Kravtsov, Vadim; Veledina, Alexandra; Berdyugin, Andrei V.; Zdziarski, Andrzej A.; Henson, Gary D.; Piirola, Vilppu; Sakanoi, Takeshi; Kagitani, Masato; Berdyugina, Svetlana V.; Poutanen, Juri
Peering into the tilted heart of Cyg X-1 with high-precision optical polarimetry Journal Article
In: Astronomy and Astrophysics, vol. 678, pp. A58, 2023.
@article{2023A&A...678A..58K,
title = {Peering into the tilted heart of Cyg X-1 with high-precision optical polarimetry},
author = {Vadim Kravtsov and Alexandra Veledina and Andrei V. Berdyugin and Andrzej A. Zdziarski and Gary D. Henson and Vilppu Piirola and Takeshi Sakanoi and Masato Kagitani and Svetlana V. Berdyugina and Juri Poutanen},
doi = {10.1051/0004-6361/202346932},
year = {2023},
date = {2023-10-01},
urldate = {2023-10-01},
journal = {Astronomy and Astrophysics},
volume = {678},
pages = {A58},
abstract = {We present high-precision optical polarimetric observations of the black
hole X-ray binary Cygnus X-1 that span several cycles of its
5.6-day orbital period. The week-long observations on two
telescopes located in opposite hemispheres allowed us to track
the evolution of the polarization within one orbital cycle with
the highest temporal resolution to date. Using the field stars,
we determined the interstellar polarization in the source
direction and subsequently its intrinsic polarization P$_int$ = 0.82%ensuremathpm0.15% with a polarization angle ensuremaththeta$_int$ = 155textdegree
ensuremathpm5textdegree. The optical polarization angle
is aligned with that in the X-rays recently obtained with the
Imaging X-ray Polarimetry Explorer. Furthermore, it is
consistent within the uncertainties with the position angle of
the radio ejections. We show that the intrinsic polarization
degree is variable with the orbital period with an amplitude of
ensuremathsim0.2% and discuss various sites of its
production. Assuming that the polarization arises from a single
Thomson scattering of the primary star radiation by the matter
that follows the black hole in its orbital motion, we
constrained the inclination of the binary orbit i >
120textdegree and its eccentricity e < 0.08. The asymmetric
shape of the orbital profiles of the Stokes parameters also
implies the asymmetry of the scattering matter distribution in
the orbital plane, which may arise from the tilted accretion
disk. We compared our data to the polarimetric observations made
in 1975-1987 and find good agrement within 1textdegree
between the intrinsic polarization angles. On the other hand,
the polarization degree decreased by 0.4% over half a century,
suggesting secular changes in the geometry of the accreting
matter.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present high-precision optical polarimetric observations of the black
hole X-ray binary Cygnus X-1 that span several cycles of its
5.6-day orbital period. The week-long observations on two
telescopes located in opposite hemispheres allowed us to track
the evolution of the polarization within one orbital cycle with
the highest temporal resolution to date. Using the field stars,
we determined the interstellar polarization in the source
direction and subsequently its intrinsic polarization P$_int$ = 0.82%ensuremathpm0.15% with a polarization angle ensuremaththeta$_int$ = 155textdegree
ensuremathpm5textdegree. The optical polarization angle
is aligned with that in the X-rays recently obtained with the
Imaging X-ray Polarimetry Explorer. Furthermore, it is
consistent within the uncertainties with the position angle of
the radio ejections. We show that the intrinsic polarization
degree is variable with the orbital period with an amplitude of
ensuremathsim0.2% and discuss various sites of its
production. Assuming that the polarization arises from a single
Thomson scattering of the primary star radiation by the matter
that follows the black hole in its orbital motion, we
constrained the inclination of the binary orbit i >
120textdegree and its eccentricity e < 0.08. The asymmetric
shape of the orbital profiles of the Stokes parameters also
implies the asymmetry of the scattering matter distribution in
the orbital plane, which may arise from the tilted accretion
disk. We compared our data to the polarimetric observations made
in 1975-1987 and find good agrement within 1textdegree
between the intrinsic polarization angles. On the other hand,
the polarization degree decreased by 0.4% over half a century,
suggesting secular changes in the geometry of the accreting
matter.
hole X-ray binary Cygnus X-1 that span several cycles of its
5.6-day orbital period. The week-long observations on two
telescopes located in opposite hemispheres allowed us to track
the evolution of the polarization within one orbital cycle with
the highest temporal resolution to date. Using the field stars,
we determined the interstellar polarization in the source
direction and subsequently its intrinsic polarization P$_int$ = 0.82%ensuremathpm0.15% with a polarization angle ensuremaththeta$_int$ = 155textdegree
ensuremathpm5textdegree. The optical polarization angle
is aligned with that in the X-rays recently obtained with the
Imaging X-ray Polarimetry Explorer. Furthermore, it is
consistent within the uncertainties with the position angle of
the radio ejections. We show that the intrinsic polarization
degree is variable with the orbital period with an amplitude of
ensuremathsim0.2% and discuss various sites of its
production. Assuming that the polarization arises from a single
Thomson scattering of the primary star radiation by the matter
that follows the black hole in its orbital motion, we
constrained the inclination of the binary orbit i >
120textdegree and its eccentricity e < 0.08. The asymmetric
shape of the orbital profiles of the Stokes parameters also
implies the asymmetry of the scattering matter distribution in
the orbital plane, which may arise from the tilted accretion
disk. We compared our data to the polarimetric observations made
in 1975-1987 and find good agrement within 1textdegree
between the intrinsic polarization angles. On the other hand,
the polarization degree decreased by 0.4% over half a century,
suggesting secular changes in the geometry of the accreting
matter.
Fischer, Catherine; Woeger, Friedrich; Rimmele, Thomas; Keys, Peter; Steiner, Oskar; Gangadharan, Vigeesh; Jafarzadeh, Shahin; Cuissa, Jose Roberto Canivete
Chromospheric horizontal propagating shock waves revealed by fast cadence imaging in Ca II K with DKIST's Visible Broadband Imager Proceedings Article
In: AAS/Solar Physics Division Meeting, pp. 407.03, 2023.
@inproceedings{2023SPD....5440703F,
title = {Chromospheric horizontal propagating shock waves revealed by fast cadence imaging in Ca II K with DKIST's Visible Broadband Imager},
author = {Catherine Fischer and Friedrich Woeger and Thomas Rimmele and Peter Keys and Oskar Steiner and Vigeesh Gangadharan and Shahin Jafarzadeh and Jose Roberto Canivete Cuissa},
year = {2023},
date = {2023-10-01},
urldate = {2023-10-01},
booktitle = {AAS/Solar Physics Division Meeting},
volume = {55},
pages = {407.03},
series = {AAS/Solar Physics Division Meeting},
abstract = {The Daniel K. Inouye Solar Telescope is currently acquiring first
science data as part of its Operations Commissioning Phase.
High-resolution, fast-cadence imaging in the chromospheric Ca II
K filter of the Visible Broadband Imager reveals signatures of
bright arches emanating radially from the locations of G-band
bright points. The G-band bright points denote small-scale
magnetic elements harboring strong magnetic fields. Comparison
with 3-D simulations suggest that the traveling bright arches
are acoustic waves or shock fronts, triggered by the movements
of magnetic elements. Inspecting several examples of the events
we indeed see the photospheric bright points changing their
appearance and position, indicating either a horizontal
movement, perhaps swaying, or rotation and seem to be the source
location for the bright arches.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
The Daniel K. Inouye Solar Telescope is currently acquiring first
science data as part of its Operations Commissioning Phase.
High-resolution, fast-cadence imaging in the chromospheric Ca II
K filter of the Visible Broadband Imager reveals signatures of
bright arches emanating radially from the locations of G-band
bright points. The G-band bright points denote small-scale
magnetic elements harboring strong magnetic fields. Comparison
with 3-D simulations suggest that the traveling bright arches
are acoustic waves or shock fronts, triggered by the movements
of magnetic elements. Inspecting several examples of the events
we indeed see the photospheric bright points changing their
appearance and position, indicating either a horizontal
movement, perhaps swaying, or rotation and seem to be the source
location for the bright arches.
science data as part of its Operations Commissioning Phase.
High-resolution, fast-cadence imaging in the chromospheric Ca II
K filter of the Visible Broadband Imager reveals signatures of
bright arches emanating radially from the locations of G-band
bright points. The G-band bright points denote small-scale
magnetic elements harboring strong magnetic fields. Comparison
with 3-D simulations suggest that the traveling bright arches
are acoustic waves or shock fronts, triggered by the movements
of magnetic elements. Inspecting several examples of the events
we indeed see the photospheric bright points changing their
appearance and position, indicating either a horizontal
movement, perhaps swaying, or rotation and seem to be the source
location for the bright arches.
McKenzie, David; Ishikawa, Ryohko; Bueno, Javier Trujillo; Auch`ere, Frédéric; Kobayashi, Ken; Winebarger, Amy; Kano, Ryouhei; Song, Donguk; Okamoto, Takenori; Kobelski, Adam; Rachmeler, Laurel; Pontieu, Bart De; Vigil, Genevieve; Belluzzi, Luca; Ballester, Ernest Alsina; Aleman, Tanaus'u Pino; Bethge, Christian; Sakao, Taro; Stepan, Jiri
Demonstration of Chromospheric Magnetic Mapping with CLASP2.1 Proceedings Article
In: AAS/Solar Physics Division Meeting, pp. 401.04, 2023.
