Found 34 talks archived in The Sun
Mark I is a part of the origin of the IAC, operating in the El Teide Observatory since 1975, in three different locations until reaching the Solar Pyramid "van der Raay" in 1987. Every day, weather permitting, it has been providing precise measurements of the radial velocity of our star. It began to perform continuous daily observations from July 1984 and, until December 2020, 10169 out of 13408 possible days (76%) useful data has been gathered. Designed, updated, maintained and operated by the Helioseismology team at the IAC and the University of Birmingham (UK), more than 100 people, from TOTs and weekend fellows to professors, have contributed to this endeavour. It was a true pioneer, key in the birth and development of Helioseismology and Astroseismology as branches of modern Astronomy.
Mark I is a resonant scattering spectrophotometer that measures the radial velocity of integral sunlight using the KI-769.9 nm spectral line. It has been a pioneer and reference for calibration of other instruments: MarkII, IRIS, Cannon, Stellar, Space, BiSON, GOLF, which have also worked in different ground-based observatories and in space missions such as SoHO (1995-).
Its precision, in a single measurement of the solar radial velocity, is less than 1 m/s, and the one achieved so far is less than 1 cm/s at frequencies around 0.1 mHz (gravity modes zone) and less than 1 mm/s at 3 mHz (acoustic modes zone). It measured for the first time the spectrum of solar acoustic modes (from 1.8 to 4.2 mHz) of small degree (ℓ <= 3): their frequencies, amplitudes and lifetimes, their rotational splitting; also its variations with the cycle of solar activity. He has explored gravity modes, measured the spectrum's background, and determined the acoustic cut-off frequency in the solar photosphere. All this has led to numerous discoveries that have been published in around 40 doctoral theses at different universities and more than 600 papers in international journals and books. These works have been already cited around 10,000 times in scientific literature.
In this talk I will briefly review its history throughout more than 45 years, an entire academic life, and I will raise some suggestions on its scientific use from now on.
The phenomenon of magnetic reconnection in a magnetized plasma has been a subject of numerous studies over the past several decades in a variety of contexts, from high energy astrophysics, to solar and space physics, to laboratory-based experiments. However, most magnetic reconnection studies have been devoted to exploring different collisionality regimes in a fully ionized single specie plasma. Until recently, the physics of magnetic reconnection in partially, and weakly, ionized plasmas has received relatively little attention. In this talk, I will provide a brief overview of the physical effects that partial ionization of the ambient medium may introduce in the dynamics of magnetic reconnection, with a particular focus on the environment of the lower solar atmosphere.
A solar flare involves the conversion of magnetic energy stored in the coronal magnetic field into the kinetic energy of thermal and non-thermal particles, mass motion, and radiation. How this happens remains a central question in solar physics. A particular long-standing puzzle is how such a high fraction of the stored magnetic energy - up to a half - arrives in the kinetic energy of accelerated non-thermal particles. In this talk I will present an observational overview of solar flares with an emphasis on accelerated particles, discuss some ideas and constraints on particle acceleration, and present some new observations of the possible role of plasma turbulence in the acceleration process.
The Sun is an active star that influences the Earth as well as the entire solar system. Most dynamic phenomena on the Sun are observed as coronal mass ejections (CMEs) and flares. CMEs present massive clouds of magnetized plasma having speeds up to a few thousand km/s, that may propagate over Sun-Earth distance within less than a day and may cause strong geomagnetic disturbances at Earth (Space Weather). As CMEs are optically thin, using remote sensing data measurements of intrinsic properties such as speed, width, propagation direction, density etc. are severely affected by projection effects. By combining image data with in-situ measurements, valuable information is provided enabling CME 3D analyzes, and with that facilitate a better quantification of the uncertainties in the observational measurements that are used to feed CME propagation models. With that, a much better understanding of CMEs as they propagate in interplanetary space could be gained.
The talk will cover the physisc about CME-flare phenomena, the interplanetary propagation behavior of CMEs related to the background solar wind, and Space Weather forecasting.
