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Author name code: ruedi
ADS astronomy entries on 2022-09-14
author:"Ruedi, Isabelle"
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Title: LYRA, a solar UV radiometer on Proba2
Authors: Hochedez, J. -F.; Schmutz, W.; Stockman, Y.; Schühle, U.;
Benmoussa, A.; Koller, S.; Haenen, K.; Berghmans, D.; Defise, J. -M.;
Halain, J. -P.; Theissen, A.; Delouille, V.; Slemzin, V.; Gillotay, D.;
Fussen, D.; Dominique, M.; Vanhellemont, F.; McMullin, D.; Kretzschmar,
M.; Mitrofanov, A.; Nicula, B.; Wauters, L.; Roth, H.; Rozanov, E.;
Rüedi, I.; Wehrli, C.; Soltani, A.; Amano, H.; van der Linden, R.;
Zhukov, A.; Clette, F.; Koizumi, S.; Mortet, V.; Remes, Z.; Petersen,
R.; Nesládek, M.; D'Olieslaeger, M.; Roggen, J.; Rochus, P.
2006AdSpR..37..303H Altcode:
LYRA is the solar UV radiometer that will embark in 2006 onboard
Proba2, a technologically oriented ESA micro-mission. LYRA is
designed and manufactured by a Belgian Swiss German consortium (ROB,
PMOD/WRC, IMOMEC, CSL, MPS and BISA) with additional international
collaborations. It will monitor the solar irradiance in four UV
passbands. They have been chosen for their relevance to Solar Physics,
Aeronomy and Space Weather: (1) the 115 125 nm Lyman-α channel,
(2) the 200 220 nm Herzberg continuum range, (3) the Aluminium
filter channel (17 70 nm) including He II at 30.4 nm and (4) the
Zirconium filter channel (1 20 nm). The radiometric calibration will
be traceable to synchrotron source standards (PTB and NIST). The
stability will be monitored by onboard calibration sources (LEDs),
which allow to distinguish between potential degradations of the
detectors and filters. Additionally, a redundancy strategy maximizes
the accuracy and the stability of the measurements. LYRA will benefit
from wide bandgap detectors based on diamond: it will be the first space
assessment of a pioneering UV detectors program. Diamond sensors make
the instruments radiation-hard and solar-blind: their high bandgap
energy makes them insensitive to visible light and, therefore, make
dispensable visible light blocking filters, which seriously attenuate
the desired ultraviolet signal. Their elimination augments the effective
area and hence the signal-to-noise, therefore increasing the precision
and the cadence. The SWAP EUV imaging telescope will operate next to
LYRA on Proba2. Together, they will establish a high performance solar
monitor for operational space weather nowcasting and research. LYRA
demonstrates technologies important for future missions such as the
ESA Solar Orbiter.
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Title: Preface (The Sun, solar analogs and the climate)
Authors: Rüedi, Isabelle; Güdel, Manuel; Schmutz, Werner
2005ssac.confD...5R Altcode: 2005SAAS...34D...5R
No abstract at ADS
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Title: The Sun, Solar Analogs and the Climate
Authors: Haigh, Joanna D.; Lockwood, Michael; Giampapa, Mark S.;
Rüedi, Isabelle; Güdel, Manuel; Schmutz, Werner
2005ssac.conf.....H Altcode: 2005SAAS...34.....H
This book presents the lecture notes of the 34th Saas-Fee Advanced
Course "The Sun, Solar Analogs and the Climate" given by leading
scientists in the field. Emphasis is on the observed variability of
the Sun and the present understanding of the variability's origin
as well as its impact on the Earth's climate. The solar variability
is then studied in the broader context of solar-type stars, allowing
for better understanding of the solar-activity cycle and the magnetic
activity in general. This book provides an accessible and up-to-date
introduction to the field for graduate students and serves as a modern
source of reference for active researchers in this field.
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Title: A comparison between model calculations and observations of
sunspot oscillations
Authors: Rüedi, I.; Cally, P. S.
2003A&A...410.1023R Altcode:
We investigate the signal which is expected to be produced by magnetic
field oscillations in sunspots umbrae due to the combination of the
oscillation model, radiative transfer and observing procedure. For
this purpose we investigate the signal expected to be produced by
theoretical models of sunspot oscillations and compare them with the
signal seen in observed power spectra of sunspot magnetograms. We show
that the amplitudes of the observed oscillations are compatible with
the predictions of the theoretical model of magnetoacoustic oscillations
for the 5-min as well as for the 3-min band. For the particular sunspot
umbral oscillation models used, our analysis suggests that most of
the expected observed power in the magnetogram signal oscillations is
actually due to cross-talk from the temperature and density oscillations
associated with the magnetoacoustic wave. A detailed modelling of
the observing procedure turns out to be of central importance for the
assignment of the observed oscillations to a specific wave type.
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Title: Spatial and temporal fluctuations in sunspots derived from
MDI data
Authors: Solanki, S. K.; Rüedi, I.
2003A&A...411..249S Altcode:
The penumbra radiates an energy flux that is 0.75-0.8 times the
photospheric value. One mechanism proposed to bring this flux to the
surface is interchange convection according to which hot flux tubes
rise to the surface, lie horizontally there while they cool and finally
sink down again. We search for possible signatures of such a process
using time series of magnetograms and continuum images recorded by the
Michelson Doppler Imager (MDI) in its high resolution mode (0.6\arcsec
pixels). The data reveal that at the spatial scales accessible to MDI,
magnetic structures are on average smaller in the azimuthal direction
than brightness features. The small-scale magnetic pattern resolvable
by MDI lives for well over two hours, i.e. longer than the brightness
pattern. As shown in a parallel paper (Schlichenmaier & Solanki
\cite{Sch03}) this result, taken together with theoretical predictions,
suggests that interchange convection is unable to account for the
observed penumbral radiative flux. The need for higher resolution data
obtained under stable conditions is pointed out.
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Title: Representation of Opacity Data in Solar Model Atmosphere
Calculations
Authors: Haberreiter, M.; Rozanov, E.; Rüedi, I.; Schmutz, W.
2003ASPC..288..165H Altcode: 2003sam..conf..165H
Rozanov et al. (2002) have determined that the influence of the
solar irradiance variability on the chemical composition in the
stratosphere is dominated by two narrow bands in the UV centered around
215 nm and 265 nm. We have evaluated the dominant opacity sources
at these wavelengths and find it necessary to include the complex
continuum absorption cross sections from the lower levels of neutral
metals. We present our straightforward solution how to describe these
opacities. There is the obvious need to treat the line blanketing
which mainly depends on the completeness of the line list. We base
our calculations on a combination of the spherically symmetric non-LTE
`Kiel-code' and the spectral synthesis by the SYNSPEC code. In order
to evaluate the quality of our computations we compare our predictions
with the UV spectrum observed by SUSIM.
