD waves are calculated. The amount of energy remaining after the damping processes have occurred in different types of waves is estimated. The results show that lower acoustic fluxes should be expected in layered DA and homogeneous DB white dwarfs than had previously been estimated. Acoustic emission manifests itself in an enhancement of the quadrupole term, but this term may become comparable to or even lower than the dipole term for cool white dwarfs. Energy carried by the acoustic waves is significantly dissipated in deep photospheric layers, mainly because of radiative damping. Acoustically heated corona cannot exist around DA and DB white dwarfs in a range T(eff) = 10,000-30,000 K and for log g = 7 and 8. However, relatively hot and massive white dwarfs could be exceptions.

  10. Evolution of the magnetic field inclination in a forming penumbra

    SciTech Connect

    Romano, P.; Guglielmino, S. L.; Cristaldi, A.; Falco, M.; Zuccarello, F.; Ermolli, I.

    2014-03-20

    We describe the evolution of the magnetic and velocity fields in the annular zone around a pore a few hours before the formation of its penumbra. We detected the presence of several patches at the edge of the annular zone, with a typical size of about 1''. These patches are characterized by a rather vertical magnetic field with polarity opposite to that of the pore. They correspond to regions of plasma upflow up to 2.5 km s{sup –1} and are characterized by radially outward displacements with horizontal velocities up to 2 km s{sup –1}. We interpret these features as portions of the pore magnetic field lines returning beneath the photosphere being progressively stretched and pushed down by the overlying magnetic fields. Our results confirm that the penumbra formation results from changes in the inclination of the field lines in the magnetic canopy overlying the pore, until they reach the photosphere.

  11. Three-dimensional Simulations of Magnetohydrodynamic Waves in Magnetized Solar Atmosphere

    NASA Astrophysics Data System (ADS)

    Vigeesh, G.; Fedun, V.; Hasan, S. S.; Erdélyi, R.

    2012-08-01

    We present results of three-dimensional numerical simulations of magnetohydrodynamic (MHD) wave propagation in a solar magnetic flux tube. Our study aims at understanding the properties of a range of MHD wave modes generated by different photospheric motions. We consider two scenarios observed in the lower solar photosphere, namely, granular buffeting and vortex-like motion, among the simplest mechanism for the generation of waves within a strong, localized magnetic flux concentration. We show that granular buffeting is likely to generate stronger slow and fast magnetoacoustic waves as compared to swirly motions. Correspondingly, the energy flux transported differs as a result of the driving motions. We also demonstrate that the waves generated by granular buffeting are likely to manifest in stronger emission in the chromospheric network. We argue that different mechanisms of wave generation are active during the evolution of a magnetic element in the intergranular lane, resulting in temporally varying emission at chromospheric heights.

  12. THREE-DIMENSIONAL SIMULATIONS OF MAGNETOHYDRODYNAMIC WAVES IN MAGNETIZED SOLAR ATMOSPHERE

    SciTech Connect

    Vigeesh, G.; Fedun, V.; Erdelyi, R.; Hasan, S. S.

    2012-08-10

    We present results of three-dimensional numerical simulations of magnetohydrodynamic (MHD) wave propagation in a solar magnetic flux tube. Our study aims at understanding the properties of a range of MHD wave modes generated by different photospheric motions. We consider two scenarios observed in the lower solar photosphere, namely, granular buffeting and vortex-like motion, among the simplest mechanism for the generation of waves within a strong, localized magnetic flux concentration. We show that granular buffeting is likely to generate stronger slow and fast magnetoacoustic waves as compared to swirly motions. Correspondingly, the energy flux transported differs as a result of the driving motions. We also demonstrate that the waves generated by granular buffeting are likely to manifest in stronger emission in the chromospheric network. We argue that different mechanisms of wave generation are active during the evolution of a magnetic element in the intergranular lane, resulting in temporally varying emission at chromospheric heights.

  13. Comments concerning magnetic fields as a possible cause of rapid, irregular variability of early-type stars

    NASA Technical Reports Server (NTRS)

    Underhill, A. B.

    1983-01-01

    It is noted that it is helpful to divide the atmosphere of an early-type star into two parts: a photosphere and a mantle. The photosphere can be modeled satisfactorily by normal model-atmosphere procedures. When modeling the mantle, one must take account of the deposition of nonradiative heat and momentum and one should recognize that the mantles of hot stars do not appear to be uniform or spherically symmetric. Five areas of discrepancy between classical theory and observation are noted and a possible way of modeling the mantles of early-type stars is outlined. The model consists of arcades of magnetic loops which form helmet-type structures in the equatorial band of the star, and of coronal-hole-type structures emmanating from weak unipolar regions which are chiefly distributed at polar latitudes.

  14. Hot explosions in the cool atmosphere of the Sun.

    PubMed

    Peter, H; Tian, H; Curdt, W; Schmit, D; Innes, D; De Pontieu, B; Lemen, J; Title, A; Boerner, P; Hurlburt, N; Tarbell, T D; Wuelser, J P; Martínez-Sykora, Juan; Kleint, L; Golub, L; McKillop, S; Reeves, K K; Saar, S; Testa, P; Kankelborg, C; Jaeggli, S; Carlsson, M; Hansteen, V

    2014-10-17

    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. PMID:25324397

  15. Test particle acceleration in a numerical MHD experiment of an anemone jet

    NASA Astrophysics Data System (ADS)

    Rosdahl, K. J.; Galsgaard, K.