@inproceedings{2023SPD....5440104M,
title = {Demonstration of Chromospheric Magnetic Mapping with CLASP2.1},
author = {David McKenzie and Ryohko Ishikawa and Javier Trujillo Bueno and Frédéric Auch`ere and Ken Kobayashi and Amy Winebarger and Ryouhei Kano and Donguk Song and Takenori Okamoto and Adam Kobelski and Laurel Rachmeler and Bart De Pontieu and Genevieve Vigil and Luca Belluzzi and Ernest Alsina Ballester and Tanaus'u Pino Aleman and Christian Bethge and Taro Sakao and Jiri Stepan},
year = {2023},
date = {2023-10-01},
urldate = {2023-10-01},
booktitle = {AAS/Solar Physics Division Meeting},
volume = {55},
pages = {401.04},
series = {AAS/Solar Physics Division Meeting},
abstract = {Probing the magnetic nature of the Sun's chromosphere requires
measurement of the polarization profiles of relevant
magnetically sensitive spectral lines, many of which are in the
ultraviolet spectrum, necessitating observations above the
absorbing terrestrial atmosphere. The CLASP series of sounding
rocket missions were designed to develop and test a technique
for observing the Sun in ultraviolet light, and for quantifying
the polarization of that light. By demonstrating successful
measurement and interpretation of the polarization in hydrogen
Lyman-ensuremathalpha and the Mg II h and k spectral
lines, these missions are crucial steps towards routine
quantitative characterization of the local thermal and magnetic
conditions in the solar chromosphere. In the most recent
observations, CLASP2.1, the spectrograph slit was scanned across
an active region plage to acquire a two-dimensional map of
Stokes V/I, to demonstrate the ability of UV spectropolarimetry
to yield chromospheric magnetic fields over a large area. The
technique yields a set of simultaneous line-of-sight
magnetograms at multiple heights within the plage atmosphere. By
combining the CLASP2.1 measurements with magnetograms from
Hinode/SOT or SDO/HMI, a wide range of atmospheric heights are
mapped, from the photosphere to the upper chromosphere.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
Probing the magnetic nature of the Sun's chromosphere requires
measurement of the polarization profiles of relevant
magnetically sensitive spectral lines, many of which are in the
ultraviolet spectrum, necessitating observations above the
absorbing terrestrial atmosphere. The CLASP series of sounding
rocket missions were designed to develop and test a technique
for observing the Sun in ultraviolet light, and for quantifying
the polarization of that light. By demonstrating successful
measurement and interpretation of the polarization in hydrogen
Lyman-ensuremathalpha and the Mg II h and k spectral
lines, these missions are crucial steps towards routine
quantitative characterization of the local thermal and magnetic
conditions in the solar chromosphere. In the most recent
observations, CLASP2.1, the spectrograph slit was scanned across
an active region plage to acquire a two-dimensional map of
Stokes V/I, to demonstrate the ability of UV spectropolarimetry
to yield chromospheric magnetic fields over a large area. The
technique yields a set of simultaneous line-of-sight
magnetograms at multiple heights within the plage atmosphere. By
combining the CLASP2.1 measurements with magnetograms from
Hinode/SOT or SDO/HMI, a wide range of atmospheric heights are
mapped, from the photosphere to the upper chromosphere.
measurement of the polarization profiles of relevant
magnetically sensitive spectral lines, many of which are in the
ultraviolet spectrum, necessitating observations above the
absorbing terrestrial atmosphere. The CLASP series of sounding
rocket missions were designed to develop and test a technique
for observing the Sun in ultraviolet light, and for quantifying
the polarization of that light. By demonstrating successful
measurement and interpretation of the polarization in hydrogen
Lyman-ensuremathalpha and the Mg II h and k spectral
lines, these missions are crucial steps towards routine
quantitative characterization of the local thermal and magnetic
conditions in the solar chromosphere. In the most recent
observations, CLASP2.1, the spectrograph slit was scanned across
an active region plage to acquire a two-dimensional map of
Stokes V/I, to demonstrate the ability of UV spectropolarimetry
to yield chromospheric magnetic fields over a large area. The
technique yields a set of simultaneous line-of-sight
magnetograms at multiple heights within the plage atmosphere. By
combining the CLASP2.1 measurements with magnetograms from
Hinode/SOT or SDO/HMI, a wide range of atmospheric heights are
mapped, from the photosphere to the upper chromosphere.
Janett, Gioele; Ballester, Ernest Alsina; Belluzzi, Luca; Alemán, Tanaus'u Pino; Bueno, Javier Trujillo
The impact of angle-dependent partial frequency redistribution on the scattering polarization of the solar Na i D lines Journal Article
In: arXiv e-prints, pp. arXiv:2309.12880, 2023.
@article{2023arXiv230912880J,
title = {The impact of angle-dependent partial frequency redistribution on the scattering polarization of the solar Na i D lines},
author = {Gioele Janett and Ernest Alsina Ballester and Luca Belluzzi and Tanaus'u Pino Alemán and Javier Trujillo Bueno},
doi = {10.48550/arXiv.2309.12880},
year = {2023},
date = {2023-09-01},
urldate = {2023-09-01},
journal = {arXiv e-prints},
pages = {arXiv:2309.12880},
abstract = {The long-standing paradox of the linear polarization signal of the Na i
D1 line was recently resolved by accounting for the atom's
hyperfine structure and the detailed spectral structure of the
incident radiation field. That modeling relied on the
simplifying angle-averaged (AA) approximation for partial
frequency redistribution (PRD) in scattering, which potentially
neglects important angle-frequency couplings. This work aims at
evaluating the suitability of a PRD-AA modeling for the D1 and
D2 lines through comparisons with general angle-dependent (AD)
PRD calculations, both in the absence and presence of magnetic
fields. We solved the radiative transfer problem for polarized
radiation in a one-dimensional semi-empirical atmospheric model
with microturbulent and isotropic magnetic fields, accounting
for PRD effects, comparing PRD-AA and PRD-AD modelings. The D1
and D2 lines are modeled separately as two-level atomic system
with hyperfine structure. The numerical results confirm that a
spectrally structured radiation field induces linear
polarization in the D1 line. However, the PRD-AA approximation
greatly impacts the Q/I shape, producing an antisymmetric
pattern instead of the more symmetric PRD-AD one, while
presenting a similar sensitivity to magnetic fields between 10
and 200 G. Under the PRD-AA approximation, the Q/I profile of
the D2 line presents an artificial dip in its core, which is not
found for the PRD-AD case. We conclude that accounting for PRD-
AD effects is essential to suitably model the scattering
polarization of the Na i D lines. These results bring us closer
to exploiting the full diagnostic potential of these lines for
the elusive chromospheric magnetic fields.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The long-standing paradox of the linear polarization signal of the Na i
D1 line was recently resolved by accounting for the atom's
hyperfine structure and the detailed spectral structure of the
incident radiation field. That modeling relied on the
simplifying angle-averaged (AA) approximation for partial
frequency redistribution (PRD) in scattering, which potentially
neglects important angle-frequency couplings. This work aims at
evaluating the suitability of a PRD-AA modeling for the D1 and
D2 lines through comparisons with general angle-dependent (AD)
PRD calculations, both in the absence and presence of magnetic
fields. We solved the radiative transfer problem for polarized
radiation in a one-dimensional semi-empirical atmospheric model
with microturbulent and isotropic magnetic fields, accounting
for PRD effects, comparing PRD-AA and PRD-AD modelings. The D1
and D2 lines are modeled separately as two-level atomic system
with hyperfine structure. The numerical results confirm that a
spectrally structured radiation field induces linear
polarization in the D1 line. However, the PRD-AA approximation
greatly impacts the Q/I shape, producing an antisymmetric
pattern instead of the more symmetric PRD-AD one, while
presenting a similar sensitivity to magnetic fields between 10
and 200 G. Under the PRD-AA approximation, the Q/I profile of
the D2 line presents an artificial dip in its core, which is not
found for the PRD-AD case. We conclude that accounting for PRD-
AD effects is essential to suitably model the scattering
polarization of the Na i D lines. These results bring us closer
to exploiting the full diagnostic potential of these lines for
the elusive chromospheric magnetic fields.