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Title: Towards a spherical code for the evaluation of solar UV-bands
that influence the chemical composition in the stratosphere
Authors: Haberreiter, M.; Hubeny, I.; Rozanov, E.; Rüedi, I.; Schmutz,
W.; Wenzler, T.
2002ESASP.508..209H Altcode: 2002soho...11..209H
We present our analysis of data taken by SUSIM onboard UARS. We
reconstruct the variability of the UV irradiance and compare it to
available data. Up to now we model the solar irradiance according to
the 3-component model by Unruh et al. (1999) based on LTE synthetic
spectra modeled with Kurucz' ATLAS9 code. Our new approach will be that
with COSI (COde for Solar Irradiance) we model solar continuum and
line formation in spherical symmetry and in non-local thermodynamic
equilibrium (non-LTE). We present our first synthetic solar spectra
(calculated in LTE) and validate them against spectra computed with
Kurucz' ATLAS9 code.
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Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schühle, U.; Solanki, S. K.; Wilhelm,
K.; Pike, C. D.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber,
M. C. E.
2002ESASP.508..223P Altcode: 2002soho...11..223P
The outcome of the Joint Observing Programme (JOP) Intercal-01, which
is the intercalibration of the SUMER (Solar Ultraviolet Measurements
of Emitted Radiation) instrument (detectors A and B) and the two CDS
(Coronal Diagnostic Spectrometer) instruments, the Normal Incidence
Spectrometer (NIS) and the Grazing Incidence Spectrometer (GIS),
is presented. Recent calibration updates of both instruments have
been employed, and the results indicate a very good correlation and
agreement of the measured radiances within the individual uncertainties.
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Title: Quiet-Sun variability observed with SUMER and CDS
Authors: Brković, A.; Solanki, S. K.; Rüedi, I.
2002A&A...385..257B Altcode:
Brightness variations of solar features are investigated using time
series of images and spectra of quiet-Sun regions at disc centre
obtained with the Coronal Diagnostic Spectrometer (CDS) and the Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) instrument onboard
the SOHO spacecraft. Ultraviolet emission lines sampling temperatures
of the chromosphere, transition region and corona were recorded, with
the \hei 584.3 Å and \oxv 629.7 Å lines being recorded simultaneously
by both instruments. A comparison shows that both instruments give
similar results except that SUMER reveals a factor of three higher
absolute and relative variability than CDS. Simple tests suggest
that the higher spatial resolution of SUMER compared to CDS, and the
broad slit used for the CDS observations, are responsible for this
difference. This points to the need for higher spatial resolution for
future variability studies. The SUMER results confirm and extend to
lower temperatures the trends deduced in an earlier paper from CDS data.
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Title: Models for solar magnetic loops. II. Comparison with SOHO-CDS
observations on the solar disk
Authors: Brković, A.; Landi, E.; Landini, M.; Rüedi, I.; Solanki,
S. K.
2002A&A...383..661B Altcode:
The present work describes a detailed comparison between SOHO-CDS
observations of active region loops with a static, isobaric loop
model developed assuming a temperature-independent heating function
in the energy balance equation and a variable loop cross-section. The
loop model is described in Landini & Landi (2002). Observations
of an active region recorded by CDS have been analyzed. Additional
data from the EIT and MDI instruments on board the SOHO satellite,
and broad band soft X-rays images from the Yohkoh satellite, have
been used to complement the CDS dataset. CDS monochromatic images
from lines at different temperatures have been co-aligned with EIT,
MDI and Yohkoh images and a loop structure has been identified. Two
other loop structures are visible but their footpoints are not clearly
identified, and have not been analyzed. Electron density, temperature
and pressure along the selected loop structure have been measured by
means of line ratio techniques. These quantities have been used to test
the assumption of constant pressure adopted in the theoretical model,
and to compare their values with its predictions. The loop filling
factor has also been estimated from the CDS data after assumptions on
the loop geometry have been made. Comparison with CDS data has shown
that a classical model is not able to reproduce the observations;
despite the large uncertainties, mainly given by the limited CDS
spatial resolution, indications suggest that agreement occurs only if an
“ad hoc” isothermal region is added on top of the loop and a large
conductive flux at the base is assumed. Suggestions for improvements
of theoretical loop models and further studies with the EIS instrument
on Solar-B, due for launch in 2005, are given.
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Title: Intercalibration of CDS and SUMER
Authors: Pauluhn, A.; Lang, J.; Schuhle, U.; Solanki, S. K.; Wilhelm,
K.; Thompson, W. T.; Pike, C. D.; Ruedi, I.; Hollandt, J.; Huber,
M. C. E.
2002ISSIR...2..235P Altcode: 2002rcs..conf..235P; 2002ESASR...2..235P
Simultaneous observations of the same solar features with different
instruments provide a way to compare radiometric calibrations and
detect changes in responsivity with time of EUV instruments in space
within the combined uncertainties of the individual instruments. Here
we present the intercalibration of the SUMER (Solar Ultraviolet
Measurements of Emitted Radiation) instrument (detectors A and B) and
the two CDS (Coronal Diagnostic Spectrometer) instruments, the Normal
Incidence Spectrometer (NIS) and the Grazing Incidence Spectrometer
(GIS) on the Solar and Heliospheric Observatory (SOHO). This work
describes the results of the Joint Observing Programme Intercal 01
and presents quiet-Sun comparisons from March 1996 up to February
2001, which represents the complete set of all available Intercal
01 measurements. Recent calibration updates of both instruments are
employed, and the results indicate a very good correlation and agreement
of the measured radiances within the combined uncertainties.
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Title: Properties of ultraviolet lines observed with the Coronal
Diagnostic Spectrometer (CDS/SOHO) in coronal holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Pike, C. D.; Schühle, U.;
Rüedi, I.; Pauluhn, A.; Brković, A.