    2010-02-01

    Aims: To use a 3D numerical MHD experiment representing magnetic flux emerging into an open field region as a background field for tracing charged particles. The interaction between the two flux systems generates a localised current sheet where MHD reconnection takes place. We investigate how efficiently the reconnection region accelerates charged particles and what kind of energy distribution they acquire. Methods: The particle tracing is done numerically using the Guiding Center Approximation on individual data sets from the numerical MHD experiment. Results: We derive particle and implied photon distribution functions having power law forms, and look at the impact patterns of particles hitting the photosphere. We find that particles reach energies far in excess of those seen in observations of solar flares. However the structure of the impact region in the photosphere gives a good representation of the topological structure of the magnetic field. Three movies are only available in electronic form at http://www.aanda.org

  16. On the Velocity Field and the 3D Structure of the Galactic Soccer Ball Abell 43

    NASA Astrophysics Data System (ADS)

    Rauch, Thomas; Werner, Klaus; Ercolano, Barbara; Köppen, Joachim

    2005-11-01

    Planetary nebulae (PNe) and their central stars (CSs) are ideal tools to test evolutionary theory: photospheric properties of their exciting stars give stringent constraints for theoretical predictions of stellar evolution. The nebular abundances display the star's photosphere chemical composition at the time of the nebula's ejection which allows to look back into the history of stellar evolution. More importantly, they even provide a possibility to investigate on the chemical evolution of our Galaxy because most of the nuclear processed material goes back into the interstellar medium via PNe. The recent developments in observation techniques and the new three-dimensional photoionization code MOCASSIN (Ercolano et al. 2003) enable us to analyze PNe properties accurately by the construction of consistent models of PNe and CSs. In addition to PNe imaging and spectroscopy, detailed information about the velocity field within the PNe is a pre-requisite to employ de-projection techniques in modeling the physical structure of the PNe.

  17. A spectroscopic and photometric study of FK Comae in 1989

    NASA Technical Reports Server (NTRS)

    Huenemoerder, David P.; Ramsey, Lawrence W.; Buzasi, Derek L.; Nations, Harold L.

    1993-01-01

    Results of an observational campaign, coordinated between visual photometry, optical spectroscopy, and UV spectroscopy, to elucidate the characteristics of FK Comae are presented. The photometry showed complicated but systematic behavior. Photospheric absorption lines were distorted by a Doppler-shifted bump caused by dark starspots resulting in small apparent radial velocity variations. No radial velocity variations characteristic of orbital motion were seen to a level of 3 km/s. Broad emission in H-alpha was modulated at the photospheric rotational amplitude, implying an origin no farther from the rotational axis than 1 stellar radius. The strengths of Ca II lines are modulated in phase with H-alpha but do not have velocity-modulated wings like H-alpha.

  18. Multiwavelength Observations of Two Moderate Rotation RS CVn Systems: V815 Herculis and IM Pegasi

    NASA Astrophysics Data System (ADS)

    Dempsey, Robert C.; Neff, James E.; O'Neal, Douglas; Olah, Katalin

    1996-03-01

    Near-to-simultaneous ultraviolet and visual spectroscopy of two moderate v sin i RS CVn systems, V815 Herculis (v sin i=27 km s-1) and IM Pegasi (v sin i=24 km s-1), are presented along with contemporaneous UBV(RI)c photometry. These data were used to probe inhomogeneities in the chromospheres and photospheres, and the possible relationship between them. Variability is observed at all wavelengths, some indicators showing rotationally modulated fluctuations. We use UBVRI photometry and TiO spectra to estimate temperatures, area, and locations of photospheric spots on IM Peg. Evidence is presented that the spot temperature in IM Peg has changed over a possible solar-like spot cycle. Radial velocities of V815 Her indicates that the system is actually triple.

  19. Dynamics and energetics of the solar corona

    NASA Technical Reports Server (NTRS)

    Steinolfson, R. S.

    1992-01-01

    The primary objective of this research program is to improve our understanding of the dynamics and energetics of the solar corona both in the quiescent dynamic equilibrium state when coronal structure is dominated by the equatorial streamer belt and in the eruptive state when coronal plasma is ejected into the interplanetary medium. Numerical solutions of the time-dependent magnetohydrodynamic (MHD) equations and comparisons of the computed results with observations form the core of the approach to achieving this objective. Some of the specific topics that have been studied are: (1) quiescent coronal streamers in an atmosphere dominated by a dipole magnetic field at large radii, (2) the formation of coronal mass ejections (CMEs) in quiescent streamers due to the emergence of new magnetic flux and due to photospheric shear motion, (3) MHD shock formation near the leading edge of CMEs, (4) coronal magnetic arcade eruption as a result of applied photospheric shear motion, and (5) the three-dimensional structure of CMEs.

  20. Sensitive Identification of Nearby Debris Disks via Precise Calibration of WISE Data

    NASA Astrophysics Data System (ADS)

    Patel, Rahul; Metchev, Stanimir; Heinze, Aren; Trollo, Joe

    2016-01-01

    Using data from the WISE All-Sky Survey, we have found >100 new infrared excess sources around main-sequence Hipparcos stars within 75 pc. Our empirical calibration of WISE photospheric colors and removal of non-trivial false-positive sources are responsible for the high confidence (>99.5%) of detections, while our corrections to saturated W1 and W2 photometry have for the first time allowed us to search for new infrared excess sources around bright field stars in WISE. The careful calibration and filtering of the WISE data have allowed us to probe excess fluxes down to roughly 8% of the photospheric emission at 22μm around saturated stars in WISE. We expect that the increased sensitivity of our survey will not only aid in understanding the evolution of debris disks, but will also benefit future studies using WISE.