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Author name code: anzer
ADS astronomy entries on 2022-09-14
author:"Anzer, Ulrich"
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Title: 3D modelling of magnetic field and plasma structure of entire
prominences
Authors: Gunár, Stanislav; Anzer, Ulrich; Heinzel, Petr; Mackay,
Duncan
2018cosp...42E1315G Altcode:
The 3D Whole-Prominence Fine Structure (WPFS) model allows us for
the first time to simulate entire prominences/filaments including
their numerous fine structures. This model combines a 3D magnetic
field configuration of an entire prominence obtained from non-linear
force-free field simulations, with a detailed description of the
prominence plasma. The plasma is located in magnetic dips in hydrostatic
equilibrium and is distributed along hundreds of fine structures
within the 3D magnetic model. The prominence plasma has realistic
density and temperature distributions including the prominence-corona
transition region. This allows us to produce synthetic H-alpha images
of simulated prominences both in emission on the solar limb and in
absorption against the solar disk (viewed as filaments) using a single
model.Such 3D WPFS model provides us with consistent information about
the prominence magnetic field configuration, prominence fine structure
plasma and its radiative output. Moreover, we are able to follow the
evolution of modeled prominences caused by changes of the underlying
photospheric magnetic flux distribution. Thanks to these capabilities we
can study links between the photospheric flux distribution, prominence
magnetic field configuration, distribution and composition of the
prominence plasma and its observable signatures. These relationships
are important for interpretation of the observed imaging and
spectral/spectropolarimetric data and for inference of the properties
of the prominence magnetic field.
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Title: Plasma physical parameters of a prominence embedded in the
core of a Coronal Mass Ejection
Authors: Bemporad, Alessandro; Anzer, Ulrich; Heinzel, Petr; Jejcic,
Sonja; Susino, Roberto
2018cosp...42E.267B Altcode:
We determine the plasma physical parameters of an erupting prominence
embedded in the core of a CME, combininging visible light coronagraphic
images from SOHO/LASCO with UV spectra acquired by SOHO/UVCS. Strong
UV emissions were detected in the hydrogen Lyman-α and Lyman-β
lines and C III line. Visible light and UV intensities have been used
to estimate the projected thickness and velocity of the prominence,
together with the effective plasma temperature, microturbolent velocity,
and column density. These parameters have been used to constrain
1D NLTE modeling of the erupting plasma, taking into account the
effects of large flow velocities (Doppler dimming). Roughly one-half
of considered points in the prominence body show a non-negligible
Lyman-α optical thickness. Comparison between the calculated and the
measured intensities of the two Lyman lines was also used to derive the
geometrical filling factor. Results show that the erupting prominence
plasma is relatively hot, with a low electron density, a wide range of
effective thicknesses, a rather narrow range of radial flow velocities,
and a microturbulence of about 25 km/s. This analysis provides a basis
for future diagnostics of prominences using the METIS coronagraph on
board the Solar Orbiter mission.
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Title: Hot Erupting Prominences in Cores of Cme's
Authors: Heinzel, Petr; Bemporad, Alessandro; Anzer, Ulrich; Jejcic,
Sonja; Susino, Roberto; Dzifcakova, Elena
2018cosp...42E1421H Altcode:
Coronal mass ejections (CME) associated with prominence eruptions
exhibit relatively coolmaterial in their cores. Such prominence
plasmas were frequently detected in various spectrallines by SOHO/UVCS
coronagraph and in the visible light by SOHO/LASCO as well as bySTEREO
coronagraphs. UVCS provided excellent spectra of CME-core prominences
and anextended catalogue of these data is available. We will present
recent results of a hot prominence diagnostics using the hydrogen Lyman
lines and the CIII line . The erupting prominence parameters are further
constrained by the visible light observations from LASCO-C2. A novel
non-LTE modeling based on such observations will be presented and we
will highlight the diagnostic potential of the UV and visible light for
future space coronagraphs like Metis on board the ESA Solar Orbiter
mission. The plasma parameters of such hot prominences are compared
with those obtained from numerical MHD simulations of erupting flux
ropes surrounded by CMEs. Finally, we will also mention synergies with
stellar analogues.
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Title: Can 3D whole-prominence fine structure models be used for
assessment of the prominence plasma mass and distribution prior to
the onset of CMEs?
Authors: Gunár, Stanislav; Schmieder, Brigitte; Aulanier, Guillaume;
Anzer, Ulrich; Heinzel, Petr; Mackay, Duncan; Dudik, Jaroslav
2018cosp...42E1316G Altcode:
Two complex 3D models of entire prominences including their numerous
fine structures were recently developed. The first 3D Whole-Prominence
Fine Structure (WPFS) model was developed by Gunár and Mackay. The
second 3D WPFS model was put forward by Gunár, Aulanier, Dudík,
Heinzel, and Schmieder. These 3D prominence models combine simulations
of the 3D magnetic field configuration of an entire prominence with a
detailed description of the prominence plasma. The plasma is located
in magnetic dips in hydrostatic equilibrium and is distributed
along hundreds of fine structures. The assumed prominence plasma
has realistic density and temperature distributions including the
prominence-corona transition region.These 3D WPFS models allow us
to study the distribution and the mass of the prominence plasma
contained in prominence magnetic field configurations. These can
be crucial during the onset and early evolution of CMEs. Moreover,
prominence plasma represents a bulk of the material ejected by CMEs
into the interplanetary space. Here, we investigate the potential of
using the 3D WPFS models for assessment of the role the prominence
plasma plays in the initiation and evolution of CMEs.
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Title: Quiescent Prominences in the Era of ALMA. II. Kinetic
Temperature Diagnostics
Authors: Gunár, Stanislav; Heinzel, Petr; Anzer, Ulrich; Mackay,
Duncan H.
2018ApJ...853...21G Altcode:
We provide the theoretical background for diagnostics of the thermal
properties of solar prominences observed by the Atacama Large
Millimeter/submillimeter Array (ALMA). To do this, we employ the 3D
Whole-Prominence Fine Structure (WPFS) model that produces synthetic
ALMA-like observations of a complex simulated prominence. We use
synthetic observations derived at two different submillimeter/millimeter
(SMM) wavelengths—one at a wavelength at which the simulated
prominence is completely optically thin and another at a wavelength at
which a significant portion of the simulated prominence is optically
thick—as if these were the actual ALMA observations. This allows
us to develop a technique for an analysis of the prominence plasma
thermal properties from such a pair of simultaneous high-resolution ALMA
observations. The 3D WPFS model also provides detailed information about
the distribution of the kinetic temperature and the optical thickness
along any line of sight. We can thus assess whether the measure of the
kinetic temperature derived from observations accurately represents
the actual kinetic temperature properties of the observed plasma. We
demonstrate here that in a given pixel the optical thickness at the
wavelength at which the prominence plasma is optically thick needs
to be above unity or even larger to achieve a sufficient accuracy of
the derived information about the kinetic temperature of the analyzed
plasma. Information about the optical thickness cannot be directly
discerned from observations at the SMM wavelengths alone. However,
we show that a criterion that can identify those pixels in which
the derived kinetic temperature values correspond well to the actual
thermal properties in which the observed prominence can be established.
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Title: Hot prominence detected in the core of a coronal mass
ejection. II. Analysis of the C III line detected by SOHO/UVCS
Authors: Jejčič, S.; Susino, R.; Heinzel, P.; Dzifčáková, E.;
Bemporad, A.; Anzer, U.
2017A&A...607A..80J Altcode:
Context. We study the physics of erupting prominences in the core
of coronal mass ejections (CMEs) and present a continuation of a
previous analysis. <BR /> Aims: We determine the kinetic temperature
and microturbulent velocity of an erupting prominence embedded in the
core of a CME that occurred on August 2, 2000 using the Ultraviolet
Coronagraph and Spectrometer observations (UVCS) on board the Solar
and Heliospheric Observatory (SOHO) simultaneously in the hydrogen
Lα and C III lines. We develop the non-LTE (departures from the local
thermodynamic equilibrium - LTE) spectral diagnostics based on Lα and
Lβ measured integrated intensities to derive other physical quantities
of the hot erupting prominence. Based on this, we synthesize the C
III line intensity to compare it with observations. <BR /> Methods:
Our method is based on non-LTE modeling of eruptive prominences. We
used a general non-LTE radiative-transfer code only for optically thin
prominence points because optically thick points do not allow the
direct determination of the kinetic temperature and microturbulence
from the line profiles. The input parameters of the code were the
kinetic temperature and microturbulent velocity derived from the Lα
and C III line widths, as well as the integrated intensity of the Lα
and Lβ lines. The code runs in three loops to compute the radial flow
velocity, electron density, and effective thickness as the best fit
to the Lα and Lβ integrated intensities within the accuracy defined
by the absolute radiometric calibration of UVCS data. <BR /> Results:
We analyzed 39 observational points along the whole erupting prominence
because for these points we found a solution for the kinetic temperature
and microturbulent velocity. For these points we ran the non-LTE code to
determine best-fit models. All models with τ<SUB>0</SUB>(Lα) ≤ 0.3
and τ<SUB>0</SUB>(C III) ≤ 0.3 were analyzed further, for which we
computed the integrated intensity of the C III line using a two-level
atom. The best agreement between computed and observed integrated
intensity led to 30 optically thin points along the prominence. The
results are presented as histograms of the kinetic temperature,
microturbulent velocity, effective thickness, radial flow velocity,
electron density, and gas pressure. We also show the relation between
the microturbulence and kinetic temperature together with a scatter plot
of computed versus observed C III integrated intensities and the ratio
of the computed to observed C III integrated intensities versus kinetic
temperature. <BR /> Conclusions: The erupting prominence embedded in
the CME is relatively hot with a low electron density, a wide range of
effective thicknesses, a rather narrow range of radial flow velocities,
and a microturbulence of about 25 km s<SUP>-1</SUP>. This analysis shows
a disagreement between observed and synthetic intensities of the C III
line, the reason for which most probably is that photoionization is
neglected in calculations of the ionization equilibrium. Alternatively,
the disagreement might be due to non-equilibrium processes.
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Title: Quiescent Prominences in the Era of ALMA: Simulated
Observations Using the 3D Whole-prominence Fine Structure Model
Authors: Gunár, Stanislav; Heinzel, Petr; Mackay, Duncan H.; Anzer,
Ulrich
2016ApJ...833..141G Altcode:
We use the detailed 3D whole-prominence fine structure model to
produce the first simulated high-resolution ALMA observations
of a modeled quiescent solar prominence. The maps of synthetic
brightness temperature and optical thickness shown in the present
paper are produced using a visualization method for synthesis of the
submillimeter/millimeter radio continua. We have obtained the simulated
observations of both the prominence at the limb and the filament
on the disk at wavelengths covering a broad range that encompasses
the full potential of ALMA. We demonstrate here extent to which the
small-scale and large-scale prominence and filament structures will be
visible in the ALMA observations spanning both the optically thin and
thick regimes. We analyze the relationship between the brightness and
kinetic temperature of the prominence plasma. We also illustrate the
opportunities ALMA will provide for studying the thermal structure
of the prominence plasma from the cores of the cool prominence fine
structure to the prominence-corona transition region. In addition, we
show that detailed 3D modeling of entire prominences with their numerous
fine structures will be important for the correct interpretation of
future ALMA observations of prominences.
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Title: Hot prominence detected in the core of a coronal mass ejection:
Analysis of SOHO/UVCS Lα and SOHO/LASCO visible-light observations
Authors: Heinzel, P.; Susino, R.; Jejčič, S.; Bemporad, A.; Anzer, U.
2016A&A...589A.128H Altcode:
Context. The paper deals with the physics of erupting prominences in
the core of coronal mass ejections (CME). <BR /> Aims: We determine the
physical parameters of an erupting prominence embedded in the core of a
CME using SOHO/UVCS hydrogen Lα and Lβ lines and SOHO/LASCO visible
light observations. In particular we analyze the CME event observed
on August 2, 2000. We develop the non-LTE (NLTE; I.e. considering
departures from the local thermodynamic equilibrium - LTE) spectral
diagnostics based on Lα and visible light observations. <BR /> Methods:
Our method is based on 1D NLTE modeling of eruptive prominences and
takes into account the effect of large flow velocities, which reach
up to 300 km s<SUP>-1</SUP> for the studied event (the so-called
Doppler dimming). The NLTE radiative-transfer method can be used
for both optically thin and thick prominence structures. We combine
spectroscopic UVCS observations of an erupting prominence in the core
of a CME with visible light images from LASCO-C2 in order to derive the
geometrical parameters like projected thickness and velocity, together
with the effective temperature and column density of electrons. These
are then used to constrain our NLTE radiative transfer modeling which
provides the kinetic temperature, microturbulent velocity, gas pressure,
ionization degree, the line opacities, and the prominence effective
thickness (geometrical filling factor). <BR /> Results: Analysis was
made for 69 observational points (spatial pixels) inside the whole
erupting prominence. Roughly one-half of them show a non-negligible Lα
optical thickness for flow velocity 300 km s<SUP>-1</SUP> and about
one-third for flow velocity 150 km s<SUP>-1</SUP>. All pixels with
Lατ<SUB>0</SUB> ≤ 0.3 have been considered for further analysis,
which is presented in the form of statistical distributions (histograms)
of various physical quantities such as the kinetic temperature, gas
pressure, and electron density for two representative flow velocities
(150 and 300 km s<SUP>-1</SUP>) and non-zero microturbulence. For
two pixels co-temporal LASCO visible-light data are also available,
which further constrains the diagnostics of the electron density and
effective thickness. Detailed NLTE modeling is presented for various
sets of input parameters. <BR /> Conclusions: The studied CME event
shows that the erupting prominence expands to large volumes, meaning
that it is a low-pressure structure with low electron densities and
high temperatures. This analysis provides a basis for future diagnostics
using the METIS coronagraph on board the Solar Orbiter mission.
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Title: Is it Possible to Use the Green Coronal Line Instead of X rays
to Cancel an Effect of the Coronal Emissivity Deficit in Estimation of
the Prominence Total Mass from Decrease of the EUV-corona Intensities?
Authors: Schwartz, P.; Heinzel, P.; Jejčič, S.; Rybák, J.; Kotrč,
P.; Fárník, F.; Kupryakov, Yu. A.; Deluca, E. E.; Golub, L.; Jibben,
P. R.; Anzer, U.; Tlatov, A. G. .; Guseva, S. A.
2016ASPC..504...89S Altcode:
Total masses of six quiescent prominences observed from April through
June 2011 were estimated using multi-spectral observations (in EUV,
X-rays, Hα, and Ca <small>II</small> H). The method for
the total mass estimation is based on the fact that the intensity
of the EUV solar corona at wavelengths below 912 Å is reduced at a
prominence by the absorption in resonance continua (photoionisation)
of hydrogen and possibly by helium and subsequently an amount of
absorbed radiation is proportional to the column density of hydrogen
and helium plasma. Moreover, the deficit of the coronal emissivity in
volume occupied by the cool prominence plasma also contributes to the
intensity decrease. The observations in X-rays which are not absorbed
by the prominence plasma, allow us to separate these two mechanisms
from each other. The X-ray observations of XRT onboard the Hinode
satellite made with the Al-mesh focal filter were used because the
X-ray coronal radiation formed in plasma of temperatures of the order
of 10<SUP>6</SUP> K was registered and EUV spectral lines occurring in
the 193, 211 and 335 Å channels of the Atmospheric Imaging Assembly
of the Solar Dynamics Observatory satellite are also formed at such
temperatures. Unfortunately, the Al-mesh filter has a secondary peak
of the transmittance at around 171 Å which causes a contribution
from the EUV corona to the measured data of up to 11 % in the quiet
corona. Thus, absorption in prominence plasma influences XRT X-ray
data when using the Al-mesh filter. On the other hand, other X-ray XRT
filters are more sensitive to plasma of much higher temperatures (log
T of the order of 7), thus observations using these filters cannot
be used together with the AIA observations in the method for mass
estimations. This problem could be solved using observations in the
green coronal line instead of X-rays. Absorption of the green coronal
line by a prominence plasma is negligible and this line is formed at
temperatures of the order of 10<SUP>6</SUP> K. We compare values of
the total mass of the prominence observed on 20 October 2012 on the
SE limb estimated when using XRT X-ray observations and observations
in the green coronal line obtained at Kislovodsk Mountain Astronomical
Station of the Pulkovo observatory (Russia).