D1 line was recently resolved by accounting for the atom's
hyperfine structure and the detailed spectral structure of the
incident radiation field. That modeling relied on the
simplifying angle-averaged (AA) approximation for partial
frequency redistribution (PRD) in scattering, which potentially
neglects important angle-frequency couplings. This work aims at
evaluating the suitability of a PRD-AA modeling for the D1 and
D2 lines through comparisons with general angle-dependent (AD)
PRD calculations, both in the absence and presence of magnetic
fields. We solved the radiative transfer problem for polarized
radiation in a one-dimensional semi-empirical atmospheric model
with microturbulent and isotropic magnetic fields, accounting
for PRD effects, comparing PRD-AA and PRD-AD modelings. The D1
and D2 lines are modeled separately as two-level atomic system
with hyperfine structure. The numerical results confirm that a
spectrally structured radiation field induces linear
polarization in the D1 line. However, the PRD-AA approximation
greatly impacts the Q/I shape, producing an antisymmetric
pattern instead of the more symmetric PRD-AD one, while
presenting a similar sensitivity to magnetic fields between 10
and 200 G. Under the PRD-AA approximation, the Q/I profile of
the D2 line presents an artificial dip in its core, which is not
found for the PRD-AD case. We conclude that accounting for PRD-
AD effects is essential to suitably model the scattering
polarization of the Na i D lines. These results bring us closer
to exploiting the full diagnostic potential of these lines for
the elusive chromospheric magnetic fields.
Makela, Jonathan; Wu, Qian; Monstein, Christian; Habarulema, John Bosco; Groves, Keith; Jakowski, Norbert; Amory, Cristine
Ground-based infrastructure for improved space weather specification at low latitudes Journal Article
In: Bulletin of the AAS, vol. 55, no. 3, 2023, (https://baas.aas.org/pub/2023n3i259).
@article{Makela2023Ground,
title = {Ground-based infrastructure for improved space weather specification at low latitudes},
author = {Jonathan Makela and Qian Wu and Christian Monstein and John Bosco Habarulema and Keith Groves and Norbert Jakowski and Cristine Amory},
year = {2023},
date = {2023-07-01},
urldate = {2023-07-01},
journal = {Bulletin of the AAS},
volume = {55},
number = {3},
note = {https://baas.aas.org/pub/2023n3i259},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Gordo, Javier Bussons; Ruiz, Mario Fernández; Mateo, Manuel Prieto; D'iaz, Jorge Alvarado; de la O, Francisco Chávez; Hidalgo, J. Ignacio; Monstein, Christian
Automatic Burst Detection in Solar Radio Spectrograms Using Deep Learning: deARCE Method Journal Article
In: Solar Physics, vol. 298, no. 6, pp. 82, 2023.
@article{2023SoPh..298...82B,
title = {Automatic Burst Detection in Solar Radio Spectrograms Using Deep Learning: deARCE Method},
author = {Javier Bussons Gordo and Mario Fernández Ruiz and Manuel Prieto Mateo and Jorge Alvarado D'iaz and Francisco Chávez de la O and J. Ignacio Hidalgo and Christian Monstein},
doi = {10.1007/s11207-023-02171-0},
year = {2023},
date = {2023-06-01},
urldate = {2023-06-01},
journal = {Solar Physics},
volume = {298},
number = {6},
pages = {82},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ballester, E. Alsina; Belluzzi, L.; Bueno, J. Trujillo
The Potential of the Wavelength-integrated Scattering Polarization of the Hydrogen Lyensuremathalpha Line for Probing the Solar Chromosphere Journal Article
In: Astrophysical Journal, vol. 947, no. 2, pp. 71, 2023.
@article{2023ApJ...947...71A,
title = {The Potential of the Wavelength-integrated Scattering Polarization of the Hydrogen Lyensuremathalpha Line for Probing the Solar Chromosphere},
author = {E. Alsina Ballester and L. Belluzzi and J. Trujillo Bueno},
doi = {10.3847/1538-4357/acc186},
year = {2023},
date = {2023-04-01},
urldate = {2023-04-01},
journal = {Astrophysical Journal},
volume = {947},
number = {2},
pages = {71},
abstract = {The intensity and the linear scattering polarization profiles of the
hydrogen Lyensuremathalpha line encode valuable
information on the thermodynamic and magnetic structure of the
upper layers of the solar chromosphere. The Chromospheric Lyman-
Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment
provided unprecedented spectropolarimetric data of this line, as
well as two-dimensional broadband images in intensity and linear
polarization. We theoretically investigate the potential of the
Lyensuremathalpha broadband polarimetric signals for
probing the solar chromosphere and its magnetic fields. We
analyze the synthetic Stokes profiles obtained from a series of
radiative transfer (RT) calculations out of local thermodynamic
equilibrium, considering semi-empirical one-dimensional models
of the solar atmosphere. The wavelength-integrated linear
polarization signal is found to be dominated by the contribution
from the wings when considering a Gaussian weighting function
with a FWHM that corresponds to the CLASP slit-jaw broadband
filter. These broadband linear polarization signals are strongly
sensitive to magnetic fields of strengths on the order of 50 G,
via the action of magneto-optical (MO) effects, and are expected
to encode information on the middle-upper chromosphere. The two-
dimensional broadband intensity and linear polarization images
observed by CLASP can be suitably mimicked using synthetic
wavelength-integrated signals obtained considering atmospheric
models and magnetic fields that are representative of solar
regions with different levels of activity, provided that the
impact of MO effects is taken into account. Despite the
limitations of a one-dimensional RT modeling, this work
illustrates the diagnostic potential of filter-polarimetric
Lyensuremathalpha signals for probing the solar
chromosphere and its magnetism.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The intensity and the linear scattering polarization profiles of the
hydrogen Lyensuremathalpha line encode valuable
information on the thermodynamic and magnetic structure of the
upper layers of the solar chromosphere. The Chromospheric Lyman-
Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment
provided unprecedented spectropolarimetric data of this line, as
well as two-dimensional broadband images in intensity and linear
polarization. We theoretically investigate the potential of the
Lyensuremathalpha broadband polarimetric signals for
probing the solar chromosphere and its magnetic fields. We
analyze the synthetic Stokes profiles obtained from a series of
radiative transfer (RT) calculations out of local thermodynamic
equilibrium, considering semi-empirical one-dimensional models
of the solar atmosphere. The wavelength-integrated linear
polarization signal is found to be dominated by the contribution
from the wings when considering a Gaussian weighting function
with a FWHM that corresponds to the CLASP slit-jaw broadband
filter. These broadband linear polarization signals are strongly
sensitive to magnetic fields of strengths on the order of 50 G,
via the action of magneto-optical (MO) effects, and are expected
to encode information on the middle-upper chromosphere. The two-
dimensional broadband intensity and linear polarization images
observed by CLASP can be suitably mimicked using synthetic
wavelength-integrated signals obtained considering atmospheric
models and magnetic fields that are representative of solar
regions with different levels of activity, provided that the
impact of MO effects is taken into account. Despite the
limitations of a one-dimensional RT modeling, this work
illustrates the diagnostic potential of filter-polarimetric
Lyensuremathalpha signals for probing the solar
chromosphere and its magnetism.
hydrogen Lyensuremathalpha line encode valuable
information on the thermodynamic and magnetic structure of the
upper layers of the solar chromosphere. The Chromospheric Lyman-
Alpha Spectro-Polarimeter (CLASP) sounding rocket experiment
provided unprecedented spectropolarimetric data of this line, as
well as two-dimensional broadband images in intensity and linear
polarization. We theoretically investigate the potential of the
Lyensuremathalpha broadband polarimetric signals for
probing the solar chromosphere and its magnetic fields. We
analyze the synthetic Stokes profiles obtained from a series of
radiative transfer (RT) calculations out of local thermodynamic
equilibrium, considering semi-empirical one-dimensional models
of the solar atmosphere. The wavelength-integrated linear
polarization signal is found to be dominated by the contribution
from the wings when considering a Gaussian weighting function
with a FWHM that corresponds to the CLASP slit-jaw broadband
filter. These broadband linear polarization signals are strongly
sensitive to magnetic fields of strengths on the order of 50 G,
via the action of magneto-optical (MO) effects, and are expected
to encode information on the middle-upper chromosphere. The two-
dimensional broadband intensity and linear polarization images
observed by CLASP can be suitably mimicked using synthetic
wavelength-integrated signals obtained considering atmospheric
models and magnetic fields that are representative of solar
regions with different levels of activity, provided that the
impact of MO effects is taken into account. Despite the
limitations of a one-dimensional RT modeling, this work
illustrates the diagnostic potential of filter-polarimetric
Lyensuremathalpha signals for probing the solar
chromosphere and its magnetism.
Benedusi, Pietro; Riva, Simone; Zulian, Patrick; Štěpán, Jiř'i; Belluzzi, Luca; Krause, Rolf
Scalable matrix-free solver for 3D transfer of polarized radiation in stellar atmospheres Journal Article
In: Journal of Computational Physics, vol. 479, pp. 112013, 2023.
