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Author name code: frutiger
ADS astronomy entries on 2022-09-14
author:"Frutiger, C."
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Title: Fundamental parameters and granulation properties of Alpha
Centauri A and B obtained from inversions of their spectra
Authors: Frutiger, C.; Solanki, S. K.; Mathys, G.
2005A&A...444..549F Altcode:
Properties of stellar granulation are obtained by inverting spectra
of the late-type stars α Centauri A and B. Our inversions are based
on a multi-component model of the stellar photosphere and take into
account the center-to-limb variation and rotational broadening. The
different atmospheric components describe the areas harboring up-,
down- and horizontal flows. The inversions are constrained by
fitting not only the flux profiles, but also their line bisectors,
and by using a simple mass conservation scheme. The inversions return
the properties of convection at the stellar surface, including the
stratification of the thermodynamic parameters, as well as fundamental
parameters such as the gravitational acceleration, v sin i and the
element abundances. For α Cen A (G2V) the derived stratifications of
the temperature and convective velocity are very similar to the Sun,
while for α Cen B (K1V) we find similar up- and downflow velocities,
but lower horizontal speeds and a reduced overshoot. The latter is
consistent with the smaller scale height of the atmosphere, while mass
conservation arguments taken with the lower horizontal speed imply
that the granules on α Cen B are smaller than on the Sun. Both these
properties are in good agreement with the hydrodynamic simulation of
Nordlund & Dravins (1990, A&A, 228, 155). The inversions also
return the fundamental parameters (T_eff, log g, abundances, v sin i,
etc.) of the two stars. These values are on the whole in good agreement
with literature values. Also, most of them do not strongly depend on the
details of the inversion. However, importantly, the element abundances
are 0.1 to 0.15 dex lower when a 2- or 3-component inversion is carried
out than with a 1-component inversion. <P />Based on observations
collected at the European Southern Observatories, La Silla, Chile.
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Title: The molecular Zeeman effect and diagnostics of solar and
stellar magnetic fields. II. Synthetic Stokes profiles in the
Zeeman regime
Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C.
2003A&A...412..513B Altcode:
Recent advances in the computation of the Zeeman splitting of
molecular lines have paved the way for their use as diagnostics
of solar and stellar magnetic fields. A systematic study of their
diagnostic capabilities had not been carried out so far, however. Here
we investigate how molecular lines can be used to deduce the magnetic
and thermal structure of sunspots, starspots and cool stars. First, we
briefly describe the Stokes radiative transfer of Zeeman-split molecular
lines. Then, we compute Stokes spectra of TiO, OH, CH and FeH lines and
investigate their diagnostic capabilities. We also compare the synthetic
profiles with observations. Spectra of TiO, OH and FeH are found to be
interesting diagnostics of sunspot magnetic fields. This is also true
for cool stars, where, however, the OH Stokes V profiles may require
very high S/N data to be reliably employed. Finally we investigate
the potential of various molecular bands for high-contrast imaging
of the solar surface. The violet CN and CH bands turn out to be most
promising for imaging the photosphere, the TiO bands are excellent for
imaging sunspot umbrae, while the UV OH band can be used for imaging
both the photosphere and sunspots.
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Title: Three dimensional structure of a regular sunspot from the
inversion of IR Stokes profiles
Authors: Mathew, S. K.; Lagg, A.; Solanki, S. K.; Collados, M.;
Borrero, J. M.; Berdyugina, S.; Krupp, N.; Woch, J.; Frutiger, C.