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Title: Observed IRIS Profiles of the h and k Doublet of Mg II and
Comparison with Profiles from Quiescent Prominence NLTE Models
Authors: Vial, Jean-Claude; Pelouze, Gabriel; Heinzel, Petr; Kleint,
Lucia; Anzer, Ulrich
2016SoPh..291...67V Altcode: 2015SoPh..tmp..173V
With the launch of the Interface Region Imaging Spectrograph (IRIS)
mission, it is now possible to obtain high-resolution solar prominence
spectra and to begin to distinguish the contributions of the many
(apparent or not) threads that structure prominences. We aim at
comparing unique observations obtained in the Mg II h and k lines of a
polar crown prominence with the radiative outputs from one-dimensional
models built with non-local-thermodynamic equilibrium codes (Heinzel et
al.Astron. Astrophys.564, A132, 2014). We characterize the profiles
obtained through thorough calibration procedures, with attention
paid to the absolute values, full-width at half-maximum, and the
ratio of k to h intensities. We also show that at the top of some
structures, line-of-sight velocities of about 9 kms−<SUP>1</SUP> can
be detected. We find a range of static, low-pressure, low-thickness,
low-temperature models that could fit k or h observed values, but that
cannot satisfy the low observed k/h ratio. We investigate whether these
low values might be explained by the inclusion of horizontal flows in
small-scale threads. These flows are also necessary in another class
of models, where the pressure is kept low but thickness and temperature
are increased up to the observed thickness and up to 15 000 K.
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Title: High-resolution fine-structure synthetic imaging of an entire
prominence using 3D whole-prominence fine structure modelling
Authors: Gunar, Stanislav; Mackay, Duncan; Heinzel, Petr; Anzer, Ulrich
2015IAUGA..2251323G Altcode:
The newly developed 3D whole-prominence fine structure (WPFS)
model (Gunár & Mackay 2015) allows us for the first time to
simulate entire prominences/filaments including their numerous fine
structures. This model combines a 3D magnetic field configuration of an
entire prominence obtained from non-linear force-free field simulations,
with a detailed description of the prominence plasma. The plasma is
located in magnetic dips in hydrostatic equilibrium and is distributed
along hundreds of fine structures within the 3D magnetic model. The
prominence plasma has realistic density and temperature distributions
including the prominence-corona transition region.To produce the
high-resolution synthetic H-alpha images of the WPFS model we use
a novel fast approximate radiative transfer visualization technique
(Heinzel et al. 2015). This allows us for the first time to produce
images of the prominences in emission on the solar limb and filaments in
absorption against the solar disk using a single model. The prominence
plasma and magnetic field are described in the WPFS model on scales
that allow us to produce synthetic images with resolution matching that
of the state-of-the-art observations, or indeed that of the upcoming
solar observatories, such as DKIST or Solar-C. Moreover, to complement
the prominence/filament synthetic images we have consistent information
about the magnetic field and plasma parameters everywhere in the modeled
prominences. This allows us to investigate the apparent puzzling nature
of the observed prominence and filament fine structures. We can also
study the connections between the local configuration of the magnetic
field and the observable structure of the finest prominence/filament
features. In addition, we are able to investigate the prominence
evolution. We can consistently study the influence of the varying
photospheric flux distribution on the prominence magnetic field
configuration and its effect on the observable prominence plasma.
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Title: Fast approximate radiative transfer method for visualizing
the fine structure of prominences in the hydrogen Hα line
Authors: Heinzel, P.; Gunár, S.; Anzer, U.
2015A&A...579A..16H Altcode:
<BR /> Aims: We present a novel approximate radiative transfer method
developed to visualize 3D whole-prominence models with multiple fine
structures using the hydrogen Hα spectral line. <BR /> Methods: This
method employs a fast line-of-sight synthesis of the Hα line profiles
through the whole 3D prominence volume and realistically reflects the
basic properties of the Hα line formation in the cool and low-density
prominence medium. The method can be applied both to prominences seen
above the limb and filaments seen against the disk. <BR /> Results:
We provide recipes for the use of this method for visualizing the
prominence or filament models that have multiple fine structures. We
also perform tests of the method that demonstrate its accuracy
under prominence conditions. <BR /> Conclusions: We demonstrate that
this fast approximate radiative transfer method provides realistic
synthetic Hα intensities useful for a reliable visualization of
prominences and filaments. Such synthetic high-resolution images of
modeled prominences/filaments can be used for a direct comparison with
high-resolution observations.
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Title: Prominence Visibility in Hinode/XRT Images
Authors: Schwartz, P.; Jejčič, S.; Heinzel, P.; Anzer, U.; Jibben,
P. R.
2015ApJ...807...97S Altcode: 2015arXiv150606078S
In this paper we study the soft X-ray (SXR) signatures of one
particular prominence. The X-ray observations used here were made by the
Hinode/X-Ray Telescope instrument using two different filters. Both of
them have a pronounced peak of the response function around 10 Å. One
of them has a secondary smaller peak around 170 Å, which leads to a
contamination of SXR images. The observed darkening in both of these
filters has a very large vertical extension. The position and shape of
the darkening correspond nicely with the prominence structure seen in
SDO/AIA images. First, we have investigated the possibility that the
darkening is caused by X-ray absorption. However, detailed calculations
of the optical thickness in this spectral range show clearly that
this effect is completely negligible. Therefore, the alternative is
the presence of an extended region with a large emissivity deficit,
which can be caused by the presence of cool prominence plasmas within
an otherwise hot corona. To reproduce the observed darkening, one needs
a very large extension along the line of sight of the region amounting
to around 10<SUP>5</SUP> km. We interpret this region as the prominence
spine, which is also consistent with SDO/AIA observations in EUV.
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Title: On the formation of Mg ii h and k lines in solar prominences
Authors: Heinzel, P.; Vial, J. -C.; Anzer, U.
2014A&A...564A.132H Altcode:
<BR /> Aims: With the recent launch of the IRIS mission, it has become
urgent to develop the spectral diagnostics using the Mg ii resonance
h and k lines. In this paper, we aim to demonstrate the behavior of
these lines under various prominence conditions. Our results serve
as a basis for analysis of new IRIS data and for more sophisticated
prominence modeling. <BR /> Methods: For this exploratory work,
we use a canonical 1D prominence-slab model, which is isobaric
and may have three different temperature structures: isothermal,
PCTR-like (prominence-corona transition region), and consistent with
the radiative equilibrium. The slabs are illuminated by a realistic
incident solar radiation obtained from the UV observations. A five-level
plus continuum Mg ii model atom is used to solve the full NLTE problem
of the radiative transfer. We use the numerical code based on the ALI
techniques and apply the partial frequency redistribution for both
Mg ii resonance lines. We also use the velocity-dependent boundary
conditions to study the effect of Doppler dimming in the case of
moving prominences. Finally, the relaxation technique is used to
compute a grid of models in radiative equilibrium. <BR /> Results:
We computed the Mg ii h and k line profiles that are emergent from
prominence-slab models and show their dependence on kinetic temperature,
gas pressure, geometrical extension, and microturbulent velocity. By
increasing the line opacity, significant departures from the complete
frequency redistribution take place in the line wings. Models with a
PCTR temperature structure show that Mg ii becomes ionized to Mg iii
in the temperature range between roughly 15 000 and 30 000 K. Doppler
dimming is significant for Mg ii resonance lines. At the velocity 300
km s<SUP>-1</SUP>, the line intensity decreases to about 20% of the
value for static prominences. Finally, we demonstrate the role of Mg
ii h and k radiation losses on the prominence energy balance. Their
dominant role is at lower pressures, while the losses due to hydrogen
and Ca ii dominate at higher pressures.
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Title: A comparison between observed IRIS profiles of the h &
k doublet of Mg II and profiles from quiescent prominence NLTE models
Authors: Vial, Jean-Claude; Anzer, Ulrich; Heinzel, Petr; Kleint, Lucia
2014cosp...40E3515V Altcode:
With the advent of IRIS, it is now possible to investigate the cool core
of prominences through the detailed profiles of the Mg II resonance
lines with an unprecedented spatial resolution of 0.33 arcsecond. The
slit-jaw camera also allows to record the temporal evolution of the
prominence fine structure. We present IRIS observations of quiescent
prominence profiles that we analyse in terms of reversal (if any),
width, k/h line ratio, prominence/ quiet Sun line ratio. Comparing these
parameters with the results of NLTE modelling (see Heinzel et al. 2014),
we can derive thermodynamic parameters of the cool prominence plasma,
along with the (line-of-sight) velocities and mass flows.
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Title: Puzzling nature of the fine structure of quiescent prominences
and filaments
Authors: Gunár, Stanislav; Heinzel, Petr; Anzer, Ulrich; Mackay,
Duncan H.
2013JPhCS.440a2035G Altcode:
Even after more than 160 years of observations and modelling of solar
prominences their true nature contains many open questions. In this
work we argue that current 2D prominence fine structure models can
help us to understand the puzzling connection between quasi-vertical
fine structures often seen in quiescent prominences observed on the
solar limb and horizontally aligned dark fibrils representing the fine
structures of prominences observed in absorption against the solar disk
(filaments).
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Title: Non-linear force-free magnetic dip models of quiescent
prominence fine structures
Authors: Gunár, S.; Mackay, D. H.; Anzer, U.; Heinzel, P.
2013A&A...551A...3G Altcode:
<BR /> Aims: We use 3D non-linear force-free magnetic field modeling
of prominence/filament magnetic fields to develop the first 2D models
of individual prominence fine structures based on the 3D configuration
of the magnetic field of the whole prominence. <BR /> Methods: We use
an iterative technique to fill the magnetic dips produced by the 3D
modeling with realistic prominence plasma in hydrostatic equilibrium
and with a temperature structure that contains the prominence-corona
transition region. With this well-defined plasma structure the radiative
transfer can be treated in detail in 2D and the resulting synthetic
emission can be compared with prominence/filament observations. <BR
/> Results: Newly developed non-linear force-free magnetic dip models
are able to produce synthetic hydrogen Lyman spectra in a qualitative
agreement with a range of quiescent prominence observations. Moreover,
the plasma structure of these models agrees with the gravity induced
prominence fine structure models which have already been shown to
produce synthetic spectra in good qualitative agreement with several
observed prominences. <BR /> Conclusions: We describe in detail the
iterative technique which can be used to produce realistic plasma
models of prominence fine structures located in prominence magnetic
field configurations containing dips, obtained using any kind of
magnetic field modeling.
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Title: Velocity Vector, Ionization Degree, and Temperature of
Prominence Fine Structures Observed by Hinode/SOT
Authors: Schmieder, B.; Mein, P.; Chandra, R.; Molodij, G.; Heinzel,
P.; Berlicki, A.; Schwartz, P.; Fárník, F.; Labrosse, N.; Anzer,
U.; Watanabe, T.
2012ASPC..454..107S Altcode:
Prominences have been successfully observed by Hinode in April 2007
exhibiting a strong dynamics of their fine structures. The dynamics
of a prominence is a challenge to understand the formation of cool
prominence plasma embedded in the hot corona. Combining simultaneous
observations obtained in Hα with Hinode/SOT and the MSDP spectrograph
operating at the Meudon solar tower, velocity vectors have been
derived. The Doppler-shifts of bright threads are of the same order
as the velocities measured perpendicular to the line of sight. This
suggests that the vertical structures of the prominence could be a pile
up of dips in magnetic field lines viewed in 3D. Using Hα, Hinode/XRT
and TRACE data, the hydrogen ionization degree has been determined to
be 0.5-0.8, and the optical thickness in Hα between 0.2 and 1.3. The
Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode produced images
of the prominence in 11 selected lines with formation temperatures
between log(T) = 4.7 and log(T) = 6.1. We comment on the absorption,
emissivity blocking and emission involved for interpreting the different
structures of the prominence in terms of the temperature and density.
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Title: Mass of Solar Prominences Estimated from Multi-Wavelength Data
Authors: Schwartz, P.; Fárník, F.; Heinzel, P.; Kotrč, P.; Anzer, U.
2012ASPC..454..117S Altcode:
The mass of selected prominences was estimated using their
multi-wavelength observations: in Hα by the HSFA2 spectrograph of
the Ondřejov observatory, in EUV by SoHO/EIT and in the soft X-rays
by Hinode XRT. The results are compared with values estimated by
other authors.
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Title: Mass Loading of Quiescent Prominences
Authors: Schwartz, P.; Heinzel, 2. P.; Kotrč, P.; Anzer, U.;
Kupryakov, Y.; DeLuca, E.
2012ASPC..456...73S Altcode:
From April through June 2011 a multi-spectral observing campaign of
quiescent prominences was made. Observations were carried out in EUV
by SDO/AIA, in soft X-rays by XRT on Hinode and in Hα by horizontal
spectrographs of the Ondrřejov observatory. In this work the masses of
selected prominences, observed on May 18 and April 19, were determined
in order to test the method and our semi-automatic computer code.
---------------------------------------------------------
Title: Radiative equilibrium in solar prominences reconsidered
Authors: Heinzel, P.; Anzer, U.
2012A&A...539A..49H Altcode:
<BR /> Aims: We reconsider the question which kinetic temperatures
can lead to prominence configurations that are in radiative
equilibrium. We compare these temperatures to those from other
calculations. <BR /> Methods: For this purpose we solved the full
non-LTE radiative-transfer problem for a gas consisting of hydrogen,
helium and calcium. We used simple isobaric 1D slabs and began with
isothermal models. Then we solved the radiative-relaxation problem
and determined the radiative-equilibrium conditions within the
whole slab. <BR /> Results: By adding the calcium radiative losses,
we found that these equilibrium temperatures are considerably lower
than those obtained for a pure hydrogen gas. This is because the newly
calculated CaII line losses appear to play a significant role in the
energy balance, similar to chromospheric conditions. The equilibrium
temperatures obtained span the range between 4400-9500 K, depending
on the gas pressure and slab thickness.
---------------------------------------------------------
Title: Synthetic differential emission measure curves of prominence
fine structures. II. The SoHO/SUMER prominence of 8 June 2004
Authors: Gunár, S.; Parenti, S.; Anzer, U.; Heinzel, P.; Vial, J. -C.
2011A&A...535A.122G Altcode:
<BR /> Aims: This study is the first attempt to combine the prominence
observations in Lyman, UV, and EUV lines with the determination of the
prominence differential emission measure derived using two different
techniques, one based on the inversion of the observed UV and EUV lines
and the other employing 2D non-LTE prominence fine-structure modeling
of the Lyman spectra. <BR /> Methods: We use a trial-and-error method
to derive the 2D multi-thread prominence fine-structure model producing
synthetic Lyman spectra in good agreement with the observations. We then
employ a numerical method to perform the forward determination of the
DEM from 2D multi-thread models and compare the synthetic DEM curves
with those derived from observations using inversion techniques. <BR
/> Results: A set of available observations of the June 8, 2004
prominence allows us to determine the range of input parameters, which
contains models producing synthetic Lyman spectra in good agreement
with the observations. We select three models, which represent this
parametric-space area well and compute the synthetic DEM curves for
multi-thread realizations of these models. The synthetic DEM curves
of selected models are in good agreement with the DEM curves derived
from the observations. <BR /> Conclusions: We show that the evaluation
of the prominence fine-structure DEM complements the analysis of the
prominence hydrogen Lyman spectra and that its combination with the
detailed radiative-transfer modeling of prominence fine structures
provides a useful tool for investigating the prominence temperature
structure from the cool core to the prominence-corona transition region.
---------------------------------------------------------
Title: Synthetic differential emission measure curves of prominence
fine structures
Authors: Gunár, S.; Heinzel, P.; Anzer, U.
2011A&A...528A..47G Altcode:
<BR /> Aims: We use 2D single and multi-thread prominence fine-structure
models to obtain the synthetic DEM curves. These are then compared
with the DEM curves derived from observations. <BR /> Methods: We use
the temperature and electron density structure resulting from the
2D models and numerically compute the average synthetic DEM curves
for different orientations of the threads with respect to the line of
sight. <BR /> Results: We show that the synthetic DEM curves obtained
by 2D modelling are similar to the DEM curves derived from observations
of quiescent prominences. <BR /> Conclusions: The DEM curves derived
from observations, which are most reliable above temperatures of 20
000 K, can be extended towards cool prominence-core temperatures by
supplementing them with synthetic DEM values obtained by modelling
hydrogen Lyman spectra originating mainly at temperatures below 20 000
K. On the other hand, the observed DEM can constrain the temperature
structure of the prominence fine structures above the formation
temperatures of the Lyman spectrum.
