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Topka, K.

Publications and source records attributed to Topka, K..

18 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

High resolution observations: The state of the art and beyond

The meaning of high resolution and its scientific importance with regard to solar observations is discussed. The state of the art is reviewed, looking into Solar Optical Universal Polarimeter (SOUP) observations, image selection techniques, and adaptive optics. It is concluded that until there are observations in space, complete understanding of processes in the solar photosphere, chromosphere, transition region, and corona will be impossible. The importance of high resolution is considered with regard to solar surface and convection, solar photosphere inside and outside magnetic fields, and sunspot geometry.

Title, A.↗
NASA NTRS1990

Magnetic flux tubes and their relation to continuum and photospheric features

An investigation is made of the relationship between photospheric 'filigree' light points, line-center brightness, and magnetic field, as inferred from sets of individual images and films showing a distinct difference between two classes of magnetic regions. While in the first such region the vertical velocity field is average and the magnetic field is mostly confined in narrow lanes, the granulation pattern of the second scale is much smaller, the vertical velocity is lower, and the magnetic field is less compact. Where granulation is normal, excellent correlation is obtained between bright continuum, line-center, and magnetic field line structure.

Title, A.↗
NASA NTRS1989

Investigation of active regions at high resolution by balloon flights of the Solar Optical Universal Polarimeter (SOUP)

SOUP is a versatile, visible-light solar observatory, built for space or balloon flight. It is designed to study magnetic and velocity fields in the solar atmosphere with high spatial resolution and temporal uniformity, which cannot be achieved from the surface of the earth. The SOUP investigation is carried out by the Lockheed Palo Alto Research Laboratory, under contract to NASA's Marshall Space Flight Center. Co-investigators include staff members at a dozen observatories and universities in the U.S. and Europe. The primary objectives of the SOUP experiment are: to measure vector magnetic and velocity fields in the solar atmosphere with much better spatial resolution than can be achieved from the ground; to study the physical processes that store magnetic energy in active regions and the conditions that trigger its release; and to understand how magnetic flux emerges, evolves, combines, and disappears on spatial scales of 400 to 100,000 km. SOUP is designed to study intensity, magnetic, and velocity fields in the photosphere and low chromosphere with 0.5 arcsec resolution, free of atmospheric disturbances. The instrument includes: a 30 cm Cassegrain telescope; an active mirror for image stabilization; broadband film and TV cameras; a birefringent filter, tunable over 5100 to 6600 A with 0.05 A bandpass; a 35 mm film camera and a digital CCD camera behind the filter; and a high-speed digital image processor.

Tarbell, T.↗
NASA NTRS1988

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

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.

Tarbell, T.↗
NASA NTRS1988

High-resolution digital movies of emerging flux and horizontal flows in active regions on the sun

High-resolution observations of active regions in many wavelength bands obtained at the Vacuum Tower Telescope of NSO/Sunspot (Sacramento Peak) are presented. The SOUP tunable filter, HRSO 1024 x 1024 CCD camera, and a sunspot tracker for image stabilization were used. Subarrays of 512 x 512 pixels were processed digitally and recorded on videodisk in movie format. The movies with 0.5 to 1 arcsecond resolution of the following simultaneous observations were shown: green continuum, longitudinal magnetogram, Doppler velocity, Fe I 5576 A line center, H alpha wings, and H alpha line center. The best set of 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. Flux emergence is most easily discovered in line center movies: an elongated dark feature appears first, followed soon after by bright points at one or both ends. A brief, strong upflow is seen when the dark feature first appears; downflow in the bright points persists much longer. The magnetic flux appears to increase gradually over this extended period. Some of the flux emergence events were studied in detail, with measurements of horizontal and vertical velocities and magnetic flux versus time within one footpoint of the loop.

Topka, K.↗
NASA NTRS1988

Statistical properties of solar granulation from the SOUP instrument on Spacelab 2

The Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 collected movies of solar granulation completely free from atmospheric blurring, and are not degraded by pointint jitter (the pointing stability was 0.003 sec root mean square). The movies illustrate that the solar five minute oscillation has a major role in the appearance of solar granulation and that exploding granules are a common feature of the granule evolution. Using 3-D Fourier filtering techniques the oscillations were removed and it was demonstrated that the autocorrelation lifetime of granulation is a factor of two greater in magnetic field regions than in field-free quiet sun. Horizontal velocities were measured and flow patterns were observed on the scale of meso- and super granulation. In quiet regions the mean flow velocity is 370 m/s while in the magnetic regions it is about 125 m/s. It was also found that the root mean square (RMS) fluctuating horizonal velocity field is substantially greater in quiet sun than in strong magnetic field regions. By superimposing the location of exploding granules on the average flow maps it was found that they appear almost exclusively in the center of mesogranulation size flow cells. Because of the nonuniformity of the distribution of exploding granules, the evolution of the granulation pattern in mesogranule cell centers and boundaries differs fundamentally. It is clear from this study there is neither a typical granule nor a typical granule evolution.