@article{2023JCoPh.47912013B,
title = {Scalable matrix-free solver for 3D transfer of polarized radiation in stellar atmospheres},
author = {Pietro Benedusi and Simone Riva and Patrick Zulian and Jiř'i Štěpán and Luca Belluzzi and Rolf Krause},
doi = {10.1016/j.jcp.2023.112013},
year = {2023},
date = {2023-04-01},
urldate = {2023-04-01},
journal = {Journal of Computational Physics},
volume = {479},
pages = {112013},
abstract = {We present an efficient and massively parallel solution strategy for the
transfer problem of polarized radiation, for a 3D stationary
medium out of local thermodynamic equilibrium. Scattering
processes are included accounting for partial frequency
redistribution effects. Such a setting is one of the most
challenging ones in radiative transfer modeling. The problem is
formulated for a two-level atomic model, which allows
linearization. The discrete ordinate method alongside an
exponential integrator are used for discretization. Efficient
solution is obtained with a Krylov method equipped with a
tailored physics-based preconditioner. A matrix-free approach
results in a lightweight implementation, suited for tackling
large problems. Near-optimal strong and weak scalability are
obtained with two complementary decompositions of the
computational domain. The presented approach made it possible to
perform simulations for the Ca I line at 4227 Å with more
than 10$^9$ degrees of freedom in less than half an hour on
massively parallel machines, always converging in a few
iterations for the proposed tests.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We present an efficient and massively parallel solution strategy for the
transfer problem of polarized radiation, for a 3D stationary
medium out of local thermodynamic equilibrium. Scattering
processes are included accounting for partial frequency
redistribution effects. Such a setting is one of the most
challenging ones in radiative transfer modeling. The problem is
formulated for a two-level atomic model, which allows
linearization. The discrete ordinate method alongside an
exponential integrator are used for discretization. Efficient
solution is obtained with a Krylov method equipped with a
tailored physics-based preconditioner. A matrix-free approach
results in a lightweight implementation, suited for tackling
large problems. Near-optimal strong and weak scalability are
obtained with two complementary decompositions of the
computational domain. The presented approach made it possible to
perform simulations for the Ca I line at 4227 Å with more
than 10$^9$ degrees of freedom in less than half an hour on
massively parallel machines, always converging in a few
iterations for the proposed tests.
transfer problem of polarized radiation, for a 3D stationary
medium out of local thermodynamic equilibrium. Scattering
processes are included accounting for partial frequency
redistribution effects. Such a setting is one of the most
challenging ones in radiative transfer modeling. The problem is
formulated for a two-level atomic model, which allows
linearization. The discrete ordinate method alongside an
exponential integrator are used for discretization. Efficient
solution is obtained with a Krylov method equipped with a
tailored physics-based preconditioner. A matrix-free approach
results in a lightweight implementation, suited for tackling
large problems. Near-optimal strong and weak scalability are
obtained with two complementary decompositions of the
computational domain. The presented approach made it possible to
perform simulations for the Ca I line at 4227 Å with more
than 10$^9$ degrees of freedom in less than half an hour on
massively parallel machines, always converging in a few
iterations for the proposed tests.
Ishikawa, Ryohko; Bueno, Javier Trujillo; Ballester, Ernest Alsina; Belluzzi, Luca; Alemán, Tanaus'u Pino; McKenzie, David E.; Auch`ere, Frédéric; Kobayashi, Ken; Okamoto, Takenori J.; Rachmeler, Laurel A.; Song, Donguk
In: Astrophysical Journal, vol. 945, no. 2, pp. 125, 2023.
@article{2023ApJ...945..125I,
title = {Evidence for the Operation of the Hanle and Magneto-optical Effects in the Scattering Polarization Signals Observed by CLASP2 across the Mg II h and k Lines},
author = {Ryohko Ishikawa and Javier Trujillo Bueno and Ernest Alsina Ballester and Luca Belluzzi and Tanaus'u Pino Alemán and David E. McKenzie and Frédéric Auch`ere and Ken Kobayashi and Takenori J. Okamoto and Laurel A. Rachmeler and Donguk Song},
doi = {10.3847/1538-4357/acb64e},
year = {2023},
date = {2023-03-01},
urldate = {2023-03-01},
journal = {Astrophysical Journal},
volume = {945},
number = {2},
pages = {125},
abstract = {Radiative transfer investigations of the solar Mg II h and k resonance
lines around 280 nm have shown that, while their circular
polarization (Stokes V) signals arise from the Zeeman effect,
the linear polarization profiles (Stokes Q and U) are dominated
by the scattering of anisotropic radiation and the Hanle and
magneto-optical (MO) effects. Using the unprecedented
observations of the Mg II and Mn I resonance lines obtained by
the Chromospheric LAyer Spectro-Polarimeter (CLASP2), here we
investigate how the linear polarization signals at different
wavelengths (i.e., at the center, and at the near and far wings
of the k line) vary with the longitudinal component of the
magnetic field (B $_ L $) at their approximate height of
formation. The B $_ L $ is estimated from the V signals in the
aforementioned spectral lines. Particular attention is given to
the following quantities that are expected to be influenced by
the presence of magnetic fields through the Hanle and MO
effects: the sign of the U signals, the total linear
polarization amplitude (LP) and its direction
(ensuremathchi) with respect to a reference direction. We
find that at the center and near wings of the k line, the
behavior of these quantities is significantly different in the
observed quiet and plage regions, and that both LP and
ensuremathchi seem to depend on B $_ L $. These
observational results are indicative of the operation of the
Hanle effect at the center of the k line and of the MO effects
at the near wings of the k line.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Radiative transfer investigations of the solar Mg II h and k resonance
lines around 280 nm have shown that, while their circular
polarization (Stokes V) signals arise from the Zeeman effect,
the linear polarization profiles (Stokes Q and U) are dominated
by the scattering of anisotropic radiation and the Hanle and
magneto-optical (MO) effects. Using the unprecedented
observations of the Mg II and Mn I resonance lines obtained by
the Chromospheric LAyer Spectro-Polarimeter (CLASP2), here we
investigate how the linear polarization signals at different
wavelengths (i.e., at the center, and at the near and far wings
of the k line) vary with the longitudinal component of the
magnetic field (B $_ L $) at their approximate height of
formation. The B $_ L $ is estimated from the V signals in the
aforementioned spectral lines. Particular attention is given to
the following quantities that are expected to be influenced by
the presence of magnetic fields through the Hanle and MO
effects: the sign of the U signals, the total linear
polarization amplitude (LP) and its direction
(ensuremathchi) with respect to a reference direction. We
find that at the center and near wings of the k line, the
behavior of these quantities is significantly different in the
observed quiet and plage regions, and that both LP and
ensuremathchi seem to depend on B $_ L $. These
observational results are indicative of the operation of the
Hanle effect at the center of the k line and of the MO effects
at the near wings of the k line.
lines around 280 nm have shown that, while their circular
polarization (Stokes V) signals arise from the Zeeman effect,
the linear polarization profiles (Stokes Q and U) are dominated
by the scattering of anisotropic radiation and the Hanle and
magneto-optical (MO) effects. Using the unprecedented
observations of the Mg II and Mn I resonance lines obtained by
the Chromospheric LAyer Spectro-Polarimeter (CLASP2), here we
investigate how the linear polarization signals at different
wavelengths (i.e., at the center, and at the near and far wings
of the k line) vary with the longitudinal component of the
magnetic field (B $_ L $) at their approximate height of
formation. The B $_ L $ is estimated from the V signals in the
aforementioned spectral lines. Particular attention is given to
the following quantities that are expected to be influenced by
the presence of magnetic fields through the Hanle and MO
effects: the sign of the U signals, the total linear
polarization amplitude (LP) and its direction
(ensuremathchi) with respect to a reference direction. We
find that at the center and near wings of the k line, the
behavior of these quantities is significantly different in the
observed quiet and plage regions, and that both LP and
ensuremathchi seem to depend on B $_ L $. These
observational results are indicative of the operation of the
Hanle effect at the center of the k line and of the MO effects
at the near wings of the k line.
Stenflo, Jan O.
Cosmological Constant from Boundary Condition and Its Implications beyond the Standard Model Journal Article
In: Universe, vol. 9, no. 2, 2023, ISSN: 2218-1997.
@article{universe9020103,
title = {Cosmological Constant from Boundary Condition and Its Implications beyond the Standard Model},
author = {Jan O. Stenflo},
url = {https://www.mdpi.com/2218-1997/9/2/103},
doi = {10.3390/universe9020103},
issn = {2218-1997},
year = {2023},
date = {2023-02-17},
urldate = {2023-01-01},
journal = {Universe},
volume = {9},
number = {2},
abstract = {Standard cosmology has long been plagued by a number of persistent problems. The origin of the apparent acceleration of the cosmic expansion remains enigmatic. The cosmological constant has been reintroduced as a free parameter with a value in energy density units that “happens” to be of the same order as the present matter energy density. There is an internal inconsistency with regards to the Hubble constant, the so-called H0 tension. The derived value of H0 depends on the type of data that is used. With supernovae as standard candles, one gets a H0 that is 4–5 σ larger than the value that one gets from CMB (Cosmic Microwave Background) data for the early universe. Here we show that these problems are related and can be solved if the cosmological constant represents a covariant integration constant that arises from a spatial boundary condition, instead of being a new type of hypothetical physical field, “dark energy”, as assumed by standard cosmology. The boundary condition only applies to the bounded 3D subspace that represents the observable universe, the hypersurface of the past light cone.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Standard cosmology has long been plagued by a number of persistent problems. The origin of the apparent acceleration of the cosmic expansion remains enigmatic. The cosmological constant has been reintroduced as a free parameter with a value in energy density units that “happens” to be of the same order as the present matter energy density. There is an internal inconsistency with regards to the Hubble constant, the so-called H0 tension. The derived value of H0 depends on the type of data that is used. With supernovae as standard candles, one gets a H0 that is 4–5 σ larger than the value that one gets from CMB (Cosmic Microwave Background) data for the early universe. Here we show that these problems are related and can be solved if the cosmological constant represents a covariant integration constant that arises from a spatial boundary condition, instead of being a new type of hypothetical physical field, “dark energy”, as assumed by standard cosmology. The boundary condition only applies to the bounded 3D subspace that represents the observable universe, the hypersurface of the past light cone.