---------------------------------------------------------
Title: Statistical comparison of the observed and synthetic hydrogen
Lyman line profiles in solar prominences
Authors: Gunár, S.; Schwartz, P.; Schmieder, B.; Heinzel, P.;
Anzer, U.
2010A&A...514A..43G Altcode:
<BR /> Aims: We analyse a unique set of prominence SOHO/SUMER
Lyman spectra by comparing it with synthetic spectra obtained by 2D
multi-thread prominence fine-structure models. <BR /> Methods: We
employed a novel statistical approach to the analysis of the observed
and synthetic Lyman spectra. We compared the statistical distributions
of the line properties of the observed and synthetic Lyman spectra using
a set of four statistical criteria. <BR /> Results: We demonstrate
the very good agreement between the observed Lyman spectra and
synthetic spectra obtained by modelling. <BR /> Conclusions: Our set
of statistical criteria is well-suited to analyses of the prominence
Lyman spectra because of its sensitivity to a number of different
parameters governing the conditions in the prominence fine structures.
---------------------------------------------------------
Title: How do unresolved motions affect the prominence hydrogen
Lyman spectrum.
Authors: Gunar, Stanislav; Schwartz, Pavol; Schmieder, Brigitte;
Heinzel, Petr; Anzer, Ulrich
2010cosp...38.2830G Altcode: 2010cosp.meet.2830G
Space-born observations of quiescent prominences in the hydrogen
Lyman line series provide a considerable amount of information
about their structure and physical properties. Lyman line series
thus represents a focus of several detailed studies. However, the
substantial asymmetries exhibited by considerable number of observed
Lyman line profiles present a strong indication for the existence of
hidden fine-structure dynamics. If attributed merely to the Doppler
shift effect, these asymmetries would correspond to radial velocities
of the order of 100 km/s. Such high velocities, however, were never
observed in quiescent prominences. Typical fine-structure velocities are
of the order of 10 km/s. To tackle this problem, we have modified our
2D multi-thread prominence models and randomly assigned line-of-sight
(LOS) velocities of the order of 10 km/s to each thread. The obtained
synthetic Lyman spectrum exhibits substantial asymme-tries of the line
profiles comparable with SOHO/SUMER observations. Moreover, our results
do indicate that the synthetic Lyman-α profiles may exhibit an opposite
asymmetry to that of the higher Lyman lines. This is consistent with
observations which often show opposite asym-metries of these lines at
the same prominence location. We have demonstrated the agreement of
synthetic and observed spectra not only by comparing asymmetries of
individual profiles but also by exploiting statistically significant
sets of the observed and synthetic data. These results represent an
important step in our understanding of hidden fine-structure dynamics
of quiescent prominences.
---------------------------------------------------------
Title: Prominence fine structures and corresponding differential
emission measures
Authors: Gunar, Stanislav; Heinzel, Petr; Anzer, Ulrich
2010cosp...38.2845G Altcode: 2010cosp.meet.2845G
We use the temperature and density structure resulting from multi-thread
prominence fine-structure models (consisting of individual 2D
vertical threads) to compute the differential emission measures
(DEM). We derive the DEM at various positions along the length of
the foremost thread of the multi-thread model and also for various
angles between the line-of-sight and the magnetic field. We compare
the calculated DEM values with those obtained by in-versions from
the observed intensities of the transition-region UV lines. We show
that the unresolved fine-structuring of quiescent prominences along a
particular line-of-sight has consid-erable effect on shape of the DEM
curve due to fracturing of the prominence-corona transition region into
many thin layers corresponding to individual prominence fine structures.
---------------------------------------------------------
Title: Solar quiescent prominences. Filamentary structure and
energetics
Authors: Heinzel, P.; Anzer, U.; Gunár, S.
2010MmSAI..81..654H Altcode:
We present a first attempt to solve the non-LTE radiative-transfer
problem within a 2D numerical domain consisting of several randomly
distributed vertical threads. This represents a starting point
to simulate mutual radiative interaction between such prominence
threads. The second part of the paper presents our new results which
concern the radiative equilibrium in prominences and in their fine
structure. We show that adding the non-hydrogenic radiative losses
significantly lowers the central equilibrium temperatures. To match the
observed temperatures, an additional heating seems to be unavoidable.
---------------------------------------------------------
Title: Global prominence oscillations
Authors: Anzer, U.
2009A&A...497..521A Altcode:
Aims: The question of the different oscillation periods for global
modes of quiescent prominences is discussed. <BR />Methods: Simple 1D
prominence configurations are used to describe the magnetohydrostatic
equilibrium and their oscillations for small amplitudes. <BR />Results:
Three basic modes of oscillations were found and their periods as a
function of the magnetic field configuration and the assumed geometry
are given.
---------------------------------------------------------
Title: On Lyman-line asymmetries in quiescent prominences
Authors: Gunár, S.; Heinzel, P.; Anzer, U.; Schmieder, B.
2008A&A...490..307G Altcode:
Aims: We study the asymmetries of the synthetic hydrogen Lyman
lines and the process responsible for their formation. <BR
/>Methods: To obtain the synthetic Lyman line profiles, we use a
multi-thread prominence fine-structure model consisting of identical
2D threads. The 2D thread models are in MHS equilibrium, include an
empirical prominence-corona transition region, and solve consistently
2D non-LTE radiative transfer. Each thread of the multi-thread model
has a randomly assigned line-of-sight (LOS) velocity. <BR />Results:
The synthetic Lyman spectrum obtained by multi-thread modelling
exhibits substantial asymmetries of the line profiles, even though
the LOS velocities of individual threads are only of the order of 10
km s<SUP>-1</SUP>. Moreover, our results indicate that the synthetic
Lyman-α profiles may exhibit an opposite asymmetry to that of the
higher Lyman lines. <BR />Conclusions: The presence and behaviour
of the asymmetrical profiles of the synthetic Lyman lines agree with
observed profiles acquired by SUMER. <P />Appendix A is only available
in electronic form at http://www.aanda.org
---------------------------------------------------------
Title: Hinode, TRACE, SOHO, and Ground-based Observations of a
Quiescent Prominence
Authors: Heinzel, P.; Schmieder, B.; Fárník, F.; Schwartz, P.;
Labrosse, N.; Kotrč, P.; Anzer, U.; Molodij, G.; Berlicki, A.;
DeLuca, E. E.; Golub, L.; Watanabe, T.; Berger, T.
2008ApJ...686.1383H Altcode:
A quiescent prominence was observed by several instruments on
2007 April 25. The temporal evolution was recorded in Hα by the
Hinode SOT, in X-rays by the Hinode XRT, and in the 195 Å channel by
TRACE. Moreover, ground-based observatories (GBOs) provided calibrated
Hα intensities. Simultaneous extreme-UV (EUV) data were also taken by
the Hinode EIS and SOHO SUMER and CDS instruments. Here we have selected
the SOT Hα image taken at 13:19 UT, which nicely shows the prominence
fine structure. We compare this image with cotemporaneous ones taken
by the XRT and TRACE and show the intensity variations along several
cuts parallel to the solar limb. EIS spectra were obtained about half
an hour later. Dark prominence structure clearly seen in the TRACE and
EIS 195 Å images is due to the prominence absorption in H I, He I,
and He II resonance continua plus the coronal emissivity blocking due
to the prominence void (cavity). The void clearly visible in the XRT
images is entirely due to X-ray emissivity blocking. We use TRACE, EIS,
and XRT data to estimate the amount of absorption and blocking. The
Hα integrated intensities independently provide us with an estimate of
the Hα opacity, which is related to the opacity of resonance continua
as follows from the non-LTE radiative-transfer modeling. However,
spatial averaging of the Hα and EUV data have quite different natures,
which must be taken into account when evaluating the true opacities. We
demonstrate this important effect here for the first time. Finally,
based on this multiwavelength analysis, we discuss the determination
of the column densities and the ionization degree of hydrogen in
the prominence.
---------------------------------------------------------
Title: On Lyman-line Asymmetries in Quiescent Prominences
Authors: Gunár, S.; Heinzel, P.; Anzer, U.; Schmieder, B.
2008ESPM...12.3.18G Altcode:
We present a new study of the asymmetries of synthetic hydrogen Lyman
line profiles and suggest the mechanism of their formation. <P />In
order to obtain the synthetic Lyman line profiles, we use multi-thread
prominence fine-structure model consisting of identical vertical
2D threads. The 2D thread models are in magnetohydrostatic (MHS)
equilibrium, include an empirical prominence-corona transition
region (PCTR) and consistently solve the 2D non-LTE radiative
transfer. Individual threads of the multi-thread fine-structure model
have a randomly assigned LOS velocities. <P />The synthetic Lyman
spectrum obtained by our multi-thread modelling exhibits substantial
asymmetries of the line profiles even thought the LOS velocities
of individual threads are only of the order of 10 km s-1. Moreover,
our results show that the synthetic Lyman-? profiles may exhibit an
opposite asymmetry as compared to higher Lyman lines. These results are
in agreement with the observed Lyman line profiles from SOHO/SUMER. <P
/>The presence and the behaviour of the asymmetrical profiles of the
synthetic Lyman spectrum is in agreement with observed profiles taken
by SUMER.
---------------------------------------------------------
Title: Prominence modelling: from observed emission measures to
temperature profiles
Authors: Anzer, U.; Heinzel, P.
2008A&A...480..537A Altcode:
Aims:We outline the construction of prominence - corona transition
region models based upon the observations of one particular
prominence. <BR />Methods: The differential emission measure curves from
observations were approximated by simple analytical functions. On this
basis we constructed the temperature curve and calculated the radiative
losses, the gains by thermal conduction, and some estimates for the
wave heating. <BR />Results: The temperature curve was calculated in
the range between 23 000 K and 450 000 K. The resulting transition
region can be divided into an inner region where the temperature is
low and the radiative losses are very large, a part with a very steep
temperature rise from 40 000 K to around 250 000 K over a width of only
500 km, and an extended high temperature region. Both the conductive
heating and our estimates for a possible wave cooling/heating peak very
sharply in the region with the very large temperature gradient. The
consequences for the energy balance are discussed.
---------------------------------------------------------
Title: Limb Prominences Seen in UV, EUV and SXR
Authors: Heinzel, P.; Fárník, F.; Anzer, U.; Dammasch, I.
2007ASPC..369..279H Altcode:
We use SOHO/SUMER, EIT and Yohkoh/SXT prominence observations to study
the absorption and/or volume blocking of UV, EUV and SXR coronal
radiation by cool prominence plasma. An example of such a complex
behaviour is the limb prominence observed on 5 September 1996. The
SUMER spectrograph has detected two coronal lines, MgX at 625 Å,
which is absorbed by the hydrogen Lyman continuum and blocked within
a volume occupied by cool prominence plasma, and FeXII at 1242 Å,
where the prominence appears dark due to blocking (no absorption at
this wavelength). A similar behaviour show also the EUV images taken by
EIT. We find that a darkening similar to that detected in the FeXII line
is quite well visible also in the SXR images obtained by Yohkoh/SXT. To
explain this feature, we exclude the absorption by the HeI and HeII
resonance continua (hydrogen absorption is quite negligible) and suggest
that it is entirely due to the volume blocking. Based on a quantitative
analysis of these data, we discuss the physical conditions in cool
prominences and their coronal environment. Finally, we propose new
high-resolution EUV and SXR observations of prominences by Solar-B,
using the EUV imaging spectrometer (EIS) and the X-ray telescope
(XRT), respectively.
---------------------------------------------------------
Title: Properties of prominence fine-structure threads derived from
SOHO/SUMER hydrogen Lyman lines
Authors: Gunár, S.; Heinzel, P.; Schmieder, B.; Schwartz, P.;
Anzer, U.
2007A&A...472..929G Altcode:
Context: The SOHO/SUMER observations provide us for the first time with
the prominence spectra in the Lyman-α line outside the attenuator
together with the higher members of the hydrogen Lyman series. <BR
/>Aims: We derive the prominence fine-structure thread properties
by comparing the SOHO/SUMER hydrogen Lyman series observations with
the synthetic Lyman lines. <BR />Methods: To obtain the synthetic
profiles of the Lyman lines, we used 2D prominence fine-structure
thread models with a PCTR and consistently solved the 2D non-LTE
multilevel radiative transfer. The trial-and-error method was applied
to find the model with the best agreement between the synthetic Lyman
line profiles and the observed ones. <BR />Results: The properties of
the resulting model with the best match of the synthetic and observed
line profiles are central (minimum) temperature T<SUB>0</SUB> = 7000
K, maximum column mass in the centre of the thread M<SUB>0</SUB> =
1.1×10<SUP>-4</SUP> g cm<SUP>-2</SUP>, horizontal field strength in
the middle of the thread B<SUB>x</SUB>(0) = 6 Gauss and the boundary
pressure p<SUB>0</SUB> = 0.015 dyn cm<SUP>-2</SUP>. <BR />Conclusions:
The Lyman line profiles observed by SOHO/SUMER can be better reproduced
by using multi-thread models consisting of a set of the 2D prominence
fine-structure threads placed perpendicularly to the line-of-sight,
rather than with the single-thread model.
---------------------------------------------------------
Title: Is the magnetic field in quiescent prominences force-free?
Authors: Anzer, U.; Heinzel, P.
2007A&A...467.1285A Altcode:
Aims:We describe under which conditions the magnetic fields of quiescent
prominences are force-free and under which gravity plays the dominant
role. <BR />Methods: The existing observational determinations of the
magnetic field are summarised and the calculation of the plasma β
is outlined. We derive the dependence of β on the prominence weight
and the field strength. <BR />Results: We show that in many cases of
well-developed quiescent prominences the field can deviate substantially
from the force-free situation and gravity fully determines the structure
of the magnetic dips.
---------------------------------------------------------
Title: Prominence Parameters from 2D Modeling of Lyman Lines Measured
with SUMER
Authors: Gunár, S.; Heinzel, P.; Schmieder, B.; Anzer, U.
2007ASPC..368..317G Altcode:
We present SOHO/SUMER observations of a solar prominence in the hydrogen
Lyman series lines and compare the line profiles with the synthetic
ones obtained using our 2D prominence modeling. The observations
contain the Ly-β, Ly-γ, and Ly-δ lines on 25 May 2005. <P />In
order to derive the prominence parameters we used our 2D fine structure
models of vertical threads in magnetohydrostatic (MHS) equilibrium. By
varying the input model parameters (central temperature, boundary
pressure, magnetic field, central column mass and turbulent velocity)
we obtained a model having the synthetic Lyman line profiles in good
agreement with the observed ones. In this way we are able to determine
the structure of the magnetic dip and the thermodynamical parameters
in the observed prominence.
---------------------------------------------------------
Title: Prominences on the Limb: Diagnostics with UV EUV Lines and
the Soft X-Ray Continuum
Authors: Anzer, U.; Heinzel, P.; Fárnik, F.
2007SoPh..242...43A Altcode:
In this paper we discuss the two mechanisms by which solar prominences
on the limb can manifest themselves when observed in coronal UV -
EUV lines and in the soft X-ray continuum. These mechanisms are the
absorption in the resonance continua of hydrogen and helium on one hand
and the reduction of the emissivity in a part of the coronal volume
occupied by a prominence on the other one. We briefly describe earlier
observations made with SOHO/SUMER, EIT and Yohkoh/SXT. We then discuss
how the instruments on the new Japanese satellite Hinode can be used
for more detailed studies of prominences. We also propose some combined
observations between the Hinode satellite and the SOHO/SUMER instrument.
---------------------------------------------------------
Title: Spectral Diagnostics of the Magnetic Field Orientation in a
Prominence Observed with SOHO/SUMER
Authors: Schmieder, B.; Gunár, S.; Heinzel, P.; Anzer, U.
2007SoPh..241...53S Altcode:
During several campaigns focused on prominences we have obtained
coordinated spectral observations from the ground and from space. The
SOHO/SUMER spectrometer allows us to observe, among others, the
whole Lyman series of hydrogen, while the Hα line was observed
by the MSDP spectrograph at the VTT. For the Lyman lines, non-LTE
radiative-transfer computations have shown the importance of the optical
thickness of the prominence - corona transition region (PCTR) and its
relation to the magnetic field orientation for the explanation of the
observed line profiles. Moreover, Heinzel, Anzer, and Gunár (2005,
Astron. Astrophys.442, 331) developed a 2D magnetostatic model of
prominence fine structures that demonstrates how the shapes of Lyman
lines vary, depending on the orientation of the magnetic field with
respect to the line of sight. To support this result observationally,
we focus here on a round-shaped filament observed during three days as
it was crossing the limb. The Lyman profiles observed on the limb are
different from day to day. We interpret these differences as being due
to the change of orientation of the prominence axis (and therefore the
magnetic field direction) with respect to the line of sight. The Lyman
lines are more reversed if the line of sight is across the prominence
axis as compared to the case when it is aligned along its axis.