Topka, K.↗
NASA NTRS1988

Correlation lifetimes of quiet and magnetic granulation from the SOUP instrument on Spacelab 2

The time sequences of diffraction limited granulation images obtained by the Solar Optical Universal Polarimeter on Spacelab 2 are presented. The uncorrection autocorrelation limetime in magnetic regions is dominated by the 5-min oscillation. The removal of this oscillation causes the autocorrelation lifetime to increase by more than a factor of 2. The results suggest that a significant fraction of granule lifetimes are terminated by nearby explosions. Horizontal displacements and transverse velocities in the intensity field are measured. Lower limits to the lifetime in the quiet and magnetic sun are set at 440 s and 950 s, respectively.

Title, A.↗
NASA NTRS1982

A magnitude limited stellar X-ray survey and the F star X-ray luminosity function

An X-ray survey has been conducted of stars brighter than visual magnitude 8.5 that have serendipitously fallen into the fields of view of the Imaging Proportional Counter of the Einstein Observatory. The survey includes 227 separate 1 x 1 deg fields, containing 274 stars with a visual magnitude of no more than 8.5 and covering a wide range of spectral types and luminosity classes. X-ray emission was detected from 33 stars, and upper limits have been determined for the remainder of the sample. F type stars dominate the detected sample, and most of these are shown to be dwarfs. An X-ray luminosity function for dF stars has been deduced, and reveals that the average 0.2-4.0 keV luminosity of these stars is around 10 to the 29th erg/sec. Constraints have been placed on the high luminosity tails and medians of the X-ray luminosity functions for other types of stars.

Topka, K.↗
NASA NTRS1982

Evidence for a poleward meridional flow on the sun

Two subsets of all polar zone filaments, designated polemost filament and polar filament bands, are defined for observational study of their behavior, which is compared with the evolution of the polar magnetic field over Howard and LaBonte's (1981) activity cycle. The magnetic data show that the polar magnetic fields are built up and maintained by the episodic arrival of discrete f-polarity regions originating in active region latitudes and subsequently drifting to the poles. F-polarity regions are carried poleward by a meridional flow, rather than by diffusion. It is noted that the mean latitude of the polemost filaments tracks the boundary of the polar field cap, and undergoes an equatorward dip during each arrival of additional polar field, and that the polar filament bands track the boundary latitudes of the unipolar regions, drifting poleward with the regions at about 10 m/sec.

Topka, K.↗
NASA NTRS1982

Detection of microwave emission from both components of the red dwarf binary EQ Pegasi

The detection at 4.9 GHz of the late main sequence binary EQ Pegasi (dM3.5e + dM4.5e) with the VLA is reported. Both components were detected, as flux levels of 0.69 mJy and 0.4 mJy, respectively. Thermal gyroresonance emission from the quiescent coronae of these stars appears to explain observations of the authors, as it does those of Gary and Linsky (1981) for chi Ori and UV Ceti, provided coronal magnetic fields in excess of 300 gauss exist over a region that has a length scale of at least twice the radii of these stars. Support for this model is provided by the unlikelihood of both stars flaring simultaneously, and by the fact that the emission was confined to each star within the observational uncertainty of a few AU.

Topka, K.↗
NASA NTRS1981

The stellar contribution to the galactic soft X-ray background

Log N-log S relations for stars are constructed based on median X-ray luminosities for dF, dG, and dK stars previously reported for the Einstein Observatory/Center for Astrophysics stellar survey and on a detailed X-ray luminosity function derived here for dM stars, and the stellar contribution to the diffuse soft X-ray background is investigated. The principal results are that stars provide approximately 20% of the soft X-ray background in the 0.28-1.0 keV passband and therefore contribute significantly to the soft X-ray background in this energy range (with dM stars constituting the dominant contributing class), and that the stellar contribution to the diffuse X-ray background in the 0.15-0.28 keV passband is less than approximately 3%.

Rosner, R.↗
NASA NTRS1979

Discovery of an X-ray star association in VI Cygni /Cyg OB2/

A group of six X-ray sources located within 0.4 deg of Cygnus X-3 has been discovered with the Einstein Observatory. These sources have been positively identified and five of them correspond to stars in the heavily obscured OB association VI Cygni. The optical counterparts include four of the most luminous O stars within the field of view and a B5 supergiant. These sources are found to have typical X-ray luminosities of 5 x 10 to the 33rd ergs/s, with temperatures of 10 to the 6.8th K and hydrogen column densities of 10 to the 22nd/sq cm, and therefore comprise a new class of low-luminosity galactic X-ray sources associated with early-type stars.