2003A&A...410..695M Altcode:
The magnetic, thermal and velocity structure of a regular sunspot,
observed close to solar disk center is presented. Spectropolarimetric
data obtained with the Tenerife Infrared Polarimeter (TIP) in two
infrared FeI lines at 15 648.5 Å and 15 652.8 Å are inverted
employing a technique based on response functions to retrieve the
atmospheric stratification at every point in the sunspot. In order
to improve the results for the umbra, profiles of Zeeman split OH
lines blending the FeI 15 652.8 Å are also consistently fit. Thus
we obtain maps of temperature, line-of-sight velocity, magnetic
field strength, inclination, and azimuth, as a function of both
location within the sunspot and height in the atmosphere. We present
these maps for an optical depth range between log tau<SUB>5</SUB> =
0 and log tau<SUB>5</SUB> = -1.5, where these lines provide accurate
results. We find decreasing magnetic field strength with increasing
height all over the sunspot, with a particularly large vertical field
gradient of ~ -4 G km<SUP>-1</SUP> in the umbra. We also observe the
so called “spine” structures in the penumbra, i.e. extended radial
features with a stronger and more vertical magnetic field than the
surroundings. Also we found that the magnetic field zenith angle
increases with height. From the velocity map it is clear that the
Evershed flow avoids the spines and mostly concentrates in the more
inclined intervening field. The field inclination at a few locations
in the outer penumbra in lower layers goes beyond 90<SUP>o</SUP>. These
locations coincide with the strongest flows in the velocity map.
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Title: Structure of a simple sunspot from the inversion of IR
spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Collados, M.;
Berdyugina, S. V.; Frutiger, C.; Krupp, N.; Woch, J.
2003AN....324..388M Altcode:
Analysis of spectral data of two neighboring infrared lines, Fe i
15648.5 Å (g = 3) and Fe i 15652.9 Å (g_eff = 1.53) are carried out
for a simple sunspot when it was near the solar disk center (mu = 0.92),
to understand the basic structure of sunspot magnetic field. Inversions
of Stokes profiles are carried out to derive different atmospheric
parameters both as a function of location within the sunspot and height
in the atmosphere. As a result of the inversion we have obtained maps
of magnetic field strength, temperature, line-of-sight velocity, field
inclination and azimuth for different optical depth layers between log
(tau_ {5}) = 0 and log (tau_ {5}) = -2.0 . In this paper we present
few results from our inversion for a layer averaged between log (tau_
{5}) from 0.0 to -0.5.
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Title: Magnetic Elements Near the Solar Limb: Inversions Based on
a Flux-tube Model
Authors: Frutiger, C.; Solanki, S. K.; Gandorfer, A.
2003ASPC..307..344F Altcode:
No abstract at ADS
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Title: Modeling the Fine Structure of a Sunspot Penumbra through
the Inversion of Stokes Profiles
Authors: Borrero, J. M.; Lagg, A.; Solanki, S. K.; Frutiger, C.;
Collados, M.; Bellot Rubio, L. R.
2003ASPC..286..235B Altcode: 2003ctmf.conf..235B
No abstract at ADS
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Title: Thermal-magnetic relation of a sunspot as inferred from the
inversion of 1.5 μm spectral data
Authors: Mathew, S. K.; Solanki, S. K.; Lagg, A.; Krupp, N.; Woch,
J.; Collados, M.; Berdyugina, S.; Frutiger, C.
2002ESASP.505..501M Altcode: 2002IAUCo.188..501M; 2002solm.conf..501M
We present the thermal-magnetic relation in a simple, isolated sunspot
deduced from the inversion of 1.56 μm spectropolarimetric data. Due to
the high Zeeman sensitivity of the g = 3, Fe I 1.5648 μm line, we can
study this relationship in the entire sunspot. An inversion technique
based on response functions is used to derive various parameters,
both as a function of location within the sunspot and of height in the
atmosphere. In this paper we attempt to relate field strength, vertical
and radial field components and the field inclination with temperature.
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Title: Modelling solar irradiance variations: separate models for
the network and active region faculae
Authors: Wenzler, T.; Solanki, S. K.; Fluri, D. M.; Frutiger, C.;
Fligge, M.; Ortiz, A.
2002ESASP.508..231W Altcode: 2002soho...11..231W
In order to determine to what extent solar surface magnetism
affects solar irradiance we need to reconstruct the irradiance from
magnetograms. This process requires the use of model atmospheres. Here
we present two model atmospheres describing faculae in active regions
and the network. The models have been constructed such that they
reproduce various data sets simultaneously.
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Title: Empirical models of solar magnetic flux-tubes and their
non-magnetic surroundings
Authors: Frutiger, C.; Solanki, S. K.