---------------------------------------------------------
Title: Prominence fine structures in a magnetic
equilibrium. III. Lyman continuum in 2D configurations
Authors: Gunár, S.; Heinzel, P.; Anzer, U.
2007A&A...463..737G Altcode:
Aims:We discuss the behavior of the Lyman continuum profiles
studied on the grid of 2D vertical-thread models for prominence fine
structures. <BR />Methods: Multilevel non-LTE transfer calculations for
a 12-level plus continuum hydrogen model atom are used. <BR />Results:
Since the Lyman continuum is formed in regions with different
temperatures for different orientations between the magnetic field
direction and the line-of-sight, our Lyman continuum modeling, together
with additional information from Lyman lines, represents a very useful
tool for the determination of the thread structure. <BR />Conclusions:
.A comparison between our theoretical Lyman continuum models between
800 Å and 911 Å with the observed values shows that such a modeling
can give interesting new constraints on the temperature structure in
prominence threads.
---------------------------------------------------------
Title: Study of an extended EUV filament using SoHO/SUMER observations
of the hydrogen Lyman lines
Authors: Schwartz, P.; Heinzel, P.; Schmieder, B.; Anzer, U.
2006A&A...459..651S Altcode:
Context: .In previous work we determined the 3D structure of an
EUV extension of the filament observed by SoHO/CDS on 15 October
1999. The determination of the 3D structure depends on the optical
thickness τ<SUB>912</SUB> at the hydrogen Lyman-continuum edge at
912 Å. The τ<SUB>912</SUB> value was unknown, therefore it was taken
as a free parameter for the 3D-structure determinations.<BR /> Aims:
.The plasma properties (including τ<SUB>912</SUB>) of this EUV filament
are estimated using non-LTE modelling of profiles of the hydrogen Lyman
lines.<BR /> Methods: .The lines Lβ, Lδ, L ɛ, L6 and L7 were observed
by SoHO/SUMER with the slit positioned across the EUV filament. In our
modelling the EUV filament was approximated by a horizontal 1D slab with
constant pressure and the temperature decreasing vertically from the
edges to interior of the slab. The values of the geometrical thickness
of the slab in the EUV extension were taken from its 3D structure
determined for the τ<SUB>912</SUB> values estimated iteratively. The
synthetic profiles were fitted to observed ones using the χ<SUP>2</SUP>
minimization.<BR /> Results: .For the Hα-filament part we obtained
the expected results: a small geometrical thickness between several
thousand and 15 000 km, temperatures around 5000 K in the interior and
around 20 000 K in PCTRs, and pressure ~0.1~dyn~cm<SUP>-2</SUP>. That
leads to an optical thickness in the Hα line center larger than 1. In
the EUV extension, temperatures of 10 000-40 000 K in the interior
and 35 000-50 000 K in the vertically extended PCTRs and a pressure
of ~0.01~dyn~cm<SUP>-2</SUP> were determined. Such large variations
of the temperature lead to large variations of τ<SUB>912</SUB>.<BR />
Conclusions: .The EUV extension is inhomogeneous - areas both optically
thick and thin at 912 Å are present close to each other. Parts
optically thick at 912 Å are visible also in Hα as faint and tiny dark
structures around the very dark and well pronounced Hα filament. The
volume blocking mechanism is an important mechanism throughout the
whole EUV extension even in its optically thick parts. The absorption
dominates only in the Hα-filament part of the EUV filament.
---------------------------------------------------------
Title: Darkening of Coronal Lines by Limb Prominences Observed
by SOHO/SUMER
Authors: Dammasch, I. E.; Heinzel, P.; Anzer, U.
2006ESASP.617E..66D Altcode: 2006soho...17E..66D
No abstract at ADS
---------------------------------------------------------
Title: On the Fine Structure of Solar Filaments
Authors: Heinzel, P.; Anzer, U.
2006ApJ...643L..65H Altcode:
High-resolution Hα images of solar filaments show a variety of
dark fine-structure fibrils, most of them aligned with the magnetic
field that is sheared with respect to the filament long axis. Here we
demonstrate how such fibrils can be explained in terms of the magnetic
field dips produced by realistic mass loading due to plasma condensation
along the top of a magnetic prominence arcade. Our interpretation is
supported by (2+1)-dimensional radiation-magnetohydrostatic simulations
that predict quantitatively the properties of such condensations that
are suspended in the dipped magnetic field.
---------------------------------------------------------
Title: A periodic arcade model for extended EUV filaments
Authors: Anzer, U.; Heinzel, P.
2006A&A...446..301A Altcode:
The extensions of Hα filaments that are observed in EUV spectral lines
require the presence of cool material in a large volume surrounding
these filaments. This material can only be supported by magnetic fields
with dips. Such dips can be generated by a sufficiently strong twisting
of magnetic flux tubes. In the present paper we have extended earlier
work to more realistic magnetic field configurations that are periodic
in the x-direction. We derived approximate equilibria for twisted
slender flux tubes and determined the region that contains dips. In
addition we investigated the effects on our models of the mass loading
due to a heavy prominence. Finally we compared our theoretical models
with the EUV - observations. We conclude that these types of models
are capable of explaining the basic features of the observations.
---------------------------------------------------------
Title: Prominence Fine Structures in Amagnetic Equilibrium: a Grid
Oftwo-Dimensional Models
Authors: Gunár, S.; Heinzel, P.; Anzer, U.
2005ESASP.600E..85G Altcode: 2005dysu.confE..85G; 2005ESPM...11...85G
No abstract at ADS
---------------------------------------------------------
Title: Radiative effects in supersonic wind accretion onto gravitating
objects
Authors: Kryukov, I.; Pogorelov, N.; Anzer, U.; Börner, G.;
Bisnovatyi-Kogan, G.
2005A&A...441..863K Altcode:
We investigate the influence of radiative effects <P />on supersonic
wind accretion onto gravitating objects. The accreting matter is assumed
to be optically thin. The physical mechanisms taken into account include
cooling due to free-free and free-bound transitions, the Compton heating
via X-ray scattering on electrons and the inverse Compton cooling in
the regions where the temperature of the matter becomes sufficiently
large to be able to transfer part of its internal energy to photons. A
wide range of determining parameters was covered, including the values
applicable to the Vela X-1 binary system, but our main emphasis is
on the study of the effects of radiative processes on the behavior
of accretion flows. It is shown that the applicability of polytropic
accretion models is very limited and the actual accretion rate can
be considerably lower than that provided by the Bondi-Hoyle-Lyttleton
formula. The detailed consideration of the realistic radiative effects
proved to be of great importance in our understanding of the accretion
phenomenon, since they can substantially affect it both qualitatively
and quantitatively.
---------------------------------------------------------
Title: Prominence fine structures in a magnetic equilibrium. II. A
grid of two-dimensional models
Authors: Heinzel, P.; Anzer, U.; Gunár, S.
2005A&A...442..331H Altcode:
We construct a grid of 2D vertical-thread models for prominence fine
structures which are in magnetohydrostatic (MHS) equilibrium. Such
thread models have been described in a previous paper by Heinzel
& Anzer (2001), but here we use a modified 2D transfer code with
an adaptive MHS grid. Multilevel non-LTE transfer calculations are
now performed for a 12-level plus continuum hydrogen model atom,
in order to study the behaviour of the Lyman-series lines observed
by SOHO/SUMER. Our grid consists of 18 models which cover a range of
central column masses, magnetic-field intensities and two parameters
characterising the 2D temperature structure of the thread. Since
different Lyman lines and their parts (line center, peak, wings) are
formed at different places within the thread, the Lyman series may
serve as a good diagnostic tool for thermodynamic conditions varying
from central cool parts to a prominence-corona transition region. We
demonstrate this behaviour for various lines, showing their synthetic
profiles as seen from two perpendicular directions along and across
the magnetic field lines, respectively, and displaying the respective
contribution functions. This study confirms our earlier conclusion
that the Lyman line profiles are much more reversed when seen across
the field lines, compared to those seen along the lines. The latter
can be even unreversed. We also show the geometrical cross-section
(shape) of all 18 models. Their thread-like shape with a considerable
aspect ratio resembles recent high-resolution Hα images. Finally,
we discuss the relation of our thread models to the vertical threads
studied by Fontenla et al. (1996, ApJ, 466, 496).
---------------------------------------------------------
Title: On the Nature of Dark Extreme Ultraviolet Structures Seen by
SOHO/EIT and TRACE
Authors: Anzer, U.; Heinzel, P.
2005ApJ...622..714A Altcode:
Spectral lines in the extreme ultraviolet (EUV) observed on the Sun
can originate either from the hot corona or the cooler chromosphere
to corona transition region. In the present paper we concentrate on
coronal lines and in particular on iron lines at 171, 195, and 284
Å, which have been frequently observed by the Solar and Heliospheric
Observatory (SOHO)/Extreme Ultraviolet Imaging Telescope (EIT) and the
Transition Region and Coronal Explorer (TRACE). The intensity of these
lines emitted by the corona can be reduced by the presence of a cool
gas, e.g., by prominence-like material, located in the corona. There
are two mechanisms that can lead to a reduction of the line intensity:
absorption and volume blocking. That part of the coronal radiation
that comes from behind the cool gas can be partially absorbed. The
main absorbers for the iron lines studied here are neutral hydrogen
and neutral plus singly ionized helium. In this paper we calculate
the optical thickness of their resonance continua at the wavelength
positions of iron lines and compare it with that in the Hα line
center. The comparison of the derived values shows that they are quite
similar. The second effect is due to the fact that cool structures in
the corona do not emit any radiation in the EUV lines, which gives rise
to an additional reduction of the observed intensity as compared with
the surrounding corona-we have termed this “volume blocking.” We
further describe in this paper how these two effects can be used in
a new way of performing prominence diagnostics. Our results are also
applicable to other coronal lines detected by, e.g., the SOHO CDS or
SUMER instruments.
---------------------------------------------------------
Title: Determination of the 3D structure of an EUV-filament observed
by SoHO/CDS, SoHO/SUMER and VTT/MSDP
Authors: Schwartz, P.; Heinzel, P.; Anzer, U.; Schmieder, B.
2004A&A...421..323S Altcode:
Heinzel et al. (\cite{hein1}) found that filaments seem to be much
more extended in EUV spectral lines than in Hα. In this paper we
reconstruct the 3D structure of the extensions of the EUV-filament
observed on 15 October 1999 by SoHO/CDS and SoHO/SUMER. Small Hα
structures were observed by VTT/MSDP. We computed the bottom and top
heights of the EUV-filament extensions for several values of the
hydrogen Lyman-continuum optical thickness τ<SUB>912</SUB> using
the spectroscopic model of Heinzel et al. (\cite{hein2}). For this
we used CDS observations of the two coronal lines Mg X 624.94 Å and
Si XII 520.60 Å. Further, we develop a new method for estimating
τ<SUB>912</SUB> using the O V line measured by CDS and the O VI
measured by SUMER onboard SoHO. The latter line is used as a proxy to
deduce the intensity variations of O V underneath the filament. This
method also takes into account the presence of prominence-corona
transition regions. <P />Resulting heights of the EUV-filament
extensions are around 15 000 km for the bottom and around 40 000 km
for the top boundaries. However, there are significant variations
around these representative values and we show that in about half
of observed pixels the Lyman-continuum absorption dominates in
the coronal-line depression, while in the other half it is the
volume blocking effect. The latter situation corresponds to a large
(larger than 30 000 km) geometrical thickness of the EUV-filament
extension. From the heights of the boundaries of the EUV-filament the
geometrical thickness can be computed and used to estimate the total
mass loading which was found to be comparable to that of typical CMEs.
---------------------------------------------------------
Title: Multiwavelength determination of the density and total mass
of the EUV filament observed by SoHO/CDS, SoHO/SUMER and MSDP/VTT
Authors: Schwartz, P.; Schmieder, B.; Heinzel, P.; Anzer, U.
2004IAUS..223..219S Altcode: 2005IAUS..223..219S
It was found that filaments observed in EUV could be much more extended
than in Halpha. These extended dark structures visible in EUV are named
EUV filaments. Their parts seen only in EUV (not observable in Halpha
because of low opacity at the Halpha wavelength) are called EUV-filament
extensions (or simply EUV extensions). For the EUV filament observed
by SoHO on 15 October 1999 as northern polar crown filament, only
a few small dark structures were seen in Halpha. This suggests that
the mass of the EUV extension is larger than, or at least comparable
with, the mass of the parts of the filament observed in Halpha. In
our previous work we determined the 3D structure of the EUV extension
of this EUV filament. In this paper we present the determinations of
mass and average density of this EUV extension. For better density
estimates we interpret the hydrogen Lyman lines observed by SUMER
using non-LTE radiative transfer code. From the best fitting of Lyman
lines we obtained a reasonable model of the EUV extension with low gas
pressure, temperatures from 2times10^4 K to 10^5 K and with extended
prominence-corona transition regions.
---------------------------------------------------------
Title: A Spectroscopic Model of euv Filaments
Authors: Heinzel, P.; Anzer, U.; Schmieder, B.
2003SoPh..216..159H Altcode:
We propose a new spectroscopic model for extended dark structures
around Hα filaments observed in EUV lines. As in previous papers,
we call these structures EUV filaments. Our model uses at least three
observed EUV lines (located shortward the hydrogen Lyman-continuum
limit) to compute iteratively the altitudes at which the EUV filament
extensions are located. A transition-region line (O v in the present
case) can be used to derive the opacity of the Lyman continuum and the
other two coronal lines (e.g., Mg x and Si xii) then give two heights:
the bottom and top of the EUV filament. The method takes into account
self-consistently the absorption of EUV-line radiation by the Lyman
continuum, as well as the volume-blocking effect potentially important
for coronal lines. As an example we compute the heights of the EUV
filament at one particular position, using CDS data for the 5 May 2000
filament. At this position, the EUV filament extension lies between
altitudes 28 700 and 39 000 km, so that the geometrical thickness of the
structure is 10300 km (we discuss also the sensitivity of our models
to variations of the line intensities). These heights are consistent
with the concept of twisted magnetic flux tubes, but there could be
also some influence on our results due to additional low lying cool
structures from parasitic polarities.
---------------------------------------------------------
Title: Determination of the 3D-topology of an EUV-filament observed
by SoHO/CDS SoHO/SUMER and VTT/MSDP
Authors: Schwartz, P.; Heinzel, P.; Schmieder, B.; Anzer, U.
2003ESASP.535..495S Altcode: 2003iscs.symp..495S
We have constructed a spatial model of an extended EUV-filament
observed on 15 October 1999 (polar crown N 38 deg) by SoHO/CDS. The
narrow Hα counterparts were observed by VTT/MSDP. As found in 2001,
EUV-filaments are much more extended than those parts visible in Hα. We
have computed the bottom and top heights of this EUV-filament for the
whole CDS raster for different values of the Lyman-continuum optical
thickness using CDS measurements of two coronal lines (Mg X 624.94
Å and Si XII 520.60 Å) and the model of Heinzel et al., 2003. For
the scale height of the MgX line we used the value from Fludra et
al. 1999, assuming that this line is not solar cycle and activity
dependent. We created a new method for τ<SUB>912</SUB> determination
from O VI and O V line intensities. Because of the inhomogeneity in
the O V 629.37 Å line intensity distribution in the vicinitiy of
the EUV-filament it was not possible to estimate this intensity under
the filament. So we used observations made by SoHO/SUMER of the O VI
1031.91 Å line not absorbed by EUV-filament cold plasma. The knowledge
of the heights of the bottom and top boundaries of an EUV-filament
gives us the EUV-filament geometrical thickness. From this the mass
of the EUV-filament was computed.
---------------------------------------------------------
Title: EUV-filaments and their mass loading
Authors: Heinzel, P.; Anzer, U.; Schmieder, B.; Schwartz, P.
