Maria L. Luoni

A new model-independent method to compute magnetic helicity in magnetic clouds

Fil: Dasso, Sergio Ricardo. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Astronomia y Fisica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomia y Fisica del Espacio; Argentina

LONG-TERM CHROMOSPHERIC ACTIVITY IN SOUTHERN M DWARFS: Gl 229 A AND Gl 752 A

Several late-type stars present activity cycles similar to that of the Sun. However, these cycles have been mostly studied in F to K stars. Due to their small intrinsic brightness, M dwarfs are not usually the targets of long-term observational studies of stellar activity, and their long-term variability is generally not known. In this work, we study the long-term activity of two M dwarf stars: Gl 229 A (M1/2) and Gl 752 A (M2.5). We employ medium-resolution echelle spectra obtained at the 2.15 m telescope at the Argentinian observatory CASLEO between 2000 and 2010, and photometric observations obtained from the ASAS database. We analyze Ca II K line-core fluxes and the mean V magnitude with the Lomb-Scargle periodogram, and we obtain possible activity cycles of ~4 yr for Gl 229 A and ~7 yr for Gl 752 A.

Blue Lines as Chromospheric Diagnostics: The Al I Lines at 3944 and 3961 Å

We present a simple atomic model for the synthesis of the Al I resonance lines, near the Ca II H and K lines. We study whether the computed profiles are influenced by the choice of the atomic parameters and find that, although several cross sections are not known accurately, the line profiles do not depend on them and are therefore useful as diagnostics of the atmospheric structure. We study which transitions need not to be included in the model, in order to reduce as much as possible the computing time. We compare the profiles computed for a standard model of the quiet solar atmosphere with the observations and find very good agreement. We found that the inclusion of the proper line-blanketing opacity is fundamental for an accurate calculation of the ionization balance and that irradiation by UV lines originating in the transition region does not affect the Al I emission.

Hα Moreton waves observed on December 06, 2006 - A 2D case study

Fil: Francile, Carlos Natale. Universidad Nacional de San Juan. Facultad de Cs.exactas Fisicas y Naturales. Departamento de Informatica. Observat.astron. Felix Aguilar;

Moreton and EUV Waves Associated with an X1.0 Flare and CME Ejection

A Moreton wave was detected in active region (AR) 12017 on 29 March 2014 with very high cadence with the H-Alpha Solar Telescope for Argentina (HASTA) in association with an X1.0 flare (SOL2014-03-29T17:48). Several other phenomena took place in connection with this event, such as low-coronal waves and a coronal mass ejection (CME). We analyze the association between the Moreton wave and the EUV signatures observed with the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory. These include their low-coronal surface-imprint, and the signatures of the full wave and shock dome propagating outward in the corona. We also study their relation to the white-light CME. We perform a kinematic analysis by tracking the wavefronts in several directions. This analysis reveals a high-directional dependence of accelerations and speeds determined from data at various wavelengths. We speculate that a region of open magnetic field lines northward of our defined radiant point sets favorable conditions for the propagation of a coronal magnetohydrodynamic shock in this direction. The hypothesis that the Moreton wavefront is produced by a coronal shock-wave that pushes the chromosphere downward is supported by the high compression ratio in that region. Furthermore, we propose a 3D geometrical model to explain the observed wavefronts as the chromospheric and low-coronal traces of an expanding and outward-traveling bubble intersecting the Sun. The results of the model are in agreement with the coronal shock-wave being generated by a 3D piston that expands at the speed of the associated rising filament. The piston is attributed to the fast ejection of the filament–CME ensemble, which is also consistent with the good match between the speed profiles of the low-coronal and white-light shock waves.

Linking Coronal to Interplanetary Magnetic Helicity

Magnetic helicity (MH) has been recognized as a useful tool to study the link between active regions (ARs) and magnetic clouds (MCs). In this work, we compare the MH and flux of the MC of October 18–19, 1995, and its associated AR. We compute both quantities and we find that the AR flux is one order of magnitude larger than in the MC, while the coronal MH is lower after an ejection linked to a long duration event and comparable to the MC helicity. We conclude that the MH in the interplanetary flux rope comes from the coronal one.

12 years of stellar activity observations in Argentina

We present an observational program we started in 1999, to systematically obtain mid-resolution spectra of late-type stars, to study in particular chromospheric activity. In particular, we found cyclic activity in four dM stars, including Prox-Cen. We directly derived the conversion factor that translates the known S index to flux in the Ca II cores, and extend its calibration to a wider spectral range. We investigated the relation between the activity measurements in the calcium and hydrogen lines, and found that the usual correlation observed is the product of the dependence of each flux on stellar color, and it is not always preserved when simultaneous observations of a particular star are considered. We also used our observations to model the chromospheres of stars of different spectral types and activity levels, and found that the integrated chromospheric radiative losses, normalized to the surface luminosity, show a unique trend for G and K dwarfs when plotted against the S index.