2002A&A...381..653S Altcode:
We present an analysis of 14 ultraviolet emission lines belonging to
different atoms and ions observed inside polar coronal holes and in
the normal quiet Sun. The observations were made with the Coronal
Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
Observatory (SOHO). This study extends previous investigations made
with the Solar Ultraviolet Measurements of Emitted Radiation (SUMER)
spectrometer to higher temperatures. We compare line intensities,
shifts and widths in coronal holes with the corresponding values
obtained in the quiet Sun. While all lines formed at temperatures above
7 x 10<SUP>5</SUP> K show clearly the presence of the hole in their
intensities, differences in line width are more subtle, with cooler
lines being broader in coronal holes, while hotter lines tend to be
narrower. According to the present data all lines are blueshifted inside
the coronal hole compared to the normal quiet Sun. Almost all the lines
formed between 80 000 K and 600 000 K (i.e. transition-region lines)
show a correlation between blueshifts and brightness within coronal
holes. This is in agreement with the conclusion reached by Hassler et
al. (\cite{Hassler1999}) that the fast solar wind emanates from the
network and supports our previous study (Stucki et al. 2000b). For
coronal lines, this trend seems to be reversed.
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Title: Intercalibration of SUMER and CDS on SOHO. II. SUMER detectors
A and B and CDS NIS
Authors: Pauluhn, Anuschka; Rüedi, Isabelle; Solanki, Sami K.;
Schühle, Udo; Wilhelm, Klaus; Lang, Jim; Thompson, William T.;
Hollandt, Jörg
2001ApOpt..40.6292P Altcode:
Results of an intercalibration between the extreme-ultraviolet
spectrometers Coronal Diagnostic Spectrometer (CDS) and Solar
Ultraviolet Measurements of Emitted Radiation (SUMER) on board the Solar
and Heliospheric Observatory (SOHO) are reported. The results of the
joint observing program Intercal_01 are described, and intercalibration
results up to July 2000 of both SUMER detectors A and B and of the
CDS Normal Incidence Spectrometer (NIS) are presented. The instruments
simultaneously observed radiance of emission lines at the center of the
Sun, and three lines have been chosen for intercomparison: He I 584 Å,
Mg X 609 Å, and Mg X 624 Å. Initially the same area was observed by
both instruments, but, after restrictions were imposed by the scanning
mechanism of SUMER in November 1996, the instruments viewed areas of
different sizes. Nevertheless, the temporal correlation between the
two instruments remained good through June 1998, when contact with
the SOHO spacecraft was lost. Until then the CDS instrument measured
(33+/-5)% and (38+/-7)% (+/-1σ) higher intensity than SUMER in the
Hz I 584-Å line on average for detectors A and B, respectively. Data
from SUMER detector B agreed well for Mg X 609 Å and Mg X 624 Å
with the CDS intensities, showing offsets of (2+/-10)% and (9+/-15)%,
much less than the data of detector A with offsets of (7+/-8)% and
(16+/-7)% for the two lines, respectively, relative to CDS. Finally,
the intercalibration measurements after the loss and recovery of the
SOHO spacecraft are analyzed. The data for observations from November
1998 to July 2000 are compared, and it is shown that, although the
responses of the instruments have changed, the CDS and the SUMER still
perform well, and their temporal correlation is good.
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Title: SIM3D: Solar Irradiance Monitor-3D-view
Authors: Schmutz, W.; Fröhlich, C.; Rüedi, I.; Roth, H.; Wehrli,
Ch.; Wyss, J.
2001ESASP.493..447S Altcode: 2001sefs.work..447S
No abstract at ADS
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Title: Analysis of blinkers and EUV brightenings in the quiet Sun
observed with CDS
Authors: Brković, A.; Solanki, S. K.; Rüedi, I.
2001A&A...373.1056B Altcode:
Movies of quiet Sun regions at disc centre obtained with the
Coronal Diagnostic Spectrometer (CDS) onboard the SOHO spacecraft
are used to study the properties of transient brightenings seen in
the extreme ultraviolet (EUV), so-called blinkers, at three different
temperatures sampled simultaneously in the chromospheric He I 584.3
Å (2 x 10<SUP>4</SUP> K), the transition region O V 629.7 Å (2.5
x 10<SUP>5</SUP> K) and coronal Mg IX 368.1 Å (10<SUP>6</SUP> K)
lines. Blinkers, here defined somewhat differently than in previous
studies, were clearly detected in the O V and He I lines. Brightenings
of the Mg IX line were also seen. A thorough analysis of blinker
properties is carried out and their detailed properties are
determined. Blinkers are found to be present in both bright (network)
and dark (intranetwork) regions, but their number density is larger
in the brighter areas (in O V) although the rest of their properties
appear to be unaffected. The average sizes of brightenings range
from 2.8 Mm<SUP>2</SUP> in Mg IX, 12.4 Mm<SUP>2</SUP> in He I to 23.5
Mm<SUP>2</SUP> in O V. The durations of blinkers are in the range 3-110
min, with the average durations being 23 min in He I, about 16 min in
O V and 12 min in Mg IX. The frequency distributions of ratio of peak
to background intensity, excess energy and size follow power laws with
exponents <-5 for the intensity ratio, and between -1 and -3 for
the other two parameters. The correlation coefficients between pairs of
ratio, energy and size are at least 0.5, while other pairs of parameters
describing the blinkers appear to be uncorrelated. The best correlation
is between size and energy. The blinker durations exhibit a distribution
whose form is compatible with a log-normal function. Finally, blinkers
in the 3 lines (i.e. 3 temperature regimes) are poorly correlated; with
the correlation coefficient being always less than 0.4. This suggests
that to a large extent the transition region reacts independently of the
corona and chromosphere to energy deposition, so that these parts of the
atmosphere are at least partly decoupled from each other. This agrees
with the expectations from models having separate transition-region
loops, but contradicts the classical picture of the transition region,
as being heated dominantly by energy conduction from the corona.
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Title: Comparison of quiet-Sun radiances measured by CDS and SUMER
on SOHO
Authors: Pauluhn, A.; Solanki, S. K.; Schühle, U.; Wilhelm, K.;
Lang, J.; Thompson, W. T.; Rüedi, I.; Hollandt, J.; Huber, M. C. E.
2001SSRv...97...63P Altcode:
Since the beginning of the SOHO (Solar and Heliospheric Observatory)
mission an intercalibration programme was carried out which included
simultaneous observations of the EUV instruments CDS (Coronal Diagnostic
Spectrometer) and SUMER (Solar Ultraviolet Measurements of Emitted
Radiation) of common targets on the quiet Sun. The observations in the
chromospheric line of He i (584 Å) and the two coronal lines of Mg x
(609 Å and 624 Å) thus cover the long period of 4 years and provide a
data set highly suitable not only for instrumental comparison but also
for studies of the quiet Sun's long term variability. Up to the SOHO
accident, both instruments show a very good temporal correlation and
stability. Even after the loss and recovery of the spacecraft, when
the instruments had been exposed to extreme temperature conditions,
the performance of the CDS and SUMER instruments is still good, as is
the temporal correlation. However, the ratio between the efficiencies
of the two instruments, which remained constant with time until the
SOHO accident seems to have changed afterwards. In the coronal lines
both instruments show an increase of average radiances towards the
solar maximum.