Berdyugin, Andrei V.; Piirola, Vilppu; Bagnulo, Stefano; Landstreet, John D.; Berdyugina, Svetlana V.
Discovery of magnetic fields in five DC white dwarfs Journal Article
In: Astronomy and Astrophysics, vol. 670, pp. A2, 2023.
@article{2023A&A...670A...2B,
title = {Discovery of magnetic fields in five DC white dwarfs},
author = {Andrei V. Berdyugin and Vilppu Piirola and Stefano Bagnulo and John D. Landstreet and Svetlana V. Berdyugina},
doi = {10.1051/0004-6361/202245149},
year = {2023},
date = {2023-02-01},
urldate = {2023-02-01},
journal = {Astronomy and Astrophysics},
volume = {670},
pages = {A2},
abstract = {About half of white dwarfs (WDs) evolve to the DC state as they cool;
the others become DQ or (temporarily?) DZ WDs. The recent
magnetic survey of the local 20 pc volume has established a high
frequency of magnetic fields among WDs older than 2-3 Gyr,
demonstrating that in low- and average-mass WDs, the effects of
magnetism become more common as they age, and the fields on
average become stronger. However, the available statistics of
WDs older than about 5 Gyr do not clearly establish how fields
evolve beyond this age. We are carrying out a survey to clarify
the occurrence of magnetism in DC-type WDs in order to better
understand this late evolution. We use broadband filter
polarimetry, arguably the most efficient way to detect magnetic
fields in featureless WDs via continuum circular polarization.
Here we report the discovery of a magnetic field in five DC WDs
(of 23 observed), almost doubling the total sample of known
magnetic WDs belonging to the DC spectral class.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
About half of white dwarfs (WDs) evolve to the DC state as they cool;
the others become DQ or (temporarily?) DZ WDs. The recent
magnetic survey of the local 20 pc volume has established a high
frequency of magnetic fields among WDs older than 2-3 Gyr,
demonstrating that in low- and average-mass WDs, the effects of
magnetism become more common as they age, and the fields on
average become stronger. However, the available statistics of
WDs older than about 5 Gyr do not clearly establish how fields
evolve beyond this age. We are carrying out a survey to clarify
the occurrence of magnetism in DC-type WDs in order to better
understand this late evolution. We use broadband filter
polarimetry, arguably the most efficient way to detect magnetic
fields in featureless WDs via continuum circular polarization.
Here we report the discovery of a magnetic field in five DC WDs
(of 23 observed), almost doubling the total sample of known
magnetic WDs belonging to the DC spectral class.
the others become DQ or (temporarily?) DZ WDs. The recent
magnetic survey of the local 20 pc volume has established a high
frequency of magnetic fields among WDs older than 2-3 Gyr,
demonstrating that in low- and average-mass WDs, the effects of
magnetism become more common as they age, and the fields on
average become stronger. However, the available statistics of
WDs older than about 5 Gyr do not clearly establish how fields
evolve beyond this age. We are carrying out a survey to clarify
the occurrence of magnetism in DC-type WDs in order to better
understand this late evolution. We use broadband filter
polarimetry, arguably the most efficient way to detect magnetic
fields in featureless WDs via continuum circular polarization.
Here we report the discovery of a magnetic field in five DC WDs
(of 23 observed), almost doubling the total sample of known
magnetic WDs belonging to the DC spectral class.
Tziotziou, K.; Scullion, E.; Shelyag, S.; Steiner, O.; Khomenko, E.; Tsiropoula, G.; Cuissa, J. R. Canivete; Wedemeyer, S.; Kontogiannis, I.; Yadav, N.; Kitiashvili, I. N.; Skirvin, S. J.; Dakanalis, I.; Kosovichev, A. G.; Fedun, V.
Vortex Motions in the Solar Atmosphere Journal Article
In: Space Science Reviews, vol. 219, no. 1, pp. 1, 2023.
@article{2023SSRv..219....1T,
title = {Vortex Motions in the Solar Atmosphere},
author = {K. Tziotziou and E. Scullion and S. Shelyag and O. Steiner and E. Khomenko and G. Tsiropoula and J. R. Canivete Cuissa and S. Wedemeyer and I. Kontogiannis and N. Yadav and I. N. Kitiashvili and S. J. Skirvin and I. Dakanalis and A. G. Kosovichev and V. Fedun},
doi = {10.1007/s11214-022-00946-8},
year = {2023},
date = {2023-02-01},
urldate = {2023-02-01},
journal = {Space Science Reviews},
volume = {219},
number = {1},
pages = {1},
abstract = {Vortex flows, related to solar convective turbulent dynamics at granular
scales and their interplay with magnetic fields within
intergranular lanes, occur abundantly on the solar surface and
in the atmosphere above. Their presence is revealed in high-
resolution and high-cadence solar observations from the ground
and from space and with state-of-the-art magnetoconvection
simulations. Vortical flows exhibit complex characteristics and
dynamics, excite a wide range of different waves, and couple
different layers of the solar atmosphere, which facilitates the
channeling and transfer of mass, momentum and energy from the
solar surface up to the low corona. Here we provide a
comprehensive review of documented research and new developments
in theory, observations, and modelling of vortices over the past
couple of decades after their observational discovery, including
recent observations in Hensuremathalpha , innovative
detection techniques, diverse hydrostatic modelling of waves and
forefront magnetohydrodynamic simulations incorporating effects
of a non-ideal plasma. It is the first systematic overview of
solar vortex flows at granular scales, a field with a plethora
of names for phenomena that exhibit similarities and differences
and often interconnect and rely on the same physics. With the
advent of the 4-m Daniel K. Inouye Solar Telescope and the
forthcoming European Solar Telescope, the ongoing Solar Orbiter
mission, and the development of cutting-edge simulations, this
review timely addresses the state-of-the-art on vortex flows and
outlines both theoretical and observational future research
directions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Vortex flows, related to solar convective turbulent dynamics at granular
scales and their interplay with magnetic fields within
intergranular lanes, occur abundantly on the solar surface and
in the atmosphere above. Their presence is revealed in high-
resolution and high-cadence solar observations from the ground
and from space and with state-of-the-art magnetoconvection
simulations. Vortical flows exhibit complex characteristics and
dynamics, excite a wide range of different waves, and couple
different layers of the solar atmosphere, which facilitates the
channeling and transfer of mass, momentum and energy from the
solar surface up to the low corona. Here we provide a
comprehensive review of documented research and new developments
in theory, observations, and modelling of vortices over the past
couple of decades after their observational discovery, including
recent observations in Hensuremathalpha , innovative
detection techniques, diverse hydrostatic modelling of waves and
forefront magnetohydrodynamic simulations incorporating effects
of a non-ideal plasma. It is the first systematic overview of
solar vortex flows at granular scales, a field with a plethora
of names for phenomena that exhibit similarities and differences
and often interconnect and rely on the same physics. With the
advent of the 4-m Daniel K. Inouye Solar Telescope and the
forthcoming European Solar Telescope, the ongoing Solar Orbiter
mission, and the development of cutting-edge simulations, this
review timely addresses the state-of-the-art on vortex flows and
outlines both theoretical and observational future research
directions.
scales and their interplay with magnetic fields within
intergranular lanes, occur abundantly on the solar surface and
in the atmosphere above. Their presence is revealed in high-
resolution and high-cadence solar observations from the ground
and from space and with state-of-the-art magnetoconvection
simulations. Vortical flows exhibit complex characteristics and
dynamics, excite a wide range of different waves, and couple
different layers of the solar atmosphere, which facilitates the
channeling and transfer of mass, momentum and energy from the
solar surface up to the low corona. Here we provide a
comprehensive review of documented research and new developments
in theory, observations, and modelling of vortices over the past
couple of decades after their observational discovery, including
recent observations in Hensuremathalpha , innovative
detection techniques, diverse hydrostatic modelling of waves and
forefront magnetohydrodynamic simulations incorporating effects
of a non-ideal plasma. It is the first systematic overview of
solar vortex flows at granular scales, a field with a plethora
of names for phenomena that exhibit similarities and differences
and often interconnect and rely on the same physics. With the
advent of the 4-m Daniel K. Inouye Solar Telescope and the
forthcoming European Solar Telescope, the ongoing Solar Orbiter
mission, and the development of cutting-edge simulations, this
review timely addresses the state-of-the-art on vortex flows and
outlines both theoretical and observational future research
directions.
Battaglia, Andrea Francesco; Wang, Wen; Saqri, Jonas; Podladchikova, Tatiana; Veronig, Astrid M.; Collier, Hannah; Dickson, Ewan C. M.; Podladchikova, Olena; Monstein, Christian; Warmuth, Alexander; Schuller, Frédéric; Harra, Louise; Krucker, Säm
Identifying the energy release site in a solar microflare with a jet Journal Article
In: Astronomy and Astrophysics, vol. 670, pp. A56, 2023.