Zoom link: https://rediris.zoom.us/j/92170419398
Emerging flux regions (EFRs) are seen as magnetic concentrations in the photosphere of the Sun. From a theoretical point of view, the EFRs are formed in the convection zone and then emerge because of magnetic buoyancy (Parker instability) to the solar surface. During the formation process of EFRs, merging and cancellation of different polarities occur, leading to various configurations of the magnetic field. Often, EFRs are visible in the chromosphere in form of magnetic loops loaded with plasma, which are often called “cool loops” when seen in the chromosphere along with dark fibrils and they can reach up to the corona. Nowadays, we refer to them as an arch filament system (AFS) which connects two different polarities. The AFSs are commonly observed in several chromospheric spectral lines. A suitable spectral line to investigate chromospheric features and particularly AFSs is the He I 10830 Å triplet. The new generation of solar telescopes and instruments such EST and DKIST, will allow us to record very high spectral, spatial, and temporal resolution observations necessary to investigate the dynamics, magnetic field, and characteristics of AFSs. These observations will help us to answer many open questions related to flux emergence such: (1) What are the observational consequences of the emerging flux? (2) How do EFRs evolve with time in the different layers of the solar atmosphere and how are these layers linked? (3) Is it possible to measure the height difference between the photosphere and the chromosphere connected by the legs of the AFSs?
Solar surface convection displays highly localized sinks where cold plasma returns to the solar interior. On its way to being engulfed by a downdraft the plasma can also advect and intensify magnetic fields up to kG field strengths. Such theoretical predictions strengthen the idea that localized downdrafts are places where the concentration of magnetic fields is favored. The observational discovery of convectively driven sinks is rather recent, however, and its role in the formation and evolution of quiet-Sun magnetic features is still poorly characterized. In our work, we provide both quantitative and qualitative bases for the association between sinks and magnetic fields using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board Sunrise. We find 3.1 x 10-3 sinks Mm-2 minute-1 located at mesogranular vertices. These sinks are associated to (1) horizontal velocity flows converging to a central point and (2) long-lived downdrafts. The spatial distribution of magnetic fields in the quiet Sun is also examined. The strongest magnetic fields are preferentially located at sinks. We find that 40% of the pixels with longitudinal component of the magnetic field higher than 500 G are located in the close neighborhood of sinks. The study of individual examples reveal that sinks can play an important role in the evolution of quiet-Sun magnetic features.
In mid nineteens, it was discovered that the Sun had a dipolar global magnetic field, whose temporal evolution followed the Solar Cycle. Polar regions, as well as sunspots that appear in the activity belts, changed their polarity every 11 years: sunspots during each activity minima, and the poles in activity maxima. This fact, made people think that the poles reversal was related to the arrival of opposite polarity magnetic flux dragged from active regions by a meridional flow. Such new flux reduced the dominant polarity at the poles by cancellation, and built the opposite one until next minimum of activity. In our study, we have used the high quality full disc magnetograms, recorded by the HMI instrument onboard the SDO satellite since the beginning of the mission, in april 2010. We perform a deep study of the evolution with time of the line of sight component of the magnetic field at the solar poles. In our data, we see many aspects of the solar cycle as the decay of the dominant polarity of both poles while we approach to the activity maximum. But the main result is the detection of a monthly oscillatory pattern of the pole's magnetic field. Such oscillation, related to solar rotation is a clear evidence of a non-axisymmetric component of the magnetic field. One of the possible explanations is that the global field is tilted with respect to the rotation axis. This rather usual finding in other stars, here represents a breach of modern solar dynamo theories for the generation and maintenance of the Sun's magnetic field.
In the first part of the talk, I discuss the chromospheric activity of quiet Sun. The so-called basal flux, the minimum chromospheric emission of main sequence stars, is discussed in terms of magnetic and non-magnetic heatings. The second half of the talk is about variability of the solar cycle. The extended minimum of the last cycle caused speculations about a possible long-term decline in the solar activity. Based on our observations in past 15 years, I argue that the Sun does not cease to generate sunspots in the next cycle. Finally I outline new tools to evaluate chromospheric activities.
What does space weather really mean, and why should scientists and
non-scientists be interested in it? I will discuss what we know and don’t
know about the causes and consequences of space weather, how the
fundamental physics of our heliosphere also applies to astrophysical
objects and exoplanetary systems, and how the lessons learned affect our
technology on the ground and in space.
The Sun is a magnetic star, not as magnetic as some stars, or as it was when it
was younger, but nonetheless magnetic fields dominate and even construct its
atmosphere. There would be no corona without magnetic fields. The surface is
also dappled with small scale magnetic field associated with surface convection
cells, granules and supergranules. But sometimes we also see much larger and
more powerful Active Regions containing sunspots. These are wounds in the
surface of the Sun that allow waves and oscillations in the solar interior and
atmosphere to be coupled much more directly than they usually are. In
particular, they allow the Sun's internal seismology (the p-modes) to drive a
variety of waves through the Active Region atmosphere, and conversely, the
atmospheres to pollute the internal seismology. This makes active region
helioseismology a very challenging field.
- A tale of caution: the tails of open clusters are much longer than thought, but more difficult to findDr. Henri BoffinThursday October 6, 2022 - 10:30 GMT+1 (Aula)