Harnden, F. R., Jr.↗
NASA NTRS1979

Soft X-ray structure of the Coma cluster of galaxies

Results are reported for an observation of the Coma cluster with an imaging X-ray telescope system aboard a sounding rocket. A two-dimensional X-ray map of the cluster in the energy range from 0.15 to 2.0 keV is presented. The radial distribution, granularity, and ellipticity of the X-ray surface brightness are investigated, and the spectrum and flux within the field of view are analyzed. These properties are then examined quantitatively by comparing the observations with models through the use of a chi-squared test. It is found that: (1) no single galaxy contributes more than a few percent of the total X-ray flux of the Coma cluster; (2) the X-ray source is diffuse but granular on a scale of several arcmin, particularly in the central region; (3) the centroid of the X-ray source is at a local intensity minimum; and (4) the data are most consistent with an isothermal hydrostatic model.

Gorentstein, P.↗
NASA NTRS1979

Detection of soft X-rays from Alpha Lyrae and Eta Bootis with an imaging X-ray telescope

Results are presented for observations of Alpha Lyr (Vega) and Eta Boo with an imaging X-ray telescope during two rocket flights. It is found that Vega and Eta Boo are soft X-ray sources with respective luminosities of approximately 3 x 10 to the 28th erg/s (0.15-0.8 keV) and 1 x 10 to the 29th erg/s (0.15-1.5 keV). Surface X-ray luminosities of about 640,000 erg/sq cm per sec for Vega and 300,000 erg/sq cm per sec for Eta Boo are estimated and shown to fall within the range of solar coronal X-ray emission. It is concluded that in view of the substantially larger surface areas of these stars, the relatively large total soft X-ray luminosity (as compared with that of the sun) can in both cases be understood as resulting from a moderately active corona, although the Vega observation is in severe conflict with simple models for X-ray emission from single main-sequence stars.

Topka, K.↗
NASA NTRS1978

Soft X-ray structure of the Perseus cluster of galaxies

A 0.5-1.5-keV X-ray image of the Perseus cluster of galaxies was obtained with a focusing telescope system aboard a sounding rocket. The source consists of a region of diffuse emission plus a superposed central source in the vicinity of NGC 1275 smaller than 4 arcmin in diameter that accounts for one-quarter of the total intensity within a radius of 25 arcmin. The results for the diffuse source are consistent with the isothermal-hydrostatic picture in which the hot gas has a core radius of 17 arcmin and is approximately symmetric about NGC 1275. Several isothermal-hydrostatic models are considered which relate the size and temperature of the diffuse X-ray source with the core radius of the galaxies and their velocity dispersion. Fixing the velocity dispersion at values measured by Chincarini and Rood (1971) requires the core radius of the galaxies to be 28 + or - 9 arcmin, which is larger than present measurements. Conversely, fixing the core radius of the galaxies at 8 arcmin requires a smaller velocity dispersion or a condition in which the velocity distribution is anisotropic. Upper limits on the intrinsic X-ray absorption of the central source place the bulk of its X-ray emission beyond the nuclear region of NGC 1275.

Gorenstein, P.↗
NASA NTRS1977

Structure of the X-ray source in the Virgo cluster of galaxies

High-angular-resolution observations in the 0.15-1.5-keV band with an imaging X-ray telescope shows the extended X-ray source in the Virgo cluster of galaxies to be a diffuse halo of about 15 arcmin core radius surrounding M87. The angular structure of the surface brightness is marginally consistent with either of two simple models: (1) an isothermal (or adiabatic or hydrostatic) sphere plus a point source at M87 accounting for 12% of the total 0.5-1.5-keV intensity or (2) a power-law function without a discrete point source. No evidence for a point source is seen in the 0.15-0.28-keV band, which is consistent with self-absorption by about 10 to the 21st power per sq cm of matter having a cosmic abundance. The power-law models are motivated by the idea that radiation losses regulate the accretion of matter onto M87 and can account for the observed difference in the size of the X-ray source as seen in the present measurements and at higher energies.

Gorenstein, P.↗
NASA NTRS1977

A soft X-ray image of the Algol region

Algol (Beta Persei) has been detected in two separate exposures of an imaging X-ray telescope. The 0.15- to 2-keV X-ray luminosity is approximately 2 by 10 to the 30th power erg/s. The X-ray flux is interpreted as thermal emission produced by direct accretion of mass from the K star to the B8 member of the triple star system.

Harnden, F. R., Jr.↗