@article{2023A&A...670A..56B,
title = {Identifying the energy release site in a solar microflare with a jet},
author = {Andrea Francesco Battaglia and Wen Wang and Jonas Saqri and Tatiana Podladchikova and Astrid M. Veronig and Hannah Collier and Ewan C. M. Dickson and Olena Podladchikova and Christian Monstein and Alexander Warmuth and Frédéric Schuller and Louise Harra and Säm Krucker},
doi = {10.1051/0004-6361/202244996},
year = {2023},
date = {2023-02-01},
urldate = {2023-02-01},
journal = {Astronomy and Astrophysics},
volume = {670},
pages = {A56},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris, Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.; Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas; Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier, Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg; Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder, Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh; Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato, Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson, Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven; Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.; Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert, Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik, Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
In: RAS Techniques and Instruments, vol. 2, no. 1, pp. 148-206, 2023.
@article{2023RASTI...2..148Rb,
title = {The effect of stellar contamination on low-resolution transmission spectroscopy: needs identified by NASA's Exoplanet Exploration Program Study Analysis Group 21},
author = {Benjamin V. Rackham and Néstor Espinoza and Svetlana V. Berdyugina and Heidi Korhonen and Ryan J. MacDonald and Benjamin T. Montet and Brett M. Morris and Mahmoudreza Oshagh and Alexander I. Shapiro and Yvonne C. Unruh and Elisa V. Quintana and Robert T. Zellem and Dániel Apai and Thomas Barclay and Joanna K. Barstow and Giovanni Bruno and Ludmila Carone and Sarah L. Casewell and Heather M. Cegla and Serena Criscuoli and Catherine Fischer and Damien Fournier and Mark S. Giampapa and Helen Giles and Aishwarya Iyer and Greg Kopp and Nadiia M. Kostogryz and Natalie Krivova and Matthias Mallonn and Chima McGruder and Karan Molaverdikhani and Elisabeth R. Newton and Mayukh Panja and Sarah Peacock and Kevin Reardon and Rachael M. Roettenbacher and Gaetano Scandariato and Sami Solanki and Keivan G. Stassun and Oskar Steiner and Kevin B. Stevenson and Jeremy Tregloan-Reed and Adriana Valio and Sven Wedemeyer and Luis Welbanks and Jie Yu and Munazza K. Alam and James R. A. Davenport and Drake Deming and Chuanfei Dong and Elsa Ducrot and Chloe Fisher and Emily Gilbert and Veselin Kostov and Mercedes López-Morales and Mike Line and Teo Močnik and Susan Mullally and Rishi R. Paudel and Ignasi Ribas and Jeff A. Valenti},
doi = {10.1093/rasti/rzad009},
year = {2023},
date = {2023-01-01},
journal = {RAS Techniques and Instruments},
volume = {2},
number = {1},
pages = {148-206},
abstract = {Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program
Analysis Group was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method
for studying exoplanetary atmospheres by measuring the
wavelength-dependent radius of a planet as it transits its star.
Transmission spectroscopy relies on a precise understanding of
the spectrum of the star being occulted. However, stars are not
homogeneous, constant light sources but have temporally evolving
photospheres and chromospheres with inhomogeneities like spots,
faculae, plages, granules, and flares. This SAG brought together
an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar
astrophysics, planetary science, and exoplanetary atmosphere
research communities, to study the current research needs that
can be addressed in this context to make the most of transit
studies from current NASA facilities like Hubble Space Telescope
and JWST. The analysis produced 14 findings, which fall into
three science themes encompassing (i) how the Sun is used as our
best laboratory to calibrate our understanding of stellar
heterogeneities ('The Sun as the Stellar Benchmark'), (ii) how
stars other than the Sun extend our knowledge of heterogeneities
('Surface Heterogeneities of Other Stars'), and (iii) how to
incorporate information gathered for the Sun and other stars
into transit studies ('Mapping Stellar Knowledge to Transit
Studies'). In this invited review, we largely reproduce the
final report of SAG21 as a contribution to the peer-reviewed
literature.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program
Analysis Group was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method
for studying exoplanetary atmospheres by measuring the
wavelength-dependent radius of a planet as it transits its star.
Transmission spectroscopy relies on a precise understanding of
the spectrum of the star being occulted. However, stars are not
homogeneous, constant light sources but have temporally evolving
photospheres and chromospheres with inhomogeneities like spots,
faculae, plages, granules, and flares. This SAG brought together
an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar
astrophysics, planetary science, and exoplanetary atmosphere
research communities, to study the current research needs that
can be addressed in this context to make the most of transit
studies from current NASA facilities like Hubble Space Telescope
and JWST. The analysis produced 14 findings, which fall into
three science themes encompassing (i) how the Sun is used as our
best laboratory to calibrate our understanding of stellar
heterogeneities ('The Sun as the Stellar Benchmark'), (ii) how
stars other than the Sun extend our knowledge of heterogeneities
('Surface Heterogeneities of Other Stars'), and (iii) how to
incorporate information gathered for the Sun and other stars
into transit studies ('Mapping Stellar Knowledge to Transit
Studies'). In this invited review, we largely reproduce the
final report of SAG21 as a contribution to the peer-reviewed
literature.
Analysis Group was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method
for studying exoplanetary atmospheres by measuring the
wavelength-dependent radius of a planet as it transits its star.
Transmission spectroscopy relies on a precise understanding of
the spectrum of the star being occulted. However, stars are not
homogeneous, constant light sources but have temporally evolving
photospheres and chromospheres with inhomogeneities like spots,
faculae, plages, granules, and flares. This SAG brought together
an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar
astrophysics, planetary science, and exoplanetary atmosphere
research communities, to study the current research needs that
can be addressed in this context to make the most of transit
studies from current NASA facilities like Hubble Space Telescope
and JWST. The analysis produced 14 findings, which fall into
three science themes encompassing (i) how the Sun is used as our
best laboratory to calibrate our understanding of stellar
heterogeneities ('The Sun as the Stellar Benchmark'), (ii) how
stars other than the Sun extend our knowledge of heterogeneities
('Surface Heterogeneities of Other Stars'), and (iii) how to
incorporate information gathered for the Sun and other stars
into transit studies ('Mapping Stellar Knowledge to Transit
Studies'). In this invited review, we largely reproduce the
final report of SAG21 as a contribution to the peer-reviewed
literature.
Rackham, Benjamin V.; Espinoza, Néstor; Berdyugina, Svetlana V.; Korhonen, Heidi; MacDonald, Ryan J.; Montet, Benjamin T.; Morris, Brett M.; Oshagh, Mahmoudreza; Shapiro, Alexander I.; Unruh, Yvonne C.; Quintana, Elisa V.; Zellem, Robert T.; Apai, Dániel; Barclay, Thomas; Barstow, Joanna K.; Bruno, Giovanni; Carone, Ludmila; Casewell, Sarah L.; Cegla, Heather M.; Criscuoli, Serena; Fischer, Catherine; Fournier, Damien; Giampapa, Mark S.; Giles, Helen; Iyer, Aishwarya; Kopp, Greg; Kostogryz, Nadiia M.; Krivova, Natalie; Mallonn, Matthias; McGruder, Chima; Molaverdikhani, Karan; Newton, Elisabeth R.; Panja, Mayukh; Peacock, Sarah; Reardon, Kevin; Roettenbacher, Rachael M.; Scandariato, Gaetano; Solanki, Sami; Stassun, Keivan G.; Steiner, Oskar; Stevenson, Kevin B.; Tregloan-Reed, Jeremy; Valio, Adriana; Wedemeyer, Sven; Welbanks, Luis; Yu, Jie; Alam, Munazza K.; Davenport, James R. A.; Deming, Drake; Dong, Chuanfei; Ducrot, Elsa; Fisher, Chloe; Gilbert, Emily; Kostov, Veselin; López-Morales, Mercedes; Line, Mike; Močnik, Teo; Mullally, Susan; Paudel, Rishi R.; Ribas, Ignasi; Valenti, Jeff A.
In: RAS Techniques and Instruments, vol. 2, no. 1, pp. 148-206, 2023.
@article{2023RASTI...2..148R,
title = {The effect of stellar contamination on low-resolution transmission spectroscopy: needs identified by NASA's Exoplanet Exploration Program Study Analysis Group 21},
author = {Benjamin V. Rackham and Néstor Espinoza and Svetlana V. Berdyugina and Heidi Korhonen and Ryan J. MacDonald and Benjamin T. Montet and Brett M. Morris and Mahmoudreza Oshagh and Alexander I. Shapiro and Yvonne C. Unruh and Elisa V. Quintana and Robert T. Zellem and Dániel Apai and Thomas Barclay and Joanna K. Barstow and Giovanni Bruno and Ludmila Carone and Sarah L. Casewell and Heather M. Cegla and Serena Criscuoli and Catherine Fischer and Damien Fournier and Mark S. Giampapa and Helen Giles and Aishwarya Iyer and Greg Kopp and Nadiia M. Kostogryz and Natalie Krivova and Matthias Mallonn and Chima McGruder and Karan Molaverdikhani and Elisabeth R. Newton and Mayukh Panja and Sarah Peacock and Kevin Reardon and Rachael M. Roettenbacher and Gaetano Scandariato and Sami Solanki and Keivan G. Stassun and Oskar Steiner and Kevin B. Stevenson and Jeremy Tregloan-Reed and Adriana Valio and Sven Wedemeyer and Luis Welbanks and Jie Yu and Munazza K. Alam and James R. A. Davenport and Drake Deming and Chuanfei Dong and Elsa Ducrot and Chloe Fisher and Emily Gilbert and Veselin Kostov and Mercedes López-Morales and Mike Line and Teo Močnik and Susan Mullally and Rishi R. Paudel and Ignasi Ribas and Jeff A. Valenti},
doi = {10.1093/rasti/rzad009},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {RAS Techniques and Instruments},
volume = {2},
number = {1},
pages = {148-206},
abstract = {Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program
Analysis Group was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method
for studying exoplanetary atmospheres by measuring the
wavelength-dependent radius of a planet as it transits its star.