2003ESASP.535..447H Altcode: 2003iscs.symp..447H
It was found recently (Heinzel et al., 2001; Schmieder et al., 2003)
that solar filaments observed in EUV lines by SOHO/CDS are much more
extended than their Hα counterparts. This was explained by a large
difference between the hydrogen Lyman-continuum and Hα opacities. Two
different MHD models were suggested to explain the EUV-filament
extensions: the model based on parasitic polarities (Aulanier &
Schmieder, 2002) and the model with twisted flux tubes (Anzer &
Heinzel, 2003). The latter model can explain our recent findings
that at least some parts of the EUV-filament extensions are located
relatively high in the corona. These heights can be computed using a
new spectroscopic model of EUV-filaments. The mass which is loaded into
the EUV-filament extensions is then estimated on the basis of non-LTE
transfer calculation. The total filament mass is larger than that
derived for the Hα filament itself and this may have consequences
for the structure and mass loading of CMEs whenever they form from
such filaments - this may answer the question how the extended CME
structures can form from rather narrow Hα filaments. We summarize
the basic properties of EUV-filaments, present their spectroscopic
analysis and give some estimates for mass loading. We then discuss
possible relations between EUV-filaments and CMEs, in particular the
problems of their masses.
---------------------------------------------------------
Title: On the nature of extended EUV filaments
Authors: Anzer, U.; Heinzel, P.
2003A&A...404.1139A Altcode:
This paper describes the properties of extended EUV filaments and the
theoretical modelling of them. We summarise the general aspects of the
depression of EUV-line emission and give an interpretation of recent
filament observations in transition-region and coronal lines. The
EUV filament was found to be located relatively high in the corona
(at least 20 000 km above the solar surface) and this requires an
MHD scenario alternative to the parasitic-polarity model of Aulanier
& Schmieder (\cite{Aulanier02}). Here we present a new idea
for the support of cool gas in the magnetic arcade of a prominence
which is capable of explaining both wide and vertically extended EUV
filaments. Our mechanism is based upon the twisting of individual
flux tubes, similar to the one which was suggested by Priest et
al. (\cite{Priest89}). Finally, the consequences of this new model
are discussed.
---------------------------------------------------------
Title: The influence of radiative effects on the accretion onto
stellar magnetospheres
Authors: Kryukov, I. A.; Pogorelov, N. V.; Anzer, U.; Bisnovatyi-Kogan,
G. S.; Börner, G.
2003A&A...402...13K Altcode:
The influence of radiative effects on the accretion onto stellar
magnetospheres is investigated by performing global 2- and
2.5-dimensional simulations on the basis of high-resolution numerical
schemes with the application of irregular grids adapted to the shape
of the magnetopause. The latter is represented by an impermeable,
contracted dipole magnetic field surface with polar holes. Accreting
matter is assumed to be optically thin. The physical mechanisms which
are taken into account include cooling due to free-free and free-bound
transitions, the Compton heating via X-ray scattering on electrons, and
the inverse Compton cooling in the regions where the temperature of the
matter becomes sufficiently large to be able to transfer part of its
internal energy to photons. Depending on the determining parameters,
both steady-state solutions with a system of discontinuities and
unsteady flows with expanding shock waves can be obtained. It is shown
that efficient cooling of the matter can substantially facilitate
the penetration of the matter through the polar holes. The detailed
consideration of the realistic radiative effects proved to be of great
importance in our understanding of the accretion phenomenon, since
they can substantially affect it both qualitatively and quantitatively.
---------------------------------------------------------
Title: 2D Radiative Transfer in Magnetically Confined Structures
Authors: Heinzel, P.; Anzer, U.
2003ASPC..288..441H Altcode: 2003sam..conf..441H
Magnetically confined structures in the solar atmosphere exhibit
a large complexity in their shapes and physical conditions. As an
example, we show the case of so-called magnetic dips in prominences
which are in magnetohydrostatic equilibria. For such models we solve
2D non-LTE multilevel problem for hydrogen with PRD in Lyman resonance
lines. The iterative technique used is based on the MALI approach with
simple diagonal ALO and SC formal solver. <P />To compute the hydrogen
ionization balance, the preconditioned MALI equations are linearized
with respect to atomic level populations and electron density and
solved iteratively using the Newton-Raphson scheme. Two additional
problems are addressed: (i) an adequate iteration method for cases when
the column-mass scale is used in one of the two dimensions but varies
along the other dimension (which has a geometrical scaling); and (ii)
a possibility of using AMR (Adaptive Mesh Refinement) algorithms to
account for steep 2D gradients of selected variables (temperature,
density, etc.).
---------------------------------------------------------
Title: Radiative Effects in the Modelling of Accretion onto Stellar
Magnetospheres
Authors: Pogorelov, Nikolai; Kryukov, Igor; Anzer, Ulrich;
Bisnovatyi-Kogan, Guennadii; Börner, Gerhard
2003acfp.conf..473P Altcode:
Accretion onto neutron stars and black holes is the main energy supply
in galactic X-ray sources. The angular momentum captured by the X-ray
star from the optical companion's wind with velocity V_{infty} and
the binary period P is proportional to V^{-4}_{infty}P^{-1} [4]. If
V_{infty} is high or the binary components are widely separated, the
angular momentum is not sufficient for the accretion disk formation
at distances of the Alfvén radius where the magnetic pressure of the
star is balanced by the dynamic pressure of infalling matter, and the
accretion at large distances from the star becomes nearly spherically
symmetric. This occurs, for example, in some X-ray sources with a
massive companion star where long-periodic pulsars are observed [1],
[3].
---------------------------------------------------------
Title: A prominence with transition region: horizontal two-dimensional
filament model
Authors: Gorshkov, A. B.; Anzer, U.; Heinzel, P.
2002ESASP.506..405G Altcode: 2002ESPM...10..405G; 2002svco.conf..405G
SOHO/SUMER observations of solar filaments in Lyman lines of hydrogen
have revealed, in general, a two-peak form of the emission line
profiles with peak to center ratio less than an order of magnitude. This
fact strongly contradicts the results of numerical radiative transfer
simulations, where profiles with strong dips and large (1.5-2 orders of
magnitude) peak to center ratio are usually obtained due to the absence
of incident radiation from above the filament and, as a consequence,
very low atomic populations on the upper energy levels at the top of
the filament. Recently it was shown (Schmieder et al. 1998) that this
discrepancy can be removed by introducing a prominence-corona transition
region (PCTR) to the radiative transfer models. This paper continues
a set of publications (Anzer & Heinzel, 1999 and Heinzel &
Anzer, 2001) devoted to the modelling of prominences as structures in
MHS equilibrium. Here the prominence is represented by a horizontal
2D slab supported by a magnetic field. In our model we use a constant
gas pressure and assume that the kinetic temperature profile and the
PCTR extension are different in the vertical and horizontal directions
due to magnetic field. In the PCTR the temperature sharply increases
outwards from 8000K to 50000K on the scale of 100-600 km. To solve
the radiative transfer problem we apply a 2D code based on the MALI
iteration scheme and the modified long characteristics method.
---------------------------------------------------------
Title: Magnetic dips and the physics of quiescent prominences
Authors: Anzer, Ulrich
2002ESASP.506..389A Altcode: 2002svco.conf..389A; 2002ESPM...10..389A
This paper discusses the recent developments of prominence
modelling. The basic aspect of our discussion is the presence of
magnetic dips in all the models. We first show that "initial" dips
are needed for prominence formation and stability. We then give some
typical examples for different field configurations with dips. Next we
discuss those dips which are required for prominence support. We present
both 1D (slab) and 2D (thread) models. In addition the problem with the
theoretical modelling of extended EUV filaments is described. Then we
explain the difficulties with the observational confirmation of dipped
structures. We also comment on a model which suggests that equilibria
can be obtained for configurations without dips and finally we summarise
the most relevant aspects.
---------------------------------------------------------
Title: Spectral diagnostics of the magnetic field orientation in a
round-shaped filament
Authors: Schmieder, B.; Mein, N.; Heinzel, P.; Anzer, U.
2002ESASP.506..469S Altcode: 2002ESPM...10..469S; 2002svco.conf..469S
During several campaigns focused on prominences we have obtained
coordinated spectral observations from the ground and from space. The
SOHO/SUMER spectrometer allows us to observe, among others, the whole
Lyman series of hydrogen, while the Hα line was observed by the MSDP
spectrograph at the VTT. For Lyman lines, the non-LTE radiative-transfer
computations have shown the importance of the prominence-corona
transition region (PCTR) and its relation to the magnetic field
orientation for the explanation of the observed line profiles (Schmieder
et al. 1998, Heinzel et al. 2001). Moreover, Heinzel and Anzer (2001)
developed new 2D models which demonstrate how the shapes of Lyman
lines vary depending on the orientation of the magnetic field with
respect to the line of sight. To confirm this result observationally,
we focus here on a round-shaped filament observed during three days
as it was crossing the limb. The Lyman profiles observed on the limb
are different from day to day and we interpret these differences by
the change of orientation of the prominence axis (and therefore the
magnetic field direction) with respect to the line-of-sight.
---------------------------------------------------------
Title: Prominence fine structures in a magnetic equilibrium:
Two-dimensional models with multilevel radiative transfer
Authors: Heinzel, P.; Anzer, U.
2001A&A...375.1082H Altcode:
In this paper we construct theoretical models for vertical prominence
threads which are in magnetohydrostatic (MHS) equilibrium. These
models are fully two-dimensional (2D) and take the form of vertically
infinite threads hanging in a horizontal magnetic field. A typical
example of such a 2D magnetic-dip structure is shown for the case
when the central cool parts are surrounded by the prominence-corona
transition region (PCTR). We display 2D variations of the pressure,
density and temperature. While the pressure variations follow from the
MHS equilibrium, the kinetic temperature was specified empirically. As a
next step, we have solved the 2D multilevel non-LTE transfer problem in
such thread-like structures, in order to predict the spatial variations
of the emergent hydrogen spectrum. It is demonstrated that the hydrogen
Lyman lines (treated with partial redistribution) show significant
spatial variations of the intensity and that an important difference
exists between the line profiles emergent along and across the magnetic
field lines. We also discuss how these intensity variations compare to
recent SOHO/SUMER prominence observations, namely we show the effects
of line-profile averaging over the fine-structure threads which are
below the instrumental resolution. Finally we make some suggestions
for future modelling and observations.
---------------------------------------------------------
Title: Hydrodynamic modeling of accretion onto stellar magnetospheres
Authors: Kryukov, I. A.; Pogorelov, N. V.; Bisnovatyi-Kogan, G. S.;
Anzer, U.; Börner, G.
2000A&A...364..901K Altcode:
A numerical investigation is performed of the accretion of slowly
rotating matter onto a stellar magnetosphere. The shape of the
magnetosphere is represented by an impermeable, contracted dipole
magnetic field surface with polar holes. Depending on the governing
parameters, both steady-state solutions with a system of discontinuities
and unsteady flows with expanding shock waves can be obtained. Certain
solutions exhibit extended outflow regions. The simulation is performed
using a high-resolution finite volume numerical scheme and structured
irregular grids adapted to the shape of the accreting body.
---------------------------------------------------------
Title: Energy considerations for solar prominences with mass inflow
Authors: Anzer, U.; Heinzel, P.
2000A&A...358L..75A Altcode:
In this Letter we study the inflow of enthalpy and ionisation
energy into solar prominences. We use 1D stationary slab models for
the prominence to calculate this inflow. We compare the resulting
energy gain with the integrated radiative losses obtained for such
slab models. We find that for reasonable inflow velocities many of our
models can be in energy equilibrium; only the very massive prominences
will either require some additional heating or they have to cool down
to low central temperatures. We also discuss the possibility or heating
the prominence by vertical downflows.
---------------------------------------------------------
Title: The energy balance in solar prominences
Authors: Anzer, U.; Heinzel, P.
1999A&A...349..974A Altcode:
In this paper we study the energy balance in quiescent solar
prominences. For this investigation we use a simple 1D slab model in
magneto-hydrostatic equilibrium. We divide the studied region into two
parts: The inner region consisting of the prominence itself and the
cool part of the transition region (up to 30000 K). In this region the
plasma is optically thick in several atomic transitions and therefore we
have to solve the non-LTE radiative transfer problem in this part. This
allows us to derive self-consistently the gas density, the ionization
degree of hydrogen and the hydrogenic radiation losses. The energy
transport by thermal conduction can be neglected in this region. In the
outer part of the transition region, the thermal conduction becomes very
important but the treatment of radiation is simplified by the fact that
the plasma is optically thin. We find that energy balance in prominences
can only be obtained for special forms of the heating function. This
requirement is very stringent for the inner parts, while in the outer
region thermal conduction can transport large amounts of the heat
energy and therefore a wider class of heating functions will be allowed.
---------------------------------------------------------
Title: Magnetic Dips in Prominences
Authors: Heinzel, P.; Anzer, U.
1999SoPh..184..103H Altcode:
Magnetic dips are generally assumed to be basic equilibrium
configurations in quiescent solar prominences. Here we discuss two types
of the magnetic dips which were considered in the literature: (1) dips
resulting from a force-free magnetic equilibrium in the corona, and (2)
magnetic dips which are formed in situations where the Lorentz force
balances the weight of the prominence plasma. An important parameter
which decides between these two cases is the plasma β. For β⋘1,
the effect of the prominence material on the equilibrium structure is
quite negligible and the case (1) holds. If, however, β is larger,
say between 0.1 and 1 or even higher, magnetic dips of the second kind
are formed and they can be characterized by the angle ψ1 between the
vertical and the direction of the field lines at the surface of the
prominence structure. A simple and illustratory formula is derived
to relate this angle to the plasma β at the prominence center,
namely βc≃cot2ψ1. βc=1 thus corresponds to ψ1=45°. Finally,
we discuss the range of values of both βc and ψ1 as deduced from
various observations and conclude that the dips of the second kind are
important for the prominence equilibria. We also suggest a new method
for determination of the field-line inclination.
---------------------------------------------------------
Title: Numerical Computation of Two-Dimensional Wind Accretion of
Isothermal Gas
Authors: Shima, E.; Matsuda, T.; Anzer, U.; Börner, G.; Boffin,
H. M. J.
1999ASSL..240..225S Altcode: 1999numa.conf..225S
No abstract at ADS
---------------------------------------------------------
Title: Numerical computation of two dimensional wind accretion of
isothermal gas
Authors: Shima, Eiji; Matsuda, Takuya; Anzer, Ulrich; Boerner, Gerhard;
Boffin, Henri M. J.
1998A&A...337..311S Altcode: 1998astro.ph..5343S
A new numerical algorithm for calculating isothermal wind accretion
flows has been developed and is applied here to the analysis of the
hydrodynamics of two-dimensional plane symmetric accretion flows in
wind-fed sources. Polar coordinates are used to ensure fine resolution
near the object. It is found that a thin accretion column is formed
which shows wave-like oscillations. Small accretion disks are formed
temporarily around the object. Mass accretion rate and angular momentum
accretion rate exhibit quasi-periodic oscillations. The amplitudes of
the oscillations depend on the size of the inner boundary, the number
of grid points and the method of calculation. For a smaller size of
the inner boundary, finer grids and more accurate numerical schemes,
the amplitudes of the oscillation become larger.
---------------------------------------------------------
Title: Prominence Parameters Derived from Magnetic-Field Measurements
and NLTE Diagnostics
Authors: Anzer, U.; Heinzel, P.
1998SoPh..179...75A Altcode:
In this paper we present a detailed analysis of a number of quiescent
prominences for which the components of the magnetic field as well as
the electron density and emission measure were previously obtained from
quasi-simultaneous measurements in hydrogen Hα and helium D<SUB>3</SUB>
lines. From magnetic equilibrium models of the Kippenhahn-Schlüter
type one can calculate the gas pressure, density, column mass and
geometrical width. The same set of physical parameters can also
be derived from a NLTE hydrogen-line analysis. We have studied the
mutual correlations between these two sets of parameters. Very large
differences, reaching an order of magnitude, were found between these
two sets, both for individual prominences and for the mean values over
all prominences used in this investigation. Finally, we discuss some
implications of our results.
---------------------------------------------------------
Title: Modelling of Non-Uniform Prominence Slabs
Authors: Heinzel, P.; Anzer, U.
1998ASPC..150..213H Altcode: 1998IAUCo.167..213H; 1998npsp.conf..213H
No abstract at ADS
---------------------------------------------------------
Title: VELA X-1: how to produce asymmetric eclipses.
Authors: Feldmeier, A.; Anzer, U.; Boerner, G.; Nagase, F.
