Author name code: andersen
ADS astronomy entries on 2022-09-14
author:"Andersen, Bo" NOT =author:"Andersen, B.C."
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Title: Multiband Detections of Repeating FRB 180916.J0158+65
Authors: Faber, J.; Gajjar, V.; Sand, K.; Michilli, D.; Andersen, B.
Bibcode: 2021AAS...23713005F
Altcode:
We report a series of joint detections of FRB 180916.J0158+65, recently
discovered to exhibit a 16.35-day periodicity with a ~4-day active phase
window, between the GBT (600-1000 MHz), uGMRT (300-500 MHz), and CHIME
(400-800 MHz) radio observatories. We observed a total of 7, 4, and 1
bursts from the source, respectively, which collectively spanned the
700 MHz bandwidth over the course of ~3 days, with 1 hour of overlapping
observations. The GBT detections were made earlier in the active phase
window and exhibited a significantly higher burst-rate compared to
those made by uGMRT, hinting at a likely frequency dependence of burst
activity phase. In both GBT and uGMRT detections, we observe clear
downward drifting emissions and complex multi-component time-frequency
modulations at narrow scales, which motivate the use of baseband data
for investigations of FRB sub-structure. We performed our analysis
using the transient detection pipeline SPANDAK and analysis pipeline
FLITS, which currently run on the 64-node Breakthrough Listen Digital
Instrument at the GBT. SPANDAK uses SIGPROC filterbank data products
to search for transient signals (FRBs and ETIs). FLITS successively
extracts the baseband raw voltages, stored at the GBT native time
and frequency resolutions, which enable coherent dedispersion,
calibration with full-Stokes parameters, and comprehensive offline
analysis. We leverage these analysis techniques for both GBT and uGMRT
bursts to fully resolve spectral, temporal, and polarization angle
variability in emission signatures. In this process, we employ a DM
metric that maximizes frequency-averaged pulse structure, rather than
signal-to-noise. Furthermore, to constrain potential source models, we
consider features which could be intrinsic to the emission mechanism,
and how they might reasonably differ from those superimposed by
propagation effects in the surrounding medium.
Title: First TSI results and status report of the CLARA/NorSat-1
solar absolute radiometer
Authors: Walter, Benjamin; Andersen, Bo; Beattie, Alexander; Finsterle,
Wolfgang; Kopp, Greg; Pfiffner, Daniel; Schmutz, Werner
Bibcode: 2020IAUGA..30..358W
Altcode:
The Compact Lightweight Absolute Radiometer (CLARA) is orbiting Earth
on-board the Norwegian NorSat-1 micro-satellite since 14th
of July 2017. The first light total solar irradiance (TSI) measurement
result of CLARA is 1360.18 W m-2 for the so far single
reliable Channel B. Channel A and C measured significantly lower
(higher) TSI values and were found being sensitive to satellite pointing
instabilities. These channels most likely suffer from electrical
interference between satellite components and CLARA, an effect that
is currently under investigation. Problems with the satellite attitude
control currently inhibit stable pointing of CLARA to the Sun.
Title: A repeating fast radio burst source localized to a nearby
spiral galaxy
Authors: Marcote, B.; Nimmo, K.; Hessels, J. W. T.; Tendulkar, S. P.;
Bassa, C. G.; Paragi, Z.; Keimpema, A.; Bhardwaj, M.; Karuppusamy,
R.; Kaspi, V. M.; Law, C. J.; Michilli, D.; Aggarwal, K.; Andersen,
B.; Archibald, A. M.; Bandura, K.; Bower, G. C.; Boyle, P. J.; Brar,
C.; Burke-Spolaor, S.; Butler, B. J.; Cassanelli, T.; Chawla, P.;
Demorest, P.; Dobbs, M.; Fonseca, E.; Giri, U.; Good, D. C.; Gourdji,
K.; Josephy, A.; Kirichenko, A. Yu.; Kirsten, F.; Landecker, T. L.;
Lang, D.; Lazio, T. J. W.; Li, D. Z.; Lin, H. -H.; Linford, J. D.;
Masui, K.; Mena-Parra, J.; Naidu, A.; Ng, C.; Patel, C.; Pen, U. -L.;
Pleunis, Z.; Rafiei-Ravandi, M.; Rahman, M.; Renard, A.; Scholz, P.;
Siegel, S. R.; Smith, K. M.; Stairs, I. H.; Vanderlinde, K.; Zwaniga,
A. V.
Bibcode: 2020Natur.577..190M
Altcode: 2020arXiv200102222M
Fast radio bursts (FRBs) are brief, bright, extragalactic radio
flashes1,2. Their physical origin remains unknown, but dozens
of possible models have been postulated3. Some FRB sources
exhibit repeat bursts4-7. Although over a hundred FRB sources
have been discovered8, only four have been localized and
associated with a host galaxy9-12, and just one of these
four is known to emit repeating FRBs9. The properties
of the host galaxies, and the local environments of FRBs, could
provide important clues about their physical origins. The first known
repeating FRB, however, was localized to a low-metallicity, irregular
dwarf galaxy, and the apparently non-repeating sources were localized
to higher-metallicity, massive elliptical or star-forming galaxies,
suggesting that perhaps the repeating and apparently non-repeating
sources could have distinct physical origins. Here we report the
precise localization of a second repeating FRB source6,
FRB 180916.J0158+65, to a star-forming region in a nearby (redshift
0.0337 ± 0.0002) massive spiral galaxy, whose properties and proximity
distinguish it from all known hosts. The lack of both a comparably
luminous persistent radio counterpart and a high Faraday rotation
measure6 further distinguish the local environment of FRB
180916.J0158+65 from that of the single previously localized repeating
FRB source, FRB 121102. This suggests that repeating FRBs may have a
wide range of luminosities, and originate from diverse host galaxies
and local environments.
Title: CLARA - A compact and light-weight absolute radiometer on
the NORSAT-1 mission
Authors: Schmutz, Werner; Finsterle, Wolfgang; Walter, Benjamin;
Suter, Markus; Andersen, Bo; Osmundsen, Magne
Bibcode: 2014cosp...40E2930S
Altcode:
PMOD/WRC is building the Compact and Light-weight Absolut RAdiometer
(CLARA) to fly on the Norwegian Space Centre's (NCS) NORSAT-1
mission. CLARA is based on a new design by PMOD/WRC which minimizes
size and weight while improving the radiometric performance. The
NORSAT-1 mission is planned to be launched to a polar LEO in Q4 2015
or Q1 2016. NSC intends to extend the initial three-years mission for
as long as the platform and payload remain functional.
Title: The quest for the solar g modes
Authors: Appourchaux, T.; Belkacem, K.; Broomhall, A. -M.; Chaplin,
W. J.; Gough, D. O.; Houdek, G.; Provost, J.; Baudin, F.; Boumier,
P.; Elsworth, Y.; García, R. A.; Andersen, B. N.; Finsterle, W.;
Fröhlich, C.; Gabriel, A.; Grec, G.; Jiménez, A.; Kosovichev, A.;
Sekii, T.; Toutain, T.; Turck-Chièze, S.
Bibcode: 2010A&ARv..18..197A
Altcode: 2010A&ARv.tmp....1A; 2009arXiv0910.0848A
Solar gravity modes (or g modes)—oscillations of the solar interior
on which buoyancy acts as the restoring force—have the potential
to provide unprecedented inference on the structure and dynamics of
the solar core, inference that is not possible with the well-observed
acoustic modes (or p modes). The relative high amplitude of the g-mode
eigenfunctions in the core and the evanesence of the modes in the
convection zone make the modes particularly sensitive to the physical
and dynamical conditions in the core. Owing to the existence of the
convection zone, the g modes have very low amplitudes at photospheric
levels, which makes the modes extremely hard to detect. In this article,
we review the current state of play regarding attempts to detect g
modes. We review the theory of g modes, including theoretical estimation
of the g-mode frequencies, amplitudes and damping rates. Then we go
on to discuss the techniques that have been used to try to detect g
modes. We review results in the literature, and finish by looking to
the future, and the potential advances that can be made—from both
data and data-analysis perspectives—to give unambiguous detections
of individual g modes. The review ends by concluding that, at the time
of writing, there is indeed a consensus amongst the authors that there
is currently no undisputed detection of solar g modes.
