Average Variations of Photospheric FeI and FeII Line Parameters as Function of the Magnetic Filling Factor

A series of 17 Fourier transform spectra taken at the McMath telescope near disk center in regions of different magnetic field strengths were analyzed. Applying a multi-variate regression analysis magnetic filling factors 0 < α ≥ 0.11 were determined. With α increasing from 0 to 0.11, line bisectors averaged over groups of lines of similar depth are found to show a blue shift decreasing from 0.35 km s–1 to nearly 0.1 km s–1, when referred to the MgI line λ5172.7å. The bisectors of FeII lines exhibit smaller blue shifts than FeI lines. The increase of bisector red shift near the continuum with increasing α, found earlier by Brandt and Solanki (1987), was confirmed and is tentatively interpreted as a manifestation of downdrafts in the vicinity of flux tubes (Deinzer et al., 1984).A significant increase of line width (typically between 3 and 8%, depending on line strength) and a decrease of line depth is found with increasing filling factor. For strong lines the equivalent width W shows no variation or a slight increase, while for the weaker lines a reduction of W between a few % and > 10% is found.

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Numerical Simulation of Granular Convection: Effects on Photospheric Spectral Line Profiles

International Astronomical Union Colloquium ◽

10.1017/s0252921100075412 ◽

1980 ◽

Vol 51 ◽

pp. 213-224

Author(s):

Åke Nordlund

Keyword(s):

Spectral Line ◽

Line Strength ◽

Blue Shift ◽

Spectral Lines ◽

Line Profiles ◽

Pressure Broadening ◽

Solar Granulation ◽

Velocity Fluctuations ◽

Excitation Potential ◽

On Line

AbstractThe results of numerical simulations of the solar granulation are used to investigate the effects on photospheric apectral lines of the correlated velocity and temperature fluctuations of the convective granular motions. It is verified that the granular velocity field is the main cause for the observed broadening and strengthening of photospheric spectral lines relative to values expected from pure thermal and pressure broadening. These effects are normally referred to as being due to “macro-turbulence” and “micro-turbulence”, respectively. It is also shown that the correlated temperature and velocity fluctuations produce a “convective blue shift” in agreement with the observed blue shift of photospheric spectral lines. Reasons are given for the characteristic shapes of spectral line bisectors, and the dependence of these shapes on line strength, excitation potential, and center to limb distance are discussed.

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Phase Spectra Seen from Space

Symposium - International Astronomical Union ◽

10.1017/s007418090023917x ◽

1998 ◽

Vol 185 ◽

pp. 455-456

Author(s):

Th. Straus ◽

F.-L. Deubner ◽

B. Fleck ◽

C. Marmolino ◽

G. Severino ◽

...

Keyword(s):

Time Series ◽

Line Intensity ◽

Solar Rotation ◽

Disk Center ◽

Mean Velocity ◽

Continuum Intensity ◽

Doppler Imager ◽

Low Pass ◽

Line Depth ◽

The Continuum

A 15 hour time series of simultaneous spectroscopic measurements of the continuum intensity, Doppler shift, and line depth in the Ni I 6768Å line at disk center of the quiet sun has been obtained during a guest investigator campaign with the Michelson Doppler Imager (MDI, see Scherrer et al. 1995). In addition, the line intensity has been calculated from the continuum intensity and the line depth data. The spatial shifts due to solar rotation have been approximately removed during the observation run by shifting the CCD read-out area by 1 pixel every 4 minutes. Small residual shifts have been removed during the data analysis. Before applying the Fourier analysis, a (temporal) low pass filtered mean velocity (line of sight component of solar rotation) and mean intensity (center-limb variation) has been removed from each frame. Finally, the continuum intensity (C), line intensity (I), and velocity (V) time series have been subjected to a 3D Fourier transform, yielding κ - ω power, cross power, phase difference, and coherence spectra. The data can now be compared to recent ground-based observations (Deubner, 1990; Deubner et al., 1992; Straus & Bonaccini, 1997).