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Title: The Quiet-Sun Variability as seen by CDS and by SUMER
Authors: Brkovic, A.; Solanki, S. K.; Rüedi, I.
2001IAUS..203..381B Altcode:
Blinkers are transient brightenings seen in the extreme
ultraviolet. These brightenings are candidates for microflare
activity. Here we determine their properties, using co-aligned
observations with SUMER and CDS, in the latter case with an open
slit. We use CDS to find evidence for blinkers in the quiet Sun, and
SUMER to measure the velocities, and line width changes associated
with them.
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Title: Statistical Features of the Quiet Sun in EUV
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
Schühle, U.
2001IAUS..203..416P Altcode:
The frequency distribution of the extreme ultraviolet (EUV) intensities
in the quiet Sun has in the past usually been modelled using two
Gaussians. Here we test this and other distribution functions against
observed distributions with exceptional statistics. The data were
obtained in a number of spectral lines observed with two extreme
ultraviolet spectrometers, CDS (Coronal Diagnostic Spectrometer)
and SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on
board the Solar and Heliospheric Observatory (SOHO). We show that the
frequency distribution of the radiance is best modelled by a lognormal
distribution or by a sum of a lognormal and a Gaussian. The fact that
the radiance distribution of the quiet Sun including the network and
the intranetwork is better reproduced by a single lognormal distribution
function than by two Gaussians suggests that the same heating processes
are acting in both types of features. The shape of the distribution
function shows a clear temperature dependence.
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Title: Radiance of Solar Spectral Lines observed with CDS and SUMER
on SOHO (CD-ROM Directory: contribs/pauluhn)
Authors: Pauluhn, A.; Schühle, U.; Solanki, S. K.; Rüedi, I.; Lang,
J.; Pike, C. D.; Thompson, W. T.; Huber, M. C. E.
2001ASPC..223..721P Altcode: 2001csss...11..721P
No abstract at ADS
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Title: Comparison of far-ultraviolet emission lines formed in coronal
holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.; Wilhelm,
K.; Stenflo, J. O.; Brković, A.; Huber, M. C. E.
2000A&A...363.1145S Altcode:
We present an analysis of 26 far-ultraviolet emission lines belonging
to 19 atoms and ions observed on both sides of the boundary of polar
coronal holes as well as other quiet Sun areas along the limb. The
observations were made with the SUMER instrument (Solar Ultraviolet
Measurements of Emitted Radiation) onboard the Solar and Heliospheric
Observatory (SOHO). We compare line intensities, shifts and widths
in coronal holes with the corresponding values obtained in the quiet
Sun. We find that with increasing formation temperature, spectral
lines show on average an increasingly stronger blueshift in coronal
holes relative to the quiet Sun at equal heliospheric angle, with the
coolest lines in our sample (formation temperature ~ 10<SUP>4</SUP>
K) indicating a small relative redshift. With respect to the rest
wavelength, however, only lines formed above 5 * 10<SUP>5</SUP> K
show blueshifts in coronal holes, which is not very different from
the quiet Sun. The width of the lines is generally larger (by a few
kilometers per second) inside the coronal hole. Intensity measurements
clearly show the presence of the coronal hole in Ne VIII lines as well
as in Fe XII, and provide evidence for a slightly enhanced emission
in polar coronal holes for lines formed below 10<SUP>5</SUP> K. This
last result is, however, less certain than the rest due to relatively
poor statistics. Intensity histograms also exhibit distinct differences
between coronal hole and quiet-Sun data. For cooler chromospheric lines,
such as Ni II, the coronal holes display a greater spread in intensities
than the quiet Sun. Transition-region lines, e.g. O IV, do not reveal
such differences, while Ne VIII shows characteristics of a coronal line
with lower average intensity and lower intensity spread inside holes.
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Title: Statistics of quiet Sun extreme ultraviolet intensities
Authors: Pauluhn, A.; Solanki, S. K.; Rüedi, I.; Landi, E.;
Schühle, U.
2000A&A...362..737P Altcode:
The frequency distribution of the extreme ultraviolet (EUV) emission
line intensities in the quiet Sun has in the past often been modelled
using two Gaussians. This gives adequate fits to observed distributions
of average statistical significance. In this paper we test this
and other distribution functions against observed distributions with
exceptional statistical significance. The data were obtained in a number
of spectral lines observed with two extreme ultraviolet spectrometers
on board the Solar and Heliospheric Observatory (SOHO). In this way,
the influence of spatial resolution and other instrument-specific
parameters can be identified. The observations span a period of
more than two years and provide a very large data set of radiance
measurements of the quiet Sun at or near solar disk centre. We show
that the frequency distribution of the radiance is best modelled by
a lognormal distribution. The fact that the radiance distribution of
the quiet Sun including the network and the intranetwork is better
reproduced by a single lognormal distribution function than by two
Gaussians suggests that the same heating processes are acting in both
types of features. The parameters of the lognormal fit show a clear
temperature dependence, with the transition region lines exhibiting the
largest skewness of the distribution and the chromospheric intensity
distributions being the most symmetric.
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Title: On the relationship between shift and intensity of ultraviolet
lines in coronal holes and the quiet Sun
Authors: Stucki, K.; Solanki, S. K.; Schühle, U.; Rüedi, I.
2000A&A...362L..49S Altcode:
We study the relationship between wavelength shifts and intensities
of chromospheric, transition-region and coronal ultraviolet emission
lines in polar coronal holes and in the normal quiet Sun using SUMER
data. Within coronal holes almost all the lines showing the network
and formed above 30 000 K show a correlation between blueshifts
and brightness. This extends and supports the conclusion reached
by Hassler et al. (1999) that the fast solar wind emanates from the
network. In the normal quiet Sun, however, we find that only lines
formed above 2-3 * 10<SUP>5</SUP> K show such a trend, the cooler
lines being more redshifted in the network. This suggests that either
there is a fundamental difference in the initial acceleration of
the solar wind in coronal holes and the normal quiet Sun, or that
the wavelength-shift versus brightness relationship in the quiet Sun
stems from other processes or structures (loops) than in coronal holes
(open field lines).