1996A&A...311..793F Altcode:
Light curves of the X-ray pulsar Vela X-1 obtained with the ASCA
satellite show a strong asymmetry in the hard energy band during
the eclipse of the X-ray source: a steep drop at ingress is followed
by a gradual decline, whereas only a steep increase is observed at
egress. X-ray scattering off the dense accretion wake trailing the
neutron star cannot explain the gradual decline because of the long
persistence of the latter ({DELTA}φ=0.11). Instead we propose that
scattering in an extended photoionization wake is responsible. This
wake is caused by the switch-off of the radiative force that drives
the B supergiant wind during the passage through the highly ionized
Stroemgren region surrounding the X-ray source. The stalled gas then
trails the neutron star, which moves relative to the B star surface (no
corotation). A model for the Vela X-1 system which assumes that the B
star does not rotate gives too large a phase extent for the dense wake
and can be ruled out. Including the B star rotation in an approximate
way, the relative azimuthal motion of the neutron star is slower and
the wake covers a smaller phase interval. Finally, we assume that the
Stroemgren sphere does not reach too deep into the wind accelerating
region. The wind can then reach a certain fraction of the terminal
velocity before the radiative force is switched off. This elongates
the photoionization wake further and both its phase extent and its
scattering efficiency match the observations.
---------------------------------------------------------
Title: Modeling Accretion onto a Closed Pulsar Magnetosphere
Authors: Morris, J. P.; Boerner, G.; Anzer, U.
1995AAS...187.3306M Altcode: 1995BAAS...27Q1330M
A method for modeling accretion onto a closed magnetosphere employing
the numerical method of SPH is presented. This method allows the dynamic
interaction of the magnetosphere and surrounding field-free plasma to be
simulated. Results obtained for some steady configurations are compared
with previous work for closed magnetospheres. Future application of the
technique, with a view to modeling spin up and spin down of pulsars is
discussed. Other possible applications and enhancements of the method
are outlined.
---------------------------------------------------------
Title: Parameters of Quiescent Prominences Derived from Magnetic
Field Measurements
Authors: Anzer, Ulrich
1995SoPh..161...49A Altcode:
Based upon the new magnetic field vector measurements of
Bommieret al. (1994) we construct prominence models which are in
magnetohydrostatic equilibrium. We compare these new models with
earlier ones and find that they are on average more massive and also
considerably narrower.
---------------------------------------------------------
Title: Random variations of the pulse period of X-ray binaries with
wind accretion.
Authors: Anzer, U.; Boerner, G.
1995A&A...299...62A Altcode:
In this paper we first summarise earlier results about the randomness
of pulse period variations in wind fed X-ray pulsars. Then we
present two types of models for the random spin-up and spin-down of
rotating neutron stars which accrete mass from a stellar wind. We
show that the irregularities in accretion flows which were discovered
in numerical models have too low amplitudes in order to explain the
observations. Therefore we discuss an alternative model which is based
upon the existence of a Kepler disc around the neutron star. We argue
that such a model can give an explanation of the observations.
---------------------------------------------------------
Title: Book Review: Fragmented energy release in sun and stars,
the interface between MHD and plasma physics / Kluwer, 1994
Authors: Anzer, U.
1995SoPh..158R.399V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book reviews
Authors: Valníček, B.; Anzer, U.
1995SoPh..158..399V Altcode: 1995SoPh..158..399A
No abstract at ADS
---------------------------------------------------------
Title: Bondi-Hoyle accretion simulations including velocity gradients.
Authors: Ruffert, M.; Anzer, U.
1995A&A...295..108R Altcode:
We investigate the hydrodynamics of three-dimensional classical
Bondi-Hoyle accretion, especially the accretion of angular momentum
from a non-homogeneous medium and discuss some consequences for models
of wind-fed X-ray sources. A medium taken to be an ideal gas (γ=5/3)
moves at Mach 3 past a totally absorbing sphere with a radius of 0.1
accretion radii. The velocity of this medium is given a gradient of 3%
(per accretion radius distance) perpendicular to the bulk flow. The
hydrodynamics is modeled by the "Piecewise Parabolic Method" and
the resolution around the accretor is increased using 7 multiply
nested grids. The flow in the shock cone is not steady, but does not
exhibit large scale "flip-flop"-flow. The average specific angular
momentum accreted is 0.097 (in units of accretion radii and sound
speed). Although the magnitude is large compared to cases without
velocity gradient, it still is not large enough to sustain the random
walk model of wind-fed X-ray sources.
---------------------------------------------------------
Title: Numerical studies of wind accretion using SPH I. 2D
simulations.
Authors: Boffin, Henri M. J.; Anzer, Ulrich
1994A&A...284.1026B Altcode:
Two-dimensional numerical simulations of accretion by a gravitating
object from a homogeneous wind are performed using SPH. The effects of
several parameters changes as well as the algorithm modifications are
studied. The flow is in most cases weakly unstable with a very small,
quasi-periodic oscillation of the shock cone. Comparison with previous
works is also done.
---------------------------------------------------------
Title: Remarks on Two-Dimensional Magnetic Arcade Models of Coronal
Structures
Authors: Anzer, U.
1994scs..conf..309A Altcode: 1994IAUCo.144..309A
A critical evaluation of some recent models for coronal structures using
two-dimensional magnetic arcades is given. Prominences with inverse
polarity as well as the evolution of sheared arcades are discussed.
---------------------------------------------------------
Title: Tests of Wind Accretion Models
Authors: Anzer, U.; Börner, G.; Nagase, F.
1994nhxr.conf..611A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A simple analysis of period noise in binary X-ray pulsars.
Authors: de Kool, Martijn; Anzer, Ulrich
1993MNRAS.262..726D Altcode:
A simple method is presented for determining whether the noise in the
pulse period history of X-ray pulsars can be described by a random
walk process. This is accomplished by calculating the mean difference
in angular velocity between different observations as a function of
the time interval between these observations. The method is applied
to 10 X-ray pulsars for which more than 10 period determinations
are available. For Vela X-1, earlier results that the pulse period
behavior is very well fitted by a random walk in period is confirmed. In
GX 301-2 the pulse period behavior is also consistent with a random
walk. Analysis of the pulse period history of three X-ray pulsars with
a Be companion shows that a random walk is not consistent with the data.
---------------------------------------------------------
Title: Numerical Simulations of Two-dimensional and Three-dimensional
Wind Accretion Flows of an Isothermal Gas
Authors: Ishii, Takanori; Matsuda, Takuya; Shima, Eiji; Livio, Mario;
Anzer, Ulrich; Boerner, Gerhard
1993ApJ...404..706I Altcode:
We present the results of 2D and 3D numerical hydrodynamical
calculations of accretion flows of an isothermal gas past a gravitating
compact object. The calculations were performed both for a homogeneous
medium and for a medium containing a transverse density or velocity
gradient. We find that 2D isothermal flows exhibit the 'flip-flop'
instability (previously seen in adiabatic calculations) both in the
homogeneous and the inhomogeneous cases. In the 3D case, while some
unsteadiness is observed, the instability is much less violent than
in 2D. We calculate (for the first time with a 3D hydrocode) the
rate of accretion of mass and angular momentum from an inhomogeneous
medium. The mass accretion rate agrees quite well with the prediction
of the Bondi-Hoyle theory. However, the rate of accretion of angular
momentum is considerably lower than the rate at which angular momentum
is deposited into the accretion cylinder. A possible consequence of
our results for wind-fed X-ray binaries is discussed.
---------------------------------------------------------
Title: Some Aspects of Magnetic Arcades in the Solar Corona
Authors: Anzer, U.
1993ComAp..16..305A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Variations of the pulse periods in X-ray binaries: modelling
attempts
Authors: Anzer, U.
1993heac.conf...15A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Fibril Structure of Prominences
Authors: Hood, A. W.; Priest, E. R.; Anzer, U.
1992SoPh..138..331H Altcode:
In this paper we present several magneto-hydrostatic equilibrium
models for prominences with fibril-like fine structure. For all the
models ad hoc temperature profiles are used without discussing the
energetics. For our models we assume fine structure to occur either
across the prominence axis or along it. This approach is intended
as a first step towards more realistic models based upon a series of
vertical fibril structures.
---------------------------------------------------------
Title: Numerical simulations of two-dimensional and three-dimensional
accretion flows
Authors: Matsuda, Takuya; Ishii, Takanori; Sekino, Nobuhiro; Sawada,
Keisuke; Shima, Eiji; Livio, Mario; Anzer, Ulrich
1992MNRAS.255..183M Altcode:
Numerical simulations of 2D and 3D accretion flows past a gravitating
compact object from a uniform flow at a large distance upstream are
performed by solving the Eulerian equations. The 2D flows exhibit a
'flip-flop instability' if the central accreting body is small. If
the central body is enlarged at some instance in the oscillating flow,
then the accretion shock shows a rather periodic oscillation similar
to the von Karman vortex street. In the case of 3D flows, it is found
that the shock cone is much more robust than in 2D, and the flip-flop
instability takes a different, probably less violent, form. The causes
of the instabilities are discussed.
---------------------------------------------------------
Title: Pulsating X-Ray Sources - Longterm Period Variations
Authors: Anzer, U.; Borner, G.
1992ComAp..16...31A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Flip-Flop Instability of Wind-Fed Accretion Flow - 2D and
3D Calculations
Authors: Matsuda, T.; Ishii, T.; Livio, M.; Anzer, U.; Börner, G.
1992fxra.conf..177M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the 'flip-flop' instability of Bondi-Hoyle accretion flows
Authors: Livio, Mario; Soker, Noam; Matsuda, Takuya; Anzer, Ulrich
1991MNRAS.253..633L Altcode:
A simple physical interpretation is advanced by means of an analysis
of the shock cone in the accretion flows past a compact object and with
an examination of the accretion-line stability analyses. The stability
of the conical shock is examined against small angular deflections with
attention given to several simplifying assumptions. A line instability
is identified in the Bondi-Hoyle accretion flows that leads to the
formation of a large opening-angle shock. When the opening angle becomes
large the instability becomes irregular oscillation. The analytical
methodology is compared to previous numerical configurations that
demonstrate different shock morphologies. The Bondi-Hoyle accretion
onto a compact object is concluded to generate a range of nonlinear
instabilities in both homogeneous and inhomogeneous cases with a
quasiperiodic oscillation in the linear regime.
---------------------------------------------------------
Title: On the stability of wind accretion.
Authors: Matsuda, T.; Sekino, N.; Sawada, K.; Shima, E.; Livio, M.;
Anzer, U.; Boerner, G.
1991A&A...248..301M Altcode:
Results of numerical investigations of accretion flows past a compact
object are reported. A strong tendency toward nonsteady flow is
found to exist in both 2D and 3D computations. Steady flows are
obtained only when the numerical resolution is low or the central
absorbing body is large. It is concluded that: (1) accretion from a
homogeneous medium onto a compact object is intrinsically nonsteady;
(2) the instability manifests itself in 'flip-flop' oscillations of
the accretion shock cone, accompanied by short phases of quasi-disk
formation, with the sense of rotation reversing periodically; and (3)
no density or velocity gradients in the incoming flow are required
for the instability to develop.
---------------------------------------------------------
Title: The Fibril Structure of Prominences
Authors: Priest, E. R.; Hood, A. W.; Anzer, U.
1991SoPh..132..199P Altcode:
We suggest that the fibril structure of prominences may be caused by
filamentation during its formation by radiative instability. We also
discuss the effects of other types of instability and give a mechanism
for the formation of vertical threads. The models indicate that highly
inhomogeneous density structures can exist in the presence of smooth
profiles for the plasma pressure and magnetic field. In our particular
models the plasma pressure of a fibril prominence is higher and the
vertical magnetical field is weaker than in a uniform prominence model,
while the mass is substantially smaller.
---------------------------------------------------------
Title: Binary X-Ray Sources: Some Aspects of Wind Accretion
Authors: Anzer, U.; Börner, G.
1991heac.conf....3A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Field Configurations which can Produce Prominences
with Inverse Polarity
Authors: Anzer, U.
1990SoPh..130..403A Altcode:
In this Letter several observational aspects of prominences with inverse
magnetic polarity are summarised. It is shown that these features can
be explained in a natural way if inverse polarity prominences result
from the merging of two adjacent bipolar magnetic regions.
---------------------------------------------------------
Title: Prominence models with line currents - Stabilisation by
flux conservation
Authors: Anzer, U.; Ballester, J. L.
1990A&A...238..365A Altcode:
A model of prominence eruption, based on a filament with circular cross
section as different from the filament of a single line current used in
earlier models, is presented. For configurations with normal and inverse
polarity, the model is considered to be stable with respect to the
vertical displacements. This implies that simple configurations cannot
model prominence eruptions unless the effect of flux conservation is
also included. It is found that if the magnetic flux below a finite size
filament is conserved, a run-away instability no longer exists. The
results apply to a limited class of 2-D equilibria containing a
cylindrical filament and subjected to strictly 2-D perturbation. Models
that are more realistic can be unstable.
---------------------------------------------------------
Title: A Model for Quiescent Solar Prominences with Normal Polarity
Authors: Hood, A. W.; Anzer, U.
1990SoPh..126..117H Altcode:
A class of 2-D models of solar quiescent prominences, with normal
polarity, is presented. These represent an extension to the
Kippenhahn-Schlüter model for which the prominence configuration
matches smoothly onto an external non-potential coronal solution
of a constant α field. Using typical prominence values a model is
constructed which also matches the coronal conditions. It is found
that the magnetic field component along the prominence influences
the internal structure of the prominence. A simple extension to the
basic models is indicated as a means of taking a lower boundary of
the prominence and eliminating parasitic polarities in the photosphere.
---------------------------------------------------------
Title: Structure and stability of prominences
Authors: Anzer, U.
1990GMS....58..307A Altcode:
The present consideration of the magnetohydrostatic equilibria of
quiescent solar prominences proceeds from the conceptual framework of
field configurations having normal and inverse magnetic polarities to an
evaluation of the principal models for both types of configuration. A
novel model based on the twisted flux tube phenomenon is presented
with a view to the visualization of the prominence as a sheet within
such a flux rope. Questions as to the energy balance of prominences
are left out of account.
---------------------------------------------------------
Title: Prominence Models with Line Currents: Stabilization by Flux
Conservation
Authors: Anzer, U.; Ballester, J. L.
1990PDHO....7..156A Altcode: 1990ESPM....6..156A; 1990dysu.conf..156A
No abstract at ADS
---------------------------------------------------------
Title: A normal polarity quiescent prominence model.
Authors: Hood, A. W.; Anzer, U.
1990PDHO....7..130H Altcode: 1990dysu.conf..130H
A class of simple 2-D non-isothermal models for quiescent
prominences with normal polarity are presented. These extended the
Kippenhahn-Schlüter and Menzel models by smoothly matching the
prominence region onto an external, force-free coronal field. In
addition, the field component along the prominences is an integral
part of the solution and modifies the internal structure.
---------------------------------------------------------
Title: A Model for Quiescent Solar Prominences with Normal Polarity
Authors: Hood, A. W.; Anzer, U.
1990LNP...363..271H Altcode: 1990doqp.coll..271H; 1990IAUCo.117..271H
No abstract at ADS
---------------------------------------------------------
Title: A three-dimensional model for solar prominences
Authors: Démoulin, P.; Priest, E. R.; Anzer, U.
1990LNP...363..268D Altcode: 1990doqp.coll..268P; 1990LNP...363..268P; 1990IAUCo.117..268P
We suggest here a model for the 3D structure of quiescent prominences by
a superposition of two fields. A 3D force-free field with constant is
assumed to exist in the corona prior to the prominence formation. The
prominence itself is represented by a line current which interacts
with the coronal field. The three-dimensional field is represented by
analytical functions and concentration of the magnetic field at the
photospheric level by convection cells is taken into account. When the
field created by the photospheric pattern supports the prominence,
the prominence feet are found to be located at supergranule centres
otherwise; they are located at cell boundaries.
---------------------------------------------------------
Title: A three-dimensional model for solar prominences
Authors: Demoulin, P.; Priest, E. R.; Anzer, U.
1989A&A...221..326D Altcode:
In an attempt to model the external force field of a prominence,
a three-dimensional linear force-free field configuration was
studied. The model consists of a fundamental together with a harmonic
that is periodic along the prominence. The variation of the prominence
height along the prominence is calculated and it is suggested that
feet occur where the prominence sags down to low heights.
---------------------------------------------------------
Title: A Twisted Flux-Tube Model for Solar Prominences. I. General
Properties
Authors: Priest, E. R.; Hood, A. W.; Anzer, U.