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Photo-electric Hβ and uvby photometry

Symposium - International Astronomical Union ◽

10.1017/s0074180900053407 ◽

1966 ◽

Vol 24 ◽

pp. 170-180

Author(s):

D. L. Crawford

Keyword(s):

Narrow Band ◽

Line Strength ◽

Interference Filter ◽

B Stars ◽

Relative Line ◽

The Mean ◽

F Stars ◽

Two Parameters ◽

Filter Photometry ◽

The Continuum

Early in the 1950's Strömgren (1, 2, 3, 4, 5) introduced medium to narrow-band interference filter photometry at the McDonald Observatory. He used six interference filters to obtain two parameters of astrophysical interest. These parameters he calledlandc, for line and continuum hydrogen absorption. The first measured empirically the absorption line strength of Hβby means of a filter of half width 35Å centered on Hβand compared to the mean of two filters situated in the continuum near Hβ. The second index measured empirically the Balmer discontinuity by means of a filter situated below the Balmer discontinuity and two above it. He showed that these two indices could accurately predict the spectral type and luminosity of both B stars and A and F stars. He later derived (6) an indexmfrom the same filters. This index was a measure of the relative line blanketing near 4100Å compared to two filters above 4500Å. These three indices confirmed earlier work by many people, including Lindblad and Becker. References to this earlier work and to the systems discussed today can be found in Strömgren's article inBasic Astronomical Data(7).

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From Center-Vortex Ensembles to the Confining Flux Tube

Universe ◽

10.3390/universe7080253 ◽

2021 ◽

Vol 7 (8) ◽

pp. 253

Author(s):

David R. Junior ◽

Luis E. Oxman ◽

Gustavo M. Simões

Keyword(s):

Degrees Of Freedom ◽

String Tension ◽

Effective Field ◽

Scaling Properties ◽

Flux Tubes ◽

Topological Solitons ◽

Yang Mills ◽

Center Vortex ◽

Asymptotic Scaling ◽

The Continuum

In this review, we discuss the present status of the description of confining flux tubes in SU(N) pure Yang–Mills theory in terms of ensembles of percolating center vortices. This is based on three main pillars: modeling in the continuum the ensemble components detected in the lattice, the derivation of effective field representations, and contrasting the associated properties with Monte Carlo lattice results. The integration of the present knowledge about these points is essential to get closer to a unified physical picture for confinement. Here, we shall emphasize the last advances, which point to the importance of including the non-oriented center-vortex component and non-Abelian degrees of freedom when modeling the center-vortex ensemble measure. These inputs are responsible for the emergence of topological solitons and the possibility of accommodating the asymptotic scaling properties of the confining string tension.

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High-Resolution Observations of Emerging Magnetic Fields and Flux Tubes in Active Region Photosphere

Symposium - International Astronomical Union ◽

10.1017/s0074180900044089 ◽

1990 ◽

Vol 138 ◽

pp. 147-152 ◽

Cited By ~ 4

Author(s):

T. Tarbell ◽

S. Ferguson ◽

Z. Frank ◽

R. Shine ◽

A. Title ◽

...

Keyword(s):

Magnetic Field ◽

Active Region ◽

Solar Observatory ◽

Disk Center ◽

Line Center ◽

Solar Photosphere ◽

Flux Tubes ◽

National Solar Observatory ◽

La Palma ◽

The Relationship

On 29 September 1988, filtergrams of the solar photosphere with excellent resolution (0.3 to 0.5 arcsecond) were obtained at the Swedish Solar Observatory on La Palma, Canary Islands. An outstanding 2.5 hour run of digital filtergram observations was obtained, looking at a small area within an active region near disk center. On 6 August 1987, an 80 minute run of similar observations was obtained at the Vacuum Tower Telescope of the National Solar Observatory at Sacramento Peak. Digital and video movies have been made of Dopplergrams, magnetograms, line center, continuum, and white light images. Several examples of magnetic field emergence and formation of flux tubes can be studied in detail in the movies. The relationship between photospheric bright points, “filigree”, the line center brightness, and the magnetic field has been established for individual images in analysis to date.