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Title: EUV brightness variations in the quiet Sun
Authors: Brković, A.; Rüedi, I.; Solanki, S. K.; Fludra, A.;
Harrison, R. A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
2000A&A...353.1083B Altcode:
The Coronal Diagnostic Spectrometer (CDS) onboard the SOHO satellite has
been used to obtain movies of quiet Sun regions at disc centre. These
movies were used to study brightness variations of solar features at
three different temperatures sampled simultaneously in the chromospheric
He I 584.3 Ä (2 * 10<SUP>4</SUP> K), the transition region O V 629.7
Ä (2.5 * 10<SUP>5</SUP> K) and coronal Mg IX 368.1 Ä (10<SUP>6</SUP>
K) lines. In all parts of the quiet Sun, from darkest intranetwork to
brightest network, we find significant variability in the He I and O
V line, while the variability in the Mg IX line is more marginal. The
relative variability, defined by rms of intensity normalised to the
local intensity, is independent of brightness and strongest in the
transition region line. Thus the relative variability is the same
in the network and the intranetwork. More than half of the points
on the solar surface show a relative variability, determined over a
period of 4 hours, greater than 15.5% for the O V line, but only 5%
of the points exhibit a variability above 25%. Most of the variability
appears to take place on time-scales between 5 and 80 minutes for the
He I and O V lines. Clear signs of “high variability” events are
found. For these events the variability as a function of time seen
in the different lines shows a good correlation. The correlation is
higher for more variable events. These events coincide with the (time
averaged) brightest points on the solar surface, i.e. they occur in
the network. The spatial positions of the most variable points are
identical in all the lines.
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Title: PICARD: Solar Diameter, Irradiance and Climate
Authors: Damé, L.; Cugnet, David; Herse, Michel; Crommelynck,
Dominique; Dewitte, Stevens; Joukoff, Alexandre; Ruedi, Isabelle;
Schmutz, Werner; Wehrli, Christoph; Delmas, Christian; Laclare,
Francis; Rozelot, Jean-Pierre
2000ESASP.463..223D Altcode: 2000sctc.proc..223D
No abstract at ADS
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Title: Relationship between Line Shift and Intensity Inside Coronal
Holes
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Schüehle, U.
1999ESASP.446..633S Altcode: 1999soho....8..633S
We analyse SUMER spectra of a group of lines belonging to chromospheric,
transition region and coronal ions obtained on both sides of the
boundary of polar coronal holes as well as at other locations along the
limb. We study the relationship between line shifts and intensities in
coronal holes and compare to values obtained in the quiet Sun. We find
that within coronal holes, a trend can be detected in some transition
region lines, like O V and N V, in the sense that the lines are more
strongly blueshifted in brighter regions. This is in agreement with
the conclusion reached by Hassler et al. (1999, Science 283, 810-813)
that the fast solar wind emanates from the network. Furthermore,
a correlation of line shifts of ions formed at higher temperatures
(Ne VIII, Fe XII) with intensities of lines showing network structures
(Si I, N III) is presented.
---------------------------------------------------------
Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brkovic, A.; Landi, E.; Rüedi, I.; Solanki, S.
1999ESASP.446..423L Altcode: 1999soho....8..423L
SOHO CDS, GIS and NIS, observations are used to evaluate the
electron temperature, density and pressure of active region loops. The
measurements are used to constrain empirical models of loops, which are
compared with an improved version of theoretical models from Landini
and Monsignori Fossi 1975. Energy balance is investigated to evaluate
temperature, pressure and heating release along the loop.
---------------------------------------------------------
Title: Characteristics Of Blinkers Observed With CDS
Authors: Brkovic, A.; Ruedi, I.; Solanki, S. K.
1999ESASP.446..191B Altcode: 1999soho....8..191B
Blinkers are transient brightenings seen in the extreme
ultraviolet. They probably can not heat the corona, but are candidates
for microflare activity. Here we determine their properties on the
basis of a larger sample than previously studied. We used the Normal
Incidence Spectrometer of the Coronal Diagnostic Spectrometer (CDS)
onboard the SOHO satellite in its movie mode, i.e. 90"x240" slit,
to find evidence for blinkers in the quiet Sun. The He I 584.3 A
(20'000 K), the O V 629.7 (250'000 K) and the Mg IX 368.1 (1'000'000
K) lines are recorded simultaneously at a cadence of 31 seconds
for a duration of 4 hours each on December 3 1996. Harrison (1997)
defined the blinker as a phenomenon showing an enhancement of a factor
2-3 in the flux of transition region lines at network junctions. The
criterion we used was similar to his. We applied the threshold to the
O V line, and identified 74 distinct blinkers. The average properties
of these blinkers and the scatter around these mean values were then
determined. These properties include the duration of the blinker, the
energy content of the event, ratio of maximum to minimum brightness and
the sizes of these brightenings. We find that the overall brightening
is often composed of a number of shorter events. Finally, we checked
if these blinkers were also present in the images obtained in the two
other lines, of He I and Mg IX. In the He I line we found 65 events and
in the Mg IX line 16 events. On average the brightening was smaller
in these lines than in O V. The work is still in progress. We plan
to investigate how the locations of these events are related to the
distribution of the magnetic field and if they are also related to other
phenomena. References: Harrison, R.A.: 1997, Solar Physics 162, 467.
---------------------------------------------------------
Title: Oscillations of Sunspot Magnetic Fields: MDI Observations of
a Symmetrical Sunspot
Authors: Rüedi, I.; Solanki, S. K.
1999ASPC..184..131R Altcode:
We report on sunspot magnetic field oscillations observed using the
MDI instrument on the SOHO spacecraft. Clear oscillations are seen in
both the 3- and 5-min bands, but appear to be intermittent.
---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic
features. XV. Evershed flow in cool, weak penumbral fields
Authors: Rüedi, I.; Solanki, S. K.; Keller, C. U.
1999A&A...348L..37R Altcode:
Observations of Ti I lines at 2.2 mu m show that the Evershed flow takes
place in cool, almost horizontal channels with a low magnetic field
strength (~ 500-900 G) that does not appear to change significantly
across the penumbra. This property might allow an outward directed
siphon flow to exist along such cool flux tubes.
---------------------------------------------------------
Title: Expansion of solar magnetic flux tubes large and small
Authors: Solanki, S. K.; Finsterle, W.; Rüedi, I.; Livingston, W.