2001A&A...369..646F Altcode:
A powerful method for the analysis of the structure of small
scale magnetic elements in the solar photosphere is the
inversion of Stokes spectra. In previous papers based on such
inversions \cite{BellotRubio:etal:1997, BellotRubio:etal:1999}
and \cite{Frutiger:etal:1999} have argued in favor of models with
rather different dynamic properties. In this paper we return to
this debate and compare results returned by inversions based on
new multi-component models applied to several Fe i, Fe ii and C i
spectral line profiles obtained in active region plage with a Fourier
Transform Spectrometer. These inversions differ from earlier ones by
the fact that mass conservation is strictly imposed both inside the
magnetic elements and on the surrounding external flow field. These
flux-tube models are not only able to reproduce the characteristic
Stokes V asymmetries and line-shifts observed in active regions
plages or network elements, but also the Stokes I line profiles,
including line bisectors. It is confirmed that from the quality of the
fits alone it is not possible to distinguish between the steady flow
proposed by \cite{BellotRubio:etal:1997} and the oscillatory model of
\cite{Frutiger:Solanki:1998}. If, however, physical constraints are
imposed (e.g. mass conservation or that the flow retains the same
direction over height in the flux tube) then the oscillatory model
is found to be superior. In addition, the current investigation also
provides the first inversion-based model of abnormal granulation.
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Title: The Formation of One-Lobed Stokes V Profiles in an
Inhomogeneous Atmosphere
Authors: Ploner, S. R. O.; Schussler, M.; Solanki, S. K.; Sheminova,
V. A.; Gadun, A. S.; Frutiger, C.
2001ASPC..236..371P Altcode: 2001aspt.conf..371P
We assess the diagnostic potential of the observed pathological Stokes V
profiles that differ strongly from the customary, nearly antisymmetric
two-lobed shape. In particular, we consider the formation of one-lobed
Stokes V profiles using the results of an MHD simulation. We find
that the majority of one-lobed profiles is produced in regions of
weak horizontal field with significant cancellation caused by mixed
polarity along the line of sight. A minority of one-lobed profiles
originates close to strong magnetic field concentrations with strong
gradients of velocity and magnetic field strength.
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Title: Consistent Empirical Models of Solar Magnetic Flux Tubes and
the Surrounding Convection (CD-ROM Directory: contribs/frutige2)
Authors: Frutiger, C.; Solanki, S. K.
2001ASPC..223..632F Altcode: 2001csss...11..632F
No abstract at ADS
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Title: Magnetic Splitting of Molecular Lines in Sunspot
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.
2001IAUS..203..254B Altcode:
A study of molecular lines in sunspots is of particular interest
because of their high temperature and pressure sensitivity. Many of
them are also magnetically sensitive, but this was not yet widely
investigated. With high-resolution, high signal-to-noise Fourier
spectroscopy in four Stokes parameters now available, the use of
molecular lines for studying the structure of sunspots brings real
gains. One is the extension of spot models, including magnetic field,
up to layers, where atomic lines suffer from NLTE effects but molecules
can still be treated in the LTE approximation. Equally important is the
fact that since molecular lines are extremely temperature sensitive
they can be used to probe the thermal and magnetic structure of the
coolest parts of sunspots. We present calculations of splitting and
the Stokes parameters for a number of molecular lines in the visible
and near-infrared regions. Our first selections are the green system of
MgH A<SUP>2</SUP>Π-X<SUP>2</SUP>σ and the TiO triplet α, γ' and γ
systems as the most studied band systems in the sunspot spectrum. The
calculations involve different regimes of the molecular Zeeman effect,
up to the complete Paschen-Back effect for individual lines. We look
for molecular lines which can be used along with atomic lines to derive
magnetic, thermal and dynamic properties of the umbra.
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Title: The Molecular Zeeman Effect and Solar Magnetic Fields
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingston,
W.
2001ASPC..236..551B Altcode: 2001aspt.conf..551B
No abstract at ADS
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Title: Solar and Stellar Magnetic Fields: the Molecular Zeeman Effect
as a Probe
Authors: Berdyugina, S. V.; Solanki, S. K.; Frutiger, C.
