Search results for "Solar physics"

Dynamic Temperature Structure of the Corona

2012

The solar corona is heated to million degrees and information about the temperature structure is a key to understand the heating mechanisms. Although it is not easy to measure, the temperature looks to be remarkably steady in the solar corona and in active regions outside of transient events, like flares. On the other hand, there is strong evidence of multi-thermal structures, out of equilibrium for most of the time. Is there a way to obtain a coherent scenario? The secret might be in the fine structuring of the corona, and SDO is providing new and important information on this issue.

Hot Plasma Detected in Active Regions by HINODE/XRT and SDO/AIA

2012

Multiple ratios of Hinode/XRT filters showed evidence of a minor very hot emission measure component in active regions. Recently also SDO/AIA detected hot plasma in the core of an active region. Here we provide estimates showing that the amount of emission measure of the hot component detected with SDO is consistent with that detected with Hinode/XRT.

The ‘Società degli Spettroscopisti Italiani’: birth and evolution

2008

Summary The anniversary of the death of Pietro Tacchini (1838–1905), one of the pioneers of solar physics in Italy, is commemorared by this account of his major creation, the Societa degli Spettroscopisti Italiani (1871). Established to promote cooperation among solar spectroscopists engaged in the study of the solar chromosphere, it was the first scientific Society devoted to spectroscopy and its astronomical applications. Its journal, the Memorie, collected most of the important works on solar physics by Angelo Secchi SJ (1818–1878), Tacchini himself, and many other protagonists of the newly born astrophysics. A brief history of the Society and its development draws on many previously une…

Die totale Sonnenfinsternis vom 8./21. August 1914 im Baltikum mit populären Erläuterungen dieses Phänomens [Die totale Sonnenfinsternis...im Baltiku…

1914

Temperature Diagnostics of a Solar Active Region Using a Single-Filter Observation of Hinode/XRT

2012

Broad-band X-ray observations can provide limited temperature diagnostics through filter ratios. A high cadence observation of an active region made with a single Hinode/XRT filter allows us to use an alternative approach in which we measure the time fluctuations of the pixel count rate and use the variance as temperature proxy. We show the results and discuss limitations of method.

Transverse component of the magnetic field in the solar photosphere observed by Sunrise

2010

We present the first observations of the transverse component of photospheric magnetic field acquired by the imaging magnetograph Sunrise/IMaX. Using an automated detection method, we obtain statistical properties of 4536 features with significant linear polarization signal. Their rate of occurrence is 1-2 orders of magnitude larger than values reported by previous studies. We show that these features have no characteristic size or lifetime. They appear preferentially at granule boundaries with most of them being caught in downflow lanes at some point in their evolution. Only a small percentage are entirely and constantly embedded in upflows (16%) or downflows (8%).

Thermal conduction and modeling of static stellar coronal loops

1993

We have modeled stellar coronal loops in static conditions for a wide range of loop length, plasma pressure at the base of the loop and stellar surface gravity, so as to describe physical conditions that can occur in coronae of stars ranging from low mass dwarfs to giants as well as on a significant fraction of the Main-Sequence stars.

Enhanced detection of terrestrial gamma-ray flashes by AGILE

2015

Abstract At the end of March 2015 the onboard software configuration of the Astrorivelatore Gamma a Immagini Leggero (AGILE) satellite was modified in order to disable the veto signal of the anticoincidence shield for the minicalorimeter instrument. The motivation for such a change was the understanding that the dead time induced by the anticoincidence prevented the detection of a large fraction of Terrestrial Gamma‐Ray Flashes (TGFs). The configuration change was highly successful resulting in an increase of one order of magnitude in TGF detection rate. As expected, the largest fraction of the new events has short duration (<100 μs), and part of them has simultaneous association with light…

Detection of vortex tubes in solar granulation from observations with Sunrise

2010

We have investigated a time series of continuum intensity maps and corresponding Dopplergrams of granulation in a very quiet solar region at the disk center, recorded with the Imaging Magnetograph eXperiment (IMaX) on board the balloon-borne solar observatory Sunrise. We find that granules frequently show substructure in the form of lanes composed of a leading bright rim and a trailing dark edge, which move together from the boundary of a granule into the granule itself. We find strikingly similar events in synthesized intensity maps from an ab initio numerical simulation of solar surface convection. From cross sections through the computational domain of the simulation, we conclude that th…

A Dynamical Model for the Evolution of Hot Spots in Powerful Radio Sources

2003

AbstractCompact symmetric objects are considered the young counterparts of large doubles according to advance speeds measured or inferred from spectral ageing. Here we present a simple power law model for the CSO/FR II evolution based on the study of sources with well defined hot spots. The luminosity of the hot spots is estimated under minimum energy conditions. The advance of the source is considered to proceed in ram pressure equilibrium with the ambient medium. Finally, we also assume that the jets feeding the hot spots are relativistic and have a time dependent power. Comparison with observational data points to an interpretation of the CSO–FR II evolution in terms of decreasing jet po…