1999A&A...347L..27S Altcode:
In the solar photosphere the magnetic field of magnetic elements and
sunspots is known to expand with height. In the case of sunspots this
expansion is known to be very rapid, with the field forming an almost
horizontal canopy. In this contribution we present new results on
the superpenumbral canopy of sunspots based on fits to Stokes I and
V profiles of infrared spectral lines. The new models take pressure
balance across the boundary of the canopy field into account, which
leads to significantly lower canopy base heights than previously
determined from similar data. Due to the lower canopy base height,
the density above the canopy base is larger, so that estimates of
the mass transported by the Evershed effect in the canopy need to be
revised upwards: approximately 15-50% of the mass flowing through the
penumbra travels beyond the sunspot boundary above the canopy base. A
comparison with small flux tubes leads to the surprising result that
although the two types of features have magnetic fluxes that differ by
5-6 orders of magnitude, their relative rate of expansion with height
is very similar, suggesting that at least in this respect sunspots
can be described by the thin-tube approximation. The remaining small
differences between the relative expansion of the two types of flux
tubes is qualitatively compatible with the presence of magnetic flux
that returns into the solar interior at the spot boundary, as has been
proposed by Westendorp Plaza et al. (1997).
---------------------------------------------------------
Title: Coronal Hole Properties Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
Brković , A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
1999SSRv...87..315S Altcode:
We analyze SUMER spectra of 14 lines belonging to 12 ions, obtained
on both sides of the boundary of polar coronal holes as well as at
other locations along the limb. We compare line intensities, shifts
and widths in coronal holes with values obtained in the quiet Sun. We
find that with increasing formation temperature, spectral lines show
an increasingly stronger blueshift in coronal holes relative to the
quiet Sun at an equal heliospheric angle. The width of the lines is
generally larger (by a few km/s) inside the coronal hole. Intensity
measurements show the presence of the coronal hole in Ne VIII lines
as well as in Fe XII, with evidence for a slightly enhanced emission
in polar coronal holes for lines formed below 10<SUP>5</SUP> K.
---------------------------------------------------------
Title: Coronal Holes Versus Normal Quiet Sun Observed with SUMER
Authors: Stucki, K.; Solanki, S. K.; Rüedi, I.; Stenflo, J. O.;
Brković, A.; Schühle, U.; Wilhelm, K.; Huber, M. C. E.
1999Ap&SS.264...53S Altcode: 1998Ap&SS.264...53S
We present a preliminary analysis of spectral lines obtained with the
SUMER instrument (Solar Ultraviolet Measurements of Emitted Radiation)
onboard the Solar and Heliospheric Observatory (SOHO), as observed
during three observing campaigns. From the 70 observed spectral lines,
we selected 12, representing 9 ions or atoms, in order to analyse line
intensities, shifts and widths in polar coronal holes as well as in the
normal quiet Sun. We find that coronal lines show a distinct blueshift
in coronal holes relative to the quiet Sun at equal heliospheric
angle, while there is no evidence for such a shift for lines formed at
temperatures below 10^5 K. The widths of lines formed at temperatures
above 3 - 10^4 K are slightly increased inside the coronal hole,
but unaffected for lower temperatures. Intensity measurements clearly
show the center-to-limb variation, as well as an intensity diminution
inside the coronal hole for lines formed above approximately 10^5 K.
---------------------------------------------------------
Title: Loop Models from SOHO Observations
Authors: Landini, M.; Brković , A.; Landi, E.; Rüedi, I.; Solanki, S.
1999SSRv...87..245L Altcode:
The Coronal Diagnostic Spectrometer (CDS) on SOHO is a grazing/normal
incidence spectrograph, aimed to produce stigmatic spectra of selected
regions of the solar surface in six spectral windows of the extreme
ultraviolet from 150 Å to 785 Å (Harrison et al. 1995). In the
present work, CDS, EIT, MDI and Yohkoh observations of active region
lops have been analyzed. These observations are part of JOP 54. CDS
monochromatic images from lines at different temperatures have been
co-aligned with EIT and MDI images, and loop structures have been
clearly identified using Fe XVI emission lines. Density sensitive
lines and lines from adjacent stages of ionization of Fe ions have
been used to measure electron density and temperature along the loop
length; these measurements have been used to determine the electron
pressure along the loop and test the constant pressure assumption
commonly used in loop modeling. The observations have been compared
with a static, isobaric loop model (Landini and Monsignori Fossi 1975)
assuming a temperature-constant heating function in the energy balance
equation. Good agreement is found for the temperature distribution
along the loop at the coronal level. The model pressure is somewhat
higher than obtained from density sensitive line ratios.
---------------------------------------------------------
Title: On the expansion of large and small flux tubes with height
Authors: Solanki, S. K.; Rüedi, I.; Finsterle, W.; Livingston, W.
1999ASSL..243..397S Altcode: 1999sopo.conf..397S
No abstract at ADS
---------------------------------------------------------
Title: Sunspot magnetic oscillations: Comparison between observations
and models
Authors: Rüedi, I.; Solanki, S. K.; Bogdan, T.; Cally, P.
1999ASSL..243..337R Altcode: 1999sopo.conf..337R
No abstract at ADS
---------------------------------------------------------
Title: Brightness Variations in the Solar Atmosphere as Seen by SOHO
Authors: Brkovic, A.; Rüedi, I.; Solanki, S. K.; Huber, M. C. E.;
Stenflo, J. O.; Stucki, K.; Harrison, R.; Fludra, A.
1999ASSL..239..231B Altcode: 1999msa..proc..231B
We present preliminary results of a statistical analysis of the
brightness variations of solar features at different levels in
the solar atmosphere. We observed quiet Sun regions at disc centre
using the Coronal Diagnostic Spectrometer (CDS) onboard the Solar and
Heliospheric Observatory (SOHO). We find significant variability at all
time scales in all parts of the quiet Sun, from darkest intranetwork
to brightest network. Such variations are observed simultaneously in
the chromospheric He I 584.33 Angstroms (2 \cdot 10^4 K) line, the
transition region O V 629.74 Angstroms (2.5 \cdot 10^5 K) and coronal
Mg IX 368.06 Angstroms (10^6 K) line. The relative variability is
independent of brightness and most of the variability appears to take
place on time scales longer than 5 minutes for all 3 spectral lines. No
significant differences are observed between the different data sets.
---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic features. XIV. TI
i and the cool components of sunspots
Authors: Rueedi, I.; Solanki, S. K.; Keller, C. U.; Frutiger, C.
1998A&A...338.1089R Altcode:
The first systematic observations of sunspot umbrae using the lines
of the Ti Ii multiplet at 2.2 mu m are presented. Their diagnostic
capabilities are investigated, developed and used to investigate the
magnetic and velocity structure of a sunspot. These lines are most
sensitive to cool plasma. In addition, they are extremely Zeeman
sensitive. We find that a sunspot is composed of two distinct cool
magnetic components. One of them is fairly vertical, has a large
magnetic field strength and is associated with the central (umbral)
part of the sunspot. The other component is strongest near the outer
boundary of the spot (penumbra), is much more inclined, has a very
low magnetic field strength and shows the signature of the Evershed
effect. In contrast to the smooth transition of field strength from
the darkest part of the umbra to the outer penumbral boundary usually
visible in observations carried out in other spectral lines, the Ti
Ii lines exhibit a sharp transition between the two magnetic components.
---------------------------------------------------------
Title: Oscillations of sunspot magnetic fields
Authors: Rueedi, I.; Solanki, S. K.; Stenflo, J. O.; Tarbell, T.;
Scherrer, P. H.
1998A&A...335L..97R Altcode:
We report on velocity and magnetic field oscillations observed
in sunspots using the MDI instrument onboard SOHO. In addition to
the well-known velocity oscillations, the data clearly show highly
localised oscillations of the magnetogram signal in different parts
of the sunspots. We show that only oscillations of the magnetic field
vector can produce the observed magnetogram oscillations, and that the
observed phase relations suggest an origin in terms of magnetoacoustic
gravity waves.
---------------------------------------------------------
Title: The flare of November 29, 1996 observed by SOHO/CDS
Authors: Czaykowska, A.; Rank, G.; Ruedi, I.; Solanki, S. K.; de
Pontieu, B.
1998cee..workE..32C Altcode:
We present flare and post-flare observations obtained with the Coronal
Diagnostic Spectrometer (CDS) onboard the Solar and Heliospheric
Observatory (SOHO) on November 29, 1996. On this day at around 20:40
UT, an M 1.0/1F flare occurred in the solar active region NOAA 7999 and
was accidentally observed by the Normal Incidence Spectrometer (NIS),
one of the two spectrometers of CDS (Harrison et al., 1995). The
data consist of two rasters lasting for 135 minutes each and both
cover an area of 4 times 4 arcminutes. The first raster is pointed at
the northern part of the active region during the flare whereas the
second one covers the southern part of the active region after the main
phase of the flare. The observations were part of the Joint Observing
Program (JOP) 54 which is aimed at the investigation of scaling laws in
coronal loops. Consequently the details of observations such as line
list and exposure time weren't convenient for flare observations. In
addition a flare can lead to over-exposures, i.e., saturation of the
CCD detector pixels, and a burn-in degeneration of the detector in
bright lines. Therefore observations of flares with CDS are avoided
and the flare from November 29, 1996, is so far the only noteworthy
flare observed by CDS. In our case we have remarkable saturation in
the chromospheric He I line at 584 AA and the coronal Fe XVI lines
at 335 AA and 361 AA, which are formed at an equilibrium temperature
of about 2.5 cdot 10^6 K. Another effect of illumination on the CCD
detector being too high is that the electron well of each pixel may
fill and hence bleed to adjacent pixels. This effect is clearly seen
in our data. As the flare occurred, the 2 times 240 arcseconds slit
was being rastered across the active region from west to east. We thus
have a convolution of spatial and temporal effects which are not easy
to separate. However, we have spectral information of each pixel in all
lines and exposures which are not saturated. Hence, line parameters such
as intensity and relative Doppler shifts can be calculated. Moreover,
the line list contains two density sensitive line pairs, Fe XII 338
AA/364 AA and Fe XIII 348 AA / 360 AA (see, e.g., Mason et al., 1997)
which can be used to determine the electron density. Using this data we
intend to study the temporal evolution of characteristics and geometry
of the loop during the flare.
---------------------------------------------------------
Title: Sunspot Oscillations Observed with MDI
Authors: Rüedi, I.; Solanki, S. K.; Stenflo, J. O.; Scherrer, P. H.
1998ESASP.417..281R Altcode: 1998cesh.conf..281R
No abstract at ADS
---------------------------------------------------------
Title: Translimb Spectroscopy with SOHO/SUMER
Authors: Ayres, T. R.; Lemaire, P.; Schuhle, U.; Wilhelm, K.; Ruedi,
I.; Solanki, S.
1997SPD....28.0104A Altcode: 1997BAAS...29..879A
We have used SUMER to obtain deep exposures of the 1300--1400 Angstroms
spectrum, at the extreme limb and off-limb. Previous “translimb”
studies in the thermal infrared had revealed remarkable extensions
of cold material (T ~ 3000 K)---traced by carbon monoxide emission
lines---into the heart of the hot chromosphere. A main objective of
our program was to search for corresponding far-UV signatures of the
“thermally-bifurcated” low chromosphere; for example, radiatively
fluoresced emissions of the CO A--X 4th-positive system (collisional
excitation would be negligible in cold gas). We conducted two separate
observing programs with SUMER. Both made use of the 1(”) -diameter
circular aperture, translated across the limb in the minimum motor
step increments of 0.(”) 375, along the central meridian in the
Northern polar coronal hole. The first program executed for nine hours
beginning 19UT 25 Oct 1996. The full wavelength range was 1340--1400
Angstroms. It was recorded in two overlapping segments, placing key
regions of the spectrum alternately on the KBr and bare parts of
the detector, to help isolate 2nd-order features. Each segment was
integrated for 500 s, and 32 pairs were obtained to span a 12(”)
swath centered on the optical limb. The second program was conducted
00--09UT 01 Dec 1996. It consisted of a single wavelength setting
(1300--1340 Angstroms) with exposure time 500 s, but twice the spatial
coverage of the earlier series: 64 steps, for a total displacement
of 24(”) . The strong chromospheric resonance lines of atomic oxygen
(1302--1305 Angstroms) and ionized carbon (1334--1335 Angstroms) were
observed on the bare part of the MCP camera. We report our progress
in cataloging the rich, diverse translimb emission spectrum; and our
efforts to deduce fundamental properties of the thermally heterogeneous
chromosphere. [-3mm] SOHO is a project of international cooperation;
the participation of TRA was supported by NASA grant NAG5-3226.
---------------------------------------------------------
Title: Magnetic field measurements on moderately active cool dwarfs.
Authors: Rueedi, I.; Solanki, S. K.; Mathys, G.; Saar, S. H.