Transmission spectroscopy relies on a precise understanding of
the spectrum of the star being occulted. However, stars are not
homogeneous, constant light sources but have temporally evolving
photospheres and chromospheres with inhomogeneities like spots,
faculae, plages, granules, and flares. This SAG brought together
an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar
astrophysics, planetary science, and exoplanetary atmosphere
research communities, to study the current research needs that
can be addressed in this context to make the most of transit
studies from current NASA facilities like Hubble Space Telescope
and JWST. The analysis produced 14 findings, which fall into
three science themes encompassing (i) how the Sun is used as our
best laboratory to calibrate our understanding of stellar
heterogeneities ('The Sun as the Stellar Benchmark'), (ii) how
stars other than the Sun extend our knowledge of heterogeneities
('Surface Heterogeneities of Other Stars'), and (iii) how to
incorporate information gathered for the Sun and other stars
into transit studies ('Mapping Stellar Knowledge to Transit
Studies'). In this invited review, we largely reproduce the
final report of SAG21 as a contribution to the peer-reviewed
literature.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Study Analysis Group 21 (SAG21) of NASA's Exoplanet Exploration Program
Analysis Group was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method
for studying exoplanetary atmospheres by measuring the
wavelength-dependent radius of a planet as it transits its star.
Transmission spectroscopy relies on a precise understanding of
the spectrum of the star being occulted. However, stars are not
homogeneous, constant light sources but have temporally evolving
photospheres and chromospheres with inhomogeneities like spots,
faculae, plages, granules, and flares. This SAG brought together
an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar
astrophysics, planetary science, and exoplanetary atmosphere
research communities, to study the current research needs that
can be addressed in this context to make the most of transit
studies from current NASA facilities like Hubble Space Telescope
and JWST. The analysis produced 14 findings, which fall into
three science themes encompassing (i) how the Sun is used as our
best laboratory to calibrate our understanding of stellar
heterogeneities ('The Sun as the Stellar Benchmark'), (ii) how
stars other than the Sun extend our knowledge of heterogeneities
('Surface Heterogeneities of Other Stars'), and (iii) how to
incorporate information gathered for the Sun and other stars
into transit studies ('Mapping Stellar Knowledge to Transit
Studies'). In this invited review, we largely reproduce the
final report of SAG21 as a contribution to the peer-reviewed
literature.
Analysis Group was organized to study the effect of stellar
contamination on space-based transmission spectroscopy, a method
for studying exoplanetary atmospheres by measuring the
wavelength-dependent radius of a planet as it transits its star.
Transmission spectroscopy relies on a precise understanding of
the spectrum of the star being occulted. However, stars are not
homogeneous, constant light sources but have temporally evolving
photospheres and chromospheres with inhomogeneities like spots,
faculae, plages, granules, and flares. This SAG brought together
an interdisciplinary team of more than 100 scientists, with
observers and theorists from the heliophysics, stellar
astrophysics, planetary science, and exoplanetary atmosphere
research communities, to study the current research needs that
can be addressed in this context to make the most of transit
studies from current NASA facilities like Hubble Space Telescope
and JWST. The analysis produced 14 findings, which fall into
three science themes encompassing (i) how the Sun is used as our
best laboratory to calibrate our understanding of stellar
heterogeneities ('The Sun as the Stellar Benchmark'), (ii) how
stars other than the Sun extend our knowledge of heterogeneities
('Surface Heterogeneities of Other Stars'), and (iii) how to
incorporate information gathered for the Sun and other stars
into transit studies ('Mapping Stellar Knowledge to Transit
Studies'). In this invited review, we largely reproduce the
final report of SAG21 as a contribution to the peer-reviewed
literature.
Pohjolainen, Silja; Shesvan, Nasrin Talebpour; Monstein, Christian
Separating the effects of earthside and far side solar events. A case study Journal Article
In: Advances in Space Research, 2023, ISSN: 0273-1177.
@article{POHJOLAINEN2023,
title = {Separating the effects of earthside and far side solar events. A case study},
author = {Silja Pohjolainen and Nasrin Talebpour Shesvan and Christian Monstein},
url = {https://www.sciencedirect.com/science/article/pii/S0273117723007317},
doi = {https://doi.org/10.1016/j.asr.2023.09.009},
issn = {0273-1177},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {Advances in Space Research},
abstract = {On 8 November 2013 a halo-type coronal mass ejection (CME) was observed, together with flares and type II radio bursts, but the association between the flares, radio bursts, and the CME was not clear. Our aim is to identify the origin of the CME and its direction of propagation, and to exclude features that were not connected to it. On the Earth-facing side, a GOES C5.7 class flare occurred close to the estimated CME launch time, followed by an X1.1 class flare. The latter flare was associated with an EUV wave and metric type II bursts. On the far side of the Sun, a filament eruption, EUV dimmings, and ejected CME loops were observed by imaging instruments onboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft that were viewing the backside of the Sun. The STEREO radio instruments observed an interplanetary (IP) type II radio burst at decameter-hectometric wavelengths, which was not observed by the radio instrument onboard the Wind spacecraft located at L1 near Earth. We show that the halo CME originated from the eruption on the far side of the Sun, and that the IP type II burst was created by a shock wave ahead of the halo CME. The radio burst remained unobserved from the earthside, even at heliocentric source heights larger than 9 solar radii. During the CME propagation, the X-class flare eruption caused a small plasmoid ejection earthward, the material of which was superposed on the earlier CME structures observed in projection. The estimated heights of the metric type II burst match well with the EUV wave launched by the X-class flare. As this radio emission did not continue to lower frequencies, we conclude that the shock wave did not propagate any further. Either the shock driver died out, as a blast wave, or the driver speed no longer exceeded the local Alfven speed.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
On 8 November 2013 a halo-type coronal mass ejection (CME) was observed, together with flares and type II radio bursts, but the association between the flares, radio bursts, and the CME was not clear. Our aim is to identify the origin of the CME and its direction of propagation, and to exclude features that were not connected to it. On the Earth-facing side, a GOES C5.7 class flare occurred close to the estimated CME launch time, followed by an X1.1 class flare. The latter flare was associated with an EUV wave and metric type II bursts. On the far side of the Sun, a filament eruption, EUV dimmings, and ejected CME loops were observed by imaging instruments onboard the Solar TErrestrial RElations Observatory (STEREO) spacecraft that were viewing the backside of the Sun. The STEREO radio instruments observed an interplanetary (IP) type II radio burst at decameter-hectometric wavelengths, which was not observed by the radio instrument onboard the Wind spacecraft located at L1 near Earth. We show that the halo CME originated from the eruption on the far side of the Sun, and that the IP type II burst was created by a shock wave ahead of the halo CME. The radio burst remained unobserved from the earthside, even at heliocentric source heights larger than 9 solar radii. During the CME propagation, the X-class flare eruption caused a small plasmoid ejection earthward, the material of which was superposed on the earlier CME structures observed in projection. The estimated heights of the metric type II burst match well with the EUV wave launched by the X-class flare. As this radio emission did not continue to lower frequencies, we conclude that the shock wave did not propagate any further. Either the shock driver died out, as a blast wave, or the driver speed no longer exceeded the local Alfven speed.
McKee, Sarah Ruth; Cilliers, Pierre Johannes; Lotz, Stefan; Monstein, Christian
The effects of solar radio bursts on frequency bands utilised by the aviation industry in Sub-Saharan Africa Journal Article
In: J. Space Weather Space Clim., vol. 13, pp. 4, 2023.
@article{refId0g,
title = {The effects of solar radio bursts on frequency bands utilised by the aviation industry in Sub-Saharan Africa},
author = {Sarah Ruth McKee and Pierre Johannes Cilliers and Stefan Lotz and Christian Monstein},
url = {https://doi.org/10.1051/swsc/2023001},
doi = {10.1051/swsc/2023001},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {J. Space Weather Space Clim.},
volume = {13},
pages = {4},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Ndacyayisenga, T.; Uwamahoro, J.; Uwamahoro, J. C.; Babatunde, R.; Okoh, D.; Raja, K. Sasikumar; Kwisanga, C.; Monstein, C.
In: EGUsphere, vol. 2023, pp. 1–22, 2023.