2001ASPC..248...99B Altcode: 2001mfah.conf...99B
No abstract at ADS
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Title: Empirical Models of Stellar Convection (CD-ROM Directory:
contribs/frutige1)
Authors: Frutiger, C.; Solanki, S. K.
2001ASPC..223..626F Altcode: 2001csss...11..626F
No abstract at ADS
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Title: Successful spectral synthesis of Zeeman-split molecular bands
in sunspot spectra
Authors: Berdyugina, S. V.; Frutiger, C.; Solanki, S. K.; Livingstone,
W.
2000A&A...364L.101B Altcode:
We present the first spectral synthesis of Zeeman-split Stokes profiles
of the MgH A<SUP>2</SUP>Pi -X<SUP>2</SUP>BLAigma green system and
TiO gamma -system. The calculations involve different regimes of the
molecular Zeeman effect, up to the complete Paschen-Back effect for
individual lines. The synthetic spectra are compared with observations
of Stokes I and V in sunspot umbrae. We find that although the Stokes
I spectra are reasonably reproduced, some lines are obviously still
missing from the employed line lists. The Stokes V spectra turn
out to be much cleaner since the missing lines do not appear to
be Zeeman-split. We thus provide the first good fit to Zeeman-split
molecular lines, including profiles with unconventional Stokes V shapes,
determined by the Paschen-Back effect. Based on observations from
the Canada-France-Hawaii Telescope operated by the National Research
Council of Canada, the Centre National de la Recherche Scientifique
de France and the University of Hawaii
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Title: Properties of the solar granulation obtained from the inversion
of low spatial resolution spectra
Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.
2000A&A...358.1109F Altcode:
The spectra of cool stars are rich in information on elemental
abundances, convection and non-thermal heating. Extracting this
information is by no means straightforward, however. Here we demonstrate
that an inversion technique may not only provide the stratification of
the classical parameters describing a model atmosphere, but can also
determine the properties of convection at the stellar surface. The
inversion technique is applied to spectra of photospheric lines, one
recorded at the quiet solar disk center, the other integrated over the
whole disk. We find that a model based on a single plane-parallel
atmosphere gives unsatisfactory fits to the spectral lines and
suffers from considerable uncertainties in the derived temperature
stratification. Also, the elemental abundances returned by the inversion
are not particularly reliable. These problems are greatly reduced if
two atmospheric components, corresponding to granular up- and downflows
are allowed for. The best results are obtained if the line profiles
and bisectors of a neutral and ionized species are fit and the results
are constrained using a simple mass conservation scheme. We find that
inversions based on two- and three-component models of disk-integrated
spectra give similar results to inversions of disk-center observations,
although with somewhat lower accuracy. This similarity is promising
for future applications of line profile inversions to the study of
late-type stars and in particular their convection.
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Title: Inversion of Stokes profiles
Authors: Frutiger, C.; Solanki, S. K.; Fligge, M.; Bruls, J. H. M. J.
1999ASSL..243..281F Altcode: 1999sopo.conf..281F
No abstract at ADS
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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.
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Title: Do solar magnetic elements harbor downflows?
Authors: Frutiger, C.; Solanki, S. K.
1998A&A...336L..65F Altcode:
In a recent paper Bellot Rubio et al. (1997) inverted Zeeman split
Stokes profiles to infer the stratification of the temperature,
velocity and magnetic field in the photospheric layers of solar
magnetic elements (modeled as thin flux tubes). One controversial
result of their inversions is the presence of a strong downflow
within the flux tubes. In the model underlying their inversion such
a downflow is necessary to reproduce the asymmetric shape of the
observed V profiles. We present inversions based on two different
flux-tube models, both of which reproduce the Stokes I and V profiles
obtained in plages and the network with high accuracy, including the
V profile asymmetry. One model is almost identical to that employed
by Bellot Rubio et al. (1997), and results in a significant downflow
within the flux tube. The other, although similar in most respects,
has mass conservation enforced inside the flux tubes, i.e. they contain
both an upflow and a downflow which could arise from oscillations or
siphon flows. Hence, current data may not be sufficiently sensitive
to distinguish between the two velocity structures, so that there is
no compelling evidence for a net downflow of matter inside magnetic
elements. From a physical point of view the model incorporating mass
conservation is to be preferred.