1997A&A...318..429R Altcode:
We present a careful analysis of 13 high-quality optical spectra
of low to moderately active late-type dwarfs (G1-K5) aimed at
determining their magnetic parameters. Among our sample only one
star, ɛ Eri (spatially averaged field strength=~165+/-30G), exhibits
the unambiguous signature of a magnetic field, a few are candidates
and the remaining show no sign of a magnetic field in the observed
spectra. Our analysis is based on an inversion of the spectra using
detailed numerical solutions of the Unno-Rachkovsky equations, for
multiple spectral lines at different positions on the stellar disk,
and including magneto-optical effects. It gives results for ɛ Eri
which are in good agreement with the detailed analysis of infrared
spectra by Valenti et al. (1995ApJ...439..939V). However, the low
value of the spatially averaged field strength of these recent analyses
imply that most values of the magnetic flux determined previously for
moderately active stars are probably too large, often by considerable
amounts. We find that the magnetic flux can be reliably determined if
considerable care is taken in the analysis, but the magnetic field
strength and filling factor cannot be determined separately for
moderately active stars with optical spectra of spectral resolution
<=10^5^ and S/N<=250. In the case of ɛ Eri we are able to
constrain the temperature of the detected magnetic features, which we
find to be similar to or hotter than the non-magnetic surroundings,
providing the first direct evidence that the detected field is in the
form of plages. We also find that if an inversion approach is used,
which determines various line broadening parameters simultaneously
in a self-consistent manner, the presence of a magnetic field is not
as obvious as some previous analyses have suggested. In addition,
we determine fundamental parameters of the stellar sample.
---------------------------------------------------------
Title: Properties of Brightenings Seen in CDS Movies
Authors: Rüedi, I.; Brkovic, A.; Solanki, S. K.; Harrison, R.;
Fludra, A.; Huber, M. C. E.; Stenflo, J. O.; Stucki, K.
1997ESASP.404..641R Altcode: 1997cswn.conf..641R
No abstract at ADS
---------------------------------------------------------
Title: Umbral Polarimetric Measurements Using the TI I Multiplet at
2.2 MU M %The temperature gradient of a sunspot umbra
Authors: Ruedi, I.; Solanki, S. K.; Livingston, W.
1997ASPC..118..237R Altcode: 1997fasp.conf..237R
We present the first measurements of sunspot magnetic fields using the
lines of the Ti I multiplet at 2.2 mu m. These lines are most sensitive
to the plasma in the umbra. The observed line profiles suggest that
the temperature gradient in mid-photospheric layers of a sunspot
umbra is steeper than that of the standard sunspot models of Maltby
et al. (1986).
---------------------------------------------------------
Title: Infrared lines as probes of solar magnetic
features. XII. Magnetic flux tubes: evidence of convective collapse?
Authors: Solanki, S. K.; Zufferey, D.; Lin, H.; Rueedi, I.; Kuhn, J. R.
1996A&A...310L..33S Altcode:
The magnetic field in the solar photosphere is mainly composed of
magnetic flux tubes. Their formation is not well understood, largely due
to an absence of observational tests of theoretical predictions. Here we
use infrared polarimetric data to test and confirm the prediction that
whereas the field strength of large flux tubes is almost independent
of their magnetic flux, small flux tubes show a strong dependence. Our
work thus strengthens the case for convective collapse as the source of
concentrated solar magnetic fields. We also present the first direct
measurement of the intrinsic field strength of typical intranetwork
elements. A significant fraction of them is in equipartition with the
kinetic energy of convection. Nevertheless, our results suggest that
as far as their internal structure is concerned intranetwork magnetic
features are better described by flux tubes than by turbulent fields.
---------------------------------------------------------
Title: On the detection of shocks in the solar granulation.
Authors: Solanki, S. K.; Rueedi, I.; Bianda, M.; Steffen, M.
1996A&A...308..623S Altcode:
We investigate the spectral signature of a hydrodynamic simulation of
solar granulation and compare it with high resolution observations. The
model gives the correct qualitative trend of increasing line width
with decreasing continuum intensity seen by Nesis et al. (1992)
and interpreted by them as a sign of post-shock turbulence. We find,
however, that the profiles in the dark downflow lanes are broader even
when there is no horizontal transonic flow or shock in the vicinity. We
conclude that the observations of Nesis et al. do not provide any firm
evidence for the presence of granular transonic flows. Nevertheless,
the simulation predicts a promising diagnostic of shocked horizontal
flows. We find that at the locations of the shocks the line profiles
are particularly broad, especially near the solar limb. We present
observations of quiet solar regions that show this specific signature
of shocks and thus support the theoretical prediction of transonic
granular flows.
---------------------------------------------------------
Title: Measurement of the full Stokes vector of He I 10830 Å
Authors: Rüedi, I.; Keller, C. U.; Solanki, S. K.
1996SoPh..164..265R Altcode:
First observations of the full Stokes vector in the upper chromosphere
are presented. The He I 10830 Å line, which has been shown to give
reliable measurements of the line-of-sight component of the magnetic
field vector, has been used for this purpose. It is shown that the
difference between the appearance of chromospheric and photospheric
magnetic structures observed close to the solar limb is largely
due to the difference in height to which they refer and projection
effects. The observations do suggest, however, that the magnetic field
above sunspot penumbrae is somewhat more vertical in the chromosphere
than in the photosphere.
---------------------------------------------------------
Title: The Influence of Sunspot Canopies on Magnetic Inclination
Measurements in Solar Plages
Authors: Solanki, Sami K.; Finsterle, Wolfgang; Rüedi, Isabelle
1996SoPh..164..253S Altcode:
Sunspots are known to have large, low-lying magnetic canopies,
i.e. horizontal magnetic fields overlying a field-free medium,
that cover substantial fractions of active region plage. In this
paper we consider the influence of such canopies on the inclination
of plage magnetic fields. We find that for observations in spectral
lines like 5250.2Å the neglect of a sunspot canopy when determining
magnetic inclination angles of plage fields can introduce errors
exceeding 5-10°. This is particularly true if the observations
do not have high spatial resolution. Thus this effect may explain
some of the measurements of substantially inclined fields in solar
plages. Furthermore we find that the Fe I 15648 Å line is far superior
in giving correct flux-tube inclinations in the presence of a sunspot
magnetic canopy. Finally, the inversion of full Stokes profiles is shown
to produce more reliable results than results obtained by considering
only ratios of individual Stokes profile parameters.