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Effect of Water Volume on the Growth of Silver Nanoparticles Promoted by Ultraviolet

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.96.55 ◽

2010 ◽

Vol 96 ◽

pp. 55-59 ◽

Cited By ~ 1

Author(s):

Jing Chen ◽

Ye Ling Jin

Keyword(s):

Silver Nanoparticles ◽

Blue Shift ◽

High Volume ◽

High Water ◽

Water Volume ◽

Reactive System ◽

Transmission Electron ◽

Vis Spectroscopy ◽

On Line ◽

Low Volume

The formation process of silver nanoparticles promoted by ultraviolet has been investigated by on-line UV-vis spectroscopy and transmission electron microscope (TEM). We firstly report that the volume of water will result in the growth of silver nanoparticles with different mechanism, UV-vis spectra show that the growth of nanopaticles presents blue-shift for reactive system with high volume water, but red-shift for that of low volume water. Moreover, experiments reveal that high water volume results in the change of the color of the silver sol accordingly.

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No universal connection between the vertical magnetic field and the umbra-penumbra boundary in sunspots

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037974 ◽

2020 ◽

Vol 639 ◽

pp. A106

Author(s):

B. Löptien ◽

A. Lagg ◽

M. van Noort ◽

S. K. Solanki

Keyword(s):

Magnetic Field ◽

Statistical Analysis ◽

Field Strength ◽

Magnetic Field Strength ◽

Filling Factor ◽

Spot Size ◽

Vertical Magnetic Field ◽

Continuum Intensity ◽

The Mean ◽

The Continuum

Context. It has been reported that the boundary between the umbra and the penumbra of sunspots occurs at a canonical value of the strength of the vertical magnetic field, independently of the size of the spot. This critical field strength is interpreted to be the threshold for the onset of magnetoconvection. Aims. Here we investigate the reasons why this criterion, also called the Jurčák criterion in the literature, does not always identify the boundary between the umbra and the penumbra. Methods. We performed a statistical analysis of 23 sunspots observed with Hinode/SOT. We compared the properties of the continuum intensity and the vertical magnetic field between filaments and spines and how they vary between spots of different sizes. Results. We find that the inner boundary of the penumbra is not related to a universal value of the vertical magnetic field. The properties of spines and filaments vary between spots of different sizes. Both components are darker in larger spots and the spines exhibit a stronger vertical magnetic field. These variations of the properties of filaments and spines with the spot size are also the reason for the reported invariance in the averaged vertical magnetic field at 50% of the mean continuum intensity. Conclusions. The formation of filaments and the onset of magnetoconvection are not related to a canonical value of the strength of the vertical magnetic field. The seemingly unique magnetic field strength is rather an effect of the filling factor of spines and penumbral filaments.

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Methane and the Spectra of T Dwarfs

Symposium - International Astronomical Union ◽

10.1017/s0074180900211042 ◽

2003 ◽

Vol 211 ◽

pp. 419-420 ◽

Cited By ~ 2

Author(s):

Derek Homeier ◽

Peter H. Hauschildt ◽

France Allard

Keyword(s):

Line Strength ◽

Ir Absorption ◽

Line List ◽

Near Ir ◽

Ultracool Dwarfs ◽

On Line ◽

Absorption Features

We have updated our PHOENIX model atmospheres and theoretical spectra for ultracool dwarfs with new opacity data for methane based on line strength predictions with the STDS software. By extending the line list to rotational levels of J = 40 we can significantly improve the shape of the near-IR absorption features of CH4, and in addition find an enhanced blanketing effect, resulting in up to 50% more flux emerging in the J band than seen in previous models, which may thus contribute to the brightening in J and blue IR colors observed in T dwarfs.

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