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Astrophysics and Astrononmy
The Sun as a key to interpreting the variability of cool main sequence stars and to characterizing their exoplanets
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
26.09.2023
Co-author:
Sami K. Solanki, Tanayveer Bhatia, Robert Cameron, Emre Isik, Natalie A. Krivova, Timo Reinhold, Alexander Shapiro, K. Sowmya, Veronika Witzke
Abstract:
The Sun is a typical main sequence star with an outer convection zone, where a dynamo gives rise to magnetic fields that in turn produce magnetic features such as sunspots and faculae at the solar surface. During their presence at the solar surface the spots lead to a darkening, while the faculae produce a brightening. The evolution of the field and the rotation of the Sun results in variations in the Sun’s radiative output, which have been measured for over 4 decades. Such variations have now also been observed in myriads of cool main sequence stars thanks to the high accuracy of space missions such as Kepler, TESS and CHEOPS and in future PLATO.
To properly understand and interpret these variations, models, simulations and techniques developed for this purpose for the Sun and solar variability turn out to be extremely useful. Particularly powerful has been a combination of models that
- describe the rise of magnetic flux tubes through the convection zone,
- determine their distrib
Layer-oriented adaptive optics for solar observations.
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
23.09.2023
Abstract:
The presentation starts with a description of multi-conjugate adaptive optics (AO).
Multi conjugate AO comes in two flavors: star and layer-oriented. Until now solar astronomy is based on the star oriented approach.
The slides illustrate why the layer oriented approach is very well suited for solar observations.
Sun as a star variability of solar Balmer lines
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
06.10.2023
Co-author:
S. Marchenko, M.T. DeLand, D. Choudary, G. Kopp
Abstract:
We investigate the variability of solar Balmer lines (H-α, -β, -γ, -δ) from space-borne radiometers (OSIRIS, SCIAMACHY, OMI, GOME-2) and ground-based NSO/ISS spectrograph data, linking the observed changes to the solar disk's magnetic features. On solar-rotational timescales (about 1 month), the Balmer-line activity indices (defined as line-core to line-wing ratios) closely follow variations in the total solar irradiance (which is predominantly photospheric), thus frequently (specifically, during passages of sunspot groups) deviating from behavior of activity indices that track chromospheric activity levels. On longer timescales, the correlation with chromospheric indices increases, with periods of low- or even anti-correlation found at intermediate (months to years) timescales. Comparison of these observations with estimates from semi-empirical irradiance reconstructions helps quantify the contributions of different magnetic and quiet features. We conclude that both the lower sensitiv
Solar radius measurements and evidence for coronal emission in the 18 - 26 GHz frequency range through imaging observations with INAF radio telescopes
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
30.09.2023
Co-author:
A. Pellizzoni (INAF-OAC), S. Righini (INAF-IRA), M.N. Iacolina (ASI), S. Mulas (INAF-OAC), and the SunDish collaboration
Abstract:
In this talk we present our first results about the measure of the solar radius and the evidence of the coronal physical emission in the 18-26 GHz band (up to 100 GHz in perspective) with the large single-dish radio telescopes of the Italian National Institute for Astrophysics (INAF), throughout 5 years, from 2018 to early 2023.
The coverage of the entire solar disk, the low noise, the accurate absolute calibration, and the great sensitivity of INAF radio telescopes make these data crucial to accurately observe the solar corona.
Using about 300 radio solar maps obtained in the context of the SunDish project, devoted to the radio imaging and monitoring of the solar atmosphere through the INAF radio telescopes (Medicina 32-m and SRT 64-m), we describe our methods to calculate the solar radius and to prove the physical origin of the coronal emission; finally, we discuss and comparate our results with respect to the literature.
The Sun as a Rosetta Stone for the Physics of Atom-Photon Interactions
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
08.10.2023
Abstract:
The magnetic field is the main driver of the spectacular activity of the upper solar atmosphere, including the eruptive phenomena that determine the near-Earth space weather. For this reason, one of the great challenges of astrophysics is the empirical investigation of the magnetic fields that permeate the solar atmosphere. Recent advances in our theoretical understanding of the fingerprints that photospheric, chromospheric and coronal magnetic fields leave in the solar spectrum, as well as in the development of the instrumentation needed to measure the key observables, are activating a new revolution in solar physics. Here I provide a personal view of some recent advances, such as predictions on the polarization in some spectral lines (to be confirmed by DKIST and/or EST), the solution of a long-standing paradox in solar physics, and the inference of chromospheric magnetic fields from the unprecedented ultraviolet spectropolarimetric observations enabled by the CLASP suborbital space experiments. All these novel investigations show clearly that the solar atmosphere represents a unique laboratory for improving our understanding of the physics of atom-photon interactions in astrophysical plasmas.