1989ApJ...344.1010P Altcode:
It is proposed that a solar prominence consists of cool plasma supported
in a large-scale curved and twisted magnetic flux tube. As long as
the flux tube is untwisted, its curvature is concave toward the solar
surface, and so it cannot support dense plasma against gravity. However,
when it is twisted sufficiently, individual field lines may acquire a
convex curvature near their summits and so provide support. Cool plasma
then naturally tends to accumulate in such field line dips either
by injection from below or by thermal condensation. As the tube is
twisted up further or reconnection takes place below the prominence, one
finds a transition from normal to inverse polarity. When the flux tube
becomes too long or is twisted too much, it loses stability and its true
magnetic geometry as an erupting prominence is revealed more clearly.
---------------------------------------------------------
Title: Inhomogeneous wind accretion - Comparison between 3D and
2D computations
Authors: Sawada, K.; Matsuda, T.; Anzer, U.; Boerner, G.; Livio, M.
1989A&A...221..263S Altcode:
Full three-dimensional computations of accretion flows which have
velocity gradients are presented and compared with two-dimensional
computations. It is found that the rate of accretion of the angular
momentum in three-dimensional flows is about 5 times smaller than in
the two-dimensional cases. The effect that this finding has on the
modeling of wind-fed binary X-ray sources is discussed. It is concluded
that only three-dimensional calculations can give a reliable answer
to the question of angular momentum transfer to the neutron star.
---------------------------------------------------------
Title: A Model for Quiescent Solar Prominences with Normal Polarity
Authors: Hood, A. W.; Anzer, U.
1989HvaOB..13..281H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Three-Dimensional Model for Solar Prominences
Authors: Demoulin, P.; Priest, E. R.; Anzer, U.
1989HvaOB..13..253D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Structure and equilibrium of prominences
Authors: Anzer, U.
1989ASSL..150..143A Altcode: 1988dsqs.work..143A; 1989dsqs.work..143A
The existing models for magnetohydrostatic equilibrium of quiescent
prominences are presented and critically discussed. Also considered
is the question of how the energy balance can be achieved in these
prominences. The main emphasis is on recent developments in these
areas of research.
---------------------------------------------------------
Title: Thermal Condensations in Coronal Magnetic Fields
Authors: Hood, A.; Anzer, U.
1988SoPh..115...61H Altcode:
Conditions under which cool condensations can form in the solar corona
are investigated using the powerful phase plane method to analyse the
energy and hydrostatic balance equations. The importance of the phase
plane approach is that the conclusions deduced are not sensitive to
the actual choice of boundary conditions adopted which only determine
the actual contour. The importance of heating variations and area
divergence are studied as well as the influence of gravity for their
effect on the formation of cool condensations. The cool temperature
at which optically thin radiation and heating balance is important
and the links with other cool solutions are mentioned.
---------------------------------------------------------
Title: Structure and equilibrium of prominences.
Authors: Anzer, U.
1988dssp.conf...99A Altcode:
The existing models for magnetohydrostatic equilibrium of quiescent
prominences are presented and critically discussed. The author
also investigates how the energy balance can be achieved in these
prominences. The emphasis of this review is on the recent developments
in these areas of research.
---------------------------------------------------------
Title: The influence of external magnetic fields on the structure
of thin accretion disks.
Authors: Anzer, U.; Boerner, G.; Meyer-Hofmeister, E.
1987A&A...188...85A Altcode:
The internal structure of thin accretion disks is studied for the case
where strong outside magnetic fields interact with these disks. Such
configurations are expected to occur in close binary X-ray pulsars such
as Her X-1. The authors find that the magnetic pressure exerted on the
disk has two main effects: the vertical disk structure shows a density
increase towards the interface between disk and magnetosphere; and the
thickness of the disk decreases more rapidly as one approaches the inner
edge of the disk. The second effect gives a stronger irradiation of
the disk surface close to the inner edge and this results in a higher
surface temperature.
---------------------------------------------------------
Title: The stability of line tied force-free cylindrical arcades:
Is an active region filament a requirement for a two-ribbon flare?
Authors: Hood, A.; Anzer, U.
1987SoPh..111..333H Altcode:
The MHD stability of force-free, cylindrical arcades is investigated,
including the stabilising effect of photospheric line tying. It is found
that a wide variety of fields are stable. This suggests that either a
departure from a force free equilibrium or suppression of line tying
is necessary if a two-ribbon flare is to be triggered. It is postulated
that in both circumstances, the existence of an active region filament
is an essential preflare requirement for a two-ribbon flare.
---------------------------------------------------------
Title: Disk formation at the magnetosphere of wind-fed pulsars :
applicationto VELA X-1.
Authors: Boerner, G.; Hayakawa, S.; Nagase, F.; Anzer, U.
1987A&A...182...63B Altcode:
The disk formation in a wind-fed, rotating, accreting neutron
star is considered in view of the fact that the angular momentum
transfer by wind accretion is too small to account for large rates
of spin-up and spin-down as observed. Under the assumption that the
closed magnetosphere extends to the corotation radius it is shown
that a disk will form through the interaction of the spherically
accreting matter with the rotating magnetosphere. Long term spin-up and
spin-down episodes then become possible due to the difference between
the accretion torque transmitted by the disk and the deceleration by
the accretion at the magnetosphere surface. Large rates of short-term
pulse period change are attributed to the change in the accretion
torque transmitted by the disk. Application of this model to the X-ray
source Vela X-1 requires a large magnetic moment μ ≡ 10<SUP>32</SUP>
Gauss cm<SUP>3</SUP>, but once the high value for the magnetic field
(10<SUP>13</SUP> Gauss ⪉ B ⪉ 10<SUP>14</SUP> Gauss) is accepted,
a variety of observations fit well into the picture.
---------------------------------------------------------
Title: Numerical studies of wind accretion.
Authors: Anzer, U.; Boerner, G.; Monaghan, J. J.
1987A&A...176..235A Altcode:
Wind accretion from a companion star is assumed to be the power
source for wide X-ray binaries. These winds will in general have
spatial variations both in density and in the velocity vector. The
authors have performed 2-dimensional numerical computations of such
inhomogeneous wind flows to obtain estimates on the amount of angular
momentum accreted for a given gradient of the velocity vector. They
find that the angular momentum flux is about a factor 5 smaller than
the previous estimates. This means that there is not enough angular
momentum transferred to the neutron star to explain, for example,
the long term period changes of Vela X-1. This leads the authors to
propose a different mechanism for the spin-up and spin-down of sources
of the type of Vela X-1. They outline briefly the physical features
of such a model.
---------------------------------------------------------
Title: The influence of external magnetic fields on the structure
of thin accretion disks.
Authors: Anzer, U.; Börner, G.; Meyer-Hofmeister, E.
1987imfo.work..203A Altcode:
There is a generally accepted picture of many binary X-ray sources
wherein a rotating magnetized neutron star accretes matter from
a surrounding disk of plasma. As the accreting matter approaches
the rotating neutron star it is more and more influenced by the
stellar magnetic field until eventually its motion is dominated by
the field. Finally the plasma will flow along the field lines towards
the surface of the neutron star. The equilibrium structure of a thin
accretion disk subjected to the pressure of an external magnetic field
is described.
---------------------------------------------------------
Title: Stability of Magnetic Arcades
Authors: Anzer, U.; Hood, A. W.
1987rfsm.conf..248A Altcode:
The authors conclude that sheared force-free arcades cannot become
unstable and produce solar flares. They therefore predict that
two-ribbon flares must always be associated with extended solar
prominences.
---------------------------------------------------------
Title: Structure and Equilibrium of Prominences
Authors: Anzer, U.
1987dssp.work...99A Altcode: 1987ASSL..150...99A
No abstract at ADS
---------------------------------------------------------
Title: The influence of external magnetic fields on the structure
of thin accretion disks.
Authors: Anzer, U.; Börner, G.; Meyer-Hofmeister, E.
1987MPARp.282.....A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Modelling of the magnetic field of solar prominences.
Authors: Anzer, U.
1987ppcs.work...61A Altcode:
Measurements of magnetic fields with closed structures in quiescent
prominences are discussed. It is shown that it is not possible to
construct simple equilibrium models for quiescent prominences of the
Kuperus-Raadu type. An open-field example is considered, and it is
concluded that at present there exists no theoretical equililbrium
model of the Kuperus-Raadu type which is consistent with observations.
---------------------------------------------------------
Title: Numerical studies of wind accretion.
Authors: Anzer, U.; Börner, G.; Monaghan, J. J.
1986MPARp.230.....A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Interaction of the Accretion Disk with the Magnetosphere of
a Rotating Neutron Star
Authors: Anzer, U.; Borner, G.
1986ppm..conf..101A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The global structure of magnetic fields which support quiescent
prominences
Authors: Anzer, U.
1985svmf.nasa..101A Altcode:
Magnetic fields in quiescent prominences were observed, but only
recently has it become possible to measure the full magnetic field
vector. The component of the field along the line of sight, B (parallel)
can be uniquely determined, whereas for the component perpendicular
to the line of sight B (perpendicular) and -B (perpendicular)
are indistinguishable. An ambiguity remains in the actual magnetic
field vector, in particular with respect to its orientation relative
to the prominence axis. A sample of more than 100 prominences were
studied. A more detailed analysis of 10 prominences are presented,
and then set these prominence fields into relation to the underlying
photospheric fields. It is found from statistical analysis of several
hundred prominences that in 25% of the cases the field penetrates
the prominence directly, whereas in 75% the field orientation in the
prominence is reversed.
---------------------------------------------------------
Title: Remarks on the Magnetic Support of Quiescent Prominences
Authors: Anzer, U.; Priest, E.
1985SoPh...95..263A Altcode:
The development of magnetic field structures which can
lead to prominence configurations of the Kuperus-Raadu type is
discussed. Starting from streamer type configurations and preserving the
total current in the system we find that simple two-dimensional static
configurations lead to prominences which in general lie systematically
much lower than the heights found from observations. We therefore
conclude that either more complex field configurations are needed to
explain the recent observations by Leroy et al. (1983) or the initial
configurations must be very special.
---------------------------------------------------------
Title: The global structure of magnetic fields which support quiescent
prominences.
Authors: Anzer, U.
1985NASCP2374..101A Altcode:
The author reviews and discusses models of magnetic field configurations
in prominences.
---------------------------------------------------------
Title: Theoretical modelling of inhomogeneous fields in the
chromosphere.
Authors: Anzer, U.; Galloway, D. J.
1985cdm..proc..199A Altcode:
Theoretical models of the magnetic field structure above a photosphere
with magnetic flux tubes are constructed, on the hypotheses that
the field is either current-free or is governed by the force-free
equation j = αB, with α constant. The level where the magnetic
pressure becomes equal to the ambient gas pressure is calculated,
and is shown to depend very little on which of the above hypotheses
is adopted. The resulting levels are in agreement with the "canopy
heights" given by Giovanelli (1980) and Giovanelli and Jones (1982)
for areas around active regions, but are higher than the results
for the quiet, unipolar regions in Giovanelli and Jones (1983). The
calculations suggest there are large regions of the low to middle
quiet chromosphere that require non-magnetic heating mechanisms.
---------------------------------------------------------
Title: Some aspects of the angular momentum transfer between an
accretion disk and a rotating, magnetic neutron star
Authors: Anzer, U.; Boerner, G.
1984AdSpR...3j.315A Altcode: 1984AdSpR...3..315A
No abstract at ADS
---------------------------------------------------------
Title: Remarks on the magnetic support of quiescent prominences.
Authors: Anzer, U.; Priest, E.
1984MPARp.157.....A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Some Aspects of the Angular Momentum Transfer Between an
Accretion Disk and a Rotating Magnetic Neutron Star
Authors: Anzer, U.; Borner, G.
1984heac.conf..315A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Accretion onto rotating, magnetic neutron stars : the inner
edge of the disk.
Authors: Anzer, U.; Boerner, G.
1983A&A...122...73A Altcode:
The surface of an accretion disk in a rotating neutron star's magnetic
field is subject to the Kelvin-Helmholtz instability induced by
the velocity difference of the rigidly rotating magnetosphere and
the Keplerian disk. This instability is analysed in a simplified
geometry. It is shown that a large part of the disk surface will become
unstable, leading to a turbulent diffusion of the disk plasma into
the magnetosphere. The resulting exchange of angular momentum between
the neutron star and the accreting matter is described. The present
model of a magnetic dipole axis perpendicular to the rotation axis of
the neutron star is compared to the model of an aligned rotator. The
observational consequences with respect to the rotational state of
pulsating X-ray sources are discussed.
---------------------------------------------------------
Title: A model for the magnetic field above supergranules
Authors: Anzer, U.; Galloway, D. J.
1983MNRAS.203..637A Altcode:
A model is provided for the inhomogeneous magnetic field structure above
a stellar photosphere where the field is concentrated in intense tubes
at the downflow regions of a convection pattern. By finding where the
magnetic energy is strong or weak compared with the local thermal energy
of the gas, the relative importance of magnetic and non-magnetic heating
mechanisms can be estimated for those regions where the principal
radiative losses occur in solar or stellar chromospheres. For the
quiet Sun, slightly over half of the chromospheric emission comes
from regions which are essentially non-magnetic. For other stars,
the calculations yield a simple working rule which suggests that most
late-type stars with fields strong enough to be directly observable
will have magnetically dominated chromospheres.
---------------------------------------------------------
Title: The magnetic field configuration in solar and stellar
chromospheres
Authors: Anzer, U.; Galloway, D. J.
1983IAUS..102..339A Altcode:
Calculations are presented for the inhomogeneous magnetic field
structure above a stellar photosphere which has magnetic flux tubes
located at the downdraughts of its supergranulation pattern. Regions
can be delineated where the ambient magnetic energy density is large
or small compared with the thermal energy density derived from a model
atmosphere. This enables the relative importance of magnetic versus
non-magnetic heating mechanisms to be assessed. For the quiet Sun,
over half the chromospheric emission must be supplied non-magnetically,
whilst the network and active regions require a magnetic supply. For
other late-type stars, a simple working rule suggests that when
the magnetic field is strong enough to be directly observable, the
chromosphere will be magnetically dominated.
---------------------------------------------------------
Title: Interaction of accretion disks and rotating magnetic neutron
stars.
Authors: Anzer, U.; Boerner, G.
1983heac.book..294A Altcode:
Consideration is given to some theoretical aspects of the interaction of
an accretion disk and a rotating magnetic star. The principle numerical
models of the problem are analyzed with respect to parameterizations
of the angular momentum exchange between the accretion disk and the
magnetic neutron star. On the basis of the analysis, a detailed
quantitative model is proposed. In the model, Kelvin-Helmholtz
instability leads to turbulent diffusion of disk matter onto the
magnetic lines of the neutron star near the region of corotation. The
balance and acceleration of the stars are calculated and the angular
momentum exchange is obtained. The model calculations are given in
a table. Emphasis is given to the need for greater generalization in
current numerical models of the problem in order to account for both
Kelvin-Helmholtz and Rayleigh-Taylor MHD instabilities.
---------------------------------------------------------
Title: Accretion onto rotating magnetic neutron stars: the inner
edge of the disk.
Authors: Anzer, U.; Börner, G.
1982ans..conf..155A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Reconnection and Coronal Transients
Authors: Anzer, U.; Pneuman, G. W.
1982SoPh...79..129A Altcode:
Every two-ribbon flare observed during the Skylab period produced an
observable coronal transient, provided the flare occurred close enough
to the limb. The model presented here treats these two events as a
combined process. Transients that occur without flares are believed
to involve magnetic fields that are too weak to produce significant
chromospheric emission. Adopting the hypothesis that the rising
flare loop systems observed during two-ribbon flares are exhibiting
magnetic reconnection, a model of a coronal transient is proposed which
incorporates this reconnection process as the driving force. When two
oppositely directed field lines reconnect a lower loop is created rooted
to the solar surface (the flare loop) and an upper disconnected loop is
produced which is free to rise. The magnetic flux of these upper loops
is proposed as the driver for the transient. The force is produced by
the increase in magnetic pressure under the filament and transient.
---------------------------------------------------------
Title: How disk accretion affects a rotating dipole
Authors: Anzer, U.; Börner, G.; Zhou, Y. Y.
1982MitAG..55...28A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Kelvin-Helmholtz Instabilities at the Interface Between an
Accretion Disk and the Magnetosphere of a Neutron Star
Authors: Anzer, U.; Börner, G.
1982ZNatA..37..723A Altcode: 1982ZNaT...37..723A
No abstract at ADS
---------------------------------------------------------
Title: Accretion by neutron stars - Accretion disk and rotating
magnetic field
Authors: Anzer, U.; Boerner, G.
1980A&A....83..133A Altcode:
The paper studies the interaction of a thin Keplerian accretion disk
with the magnetosphere of a rotating neutron star. The neutron star's
axis of rotation is assumed to be perpendicular to and the magnetic
dipole axis parallel to the disk plane. In such a configuration the
disk can penetrate diamagnetically into the magnetosphere. The velocity
difference between the disk material and the magnetosphere leads to
a Kelvin-Helmholtz instability of the interface. This instability
can grow to large amplitudes only within a narrow ring around the
corotation radius. It can give rise to turbulent diffusion of the disk
material into the magnetosphere. Part of this material will fall onto
the neutron star, the rest will be flung out of the system. This can
lead to an approximate balance between braking and acceleration of the
neutron star. Application of the model to the pulsating X-ray source
Her X-1 gives a natural explanation of the observed temporal variation
of the pulse period.
---------------------------------------------------------
Title: The preflare state
Authors: van Hoven, G.; Barbosa, D. D.; Birn, J.; Cheng, C. -C.;
Hansen, R. T.; Jackson, B. V.; Martin, S. F.; McIntosh, P. S.;
Nakagawa, Y.; Anzer, U.
1980sfsl.work...17V Altcode: 1980sofl.symp...17V
The accumulation, storage and irreversible release of the free
energy necessary for a solar flare are discussed on the basis of data
obtained from the Apollo Telescope Mount on Skylab and other pertinent
sources. Skylab and OSO 7 observations of possible flare precursors
and flare evolution are presented, and the evolution of the flare of
Sept. 5, 1973, the most completely observed flare of the Skylab program,
is described in detail, with account given to magnetic structures and
H alpha radiation. Theories of the preflare state are then reviewed,
with attention given to the force-free fields and coronal arcades,
thermal and magnetic structures and the MHD stability of coronal loops.
---------------------------------------------------------
Title: MHD aspects of coronal transients
Authors: Anzer, U.
1980IAUS...91..263A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Instabilities of accretion disk - magnetosphere interfaces.
Authors: Anzer, U.; Boerner, G.
1979ESASP.148..259A Altcode: 1979mbl..rept..259A
Configurations which consist of a Keplerian accretion disk and
a magnetosphere with solid rotation are investigated. Because of
the velocity difference between disk and magnetosphere the boundary
between the two is unstable to the Kelvin-Helmholtz instability. This
instability is strongest within a ring around the radius of
corotation. It leads to turbulent diffusion of disk material into the
magnetosphere, and thus gives a sufficiently high accretion rate.
---------------------------------------------------------
Title: Interaction of accretion disk and rotating magnetic field of
a neutron star.
Authors: Anzer, U.; Boerner, G.
1979ESASP.148..263A Altcode: 1979mbl..rept..263A
Utilizing the instabilities of the boundary between disk and
magnetosphere, a model for the flow of disk material into the neutron
star's magnetosphere is constructed. It is shown that within a thin
ring around the corotation radius, gas flows over. The gas is partly
accelerated towards the neutron star producing the accretion partly
outwards. In terms of this model, certain observed properties of
pulsating X-ray sources are explained.
---------------------------------------------------------
Title: Mass flow in loop type coronal transients.
Authors: Anzer, U.; Poland, A. I.
1979SoPh...61...95A Altcode:
The white light coronagraph on Skylab observed many loop type coronal
transients. These loops travel through the coronagraph's field of view
(2-6R<SUB>⊙</SUB>) over a period of a few hours, after which the legs
of the loops usually remain visible for a few days. In this paper we
investigate the temporal changes in density and mass per unit length
measured along the legs of such loops during the several days after
the initial eruption. Examination of 8 transients shows that the mass
and density in the legs decrease during the few hours after the top of
the loop has travelled beyond the coronagraph's field of view. The mass
and density then increase slowly, during the next one half to one day,
then decrease again over approximately the same period. These changes
are generally shown to be too rapid to be explained by solar rotation,
indicating that the transient legs have a lifetime of only a few days.
---------------------------------------------------------
Title: Models of Structure and Dynamics of Prominences.
Authors: Anzer, U.
1979phsp.coll..322A Altcode: 1979IAUCo..44..322A; 1979phsp.conf..322A
The degree and direction of the linear polarization of the helium D3
lines in quiescent prominences is examined. Three types of prominence
models including the Kippenhahn-Schlueter, Kuperus-Raadu, and Matville
models, each having current flows inside of them that give rise to
Lorentz forces, keeping the material from falling into the sun, are
described in detail. The main emphasis of measurements of the magnetic
force field centered on the Hanle and Zeeman effects as well as the
motions and fine structures of prominences. Results showed that it is
possible to obtain information on the field surrounding the prominences
from polarization measurements in the radio spectrum.
---------------------------------------------------------
Title: Discussion
Authors: Anzer, U.; Maltby, P.; Spicer, D. S.
1979phsp.coll..348A Altcode: 1979IAUCo..44..348A
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Anzer, U.; Raadu, M. A.; Rompolt, B.; Rust, D. M.; Sheeley,
N.; Spicer, D. S.
1979phsp.coll..171A Altcode: 1979IAUCo..44..171A
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Anzer, U.; Engvold, O.; Martin, S. F.; Pneuman,
G. W.; Rust, D. M.; Tandberg-Hanssen, E.; Zirin, H.
1979phsp.coll..164A Altcode: 1979IAUCo..44..164A
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Anzer, U.; Engvold, O.; Spicer, D. S.; van Tend, W.; Zirin, H.
1979phsp.coll..331A Altcode: 1979IAUCo..44..331A
No abstract at ADS
---------------------------------------------------------
Title: Discussion
Authors: Anzer, U.; Chiuderi-Drago, F.; Kundu, M. R.; Leroy, J. L.;
Malville, J.; Rompolt, B.; Sheeley, N.; Stenflo, J.; Tandberg-Hanssen,
E.; Öhman, Y.
1979phsp.coll...77A Altcode: 1979IAUCo..44...77A
No abstract at ADS
---------------------------------------------------------
Title: Can coronal loop transients be driven magnetically?
Authors: Anzer, U.
1978SoPh...57..111A Altcode:
In this note we investigate the possibility of magnetic driving of loop
transients. The action of local magnetic forces to balance gravity in a
coasting loop and to confine the loop has been proposed by Mouschovias
and Poland (1977). In this paper we use similar configurations but
deal with the global field structure and present models which show both
the initial phase of large acceleration and the later phase of almost
constant velocity. We use very simple one-dimensional models consisting
of a ring current which is subjected to gravitational attraction. The
velocity curves calculated for these models are in good agreement with
the observations. Therefore we conclude that if such ring currents
can be produced fast enough in the solar corona, they are capable of
driving the loop transients observed in the ATM white light coronagraph.
---------------------------------------------------------
Title: Accretion disk and rotating magnetic field of a neutron star.
Authors: Börner, G.; Anzer, U.
1978sss..meet..B16B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Stars: Disc Accretion onto a Rotating Magnetized
Neutron Star
Authors: Anzer, U.; Boerner, G.
1978MitAG..43..274A Altcode:
The interaction between a disk and a neutron star's magnetic field
is analyzed. It is assumed that the neutron star has a strong dipole
field with its axis in the plane of the disk and perpendicular to the
rotation axis, and a reason for the disk to behave like a diamagnetic
material in the stars's magnetic field is given. The role of the
Kelvin-Helmholtz instability in the interaction of disk matter and
magnetic field is examined, and some implications for the disk accretion
model are discussed.
---------------------------------------------------------
Title: Shock waves in stellar wind accretion and gamma -bursts.
Authors: Anzer, U.; Boerner, G.; Meszaros, P.
1976A&A....50..305A Altcode:
A model of cosmic gamma-ray bursts is proposed, involving spherical
accretion on compact objects from the stellar wind of a companion
star. The gamma-bursts arise when occasional flares in the companion
drive shocks in the wind, which then produce a short increase in the
accretion rate on the compact object. In the interval between flares,
the steady accretion from the wind leads to an X-ray source behavior
compatible with that of observed galactic X-ray sources. The model is
flexible enough to reproduce the large range of observed gamma-ray burst
characteristics, including luminosities, timescales and approximate
spectra. Specifically, it can explain the recently suggested possibility
that Cygnus X-1 is responsible for some of the gamma-ray events,
as well as the recently reported orbit-modulated absorption features.
---------------------------------------------------------
Title: Bremsstrahlung and the Spectra of Cosmic Gamma Bursts
Authors: Anzer, U.; Boerner, G.
1976MitAG..38..121A Altcode:
The possibility had been considered by Anzer and Boerner (1975)
that cosmic gamma-bursts are bremsstrahlung which is produced by the
interaction of a mildly relativistic beam of electrons with the protons
of a neutral plasma. An investigation concerning an occurrence of a
thermal bremsstrahlung is conducted, taking into account a comparison
between an observed spectrum reported by Metzger et al. (1974) and
calculated spectra of thermal bremsstrahlung.
---------------------------------------------------------
Title: Shock waves in stellar wind accretion and gamma
-bursts. Bremsstrahlung and the spectra of cosmic gamma bursts.
Authors: Anzer, U.; Boerner, G.; Meszaros, P.
1976swsw.book.....A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Why Syrovatskii's mechanism of dynamic dissipation of magnetic
fields does not work.
Authors: Anzer, U.
1976str..book..375A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Why Syrovatskii's mechanism of dynamic dissipation of magnetic
fields does not work
Authors: Anzer, U.
1976CoSka...6..375A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A possible mechanism for cosmic gamma ray bursts.
Authors: Anzer, U.; Boerner, G.
1975A&A....40..123A Altcode:
The recently discovered cosmic gamma-ray bursts can be explained
by the bremsstrahlung of a beam of relativistic electrons hitting a
region of high proton density. Spectra are computed, and estimates on
the particle densities and on the geometrical dimensions are derived
from the observations. The question of associated optical emission is
also discussed.
---------------------------------------------------------
Title: Why Syrovatskii's Mechanism of Dynamic Dissipation of Magnetic
Fields Does Not Work
Authors: Anzer, Ulrich
1973SoPh...30..459A Altcode:
Syrovatskii's mechanism of `dynamic dissipation of magnetic field' is
reinvestigated. In order to have this kind of `dynamic dissipation'
at a neutral line the ratio of current density to particle density
must exceed a certain critical value. For conditions in the solar
atmosphere near sunspots, this value can only be reached by a mechanism
which produces a very large compression of the magnetic field as well
as an extreme rarefaction of the density. Syrovatskii claims that his
mechanism provides both these features. His enormous field compression,
however, can only be obtained if one neglects the restoring Lorentz
force (e.g. in Syrovatskii's model the compressed field near the
neutral line is about one order of magnitude larger than the field of
the sunspots which generates it). The second effect, i.e. the large
plasma rarefaction around the neutral line, also is not real. This
rarefaction is due to the particular flow field of Syrovatskii's
model which allows for a free reconnection of the field lines across
the neutral line; the magnetic field is treated like a vacuum field,
the effects of the field accumulation near the neutral line being
neglected. The aim of the present paper is to show how more realistic
models modify Syrovatskii's results. Our numerical calculations lead to
a maximum current to density ratio which is a factor of 10<SUP>6</SUP>
smaller than the one obtained by Syrovatskii. Therefore one has to
conclude that in the solar atmosphere one cannot produce in the way
described by Syrovatskii the configurations which are necessary for
`dynamic dissipation'.
---------------------------------------------------------
Title: On a cinematographic observation of the tail of comet
Kohoutek 1973f.
Authors: Anzer, U.; Jockers, K.; Schmidt, H. U.
1973JASWA..25...14A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Zur kinematographischen Beobachtung des Schweifs des Kometen
Kohoutek 1973f.
Authors: Anzer, U.; Jockers, K.; Schmidt, H. U.
1973S&W....12..293A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Kritik an Syrovatskiis Mechanismus der dynamischen Dissipation
von Magnetfeldern
Authors: Anzer, U.
1973MitAG..32..171A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Method to Calculate Electric Currents in Quiescent
Prominences
Authors: Anzer, Ulrich
1972SoPh...24..324A Altcode:
A 2-dimensional model of the magnetic field associated with
quiescent prominences is presented. The coronal field is assumed to be
current-free, currents are only allowed in the photosphere and inside
the prominence. The prominence is taken to be infinitely thin. For this
model a method is given to calculate the field configuration from the
observed normal component of the field both in the photosphere and
the prominence. The normal field components are inferred from disc
observations and Hα limb observations. The sheet currents inside the
prominence are calculated and the resulting Lorentz force is compared
with the gravitational force. Within the range of uncertainty in the
total hydrogen density of quiescent prominences it is possible to give
models where the gravity is balanced by the Lorentz force.
---------------------------------------------------------
Title: Energy Balance in Cool Quiescent Prominences
Authors: Poland, A.; Anzer, U.
1971SoPh...19..401P Altcode:
The energy balance for cool quiescent prominences is examined using
a 6000 km, 6000 K isothermal slab model prominence with a density
gradient dictated by a modified Kippenhahn-Schlüter model. The
model is irradiated from both sides by the coronal, chromospheric,
and photospheric radiation fields. The radiative transfer problem is
solved in detail for the Lyman continuum and Hα to determine the net
radiative energy loss for hydrogen. An estimate of the energy loss for
Ca II H and K indicates that this source of energy loss is unimportant
when compared with the hydrogen radiation. The radiative energy loss
is easily balanced by the conductive energy gain from the corona.
---------------------------------------------------------
Title: Energy balance in quiescent prominences.
Authors: Poland, A.; Anzer, U.
1971BAAS....3..353P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the Orientation of Magnetic Fields in Quiescent Prominences
Authors: Anzer, U.; Tandberg-Hanssen, E.
1971IAUS...43..656A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Orientation of Magnetic Fields in Quiescent Prominences
Authors: Tandberg-Hanssen, E.; Anzer, Ulrich
1970SoPh...15..158T Altcode:
We have measured the longitudinal component, B∥, of the magnetic field
in quiescent prominences and obtained a relationship between B∥ and
θ, where θ is the angle between the long axis of the prominence and
the north-south direction on the sun. From this relationship we deduce
a distribution function for the magnetic field vector in quiescent
prominences in terms of the angle α between the field and the long
axis of the prominence. The mean angle, α, for our data is small,
∼ - 15°, indicating that the magnetic field traverses quiescent
prominences under a small, but finite angle.
---------------------------------------------------------
Title: A Model for Quiescent Prominences with Helical Structure
Authors: Anzer, Ulrich; Tandberg-Hanssen, E.
1970SoPh...11...61A Altcode:
We present a model for quiescent prominences with helical structure. The
model is described by two magnetic fields, one produced by photospheric
or subphotospheric currents, the other due to currents along the
cylindrical model prominence.
---------------------------------------------------------
Title: Stability Analysis of the Kippenhahn-Schlüter Model of
Solar Filaments
Authors: Anzer, U.
1969SoPh....8...37A Altcode:
In this paper the stability of the Kippenhahn-Schlüter model of solar
filaments against arbitrary perturbations is investigated. The problem
is treated in the MHD approximation and a modification of the energy
principle of Bernstein et al. is used. Two necessary and sufficient
stability conditions are found: (a) [B<SUB>z</SUB>] dB<SUB>x</SUB>/dz
≧ 0 and (b) B<SUB>x</SUB> d[B<SUB>z</SUB>]/dz ≦ 0. Condition
(a), in the limit of small currents, leads to the condition already
discussed by Kippenhahn and Schlüter; condition (b) requires that
the current density in the stable filament decreases with height.
---------------------------------------------------------
Title: On the Stability of Solar Filaments
Authors: Anzer, Ulrich
1969BAAS....1R.271A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Remarks on my Paper about Force-Free Magnetic Fields and
Solar Flares
Authors: Anzer, Ulrich
1968SoPh....4..101A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Stability of Force-Free Magnetic Fields with Cylindrical
Symmetry in the Context of Solar Flares
Authors: Anzer, Ulrich
1968SoPh....3..298A Altcode:
The problem of the accumulation and storage of the energy released in
solar flares is discussed; it is proposed that convective energy of the
photosphere is transformed into magnetic energy of the chromosphere
and corona. The consequences of a large ratio of magnetic pressure
to gas pressure are investigated. In this case the field must be
approximately force-free. The only suitable force-free fields which
allow an analytical treatment are those of cylindrical symmetry. The
stability of these fields is studied with the energy principle. It is
shown that they are always unstable due to kink type instabilities. The
shape of the unstable perturbations is described in detail and an
upper limit for their amplitude is estimated. The consequences for
the proposed mechanism of energy storage are briefly discussed.