Title: The internal structure of the Sun inferred from g modes and
low-frequency p modes
Authors: Elsworth, Y. P.; Baudin, F.; Chaplin, W; Andersen, B;
Appourchaux, T.; Boumier, P.; Broomhall, A. -M.; Corbard, T.;
Finsterle, W.; Fröhlich, C.; Gabriel, A.; García, R. A.; Gough,
D. O.; Grec, G.; Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii,
T.; Toutain, T.; Turck-Chièze, S.
Bibcode: 2006ESASP.624E..22E
Altcode: 2006soho...18E..22E
The Phoebus group is an international collaboration of
helioseismologists, its aim being to detect low-frequency solar g
modes. Here, we report on recent work, including the development and
application of new techniques based on the detection of coincidences
in contemporaneous datasets and the asymptotic properties of the g-mode
frequencies. The length of the time series available to the community is
now more than ten years, and this has reduced significantly the upper
detection limits on the g-mode amplitudes. Furthermore, low-degree p
modes can now be detected clearly at frequencies below 1000 μHz.
Title: Recent Progresses on g-Mode Search
Authors: Appourchaux, T.; Andersen, B.; Baudin, F.; Boumier, P.;
Broomhall, A. -M.; Chaplin, W.; Corbard, T.; Elsworth, Y.; Finsterle,
W.; Fröhlich, C.; Gabriel, A.; Garcia, R.; Gough, D. O.; Grec, G.;
Jiménez, A.; Kosovichev, A.; Provost, J.; Sekii, T.; Toutain, T.;
Turck-Chièze, S.
Bibcode: 2006ESASP.617E...2A
Altcode: 2006soho...17E...2A
No abstract at ADS
Title: Variation of Low Degree P-Mode Amplitudes
Authors: Andersen, B.; Leifsen, T.
Bibcode: 2004ESASP.559..297A
Altcode: 2004soho...14..297A
No abstract at ADS
Title: Amplitude modulation of low degree p-modes - comparison of
BISON and VIRGO
Authors: Andersen, Bo; Leifsen, Torben; Chaplin, William J.; Elsworth,
Yvonne
Bibcode: 2003ESASP.517..151A
Altcode: 2003soho...12..151A
Using both VIRGO and MDI data we have previously studied the amplitude
variation of the l=0 p-modes for radial orders 12 to 32. In this study
we extend the investigation backward in time to 1992 by including
data from the BISON network. For the large amplitude modes there is a
strong correlation between the space based radiance measurements from
VIRGO and the ground based Doppler shift measurements from BISON. The
extreme rotational modulation of l=0, n=22 is confirmed to be a
phenomenon confined to the period of minimum solar activity. Also with
neighbouring l=1, n=21 a clear modulation is seen at slightly lower
frequency. Some persistent frequencies occur in other l=0,1 modes,
but not to the same level in time and amplitude.
Title: What have we learnt with the Luminosity Oscillations Imager
over the past 6 years?
Authors: Appourchaux, T.; Andersen, B.; Sekii, T.
Bibcode: 2002ESASP.508...47A
Altcode: 2002soho...11...47A
We summarize what we achieved with 6 years of LOI data. We present
old as well as new results regarding the p-mode parameters dependence
upon solar activity. We have also derived the dependence of the solar
background noise upon solar activity and solar disk position. Inversions
done using LOI frequencies and higher-degree mode frequencies from
GONG confirm previous velocity inversions.
Title: Temporal behaviour of radial p-modes
Authors: Leifsen, T.; Andersen, B. N.; Toutain, T.
Bibcode: 2001ESASP.464...63L
Altcode: 2001soho...10...63L
The amplitude modulation of solar radial p-modes has been studied in
irradiance and radiance data from VIRGO and velocity data from MDI
onboard SOHO. The amplitudes vary substantially with time. For two
modes, l=0, n=21 and 22 we find a strong rotational modulation at
the end of the old solar cycle (number 22). The modulation vanishes
during solar minimum and only weakly reappears during the rise of the
new cycle. There is a decrease in the integrated mode amplitudes with
increased activity for the modes that show rotational modulation. At
low solar activity there is little correlation between modes of
varying order, but the correlation seems to increase with increasing
solar activity.
Title: g-mode detection: Where do we stand?
Authors: Appourchaux, T.; Andersen, B.; Berthomieu, G.; Chaplin, W.;
Elsworth, Y.; Finsterle, W.; Frölich, C.; Gough, D. O.; Hoeksema,
T.; Isaak, G.; Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.;
Toutain, T.
Bibcode: 2001ESASP.464..467A
Altcode: 2001soho...10..467A
We review the recent developments in determining the upper limits to
g-mode amplitudes obtained by SOHO instruments, GONG and BiSON. We
address how this limit can be improved by way of new helioseismic
instruments and/or new collaborations, hopefully providing in the not
too distant future unambiguous g-mode detection.
Title: Observational Upper Limits to Low-Degree Solar g-Modes
Authors: Appourchaux, T.; Fröhlich, C.; Andersen, B.; Berthomieu, G.;
Chaplin, W. J.; Elsworth, Y.; Finsterle, W.; Gough, D. O.; Hoeksema,
J. T.; Isaak, G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.;
Sekii, T.; Toutain, T.
Bibcode: 2000ApJ...538..401A
Altcode:
Observations made by the Michelson Doppler Imager (MDI) and Variability
of solar IRradiance and Gravity Oscillations (VIRGO) on the Solar and
Heliospheric Observatory (SOHO) and by the ground-based Birmingham
Solar Oscillations Network (BiSON) and Global Oscillations Network
Group (GONG) have been used in a concerted effort to search for solar
gravity oscillations. All spectra are dominated by solar noise in the
frequency region from 100 to 1000 μHz, where g-modes are expected to be
found. Several methods have been used in an effort to extract any g-mode
signal present. These include (1) the correlation of data-both full-disk
and imaged (with different spatial-mask properties)-collected over
different time intervals from the same instrument, (2) the correlation
of near-contemporaneous data from different instruments, and (3) the
extraction-through the application of complex filtering techniques-of
the coherent part of data collected at different heights in the solar
atmosphere. The detection limit is set by the loss of coherence
caused by the temporal evolution and the motion (e.g., rotation)
of superficial structures. Although we cannot identify any g-mode
signature, we have nevertheless set a firm upper limit to the amplitudes
of the modes: at 200 μHz, they are below 10 mm s-1 in
velocity, and below 0.5 parts per million in intensity. The velocity
limit corresponds very approximately to a peak-to-peak vertical
displacement of δR/Rsolar=2.3×10-8 at the
solar surface. These levels which are much lower than prior claims,
are consistent with theoretical predictions.
Title: Sources of Amplitude Modulation of Solar P-Modes
Authors: Leifsen, Torben; Andersen, Bo; Appourchaux, Thierry
Bibcode: 1998ESASP.418..939L
Altcode: 1998soho....6..939L
We study the amplitude variation with time of the solar radial
p-modes. Continuous datasets from more than two years of observations
with the SOHO/VIRGO SPM and LOI instruments were used. A Hilbert
transform method was used to study the time variation of the amplitudes
of the l = 0-3 modes with radial order 12-32. The observed amplitudes of
the modes vary substantially with time on a large range of timescales
up to more than a solar rotation. As expected the power spectra of
the amplitude variation show little or no consistent periodicities for
most of the modes. However, for some of the modes, specifically for it
l = 0, n = 21 and 22, a strong modulation is observed with the solar
sidereal rotation frequency. This is a very surprising result as the
{l} = 0 modes should be insensitive to the solar rotation. In contrast
the SPM blue channel irradiance observations show a modulation with
the solar synodic rotation frequency. This is as one would expect as
active regions rotate over the solar disc and thereby modulate the
irradiance signal. A comparison with MDI velocity data show that the
amplitude modulation of the modes closely resembles the modulation as
observed with VIRGO/SPM. This shows that the observed modulation is
not an effect of the irradiance variation due to active regions, but
rather a modulation of the mode itself by rotation. This conclusion is
strengthened by the fact that the symmetric {l} = 0 modes are modulated
by the sidereal and not the synodic rotation frequency. The two years
of observations cover times of both low and higher solar activity as
the activity of the new solar cycle started in the summer of 1997. In
the solar irradiance one can see the onset of the new solar cycle
as a frequency shift to lower frequencies as the activity appear at
higher solar latitudes. Surprisingly a similar shift is also seen in
the modulation of the two modes, indicating that the modulation of
the modes is closely connected to the latitudes of solar activity.
Title: Time Dependence of Solar Noise Observed with VIRGO
Authors: Andersen, Bo; Leifsen, Torben; Appourchaux, Thierry; Frohlich,
Claus; Jiménez, Antonio; Wehrli, Christoph
Bibcode: 1998ESASP.418...83A
Altcode: 1998soho....6...83A
The effect of non- and quasiperiodic solar surface structures dominate
the power spectra of solar irradiance and radiance over a broad range
of time scales. Only in the p-mode region above about 2 mHz and in the
rotationally dominated region below about 3 μ Hz there seems to be
narrow stationary peaks. The solar background signal, or solar noise has
clear large scale quasi-stationary structures that seems to be closely
correlated to the combination of timescales and contrasts of the solar
surface sources. The dominant sources are the solar granulation and
supergranulation. The solar noise determines the detection limit in
the search for g-modes. Thus an increased understanding of it may be
helpfull in this search. In addition this understanding will be usefull
to determine the properities of stellar small scale surface structures
from the data from future asteroseismology space missions. In this
study we use the VIRGO data to study the time variation of the solar
noise with timescales from about one day to about one year.
Title: Statistical Properties of the Amplitude Modulation of Solar
p-Modes
Authors: Andersen, Bo; Aarset, Magne; Leifsen, Torben; Appourchaux,
Thierry; Frohlich, Claus; Hoeksema, J. T.; Jiménez, Antonio; Toutain,
Thierry
Bibcode: 1998ESASP.418..897A
Altcode: 1998soho....6..897A
The low degree solar p-modes show amplitude modulation at all observable
timescales. For some modes a large fraction of this modulation seems
to be correlated to the solar rotation. For other modes there seems
to be little or no deterministic component in the modulation. Only
intermittent correlation between the modulation of different modes
have been observed. This is to be expected if the excitation of modes
is completely stochastic. None of the observational methods observe the
modes directly. In different ways they all observe the solar atmospheres
response to the modes. This implies that the modes may be modulated by
this response. By studying the statistical properties of the different
observed modes we attempt to discriminate between variations in the
modes themselves and the atmospheric response. In this work we study the
statistical properties of the mode amplitude variations for radial order
p-modes observed with the VIRGO and SOI/MDI instruments on SOHO. The
time scales studied span the region from 0.2 μ Hz to 15 muHz. Here,
we are modelling the amplitude modulation, utilising the concepts of
state space models, as a stochastic process and study the properties
of this model as function of radial order and line width of the modes.
Title: Observations of the latitudinal variation of the solar radiance
of non-active regions of the sun.
Authors: Domingo, V.; Sanchez, L.; Appourchaux, T.; Andersen, B.
Bibcode: 1998IAUS..185..111D
Altcode:
The Luminosity Oscillations Imager (LOI) of the VIRGO experiment
aboard SOHO provides continuous measurement of the solar irradiance
in a 5 nm band around 500 nm. The solar image is broken down in 12
pixels distributed in 4 latitudinal bands. The first year of operation
of the instrument has taken place during a period of solar minimum
activity. The measurements provide an indication of the distribution
of the solar irradiance variations versus latitude. Contributions to
the observed variations due to the presence of active regions are
discussed in relation to the possible effect of the evolving solar
cycle (structure of the convection zone): short term variations versus
long term variations. The problem of the photometric stability of
the measurements needed for the investigation is thoroughly treated
by self consistency and by comparison with other instruments on SOHO
(VIRGO sun- photometers and MDI intensity measurements).
Title: Observational Upper Limits for Low-Degree Solar g-modes
Authors: Fröhlich, C.; Finsterle, W.; Andersen, B.; Appourchaux, T.;
Chaplin, W. J.; Elsworth, Y.; D. O. Gough; Hoeksema, J. T.; Isaak,
G. R.; Kosovichev, A. G.; Provost, J.; Scherrer, P. H.; Sekii, T.;
Toutain, T.
Bibcode: 1998ESASP.418...67F
Altcode: 1998soho....6...67F
No abstract at ADS
Title: Amplitude modulation of radial p-modes from Virgo
Authors: Leifsen, T.; Andersen, B. N.; Appourchaux, T.; Frohlich,
C.; Jimenez, A.; Toutain, T.; Wehrli, C.
Bibcode: 1998IAUS..185..113L
Altcode:
We present results from wavelet analysis of more than one year of
data from the VIRGO Sun Photometers (SPM) and the VIRGO Luminosity
Oscillation Imager (LOI) onboard the SOHO spacecraft. The temporal
behaviour of p-modes with l=0--2 is presented. The analysis of
the l=0 modes show a modulation of the mode amplitudes with the
solar rotation. This result is quite surprising as the l=0 modes
should not be sensitive to the solar rotation. Possible effects of
varying solar activity on the modulation of the mode amplitudes is
investigated. The effect of the modulation on the fitting of mode lines
and determination of the mode frequencies is also studied. Wavelet
analysis has a fundamental limitation in the ability to achieve
simultaneous high frequency and time resolution. In order to be able
to study the rotationally split components of the l=1 modes with good
time resolution, we apply a spatial filtering technique on the LOI
data to separate the different components.
Title: Comparative Studies of Low-Order and Low-Degree Solar p Modes
Authors: Appourchaux, T.; Andersen, B.; Chaplin, W.; Elsworth, Y.;
Finsterle, W.; Frohlich, C.; Gough, D.; Hoeksema, J. T.; Isaak, G.;
Kosovichev, A.; Provost, J.; Scherrer, P.; Sekii, T.; Toutain, T.
Bibcode: 1998ESASP.418...95A
Altcode: 1998soho....6...95A
The amplitudes of solar p-modes decrease steeply with decreasing
radial order below about 17. The background solar signal (solar noise)
in general increases steadily with decreasing frequency. For the
irradiance and radiance measurements with VIRGO or SOI/MDI on SOHO this
combination makes it difficult to detect low degree modes below about
1.8 mHz. The solar noise as observed in velocity with SOI/MDI or the
ground based BISON network is significantly lower in this region than
in intensity measurements. This allows low degree modes to be observed
close to 1 mHz. We present results of detection and charaterization
of the lowest order observable p-modes both in velocity and intensity
measurements. Where applicable the properties of the modes observed
with the two methods are compared.
Title: The Effect of Amplitude Modulation on Asymmetries of Solar
p-Modes
Authors: Andersen, Bo; Leifsen, Torben; Appourchaux, Thierry; Frohlich,
Claus; Hoeksema, J. T.; Toutain, Thierry
Bibcode: 1998ESASP.418..893A
Altcode: 1998soho....6..893A
The low degree solar p-modes show an asymmetry in their line profiles
that both depend on the observational technique and on the radial
order of the modes. Typically the modes determined from observations
with Doppler shift methods show an asymmetry towards lower frequency
while the opposite is the case for modes determined from irradiance and
radiance observations. The difference in asymmetry is probably caused by
near surface effects. If the modes are fitted with symmetric functions
this leads to a systematic shift in the frequency determinations for
the two data sets. This may lead to systematic differences in the
inversions based on the different frequencies. All the mode amplitudes
show significant time variation. The typical centroid frequency also
varies with timescales from a few days to the solar cycle. These
variations may set absolute limits to the observable accuracy of the
frequency determination. These time modulations may influence the
observed line profiles and thus the frequency determinations. Here we
present results of the effect on the mode asymmetry of the amplitude
modulation of low degree modes observed with VIRGO and SOI/MDI. The
range in timescales is from a few days to a few solar rotations.
Title: Tri-Phonic Helioseismology: Comparison of Solar P Modes
Observed by the Helioseismology Instruments Aboard SOHO
Authors: Toutain, T.; Appourchaux, T.; Baudin, F.; Fröhlich, C.;
Gabriel, A.; Scherrer, P.; Andersen, B. N.; Bogart, R.; Bush, R.;
Finsterle, W.; García, R. A.; Grec, G.; Henney, C. J.; Hoeksema,
J. T.; Jiménez, A.; Kosovichev, A.; Roca Cortés, T.; Turck-Chièze,
S.; Ulrich, R.; Wehrli, C.
Bibcode: 1997SoPh..175..311T
Altcode:
The three helioseismology instruments aboard SOHO observe solar p modes
in velocity (GOLF and MDI) and in intensity (VIRGO and MDI). Time series
of two months duration are compared and confirm that the instruments
indeed observe the same Sun to a high degree of precision. Power
spectra of 108 days are compared showing systematic differences between
mode frequencies measured in intensity and in velocity. Data coverage
exceeds 97% for all the instruments during this interval. The weighted
mean differences (V-I) are −0.1 µHz for l=0, and −0.16 µHz for
l=1. The source of this systematic difference may be due to an asymmetry
effect that is stronger for modes seen in intensity. Wavelet analysis
is also used to compare the shape of the forcing functions. In these
data sets nearly all of the variations in mode amplitude are of solar
origin. Some implications for structure inversions are discussed.
Title: An estimate of the solar background irradiance power spectrum.
Authors: Rabello-Soares, M. C.; Roca Cortes, T.; Jimenez, A.; Andersen,
B. N.; Appourchaux, T.
Bibcode: 1997A&A...318..970R
Altcode:
Knowledge of the solar irradiance background is of great importance
to solar and stellar physics. In particular, its contribution
to the solar oscillations power spectrum is highly relevant as it
represents the ultimate limit to the sensitivity of solar oscillations'
observations. An analysis of the power spectra of the solar photometric
data coming from four different instruments - two space-borne (ACRIM
and IPHIR) and two earth-based instruments (SLOT and LOI-T) - has
been performed to obtain the upper limit to the solar irradiance
background's spectrum. These observations have been compared to a
numerical model computed for the non-coherent solar surface phenomena,
namely granulation, mesogranulation and supergranulation. There is an
overall good agreement between the general trend of the model and the
observed data.
Title: First results from VIRGO on SoHO
Authors: Frohlich, C.; Andersen, B. N.; Appourchaux, T.; Berthomieu,
G.; Crommelynck, D. A.; Domingo, V.; Fichot, A.; Finsterle, W.;
Gómez, M. F.; Gough, D.; Jiménez, A.; Leifsen, T.; Lombaerts, M.;
Pap, J. M.; Provost, J.; Roca Cortés, T.; Romero, J.; Roth, H. -J.;
Sekii, T.; Telljohann, U.; Toutain, T.; Wehrli, C.
Bibcode: 1997IAUS..181...67F
Altcode:
No abstract at ADS
Title: In-Flight Performance of the Virgo Luminosity Oscillations
Imager Aboard SOHO
Authors: Appourchaux, Thierry; Andersen, Bo N.; Fröhlich, Claus;
Jiménez, Antonio; Telljohann, Udo; Wehrli, Christoph
Bibcode: 1997SoPh..170...27A
Altcode:
The Luminosity Oscillations Imager (LOI) is a part of the VIRGO
instrument aboard the Solar and Heliospheric Observatory (SOHO). The
scientific objective of the LOI experiment is to identify and
characterize pressure and internal gravity oscillations of the Sun by
observing the radiance variations. The LOI is a low-resolution imager
with 12 pixels, for the measurement of the radiance distribution
over the solar disk at 500 nm. The low resolution capability of the
instrument allows the identification of individual azimuthal orders
for l = 0 to 7, without suffering the mixing that affects integrated
solar disk instruments. The performance, calibrations and instrumental
effects of the LOI are described together with the procedures for
extracting the solar p modes.
Title: First Results from VIRGO, the Experiment for Helioseismology
and Solar Irradiance Monitoring on SOHO
Authors: Fröhlich, Claus; Andersen, Bo N.; Appourchaux, Thierry;
Berthomieu, Gabrielle; Crommelynck, Dominique A.; Domingo, Vicente;
Fichot, Alain; Finsterle, Wolfgang; Gómez, Maria F.; Gough, Douglas;
Jiménez, Antonio; Leifsen, Torben; Lombaerts, Marc; Pap, Judit M.;
Provost, Janine; Roca Cortés, Teodoro; Romero, José; Roth, Hansjörg;
Sekii, Takashi; Telljohann, Udo; Toutain, Thierry; Wehrli, Christoph
Bibcode: 1997SoPh..170....1F
Altcode:
First results from the VIRGO experiment (Variability of solar IRradiance
and Gravity Oscillations) on the ESA/NASA Mission SOHO (Solar and
Heliospheric Observatory) are reported. The observations started
mid-January 1996 for the radiometers and sunphotometers and near the
end of March for the luminosity oscillation imager. The performance of
all the instruments is very good, and the time series of the first 4-6
months are evaluated in terms of solar irradiance variability, solar
background noise characteristics and p-mode oscillations. The solar
irradiance is modulated by the passage of active regions across the
disk, but not all of the modulation is straightforwardly explained in
terms of sunspot flux blocking and facular enhancement. Helioseismic
inversions of the observed p-mode frequencies are more-or-less in
agreement with the latest standard solar models. The comparison of
VIRGO results with earlier ones shows evidence that magnetic activity
plays a significant role in the dynamics of the oscillations beyond
its modulation of the resonant frequencies. Moreover, by comparing
the amplitudes of different components ofp -mode multiplets, each of
which are influenced differently by spatial inhomogeneity, we have
found that activity enhances excitation.
Title: Theoretical amplitudes of solar g-modes.
Authors: Andersen, B. N.
Bibcode: 1996A&A...312..610A
Altcode:
This work presents predictions on the amplitudes of solar g-modes. It is
based on the assumption that convective overshoot into the convectively
stable interior generates gravity waves. Based on this assumption it is
possible to estimate values for the amplitude of the g-modes below the
solar convection zone. Numerical simulations, giving the transmission
of gravity waves through the convection zone have been carried out for
5 different frequencies and horizontal extents equivalent to l-values
approximately in the range 6-18. The horizontal velocity amplitude of
solar g-modes near the solar surface is estimated to be in the range
0.01-5mm/s. The largest value assumes that all the available energy
from the excitation goes into a single mode. Using assumptions on the
ratio between intensity and velocity oscillations the amplitude in
intensity of a l=6 mode is estimated to be <=5x10^-7^.
Title: VIRGO: Experiment for Helioseismology and Solar Irradiance
Monitoring
Authors: Fröhlich, Claus; Romero, José; Roth, Hansjörg; Wehrli,
Christoph; Andersen, Bo N.; Appourchaux, Thierry; Domingo, Vicente;
Telljohann, Udo; Berthomieu, Gabrielle; Delache, Philippe; Provost,
Janine; Toutain, Thierry; Crommelynck, Dominique A.; Chevalier,
André; Fichot, Alain; Däppen, Werner; Gough, Douglas; Hoeksema,
Todd; Jiménez, Antonio; Gómez, Maria F.; Herreros, José M.; Cortés,
Teodoro Roca; Jones, Andrew R.; Pap, Judit M.; Willson, Richard C.
Bibcode: 1995SoPh..162..101F
Altcode:
The scientific objective of the VIRGO experiment (Variability of solar
IRradiance and Gravity Oscillations) is to determine the characteristics
of pressure and internal gravity oscillations by observing irradiance
and radiance variations, to measure the solar total and spectral
irradiance and to quantify their variability over periods of days to
the duration of the mission. With these data helioseismological methods
can be used to probe the solar interior. Certain characteristics of
convection and its interaction with magnetic fields, related to, for
example, activity, will be studied from the results of the irradiance
monitoring and from the comparison of amplitudes and phases of the
oscillations as manifest in brightness from VIRGO, in velocity from
GOLF, and in both velocity and continuum intensity from SOI/MDI. The
VIRGO experiment contains two different active-cavity radiometers for
monitoring the solar `constant', two three-channel sunphotometers (SPM)
for the measurement of the spectral irradiance at 402, 500 and 862 nm,
and a low-resolution imager (LOI) with 12 pixels, for the measurement
of the radiance distribution over the solar disk at 500 um. In this
paper the scientific objectives of VIRGO are presented, the instruments
and the data acquisition and control system are described in detail,
and their measured performance is given.
Title: Amplitudes of Solar G-Modes from Numerical Simulations
Authors: Andersen, B. N.
Bibcode: 1995ESASP.376b.413A
Altcode: 1995help.confP.413A; 1995soho....2..413A
No abstract at ADS
Title: Results from the Luminosity Oscillations Imager
Authors: Appourchaux, T.; Toutain, T.; Jiménez, A.; Rabello Soares,
M. C.; Andersen, B. N.; Jones, A. R.
Bibcode: 1995ESASP.376b.265A
Altcode: 1995help.confP.265A; 1995soho....2..265A
No abstract at ADS
Title: Frequencies and splittings of low-degree solar P modes:
results of the Luminosity Oscillations Imager.
Authors: Appourchaux, T.; Toutain, T.; Telljohann, U.; Jimenez, A.;
Rabello-Soares, M. C.; Andersen, B. N.; Jones, A. R.
Bibcode: 1995A&A...294L..13A
Altcode:
The Luminosity Oscillations Imager is a part of the VIRGO instrument
to be flown aboard the Solar and Heliospheric Observatory in mid
1995. Using a ground-based version of the instrument, we have detected
low-l modes with a time series spanning 163 days. The low resolution
capability of the instrument allows the identification of individual
tesseral orders for l=2 to 5. The data reduction method prevents from
observing the l=0 modes, and reduces the amplitude of the l=1 modes with
m=+/-1. The frequencies and, for the first time, the linear component
of the mode splitting (a_1_) are given for l=2 to 5 for each order
n. The frequencies and the a_1_ are obtained by fitting simultaneously
the 2l+1 spectra using maximum likelihood estimators. The splittings
are compared with other published values.
Title: Low Frequency Helioseismology
Authors: Fröhlich, C.; Andersen, B. N.
Bibcode: 1995ESASP.376a.137F
Altcode: 1995heli.conf..137F; 1995soho....1..137F
The main objective of low frequency helioseismology is the search
for solar g-modes which allows sounding of the core close to the
center. The analyses have been based on ground-based observations by
the Crimean Astrophysical Observatory, Stanford University, SCLERA,
Birmingham University, Instituto Astrofisica de Canarias and on
irradiance observations by ACRIM on the US Solar Maximum Mission
satellite and IPHIR on the Russian PHOBOS mission. The most intriguing
observation from the ground is the 160 minutes oscillation. Its
interpretation is still controversial and even the solar origin is
questioned. Interpretation of the observed spectra in the range from 45
- 140 μHz is mostly based on asymptotic theory, but the results do not
show consistent evidence that g-modes have been unambiguously detected.
Title: Virgo: Expriment for Helioseismology and Solar Irradiance
Monitoring
Authors: Fröhlich, C.; Andersen, B. N.
Bibcode: 1995ESASP.376a..83F
Altcode: 1995soho....1...83F; 1995heli.conf...83F
The scientific objective of the VIRGO experiment (Variability of solar
IRradiance and Gravity Oscillations) is to determine the characteristics
of pressure and internal gravity oscillations by observing irradiance
and radiance variations, to measure the solar total and spectral
irradiance and to quantify their variability over periods of days to
the duration of the mission. With these data helioseismological methods
can be used to probe the solar interior. Certain characteristics of
convection and its interaction with magnetic fields, related to, for
example, activity, will be studied from the results of the irradiance
monitoring and from the comparison of amplitudes and phases of the
oscillations as manifest in brightness from VIRGO, in velocity from
GOLF, and in both velocity and continuum intensity from SOI/MDI. The
VIRGO experiment contains two different active-cavity radiometers
for monitoring the solar "constant", two three-channel sunphotometers
(SPM) for the measurement of the spectral irradiance at 402, 500 and
862 nm, and a low-resolution imager (LOI) with 12 pixels, for the
measurement of the radiance distribution over the solar disk at 500
nm. The scientific objectives of VIRGO are presented, the instruments
and the data acquisition and control system are described in detail,
and their measured performance is given.
Title: Wavelet Analysis of IPHIR Data
Authors: Leifsen, T.; Hanssen, A.; Andersen, B. N.; Toutain, T.
Bibcode: 1995ASPC...76..520L
Altcode: 1995gong.conf..520L
No abstract at ADS
Title: VIRGO - the Solar Monitor Experiment on SOHO
Authors: Appourchaux, T.; Domingo, V.; Frohlich, C.; Romero, J.;
Wehrli, C.; Andersen, B. N.; Berthomieu, G.; Delache, P.; Crommelynck,
D.; Jimenez, A.; Roca Cortes, T.; Jones, A. R.
Bibcode: 1995ASPC...76..408A
Altcode: 1995gong.conf..408A
No abstract at ADS
Title: Excitation of Solar Gravity Waves
Authors: Andersen, B. N.
Bibcode: 1994SoPh..152..241A
Altcode: 1994svs..coll..241A; 1994IAUCo.143..241A
The interaction between convection and gravity waves are simulated
numerically in a model closely corresponding to the physical conditions
in the solar interior.The penetration of convective elements into
the stably stratified interior is shown to generate gravity waves. The
energy efficiency of this generation is less than 0.1 %. The simulations
also show that the convective overshoot region is very shallow,
0.02-0.06 pressure scaleheights.
Title: Solar Noise Simulations in Irradiance
Authors: Andersen, B. N.; Leifsen, T. E.; Toutain, T.
Bibcode: 1994SoPh..152..247A
Altcode: 1994IAUCo.143..247A; 1994svs..coll..247A
The global signature of granulation, meso- and supergranulation is
calculated using values for intensities and lifetimes from spatially
resolved observations. These simulations are compared with observations
from ACRIM, IPHIR and the SOVA-1 photometers. The results indicate that
the overall shape of the background signal in the simulations reproduce
the observations at low frequency. However when the granulation
lifetimes are about 500 seconds the simulated data do not correspond
to the observations between 1 and 2 mHz.
Title: Convection and Gravity Wave Interaction in the Solar Interior
Authors: Andersen, B. N.; Andreassen, O.; Wasberg, C. E.; Leifsen, T.
Bibcode: 1993ASPC...42...49A
Altcode: 1993gong.conf...49A
No abstract at ADS
Title: Gravity wave and convection interaction in the solar interior
Authors: Andreassen, O.; Andersen, B. N.; Wasberg, C. E.
Bibcode: 1992A&A...257..763A
Altcode:
Methods developed to numerically simulate hydrodynamic waves in the
terrestrial atmosphere have been utilized to investigate the similar
phenomena in the solar interior. The spectral collocation method
with open horizontal boundaries used is well suited for solar type
studies. The current study is the start of a program to investigate the
degree of penetration of gravity waves through the solar convection
zone and to investigate the possible excitation of gravity waves in
the solar interior by convection. The preliminary results indicate
that a significant fraction of the wave energy in a gravity type wave
in the convectively stable region in the solar interior may tunnel
through the solar convective zone to the surface. For a wave with a
horizontal extent equivalent to a global mode with degree l about 15
- 16 the energy transmission is of the order of 0.02 percent in the
current model.
Title: Model simulations of solar noise.
Authors: Andersen, B. N.
Bibcode: 1991dsoo.conf...15A
Altcode:
The need to understand the effects on radiance and irradiance from
the time development of solar surface structures like granulation,
mesogranulation and supergranulation is discussed in the context of
helioseismology. A simple model developed to simulate the broadband
background signal of solar origin, here designated solar noise, is
described. Some preliminary comparisons with existing observations are
given. The overall agreement between the simulations and observations
is good.
Title: Virgo-solar irradiance and radiance monitoring on SOHO
Authors: Andersen, Bo N.
Bibcode: 1991AdSpR..11d..93A
Altcode: 1991AdSpR..11...93A
The main scientific objective of the VIRGO Experiment (Variability
of solar IRradiance and Gravity Oscillations) on SOHO is to probe the
solar interior by helioseismology with p- and g-mode solar oscillations
determined from spectral irradiance (SPM) and radiance (LOI) variations
on time scales of minutes to the mission time. The emphasis will be
on the physical and dynamic structure in the vicinity of the solar
core. In combination with the two other Helioseismology experiments on
SOHO one will study excitation and damping of p and possibly global
g-modes. Moreover, the measurements of the variability of the solar
``constant'' and spectral irradiance over periods of days to the
mission time will yield information about solar surface structures,
the solar flux budget and accurate inputs for terrestrial climate
modelling. The VIRGO experiment contains two types of active cavity
radiometers for monitoring of the solar ``constant'', two three channel
sunphotometers (SPM) for the measurement of spectral irradiance at 395,
500 and 865 nm and a low resolution imager (LOI) with 12 pixels. The
status of the instrument development will be described. This
paper has been made with information provided by the VIRGO team,
see list in the paper.
Title: Gravity wave and convection interaction in the solar interior.
Authors: Andreassen, Ø.; Andersen, B. N.
Bibcode: 1991dsoo.conf...61A
Altcode:
Methods developed to numerically simulate hydrodynamic waves in the
terrestrial atmosphere have been utilized to investigate the similar
phenomena in the solar interior. The pseudo spectral method with open
horizontal boundaries used is well suited for solar type studies. The
current study is the start of a program to investigate the degree
of penetration of gravity waves through the solar convection zone
and to investigate the possible excitation of gravity waves in the
solar interior by convection. The preliminary results indicate that a
significant fraction of the wave energy in a gravity type wave in the
convectively stable region in the solar interior may tunnel through
the solar convective zone to the surface. For a wave with a horizontal
extent equivalent to a global mode with degree l about 15 - 16 the
energy transmission is of the order of 0.02% in the current model.
Title: Observations of Low-Degree Solar Oscillations with Few
Detector Elements
Authors: Appourchaux, T.; Andersen, B. N.
Bibcode: 1990SoPh..128...91A
Altcode: 1990IAUCo.121P..91A
The detection of low-degree solar oscillation modes with a specific
low-resolution detector configuration is investigated. The detector is
part of an instrument (the Luminosity Oscillations Imager) in the VIRGO
package, to be flown on SOHO. Various problems such as p- and g-mode
sensitivity, B and roll angle effects, modes isolation, cross-talk and
guiding effects are treated for a given detector configuration. The
computed sensitivity will enable the instrument to detect any type of
modes for l < 6.B and roll angle effects can be compensated by using
adequate filters for mode isolation. Guiding effects are small for
p-modes. Also some other complex high-degree mode effects are treated.
Title: Space research in Norway
Authors: Andersen, Bo; Soerensen, Berit
Bibcode: 1990ndre.rept.....A
Altcode:
Five aspects of the science program are addressed: space physics,
astrophysics, life sciences, space related facilities and ground based
observational sites. The results of the work of several scientists
and technologists, each assigned to a particular field of interest
and competence, are given. Publications and reports are included.
Title: Space research in Norway
Authors: Andersen, B. N.
Bibcode: 1990fets.nasa...39A
Altcode:
Norwegian activity in space science is summarized. Particular emphasis
is given to activities during 1988 and 1986. An overview of work carried
out in the area of space physics, astrophysics and life sciences is
presented. Study of ionospheric/magnetospheric processes carried out
at the University of Bergen is described. Substorm processes, auroral
emissions, large and small scale auroral dynamics and wave particle
interactions in the magnetosphere and polar ionosphere carried out at
the University of Oslo are outlined.
Title: The Norwegian scientific balloon, sounding-rocket and
ground-based programme for 1989-92
Authors: Andersen, B. N.; Gundersen, A.
Bibcode: 1989ESASP.291...13A
Altcode: 1989erbp.symp...13A
The Norwegian sounding rocket and balloon programs are reviewed. The
aim of these programs is to perform investigations into ionospheric
and magnetospheric processes. These investigations are supplemented
by a wide range of ground based support instrumentation. Tests with
recovery of payloads will be carried out at Andoya Rocket Range, partly
as preparation for microgravity experiments. The overall program for
the period 1989 to 1992 is reviewed.
Title: Solar Luminosity Oscillation Telescope (SLOT).
Authors: Andersen, Bo Nyborg; Domingo, V.; Jones, A. R.; Korzennik,
Sylvain G.; Jimenez, A.; Palle, Pere L.; Regulo, C.; Roca Cortés,
Teodoro
Bibcode: 1988ESASP.286..175A
Altcode: 1988ssls.rept..175A
Low degree l = 0-2 solar p-modes have been detected with the
SLOT instruments at Izaña and Baja California. The main source
of noise for these ground based observations is in the terrestrial
atmosphere. However, the data acquisition system still has to have very
slow intrinsic noise. The authors describe how this is achieved in the
SLOT instruments. They also give a general description of the design
and operating principles of the photometers and data acquisition system.
Title: VIRGO: The solar monitor experiment on SOHO.
Authors: Froehlich, C.; Andersen, Bo Nyborg; Berthomieu, G.;
Crommelynck, D.; Delache, Philippe; Domingo, V.; Jimenez, A.; Jones,
A. R.; Roca Cortés, Teodoro; Wehrli, Ch.
Bibcode: 1988ESASP.286..371F
Altcode: 1988ssls.rept..371F
The VIRGO Experiment (Variability of solar Irradiance and Gravity
Oscillations) contains two types of active cavity radiometers for
monitoring of the solar "constant", two three channel sunphotometers
(SPM) for the measurement of spectral irradiance at 335, 500 and 865 nm
and a low resolution imager (LOI) with 12 pixels. The main scientific
objective is probing the solar interior by helioseismology with p-
and g-mode solar oscillations determined from spectral irradiance
(SPM) and radiance (LOI) variations on time scales of minutes to
the mission time. Moreover, the measurements of the variability of
the solar "constant" and spectral irradiance over periods of days to
the mission time will yield information about the convection zone, as
will the comparison of the amplitudes and phases of the oscillations
as manifested in irradiance and radiance (from VIRGO) and velocity
(from GOLF and SOI).
Title: The GONG data reduction and analysis system.
Authors: Pintar, J. A.; Andersen, B.; Anderson, E. R.; Armet, D. B.;
Brown, T. M.; Hathaway, D. H.; Hill, F.; Jones, H. P.; GONG Data Team
Bibcode: 1988ESASP.286..217P
Altcode:
Each of the six GONG observing stations will produce three, 16-bit,
256×256 images of the Sun every 60 seconds of sunlight. These
data will be transferred from the observing sites to the GONG Data
Management and Analysis Center (DMAC), in Tucson, on high-density tapes
at a combined rate of over 1 gigabyte per day. The contemporaneous
processing of these data will produce several standard data products
and will require a sustained throughput in excess of 7 megaflops. Peak
rates may exceed 50 megaflops. Archives will accumulate at the rate
of approximately 1 terabyte per year, reaching nearly 3 terabytes in
three years of observing. Researchers will access the data products
with a machine-independent GONG Reduction and Analysis Software
Package (GRASP). Based on the Image Reduction and Analysis Facility
(IRAF), this package will include database facilities and helioseismic
analysis tools. Users may access the data as visitors in Tucson, or
may access DMAC remotely through networks, or may process subsets of
the data at their local institutions using GRASP or other systems of
their choice. Elements of the system will reach the prototype stage
by the end of 1988. Full operation is expected in 1992 when data
acquisition begins.
Title: Detector configurations for observations of gravity modes in
solar radiance.
Authors: Andersen, Bo Nyborg
Bibcode: 1988ESASP.286..381A
Altcode: 1988ssls.rept..381A
The VIRGO (Variability of Irradiance and Gravity Oscillations)
investigation has been selected to fly on the SOHO mission. One of the
components of VIRGO is a small imaging instrument with limited spatial
resolution. Calculations have been carried out in an attempt to find
an optimal geometrical detector configuration for the observation of
low degree g-modes in the solar luminosity. The constraints are given
as a wish of having the largest possible sensitivity and redundancy
with the smallest number of detectors. In addition the crosstalk for
different modes at same frequency should be minimized.
Title: Luminosity Oscillations Imager (LOI).
Authors: Andersen, Bo Nyborg; Domingo, V.; Jones, A. R.; Jimenez,
A.; Palle, Pere L.; Regulo, C.; Roca Cortés, Teodoro
Bibcode: 1988ESASP.286..385A
Altcode: 1988ssls.rept..385A
The VIRGO (Variability in Irradiance and Gravity Oscillations)
investigation has been selected to fly on ESA's SOHO mission. One of
the components of the VIRGO is a small imaging solar photometer. This
instrument, the Luminosity Oscillations Imager (LOI), will observe
the solar radiance with 12 pixels resolution. A prototype of the LOI
has been developed at ESTEC. This prototype was built mainly to test
possible detector configurations, the data acquisition system and the
internal guider. The prototype has been operating at Izaña, Tenerife
since April this year.
Title: VIRGO: The solar monitor experiment on SOHO
Authors: Froehlich, C.; Andersen, B. N.; Berthomieu, G.; Crommelynck,
D.; Delache, Ph.; Domingo, V.; Jimenez, A.; Jones, A. R.; Roca Cortes,
T.; Wehrli, Ch.
Bibcode: 1988sohi.rept...19F
Altcode:
The Variability of solar IRradiance and Gravity Oscillations (VIRGO)
experiment contains two types of active cavity radiometers for
monitoring of the solar constant, two three channel sunphotometers for
the measurement of spectral irradiance at 335, 500 and 865 nm and a
low resolution imager with 12 pixels. The main scientific objective
is probing the solar interior by helioseismology with p and g mode
solar oscillations determined from spectral irradiance and radiance
variations on time scales of minutes to the mission time. Information
about the convection zone is thus obtained. The comparison of the
amplitudes and phases of the oscillations as manifested in irradiance
and radiance (from VIRGO) and velocity as measured by the GOLF (global
oscillations at low frequencies) experiment are also used in analyzing
the convection zone.
Title: Diurnal photometric conditions at Teide observatory and
long-term solar irradiance variations
Authors: Andersen, B.; Domingo, V.; Jiménez, A.; Jones, A.; Korzennik,
S.; Pallé, P. L.; Pérez Hernández, F.; Régulo, C.; Roca Cortés,
T.; Tomás, L. L.
Bibcode: 1988SoPh..116..391A
Altcode:
Monochromatic extinction coefficients at four wavelengths have been
obtained over a period of more than two years at the Observatorio del
Teide (Izaña Tenerife) using a full disc, direct sunlight, quadruple
photometer devoted to the detection of integral luminosity oscillations
of the Sun. The mean extinction coefficients (0.13 at 500 nm) show
a seasonal variation of about 15%, the best atmospheric conditions
being in winter and autumn. Moreover, in anyone day the extinction
coefficient in the afternoon is always lower than the one in the
morning by ∼ 7%. A one-year period fluctuation, with an amplitude
of ∼ 0.035 mag, has been identified in the instrumental magnitudes
outside the atmosphere, and is interpreted as the variation produced
by the different Sun-Earth distance from winter to summer. Finally,
the study made to detect periodic time fluctuations in both, Sun's
magnitude and extinction coefficients, has given null results at levels
of ∼ 0.04 and ∼ 1.8%, respectively.
Title: Book reviews
Authors: Hovenier, J. W.; Kresák, Ľ.; Rawer, Karl; Zwartbol, T.;
Achterberg, A.; Marx, George; Andersen, B. N.; Icke, Vincent
Bibcode: 1988SSRv...46..199H
Altcode:
No abstract at ADS
Title: Groundbased Observations of Solar Luminosity Oscillations
Authors: Andersen, B. N.; Domingo, V.
Bibcode: 1988IAUS..123...67A
Altcode:
Results from ground based observations of low degree solar luminosity
variations are presented. By using data from up to 15 consecutive
excellent days the majority of the l = 0, 1 and 2 peaks in the region
2.5 - 3.5 mHz may marginally be identified.
Title: Radiation losses in chromospheric and transition region
emission lines from AD Leo (dM4e)
Authors: Sundland, S. R.; Pettersen, B. R.; Hawley, S. L.;
Kjeldseth-Moe, O.; Andersen, B. N.
Bibcode: 1988ASSL..143...61S
Altcode: 1988acse.conf...61S
The authors present line surface fluxes from the red dwarf flare star
AD Leo in its quiescent state. IUE and ground-based instruments cover
the UV and optical (1000 - 9000 Å) domains of the spectrum. The
observed radiation losses from chromospheric and transition region
lines amount to 4.0×106erg cm-2s-1 and
2.7×105erg cm-2s-1, respectively. The
authors estimate the total radiative energy loss in all lines formed
between 25.000K and 250.000K to be of the order of 106 -
107erg cm-2s-1.
Title: Solar Limb Effect and Meridional Flows - Results for FEI
512.4 543.4 and 709.0-NM
Authors: Andersen, B. N.
Bibcode: 1987SoPh..114..207A
Altcode:
Results of observations of the solar limb effect in the non-magnetic
lines FeI 512.4, 543.4, and 709.0 nm are presented. The detailed form of
the limb-effect curves depends on the line strength. The weakest line,
709.0, shows a relative blueshift with respect to heliocentric angle
from disc center to μ = 0.8 (μ = cos(heliocentric angle)). With
increasing line strength the relative blueshift disappears and the
redshift increases monotonically from the disc center to the limb. The
strongest line, 543.4, shows a nearly linear redshift with decreasing
μ, indicating little influence from horizontal motions.
Title: Book Review: Cosmic magnetism. / Adam Hilger
Authors: Andersen, B. N.
Bibcode: 1987SSRv...46..203A
Altcode: 1987SSRv...46..203S
No abstract at ADS
Title: The unusual rotational modulation of the UV radiation from
the spotted flare star EV Lac
Authors: Andersen, B. N.; Kjeldseth-Moe, O.; Pettersen, B. R.
Bibcode: 1986ESASP.263...87A
Altcode: 1986NIA86.......87A; 1986niia.conf...87A
The UV line spectrum of the spotted flare star EV Lac in its quiescent
state was observed with IUE. The observed rotational modulation
of chromospheric UV lines is in antiphase with the photospheric
variations in visual light. The visual variation is due to a starspot
region located near the pole of the star. The transition region lines
(80,000 K less than T less than 200,000 K) show no variation. This may
indicate a large extent in altitude of the transition region causing
the emitting regions to be visible throughout the rotation.
Title: Optical and UV observations of a giant stellar flare on AD Leo
Authors: Pettersen, B. R.; Hawley, S. L.; Andersen, B. N.
Bibcode: 1986ESASP.263..157P
Altcode: 1986NIA86......157P; 1986niia.conf..157P
A giant stellar flare has been observed on the dM4e star AD Leo
simultaneously with IUE and ground-based instrumentation. The
authors present and discuss observations obtained in a 15 minutes
interval around flare maximum. A continuum flux distribution of
flare light is obtained, based on a SWP spectrum and UBVR photometry
corrected for the influence of emission lines. A high temperature
(107K) free-free distribution describes the optical data
well, but the observed ultraviolet flux is at least one order of
magnitude smaller. No single radiation process describes the time
averaged flux distribution. Line broadening is evident in hydrogen
Balmer emission lines. The Inglis-Teller formula implies an upper
limit of 6×1013cm-3 for the electron density.
Title: The effect of spatial smearing on solar Doppler
measurements. II. General formulation and application to limb effect
and large-scale velocity fields.
Authors: Andersen, B. N.
Bibcode: 1986SoPh..107...27A
Altcode: 1987SoPh..107...27A
A general mathematical formulation of the effect of spatial smearing
on solar velocity measurements is presented. The variations of the
straylight induced error with wavelength and line parameters are
discussed. The spatial and time dependence of the error will influence
the measurement of solar limb effect and may introduce fictitious
large scale velocity fields with amplitudes of the order of a few m/s.
Title: Ground based measurements of global solar intensity
oscillations
Authors: Andersen, B. N.
Bibcode: 1986ASIC..169..339A
Altcode: 1986ssds.proc..339A
An instrument designed to observe solar-intensity oscillations with
low l values from ground sites is described. This instrument measures
the relative change in the line equivalent width. By taking the ratio
between the integrated line intensity and a nearby continuum, the effect
of variations in the atmospheric transmission is to a large extent
removed. The instrument is expected to have an accuracy of 2-5 ppm.
Title: The limb effect of the K i resonance line, 769.9 n m
Authors: Andersen, B. N.; Barth, S.; Hansteen, V.; Leifsen, T.; Lilje,
P. B.; Vikanes, F.
Bibcode: 1985SoPh...99...17A
Altcode:
Low-noise observations have been obtained to search for a possible limb
effect in the K I 769.9 nm resonance line. The observations were carried
out along the north/south diameter of the solar disc. The data were
individually corrected for the effects of straylight on the velocity
measurements. A small, but significant limb effect is detected. The
total shift in the line core from center to limb corresponds to 125
m s−1 with an uncertainty of < 30 m s−1.
Title: Straylight Correction to Doppler Rotation Measurements
Authors: Andersen, B. N.
Bibcode: 1985SoPh...98..173A
Altcode:
The data published by Pierce and LoPresto (1984) are corrected for
straylight. This correction increases the observed equatorial rotation
velocity from 1977 to 2004 m s −1. The correction has an
uncertainty of approximately 10 m s−1 because the accurate
form of the straylight function is not available.
Title: The Effect of Spatial Smearing on Solar Doppler Measurements -
Part One - Mathematical Formulation and Applicaiton to Measurements
of Solar Rotation
Authors: Albregtsen, F.; Andersen, B. N.
Bibcode: 1985SoPh...95..239A
Altcode:
A mathematical method for calculating the influence of scattered light
on solar Doppler measurements is developed and presented.
Title: Limb Effect of Solar Absorption Lines - Observational Method
and Results for FEI 557.6-NM
Authors: Andersen, B. N.
Bibcode: 1984SoPh...94...49A
Altcode:
Low-noise limb-effect observations of the non-magnetic line FeI
557.6 nm are presented. Separate measurements along the solar equator
and the meridian have been carried out and have been corrected for
scattered light. The limb-effect line shifts at the pole and at the
equatorial limb are found to be equal. The detailed shape of the limb
effect along the meridian is found to differ significantly from that
along the equator. This difference can be explained by the presence
of a meridional circulation pattern, with horizontal flows <
50 m−1 from both the equator and poles toward ± 45°
latitude. Alternatively the meridian/equator difference may be caused
by a combination of latitude dependence of the granular parameters. An
increase with latitude of the granular velocity scale height, contrast,
or mean sizes could explain the observations.
Title: Influence of active regions on global oscillation measurements
Authors: Andersen, B. N.
Bibcode: 1984MmSAI..55..339A
Altcode:
The influence of active regions on line of sight velocity measurements
is discussed. The results from a model that includes the effects of
sunspots and closely reproduces the data of Claverie et al. (1982)
are presented. The effect of sunspots on the integrated velocity signal
is closely related to the active region/photosphere line contrast. It
is shown that the resonance lines are not ideally suited for these
measurements. Other choices of spectral lines are discussed.
Title: Straylight influence on measurements of solar velocity
oscillations
Authors: Albregtsen, F.; Andersen, B. N.
Bibcode: 1984MmSAI..55..345A
Altcode:
Doppler measurements of solar velocity oscillations with apertures
without axial symmetric averaging will be strongly influenced by
the long range straylight (scattering) and its time variation. The
corresponding error signal is of the same magnitude as the global
velocity oscillation signal. For spectral lines with a large limb
effect, the straylight will also introduce appreciable errors in
observations performed with axisymmetric apertures (e.g., Stanford and
the Crimea) as well as in full disk measurements. Time variations in
the scattering will introduce quasi-periodic velocity components with
both daily and seasonal periods.
Title: A new method for measurement of granular velocities.
Authors: Andersen, B. N.
Bibcode: 1984ITABO..61.....A
Altcode:
A new, supplementary method to measure granular velocities is
presented. The method utilizes the Doppler shift caused by the line
of sight component of the solar rotation to cause a wavelength shift
through spectral lines as function of heliocentric angle. By measuring
the center-to-limb variation of the granular intensity fluctuations
at different wavelength positions in the lines, the velocities are
found. To do this, assumptions regarding the geometrical structure of
the velocity and intensity fields have to be made.
Title: Intensity Oscillations in Solar Spectral Lines
Authors: Andersen, B. N.
Bibcode: 1984LIACo..25..220A
Altcode: 1984trss.conf..220A; 1984tpss.conf..220A
No abstract at ADS
Title: A New Method for Measurement of Granular Velocities
Authors: Andersen, B. N.
Bibcode: 1984itab.rept....1A
Altcode:
No abstract at ADS
Title: Has rapid solar core rotation been observed?
Authors: Andersen, B. N.; Maltby, P.
Bibcode: 1983Natur.302..808A
Altcode:
Internal rotation and gravitational quadropole moment of the Sun are
of interest to solar physics, the study of stellar structure and to
investigations related to the test of gravitational theories. High
precision measurements of fluctuations in the limb darkening function
and in the spectral line shifts have raised the possibility that the
interior of the Sun may be studied more directly than had previously
been possible. Recently, Claverie et al.1 argued that
their detection of a 13.1+/-0.2 day velocity signal give further
experimental evidence that the solar core is rotating more rapidly
than the observable surface. We show here that the phase as well as the
magnitude of the observed signal amplitude may be predicted without any
rapid core rotation by taking into account the presence of sunspots
and their contribution to the spectral line profile as integrated
over the disk of the Sun. Hence, we conclude that the existence of
a 13.1-day apparently periodic velocity signal with amplitude 6.5 m
s-1 during the 88 days observing period cannot be taken as
evidence for a rapidly rotating solar core.
Title: An unusual flare on EV Lac
Authors: Andersen, B. N.
Bibcode: 1983ASSL..102..203A
Altcode: 1983ards.proc..203A; 1983IAUCo..71..203A
One of four flares observed photoelectrically on the flare star EV
Lac during October 1979 is shown and discussed. A clear preflare
dip of 12 percent is visible in the blue channel while no preflare
activity is visible in H-alpha. Both the primary and secondary maxima
occur about 10 s later in H-alpha than in BG12. The most anomalous
feature of this flare is the very large and sharply peaked amplitude
observed in the H-alpha filter. Even if the delayed maximum could
indicate a significant contribution from the H-alpha line, the sharp
peak demonstrates that the emission is continuum dominated. In terms
of absolute energy per wavelength unit the emission in the H-alpha
filter is roughly nine times that in BG12. This is larger than the
results indicated by Bruevich et al. (1979).
Title: Kinematics of a loop prominence.
Authors: Engvold, O.; Jensen, E.; Andersen, B. N.
Bibcode: 1979SoPh...62..331E
Altcode:
The kinematics of a loop system has been studied from high resolution
Ca II K line spectra and Hα filtergrams recorded at Oslo Solar
Observatory.
Title: Kinematics of a system of loop prominences
Authors: Engvold, O.; Jensen, E.; Andersen, B. N.
Bibcode: 1979phsp.coll..237E
Altcode: 1979IAUCo..44..237E; 1979phsp.conf..237E
An analysis of the mass motion of solar flare loop prominences
is presented based on 72 K-line and Ca II spectra of a system of
bright loop prominences observed on April 23, 1978 at the Oslo Solar
Observatory. The spectral characteristics are compared with the simplest
model possible, that of free fall of matter under gravity along the
legs of the loops, assuming that the outlines of the loops reflect
the form of the magnetic lines of force. The line of sight velocity
is then computed as a function of distance from the top of the loop
by multiplication with the cosine of the angle between the line of
sight and the tangent to the dipole line of force. The spectral data
are in accordance with a model where the matter starts from rest at
the top of the loop and falls down along the legs. The present loop
system matches the line of force of a dipole for the scale, R, of the
dipole loop between 110,000 and 150,000 km. Since the observed heights
of the loops are 60-90,000 km it is concluded that the dipole origin
is located in the neighborhood of 50,000 km below the photosphere.
Title: Bouguer anomaly map of Denmark and surrounding waters
Authors: Bedsted; Andersen; Ole
Bibcode: 1978bamd.book.....B
Altcode: 1978QB1.D256d44....
No abstract at ADS
Title: Simultaneous Two Channel Photoelectric Observations of EV Lac
Authors: Andersen, B. N.
Bibcode: 1976IBVS.1084....1A
Altcode:
No abstract at ADS
Title: Search for stellar flare activity.
Authors: Andersen, B. N.; Pettersen, B. R.
Bibcode: 1975A&A....41..459A
Altcode:
Criteria for flare star selection are derived, and a list of candidates
is presented. The BG 12 filter is found suitable for flare star search
with small telescopes. Flare activity is discovered on Gliese 109.
Title: Continuous Photoelectric Observations of EV Lac during the
1973 International Patrol
Authors: Andersen, B. N.; Pettersen, B. R.
Bibcode: 1974IBVS..874....1A
Altcode:
No abstract at ADS
Title: Continuous Photoelectric Photometry of AD Leo during the 1973
International Patrol
Authors: Pettersen, B. R.; Andersen, B. N.
Bibcode: 1973IBVS..791....1P
Altcode:
No abstract at ADS
Title: Continuous Photoelectric Monitoring of EV Lac during the
International Patrol, September 1-15, 1972
Authors: Andersen, B. N.; Pettersen, B. R.
Bibcode: 1972IBVS..723....1A
Altcode:
No abstract at ADS