Space Weather science and next generation 4m telescopes
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
06.10.2023
Abstract:
Space weather science is evolving fast, but many open questions remain. A good knowledge of solar precursors is a mandatory requirement for predicting space weather hazards well in advance. Solar observations from existing capabilities, mainly from space telescopes, are being extensively analysed even involving artificial intelligence. Nevertheless, the response to what triggers an eruptive flare instead a confined one, or to what will be the direction of the magnetic field vector when a coronal mass ejection arrives the Earth, among other questions, is missing nowadays. Next generation 4m telescopes provide a significant increase in observing capability, which should allow us to go ahead in the understanding of space weather science, increasing our forecasting capabilities. However, some changes should be made to achieve this goal, for example, in the observing schedules.
3D NLTE radiative transfer in stellar atmospheres
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
16.10.2023
Abstract:
Detailed radiative transfer calculations are essential for accurately interpreting spectra, both in solar and stellar astrophysics. The gold standard in spectral synthesis are 3D NLTE calculations, which take advantage of more realistic 3D model atmospheres and account for non-equilibrium physics (NLTE). Over the last decade, 3D NLTE calculations went from a niche to the mainstream. Solar studies have greatly helped in this transition, in two fundamental ways: by developing numerical schemes to make the 3D NLTE problem computationally tractable, and by using our closest star as a detailed laboratory to constrain atomic data and physical assumptions. The repercussions of 3D NLTE analyses in cool stars are profound. I will review a few results, including the revised solar chemical composition and stellar abundances, and finish with an eye on the future, from advances from large spectroscopic surveys, exoplanets, and stellar chromospheres.
The relationship between plage and sunspot areas
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
30.09.2023
Co-author:
N. A. Krivova, I. Ermolli
Abstract:
Climate studies require long records of solar irradiance variations. Since direct irradiance measurements cover only limited time span, reconstructions of past irradiance variations are crucial. Such models require information on the evolution of solar surface magnetic field in the past, while information on facular regions prior to the period of direct irradiance measurements is scarce. As a result, reconstructions of past irradiance changes rely mainly on sunspot data, which requires certain assumptions about the relationship between sunspots and faculae. This has led to a discrepancy in estimates of long-term change in the solar irradiance. This issue can be resolved by utilising Ca II K observations, which is a largely unexplored dataset for irradiance reconstructions at the moment. We will discuss the potential of these data focusing in particular on the relationship between sunspots and Ca II K plage areas derived from a number of different Ca II K archives.
Going to the source: using topological measures to find early-warning signatures of flares
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
05.10.2023
Abstract:
We seek signatures of topological measures, such as helicity and winding, that can indicate flares and CMEs several hours before their onset
High-resolution spectroscopy of chromospheric fibrils using DKIST observations
Natural Sciences (Astrophysics and Astrononmy)
Date of upload:
02.11.2023
Abstract:
We study the temperature structure of chromospheric network fibrils using high-
resolution observations from DKIST telescope. These first public release
observations provide simultaneous photospheric and chromospheric spectra at high
angular resolution. We use LTE and NLTE diagnostics to infer the temperature
stratification in the fibrils and compare it with numerical simulations such as
BIFROST.
Magnetic Reconnection in Relativistic Jets and Accretion Flows around Black Holes
Natural Sciences (Astrophysics and Astrononmy)
Elisabete de Gouveia Dal Pino
Date of upload:
05.10.2023
Abstract:
Relativistic jets and accretion disks from Black Hole (BH) sources, such as active galaxies, are among the most extreme particle accelerators known, producing very high energy emission. Only recently have we begun to comprehend the prevailing physical processes near these BHs, thanks to the combination of theory, numerical simulations, and observations. These investigations aim to solve significant enigmas, such as the origin of gamma-ray flares and ultra-high-energy cosmic rays. Within the inner regions of these BH sources, magnetic fields play a dominant role, and magnetic reconnection emerges as a highly plausible, if not the sole, mechanism responsible for accelerating particles to extreme energies. In this presentation, I will focus on magnetic reconnection driven by turbulence surrounding BH sources. Our latest findings, based on three-dimensional global magnetohydrodynamic relativistic simulations and the injection of test particles, demonstrate the efficiency of this mechanism
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