@article{egusphere-2023-201,
title = {An Overview of Solar Radio Type II Bursts through analysis of associated solar and near Earth space weather features during Ascending phase of SC 25},
author = {T. Ndacyayisenga and J. Uwamahoro and J. C. Uwamahoro and R. Babatunde and D. Okoh and K. Sasikumar Raja and C. Kwisanga and C. Monstein},
url = {https://egusphere.copernicus.org/preprints/egusphere-2023-201/},
doi = {10.5194/egusphere-2023-201},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {EGUsphere},
volume = {2023},
pages = {1–22},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Wisniewski, John P.; Berdyugin, Andrei V.; Berdyugina, Svetlana V.; Danchi, William C.; Dong, Ruobing; Oudmaijer, René D.; Airapetian, Vladimir S.; Brittain, Sean D.; Gayley, Ken; Ignace, Richard; Langlois, Maud; Lawson, Kellen D.; Lomax, Jamie R.; Rich, Evan A.; Tamura, Motohide; Vink, Jorick S.; Scowen, Paul A.
UV spectropolarimetry with Polstar: protoplanetary disks Journal Article
In: Astrophysics and Space Science, vol. 367, no. 12, pp. 122, 2022.
@article{2022Ap&SS.367..122W,
title = {UV spectropolarimetry with Polstar: protoplanetary disks},
author = {John P. Wisniewski and Andrei V. Berdyugin and Svetlana V. Berdyugina and William C. Danchi and Ruobing Dong and René D. Oudmaijer and Vladimir S. Airapetian and Sean D. Brittain and Ken Gayley and Richard Ignace and Maud Langlois and Kellen D. Lawson and Jamie R. Lomax and Evan A. Rich and Motohide Tamura and Jorick S. Vink and Paul A. Scowen},
doi = {10.1007/s10509-022-04125-7},
year = {2022},
date = {2022-12-01},
urldate = {2022-12-01},
journal = {Astrophysics and Space Science},
volume = {367},
number = {12},
pages = {122},
abstract = {Polstar is a proposed NASA MIDEX mission that carries a high resolution
UV spectropolarimeter capable of measure all four Stokes
parameters onboard a 60 cm telescope. The mission has been
designed to pioneer the field of time-domain UV
spectropolarimetry. Time domain UV spectropolarimetry offers the
best resource to determine the geometry and physical conditions
of protoplanetary disks from the stellar surface to <5 AU. We
detail two key objectives that a dedicated time domain UV
spectropolarimetry survey, such as that enabled by Polstar or a
similar mission concept, could achieve: 1) Test the hypothesis
that magneto-accretion operating in young planet-forming disks
around lower-mass stars transitions to boundary layer accretion
in planet-forming disks around higher mass stars; and 2)
Discriminate whether transient events in the innermost regions
of planet-forming disks of intermediate mass stars are caused by
inner disk mis-alignments or from stellar or disk emissions.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Polstar is a proposed NASA MIDEX mission that carries a high resolution
UV spectropolarimeter capable of measure all four Stokes
parameters onboard a 60 cm telescope. The mission has been
designed to pioneer the field of time-domain UV
spectropolarimetry. Time domain UV spectropolarimetry offers the
best resource to determine the geometry and physical conditions
of protoplanetary disks from the stellar surface to <5 AU. We
detail two key objectives that a dedicated time domain UV
spectropolarimetry survey, such as that enabled by Polstar or a
similar mission concept, could achieve: 1) Test the hypothesis
that magneto-accretion operating in young planet-forming disks
around lower-mass stars transitions to boundary layer accretion
in planet-forming disks around higher mass stars; and 2)
Discriminate whether transient events in the innermost regions
of planet-forming disks of intermediate mass stars are caused by
inner disk mis-alignments or from stellar or disk emissions.
UV spectropolarimeter capable of measure all four Stokes
parameters onboard a 60 cm telescope. The mission has been
designed to pioneer the field of time-domain UV
spectropolarimetry. Time domain UV spectropolarimetry offers the
best resource to determine the geometry and physical conditions
of protoplanetary disks from the stellar surface to <5 AU. We
detail two key objectives that a dedicated time domain UV
spectropolarimetry survey, such as that enabled by Polstar or a
similar mission concept, could achieve: 1) Test the hypothesis
that magneto-accretion operating in young planet-forming disks
around lower-mass stars transitions to boundary layer accretion
in planet-forming disks around higher mass stars; and 2)
Discriminate whether transient events in the innermost regions
of planet-forming disks of intermediate mass stars are caused by
inner disk mis-alignments or from stellar or disk emissions.
Riva, F.; Cuissa, J. R. Canivete; Steiner, O.
Simulations of the small scale surface dynamo of cool main sequence stars Proceedings Article
In: Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, pp. 125, 2022.
@inproceedings{2022csss.confE.125R,
title = {Simulations of the small scale surface dynamo of cool main sequence stars},
author = {F. Riva and J. R. Canivete Cuissa and O. Steiner},
doi = {10.5281/zenodo.7540550},
year = {2022},
date = {2022-12-01},
urldate = {2022-12-01},
booktitle = {Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun},
pages = {125},
series = {Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun},
abstract = {A widely accepted explanation for the origin of the ubiquitous small-
scale magnetic field observed on the solar surface is the
presence of a small-scale dynamo (SSD) operating in the sub-
surface layers of the Sun. To shed light on the functioning of
this SSD, a number of numerical studies of a realistic solar
atmosphere have been carried out in the past two decades,
greatly improving our knowledge on how an SSD operates.
Nevertheless, virtually no studies focused on SSD action on the
surface of other main-sequence stars. This motivates the work
reported here. Hydro and magneto-hydrodynamics simulations of a
small partial volume encompassing the surface layers of F5V,
G2V, K2V, and K8V main-sequence stars are carried out with the
radiative magnetohydrodynamic CO5BOLD code, investigating how
SSD action can amplify a tiny seed magnetic field. In
particular, the growth rate of the magnetic to kinetic energy
ratio is characterized in terms of the Reynolds and magnetic
Reynolds numbers of the simulations, and of the effective
temperature and surface gravity of each star. It is found that
the small-scale dynamo operating in the K2V simulation is the
fastest in amplifying the magnetic energy among the four cases
considered here. However, similar saturation values of the
magnetic to kinetic energy ratio, of about 1%, are found at the
surface for all the four stars. Ultimately, we investigate the
spatial structure of the magnetic field resulting from SSD
action and how it interacts with the plasma in the stellar
atmospheres.},
keywords = {},
pubstate = {published},
tppubtype = {inproceedings}
}
A widely accepted explanation for the origin of the ubiquitous small-
scale magnetic field observed on the solar surface is the
presence of a small-scale dynamo (SSD) operating in the sub-
surface layers of the Sun. To shed light on the functioning of
this SSD, a number of numerical studies of a realistic solar
atmosphere have been carried out in the past two decades,
greatly improving our knowledge on how an SSD operates.
Nevertheless, virtually no studies focused on SSD action on the
surface of other main-sequence stars. This motivates the work
reported here. Hydro and magneto-hydrodynamics simulations of a
small partial volume encompassing the surface layers of F5V,
G2V, K2V, and K8V main-sequence stars are carried out with the
radiative magnetohydrodynamic CO5BOLD code, investigating how
SSD action can amplify a tiny seed magnetic field. In
particular, the growth rate of the magnetic to kinetic energy
ratio is characterized in terms of the Reynolds and magnetic
Reynolds numbers of the simulations, and of the effective
temperature and surface gravity of each star. It is found that
the small-scale dynamo operating in the K2V simulation is the
fastest in amplifying the magnetic energy among the four cases
considered here. However, similar saturation values of the
magnetic to kinetic energy ratio, of about 1%, are found at the
surface for all the four stars. Ultimately, we investigate the
spatial structure of the magnetic field resulting from SSD
action and how it interacts with the plasma in the stellar
atmospheres.
scale magnetic field observed on the solar surface is the
presence of a small-scale dynamo (SSD) operating in the sub-
surface layers of the Sun. To shed light on the functioning of
this SSD, a number of numerical studies of a realistic solar
atmosphere have been carried out in the past two decades,
greatly improving our knowledge on how an SSD operates.
Nevertheless, virtually no studies focused on SSD action on the
surface of other main-sequence stars. This motivates the work
reported here. Hydro and magneto-hydrodynamics simulations of a
small partial volume encompassing the surface layers of F5V,
G2V, K2V, and K8V main-sequence stars are carried out with the
radiative magnetohydrodynamic CO5BOLD code, investigating how
SSD action can amplify a tiny seed magnetic field. In
particular, the growth rate of the magnetic to kinetic energy
ratio is characterized in terms of the Reynolds and magnetic
Reynolds numbers of the simulations, and of the effective
temperature and surface gravity of each star. It is found that
the small-scale dynamo operating in the K2V simulation is the
fastest in amplifying the magnetic energy among the four cases
considered here. However, similar saturation values of the
magnetic to kinetic energy ratio, of about 1%, are found at the
surface for all the four stars. Ultimately, we investigate the
spatial structure of the magnetic field resulting from SSD
action and how it interacts with the plasma in the stellar
atmospheres.
Publication of IRSOL by category: